System and process for foam recovery

Abstract

A system and process are disclosed for forming nonwoven webs from a foam and fiber suspension. After the web is formed, excess foam is collected and reused. The reclaimed foam is combined with further amounts of fiber at a high consistency. The high consistency fiber and foam mixture is defiberized without causing excessive foaming. The defiberized foam and fiber mixture is then diluted and fed back to a headbox for forming the nonwoven web.

Description

[0001] 65123410PC02

[0002] SYSTEM AND PROCESS FOR FOAM RECOVERY

[0003] RELATED APPLICATION

[0004] The present application is based on and claims priority to US Provisional Patent Application No. 63 / 719,296 filed on November 12, 2024, which is incorporated herein by reference in its entirety.

[0005] BACKGROUND

[0006] Surfactants including wetting agents are used in all different types of industrial processes. In the nonwovens field, surfactants can be added to an aqueous suspension of fibers in order to improve the wetting characteristics of the fibers and / or to better disperse the fibers uniformly within the aqueous suspension. In one particular type of process, the fibers are suspended in a foam that is then used to form the web. In this application, the surfactant can serve as the foaming agent in order to produce the foam formed web.

[0007] Once a nonwoven web is produced from an aqueous suspension of fibers, the resulting foam or drainage fluid can contain water in combination with the surfactant. The surfactant represents a significant cost to the process. In addition, disposing of the surfactant laden drainage fluid not only produces waste but can also be subject to various environmental regulations. Thus, ideally the surfactant is recovered in the process and reused.

[0008] However, it is difficult to manage and handle foam throughout the process of making a nonwoven web. Ideally, in foam forming systems, the foam that produces the web is recovered and reused without the foam degrading into a liquid. Recovering and reusing foam in a process for making nonwoven webs presents various problems. For instance, when collecting and recovering a foam and combining the foam with further amounts of fibers, excessive foaming can occur when the components are mixed. For instance, the amount of energy needed to defiber the fibers can cause foam formation that contains an excessive amount of air. The resulting foam, for instance, may not be able to be pumped or processed using conventional nonwoven or papermaking equipment. Consequently, recovering foam can require additional equipment and process complexities which not only leads to higher costs but also lower throughput.

[0009] In view of the above, a need exists for an efficient method and system for recovering and reusing foam in a process for producing nonwoven webs.

[0010] SUMMARY

[0011] In general, the present disclosure is directed to a method and system for managing foam in a foam forming system for making nonwoven webs, including tissue webs. More particularly, the method and system of the present disclosure is directed to an efficient process for recovering foam (and surfactant), blending the foam with further amounts of fiber, and transporting the resulting foam and 65123410PC02

[0012] fiber stock back to the beginning of the process for producing a nonwoven web. In one aspect, the recovered foam is maintained as a foam throughout the process without excessive foaming or permitting excessive amounts of entrained air to build up in the foam. In this manner, the foam and fiber stock made from the foam can be efficiently handled and transported using conventional pumping equipment, such as centrifugal pumps. In addition, no steps are needed to separate water and a surfactant during the process.

[0013] In one aspect, for instance, the present disclosure is directed to a method that comprises displacing a foam and fiber stock on a porous forming wire and draining foam through the forming wire. The drained foam is collected and sent to a defibering device. The collected foam is combined with more fiber stock to produce a relatively high consistency stock. For instance, the foam and fiber stock can have a consistency of greater than 1% by weight, such as greater than about 2% by weight, such as greater than about 3% by weight, such as greater than about 4% by weight, such as greater than about 5% by weight, such as greater than about 6% by weight, such as greater than about 7% by weight. Consistency of a fibrous slurry refers to the concentration of solid material, such as fibrous material, in the slurry and is expressed as a percentage by weight. In the defibering device, the foam and fiber stock at a relatively high consistency is mixed in a manner that causes defibration. For instance, the foam and fiber stock can be subjected to high shear conditions for causing the fibers to individualize and form a uniform suspension of fibers. It was discovered that conducting defibration at higher fiber consistencies decreases the foamability of the mixture and maintains air entrained levels within optimum ranges that makes the foam and fiber stock easy to handle and transport.

[0014] In one embodiment, the foam and fiber stock exiting the defibering device is diluted to a consistency of less than about 4% by weight, such as from about 0.5% by weight to about 3% by weight. In one aspect, the foam and fiber stock can be pumped from the defibering device using, for instance, a centrifugal pump, and fed to a mixing tank where the foam and fiber stock is diluted and subjected to further mixing. The foam and fiber stock can then be transported to a headbox for displacing on the forming wire.

[0015] In one aspect, the fiber combined with the foam comprises cellulose fibers, such as wood pulp fibers. The wood pulp fibers, for instance, can be softwood fibers. The foam and fiber stock at a relatively high consistency is mixed in the defibering device to produce a uniform suspension of fibers that has an air content of below about 80%, such as below about 70%, such as below about 65%, such as below about 60% (by volume). The foam and fiber stock contained within the defibering device can contain a surfactant in an amount from about 100 ppm to about 5,000 ppm, such as from about 300 ppm to about 1 ,000 ppm, such as from about 500 ppm to about 900 ppm. Optionally, further surfactant can be fed to the system either to the defibering device and / or to the mixing tank. 65123410PC02

[0016] Even though the foam and fiber stock is at a relatively high consistency, the foam and fiber stock can be defibered at lower than expected energy levels. For instance, the defibering device can defiber the foam and fiber stock at a mixing energy input of less than about 60 hp, such as less than about 55 hp.

[0017] Through the system and process of the present disclosure, almost all of the foam and / or surfactant is recovered and maintained within the system of making the nonwoven web. For instance, at least about 50% by weight, such as at least about 60% by weight, such as at least about 70% by weight, such as at least about 80% by weight, such as at least about 90% by weight of the surfactant that is displaced on the forming wire is fed to the defibering device. Similarly, at least about 50%, such as at least about 60%, such as at least about 70%, such as at least about 80%, such as at least about 90% of the mass or volume of the foam displaced on the forming wire is returned to the headbox during the process. In one embodiment, the surfactant can comprise a glycoside.

[0018] In one aspect, while the foam and fiber stock is being diluted, further amounts of fibers can be added. For instance, in one aspect, synthetic fibers are added to the foam and fiber stock in the mixing tank. The synthetic fibers can comprise synthetic polymer fibers, regenerated cellulose fibers, or mixtures thereof.

[0019] The present disclosure is also directed to a system comprising a headbox configured to receive a foam and fiber stock and displace the foam and fiber stock onto a forming wire. A foam return collects foam from the foam and fiber stock displaced on the forming wire and transports the foam to a defibering device. A fiber supply is in communication with the defibering device for feeding fibers to the defibering device and blending with the foam. The defibering device is configured to blend the foam and fibers together for causing defibration and produce a foam and fiber stock at a consistency of greater than 1% by weight, such as greater than about 2% by weight, such as greater than about 3% by weight, such as greater than about 4% by weight, such as greater than about 5% by weight, such as greater than about 6% by weight, such as greater than about 7% by weight, and generally less than about 12% by weight, and at an air content of less than about 80%, such as less than about 70% (by volume). In one aspect, the foam and fiber stock is at a consistency of from about 5% by weight to about 8% by weight. The foam and fiber stock is pumped from the defibering device to a mixing tank. The pump, for instance, can comprise a centrifugal pump. A water supply is in fluid communication with the mixing tank for diluting the foam and fiber stock. The mixing tank is also in fluid communication with the headbox for supplying the headbox with the diluted foam and fiber stock.

[0020] In one aspect, the defibering device comprises a chamber in communication with a mixing device. The defibering device can be configured to subject the foam and fiber stock to high shear conditions for causing defibration. 65123410PC02

[0021] In one aspect, the headbox can comprise a multi-chamber headbox. Each chamber of the headbox can be configured to receive the foam and fiber stock for forming multiple layers of fibers on the forming wire. In one embodiment, for instance, the headbox can include three chambers for forming a three-layered nonwoven web.

[0022] It was unexpectedly discovered that increasing the consistency of the foam and fiber stock in the defibering device can also result in the formation of high strength nonwoven webs at lower energy input requirements. In this regard, the present disclosure is also directed to a method of forming a nonwoven web in which a foam and fiber suspension containing cellulose fibers, such as wood pulp fibers, is displaced on a forming wire. At least some foam from the forming wire is collected and sent to a defibering device. The collected foam is combined with fiber in the defibering device in order to increase the consistency of the mixture. The resulting foam and fiber mixture is transported to a headbox for displacing on a forming wire for forming a nonwoven web. In accordance with the present disclosure, a specific energy is inputted into the defibering device during the method that is less than about 8 HP-days / MT, such as less than about 7 HP-days / MT, such as less than about 6 HP-days / MT, such as less than about 5 HP-days / MT. Even at the above lower energy levels, the resulting nonwoven web can display a tensile index of greater than about 1700 gf m / g, such as greater than about 1800 gf m / g, and less than about 5000 gf m / g. In one aspect, the nonwoven web that is formed comprises multiple layers of fibers.

[0023] Other features and aspects of the present disclosure are discussed in greater detail below.

[0024] BRIEF DESCRIPTION OF THE DRAWINGS

[0025] A full and enabling disclosure of the present disclosure is set forth more particularly in the remainder of the specification, including reference to the accompanying figures, in which:

[0026] Figure 1 is a diagram of one embodiment of a process and system in accordance with the present disclosure;

[0027] Figure 2 is a graphical representation of some of the results obtained in the examples below; Figure 3 is a graphical representation of some of the results obtained in the examples below; Figure 4 is a graphical representation of some of the results obtained in the examples below; and

[0028] Figure 5 is a graphical representation of some of the results obtained in the examples below. Repeat use of reference characters in the present specification and drawings is intended to represent the same or analogous features or elements of the present invention.

[0029] DEFINITIONS

[0030] As used herein, the term “foam formed product” means a product formed from a suspension including a mixture of a solid, a liquid, and dispersed gas bubbles. 65123410PC02

[0031] As used herein, the term “foam forming process” means a process for manufacturing a product involving a suspension including a mixture of a solid, a liquid, and dispersed gas bubbles.

[0032] As used herein, the term “foaming fluid” means any one or more known fluids compatible with the other components in the foam forming process. Suitable foaming fluids include, but are not limited to, water.

[0033] As used herein, the term “foam half life” means the time elapsed until the half of the initial frothed foam mass reverts to liquid water.

[0034] As used herein, the term “layer" refers to a structure that provides an area of a substrate in a height direction of the substrate (e.g. z direction) that is comprised of similar components and structure.

[0035] As used herein, the term "nonwoven web" means a web having a structure of individual fibers or threads which are interlaid, but not in an identifiable manner as in a knitted web.

[0036] As used herein, unless expressly indicated otherwise, when used in relation to material compositions the terms "percent", “%”, "weight percent", or "percent by weight" each refer to the quantity by weight of a component as a percentage of the total except as whether expressly noted otherwise.

[0037] The term "pulp" as used herein refers to fibers from natural sources such as woody and non-woody plants. Woody plants include, for example, deciduous and coniferous trees. Non-woody plants include, for example, cotton, flax, esparto grass, milkweed, straw, jute, hemp, and bagasse. Pulp fibers can include hardwood fibers, softwood fibers, and mixtures thereof.

[0038] As used herein the term "staple fibers" means discontinuous fibers made from synthetic polymers or regenerated cellulose, such as polypropylene, polyethylene, post consumer recycle (PCR) fibers, polyester, nylon, viscose, rayon, and the like. Staple fibers may be cut fibers or the like. Staple fibers can have configurations that are bicomponent, multicomponent, shaped cross sections (e.g. round or flat), hollow, or the like.

[0039] As used herein, “binder fibers” are fibers that can bond to other fibers in a substrate using chemical, mechanical, or thermal means. The binder fibers may comprise thermally bondable fibers that, when heated, form thermal bonds with other fibers at their point of intersection. In one aspect, the binder fibers include a surface polymer having a lower melting temperature. For instance, the binder fibers can be made from a polymer, such as a polyolefin, having a melting temperature of less than 200°C, such as less than 180°C, such as less than 160°C, such as less than 140°C, such as less than 130°C. In one aspect, the binder fibers comprise conjugate fibers, such as bicomponent fibers. The conjugate fibers can have a core and sheath structure, including a core polymer surrounded by a sheath polymer. The core polymer can have a higher melting temperature than the sheath polymer. 65123410PC02

[0040] The core polymer can be selected for its strength and high melting point and the sheath polymer can be made from a polymer selected for its lower melting temperature. The core polymer, for instance, can have a melting temperature higher than the sheath polymer. In this manner, the sheath polymer, when subjected to heat, melts and bonds to other fibers within the web at intersecting points. The core polymer, however, allows the bicomponent binder fiber to retain its shape and provide strength.

[0041] As used herein, “synthetic polymer fibers” refers to fibers made from polymers. Synthetic polymer fibers can include polyester fibers, such as fibers made from a polyethylene terephthalate polymer. Other polymer synthetic fibers include polyolefin fibers, such as polyethylene fibers, polypropylene fibers, and fibers made from copolymers of the above.

[0042] As used herein, the term “Tensile Index” is expressed in gf m / g and refers to the quotient of tensile strength in one direction (such as the machine direction) divided by basis weight.

[0043] The strength of webs can be evaluated by measuring the “tensile strength” in the machine direction and the cross-machine direction. Tensile strength can be measured using a Constant Rate of Elongation (CRE) tensile tester having a 1 -inch jaw width (sample width), a test span of 3 inches (gauge length), and a rate of jaw separation of 25.4 centimeters per minute. The "MD tensile strength" is the peak load in grams-force per inch of sample width when a sample is pulled to rupture in the machine direction. The "CD tensile strength" is the peak load in grams-force per inch of sample width when a sample is pulled to rupture in the cross direction.

[0044] The instrument used for measuring tensile strength can be an MTS Systems Synergie 200 model and the data acquisition software can be MTS TestWorks® for Windows Ver. 4.0 commercially available from MTS Systems Corp., Eden Prairie, Minn. The load cell can be an MTS 50 Newton maximum load cell. The gauge length between jaws can be 3±0.04 inches and the top and bottom jaws can be operated using pneumatic-action with maximum 60 psi. The break sensitivity can be set at 70 percent. The data acquisition rate can be set at 100 Hz (i.e., 100 samples per second). The sample can be placed in the jaws of the instrument, centered both vertically and horizontally. The test can be then started and ended when the force drops by 70 percent of peak. The peak load can be expressed in grams-force and can be recorded as the "MD tensile strength” of the specimen. All of these values are for in-use tensile strength measurements.

[0045] DETAILED DESCRIPTION

[0046] It is to be understood by one of ordinary skill in the art that the present discussion is a description of exemplary embodiments only and is not intended as limiting the broader aspects of the present disclosure.

[0047] In general, the present disclosure is directed to a system and process for producing nonwoven webs from a foam and fiber suspension. More particularly, the system and method of the present 65123410PC02

[0048] disclosure provides for an efficient method for reclaiming and reusing foam for producing the nonwoven webs without expending substantial amounts of energy.

[0049] In one aspect, for instance, a foam and fiber suspension is displaced on a porous forming wire for forming a nonwoven web. Foam is collected from the forming wire and, while remaining a foam, is fed to a defibering device. In the defi bering device, the foam is combined with a high quantity of fibers, such as cellulose fibers, to produce a foam and fiber suspension at a relatively high consistency. At the high consistency, the fibers are defiberized for producing individual fibers and a substantially homogenous foam and fiber suspension without causing excessive foaming. In particular, it is believed that the higher consistency of fibers decreases the foamability of the foam and maintains air in the foam at optimum levels. Consequently, the resulting foam and fiber suspension can be transported using conventional equipment, such as centrifugal pumps. In one aspect, the foam and fiber suspension at the high consistency can be diluted and then displaced on a forming wire without the foam ever substantially degrading. In one embodiment, for instance, the process can be continuous in forming the nonwoven web.

[0050] The system and process of the present disclosure offers various advantages and benefits. In particular, foam can be recovered and recycled in a foam forming process without the foam degrading or overfoaming. By combining the recovered foam with a high quantity of fibers at a high consistency, it was discovered that energy can be used to defiberize the fibers while the air content of the slurry or suspension stays at a level where the foam and fiber suspension can be further processed and conveyed using conventional equipment. Further, it was unexpectedly discovered that the foam and fiber mixture at a high consistency can be defiberized without expending excessive amounts of energy, in comparison to fiberizing a foam and fiber suspension at lower consistencies.

[0051] Through the process and system of the present disclosure, significant amounts of foam and / or surfactant can be recovered and recycled. For instance, greater than about 50% by mass or volume of the foam displaced on the forming wire can be recovered and reused. More particularly, greater than about 60%, such as greater than about 70%, such as greater than about 80%, such as greater than about 90%, such as greater than about 95% by volume or mass of the foam can be recovered and reused during the process. Similarly, greater than about 50% by weight, such as greater than about 60% by weight, such as greater than about 70% by weight, such as greater than about 80% by weight, such as greater than about 90% by weight, such as greater than about 95% by weight, such as greater than about 97% by weight of a surfactant used to form the foam can be recovered and reused. As described above, the foam can be recovered without the foam degrading. For instance, during the process, the air content of the foam can remain greater than about 10%, such as greater than about 20%, such as greater than about 30%, such as greater than about 40%, such as greater than about 65123410PC02

[0052] 50%. Even during defibering in the defibering device, the air content of the foam can also be maintained below about 80%, such as below about 70%, such as below about 65%, such as below about 60%, such as below about 50%, such as below about 40% (by volume).

[0053] In addition to the above, in comparison to a wetlay process, the foam forming process of the present disclosure uses much less water to form the nonwoven webs. In addition, less energy is needed to dry the webs during the process. These benefits and advantages can be realized while using conventional papermaking equipment positioned after the headbox.

[0054] Referring to FIG. 1, one embodiment of a process and system 100 in accordance with the present disclosure is shown. As illustrated, the system includes a headbox 112 that is designed to receive a foam and fiber suspension and displace the foam and fiber suspension onto a porous forming wire 114. As the foam and fiber suspension is displaced on the forming wire 114, an embryonic nonwoven web 12 is formed. Not shown, the embryonic web 12 is conveyed downstream, dried and optionally wound into a roll. The process is capable of making all different types of nonwoven materials including tissue webs that can be used as bath tissues, facial tissues, paper towels, industrial wipers, and the like. The process and system can also be designed to incorporate other materials, such as non-fibrous materials, into the web for forming various other products. For instance, in one embodiment, the nonwoven web can be designed to contain superabsorbent materials for forming absorbent structures for personal care articles

[0055] The headbox 112 can be a single chamber headbox or can be a multi-chamber headbox. Single chamber headboxes, for instance, are designed to produce single layered nonwoven webs. Multi-chambered headboxes, on the other hand, are capable of producing nonwoven webs with multiple layers. For instance, each chamber can be designed to receive the foam and fiber suspension for producing the multiple layers. For instance, a two-layered web may be formed, a three-layered web may be formed, a four-layered web may be formed, etc.

[0056] In one embodiment, the headbox 112 can be a three-chambered headbox for forming nonwoven webs containing three layers. For instance, a first foam suspension can be fed to a first chamber for forming a first layer, a second foam suspension can be fed to a second chamber for forming a second layer, and a third foam suspension can be fed to a third chamber for forming the third layer. The foam suspension fed to each chamber can be the same or different. In one aspect, for instance, the amount of materials, the type of fibers, and the presence of other components can vary between the first foam suspension, the second foam suspension, and the third foam suspension for forming a three-layered product having desired properties and characteristics.

[0057] As shown in FIG. 1, opposite the headbox 112 is a drain device 116. As the foam and fiber suspension is displaced on the forming wire 114, fluids are drained from the web 12 and collected in 65123410PC02

[0058] the drain device 116. The drain device 116 can be a static device that collects fluids through gravity. Alternatively, the drain device 116 can apply a suction force to the forming wire 114 for collecting fluids. For instance, in one aspect, the drain device 116 can comprise a vacuum box that pulls out foam and / or its constituent parts from the displaced foam and fiber suspension. In the embodiment illustrated in FIG. 1, a single drain device 116 is shown opposite the headbox 112. It should be understood, however, that multiple drain devices can be included in the system. The drain devices can be positioned anywhere along the forming wire 114 where foam can be collected. Thus, further drain devices can be positioned downstream.

[0059] From the drain device 116, the collected foam is fed through a conduit 120 to a defibering device 122. In one aspect, the foam is pumped through the conduit 120 to the defibering device 122. In other embodiments, however, the foam can also be gravity fed to the defibering device 122. The foam collected by the drain device 116 is fed to the defibering device 122 without substantially degrading. In particular, the foam collected by the drain device substantially remains as a foam as it is fed to the defibering device 122. In one embodiment, for instance, the foam is fed from the drain device 116 to the defibering device 22 in a time of less than the half life of the foam as described in U.S. Patent Publication No. 2023 / 0074870, which is incorporated herein by reference.

[0060] In one aspect, the drain device 116 can directly connect to the defibering device 22. Directly connects here means that there are no intervening devices or equipment between the drain device 116 and the defibering device 122 that are designed to defoam the foam or stir the foam, a surfactant in the foam, and / or liquid for the purpose of separating the surfactant and the liquid.

[0061] As shown in FIG. 1, the defibering device 122 is in communication with a fiber supply 124. In the defibering device, the recovered foam is combined with fibers, such as cellulose fibers, for forming a foam and fiber suspension. The defibering device is designed to combine the fibers with the foam and mix or blend the two components together to form a uniform or substantially uniform distribution of the fibers within the foam (e.g. defiber). Uniform fiber distribution promotes desirable nonwoven material characteristics including, for example, increased strength and enhanced visual appearance.

[0062] For example, in one aspect, the defibering device is designed to exert sufficient energy on the fibers and foam such that the resulting foam and fiber suspension contains primarily individual fibers instead of fiber agglomerates or clumps of fibers. Various methods exist for defi berizi ng the fibers fed to the defibering device 122. For example, the defibering device 122 can apply aggressive mechanical agitation by a mixing device, can inject compressed air into the blend, or the like. In one aspect, the foam and fibers can be mixed through the use of a high-shear, high-speed mixing device. The high-shear mixer may optionally use a series of screens and / or rotors to work the foam and fibers 65123410PC02

[0063] together. For instance, in one aspect, the mixing device can include one or more rotors or impellers. The rotors or impellers can be rotated at high speeds in order to cause flow and shear.

[0064] In the past, defiberizing fibers in the presence of a reclaimed foam caused excessive foaming to occur. The air entrained in the foam became excessive such that the resulting suspension could not be easily handled or processed. For instance, a foam and fiber suspension containing excess air cannot be pumped with conventional pumping equipment. In addition, it was discovered that foam and fiber suspensions at low consistencies, such as less than about 1% by weight, can produce nonwoven webs with an unacceptable amount of imperfections or nits.

[0065] In order to overcome the above problem, in accordance with the present disclosure, a relatively high amount of fibers are combined with the reclaimed foam. Fibers are added with the foam, for instance, such that the resulting consistency of the foam and fiber suspension is over 1% by weight. For instance, the fiber consistency can be greater than about 2% by weight, such as greater than about 3% by weight, such as greater than about 4% by weight, such as greater than about 4.5% by weight, such as greater than about 5% by weight, such as greater than about 5.5% by weight, such as greater than about 6% by weight, such as greater than about 6.5% by weight, such as greater than about 7% by weight, such as greater than about 7.5% by weight, such as greater than about 8% by weight, and less than about 12% by weight, such as less than about 10% by weight, such as less than about 9% by weight.

[0066] It was discovered that at high consistencies, the fibers can be defiberized without causing excessive foaming. In particular, it was discovered that even during defiberizing the fibers, the air content of the foam remains below about 80%, such as below about 75%, such as below about 70%, such as below about 65%, such as below about 60%, such as below about 50%, such as below about 40%, such as below about 30%, such as below about 20% (by volume). The amount of air entrained in the foam after defiberizing the fibers is generally greater than about 3%, such as greater than about 5%, such as greater than about 10%, such as greater than about 20%, such as greater than about 30% (by volume). The amount of air content of the foam can depend upon the process equipment.

[0067] It was also unexpectedly discovered that defiberizing the fibers in a foam matrix at a high consistency did not require significantly more energy than when defiberizing fibers at a lower consistency. For instance, during defibering the fibers in the foam matrix, the amount of specific energy exerted on the foam and fiber mixture in the defibering device can be less than about 8 HP-days / MT, such as less than about 7 HP-days / MT, such as less than about 6 HP-days / MT, such as less than about 5.5 HP-days / MT, such as less than about 5 HP-days / MT, such as less than about 4.5 HP-days / MT, such as less than about 4 HP-days / MT, and greater than about 2 HP-days / MT, such as greater than about 3 HP-days / MT. In one aspect, the above energy levels can be used to produce 65123410PC02

[0068] nonwoven webs having a relatively high tensile index, which is not only a measure of strength of the web but also is an indication of the defiberized state of the fibers. In one aspect, for instance, the nonwoven web can have a tensile index of greater than about 1700 gf m / g, such as greater than about 1800 gf m / g, such as greater than about 1900 gf m / g, such as greater than about 2000 gf m / g, and less than about 5000 gf m / g.

[0069] In one aspect, the foam and fiber suspension formed in the defibering device 122 is made from the recovered foam from the drain device 116 in combination with more fibers supplied by the fiber supply 124. Optionally, various other components can be fed to the defibering device 122. For instance, although unnecessary, water and / or surfactant can also be added to the defibering device and combined with the recovered foam and supplied fibers in producing the foam and fiber suspension.

[0070] The fibers supplied from the fiber supply 124 to the defibering device 122 generally comprise cellulose fibers. Various different types of cellulose fibers can be added to the defibering device 122.

[0071] In some embodiments, the fibers utilized can be conventional papermaking fibers such as wood pulp fibers formed by a variety of pulping processes, such as kraft pulp, sulfite pulp, bleached chemithermomechanical pulp (BCTMP), chemithermomechanical pulp (CTMP), pressure / pressure thermomechanical pulp (PTMP), thermomechanical pulp (TMP), thermomechanical chemical pulp (TMCP), and so forth. By way of example only, fibers and methods of making wood pulp fibers are disclosed in US4793898 to Laamanen et al.; US4594130 to Chang et al.; US3585104 to Kleinhart; US5595628 to Gordon et al.; US5522967 to Shet; and so forth. Further, the fibers may be any high-average fiber length wood pulp, low-average fiber length wood pulp, or mixtures of the same.

[0072] Examples of suitable high-average length pulp fibers include softwood fibers, such as, but not limited to, northern softwood, southern softwood, redwood, red cedar, hemlock, pine (e.g., southern pines), spruce (e.g., black spruce), and the like. Examples of suitable low-average length pulp fibers include hardwood fibers, such as, but not limited to, eucalyptus, maple, birch, aspen, and the like.

[0073] The cellulose fibers can also comprise crosslinked cellulosic fibers. Crosslinked cellulosic fibers can provide increased bulk and resiliency, as well as improved softness.

[0074] Moreover, if desired, secondary fibers obtained from recycled materials may be used, such as fiber pulp from sources such as, for example, newsprint, reclaimed paperboard, and office waste. In some embodiments, refined fibers can be such that the total amount of virgin and / or high average fiber length wood fibers, such as softwood fibers, may be reduced.

[0075] In addition, other cellulosic fibers that can be used in the present disclosure includes non-woody fibers. As used herein, the term “non-wood fiber” generally refers to cellulosic fibers derived from, for instance, non-woody monocotyledonous or dicotyledonous plant stems. Non-limiting 65123410PC02

[0076] examples of dicotyledonous plants that may be used to yield non-wood fiber include kenaf, jute, flax, ramie and hemp. Non-limiting examples of monocotyledonous plants that may be used to yield nonwood fiber include cereal straws (wheat, rye, barley, oat, etc.), stalks (corn, cotton, sorghum, Hesperaloe funifera, etc.), canes (bamboo, sisal, bagasse, etc.) and grasses (miscanthus. esparto, lemon, sabai, switchgrass, etc). In still other certain instances non-wood fiber may be derived from aquatic plants such as water hyacinth, microalgae such as Spirulina, and macroalgae seaweeds such as red or brown algae.

[0077] The foam combined with the cellulose fibers can comprise water and a surfactant. The surfactant selected can comprise any suitable surfactant capable of producing a foam. In one aspect, a surfactant is selected so as to produce a foam having a foam half life of at least 1.5 minutes, such as at least 2 minutes, such as at least 2.5 minutes, such as at least 3 minutes.

[0078] The foaming surfactant can be selected from anionic, cationic, nonionic and amphoteric surfactants provided they, alone or in combination with other components, provide the necessary foam stability, or foam half life. As will be appreciated, more than one surfactant can be used, including different types of surfactants, as long as they are compatible, and more than one surfactant of the same type. For example, a combination of a cationic surfactant and a nonionic surfactant or a combination of an anionic surfactant and a nonionic surfactant may be used in some embodiments due to their compatibilities. However, in some embodiments, a combination of a cationic surfactant and an anionic surfactant may not be satisfactory to combine due to incompatibilities between the surfactants.

[0079] Anionic surfactants believed suitable for use with the present disclosure include, without limitation, anionic sulfate surfactants, alkyl ether sulfonates, alkylaryl sulfonates, or mixtures or combinations thereof. Examples of alkylaryl sulfonates include, without limitation, alkyl benzene sulfonic acids and their salts, dialkylbenzene disulfonic acids and their salts, dialkylbenzene sulfonic acids and their salts, alkylphenol sulfonic acids / condensed alkylphenol sulfonic acids and their salts, or mixture or combinations thereof. Examples of additional anionic surfactants believed suitable for use in the present disclosure include alkali metal sulforicinates, sulfonated glyceryl esters of fatty acids such as sulfonated monoglycerides of coconut oil acids, salts of sulfonated monovalent alcohol esters such as sodium oleylisethianate, metal soaps of fatty acids, amides of amino sulfonic acids such as the sodium salt of oleyl methyl tauride, sulfonated products of fatty acids nitriles such as palmitonitrile sulfonate, alkali metal alkyl sulfates such as sodium lauryl sulfate, ammonium lauryl sulfate or triethanolamine lauryl sulfate, ether sulfates having alkyl groups of 8 or more carbon atoms such as sodium lauryl ether sulfate, ammonium lauryl ether sulfate, sodium alkyl aryl ether sulfates, and ammonium alkyl aryl ether sulfates, sulphuric esters of polyoxyethylene alkyl ether, sodium salts, potassium salts, and amine salts of alkylnapthylsulfonic acid. Certain phosphate surfactants including 65123410PC02

[0080] phosphate esters such as sodium lauryl phosphate esters or those available from the Dow Chemical Company under the tradename TRITON are also believed suitable for use herewith. A particularly desired anionic surfactant is sodium dodecyl sulfate (SDS).

[0081] Cationic surfactants are also believed suitable for use with the present disclosure for manufacturing some embodiments of substrates. In some embodiments, such as those including superabsorbent material, cationic surfactants may be less preferable to use due to potential interaction between the cationic surfactant(s) and the superabsorbent material, which may be anionic. Foaming cationic surfactants include, without limitation, monocarbyl ammonium salts, dicarbyl ammonium salts, tricarbyl ammonium salts, monocarbyl phosphonium salts, dicarbyl phosphonium salts, tricarbyl phosphonium salts, carbylcarboxy salts, quaternary ammonium salts, imidazolines, ethoxylated amines, quaternary phospholipids and so forth. Examples of additional cationic surfactants include various fatty acid amines and amides and their derivatives, and the salts of the fatty acid amines and amides. Examples of aliphatic fatty acid amines include dodecylamine acetate, octadecylamine acetate, and acetates of the amines of tallow fatty acids, homologues of aromatic amines having fatty acids such as dodecylanalin, fatty amides derived from aliphatic diamines such as undecylimidazoline, fatty amides derived from aliphatic diamines such as undecylimidazoline, fatty amides derived from disubstituted amines such as oleylaminodiethylamine, derivatives of ethylene diamine, quaternary ammonium compounds and their salts which are exemplified by tallow trimethyl ammonium chloride, dioctadecyldimethyl ammonium chloride, didodecyldimethyl ammonium chloride, dihexadecyl ammonium chloride, alkyltrimethylammonium hydroxides, dioctadecyldimethylammonium hydroxide, tallow trimethylammonium hydroxide, trimethylammonium hydroxide, methylpolyoxyethylene cocoammonium chloride, and dipalmityl hydroxyethylammonium methosulfate, amide derivatives of amino alcohols such as beta-hydroxylethylstearylamide, and amine salts of long chain fatty acids. Further examples of cationic surfactants believed suitable for use with the present disclosure include benzalkonium chloride, benzethonium chloride, cetrimonium bromide, distearyldimethylammonium chloride, tetramethylammonium hydroxide, and so forth.

[0082] Nonionic surfactants believed suitable for use in the present disclosure include, without limitation, condensates of ethylene oxide with a long chain fatty alcohol or fatty acid, condensates of ethylene oxide with an amine or an amide, condensation products of ethylene and propylene oxides, fatty acid alkylol amide and fatty amine oxides. Various additional examples of non-ionic surfactants include stearyl alcohol, sorbitan monostearate, octyl glucoside, octaethylene glycol monododecyl ether, lauryl glucoside, cetyl alcohol, cocamide MEA, monolaurin, polyoxyalkylene alkyl ethers such as polyethylene glycol long chain (12-14C) alkyl ether, polyoxyalkylene sorbitan ethers, polyoxyalkylene alkoxylate esters, polyoxyalkylene alkylphenol ethers, ethylene glycol propylene glycol copolymers, 65123410PC02

[0083] polyvinyl alcohol, alkylpolysaccharides, polyethylene glycol sorbitan monooleate, octylphenol ethylene oxide, alkyl polyglucosides, and so forth.

[0084] The foaming surfactant can be used in varying amounts as necessary to achieve the desired foam stability and air-content in the foam. In certain embodiments, the foaming surfactant can comprise between about 0.005% and about 5% of the foam (by weight). In certain embodiments the foaming surfactant can comprise between about 0.05% and about 3% of the foam or even between about 0.05% and about 2% of the foam (by weight). For example, in one embodiment, the foam and fiber stock produced in the defibering device 122 can contain one or more surfactants in an amount from about 100 ppm to about 5,000 ppm, such as from about 300 ppm to about 1,000 ppm, such as from about 500 ppm to about 900 ppm.

[0085] In some embodiments, the foam may optionally also include one or more foam stabilizers known in the art and that are compatible with the components of the foam and further do not interfere with the hydrogen bonding as between the cellulosic fibers. Foam stabilizing agents believed suitable for use in the present disclosure, without limitation, one or more zwitterionic compounds, amine oxides, alkylated polyalkylene oxides, or mixture or combinations thereof. Specific examples of foam stabilizers includes, without limitation, cocoamine oxide, isononyldimethylamine oxide, n-dodecyldimethylamine oxide, and so forth.

[0086] In some embodiments, if utilized, the foam stabilizer can comprise between about 0.01% and about 2% of the foam (by weight). In certain embodiments, the foam stabilizer can comprise between about 0.05% and 1% of the foam or even between about 0.1 and about 0.5% of the foam (by weight).

[0087] After the fibers have been defiberized in the defiberizing device 122, the resulting foam and fiber stock at a relatively high consistency can be pumped to a mixing tank 102 via a pump 126. Of particular advantage, the foam and fiber stock can be pumped using conventional pumping equipment, such as a centrifugal pump 126. From the defibering device 122, the foam and fiber stock is fed to the mixing tank 102. As shown in FIG. 1, the mixing tank 102 is in communication with a water supply 108. In the mixing tank 102, for instance, the foam and fiber stock can be diluted in order to lower the consistency for feeding the foam and fiber stock to the headbox 112. For instance, in one embodiment, the foam and fiber stock are fed to the mixing tank 102 and diluted with water from the water supply 108 to a consistency of less than about 4% by weight, such as less than about 3.5% by weight, such as less than about 3% by weight, and greater than about 0.5% by weight, such as greater than about 1 % by weight, such as greater than about 1.5% by weight, such as greater than about 2% by weight, such as greater than about 2.5% by weight. The resulting diluted foam and fiber stock 106 can then be fed to the headbox 112 via a conduit 118. As shown in FIG. 1, the mixing tank 102 can also be in communication with a surfactant supply 104 for feeding further amounts of surfactant in 65123410PC02

[0088] conjunction with diluting the foam and fiber stock. Adding further amounts of surfactant, however, is optional and may not be needed in certain applications.

[0089] The foam and fiber stock 106 produced in the mixing tank 102 can include various properties for feeding to the headbox 112 in forming nonwoven webs. For instance, the amount of entrained air in the foam and the foam density can vary depending upon the particular application. The amount of entrained air in the foam, for instance, can be from about 20% to about 80%, such as from about 30% to about 70%, such as from about 40% to about 65% (by volume).

[0090] The foam density of the foam can be greater than about 100 g / L, such as greater than about 250 g / L, such as greater than about 300 g / L. The foam density is generally less than about 800 g / L, such as less than about 500 g / L, such as less than about 400 g / L, such as less than about 350 g / L. In some implementations, for example, a lower density foam is used having a foam density of generally less than about 350 g / L, such as less than about 340 g / L, such as less than about 330 g / L.

[0091] In one embodiment, further amounts of fibers can also be fed to the mixing tank 102 in forming the diluted foam and fiber stock 106. For instance, as shown in FIG. 1, the mixing tank 102 is in communication with a fiber supply 109. In one embodiment, for instance, the fiber supply 109 can be used to add synthetic fibers to the foam and fiber stock. The synthetic fibers may comprise, for instance, regenerated cellulose fibers, polymer synthetic fibers, or mixtures thereof.

[0092] Regenerated cellulose fibers include, for instance, rayon fibers, viscose fibers, chemically-modified cellulose fibers, and the like. Such fibers are marketed under the trade names LYOCELL and TENCEL.

[0093] Synthetic polymer fibers can be made from various polymers and include binder fibers, bicomponent fibers, and the like.

[0094] Examples of synthetic polymer fibers include polyolefin, polyester (PET), polyamide, polylactic acid, or other fiber forming polymers. Polyolefin fibers, such as polyethylene (PE) and polypropylene (PP), and polyethylene terephthalate fibers are particularly well suited for use in the present disclosure. In some embodiments, synthetic fibers can be recycled fibers, compostable fibers, and / or marine degradable fibers.

[0095] The synthetic fibers can have fiber length greater than about 0.2 mm including, for example, having an average fiber size between about 0.5 mm and about 50 mm or between about 0.75 and about 30 mm or even between about 3 mm and about 8 mm.

[0096] In some embodiments, the synthetic fibers can have a crimped structure to enhance bulk generation capability of the foam formed fibrous substrate. For example, a PET crimped staple fiber may be able to generate a higher caliper (or result in a low sheet density) in comparison to a PET straight staple fiber with the same fiber diameter and fiber length. 65123410PC02

[0097] Synthetic fibers can be present in the nonwoven web in an amount greater than about 2% by weight, such as in an amount greater than about 3% by weight, such as in an amount greater than about 4% by weight, such as in an amount greater than about 6% by weight, such as in an amount greater than about 8% by weight, such as in an amount greater than about 15% by weight, and in an amount less than about 50% by weight, such as in an amount less than about 40% by weight, such as in an amount less than about 30% by weight, such as in an amount less than about 20% by weight.

[0098] As shown in FIG. 1, the diluted foam and fiber stock 106 produced in the mixing tank 102 is fed to the headbox 112 for being displaced on the forming wire 114 in forming the nonwoven 12. The nonwoven web 12 is conveyed downstream and dried. For instance, the nonwoven web 12 can be dried using a through-air dryer. Alternatively, the nonwoven web 12 can be rotated on a heated drum and optionally creped from the drum for drying the web. The web is then wound into a roll for later converting and forming into various products. The formed web can generally have a basis weight from about 10 gsm to about 200 gsm, such as from about 15 gsm to about 150 gsm. For instance, the basis weight can be greater than about 15 gsm, such as greater than about 18 gsm, such as greater than about 20 gsm, such as greater than about 22 gsm, and less than about 130 gsm, such as less than about 120 gsm, such as less than about 100 gsm, such as less than about 80 gsm, such as less than about 70 gsm.

[0099] The present disclosure may be better understood with reference to the following examples.

[0100] Example No. 1

[0101] The following examples were conducted in order to demonstrate some of the advantages and benefits of the present disclosure.

[0102] A surfactant and water mixture was blended with crosslinked cellulose fibers at a high fiber content. In particular, the consistency of the fiber suspension was 7.3% by weight. The surfactant used was a non-ionic, alkyl glucoside surfactant The amount of surfactant added to the suspension ranged from 0 to 800 ppm. A different test was run at 50 ppm intervals.

[0103] The fiber suspension was then defiberized at high shear conditions, which also produced a foam suspension. The air content of the foam was measured after the fibers were defiberized.

[0104] The following results were obtained and are also illustrated in FIG. 2.

[0105]

[0106] 65123410PC02

[0107]

[0108] As shown particularly in FIG. 2, even when containing 800 ppm of surfactant, the air content of the foam remained below 60%. In particular, none of the samples tested produced excessive amounts of foam at a consistency of 7.2% by weight.

[0109] Example No. 2

[0110] Further foam and fiber mixtures were formulated similar to the process described in Example No. 1. In particular, foam and fiber batches were produced having consistencies of 2% by weight, 3% by weight, 4% by weight, 5% by weight, and 6% by weight. The foam and fiber mixtures were created in a defiberizing device which was comprised of a mixing tank. The volume of the mixing tank was greater in this example than the one used in Example No. 1. At each consistency, measurements were taken of air content percentage by volume. Surfactant concentration was held constant at 750 ppm during this example.

[0111] The results are illustrated in FIG. 3. As shown, over the range of consistencies from 2% by weight to 6% by weight, the air content percentage by volume was maintained below about 40% even under defiberizing conditions. The air content percentage decreased as the consistency increased. 65123410PC02

[0112] In contrast, lower consistencies, such as less than 1 % by weight, can undergo excessive foaming. In addition, lower consistencies have also been found to produce nonwoven webs with a greater amount of imperfections or nits. Consequently, higher consistencies not only maintain air content within optimum ranges but also produce nonwoven webs with better properties.

[0113] Example No. 3

[0114] Fiber and foam mixtures were made similar to the method described in Example No. 1. The surfactant concentration was held constant at 750 ppm.

[0115] In this example, foam and fiber (cellulose fibers) mixtures were formulated in a defiberizing device. Foam and fiber mixtures were formulated at a consistency of 2% by weight, 3% by weight, 4% by weight, and 6% by weight. At each consistency, the specific energy input was varied. Specific energy is calculated as follows:

[0116]

[0117] & At each specific energy input, the foam and fiber mixture was formed into a nonwoven web and tested for tensile index. The results are illustrated in FIG. 4 (units for specific energy in this example are in HP-days / MT instead of kWhr / MT).

[0118] As shown, specific energy input increases as the allotted defibering time increases but decreases with the mass of fiber. An increase in tensile index is indicative of a fiber slurry going from a less defiberized state to a more defiberized state as greater defibering promotes fiber-to-fiber bonding. FIG. 4 illustrates that effective defibering takes place when defibering in a foamed media.

[0119] As also demonstrated in FIG.4, the specific energy input required to achieve a similar tensile index is much less at higher consistencies. In fact, a foam and fiber mixture at 2% by weight consistency required twice as much specific energy to achieve the same tensile index as the foam and fiber mixture at a consistency of 6% by weight.

[0120] Notably, the results illustrated in FIG. 4 demonstrate that less energy is needed to produce nonwoven webs as the consistency increases. In particular, nonwoven webs can be made in accordance with the present disclosure at specific energies of less than about 8 HP-days / MT, such as less than about 6 HP-days / MT, such as less than about 5 HP-days / MT.

[0121] Liquid water and fiber mixtures at the same consistencies were also formulated and tested. The results are illustrated in FIG. 5 showing a comparison between foam and fiber mixtures and water and fiber mixtures. The results illustrate average pulping rotor power (kW) measurements taken at different defibering time intervals (4-20 minutes) across the range of fiber consistencies. As shown in FIG. 5, a lower consistency requires lower power input to achieve a specified motor frequency (60 Hz). 65123410PC02

[0122] Unexpectedly, however, as consistency increases, a foam and fiber mixture appears to require considerably less power relative to what is needed for an identical water slurry.

[0123] These and other modifications and variations to the present invention may be practiced by those of ordinary skill in the art, without departing from the spirit and scope of the present invention, which is more particularly set forth in the appended claims. In addition, it should be understood that aspects of the various embodiments may be interchanged both in whole or in part. Furthermore, those of ordinary skill in the art will appreciate that the foregoing description is by way of example only and is not intended to limit the invention so further described in such appended claims.

Claims

65123410PC02What Is Claimed:

1. A method comprising:displacing a foam and fiber suspension on a forming wire;collecting at least some foam from the forming wire and sending the collected foam to a defibering device, the collected foam being combined with fiber such that the resulting foam and fiber mixture has a consistency of greater than 1 % by weight; andtransporting the foam and fiber mixture to a headbox for displacing on the forming wire.

2. A method as defined in claim 1, further comprising the step of diluting the resulting foam and fiber mixture to produce a diluted foam and fiber suspension prior to being displaced on the forming wire.

3. A method as defined in claim 1 , wherein the resulting foam and fiber mixture in the defibering device has a consistency of greater than about 2% by weight, such as greater than about 3% by weight, such as greater than about 4% by weight, such as greater than about 5% by weight, such as greater than about 6% by weight, such as greater than about 7% by weight.

4. A method as defined in any of the preceding claims, wherein, in the defibering device, the resulting foam and fiber mixture is mixed in a manner that causes defibration.

5. A method as defined in any of the preceding claims, wherein the resulting foam and fiber mixture contains cellulose fibers.

6. A method as defined in claim 5, wherein the cellulose fibers comprise wood pulp fibers.

7. A method as defined in any of the preceding claims, wherein the resulting foam and fiber mixture is mixed in the defibering device and wherein the foam and fiber mixture exiting the defibering device has an air content of below about 80%, such as below about 70%, such as below about 65%, such as below about 60% by volume.

8. A method as defined in any of the preceding claims, wherein the resulting foam and fiber mixture in the defibering device contains a surfactant in an amount from about 100 ppm to about 5,000 ppm, such as from about 300 ppm to about 1,000 ppm, such as from about 500 ppm to about 900 ppm.

9. A method as defined in any of the preceding claims, wherein the foam and fiber mixture is pumped from the defibering device to a mixing tank and wherein the foam and fiber mixture is diluted in the mixing tank.

10. A method as defined in claim 9, wherein the foam and fiber mixture is pumped using a centrifugal pump.65123410PC0211. A method as defined in any of the preceding claims, further comprising the step of adding surfactant to the defibering device with the foam and fiber mixture.

12. A method as defined in claim 9, further comprising the step of adding a surfactant to the mixing tank.

13. A method as defined in claim 9, further comprising the step of adding synthetic fibers to the foam and fiber mixture in the mixing tank.

14. A method as defined in claim 13, wherein the synthetic fibers comprise synthetic polymer fibers, regenerated cellulose fibers, or mixtures thereof.

15. A method as defined in claim 2, wherein the foam and fiber mixture is diluted to a consistency of from about 0.5% by weight to about 3% by weight.

16. A method as defined in any of the preceding claims, wherein the collected foam from the forming wire comprises a surfactant, the surfactant comprising a non-ionic surfactant, such as a glycoside.

17. A method as defined in any of the preceding claims, wherein the foam and fiber suspension displaced on the forming wire contains a surfactant and wherein at least about 50% by weight, such as at least about 60% by weight, such as at least about 70% by weight, such as at least about 80% by weight, such as at least about 90% by weight of the surfactant is fed to the defibering device.

18. A system comprising:a headbox configured to receive a fiber and foam suspension and displace the fiber and foam suspension onto a forming wire;a foam return that collects foam from the foam and fiber suspension displaced on the forming wire and transports the collected foam to a defibering device;a fiber supply for feeding fiber to the defibering device for blending with the foam, the defibering device being configured to blend the foam and fibers together for causing defibration and produce a foam and fiber mixture at a consistency of at least 1 % by weight and an air content of less than about 80% by volume; anda pump for pumping the foam and fiber mixture from the defiberizing device to a mixing tank or headbox.

19. A system as defined in claim 18, further comprising a water supply in fluid communication with the mixing tank for diluting the foam and fiber mixture, and wherein the mixing tank is in fluid communication with the headbox for supplying the headbox with the diluted foam and fiber mixture.

20. A system as defined in claim 18, wherein the pump comprises a centrifugal pump.65123410PC0221. A system as defined in claim 18, wherein the defibering device comprises a chamber in communication with a mixing device.

22. A system as defined in any of claims 18-21 , wherein at least about 50%, such as at least about 60%, such as at least about 70% of the mass or volume of foam displaced on the forming wire is collected.

23. A system as defined in any of claims 19, wherein the headbox comprises a multichamber headbox and wherein each chamber of the headbox is configured to receive the foam and fiber mixture in forming multiple layers of fibers on the forming wire.

24. A method comprising:displacing a foam and fiber suspension on a forming wire, the foam and fiber suspension containing cellulose fibers;collecting at least some foam from the forming wire and sending the collected foam to a defibering device, the collected foam being combined with fiber in order to increase the consistency of the resulting foam and fiber mixture;transporting the foam and fiber mixture to a headbox for displacing on the forming wire; forming a nonwoven web from the foam and fiber mixture; andwherein a specific energy inputted into the defibering device during the method is less than 8 HP-days / MT.

25. A method as defined in claim 24, wherein the specific energy inputted into the defibering device during the method is less than about 6 HP-days / MT, such as less than about 5 HP-days / MT.

26. A method as defined in claim 24, wherein the foam and fiber mixture in the defibering device after being combined with the fiber is greater than about 2% by weight.

27. A method as defined in claim 24, wherein the foam and fiber mixture in the defibering device after being combined with the fiber is from about 3% by weight to about 10% by weight.

28. A method as defined in claim 25, wherein the nonwoven web displays a tensile index of greater than about 1700 gf m / g.

29. A method as defined in claim 25, wherein the nonwoven web displays a tensile index of greater than about 1800 gf m / g.

30. A method as defined in claim 24, wherein the nonwoven web comprises multiple layers.

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