Composition, production process and starch-based adhesive

Abstract

The present invention relates to a starch-based adhesive composition that allows the bonding of various materials, including paper, glass, aluminum, and polyethylene. This composition is free of volatile solvents (e.g., ammonia), is food-compatible, and exhibits adjustable adhesion based on starch concentration. In addition, the invention includes a process for producing the adhesive by extrusion, which is scalable for industrial production. The resulting adhesive is biodegradable, non-toxic, low-cost and produced without the use of water or organic solvents, using thermoplastic processes in its manufacture.

Description

COMPOSITION, PRODUCTION PROCESS AND STARCH-BASED ADHESIVE FIELD OF THE INVENTION

[0001] The present invention relates to a composition and a process for the production of a starch-based adhesive, applicable in sectors such as the production of bandages, labels, in the sealing of boxes and packaging, in the production of carton / multilayer packaging, as a food coating, among others. The present invention is in the field of chemistry and materials engineering, especially adhesives. BACKGROUND OF THE INVENTION

[0002] Adhesives are products used to join different surfaces in a practical and efficient way. Manufactured from substances such as synthetic polymers, resins, or rubber, they have wide application in areas such as packaging, labeling, decoration, repairs, and visual communication. The global adhesives market has shown continuous growth, driven by demand in sectors such as construction, automotive, packaging, electronics, and healthcare.

[0003] With technological advancements, the development of high-performance adhesives with lower environmental impacts has become a priority. Projections indicate that the market will continue to grow, particularly in the Asia-Pacific region, which leads global production and consumption, followed by Europe and North America. Currently, there is a wide variety of adhesives, each developed to meet specific needs, both industrial and domestic. There are several types of adhesives, such as pressure-sensitive adhesives (PSA), which adhere with pressure, and contact adhesives, used in furniture and footwear for their high resistance. Structural adhesives, epoxy, polyurethane, and acrylic, are common in the automotive and aerospace industries, while hot melt adhesives are applied with heat in packaging and electronics. Water-based adhesives are environmentally friendly options, and cyanoacrylate (super glue) is ideal for small repairs due to its fast curing and strong adhesion.

[0004] Despite their versatility and essential role in various industries, adhesives present some drawbacks that deserve consideration. One of the main problems is their sensitivity to environmental conditions, as many adhesives can lose their adhesive or structural properties when exposed to extreme temperatures, excessive humidity, or aggressive chemicals, limiting their durability in certain applications. Another challenge is degradation and recycling, since many adhesives, especially synthetic ones, are difficult to remove or recycle, contributing to increased waste and complicating the separation and reuse of materials.

[0005] Furthermore, solvent-based adhesives can emit volatile organic compounds (VOCs) during application, which can be harmful to human health and the environment. Although more sustainable alternatives exist, such as water-based adhesives, many industries still rely on solvent-based products due to their greater durability and resistance in certain contexts. Another drawback is the difficulty of removal in temporary applications or when repositioning the adhesive is necessary, especially in sectors such as electronics and automotive, where precision is crucial, since removal can leave residues or even damage the surface to which it was applied. Finally, the production and application costs of some high-performance adhesives, such as structural and hot-melt adhesives, can be high, making them less accessible to certain companies.

[0006] The adhesives sector faces a number of challenges that impact its evolution and competitiveness. One of the main ones is the development of sustainable solutions. The pressure for products with less environmental impact has been growing, and many traditional adhesives still depend on synthetic materials derived from fossil fuels. Creating biodegradable or bio-based alternatives, without compromising quality and durability, represents... One of the biggest challenges for the industry. Another significant challenge is environmental regulation. In many countries, control over the use of volatile organic compounds (VOCs), present in solvent-based adhesives, is strict. The need to reduce these emissions imposes on the industry the task of adapting formulas or developing less polluting technologies, which may require high investments in research and development.

[0007] Furthermore, the sector faces demands for higher performance in extreme conditions. Many adhesives need to withstand very high or low temperatures, humidity, ultraviolet radiation, and aggressive chemicals. The technical and economic challenge of creating adhesives that maintain their effectiveness in these adverse conditions, without compromising health and safety, remains. The integration of new technologies also requires continuous innovation. Industries such as electronics, automotive, and aerospace are evolving rapidly, demanding more advanced adhesives compatible with new materials and designs, as well as automated production processes that offer greater precision. Finally, global competition represents another challenge. With emerging markets, especially in Asia, becoming major producers and consumers of adhesives, there is pressure to reduce costs without sacrificing quality.Companies in this sector need to constantly innovate to remain competitive, balancing the costs of production, research, and adaptation to regulatory requirements.

[0008] These challenges require the adhesives sector to be in constant transformation, seeking technological and sustainable alternatives to meet growing global demand. Starch, a complex carbohydrate found in many vegetables, especially in cereals such as corn and wheat, tubers such as potatoes, and legumes, is composed of glucose molecules organized in two forms: amylose, which is linear, and amylopectin, which is branched. It is an important source of energy in the human diet and an essential ingredient in various industries.

[0009] In nutrition, starch is fundamental because it is one of the main forms of energy storage in plants and is widely consumed as part of staple foods such as rice, potatoes, and corn. When ingested, it is broken down into glucose by the body and used as an energy source. Beyond its nutritional role, starch has several industrial applications. It is used as a thickener and stabilizer in processed foods such as soups, sauces, and sweets. In its modified form, it is also used in papermaking. EP1167434, for example, refers to starch compositions that combine anionic and cationic starch, with at least one of them being waxy. These compositions are cooked and added at the beginning of the paper production process, allowing for a high level of addition and eliminating the need for a press. The resulting paper and cardboard exhibit superior characteristics compared to those produced with the same components added separately.Brazilian patent EP1761568 addresses crosslinked cationic waxy starch products, a method for producing these products, and their applications in paper products. Crosslinked cationic starches are known to improve properties such as the dry strength of paper products, as well as optimize the manufacturing process by improving retention and drainage. The patent highlights that crosslinked cationic starch products should have a hot pulp viscosity of approximately 500 to 3000 cps. The invention proposes new crosslinked cationic waxy starch products with viscosities between 700 and 2500 cps, a method for producing these starches, and their use in the preparation of paper products, providing improvements in the characteristics of the resulting papers.

[0010] Another relevant application of starch is in the production of bioplastics and biodegradable packaging, which represent a sustainable alternative to conventional plastics. CN108395583 presents a biodegradable packaging material for fresh food based on starch, and also describes its preparation method. The material is composed of 99 to 120 parts starch, 12 parts filler material, and 23 parts plasticizer. The main The advantage is that, with 97.5% starch, the resulting product generates little waste after degradation and has a rapid decomposition rate, returning to the environment in the form of water and carbon dioxide. After 68 days of total exposure, the material exhibits a tensile strength of 30 MPa and an elongation of 280%. Furthermore, it has high water resistance, maintaining a strength of 16 MPa and an elongation of 160% after 12 hours of immersion. The patent seeks to improve the development of biodegradable plastics from starch, overcoming cost and complexity limitations in the production of conventional plastics, focusing on sustainability and reducing environmental impact.

[0011] Similarly, starch films can be applied in the composition of packaging. EP2074175 addresses biodegradable multilayer starch-based compositions, composed of three distinct phases: (a) a continuous phase with a matrix of at least one resistant hydrophobic polymer, incompatible with starch; (b) a dispersed nanoparticulate starch phase, with average dimensions less than 0.3 µm; and (c) an additional phase of at least one rigid and brittle polymer with a modulus greater than 1000 MPa. These compositions are insoluble in water and non-dispersible, and can be transformed into high-modulus flexible films, suitable for manufacturing bags and packaging that support heavy loads without severe deformation or fracture. They exhibit a modulus greater than 300 MPa and good isotropy in the longitudinal and transverse directions with respect to tear propagation. The reduction of starch particle size and lamellar structures is achieved through processing in extruders.The matrix may contain additives, and the hydrophobic polymer may be an aromatic aliphatic polyester. A challenge with current biodegradable bags is the lack of uniformity in mechanical properties, especially tear resistance. The proposed compositions aim to address this limitation, offering more consistent and efficient mechanical performance.

[0012] Starch can also be used in coatings. EP2251484 addresses pigmented coating compositions that utilize crosslinked starch dispersions as binders in an aqueous liquid, applicable in the coating of paper and cardboard. The process for preparing these dispersions involves mixing starch with water, processing the mixture in an extruder with a crosslinking agent, and injecting a hydroxyl liquid. The compositions improve the surface smoothness of the paper, increasing gloss and printability, and allow for high solids contents with low viscosities. Although natural binders such as starch are frequently used, the demand for synthetic binders has grown over the years. The invention demonstrates that starch dispersions can create stable and effective compositions for various applications.Similarly, EP2561 137 presents a starch mixture for the preparation of coating compositions, characterized by the inclusion of (a) an unrefined starch and (b) a refined starch, wherein the refined starch originates from a controlled degradation process aimed at altering its physicochemical properties. These compositions are used on various substrates, such as metals, plastics, textiles, and paper, improving surface protection and appearance, as well as characteristics such as water resistance and print resistance. Although synthetic binders, such as latex, are widely used, they are expensive and do not meet the growing demand for environmentally friendly products. The use of starch as a natural alternative is promising, but high concentrations can impair paper quality.The invention provides a viable solution, allowing the use of a starch mixture to replace, totally or partially, synthetic binders, while maintaining the quality of coating compositions and paper.

[0013] In the adhesives sector, starch is especially relevant in the formulation of water-based adhesives, which have a lower environmental impact and can replace more aggressive chemical compounds. US patent 9150761 B2 describes a starch-based adhesive that combines starches or starch derivatives with different molecular weights. The adhesive is composed of a starch... Unmodified or slightly refined maltodextrin or syrup solid, and a hydroxypropyl starch. It may include a plasticizer and is prepared by mixing and cooking the suspension under acidic conditions. This adhesive is designed for applications such as bonding multilayer bags, exhibiting good adhesion to polyethylene and resistance to retrogradation.

[0014] EP1629060 refers to the use of native or modified legume starch (with an amylopectin content between 25% and 60%) in adhesive compositions for labeling, especially on glass or plastic bottles. It highlights the advantages of this starch in obtaining desirable adhesive properties, including high stability during storage, rheology, and water resistance, as well as allowing easy removal without leaving residue. The composition may include other natural polymers, ensuring that the adhesive meets several essential performance criteria for labeling applications. The labeling compositions according to the invention (designated as COMPOSITIONS 1A to 3A) are prepared according to the general protocol, replacing COLLYS® BR wheat starch with legume starches. COMPOSITION 1A: Native pea starch with >98% starch, 35% amylopectin, and 0.35% protein. COMPOSITION 2A: Starch 1 physically modified by extrusion.COMPOSITION 3A: Pea starch physically modified by cooking in a drying drum, > 98% starch, 38% amylopectin and 0.20% protein. These compositions aim to improve adhesive and performance properties.

[0015] Starch-based adhesives and bioplastics have emerged as sustainable alternatives in various applications, especially due to growing environmental concerns and the search for biodegradable materials. Starch, being a natural polymer, is an abundant and renewable raw material, making it an attractive choice for the development of new products. Starch-based adhesives can be formulated using modified starch, which can be chemically or physically treated to improve its adhesive properties. These adhesives are... Starch-based adhesives are frequently used in packaging, labels, and the pulp and paper industry. One of the most important characteristics of starch-based adhesives is their biodegradability, as they decompose naturally, reducing their environmental impact compared to synthetic adhesives. Furthermore, they are versatile, applicable to various surfaces, and generally non-toxic, making them suitable for use in food environments. Processing these adhesives is simple, allowing for easy application in industrial processes such as paper bonding and packaging. However, as can be observed, the art lacks a starch-based adhesive obtainable by extrusion.

[0016] Extrusion is a forming process used to mold materials into continuous shapes, such as tubes, films, profiles, or sheets. The process involves feeding the material, usually polymers, into a cylinder where it is heated and melted. It is then forced through a die with the desired shape by means of a rotating screw or direct pressure. After exiting the die, the material is cooled, solidifying into its final shape. Extrusion is widely used in industries such as plastics, food, and biodegradable compounds, due to its efficiency and ability to produce continuous parts with complex geometries and adjustable properties, depending on the materials and additives used.

[0017] The production of starch-based adhesives by extrusion presents specific challenges due to the characteristics of starch and the demands of the process. Starch, being hydrophilic and heat-sensitive, has low thermal stability and can degrade during extrusion, especially at the high temperatures required to melt and mold the material. Furthermore, starch has low fluidity in the molten state, which hinders its application as an extruded adhesive. To improve adhesion and processability, it is common to add plasticizers and chemical modifiers, but this can compromise the balance between the viscosity required for extrusion and the final bond strength. Another obstacle is adjusting the formulation to ensure the adhesive... Maintain good adhesion and stability even under varying humidity conditions, as starch tends to absorb water and lose performance. Compatibility with other formulation components, such as resins or additives, also requires care to avoid phase separation or compromising adhesive properties. Overcoming these challenges requires optimization of both the material and the extrusion process. BRIEF DESCRIPTION OF THE INVENTION

[0018] Given the existing gap, the present invention relates to a starch-based composition characterized by comprising cationic starch and waxy starch. This composition allows the manufacture of adhesives capable of bonding various materials, including glass, paper, aluminum foil, and polyethylene. It is an ammonia-free composition, compatible with food, and with modifiable adhesiveness according to the concentration of each starch in the formulation, making it a versatile invention that allows the generation of a variety of adhesives. Furthermore, this composition allows the production of starch-based adhesives by extrusion, overcoming the limitations of the starch itself and maintaining the desired adhesive properties.

[0019] In this sense, the present invention also relates to a process for producing a starch-based adhesive characterized by comprising an extrusion step. The composition of the present invention is suitable for the extrusion process and the process is scalable to an industrial level.

[0020] Therefore, an adhesive characterized by comprising cationic starch and waxy starch, as described further in this document, is also an object of the present invention. It is a biodegradable, non-toxic, and low-cost adhesive, given that starch is a renewable and abundant raw material. Furthermore, it is an adhesive manufactured without water or organic solvents, easily processed and produced by thermoplastic routes. BRIEF DESCRIPTION OF THE FIGURES

[0021] Figure 1 presents the results of the T-peel test, with the Peel strength values ​​for each adhesive of the present invention on substrates of a) polyethylene (PE) film and b) aluminum foil (Al). The adhesive formulations are 0Cat / 100Cer, 25Cat / 75Cer, 50Cat / 50Cer, 75Cat / 25Cer and 100Cat / 0Cer. Cat: cationic starch; Cer: waxy starch.

[0022] Figure 2 shows an image of the test specimens after mechanical tests of the bonds on a) polyethylene substrates: the lower substrate (where the adhesive film was deposited first), on the left, and the upper substrate, on the right, for each adhesive. Below are micrographs of the detached surfaces containing adhesive b) 75Cat / 25Cer c) and 0Cat / 100Cer.

[0023] Figure 3 shows an image of test specimens after mechanical testing of the aluminum bonds: the lower substrate (where the adhesive film was deposited first), on the left, and the upper substrate, on the right, for each adhesive formulation.

[0024] Figure 4 shows the PEI strength values ​​for each adhesive formulation applied to cardboard substrates.

[0025] Figure 5 shows an image of test specimens after mechanical testing of the adhesives on cardboard: the lower substrate (where the adhesive film was deposited first), on the left, and the upper substrate, on the right, for each formulation.

[0026] Figure 6 shows the PEI strength values ​​for bonding to PE / PE, AI / AI, cardboard / cardboard, AI / PE, and cardboard / PE substrates using the 50Cat / 50Cel adhesive formulation.

[0027] Figure 7 shows the force values ​​for each adhesive applied to commercial self-adhesive paper (Post-it®, 3M).

[0028] Figure 8 shows test specimens after mechanical testing of the self-adhesive paper bonding: lower substrate (where the adhesive film was deposited first), on the left, and upper substrate, on the right, for each formulation.

[0029] Figure 9 shows the values ​​from the peei 180 test. s , with the PEI strength values ​​for the 50Cat / 50Cer adhesive formulation applied in two types of substrates: glass and PE, with samples stored at temperatures of -12 S C and 25 e W.

[0030] Figure 10 presents the DMTA test results for each adhesive formulation, displaying the curves for (a) storage modulus (G'), (b) loss modulus (G”), and (c) dissipation factor (tan õ).

[0031] Figure 11 shows the histograms of (a) adhesion strength and (b) energy obtained from scanning the 50Cat / 50Cer adhesive film with an aluminum-coated AFM probe under different relative humidities: 10%, 20%, 30%, 40%, and 50%. DETAILED DESCRIPTION OF THE INVENTION

[0032] The present invention relates to a starch-based composition characterized by comprising cationic starch and waxy starch, as well as a plasticizing agent, citric acid and stearic acid.

[0033] Cationic starch is a type of modified starch that has positively charged groups (cations), especially quaternary ammonium groups, in its structure. For example, a commercially available cationic starch is FOXHEAD G2241 (Ingredion Incorporated, USA).

[0034] Waxy starch is a type of starch that contains a high concentration of amylopectin (about 95% or more) and a minimal amount of amylose (usually less than 5%), and has a highly branched structure. As an example, a commercially available waxy starch is Amidex 4001 (Ingredion Incorporated, USA).

[0035] Among the plasticizing agents, those that can be chosen are from the group that includes urea, sorbitol, ethylene glycol, superbranched polyester polyol, and glycerol, with glycerol being the preferred choice.

[0036] Citric acid reduces the degree of starch polymerization, making it less viscous when melted and thus facilitating its extrusion. Stearic acid acts as a thermal stabilizer. Both acids are essential for making the formulation adequately extrudable for the formation of adhesive tapes and films.

[0037] In terms of the concentration of the ingredients in the composition, the relative amount of cationic starch can vary from 1 to 100% in relation to waxy starch. The plasticizing agent should be present in a proportion of 20 to 60 parts of the agent to 100 parts of total starch. Citric acid should be present in the composition in a proportion of one part for every 100 parts of total starch. Stearic acid follows the same proportion as citric acid, and should be present in a proportion of one part for every 100 parts of total starch.

[0038] Chemical or physical crosslinking agents to modulate the cohesion of adhesives could be applied in the composition of the present invention. For this purpose, at least one agent selected from citric acids, latexes, isocyanates, acetylated starch, succinate starch, oxidized starch, and starch reacted with aldehyde families, for example: glutaraldehyde, dialdehydes, among others, could be used.

[0039] The starch-based adhesive production process of the present invention comprises the steps of: a) mixing cationic starch and waxy starch together with the plasticizing agent, followed by conditioning the mixture; b) comminuting and homogenizing the conditioned mixture from step a) to obtain a powder; c) mixing citric acid and stearic acid; and d) extruding and pressing the mixture.

[0040] The conditioning of step (a) can be carried out at 90°C for 12 hours for complete absorption of the plasticizer. In one embodiment of the present invention, the conditioning is carried out in an oven.

[0041] Regarding the extrusion mentioned in step (d), the process can be carried out in an open twin-screw extruder. After extrusion, the pressing of the resulting material can be carried out at a temperature of 150 to 180 °C and with a pressure between 4 and 8 t.

[0042] Chemical or physical crosslinking agents to modulate cohesion. The adhesives may be mixed with the other components described in step (a) or (c) of the process. Thus, as previously stated, at least one agent selected from citric acids, latexes, isocyanates, acetylated starch, succinate starch, oxidized starch and starch reacted with aldehyde families, for example: glutaraldehyde, dialdehydes, among others, may be used.

[0043] The process of the present invention allows the formation of adhesive tapes or films. Therefore, an embodiment of the present invention is an adhesive characterized by comprising cationic starch and waxy starch, in addition to a plasticizing agent, citric acid, and stearic acid.

[0044] Again, the plasticizing agent can be chosen from the group that includes urea, sorbitol, ethylene glycol, superbranched polyester polyol, and glycerol, with glycerol being preferred.

[0045] The relative amount of cationic starch can vary from 1 to 100% in relation to waxy starch in the adhesive. When cationic starch is 100% of the total starch in the product, the adhesion is equivalent to that of a self-adhesive note paper (like Post-it®, 3M), designed to provide sufficient adhesion for the substrate to adhere to surfaces, but also allowing it to be removed without damaging the surface or leaving residue. The addition of waxy starch to the formulation, however, allows for increased adhesive strength. In the case of bonding polyethylene and aluminum substrates, the addition of waxy starch improves adhesion by up to 5 times compared to the adhesive with 100% cationic starch. In particular, the highest adhesion can be achieved when the relative proportion of cationic starch is 75% in relation to waxy starch (25%) for aluminum and polyethylene substrates.

[0046] Thus, depending on the relative proportion of cationic starch, the adhesive of the present invention can be applied in the manufacture of cardboard / multilayer packaging, in the sealing of boxes in general, in papers for self-adhesive notes, Band-aid type dressings, diaper adhesives, and micropore tape, laminated and plastic labels for packaging, including bottles. Made of glass, plastic, and other materials, and food coatings, since the adhesive can be removed with water and is made of ingredients compatible with food safety.

[0047] As previously explained, the plasticizing agent must be present in a ratio of 20 to 60 parts of the agent to 100 parts of total starch. Citric acid must be present in the composition in a ratio of one part to every 100 parts of total starch. Stearic acid follows the same ratio as citric acid, and must be present in a ratio of one part to every 100 parts of total starch. Chemical or physical crosslinking agents to modulate cohesion may be present in the adhesive, said agents being at least one of the following: citric acids, latexes, isocyanates, acetylated starch, succinate starch, oxidized starch, and starch reacted with aldehyde families, for example: glutaraldehyde, dialdehydes, among others.

[0048] What follows presents exemplary, non-restrictive examples of the object described herein, illustrating the results and advantages achieved. Examples

[0049] Example 1: preparation

[0050] Cationic starch (Cat) and waxy starch (Cer) were mixed in the proportions shown in Table 1, which presents the relative amounts of each type of starch in relation to the total.

[0051] Table 1 - Percentage of each type of starch (by dry mass) used in each formulation.

[0052] For each formulation (Table 2), the two starches (totaling 200 g of starch) and glycerol (60 g) were mixed. The material was conditioned in an oven at 90°C. e C for approximately 12 hours. After this period, the remaining additives (2 g of citric acid and 2 g of stearic acid) were added, and the material was processed in an AX plastics twin-screw extruder (model AX DR16:42) with 5 heating zones with the following temperature profile: 1 10 / 150 / 170 / 180 / 180 e C and speed of the side field at 30 rpm, of the doser at 25 rpm and of the screw at 140 rpm. The material was then hot-pressed (160 eC, 6.5 tons), forming thin adhesive films. First, these films were deposited onto substrates of polyethylene, aluminum foil, cardboard, and commercial self-adhesive paper (Post-it®, 3M). The films were exposed to ambient humidity for at least 2 days before the top substrate was bonded. The top substrates were bonded by placing them over the adhesive films and pressing them at a pressure of 2 kgf / 10 cm². 2 = 0.2 kgf / cm 2 for 2 min. Mechanical tests of T-peel and peel 180 s They were initiated starting 2 days after the top substrate was bonded.

[0053] Table 2 - Adhesive composition

[0054] Example 2: mechanical tests (T-oee / and oee / 180 s )

[0055] T-peel and peel 180 mechanical tests sThe tests were performed on a DL-2000 universal testing machine with a 5 kgf (50 N) load cell at a speed of 254 mm / min (10 in / min). With the exception of For polyethylene and glass, all substrates were reinforced (on the side without adhesive deposition) with two layers of adhesive tape (one of crepe tape and one of transparent tape, both from 3M) to reduce the number of substrate failures, enabling analysis and allowing comparison between the adhesive formulations. In the case of polyethylene substrates, there were no substrate failures and, therefore, it was not necessary to reinforce them.

[0056] For both polyethylene and aluminum foil substrates, the 75Cat / 25Cer formulation showed the highest PEI strength (Figure 1). The types of failure for each substrate were also evaluated. Cohesive failures occurred in formulations with higher PEI strength, while adhesive failures occurred in formulations with lower PEI strength (Figure 2 and Figure 3). In the case of aluminum foil (Figure 3), substrate failures also occurred in formulations with higher PEI strength, indicating that the bonded joint was stronger than the aluminum substrate itself.

[0057] Tests were also performed on cardboard substrates (Figure 4), which demonstrated the opposite behavior to that observed on polyethylene and aluminum substrates. The highest adhesion values ​​were recorded for the 25Cer / 75Cat and 0Cer / 10OCat formulations, indicating a possible greater affinity of waxy starch with the cardboard substrate.

[0058] As illustrated in Figure 5, the images of the cardboard after the T-peel test reveal different types of defects depending on the formulation used. The 0Cat / 100Cer formulation showed cohesive failure, while the 25Cat / 75Cer formulations and those with higher amounts of cationic starch exhibited adhesive failure. The 50Cat / 50Cer formulation showed substrate failure, indicating a potential to achieve even higher adhesion values.

[0059] Figure 6 shows the tests performed on polyethylene joints with cardboard and aluminum with cardboard for the 50Cat / 50Cer formulations, aiming to simulate multilayer carton packaging. The PEI strength of the heterogeneous joints showed lower values ​​than the same The formulation in PE-PE, AI-AI, and paperboard-paperboard joints was tested. However, heterogeneous joints showed considerable bonding values, with AI-PE showing a value of 15 N / m and paperboard-PE showing a value of 26 N / m.

[0060] Considering a second application case of starch adhesives, T-peel tests were performed on self-adhesive papers (Post-it® brand adhesive paper, 3M). The substrates were obtained directly from commercial self-adhesive papers, allowing comparison with the peel strength of the material itself. Figure 7 shows the peel strengths of each formulation and the T-peel value of the commercial self-adhesive paper only. The 100Cat / 0Cer formulation showed the adhesion closest to that of the self-adhesive paper bonded together. The other formulations showed values ​​higher than the adhesion of the self-adhesive paper, with the highest peel strength values ​​for the 75Cat / 25Cer and 50Cat / 50Cer formulations.

[0061] Figure 8 presents the visual results of the adhesives applied to the self-adhesive paper. It can be observed that the behavior was similar to that observed on the other aluminum and polyethylene substrates. In other words, cohesive failures were identified in the formulations that showed greater peel strength on the paper, while adhesive failures occurred in the formulations with lower peel strength.

[0062] Figure 9 addresses mechanical tests (peei 180 e This study simulated the use of 50Cat / 50Cer formulation adhesives on polyethylene labels in glass at two temperatures: an ambient temperature of 25 °C and a sample storage temperature of -12 °C. It clearly shows that labels applied with adhesives to glass and kept at -12 °C exhibited higher values ​​than samples kept at ambient temperature. This is likely due to the vitreous temperature of the starch, as detailed in Figure 10.

[0063] Example 3: Complementary characterizations

[0064] Figure 10 shows the dynamic thermal analysis curves. Mechanical diffusion testing (DMTA) is used to analyze the glass transition temperatures (Tg) of adhesives and, consequently, the miscibility of cationic and waxy starches in the mixture to form the adhesive blend. Samples were tested using a DMTA Q800 (TA Instruments® equipment), employing a geometry for film shear in the range of -100°C. e C a 100 e C, with a scan rate of 3 sC / min and a constant frequency of 1 Hz. The storage modulus (G') (Figure 10a), which represents the elastic component of the material, and the loss modulus (G'') (Figure 10b), associated with the viscous component, exhibited abrupt variations in their values ​​as a function of temperature, depending on the formulations of the mixtures of the two types of starch. The correlation of this abrupt variation between the two components provides a better representation of the Tg of these adhesives, being expressed by the broad tan õ peak (G7G'), as illustrated in Figure 10c. The waxy starch presented two Tgs at -32 and 67 °C, and the cationic starch presented a pronounced Tg at 28 °C, where the formulations of the two starches showed a variation in the intermediate Tgs to these values ​​presented for the pure starches, indicating the miscibility of the blend. This miscibility may be indicative of the synergism of the adhesive properties presented by the mixture of the two starches, as observed in the mechanical data.Furthermore, the 50Cat / 50Cer formulation showed a Tg of ~10 °C, which may explain the better adhesion effect shown by the glass stored at -12 °C.

[0065] Figure 11 presents the results of an adhesion experiment performed on an atomic force microscope (NanoWizard4, JPK / Bruker), which allows the measurement of the interactions between the probe and the surface of a 50Cat / 50Cer adhesive film formulation. The experiment was conducted in force map mode using an aluminum-coated spherical probe (SD-SPHERE-Cont-L, 4 µm diameter, spring constant of 0.2 N / m). This experimental configuration allowed the investigation of the aluminum-adhesive interaction on a micrometer scale, complementing the macroscopic analysis of the bonds. of the aluminum foils. In total, 257 force-distance curves were acquired for each experimental condition, from the approach followed by the retraction of the probe with the surface of the material. By varying the relative humidity of the air (from 10 to 50%), it was possible to construct the histograms of force (Figure 11a) and adhesion energy (Figure 11b). The results indicate that the adhesion force tends to increase with increasing relative humidity, with values ​​of 7-10■ 9 10-10 9 N. Similarly, the adhesion energy also showed this trend, with values ​​of 10-10 9 a 60- 10' 9 J, indicating greater interaction between the tip and the surface under higher humidity conditions.

Claims

CLAIMS 1. Starch-based composition characterized by comprising cationic starch and waxy starch, a plasticizing agent, citric acid, and stearic acid.

2. Composition according to claim 1, characterized in that the plasticizing agent is selected from the group comprising urea, sorbitol, ethylene glycol, superbranched polyester polyol and glycerol.

3. Composition, according to any one of claims 1 and 2, characterized in that the relative amount of cationic starch varies from 1 to 100% relative to waxy starch.

4. Composition, according to any one of claims 1 to 3, characterized in that the amount of plasticizing agent is from 20 to 60 parts of the agent per 100 parts of total starch.

5. Composition, according to any one of claims 1 to 4, characterized in that the amount of citric acid is one part per 100 parts of total starch.

6. Composition, according to any one of claims 1 to 5, characterized in that the amount of stearic acid is one part per 100 parts of total starch.

7. Composition, according to any one of claims 1 to 6, characterized by comprising at least one chemical or physical crosslinking agent selected from the group comprising citric acids, latexes, isocyanates, acetylated starch, succinate starch, starch reacted with aldehyde families and oxidized starch.

8. Production process for starch-based adhesive characterized by comprising the steps of: a) mixing cationic starch and waxy starch with the plasticizing agent. and perform the conditioning of the mixture; b) comminute and homogenize the conditioned mixture from step a) to obtain a powder; c) mix the citric acid and stearic acid; and d) perform the extrusion and pressing of the mixture.

9. Process according to claim 8, characterized by optionally comprising a mixture of at least one chemical or physical crosslinking agent selected from the group comprising citric acids, latexes, isocyanates, acetylated starch, succinate starch, starch reacted with aldehyde families and starch oxidized in step (a) or (c).

10. Process, according to claim 8 or 9, characterized in that the conditioning described in step (a) is carried out at 90°C for 12 h for complete absorption of the plasticizer.

1. Process, according to any one of claims 8 to 10, characterized in that the extrusion in step (d) is carried out in an open twin-screw extruder.

12. Process, according to any one of claims 8 to 11, characterized in that the pressing in step (d) is carried out at a temperature of 150 to 180 °C and with a pressure between 4 and 8 t.

13. Starch-based adhesive characterized by comprising cationic starch and waxy starch, a plasticizing agent, citric acid and stearic acid.

14. Adhesive, according to claim 13, characterized by comprising at least one chemical or physical crosslinking agent selected from the group comprising citric acids, latexes, isocyanates, acetylated starch, succinate starch, starch reacted with aldehyde families and oxidized starch.

15. Adhesive, according to claim 13 or 14, characterized in that the plasticizing agent is chosen from the group comprising urea, sorbitol, ethylene glycol, superbranched polyester polyol and glycerol.

16. Adhesive, according to any one of claims 13 to 15, characterized in that the relative amount of cationic starch varies from 1 to 100% relative to waxy starch.

17. Adhesive, according to any one of claims 13 to 16, characterized in that the amount of plasticizing agent is from 20 to 60 parts per 100 parts of total starch.

18. Adhesive, according to any one of claims 13 to 17, characterized in that the amount of citric acid is one part per 100 parts of total starch.

19. Adhesive, according to any one of claims 13 to 18, characterized in that the amount of stearic acid is one part per 100 parts of total starch.

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