Adhesive coacervate based on latex, nanocellulose and lignosulfonate, its production process and its uses.

Description

Adhesive coacervate based on latex, nanocellulose and lignosulfonate, its production process and its uses.

[0001] Certificate of Addition of Invention to application BR102020025955-5, filed on December 18, 2020. DESCRIPTION FIELD

[0002] The present description refers to compositions comprising modified cellulose. FUNDAMENTALS OF DESCRIPTION

[0003] Environmental problems have led to an increased demand for replacing petroleum-derived materials with materials from renewable and sustainable sources. In the adhesives industry, this paradigm shift is reflected in the search for adhesive formulations containing a low solids content, a high amount of water, and using only renewable materials, such as cellulose, lignin, and natural rubber latex.

[0004] Natural rubber latex is extracted from the bark of the rubber tree trunk and is marketed in the form of a colloidal dispersion containing rubber particles dispersed in a high-concentration ammonium hydroxide solution. In this system, the function of ammonia is to maintain colloidal stability and protect the natural rubber latex from bacterial degradation. Despite these effects, the presence of high concentrations of ammonia in natural rubber latex can lead to respiratory irritation and even more serious health problems. STATE OF THE ART

[0005] The state of the art presents some adhesive formulations comprising cellulose, latex, lignin and their derivatives.

[0006] Patent document BR102019009641-1 discloses an adhesive consisting of a solution of natural rubber latex, cellulose nanofibers (industrially produced), and sulfonated lignin, with the presence of lignin being of great relevance to the adhesive's performance on various substrates. The production process of this adhesive is also revealed, which comprises the simple mixing of the components under agitation, at ambient conditions. Therefore, ammonia Petition 870220072331, dated 12 / 08 / 2022, page 5 / 11 2 / 7 of the latex contained in natural rubber remains in the final product.

[0007] Patent document WO2019213730A1 discloses an adhesive based on natural rubber latex at pH equal to or greater than 9, lignin precipitated at acidic pH in its non-functionalized form and nanocellulose in its non-functionalized form, as well as the production process thereof.

[0008] Jayaramudu and colleagues (2019, Composites Part B, v. 156, p. 43-50) disclose an adhesive made from a mixture of poly(ethylene oxide) and lignin (PEO-L). Increasing the lignin content in the mixture showed a proportional increase in adhesive properties, with the shear stress of the pure PEO adhesive being 442 kPa, while the shear stress of the PEO-L adhesive with 30% lignin was 835 kPa, in single lap joint tests performed on films based on cellulose nanofibrillated (CNF).

[0009] Yotov et al. (2017, Bulgarian Chemical Communications, v. 49, Special Issue L, p. 92-97) disclose an adhesive whose composition comprises lignosulfonates as a partial or total replacement for the phenol-formaldehyde (PFR) resin traditionally used for this type of composite. The mechanical properties and water resistance of this natural lignosulfonate adhesive are adequate according to the specifications defined in adhesive standards for the manufacture of medium-density fiberboard (MDF). In the manufacture of this composite, the wood fibers and lignosulfonate are bonded at high temperature and pressure, a process called self-adhesion.

[0010] Patent document US6790271B2 discloses a waterproof adhesive formulation comprising isolated soy protein, a plasticizer, a vegetable oil, and lignin or a lignin derivative. The soy protein is present in a proportion above 50%, giving the adhesive water resistance. The described plasticizer is a polyol, preferably glycerol, in a concentration above 20%. The vegetable oil is modified to have at least one reactive site with the protein and the polyol. The function of the lignin or a lignin derivative is to increase the rigidity of the adhesive. The lignin derivative that showed the most advantageous results in the manufacture of the described adhesive was lignosulfonate. A disadvantage Petition 870220072331, dated 12 / 08 / 2022, page 6 / 11 3 / 7 associated with this previous technique is the need to cure the adhesive at high temperatures (around 165 °C).

[0011] No adhesive formed by electrostatic complexation, containing nanofibers and / or nanocrystals having surfaces functionalized with cationic groups, and which eliminates the need for high temperatures in a curing and / or self-adhesion step, is disclosed in the prior art. Also not disclosed in the prior art is an adhesive comprising lignosulfonate combined with another component that is not derived from petroleum, protein, vegetable oil, or polyol. Finally, no adhesive based on natural rubber latex with a low ammonia content is disclosed, thus reducing the health risk due to inhalation of this volatile toxic component. BRIEF DESCRIPTION OF THE OBJECT

[0012] One of the objectives of this description is to disclose a waterproof adhesive capable of bonding a plurality of substrates and which is easy to apply. This plurality of substrates includes glass, aluminum foil, polymers or cellulosic substrates of different compositions, including fabrics, wood, paper and cardboard, all of which can be in wet or damp conditions. It is also an objective of this description to provide an adhesive capable of bonding joints of similar or disparate substrates. An additional objective of this description is to provide an adhesive that presents a low risk of intoxication by inhalation.

[0013] The objectives of the present description are achieved by an adhesive coacervate comprising 1% to 99% (w / w) of cationized nanocellulose, 1% to 99% (w / w) of natural rubber latex dispersion and 0.01 to 80% (w / w) of sulfonated lignin.

[0014] The objectives of the present description are also achieved by a production process of said adhesive coacervate. This process comprises adding, drop by drop, a dispersion of natural rubber latex and a solution of sulfonated lignin to an aqueous dispersion of cationic nanocellulose, stirring and homogenizing the mixture. Then, centrifuging and separating the solid phase from the mixture, wherein the solid phase is the adhesive coacervate. Petition 870220072331, dated 12 / 08 / 2022, page 7 / 11 4 / 7

[0015] Adhesives are applied for bonding to wet or humid substrates, preferably polymeric or glass substrates. DETAILED DESCRIPTION OF THE OBJECT

[0016] Nanocellulose is the term used to describe cellulosic materials with dimensions in the nanometer range (10-9m). Nanocelluloses can be classified into three main categories: i) nanofibrillated cellulose (CNF), ii) nanocrystalline cellulose (CNC), and iii) bacterial nanocellulose (BNC).

[0017] The main route for obtaining CNC is via acid hydrolysis of cellulose pulp. This method promotes the removal of amorphous regions from the material, generating well-defined crystals of stable nanocellulose in colloidal suspension.

[0018] CNF is obtained by mechanical treatment of cellulose pulp. Mechanical shearing is responsible for breaking the rigid structure of cellulose fibers, which are strongly cohesive due to hydrogen bonds and Van der Waals interactions, thus reducing the size of the fibers.

[0019] Lignin is a highly cross-linked three-dimensional macromolecule consisting of three types of substituted phenols (coniferyl, sinapyl, and p-coumaryl alcohols) arranged in cross-linked covalent bonds. Its chains can have different structures and degrees of polymerization, depending on the plant species from which it is extracted.

[0020] Natural rubber latex has intrinsic characteristics that are very distinct from synthetic latexes, due to the particularities of its extraction source (in most cases, Hevea brasiliensis). In addition to the rubbery structure (1,4-cis-polyisoprene), which constitutes approximately 95% of its composition, this natural latex has a phosphoprotein membrane, which is relevant for the interaction with the other constituents of the adhesive coacervate described herein.

[0021] The term coacervate is used in colloid chemistry to denote the association of molecules with opposite charges (polyelectrolytes) that lead to the formation of a water-poor phase. When separated, these polycations and polyanions exhibit good solubility in aqueous media. However, when these species Petition 870220072331, dated 12 / 08 / 2022, page 8 / 11 When 5 / 7 are mixed, electrostatic interactions occur, leading to the formation of neutral species that are less soluble in the aqueous medium, resulting in phase separation. The colloid-rich phase is known as the coacervate phase, while the phase containing very small amounts of colloid is known as the equilibrium phase.

[0022] Adhesive coacervates based on cationic nanocellulose, natural rubber latex and lignosulfonate are described, as well as their production processes.

[0023] In the preferred embodiment of the adhesive coacervate, the nanocellulose used is derived from sugarcane bagasse, which is an environmentally sustainable raw material and an abundant agro-industrial residue.

[0024] In one embodiment of the adhesive coacervate, the nanocellulose used is derived from woody species, such as eucalyptus and pine, or from fibrous species, such as cotton, rice and corn.

[0025] In one embodiment of the adhesive coacervate, the nanocellulose used is obtained by mechanical treatment of the cellulose pulp, breaking hydrogen bonds between the fibers and fibrillating them, resulting in nanofibrillated cellulose (CNF). In this embodiment, the CNF is subjected to a cationization or oxidation pretreatment by TEMPO, before being added to the lignosulfonate for adhesive preparation.

[0026] In one embodiment of the adhesive coacervate, the nanocellulose used is obtained from the controlled acid hydrolysis of cellulose pulp, with removal of the amorphous regions of the material, generating cellulose nanocrystals in the form of very stable whiskers in colloidal suspension, resulting in nanocrystalline cellulose (CNC). In this embodiment, the CNC is subjected to a cationization or oxidation pretreatment by TEMPO, before being added to the lignosulfonate for adhesive preparation.

[0027] In one embodiment of the adhesive coacervate, the product comprises cationized nanocellulose in a proportion of 0.01% to 99.99% by mass on a dry basis, lignosulfonate in a proportion of 0.01% to 80% by mass on a dry basis and natural rubber latex in a proportion of 0.01% to 99.99% by mass on a dry basis. Petition 870220072331, dated 12 / 08 / 2022, page 9 / 11 6 / 7

[0028] In one embodiment of the present adhesive coacervate production process, the process is conducted by adding, drop by drop, a dispersion of natural rubber latex and a solution of sulfonated lignin to an aqueous dispersion of cationic nanocellulose. The aqueous dispersion of nanocellulose has a solids content of 0.1% to 10% by mass on a dry basis. For each drop added of the natural rubber latex dispersion and the lignosulfonate solution, it is necessary to homogenize the dispersion, for example, using a vortex mixer with moderate agitation, from 200 to 3000 rpm, for a period between 2 and 20 seconds. At the end of the step of adding the latex dispersion and the lignosulfonate, the mixture of components is left under moderate agitation, for example, using a vortex mixer from 200 to 3000 rpm, for 2 to 5 minutes, at room temperature, to ensure homogenization and electrostatic complexation.

[0029] Electrostatic complexation is a type of non-covalent supramolecular interaction between two species with opposite charges that generally leads to an associative phase separation. During the mixing stage of the components, electrostatic attraction occurs between them, releasing counter-ions into the medium and promoting a liquid-liquid phase separation, where the phase rich in polyelectrolytes is called the coacervate, and the phase rich in water and counter-ions is called the dilute phase.

[0030] In one embodiment of the present coacervate adhesive production process, after electrostatic complexation and homogenization of the mixture, it is centrifuged for 5 to 60 minutes at speeds between 4500 and 6000 rpm, resulting in the separation between the polyelectrolyte-rich phase and the water- and counter-ion-rich phase. Electrostatic complexation, used in the preparation of the present coacervate adhesive, is essential to maintain the stability of this material in water, as it is as if a cross-linking of the polymers occurs, which then have less sensitivity to water due to a reduced tendency to swell. Another advantage inherent to the electrostatic complexation process with phase separation is that the ammonia present in the latex dispersion migrates along with the counter-ions to the diluted phase, being easily removed. Petition 870220072331, dated 12 / 08 / 2022, page 10 / 11 7 / 7

[0031] In one embodiment, after centrifugation, the liquid supernatant is discarded and the remaining product is the adhesive coacervate of the present description, ready to be applied to the surfaces of substrates such as paper, glass, plastic and aluminum, without the need for heat and / or high pressure to cure the adhesive. The adhesive coacervate showed good adhesion to glass and plastic surfaces after being kept in contact with these dry substrates for 24 h. To test the adhesive's resistance to water, the bonded substrates were subjected to immersion tests in distilled water for approximately 24 h, with total detachment of the glass surfaces observed after this period, while the plastic surfaces showed good adhesion even after 48 h of immersion in distilled water.

[0032] Although exemplary embodiments of the processes and products described have been presented in this report, the scope of protection is not intended to be limited to the literal description thereof. Therefore, the description should be interpreted not as limiting, but merely as examples of particular embodiments that retain the inventive concept presented herein. A person skilled in the art may readily apply the teachings presented herein to analogous solutions arising therefrom, limited only by the scope of the claims in this application.

Claims

1. Waterproof adhesive coacervate, characterized by comprising in its formulation natural rubber latex, lignosulfonate and cationized nanocellulose.

2. Adhesive coacervate, according to claim 1, characterized in that the nanocellulose is derived from agro-industrial waste from a plant species selected from the group comprising sugarcane, eucalyptus, pine, cotton, rice, corn and mixtures thereof.

3. Adhesive coacervate, according to claim 2, characterized in that the cationized nanocellulose is derived from agro-industrial waste from sugarcane.

4. Adhesive coacervate, according to any one of claims 1 to 3, characterized in that the cationized nanocellulose is cationized nanofibrillated cellulose.

5. Adhesive coacervate, according to any one of claims 1 to 3, characterized in that the cationized nanocellulose is cationized nanocrystalline cellulose.

6. Adhesive coacervate, according to any one of claims 1 to 5, characterized by comprising cationized nanocellulose in a proportion of 2.5% to 97.5% by mass on a dry basis, lignosulfonate in a proportion of 0.01% to 80% by mass on a dry basis and natural rubber latex in a proportion of 2.5% to 97.5% by mass on a dry basis.

7. Production process of the adhesive coacervate based on natural rubber latex, nanocellulose and lignosulfonate of claims 1 to 6, characterized by: mixing in an aqueous dispersion of nanocellulose slowly, drop by drop, a dispersion of natural rubber latex and a solution of sulfonated lignin, under moderate, constant agitation, wherein said aqueous dispersion of nanocellulose has a solids content of 0.1% to 2% by mass on a dry basis, said dispersion of natural rubber latex has a solids content of 0.5% to 40% by mass Petition 870260067405, dated 08 / 07 / 2026, page 10 / 11 2 / 2 on a dry basis and the lignosulfonate has a solids content of 0.01% to 62% by mass on a dry basis; homogenizing the mixture of sulfonated lignin and nanocellulose, maintaining moderate agitation between 2 and 5 min; centrifuge the mixture; separate the solid phase from the centrifuged mixture, where the solid phase is the adhesive coacervate.

8. Process, according to claim 7, characterized in that centrifuging said mixture is done for a period between 14 and 18 minutes at a speed between 4500 and 6000 rpm.

9. Use of the adhesive coacervate of claims 1 to 6, characterized by being for adhesion to wet substrates or in humid conditions.

10. Use of the adhesive coacervate, according to claim 9, characterized in that it is for the adhesion of similar or disparate substrates selected from the group comprising glasses and polymers.