Environmentally friendly absorbent material and manufacturing process

Abstract

A method for manufacturing an absorbent core and / or article comprising the steps of: (i) providing a first nonwoven mesh, preferably substantially continuous, having a first void volume; (ii) selectively applying heat to said first nonwoven mesh such that a deposition area of ​​said first nonwoven mesh increases its void volume to a second void volume that is larger than said first void volume; (iii) depositing absorbent material, preferably comprising superabsorbent particles, onto the deposition area of ​​said first nonwoven mesh; (iv) passively or actively cooling the deposition area of ​​said first nonwoven mesh such that the void volume is substantially reduced to the first void volume;(v) optionally combining the first nonwoven mesh with a second and a third nonwoven mesh such that the first nonwoven mesh is interposed between the second and third nonwoven meshes, preferably joining the meshes by mechanical bonding selected from hot pressing and / or ultrasonic bonding; wherein the first nonwoven mesh consists of a high-volume fibrous nonwoven layer that is free of cellulose fibers; the high-volume fibrous nonwoven layer preferably comprising an air-bonded carded nonwoven layer or a Dryiaid thermally bonded nonwoven layer.

Description

Environmentally friendly absorbent material and manufacturing process Technical field The description refers to absorbent articles, such as disposable absorbent articles, preferably selected from the group consisting of diapers (whether for babies or adults), pull-up diapers (whether for babies or adults), underpants and combinations thereof, and the methods for their manufacture. Background Disposable absorbent products, such as diapers, are designed to contain bodily waste and prevent soiling of the user's clothing and / or other belongings (e.g., a bed, chair, blanket, etc.). The absorbent and leak-proof properties of these products are generally important. They are also designed to be cost-effective, and therefore manufacturers typically make them suitable for use by people with a wide range of body types. Consequently, there is ongoing interest in new and improved disposable absorbent products that, in addition to fitting a wide variety of body types and providing a snug fit to contain waste and limit leakage, are even more economical and environmentally friendly. One way manufacturers have attempted to address continued interest is by reducing the amount of absorbent material through the introduction of channels that aid and promote the distribution of the liquid along and through the absorbent core. Examples include those described in EP 3342386 B1, EP 3542766 B1, EP3562454 B1, EP3692963 B1, WO2019072765, and EP3562455 B1. In other examples, attempts have been made to use lint-free cores to immobilize superabsorbent polymer particles on non-woven substrates, as described in EP 3085346 B1 and EP 3348246 A1. In other more recent examples, cores are considered that comprise a raised layer on which superabsorbent polymer particles are deposited and immobilized by means of adhesive, as described in document EP 3881814 A1. Therefore, although significant technological advances have already been made in this field, there remains a need to further improve the basic constructions and articles that can allow for a reduction in the adhesive used and, in general, improve their cost and environmental impact, while preserving the overall performance (especially in terms of absorption, rewetting, and leak prevention) normally associated with today's premium absorbent articles. Summary The present invention is as defined in claim 1 and in the dependent claims thereof. Brief description of the figures Figure 1 illustrates a plan view according to an embodiment where the absorbing cores of the present memory have partially removed layers. Figure 2 illustrates a plan view according to an embodiment where the absorbing cores of the present memory have partially removed layers. Figure 3 illustrates a cross-sectional view taken around the TT axis of Figure 1. Figure 4 illustrates a plan view according to an embodiment where the absorbent articles of the present specification have partially removed layers. Figure 5 illustrates an example of a process for the production of BioSAP with a high AUL. Figure 6 is a schematic diagram illustrating a method for manufacturing absorbent cores according to an embodiment of the present specification. Figure 7 illustrates a top plan view of a first non-woven band according to an embodiment of the present document. Figure 8 illustrates a cross-section similar to that in Figure 3 according to an embodiment of the absorbing cores of this report. Figure 9 illustrates a schematic representation of the roughness according to an embodiment of the present report. Detailed description Unless otherwise defined, all terms used to describe the features of this description, including technical and scientific terms, have the meaning commonly understood by a person skilled in the art to which this description pertains. Definitions of terms are included for further guidance to enhance your understanding of the information provided in this description. As used in this report, the following terms have the following meanings: "a," "a," and "the," as used in this report, refer to both singular and plural referents, unless the context clearly indicates otherwise. By way of example, "a compartment" refers to one or more compartments. "Approximately" or "substantially," as used herein, with reference to a measurable value such as a parameter, quantity, duration, and the like, is intended to encompass variations of + / -20% or less, preferably + / -10% or less, more preferably + / -5% or less, even more preferably + / -1% or less, and still more preferably + / -0.1% or less of the specified value, to the extent that such variations are appropriate to carry out the described description. However, it should be understood that the value to which the modifier "approximately" or "substantially" refers is also specifically described. "Include," "comprising," "comprising," and "comprising" as used herein are synonymous with "include," "including," "contain," or "contain," and are inclusive or open terms that specify the presence of what follows, e.g., a component, and do not exclude or prevent the presence of additional components, features, elements, members, or stages not mentioned, known in the art or disclosed therein. The expression "% by weight" or "% w" (percent by weight), here and throughout the description, unless otherwise defined, refers to the relative weight of the respective component with respect to the total weight of the formulation. As used in this specification, the expressions "substantially free of adhesive" or "substantially free of hot melt adhesive" mean less than 15 g / m2, preferably less than 10 g / m2, more preferably less than 5 g / m2, even more preferably less than 2.5 g / m2, even more preferably less than 1.5 g / m2, even more preferably less than 1 g / m2. The term "layer" can refer to, but is not limited to, any type of substrate, such as a woven web, a nonwoven web, films, laminates, composite materials, elastomeric materials, absorbent materials (such as SAP and blends of cellulose fibers and fluff), or the like. A layer may be permeable to liquids and air, permeable to air but impermeable to liquids, impermeable to both air and liquids, or the like. When used in the singular, it can have the dual meaning of a single element or a plurality of elements, such as a laminate or multiple stacked sublayers forming a common layer. The term "absorbent article" refers to a device that absorbs and contains liquid, and more specifically, it refers to a device that is placed against or near the wearer's body to absorb and contain the various wastes / exudates discharged from the body. The terms "fixed," "adhered," or "joined" refer to elements connected or joined by clamping, adhesion, bonding, or any other method suitable for connecting such elements to each other and their constituent materials. Many methods suitable for joining elements together are well known, including adhesive bonding, pressure bonding, thermal bonding, ultrasonic bonding, mechanical bonding, etc. Such joining methods can be used to join elements over a particular area continuously or intermittently. The term "disposable" refers to absorbent articles that are generally not intended to be washed, restored, or otherwise reused as absorbent articles; that is, they are intended to be disposed of after a single use and, preferably, to be recycled, composted, or disposed of in another environmentally compatible manner. The term "arranged" is used to signify that an element(s) is (joined and positioned) in a particular place or position as a unitary structure with other elements or as a separate element joined to another element. "Adhesive," as used herein, refers broadly to a material, which may or may not flow in solution or when heated, used primarily to bond materials or layers together. This may include, for example, hot melt adhesives, UV-activatable adhesives, pressure-sensitive adhesives, solvent-based adhesives, and the like. The term "hot melt adhesive", as used in this document, refers to a specific class of adhesives and is a form of thermoplastic adhesive. The term "mechanical bonding", as used in this document, generally means the joining of one or more layers and / or components, preferably by means selected from the group consisting of ultrasonic bonding, thermal bonding, pressure bonding and combinations thereof. The terms "inner" and "outer" refer respectively to the location of an element intended to be placed against or toward a user's body when using an absorbent article, and the location of an element intended to be placed against or toward any garment worn over the absorbent article. Synonyms for "inner" and "outer" include, respectively, "inner" and "outer," as well as "inner" and "outer," or "body-facing" and "garment-facing." Additionally, when the absorbent article is oriented so that its inner surface faces upward, for example, when positioned in preparation for placing the user on top of it, synonyms include "top" and "bottom," and "top" and "bottom," respectively. The term "joined", as used in this document, encompasses configurations where one element is directly attached to another element by fixing the element directly to the other element, and configurations where one element is indirectly secured to another element by fixing the element to the intermediate element(s) which, in turn, are fixed to the other element. The term "lateral" or "transverse" refers to a direction that extends at an angle of 90 degrees with respect to the longitudinal direction and, when combined with the term "substantially", includes directions within ±45° of the lateral direction. The term "longitudinal" refers to a direction that runs parallel to the maximum linear dimension of the article and, when combined with the term "substantially," includes directions within ±45° of the longitudinal direction. The term "panties" or "panties" refers to an absorbent article generally worn by infants and incontinent persons (whether infants or adults) on the lower torso and which can be put on or taken off without unfastening. Panties typically comprise front and rear elastic waistband portions (or elastic panels) and a crotch portion connecting these waistband portions. The waistbands are typically joined together at the side seams to provide a drainage opening circumscribed by the waistbands and two leg openings circumscribed by the waistbands and / or the crotch portion.The training pants can be positioned on the user by inserting the user's legs into the leg openings and sliding the pants into position around the lower part of the user's torso. While the term "training pants" is used herein, training pants are also commonly referred to as "fastening diapers," "pre-fastening diapers," "diaper pullovers," "training pants," and "diaper briefs." "Passive cooling," as used herein, means the cooling of a material and / or substrate under ambient conditions. This typically means that there is no powered cooling source and that cooling is achieved through the temperature and relative humidity of the ambient air surrounding the material and / or substrate being processed. Passive cooling is normally carried out at a temperature of approximately 25°C to 30°C and, generally, at a relative humidity of approximately 50%. "Active cooling," as used herein, means the cooling of a material and / or substrate by means of a driven cooling source. The driven cooling source may be a cooling fan or a coolant chamber. Active cooling may also be achieved, or alternatively, by other means, such as by the use of a pressure chamber whereby the pressure in the chamber is reduced relative to the ambient pressure outside the chamber, thereby lowering the temperature inside the chamber. The temperature in the active cooling stage is typically from approximately 10°C to approximately 25°C. Active cooling may further comprise a dehumidifier such that the relative humidity in the active cooling stage is from approximately 5% to approximately 40%, preferably from 10% to 30%. The terms "releasably joined," "releasably coupled," and their variations refer to two items that are connected or can be connected in such a way that the items tend to remain connected in the absence of a separating force applied to one or both items, and that the items are capable of separating without substantial permanent deformation or breakage. The separating force required is typically greater than that obtained by using the absorbent garment. The terms "nonwoven," "nonwoven fabric," or "nonwoven web" are used interchangeably to refer to an engineered, primarily flat, fibrous assembly that has been given an engineered level of structural integrity by physical and / or chemical means, excluding weaving, knitting, or papermaking (ISO 9092:2019 definition). Directionally or randomly oriented fibers are bonded by friction, cohesion, and / or adhesion. The fibers may be of natural or synthetic origin and may be continuous or discontinuous filaments or formed in place. The fibers available on the market have diameters ranging from less than approximately 0.001 mm to more than approximately 0.2 mm and come in several different forms, such as short fibers (known as staple or chopped fibers), continuous individual fibers (filaments or monofilaments), untwisted bundles of continuous filaments (tow), and twisted bundles of continuous filaments (yarn).Nonwoven webs can be formed by many processes, such as meltblowing, spunbond, solvent forming, electrospinning, carding, and air laying. The basis weight of nonwoven webs is usually expressed in grams per square meter (g / m² or gsm). "Carded web (or layer[s] or nonwoven material)" refers to webs made from staple fibers fed through a combing or carding unit, which opens and aligns the staple fibers in the machine direction to form a fibrous nonwoven web, generally oriented in the machine direction. The web is then bonded by one or more of several known bonding methods.Nonwoven web bonding can be achieved by several methods: powder bonding, where a powdered adhesive or binder is distributed across the web and then activated, usually by heating the web and the adhesive with hot air; pattern bonding, where heated calender rolls or ultrasonic bonding equipment are used to join the fibers together, usually in a localized bonding pattern, although the web can be bonded across its entire surface if desired; through-air bonding (or airflow bonding), where a flow of air hot enough to soften at least one component of the web is directed across the material; chemical consolidation using, for example, latex adhesives deposited onto the web, for example, by spraying; and consolidation by mechanical methods such as needle punching and waterjet interlacing. "Dry laying," as used herein, refers to a process for making a nonwoven web from dry fiber; these terms apply to carded web forming as well as air-formed random web forming; a network of fibers produced by dry laying is referred to herein as a "dry lay"; a dry lay web bonded by one or more techniques to provide fabric integrity is referred to herein as a "dry lay nonwoven". The term "high volume" refers to bulky, low-density fabrics, as opposed to flat, paper-like fabrics. High volume fabrics are characterized by relatively high porosity. This means there is a relatively large amount of void space between the fibers where superabsorbent polymer particles can be distributed and / or impregnated. The high volume layer (without the superabsorbent particles) of the invention can have a density at a pressure of 4.14 kPa (0.6 psi) below 0.20 g / cm³, particularly in the range of 0.01 g / cm³ to 0.20 g / cm³, or 0.05 g / cm³ to 0.15 g / cm³, or 0.10 g / cm³ to 0.14 g / cm³. The high-volume layer (without the superabsorbent particles) of the invention can have a density at a pressure of 2.07 kPa (0.3 psi) below 0.20 g / cm3, particularly in the range of 0.05 g / cm3 to 0.15 g / cm3, or from 0.08 g / cm3 to 0.13 g / cm3.The high-volume layer (without the superabsorbent particles) of the invention can have a density at a pressure of 0.83 kPa (0.12 psi) below 0.15 g / cm3, particularly in the range of 0.01 g / cm3 to 0.15 g / cm3, or 0.05 g / cm3 to 0.12 g / cm3, or 0.08 g / cm3 to 0.10 g / cm3. The density can be calculated by dividing the basis weight of the high-volume layer by its thickness measured at the respective pressure, as indicated (for such measurements a method according to ASTM D1777 WSP 130.1 (09) may be used, and the measurements are preferably carried out on the raw material before impregnation with superabsorbent particles (i.e., the preprocessed raw material and / or the raw material supplied by a vendor). The term "curing", as used herein, normally refers to a process by which resins, binders and / or plastics (and / or UV-activatable and / or heat-activatable adhesives, as described herein) are placed on or onto fabrics (preferably a non-woven layer or substrate), normally by heating and / or light and / or UV, to make them stay in place and / or provide fixation and / or adhesion between materials and / or layers; hardening may be achieved by removing the solvent or by crosslinking to make them insoluble. The embodiments of the articles and processes will now be described according to the description. It is understood that the technical characteristics described in one or more embodiments may be combined with one or more other embodiments without departing from the intent of the description and without generalizing from it, especially when such combinations are inferred explicitly or implicitly. The absorbing core Referring to the examples in Figures 1 to 3, the absorbent cores (1) of the present specification, for use in absorbent articles (12), normally extend in a transverse (x) and longitudinal (y) direction, and may comprise: a fluid-permeable top layer (2), which is generally oriented towards the body; a bottom layer (3), which is generally oriented towards the garment compared to the top layer; one or more middle layers (4) sandwiched between the top layer (2) and the bottom layer (3), each middle layer having a front edge (5), a back edge (6), and two longitudinally extending side edges (7, 8), wherein the middle layer (4) is a high-volume fibrous nonwoven layer that is free of cellulose fibers;wherein the high-volume fibrous layer or woven fabric preferably comprises, or consists of, a carded air-consolidated nonwoven or a dry-bonded thermally bonded nonwoven; and wherein the central layer (4) is impregnated with superabsorbent particles (9) such that said particles are comprised within a thickness (z) of said central layer, said thickness extending perpendicularly to both the transverse (x) and longitudinal (y) directions, and wherein the high-volume fibrous nonwoven layer is substantially free of hot-melt adhesive and / or substantially free of adhesive, for immobilizing said superabsorbent particles (9). Preferably, the middle layer (4) comprises a void volume greater than the void volume of the fluid-permeable upper layer, preferably wherein the upper layer has an average pore size and / or void volume smaller than the average diameter of the superabsorbent particles. The lower layer may also have an average pore size (in this specification, typically its average diameter) and / or void volume smaller than the average diameter and / or volume of the superabsorbent particles. Advantageously, this allows the superabsorbent particles to be retained so that they cannot migrate to the upper surface in contact with the subject's skin (or to the lower surface in contact with the impermeable backsheet, thus limiting the risk of perforation and leakage), and may also be beneficial in further limiting rewetting. In one embodiment, the superabsorbent particles (9) are restricted and / or mechanically immobilized by a network (10) of fibers from the high-volume fibrous nonwoven layer. This allows for a reduction in the amount of adhesive required to immobilize the superabsorbent particles. Referring to Figure 8, in one embodiment, the absorbent cores (1) of the present specification comprise more than one core layer (4), wherein at least one first core layer is stacked on and / or above at least one second core layer. Preferably, each of the core layers is impregnated with superabsorbent particles, generally as described herein, and wherein an additional absorbent layer (WL) is interposed between the first core layer and the second core layer, preferably such that the liquid not absorbed by the first core layer enters into fluid communication with said absorbent layer, which acts as an intracore distribution layer to generally spread and convey the liquid to the second core layer.In this embodiment, it is preferred that the first middle layer comprises superabsorbent particles consisting essentially of SAP1 (as described later in this specification) and that the second middle layer comprises superabsorbent particles consisting essentially of SAP2 (as described below in this specification), wherein the first middle layer is positioned above the second middle layer such that it is closer to the upper layer than the second middle layer. The absorbent layer of this specification may be a nonwoven material selected from the group of dry-laid, air-laid, wet-laid, bond-spun, melt-blown, and combinations thereof, preferably an air-laid or wet-laid nonwoven material.In one embodiment, the absorbent layer is a nonwoven fabric comprising a thermal bond selected from calendering; or a mechanical bond selected from needle punching or hydrocrosslinking, preferably hydrocrosslinking. In a preferred embodiment, the absorbent layer is a hydrocrosslinked nonwoven fabric. In a highly preferred embodiment, the absorbent layer is free of synthetic fibers and typically comprises cellulose or crosslinked cellulose fibers that may form part of the nonwoven structure and / or be composed as staple fibers. In one embodiment, the absorbent layer comprises hemp fibers. Advantageously, such absorbent layers not only aid in fluid distribution but also provide an additional barrier to the migration of superabsorbent particles between the core layers.Furthermore, since the absorbent layer is placed between the middle layers (away from the subject / user's skin), non-woven fabrics, which have typically been less desirable due to their high rewetting (although they have good fluid transport capacity), are now desirable in the applications in this memory, as well as allowing for more sustainable executions without synthetic fibers. The absorbent layers in this document may have a basis weight of 10 g / m2 to 50 g / m2, preferably 15 g / m2 to 45 g / m2, even more preferably 18 g / m2 to 40 g / m2, even more preferably 19 g / m2 to 35 g / m2. In a preferred embodiment, the absorbent layer comprises a plurality of roughness features (typically in the form of a plurality of macropeaks and valleys). The roughness features are typically formed at least on the outermost top and / or bottom faces of the absorbent layer and can be formed by stamping the absorbent layer with one or more patterns (e.g., a wavy pattern or ridge) and / or by creating fiber-densified and non-densified regions, for example, by other mechanical means such as variable-speed rolling with pull and / or push along the machine direction and / or in the transverse machine direction. The densified regions on a substrate can have a thickness that is less than approximately half, preferably less than approximately 1 / 3, of the thickness of the non-densified areas of the substrate, for example.Each surface roughness can be described as having a crest (C) at its highest point and a depression (T) at its lowest point, and can be defined by a roughness length, a roughness amplitude, and a roughness frequency. The roughness length is generally defined by the linear distance in the machine direction (MD) between two adjacent crests; the amplitude (A) is generally defined by the linear distance in the z-direction between an adjacent crest (C) and a depression (T); and the frequency (F) is generally defined by the roughness length per unit length, resulting in the number of roughnesses per cm. Measurements are typically taken using optical microscopy with image analysis. A suitable instrument is a HIROX microscope (model KH7700) equipped with an OL-35 adapter and an MXG 10-C lens or equivalent. An external white light source can be used. Images are acquired and analyzed using HIROX software (version 2).10C) or equivalent 3D image analysis software. The sample to be analyzed is preferably preconditioned at 23 °C ± 2 °C and a relative humidity of 50% ± 2% for 2 hours before the test. When the absorbent layer is a nonwoven fabric comprising hydro-interlaced fibers, it is preferable that the roughness comprises fiber-densified regions and fiber-non-densified regions that can be formed by using a printed perforated plate onto which the fibers are deposited before the water jets are applied in the hydro-interlacing bonding process. For example, the printed perforated plate may comprise a plurality of openings that are aligned to form alternating first and second opening zones, wherein the first zones comprise openings that are closer together and / or have a smaller diameter than the second zones.The first and second zones can be arranged in a repeating alternating pattern that forms substantially continuous, substantially straight, or sinusoidal shapes (i.e., openings that have similar characteristics as a whole, for example, closer together or smaller in size, will be arranged together in substantially straight or substantially continuous sinusoidal lines / matrices). In this way, the resulting nonwoven fabric can comprise a plurality of alternating wave-shaped roughness patterns that can be advantageously used as absorbent layers in this specification. In one embodiment, the absorbent layer (WL) comprises a nonwoven material selected from the group consisting of a carded air-consolidated nonwoven or a dry-bonded thermally bonded nonwoven, preferably one that has not undergone void bulking and is generally substantially free of superabsorbent particles impregnated within or through it. In this embodiment, it is preferable that the basis weight of the absorbent layer (WL) be a, preferably a, of the basis weight of the core layer (4) (the latter measured in the absence of superabsorbent particles impregnated therein and through it). The roughness amplitude (A) can be from 0.5 mm to 5.0 mm, preferably from 0.8 mm to 3.5 mm; and / or the roughness frequency (F) can be from 0.5 to 10 roughnesses per cm, preferably from 1 to 5 roughnesses per cm. In one example, with reference to Figure 9, the absorbing layer may have a first plurality of roughnesses, having a first amplitude (A1) and a first frequency (F1), and a second plurality of roughnesses, having a second amplitude (A2) and a second frequency (F2); typically where the first amplitude (A1) is greater than the second amplitude (A2) and / or where the first frequency (F1) is less than the second frequency (F2). Preferably, the first plurality of roughnesses of the absorbing layer is positioned so as to substantially correspond to the deposition area (AD) of the central layer(s), and the second plurality of roughnesses is generally positioned outside of it (when viewed in a planar direction as described herein).These embodiments advantageously allow the formation of macrochannels within the core that further help to guide the liquid over a larger surface area (when viewed in a flat direction as described in this document) between the central layers for optimal, rapid, and efficient liquid absorption. Preferably, the high-volume fibrous nonwoven layer has undergone a reduction in void volume from a second void volume, which generally corresponds to the deposition of superabsorbent particles onto it, to a third void volume, which generally corresponds to a state where the superabsorbent particles have been deposited and impregnated onto it and / or where the third void volume is smaller, preferably at least 1.2 times smaller, or even more preferably at least 2 times smaller, than the second void volume. This improves the mechanical restraint effects on the impregnated superabsorbent particles within the fiber network of the high-volume fibrous nonwoven layer, while minimizing the use of adhesive. In one embodiment, the superabsorbent particles (9) are impregnated in a pattern comprising one or more substantially particle-free areas arranged to form one, two, or more continuous or discontinuous longitudinally extending channels (11) substantially free of superabsorbent particles (9), wherein said channels extend substantially parallel to the longitudinal (y) direction. Preferably, the channels (11) are flanked and / or enclosed by superabsorbent particles (9) when viewed in a planar direction where the respective plane is formed by the transverse (x) and longitudinal (y) directions. The channels are preferably positioned within a perimeter of the core.As described later, this allows for the formation not only of rapid fluid distribution zones within the core, but also creates bonding areas that can be used for the mechanical bonding of the upper / lower layers to the central layer. This limits the amount of adhesive used and, at the same time, reduces core rigidity and damage to the superabsorbent particles and / or the upper / lower layers themselves. Advantageously, this allows for the formation of fold lines to aid in cup formation and fluid flow distribution. Preferably, as exemplified in Figure 2, the channels (11) are discontinuous and where the sum of the areas (viewed from a flat view) amounts to 10% to 45%, preferably 15% to 30%, even more preferably 18% to 25%, of the total (preferably flat) surface area of ​​the absorbing core (1). Typically, the channels (11) are comprised in a plurality of preferably more than 4 channels (typically from 5 to 50, 10 to 40 and / or 15 to 30) and wherein the aspect ratio of said channels (the longest dimension divided by the shortest dimension) is greater than 1, preferably from 1.2 to 15, more preferably from 1.3 to 10, even more preferably from 1.4 to 8, even more preferably from 1.5 to 5, even more preferably from 1.6 to 3. Typically, wherein the longest dimension of the channels is substantially parallel to the longitudinal (y) axis.Advantageously, this not only allows for the formation of numerous rapid liquid distribution structures between regions with absorbent material (i.e., the absence of absorbent material along their length, which could otherwise slow the liquid flow due to its absorption / expansion effects), but also enables the formation of bonding areas where the nonwoven layers or bands can be mechanically joined together. This limits the risk of damaging the SAP and the risk of puncturing the layers, which could otherwise allow the SAP to seep through and potentially pierce the user's skin. Preferably, the channels are arranged as islands within a sea of ​​absorbent material (or superabsorbent particles), typically when viewed in a flat direction, as described herein and illustrated in the figures. Alternatively, the superabsorbent particles (9) are impregnated into a channel-free pattern (11) substantially free of superabsorbent particles (9). In this embodiment, a UV-curable adhesive (preferably in powder (or granular) or liquid form, although liquid thixotropic fluids are preferred) is preferably applied at or immediately after the deposition stage, as described later in the process section.Advantageously, this provides an alternative to hot melt adhesive and allows for limiting or even preventing the substrate from being overloaded with adhesive (using traditional coating techniques, such as spraying or groove coating) on ​​the surface of the core layer (typically closer to the top and / or bottom layers). This can affect not only product durability but also liquid absorption performance due to the typical hydrophobic nature of the core layer, which forms a film, barrier, or obstacle to the liquid. This contrasts with the discrete, network-like structure generally formed by UV-curable adhesives. When the UV-curable adhesive is a liquid, it preferably has a viscosity greater than 5000 cPs (5 Pa·s) (at 25 °C) and preferably a thixotropic index greater than 2, measured according to ISO / WD 3219-1.UV-curable adhesives for use in this document may be selected from modified acrylates, and some examples of commercially available adhesives include EA6062, EA6114, U3334, U3349TX manufactured and sold by HB Fuller Company, 9001 W. Fey Drive, Frankfort, Illinois 60423. In a preferred embodiment, the high-volume fibrous nonwoven layer is free of hot-melt adhesive and preferably channel-free, as it is substantially free of absorbent material. In one embodiment, the fibers (10) of the high-volume fibrous nonwoven layer comprise or consist of a material selected from the group consisting of: polylactic acid or derivatives thereof, polylactic-co-glycolic acid or derivatives thereof, polyhydroxyalkanoates or derivatives thereof, biopolyethylene, biopolypropylene, and mixtures thereof, preferably polylactic acid or derivatives thereof. Advantageously, this not only reduces the carbon footprint, making the entire absorbent article more environmentally friendly, but also facilitates the recycling or composting of the used absorbent article.As described in more detail below, these materials are normally associated with poor softness and their widespread use has been somewhat limited so far due to performance drawbacks that the inventors have mitigated in the core layers and processes of the present memory, particularly by increasing / decreasing the volume of gaps, as described in more detail in the present memory. In one embodiment, the middle layer (4) differs from the upper and lower layers (2, 3), preferably comprising a multilayer nonwoven material made of spunbond and / or meltblown fibers. Preferably, the multilayer nonwoven material is selected from the group consisting of SS, SSS, SM, SMS, and SMMS. Advantageously, structures with greater mechanical integrity are formed, and they can also have lower porosity and / or pore size to mitigate particle migration. The absorbent cores of the present specification may comprise at least 60% by weight of superabsorbent particles, in particular at least 70% by weight, preferably at least 80% by weight, preferably at least 90% by weight, in total weight of the core. In one embodiment, the superabsorbent particles comprise a mixture of superabsorbent particles comprising a first superabsorbent particle (SAP1) and a second superabsorbent particle (SAP2), wherein the first superabsorbent particles (SAP1) have an AUL that is greater than the AUL of the second superabsorbent particles (SAP2), and wherein the first superabsorbent particles (SAP1) have an AUL greater than 15 g / g, according to the test method of the present specification, preferably wherein the first superabsorbent particles (SAP1) have a particle size distribution that is greater than that of the second superabsorbent particles (SAP2).Preferably, wherein at least the second superabsorbent particles (SAP2) comprise, preferably consist of, bio-based superabsorbent composite polymer particles comprising a synthetic hydrophobic polymer and a natural biopolymer, more preferably composed of a composite polymer comprising a copolymer of styrene and maleic acid and a biopolymer of animal or vegetable origin; or non-composite polymeric particles selected from polyacrylic acid, sodium salt, crosslinked and partially neutralized superabsorbent particles. Preferably, the second superabsorbent particles (SAP2) comprise, preferably consist of, BioSAP with low AUL content. "BioSAP with low AUL content" means that they generally have an AUL (measured according to the test method in this specification) of less than 20 g / g, typically less than 15 g / g, and typically belong to the following classes: (a) materials consisting solely of crosslinked biopolymers; (b) materials consisting solely of crosslinked synthetic polymers; (c) composite materials consisting of synthetic polymers and biopolymers in certain variations: crosslinked type with or without chemical agents; graft type; intercomplex type; and interpenetrating type. Copolymers such as styrene-maleic acid are typically used in copolymerization processes to achieve a BioSAP with low AUL content.Other exemplary sources include alpha-1,3-glucan, starch, starch and / or sodium salts, sugar, and derivatives. Examples of low AUL BioSAPs available on the market for use in this specification include: Loaded modified starch-derived SAPs sold by TETHIS, 5237 Capital Blvd., Raleigh, NC 27616, USA, and further exemplified in US Patent 20200054782 A1; SAPs comprising 100% acrylic acid coacrylamide with little or no crosslinking layer, and the like, which generally have an AUL of less than 20 g / g according to the test method in this specification. Preferably, the first superabsorbent particles (SAP1) are BioSAP-free with low AUL content. Advantageously, this limits the rewetting drawbacks as described herein. In one embodiment, SAP1 is a BioSAP "composite polymer" with high AUL content (i.e., a biodegradable superabsorbent composite polymer having an AUL greater than 15 g / g, preferably greater than 20 g / g, as will be described in further detail herein). The composite polymer may comprise a synthetic hydrophobic polymer and a natural biopolymer. More specifically, the composite polymer may comprise a styrene-maleic acid copolymer and a biopolymer of animal or plant origin according to the technological flow diagram presented in Figure 5. The styrene-maleic acid copolymer is preferably in the form of a salt, more preferably in the form of a monovalent cationic salt.Alternatively, high AUL BioSAP, although less preferred, may comprise "non-composite polymers" and instead be selected from certified biomass superabsorbent polymers having an AUL greater than 15 g / g, preferably greater than 20 g / g, and typically certified by RedCert2 (https: / / www.redcert.org / images / SP_RC%C2%B2_Biomass-balanced_products_V1.0.pdf). An example might be a crosslinked and partially neutralized polyacrylic acid, sodium salt SAP made from up to 100% allocated biomass feedstock, such as the commercially available HySorb® B 6600MB manufactured and marketed by BASF SE, Ludwigshafen, Germany. In an embodiment of the BioSAP "composite polymer" with high AUL content, the styrene fraction of the synthetic polymer can be replaced by other hydrophobic fractions. Examples of synthetic polymers include: poly(maleic anhydride-co-methyl vinyl ether) (Gantrez), poly(vinyl chloride-co-maleic acid), and poly(maleic anhydride)-alt-(vinyl acetate). The term "compound," as used herein, refers to a polymeric substance that (a) is formed from at least two polymers with different macromolecular chemical structures; and (b) the resulting compound is a single entity that does not spontaneously separate into its components during application. It is understood that the term "compound" may include other substances such as drugs, stimulants, inhibitors, odorants, emollients, plasticizers, and others. The term "anionic" refers to a polymeric compound that generates a negative electrochemical potential in aqueous media as a result of the presence in its structure of some free acid functional groups capable of dissociating into anions. In an embodiment described in Figure 5, the production process begins with the synthesis of the copolymer (styrene-maleic anhydride) by bulk copolymerization using an excess of approximately 60-90% of maleic anhydride relative to styrene, while the maleic anhydride also functions as a solvent (operation 100). Copolymerization is typically performed in Sigma-type mixing machines called hermetic machines to be able to work at high pressures, for example, not exceeding 10 bar (1 MPa) or under vacuum conditions (less than 10 mbar (1 kPa)) with a double mantle and with arms equipped with a heating and cooling system. The copolymerization process for the production of a superabsorbent polymer typically uses styrene monomer stabilized with organic compounds that inhibit the homopolymerization process during storage and transport. Such inhibitors are, for example, substances such as: amino derivatives, thiol derivatives and hydroxyl derivatives (such as (2-hydroxypropyl)-ethylenediamine compounds, 4-tert-butylcatechol and others), 4-tert-butylcatechol being preferred in a proportion of 0.002-0.008% to the monomer, more preferably 0.003-0.007% to styrene and most preferably 0.004-0.006% to styrene and the mole fraction of styrene in the reaction mass being 0.05-0.08, preferably 0.1-0.15 and most preferably 0.18-0.21.The copolymerization may also contain maleic anhydride which is either fresh maleic anhydride MAnh or recovered maleic anhydride MAnh-R that is recycled from a previous batch as shown schematically in Figure 5, and the amount of fresh maleic anhydride MAnh relative to the recovered maleic anhydride MAnh-R is approximately 1.-40% (relative to the dry substance). For copolymerization, other common agents such as peroxides, azo compounds, etc., which form free radicals by thermal decomposition, can be used, while the amount of initiator is 0.05-0.15%, preferably 0.07-0.009% and most preferably 0.08-0.12% to twice the amount of styrene adopted for copolymerization. Next, you can proceed to the conversion of the styrene-alt-maleic anhydride copolymer to a styrene-alt-maleic acid copolymer by hydrolysis with water (process 200), which is carried out in the same equipment where the copolymerization was performed. Conversion of the styrene-alt-maleic anhydride copolymer to a styrene-alt-maleic acid copolymer by hydrolysis using a quantity of water greater than the stoichiometric amount required for total hydrolysis (Ws), with an excess representing 2-3% relative to the stoichiometric value, preferably more than 4-5% relative to the stoichiometric water, and most preferably 5-10% in excess relative to the stoichiometric water. The total amount of water required for the hydrolysis of styrene and maleic anhydride copolymer is typically inserted into the reaction mass in two stages, of which 50% is in the form of 0.005 N hydrochloric acid solution and the remainder as unacidified water. The acidified water is typically added to the reaction mass in two parts at a bulk reaction temperature not exceeding 60 °C, with 15-minute intervals between each addition. The unacidified water is also added to the reaction mass in two parts, the first being added 60 minutes after the last portion of acidified water. The final portion of unacidified water is then added, and the reaction mass is mixed for 45–60 minutes under cooling conditions of 35–40 °C. The resulting reaction mass after hydrolysis is a moist, white, powdery solid with an apparent density of 0.6–0.8 g / cm³.In addition, the reaction mass produced after copolymerization and hydrolysis (which is a combination of styrene-maleic acid copolymer (SMAC) and maleic acid-free (MAC), containing a trace amount of unreacted styrene and stabilizer for styrene, as well as traces of hydrochloric acid) is transferred to carry out the purification process of the styrene-maleic acid copolymer (process 220). The purification process representing the extraction of the free maleic acid fraction from the SMAC polymer mass is typically carried out in equipment such as a mixing tank type where the reaction mass resulting after the hydrolysis of the synthetic copolymer is added to an amount of deionized water for purification [Wp] that represents an amount correlated with the wet reaction mass (RM) according to the ratio Wp = 2 * RM or Wp = 5 * RM, preferably Wp = 3 * RM. Purification generally consists of 3–5 extraction stages followed by filtration each time. The number of extraction and filtration operations is set so that the content of free carboxylic groups found in the SMAC polymer is between 0.00909–0.0095 mol / gram, preferably between 0.0091–0.0094 mol / gram, and more preferably between 0.0092–0.0093 mol / gram. In fact, the extraction is preferably carried out at a temperature of 60 °C for 30 minutes, and each filtration (process 230) is performed using equipment known as a filter press or Nuce filter. All the solutions resulting from the filtration are collected in a supernatant tank for processing the maleic acid they contain. The processing of the aqueous maleic acid solution for the recovery of maleic anhydride preferably consists of the following operations: a) concentration of the maleic acid solution by reverse osmosis; b) spray drying of the concentrated maleic acid solution to obtain maleic acid powder and water; c) conversion of the maleic acid powder to maleic anhydride by thermal vacuum dehydration (with technological parameters modified from those mentioned in US patent 4,414,398) to obtain a material called recovered maleic anhydride (MANH-r). The purified filtrate of the SMAC polymer is typically collected in a Sigma mixer-type unit for processing with biopolymers to obtain the water-soluble composite polymer containing the synthetic SMAC polymer and biopolymer [WSPC] (process 300).The process of preparing the polymer compound [WSPC] containing SMAC and a biopolymer of animal or vegetable origin is preferably preceded by other operations such as the following: a) The preparation of a basic solution is obtained by dissolving a solid hydroxide compound in water up to 40% by weight, while examples of preferred base hydroxide compounds are sodium hydroxide, lithium hydroxide, potassium hydroxide, ammonium hydroxide, preferably sodium hydroxide; b) transformation of the styrene-maleic acid copolymer obtained in step 230 into a monovalent cationic styrene-maleic acid salt by eutralization with the basic solution prepared in a) above to obtain a copolymer salt solution with a concentration greater than 25%, preferably greater than 35% and most preferably greater than 50%.The neutralization of the SMAC copolymer is 48-58%, preferably 50-56% and most preferably 52-54%; c) preparation of the biopolymer (such as gelatin, albumin, casein, soy, guar or starch, preferably gelatin) as a 40% wt% aqueous solution in water; d) the preparation of the polymer compound is carried out by treating the styrene maleic acid salt solution with a biopolymer solution at a temperature of 55-75 °C for 30 minutes. The amount of biopolymer relative to the copolymer in the compound is preferably 4-6% (dry basis), preferably 8-10% (dry basis), and most preferably 12-14% (dry basis). The mixing of the compound mass typically continues for 4-5 hours until the polymer mass transforms from a viscous solution into a partially dry granular mass with a moisture content not exceeding 20%. This partially dried, granular WSPC polymer composite is typically subjected to further drying (process 320) at temperatures preferably of 75-85 °C using a conveyor belt or rotary type to achieve final drying to a moisture content of less than 14%, preferably less than 12%, and most preferably less than 8%. Preferably, additional dehydration, crushing, and sieving steps (process 330 + process 340) are carried out to obtain two types of solid phases, referred to herein as large solid phase (LSP) with a particle size distribution greater than 100 micrometers, preferably 100–850 micrometers, corresponding to its use in diaper manufacturing, and small solid phase (SSF) with a particle size distribution up to 100 micrometers. The small solid phase SSF is reused in the preparation of the next new batch of SAP that enters process 300. Large solid-phase LSP can be subjected to post-treatment surface coating processes using chemicals such as glycerin, ethylene glycol, propylene glycol, or polyhydroxyl ether with biodegradable properties. Examples of preferred coating materials are polyhydroxyl ether, most preferably polyethylene glycol (PEG 200) used at a ratio of 0.2–2% wt (dry basis) with respect to LSP, preferably at a ratio of 0.5–1.5% wt, and most preferably at a ratio of 0.8–1.2% wt with respect to LSP. The surface coating can be applied using equipment such as powder coating machines at temperatures generally of 30-70 °C, preferably at temperatures of 35-65 °C and most preferably at temperatures of 40-60 °C for 30-90 minutes, preferably for 40-75 minutes and most preferably for 50-60 minutes. As a result of this process, the material obtained is called treated coated polymer composite (PCC) (operation 350). The material obtained after surface coating (polymer composite coating) can be subjected to a heat treatment called first heat treatment (TT1) (operation 400) which consists of heating the mass of particles in hot air at a temperature of 90-140 °C for 30-150 minutes, preferably with temperatures of 100-135 °C for 45-120 minutes and most preferably by bulk thermal crosslinking at temperatures of 110-120 °C, for 60-90 minutes using conveyor belt or rotary vibratory type equipment when an intermediate material called first crosslinked coated polymer composite (PCC-CL-1) is obtained. The PCC-CL-1 material can be subjected to a further heat treatment (TT2) (operation 410) in hot air at a temperature of 120-150 °C for 5-30 minutes, preferably at temperatures of 125-145 °C for 10-25 minutes, and most preferably at a temperature of 120-140 °C for 15-20 minutes in the same type of equipment used for TT1, yielding the second crosslinked coated polymer compound (PCC-CL-2). The material (PCC-CL-2) can then be conditioned for 24 hours in an atmosphere where the air has a humidity content of 65% and a temperature of 20 °C and subsequently packaged in sealed polyethylene bags (operation 500). The resulting material after conditioning is a biodegradable SAP with an AUL greater than 20 g / g in 0.9% aqueous NaCl solution at a pressure of 0.9 psi, which represents the final product of the manufacturing process that is the subject of the present invention, i.e., the "biodegradable superabsorbent composite polymer with high AUL content" referred to in this document. Reference is made to joint application EP21152698.3 for further examples of BioSAP with low AUL content and BioSAP with high AUL content that can be used in absorbent cores in this document, with particular reference to Example 1. In one embodiment, the first superabsorbent particles (SAP1) comprise a level of less than 80% by weight, preferably from 10% to 32% by weight; and the second superabsorbent particles (SAP2) comprise a level of at least 20% by weight, preferably from 25% to 100% by weight, more preferably from 30% to 90%, even more preferably from 35% to 80%, even more preferably from 40% to 70%, even more preferably from 45% to 68%, by total weight of superabsorbent particles. Preferably, the AUL ratio (AULSAP1 / AULSAP2) of the first superabsorbent particles (SAP1) and the second superabsorbent particles (SAP2) is greater than 1.4, preferably greater than 1.5, more preferably 1.6 to 5, and even more preferably 1.7 to 3. Advantageously, this allows for ensuring the right balance between reduced rewetting and rapid liquid absorption, especially in the lower layer, and optimal performance under load. In one embodiment, the first superabsorbent particles (SAP1) have a lower absorption rate (typically according to the vortex method described herein) than the second superabsorbent particles (SAP2). Preferably, the vortex time (according to the vortex method described herein) of SAP1 is greater than 50 seconds, preferably from 60 to 90 seconds. Preferably, the absorption rate of SAP2 is less than 45 seconds, preferably less than 40 seconds, and even more preferably from 15 to 35 seconds. Suitable core layers for use in this document may be, for example, a triple-layer non-woven material having a basis weight of 55 to 150 g / m2 that has: - a first layer that corresponds to 15-25% of the weight (for example, 37.5 g / m2) and consists of a mixture of fibers (as described in this document) that has a value between 2 dtex (0.0000002 kg / m) and 28 dtex (0.0000028 kg / m); - a second layer corresponding to 15-25% of the weight (for example, 37.5 g / m2) and consisting of a mixture of fibers (as described in this document) having a value between 0 dtex (0 kg / m) and 7 dtex (0.0000007 kg / m), and The third layer comprises 50–70% of the weight (e.g., 75 g / m²) and consists of a fiber blend (as described herein) with a density between 2 dtex (0.0000002 kg / m²) and 28 dtex (0.0000028 kg / m²). Without intending to impose any theory, a material's ability to increase or decrease its void volume generally depends on at least one of the following characteristics: the material's chemical composition, the spatial shape (of the fibers and / or their bonding pattern), the material's curvature, the fiber type, and the fiber composition. Preferably, the middle layer comprises at least two types of fibers: (i) binding fibers and (ii) carrier fibers. The binding fibers can be, for example, two-component core-sheath fibers, and the carrier fibers can be, for example, bioPE fibers. In a preferred embodiment, the high-volume fibrous nonwoven layer preferably comprises a blend of fibers and / or bicomponent fibers (such as binder fibers and carrier fibers as described herein) of a material selected from the group consisting of: polylactic acid (PLA) or derivatives thereof, polylactic-co-glycolic acid (PLGA) or derivatives thereof, polyhydroxyalkanoates (PHA) or derivatives thereof, biopolyethylene (bioPE), biopolypropylene (bioPP), and blends thereof. For example, the fibers may be selected from Bio-PE / Bio-PP, PLA / Bio-PP, PLA / PHA, PLA / PLGA, PHA / PLGA, PLA / PLGA, PLA / Bio-PE, PHA / Bio-PP, and PLGA / Bio-PP, and / or combinations thereof. In particular, PLA and its blends are preferred for their sustainable nature, although traditionally it has been associated with poor smoothness, particularly exacerbated in structures with a high adhesive load.Advantageously, the use of PLA and blends within the central layers of the present memory and the reduced use of adhesive allow for a flexible structure that is sustainable and, moreover, does not provide consequences that harm the roughness or smoothness on the user's skin. In one example, the middle layer or layers comprise void volumes that are larger than the void volumes of the fluid-permeable upper layer, preferably where the upper layer has an average pore size and / or void volumes that are smaller than the average diameter of the superabsorbent particles. Typically, the middle layer or layers are porous layers, where porosity is defined in this document by a void volume ranging from approximately 300 to approximately 500 cm3 of void volume / m2, while the top layer is composed of fine hydrophilic fibers, ranging from 0.7 to 30 dtex (0.00000007 kg / m to 0.000003 kg / m) and preferably from 1.5 to 7 dtex (0.00000015 kg / m to 0.0000007 kg / m), which produces small voids and thus prevents the liquid from returning to the surface and also limits the possibility of superabsorbent particles migrating through it. Void volumes are related to the space between fibers, which are joined at multiple points, thus forming a matrix with cavities or voids. The void volume in a nonwoven material is a well-known parameter among those skilled in the art and corresponds to all the available space in a material that is not filled with material, such as fibers and SAP. Calculation and measurement can be performed using PMI porosimetry or air permeability. Preferably, the void volume, measured by air permeability at 100 Pa - 20 cm², corresponds to an air permeability between 1000 L / m² / s (1 m³ / m² / s) and 12000 L / m² / s (12 m³ / m² / s), more preferably between 2000 L / m² / s (2 m³ / m² / s) and 3000 L / m² / s (3 m³ / m² / s). The top and bottom layers are typically nonwoven or tissue paper; however, the bottom layer may be a film and may be impermeable to liquids, although it is preferably nonwoven. Low basis weight tissue paper, for example, is readily available and a relatively inexpensive substrate. The absorbent core may also comprise a wrapper layer (or center wrap) that completely covers and / or envelops the bottom or top layer and may form a C-wrap, sandwich wrap, or G-wrap around the lateral edges of the center layer(s). This wrapper extends longitudinally to at least partially cover the top or bottom layer, respectively, and provides better containment of the superabsorbent particles within the absorbent core, thus preventing particle loss, especially at the core's lateral edges.Alternatively, this central envelope can also be formed by the top layer or the bottom layer. The absorbent cores of the present specification may also comprise a multi-layered construction consisting of a first high-volume core layer and a second (or more) high-volume core layer. This construction may provide additional benefits, for example, in that a greater number of superabsorbent particles can be distributed within the multiple layers, and it also allows for the combination of even more superabsorbent grades and / or types of polymers between the layers for optimal liquid absorption performance throughout the core thickness. These and other optional features of the invention will be described herein. The thickness, basis weight, and density of the core layer are normally substantially homogeneous in both the transverse (x) and longitudinal (y) directions. The fiber orientation in the core layer is normally non-homogeneous, such as the predominant fiber orientation in an x-y direction, as is the case in carded nonwoven fabrics. Furthermore, the fiber orientation in the core layer in the z-thickness direction may differ from the predominant orientation in one or both the xy / y directions. The high-volume layer may, in particular, have a thickness of at least 0.30 mm, specifically ranging from 0.35 mm to 2.00 mm, or from 0.50 mm to 1.5 mm, measured at a pressure of 4.14 kPa (0.6 psi) (therefore, a method according to ASTM D1777 NWSP 120 may be used).2 (09) for such measurements, although a person skilled in the art will understand that other less preferred methods may be used, such as measurements of the gripper using an SDL Model No. 258b Portable Thickness Gauge (0.01 mm graduation) or equivalent; such method is preferably carried out for the nonwoven in the absence of entrained superabsorbent particles (e.g., directly from the unused raw material prior to entrainment / deposition of superabsorbent particles). The high-volume layer may, in particular, have a thickness ranging from 0.30 mm to 2.50 mm or from 0.5 to 2.0 mm or from 0.7 to 1.3 mm, measured at a pressure of 0.83 kPa (0.12 psi) (similarly to the above, a method according to ASTM D1777 NWSP 120 may be used).2 (09) but at the adjusted pressure; this method is preferably carried out for nonwovens in the absence of entrained superabsorbent particles (e.g., directly from the unused raw material before the entrainment / deposition of superabsorbent particles). The basis weight of the high-volume core layer can range, for example, from 15 g / m² to 500 g / m², preferably from 30 g / m² to 200 g / m², or, for example, from 55 g / m² to 150 g / m². The values ​​stated herein for the core layer are considered for the high-volume material taken in isolation, i.e., before the superabsorbent particles have been deposited between the fibers. When the absorbent core comprises two or more high-volume core layers, these may be the same or different. The central layer(s) of this material can generally serve as a substrate for superabsorbent particles that are at least partially distributed within its pores. The superabsorbent particles can be substantially uniformly mixed throughout the thickness of the high-volume layer or, preferably, heterogeneously distributed in the vertical and / or thickness direction.Preferably, the increase in void volume, generally during the heating stage (and typically the deposition stage) according to the processes described herein, comprises a gradient such that the void volume of the core layer closer to the upper layer is greater than the void volume of the core layer closer to the lower layer, and wherein the superabsorbent particles are heterogeneously distributed in the vertical and / or thickness direction, and preferably wherein the basis weight (in g / m²) of the superabsorbent particles is greater closer to the upper layer than closer to the lower layer, or vice versa. Advantageously, this allows for a reduction in gel blocking effects and modulation of liquid absorption along the core thickness direction.Superabsorbent particles are typically deposited on one side of the nonwoven fabric and drawn into the high-volume nonwoven layer, for example, by a combination of gravity, negative pressure on the opposite side of the nonwoven fabric, and optionally, an active medium that imparts kinetic energy, as will be described in more detail below. In this way, some particles remain near the surface of the high-volume core layer, while other, typically smaller, particles can penetrate deeper into the fiber network of the high-volume nonwoven. Superabsorbent particles that are not trapped within the pores of the high-volume fabric, but remain on the surface, can be further immobilized by forcing them through the fiber network using the kinetic energy transfer means and / or removed using removal methods such as air blowing and / or brushing.Preferably, the adhesive is not applied directly to the core layer. Small amounts of adhesive may be present when the top and bottom layers are combined with the core layer; however, when adhesive is present on the top and bottom layers, it is preferably applied substantially outside the deposition area and / or in a discontinuous pattern, typically to limit the amount of adhesive in the deposition area. Preferably, the top and bottom layers are bonded to the core layer(s) by mechanical bonding, such as ultrasonic bonding or other heat-sealing methods, as described in more detail herein. In a highly preferred embodiment, the core layer comprises a deposition area interposed between two longitudinally extending side areas, preferably arranged continuously and oppositely (typically extending along the machine direction and / or flanking the deposition area along the longitudinal edges of a perimeter of the core layer), wherein the sum of the areas of the side areas is less than the area of ​​the deposition area, typically when viewed in a planar direction as described herein and illustrated in the figures. In this embodiment, the deposition area comprises superabsorbent particles throughout the thickness of the core layer, and the side areas are substantially free of superabsorbent particles throughout the thickness of the core layer.The superabsorbent particles may be contained on an upper surface (generally facing the top layer) of the core layer in these lateral areas, but generally not in the direction of the core thickness. Advantageously, this allows for greater flexibility and a reduction in the stiffening effects associated with the highly loaded superabsorbent particle cores, and also enables the formation of a leak barrier, as described in more detail in the following embodiments. Preferably, the deposition area (AD) comprises at least a first zone and at least a second zone, where the first zone has a first basis weight of superabsorbent particles (in g / m²) and the second zone has a second basis weight of superabsorbent particles (in g / m²), and where the basis weight of the first superabsorbent particle is greater than the second basis weight of superabsorbent particles. Preferably, the basis weight of the first superabsorbent particle is greater than 250 g / m², more preferably from 300 g / m² to 500 g / m²; and where the basis weight of the second superabsorbent particle is less than 300 g / m², more preferably from 50 g / m² to 250 g / m². Advantageously, this not only allows for benefits in reducing monolithic stiffness effects but also enables better localized absorption. In the embodiment described above, it is preferable that the first and second zones be concentric, such that the first zone is substantially contained and / or surrounded by the second zone, or vice versa (generally when viewed in a planar direction as described herein and illustrated in the figures). Preferably, the first zone has a perimeter that substantially corresponds (in size, for example, mm) to a perimeter of an acquisition distribution layer, as described below. Alternatively or additionally, the first zone may comprise a surface area (generally when viewed in a planar direction) that substantially coincides (in position, for example, one overlapping or stacked on top of the other) with a surface area of ​​an acquisition distribution layer, as described below. The absorbent article Referring to the exemplary Figure 4, the absorbent articles (12) of this specification generally comprise a liquid-permeable top sheet (13), a liquid-impermeable back sheet (14), and an absorbent core (1) sandwiched between them, wherein the absorbent core (1) is as described above. The articles of this specification are preferably selected from the group consisting of disposable diapers and / or panties (including refastenable panties, i.e., panties with seams that can be detachably joined). The absorbent article further typically comprises a front portion (F), a back portion (B), and a crotch portion extending between them. Preferably, the absorbent article further comprises a collection and distribution layer (15) placed between the top sheet (13) and the absorbent core (1), wherein said collection and distribution layer (15) is a carded, spunbonded and / or hydro-linked nonwoven, preferably a carded air-consolidated nonwoven or a hydro-linked nonwoven; and / or wherein the collection and distribution layer (15) has a basis weight of 15 to 55 g / m2 and comprises fibers having an average diameter of 10 to 35 microns, preferably 15 to 30 microns, more preferably 17 to 27 microns. It is understood that the absorbent articles of this document may comprise one or more features common to such articles, such as one or more of: transverse and / or longitudinal sleeves to prevent leakage; one or more elastic panels and / or straps; one or more waist elastics; one or more male / female fastening tapes to hold the article in an open / closed position; and the like. The manufacturing process The process for manufacturing absorbent cores and / or articles in this specification, as illustrated in Figure 6 by way of example, normally comprises the steps of: (i) providing a first nonwoven band (N1), preferably substantially continuous, having a first void volume; (ii) selectively applying heat to said first nonwoven band (N1) such that a deposition area (AD) of said first nonwoven band (N1) increases its void volume to a second void volume that is greater than said first void volume; (iii) depositing and / or impregnating absorbent material, preferably comprising superabsorbent particles, onto the deposition area (AD) of said first nonwoven band (N1); (iv) passively or actively cooling the deposition area (AD) of said first nonwoven band (N1) so that the void volume is substantially reduced to the first void volume;(v) combining the first nonwoven band with the second and third nonwoven bands (N2, N3) such that the first nonwoven band (N1) is interposed between the second and third nonwoven bands (N2, N3), preferably joining the bands by mechanical bonding selected from hot pressing and / or ultrasonic bonding; wherein the first nonwoven band (N1) consists of a high-volume fibrous nonwoven layer that is free of cellulose fibers; the high-volume fibrous nonwoven layer preferably comprises a carded air-consolidated nonwoven or a dry-bonded thermally bonded nonwoven. Advantageously, this process allows the production of absorbent articles with a reduction in the use of adhesive to immobilize the superabsorbent particles. In a preferred embodiment, the fibers of the high-volume fibrous nonwoven layer (as described in more detail earlier in this specification) comprise, or consist of, a material selected from the group consisting of: polylactic acid or derivatives thereof, polylactic-co-glycolic acid or derivatives thereof, polyhydroxyalkanoates or derivatives thereof, biopolyethylene, biopolypropylene, and mixtures thereof, preferably polylactic acid or derivatives thereof. Advantageously, such materials not only allow for a reduction in microplastic content and an overall improvement in sustainability impacts, but are also beneficial because they react to heat (i.e., soften) to achieve the desired void volume expansion without necessarily requiring exposure to high temperatures (i.e., they also reduce the overall energy consumption of production). The first nonwoven band (N1) is different from the second and third nonwoven bands (N2, N3), preferably comprising a multilayer nonwoven fabric made of spunbond and / or meltblown fibers. The multilayer nonwoven fabric may be selected from the group consisting of: spunbond-spunbond (SS) nonwoven fabric, spunbond-spunbond-spunbond (SSS) nonwoven fabric, spunbond-meltblown (SM) nonwoven fabric, spunbond-meltblown-spunbond (SMS) nonwoven fabric, and spunbond-meltblown-meltblown-spunbond (SMMS) nonwoven fabric. In a preferred embodiment, the superabsorbent particles comprise a mixture of superabsorbent particles comprising a first superabsorbent particle (SAP1) and a second superabsorbent particle (SAP2), wherein the first superabsorbent particles (SAP1) have an AUL that is greater than the AUL of the second superabsorbent particles (SAP2), and wherein the first superabsorbent particles (SAP1) have an AUL greater than 15 g / g, according to the test method described herein, preferably wherein the first superabsorbent particles (SAP1) have a particle size distribution that is larger than that of the second superabsorbent particles (SAP2). Advantageously, SAP1 will tend to remain closer to the upper surface of the core layer, while SAP2 will tend to impregnate itself more deeply and closer to the lower surface of the core layer.This also allows for an improved balance between absorption rate and reduced rewetting, while mitigating gel-blocking effects that can be particularly undesirable in the absence of cellulose fibers and / or spongy pulp. Preferably, at least the second superabsorbent particles (SAP2) comprise, preferably consist of, bio-based superabsorbent composite polymer particles comprising a synthetic hydrophobic polymer and a natural biopolymer, more preferably composed of a composite polymer comprising a styrene-maleic acid copolymer and a biopolymer of animal or vegetable origin; or non-composite polymeric particles selected from polyacrylic acid, sodium salt, crosslinked, and partially neutralized superabsorbent particles. Further details and advantages are provided in the above embodiments. The first superabsorbent particles (SAP1) comprise less than 80% by weight, preferably from 10% to 32% by weight; and the second superabsorbent particles (SAP2) comprise at least 20% by weight, preferably from 25% to 100% by weight, more preferably from 30% to 90%, even more preferably from 35% to 80%, even more preferably from 40% to 70%, and even more preferably from 45% to 68%, by total weight of superabsorbent particles. Further details and advantages are provided in the preceding embodiments. In one embodiment, the AUL ratio (AULSAP1 / AULSAP2) of the first superabsorbent particles (SAP1) and the second superabsorbent particles (SAP2) is greater than 1.4, preferably greater than 1.5, more preferably from 1.6 to 5, and even more preferably from 1.7 to 3. Further details and advantages are provided in the above embodiments. In one embodiment, the second and third nonwoven bands (N2, N3) comprise, or consist of, fibers of a material selected from the group consisting of: polylactic acid or derivatives thereof, polylactic-co-glycolic acid or derivatives thereof, polyhydroxyalkanoates or derivatives thereof, biopolyethylene, biopolypropylene, and mixtures thereof, preferably polylactic acid or derivatives thereof. In this way, the content of non-biodegradable and / or difficult-to-compost polymers can be advantageously reduced. Preferably, the superabsorbent particles are applied in a pattern, such as in the form of at least two spaced continuous or discontinuous strips, to form one or more areas that are substantially free of said superabsorbent particles and to form one, two or more continuous or discontinuous longitudinally extending channels substantially free of superabsorbent particles, preferably wherein said channels extend along an axis that is parallel to the machine direction (MD) and one dimension longer than the first nonwoven strip (N1).Preferably (and as described in more detail above) the channels are discontinuous and comprise a plurality of preferably more than 4 (normally 5 to 50, 10 to 40 and / or 15 to 30) channels and wherein the aspect ratio of said channels (the longest dimension divided by the shortest dimension) is greater than 1, preferably 1.2 to 15, more preferably 1.3 to 10, even more preferably 1.4 to 8, even more preferably 1.5 to 5, even more preferably 1.6 to 3. Normally, wherein the longest dimension of the channels is substantially parallel to the longitudinal (y) axis.Advantageously, this not only allows the formation of rapid liquid distribution structures between regions with absorbent material (i.e., the absence of absorbent material along them which might otherwise slow the flow of liquid due to its absorption / expansion effects), but also allows the formation of bonding areas where the layers, or non-woven bands, of the present memory can be joined together by mechanical bonding, while limiting the risk of damaging the SAP and limiting the risk of perforating the layers, which would otherwise allow the SAP to leak out and cause a possible perforation in a subject's skin. The second and third nonwoven bands (N2, N3), which generally correspond to the upper and lower layers (2, 3) described herein, can be joined to the first nonwoven band (N1), which generally corresponds to the middle layer(s) (4) described herein, by mechanical bonding selected from hot pressing and / or ultrasonic bonding in the continuous or discontinuous longitudinal channels substantially free of superabsorbent particles. This can be done with a rotating roller (R1) and an opposing counter-roller (R2), wherein roller R1 comprises one or more raised elements corresponding to the channel pattern and the opposing counter-roller R2 comprises a smooth outer surface or one or more recesses corresponding to the raised element pattern such that they substantially mesh with each other when radially aligned.The raised elements may comprise heated elements that come into contact with the nonwoven surface or sonotrodes for non-contact ultrasonic welding. Although the use of a roller arrangement has been exemplified, other means may also be considered. The upper and lower layers (2, 3) and / or the central wrapping layers, described herein, are preferably further bonded to the first nonwoven band (N1) at the longitudinal side edges (running substantially parallel to the MD machine direction); and preferably further along the front and rear transverse edges that run perpendicular to and connect the longitudinal side edges (to form individual cores in an in-line process). In an alternative, though preferred, embodiment, the superabsorbent particles are deposited onto the first nonwoven band (N1) in a pattern such that substantially no channels free of absorbent material are formed. In this embodiment, the superabsorbent particles substantially cover at least the entire deposition area of ​​the first nonwoven band (N1) when viewed in a plan view. Preferably, the weight distribution of the superabsorbent particles is not uniform over the deposition area (e.g., more or fewer particles impregnated in the z-thickness direction, as described in more detail above). In this embodiment, it is preferred to apply an adhesive (typically in powder or liquid form) that is subsequently UV-cured or heat-cured, as described in more detail herein.The adhesive can be in powder (or granular) form (at an ambient temperature of approximately 25°C) and mixed with the superabsorbent particles before application onto the first nonwoven (N1) layer. This allows for precise placement of the adhesive where needed for enhanced immobilization of the superabsorbent polymer particles and bonding of the nonwoven layers. Advantageously, this significantly reduces the total amount of adhesive required compared to using hot-melt adhesives by other traditional methods, such as spraying and / or groove coating, resulting in a core layer or laminate that is substantially adhesive-free. In one example, the deposition stage comprises increasing the kinetic energy of the superabsorbent particles by means of one or more vibrations, electrostatic fields, electric fields, and / or ultrasonic waves, preferably using a kinetic energy enhancement device (KED), to improve the penetration of the absorbent particles through a thickness (z) of the first nonwoven band (N1). This thickness generally extends perpendicular to the width and length of the first nonwoven band (N1), typically where the length and width lie in a plane perpendicular to the thickness (z) and the particle deposition direction. For example, a Fibroline module with flat electrodes can be used at a speed of 10 to 30 m / min (typically approximately 20 m / min). Alternatively or additionally, a vacuum (V) can be used to further assist the superabsorbent particles in penetrating and impregnating the first nonwoven band (N1). The selective heating described herein can be applied in various ways using one or more heat application units (H1, H2). For example, the core layer (or the first nonwoven web) can be provided on a rotating element or belt and guided through a heating chamber where a heat source, such as an oven, microwave heater, infrared lamp, and / or hot air fan(s), produces heat that can be transferred to the core layer (or the first nonwoven web). Preferably, a microwave heater, infrared lamp, and / or hot air fan sized substantially according to the deposition area (AD) described herein is used for localized heating of the core layer (or first nonwoven web) in the deposition area. In one example, especially when the nonwoven core or first web (N1) comprises both binding and carrier fibers, as the temperature of the core or first web (N1) increases, the binding fibers will typically begin to soften. Some of the binding and / or carrier fibers will align themselves approximately parallel to the softened binding fibers as they detach. This realignment and / or separation will cause the nonwoven core or first web (N1) to increase its raised structure as the volume of voids within it increases. In the exemplified embodiment, the apparatus (100) used in the methods described herein typically comprises a first heat application unit (H1) comprising a first hot air, microwave, and / or infrared device (i.e., a heating device), positioned upstream of a particle deposition unit (PDU). Preferably, the upstream first heating device is positioned so as to apply heat to the nonwoven core layer or first web (N1) before the nonwoven core layer or first web (N1) reaches an outer surface (S) of the conveying device (TD), such as a rotary drum former.In this way, the superabsorbent particles can be deposited onto the nonwoven core layer or first band (N1) directly after the core layer or first band (N1) has been heated by the first heating device. Alternatively, the upstream first heating device is positioned above the outer surface (S) of the conveying device (TD) so that it can apply heat to the nonwoven core layer or first band (N1), while the nonwoven core layer or first band (N1) is guided over the outer surface (S) of the conveying device (TD), so that the superabsorbent particles can be deposited onto the core layer or first band (N1) substantially simultaneously with the heating of the core layer or first band (N1) by the first heating device.The first heating device is configured to generate and direct heat toward the nonwoven core layer or first web (N1). By directing the heat toward the heat-sensitive core layer or first web (N1), the fibers within the core layer or first web (N1) will tend to curl under the influence of this heat, causing the core layer or first web (N1) to open up. This increases the volume available to accommodate the superabsorbent particles provided by the particle deposition unit (PDU) within the substrate layer, without damaging the fibers of the core layer or first web (N1) and without negatively affecting the wet and / or dry integrity of the absorbent structure.Furthermore, by opening the fibrous core layer or the first nonwoven band (N1) through the direct or indirect application of hot air, deep penetration of the superabsorbent particles into the substrate layer can be achieved. This allows for a higher density of superabsorbent particles distributed within the core layer or the first nonwoven band (N1), particularly when combined with a cooperative vacuum (V) and other kinetic energy enhancement devices (KED) as described herein. The extent to which the available volume within the core layer or the first nonwoven band (N1) increases generally depends on the material of the fibrous core layer or the first nonwoven band (N1), the temperature to which the core layer or the first nonwoven band (N1) is exposed, and the duration of exposure to the high temperature. Typically, the drum former, as described herein, comprises a plurality of bags around its circumference, each bag comprising a cavity having the desired shape for each absorbent core that is subsequently laminated and cut to be contained within each absorbent article manufactured by the process described herein. Each bag normally has a perimeter and / or a flange, whereby the central layer of the product is encapsulated, sealed, and / or enclosed by upper / lower layers and / or an additional central wrapper, as described herein. The flange generally extends along the entire perimeter of the cavity (comprising both opposite transverse edges and longitudinal edges connecting said transverse edges).In general, only the deposition area corresponding to, preferably each, of said bags is loaded with superabsorbent particles, and where the deposition areas of the first nonwoven band (or middle layer) that overlap said flange are free of superabsorbent particles. The temperature that can be used to change the volume of voids in the central layer(s) or the first non-woven band (N1), as described in this document, can vary between 45 °C and 180 °C, but is preferably between 75 °C and 125 °C. In one embodiment, the nonwoven core layer or first web (N1) is heated on its upper surface and / or on its upper and lower surfaces. When heated on its upper and lower surfaces, it is preferable that the heat (and / or airflow) applied by an auxiliary heater (HA) be less than that applied by a first heating unit (H1). The auxiliary heater (HA) may be positioned substantially parallel to or downstream, along a machine direction MD, of the first heating unit (H1). Typically, the superabsorbent particle deposition step that generally follows is arranged to deposit superabsorbent particles onto the upper surface of the nonwoven core layer or first web (N1).Advantageously, this allows for improved expansion of the void volume across the z-thickness of the nonwoven material and enables a reduction in the overall airflow and / or heating temperature requirements of each individual heating unit. Furthermore, a double gradient can be formed, as the fibers are allowed to realign and slide along multiple axes. In a preferred embodiment, the first nonwoven web (N1) is heated in at least two sequential stages by at least a first heating unit (H1) and at least a second heating unit (H2), wherein the second heating unit (H2) is positioned downstream of the first heating unit (H1) in the machine direction (MD) and generally upstream of the superabsorbent particle deposition unit (PDU). Typically, the first temperature applied by the first heating unit (H1) is lower than the second temperature applied by the second heating unit (H2), preferably the first temperature being between 30°C and 75°C and the second temperature being between 75°C and 125°C.Advantageously, this allows for greater expansion of the void volume, as it enables the fibers to achieve greater alignment per unit of time without the risk of collapse due to inadvertent hot spots that cause excessive melting. Furthermore, it reduces the total heating time of the nonwoven fabric, allowing for higher line speeds of over 4 m / s, preferably over 5 m / s, through the heating segments of the apparatus. In addition, or alternatively, the second heating unit or the second additional heating unit (H2') may be placed downstream of the superabsorbent particle deposition unit (PDU). In this embodiment, the temperature applied by the second additional heating unit (H2') is normally lower than that of the second heating unit (H2) and is preferably between 35°C and 75°C. Preferably, the second additional heating unit (H2') is arranged to provide heat to the nonwoven core layer or first web (N1) substantially simultaneously with a vacuum (V) that is normally applied by the conveying device (TD), which provides a pulling force to the particles through the thickness (z) of the nonwoven core layer or first web (N1). Preferably, the second additional heating unit (H2') is a hot air blowing device.Advantageously, this arrangement allows for the optimization of particle penetration by simultaneously heating (i.e., substantially avoiding void volume contraction), blowing (i.e., pushing) the superabsorbent particles, and dragging these particles along by means of the vacuum to further facilitate particle penetration and entrapment. In the embodiments described herein, where the heating device is a hot air fan, said fan may normally be arranged to provide an airflow of 1 m³ / s to 20 m / s, preferably 2 m³ / s to 15 m / s, and even more preferably 3 m³ / s to 10 m / s. Although a positive airflow may be beneficial to further aid heat penetration through the core layer or thickness (z) of the first nonwoven web (N1), excessively high heat flows may cause the heated fibers to collapse rather than promote lifting. Furthermore, when a heat flow is applied downstream of the superabsorbent particle deposition stage, the airflow may be beneficial in providing a buoyant force to the particles, but if it is too high, the particles will be projected away from the surface of the core layer or the first nonwoven web (N1).Preferably, air filters are used to maintain substantially laminar flow. In one embodiment, as exemplified in Figure 7, the selective heating stage is arranged to heat only the deposition area (AD) of said first nonwoven web (N1), and wherein the deposition area (AD) has a width (WD) that is less than the width (WN1) of the first nonwoven web (N1) that is substantially perpendicular to the longer length of said web and / or to the machine direction (MD), preferably wherein the deposition area has a width that is 50% to 95% of the width of the web (N1), more preferably 60% to 90%, and even more preferably 70% to 85%, of the width of the web (N1).Advantageously, this allows the longitudinal edges of the core to not be substantially impregnated (in the z-thickness direction) with superabsorbent particles in the subsequent deposition stage, which allows, on the one hand, greater flexibility and / or conformability at said edges, as well as the possibility of accumulating superabsorbent particles substantially only on the upper surface of said edges to form a functional leakage barrier for liquids that tend to escape towards the upper edges of the core (in this latter example, the superabsorbent particles can be further immobilized by one or more of the techniques described in this dissertation). In one embodiment, a UV-activatable adhesive in particulate (or granular) or liquid form (at an ambient temperature of approximately 25°C) is applied, preferably along with or immediately after the superabsorbent particles and substantially in the same pattern, to the first nonwoven web, followed by curing under a UV light source, preferably where said UV light source is positioned downstream of the kinetic energy enhancement device (KED) and / or the particle deposition unit (PDU). Advantageously, this allows for avoiding the use of hot-melt adhesive and the overall reduction of energy during the process, as well as a reduced overall quantity as described above. This can, for example, be used to further immobilize the superabsorbent particles in the aforementioned embodiment and / or to at least partially bond the second and / or third nonwoven webs (N2, N3) to the first nonwoven web (N1). In one embodiment, a heat-activated adhesive in particulate (or granular) form (at an ambient temperature of approximately 25°C), preferably along with (or immediately after) the superabsorbent particles and substantially in the same pattern, is applied to the first nonwoven web, followed by curing under a heat source, preferably located downstream of the kinetic energy enhancement device (KED) and / or the particle deposition unit (PDU). The heat source may be one of the suitable heat sources described herein. Advantageously, this may allow for avoiding the use of traditionally higher quantities of adhesive and an overall reduction in energy consumption during the process, as described above.This, for example, can be used to further immobilize the superabsorbent particles in the above-mentioned embodiment and / or to at least partially bond the second and / or third non-woven bands (N2, N3) to the first non-woven band (N1). In one embodiment, a bioadhesive is applied to one or both of the second and third nonwoven bands (N2, N3) in a pattern, preferably comprising continuous or discontinuous strips, before combining it with the first nonwoven band (N1), such that at least a portion of the bioadhesive comes into contact with the first nonwoven band (N1). The pattern of the bioadhesive substantially corresponds to the pattern of superabsorbent particles for further immobilizing superabsorbent particles. The bioadhesive preferably comprises more than 90%, preferably more than 95%, and even more preferably more than 99% bio-derived and compostable content. The bioadhesive may be a polyester-based hot melt adhesive. The bioadhesive preferably has a softening point, according to ASTM D-3461, of 40°C to 70°C.An exemplary bioadhesive that may be suitable in this memory is Full-Care® Evolution™ 5944, available on the market, manufactured and sold by HB Fuller (see above for more details about the company). In one example, superabsorbent particles that are not trapped within the pores of high-volume fabric, but remain on the surface, can be removed by the use of removal methods (RM), such as air blowing and / or the use of a brush, preferably a rotating one. Test methods AUL (absorption under load, 0.7 psi (4.83 kPa)) Absorbance under load is determined similarly to the EDANA (European Disposables and Nonwovens Association) pressure absorption test method 442.2-02, except that for each example, the actual sample with the particle size distribution indicated in the example is measured. The measuring cell for determining AUL 0.7 psi (4.83 kPa) is a Plexiglas cylinder with an internal diameter of 60 mm and a height of 50 mm. A stainless steel sieve bottom with a mesh size of 36 µm is bonded to its underside. The measuring cell also includes a plastic plate with a diameter of 59 mm and a weight that can be placed inside the measuring cell along with the plastic plate. The combined weight of the plastic plate and the measuring cell is 1345 g. The AUL 0.7 psi (4.83 kPa) is determined by determining the weight of the empty plexiglass cylinder and the plastic plate and recording it as WO.Next, 0.900 ± 0.005 g of polymer or water-absorbent material (particle size distribution of 150 to 800 µm or as specifically indicated in the examples below) is weighed into the Plexiglas cylinder and spread very evenly over the bottom of the stainless steel sieve. The plastic plate is then carefully placed on the Plexiglas cylinder, the entire unit is weighed, and the weight is recorded as Wa. The weight is then placed on the plastic plate of the Plexiglas cylinder. Next, a ceramic filter plate 120 mm in diameter, 10 mm high and 0 porosity (Duran, by Schott) is placed in the center of the Petri dish 200 mm in diameter and 30 mm high and enough 0.9% by weight sodium chloride solution is introduced so that the surface of the liquid is level with the surface of the filter plate without the surface of the filter plate becoming wet.Next, a 90 mm diameter round filter paper with a pore size of <20 µm (S&S 589 Schwarzband from Schleicher & Schüll) is placed on the ceramic plate. The plexiglass cylinder containing the material or polymer is then placed on the filter paper along with the plastic plate and the weight, and left there for 60 minutes. At the end of this period, the entire unit is removed from the filter paper in the Petri dish, and the weight is then removed from the plexiglass cylinder. The plexiglass cylinder containing the swollen, water-absorbing material or polymer is weighed along with the plastic plate, and the weight is recorded as Wb. The absorption under load (AUL) is calculated as follows: AUL0, 7psig / g=Wb-Wa / Wa-W0 The AUL of 0.3 psi (2.07 kPa) and 0.5 psi (3.45 kPa) are measured similarly to the lowest suitable pressure. Absorption rate (vortex) measurement: The vortex test measures the amount of time, in seconds, required for 2 grams of a superabsorbent material to close a vortex created by stirring 50 milliliters of saline solution at 600 revolutions per minute on a magnetic stirrer. The time it takes for the vortex to close (i.e., for the fluid surface to flatten—meaning that initially, the centrifugal force caused by the fluid's rotation creates a "cone" on the surface, but as the SAP gels, the fluid's viscosity increases, so the depth of the indentation decreases until it eventually becomes substantially flat) is an indicator of the superabsorbent material's swell-free absorption rate. Equipment and materials: 1. Beaker, 100 ml. 2. Programmable magnetic stirring plate, capable of providing 600 revolutions per minute. 3. Magnetic stir bar without rings, 7.9 mm × 32 mm, Teflon coated. 4. Stopwatch. 5. Scale, with an accuracy of ± 0.01 g. 6. 0.9% saline solution. 7. Weighing paper. 8. Room with environment under conventional conditions: Temperature = 23 °C ± 1 °C and relative humidity = 50 % ± 2 %. Test procedure: 1. Measure 50 g ± 0.01 g of saline solution into the 100 ml beaker. 2. Place the magnetic stir bar in the beaker. 3. Program the magnetic stirring plate to 600 revolutions per minute. 4. Place the beaker in the center of the magnetic stir plate so that the magnetic stir bar is activated. The bottom of the vortex should be close to the top of the stir bar. 5. Weigh 2 g ± 0.01 g of the superabsorbent material to be tested on weighing paper. 6. While stirring the saline solution, pour the superabsorbent material to be tested into the saline solution and start the timer. The superabsorbent material to be tested should be added to the saline solution between the center of the vortex and the side of the beaker. 7. Stop the timer when the surface of the saline solution becomes flat and record the time. 8. The time, recorded in seconds, is recorded as the vortex time. The present invention is not supposed to be restricted to any embodiment described above, and some modifications may be added to the embodiments presented without re-evaluating the appended claims.

Claims

1. A method for manufacturing an absorbent core comprising the steps of: (i) providing a first nonwoven web (N1), preferably substantially continuous, having a first void volume; (ii) selectively applying heat to said first nonwoven web (N1) such that a deposition area (AD) of said first nonwoven web (N1) increases its void volume to a second void volume that is larger than said first void volume, wherein the selective heating is applied by means of one or more heat application units (H1, H2), and wherein said first nonwoven web (N1) is provided on a rotating element or belt and is guided through a heating chamber in which a heating source produces heat that can be transferred to the first nonwoven web (N1); (iii) depositing and / or impregnating absorbent material comprising, preferably composed of,superabsorbent particles on the deposition area (AD) of said first nonwoven band (N1); (iv) passively or actively cooling the deposition area (AD) of said first nonwoven band (N1) so that the void volume is substantially reduced to the first void volume; (v) combining the first nonwoven band with the second and third nonwoven bands (N2, N3) such that said first nonwoven band (N1) is interposed between said second and third nonwoven bands (N2, N3), preferably joining said bands by mechanical bonding selected from hot pressing and / or ultrasonic bonding; wherein the first nonwoven band (N1) consists of a high-volume fibrous nonwoven layer that is free of cellulose fibers; said high-volume fibrous nonwoven layer preferably comprises a carded air-consolidated nonwoven or a dry-thermo-bonded nonwoven,and wherein the first nonwoven band (N1) is different from the second and third nonwoven bands (N2, N3).

2. A method according to claim 1, wherein the fibers of said high-volume fibrous nonwoven layer comprise, or consist of, a material selected from the group consisting of: polylactic acid or derivatives thereof, polylactic-co-glycolic acid or derivatives thereof, polyhydroxyalkanoates or derivatives thereof, biopolyethylene, biopolypropylene, and mixtures thereof, preferably polylactic acid or derivatives thereof.

3. A method according to any of the preceding claims, wherein the second and third nonwoven bands (N2, N3) comprise, preferably consist of, a multilayer nonwoven comprising spunbond and / or meltblown fibers.

4. A method according to claim 3, wherein the multilayer nonwoven is selected from the group consisting of: SS, SSS, SM,SMS and SMMS.

5. A method according to any of the preceding claims, wherein the superabsorbent particles comprise a mixture of superabsorbent particles comprising a first superabsorbent particle (SAP1) and a second superabsorbent particle (SAP2), wherein the first superabsorbent particles (SAP1) have an AUL that is greater than the AUL of the second superabsorbent particles (SAP2), and wherein the first superabsorbent particles (SAP1) have an AUL greater than 15 g / g, according to the test method of the present specification, preferably wherein the first superabsorbent particles (SAP1) have a particle size distribution that is greater than that of the second superabsorbent particles (SAP2).

6. A method according to claim 5, wherein at least the second superabsorbent particles (SAP2) comprise, preferably consist of,Bio-based superabsorbent composite polymer particles comprising a synthetic hydrophobic polymer and a natural biopolymer, more preferably composed of a composite polymer comprising a styrene-maleic acid copolymer and a biopolymer of animal or vegetable origin; or non-composite polymer particles selected from polyacrylic acid, sodium salt, crosslinked superabsorbent particles, and partially neutralized superabsorbent particles.

7. A method according to claims 5 to 6, wherein the first superabsorbent particles (SAP1) comprise less than 80% by weight, preferably from 10% to 32% by weight of the total superabsorbent particles; and the second superabsorbent particles (SAP2) comprise at least 20% by weight, preferably from 25% to 100% by weight, more preferably from 30% to 90%, even more preferably from 35% to 80%, even more preferably from 40% to 70%.even more preferably from 45% to 68%, by total weight of superabsorbent particles.

8. A method according to claims 5 to 7 wherein the AUL ratio (AULSAP1 / AULSAP2) of the first superabsorbent particles (SAP1) and the second superabsorbent particles (SAP2) is greater than 1.4, preferably greater than 1.5, more preferably from 1.6 to 5, even more preferably from 1.7 to 3.

9. A method according to any of the preceding claims, wherein the second and third nonwoven bands (N2, N3) comprise or consist of fibers of a material selected from the group consisting of: polylactic acid or derivatives thereof, polylactic-co-glycolic acid or derivatives thereof, polyhydroxyalkanoates or derivatives thereof, biopolyethylene, biopolypropylene and mixtures thereof, preferably polylactic acid or derivatives thereof.

10. A method according to any of the preceding claims,wherein the superabsorbent particles are applied in a pattern, such as in the form of at least two spaced continuous or discontinuous strips, to form one or more areas that are substantially free of said superabsorbent particles and to form one, two, or more continuous or discontinuous longitudinally extending channels substantially free of superabsorbent particles, preferably wherein said channels extend along an axis parallel to the machine direction (MD) and a dimension longer than the first nonwoven strip (N1).

11. A method according to any of the preceding claims, wherein the deposition step comprises the step of increasing the kinetic energy of the superabsorbent particles by means of one or more vibrations, electrostatic fields, electric fields, and / or ultrasonic waves, preferably by means of a kinetic energy enhancement device (KED).to improve the penetration of the absorbent particles through a thickness (z) of the first nonwoven band (N1) that generally extends perpendicular to the width and length of said first nonwoven band (N1), typically where the length and width are in a plane perpendicular to the thickness (z) and the particle deposition direction.

12. A method according to any of the preceding claims, wherein the heating step comprises heating the first nonwoven band to a temperature of 45°C to 180°C, preferably between 75°C and 125°C.

13. A method according to any of the preceding claims, wherein the selective heating step is arranged to heat only the deposition area (AD) of said first nonwoven band (N1),and wherein the deposition area (AD) has a width (WD) that is less than the width (WN1) of the first nonwoven web (N1) that is substantially perpendicular to the longer length of said web and / or to the machine direction (MD), preferably wherein the deposition area (AD) has a width (WD) ranging from 50% to 95% of the width of the web (N1), more preferably from 60% to 90%, and even more preferably from 70% to 85%, of the width of the web (N1).

14. A method according to any of the preceding claims, wherein a UV-activatable adhesive in particulate or liquid form, preferably together with the superabsorbent particles and substantially in the same pattern, is applied to the first nonwoven web and then cured under a UV light source.preferably wherein said UV light source is placed downstream of the kinetic energy enhancement device (KED).

15. A method according to any of the preceding claims, wherein a bioadhesive is applied to one or both of the second and third nonwoven bands (N2, N3) in a pattern, preferably comprising continuous or discontinuous strips, before combining them with the first nonwoven band (N1), such that at least a portion of said bioadhesive comes into contact with said first nonwoven band (N1), and wherein the pattern of the bioadhesive substantially corresponds to the pattern of superabsorbent particles to further immobilize the superabsorbent particles.

16. A method according to any of the preceding claims, wherein the first nonwoven band (N1) is heated in at least two sequential stages by means of at least a first heating unit (H1) and at least a second heating unit (H2),wherein the second heating unit (H2) is placed downstream of the first heating unit (H1) in the machine direction (MD) and upstream of the superabsorbent particle deposition unit (PDU) and / or downstream of the superabsorbent particle deposition unit (PDU).

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