Process for preparing a thermoplastic composite of cellulose pulp modified by reactive extrusion with anhydrides, and thermoplastic composite

Abstract

The present invention aims to provide a process for preparing a thermoplastic composite from cellulose pulp modified by reactive extrusion with anhydrides, and a thermoplastic composite prepared by means of said process. The process is used to modify cellulose in the form of chemical pulp, microfibrillated cellulose (MFC) or nanofibrillated cellulose (NFC) by means of reactive extrusion (REX) in the presence of an aprotic solvent with the ability to swell the cellulose, for subsequent use of the product obtained as a reinforcement in composites with thermoplastic resin.

Description

PROCESS FOR PREPARING THERMOPLASTIC COMPOSITE FROM MODIFIED CELLULOSE PULP VIA REACTIVE EXTRUSION WITH ANHYDRIDES, AND THERMOPLASTIC COMPOSITE TECHNICAL FIELD

[0001] The present invention pertains to the field of thermoplastic composite materials and relates to a process for preparing a thermoplastic composite from cellulose pulp modified via reactive extrusion (REX) with long-chain anhydrides, and to a thermoplastic composite prepared from said process. Said thermoplastic composite exhibits good cellulose fiber dispersion characteristics and better mechanical properties than synthetic thermoplastic polymers. Modification of the cellulose pulp by reactive extrusion with anhydrides is performed prior to obtaining the composite with the thermoplastic polymer; thus, the good fiber dispersion also provides better reinforcement of the composite material. BACKGROUND OF THE INVENTION

[0002] In the current context in which sustainability has gained increasing relevance, the search for thermoplastic composites consisting of high-quality materials from renewable sources has intensified, in which the replacement of synthetic polymers with natural polymers is particularly advantageous.

[0003] Lignocellulosic materials can be used as fillers or reinforcing agents in thermoplastic composites, and such materials have become important in polymer matrices due to their advantages over other inorganic or synthetic materials. The addition of mineral fillers and synthetic fibers, aimed at improving mechanical properties, leads to a reduction in non-renewable content.

[0004] Eucalyptus or pine cellulose fibers can be subdivided into chemical, semi-chemical bleached and unbleached cellulose pulp, and have several advantages, such as low density, natural and renewable origin, low cost, and good mechanical properties.

[0005] Furthermore, chemical cellulose pulp is a commodity, composed mainly of cellulose and comes from a natural and renewable source, favoring interest in its use in a more sustainability-oriented approach.

[0006] In this sense, cellulose is an attractive candidate for materials development due to its biocompatibility, biodegradability, and chemical modification potential. Specifically, cellulose fiber has excellent properties, such as lightness, high mechanical strength, high modulus of elasticity and low linear thermal expansion, and its use in obtaining reinforced thermoplastic composites is strategic.

[0007] Similarly, reinforced polymer composites with improved properties can replace conventional materials such as metals, plastics, and wood in many types of applications, for example, the construction, packaging, automotive, furniture, and aerospace industries.

[0008] Furthermore, the use of additives in polymer processing is common. However, the use of a hydrophilic material, such as cellulose pulp, to improve the yield, physical properties, and processing of thermoplastic polymer resins still presents several barriers, primarily due to the low compatibility between a hydrophilic and a hydrophobic material.

[0009] The document by STANCIU, ND et al. (2009) - “Preliminary studies on the synthesis and characterization of cellulose - Maleic anhydride - Dicyclopentadiene composites”, reveals studies of the properties of cellulose composites with maleic anhydride-dicyclopentadiene copolymer. The syntheses of the composites were carried out in two different solvents: toluene and dioxane.

[0010] The document by GAUTHIER, R. et al. (1998) “Interfaces in polyolefin / cellulosic fiber composites: Chemical coupling, morphology, correlation with adhesion and aging in moisture", details the characteristics of cellulose and wood fibers when associated with thermoplastic matrices for composite applications.

[0011] Indeed, there are a number of challenges related to the processing of synthetic solid polymers, particularly with regard to compatibility with other components.

[0012] In particular, cellulose fiber is highly hydrophilic and therefore has low affinity for hydrophobic resins (such as polypropylene, polyethylene and similar), so that simple mechanical mixing through an extruder or similar method may not generate composites with good fiber dispersion and therefore with satisfactory mechanical properties.

[0013] Thus, considering that cellulose pulp is a hydrophilic material, that is, it has an affinity for water, and that synthetic polymers are hydrophobic, that is, they are resistant to water, the preparation of a thermoplastic composite material that combines a hydrophilic element and a hydrophobic element is still a challenge.

[0014] In this sense, the production of a composite containing cellulose fiber and a thermoplastic resin with a hydrophobic character, such as polypropylene, polyethylene and similar, represents a great challenge due to the low dispersion property of cellulose fiber, which makes it very difficult to form a composite with adequate properties.

[0015] In other words, the desired approach is to modify hydrophilic cellulose pulp for use as a mechanical reinforcement in hydrophobic thermoplastic resins. An alternative is to modify the cellulose pulp fibers by replacing the water in the pulp with a long-chain anhydride (e.g., alkenyl succinic anhydride - ASA), which provides a hydrophobic characteristic and enhances matrix / fiber interaction.

[0016] However, the amount of solvent used in known processes for modifying hydrophilic cellulose pulp presents a technical and economic challenge for the viability of this type of process.

[0017] Additionally, there are several problems associated with this non-uniform dispersion of cellulose fibers in a polymer matrix. Indeed, cellulose pulp agglomerates, and thus, dispersing the pulp in a non-polar polymer matrix presents considerable difficulties and also a challenge regarding achieving good matrix / fiber compatibility and thus providing good anchoring of the cellulose fibers to the polymer matrix. Both fiber dispersion and anchoring are essential for achieving superior mechanical properties.

[0018] Furthermore, the lower the amount of polymer in the cellulose fiber / polymer mixture, the more difficult it becomes to disperse the cellulosic fiber in the polymer matrix.

[0019] In turn, as the amount of fiber increases, the more viscous the fiber / polymer mixture becomes, making it more difficult to move the fibers within the polymer matrix to provide dispersion.

[0020] Therefore, a thermoplastic composite preparation process that combines two materials with different characteristics is still needed. In this context, it is advantageous to develop new process alternatives for preparing composite materials that combine highly hydrophilic components, such as cellulose pulp, and hydrophobic components, such as polymers, to facilitate the dispersion of a polymer matrix in an apolar material, while also reducing the amount of solvents used in the composite preparation process.

[0021] Therefore, the present invention relates to a new and inventive process for modifying cellulose pulp fibers via reactive extrusion (REX) in the presence of an aprotic solvent with the swelling capacity of cellulose for the preparation of thermoplastic composite materials that exhibit good dispersion characteristics, as well as improved mechanical properties compared to the thermoplastic polymer, while reducing the amount of swelling solvent and aprotic solvent used. The present invention also relates to a thermoplastic composite prepared from said process. SUMMARY OF THE INVENTION

[0022] The present invention discloses a process for preparing thermoplastic composites from modified cellulose pulp via reactive extrusion in the presence of an aprotic solvent capable of swelling cellulose, and the thermoplastic composite prepared from said process for coating and modifying cellulose fibers so that it presents good fiber dispersion in the apolar matrix, without the presence of fiber agglomerates, in addition to good mechanical properties. The process of the present invention allows a reduction in the amount of swelling solvent or aprotic solvent used compared to other processes.

[0023] The modifying agent is from the anhydride class of the alkenyl succinic anhydride - ASA type (or similar reagent) while the swelling solvent is selected from the group consisting of N-methyl-2-pyrrolidone (NMP) and dihydrolevoglucosenone (Cyrene).

[0024] Specifically, the invention relates to a process for treating cellulose fibers via reactive extrusion with anhydrides, in which the cellulose fibers are modified so as to facilitate subsequent dispersion in a thermoplastic polymer, thus forming a composite containing cellulose and the thermoplastic polymer, with a reduction in the amount of solvents used.

[0025] One embodiment of the invention relates to a process for preparing thermoplastic composite from modified cellulose pulp via reactive extrusion with anhydrides, which comprises the following steps: a) dewatering the wet pulp, microfibrillated cellulose (MFC) or nanofibrillated cellulose (NFC) by pressing and filtration; b) adding isopropanol or another solvent miscible in water and easily removable; c) pressing and filtering the mixture to eliminate excess liquid; d) repeating the process of adding isopropanol, pressing and filtration at least two more times; e) add to the resulting material an aprotic solvent until the cellulose / aprotic solvent ratio is 1:1 by mass or greater; f) evaporate the isopropanol in a vessel with stirring under a nitrogen flow and application of vacuum; g) obtain a composition with 50% pulp in aprotic solvent and a residual water in relation to cellulose of less than 5%; h) add ASA anhydride and K2CO3 in an ASA / K2CO3 molar ratio of 1:1 (mol / ml); i) extrude the material from step h) generating a pulp modified with partially defibrillated ASA; j) disperse the resulting product in ethanol, press and filter; k) carry out the same process carried out with ethanol with a diluted 1% acetic acid solution, water and isopropanol; l) press and dry the resulting product; m) process and compost the material obtained in step i) to incorporate the thermoplastic polymer; en) obtain a composite material with excellent fiber dispersion.

[0026] Preferably, the aprotic solvent is selected from the group consisting of N-methyl-2-pyrrolidone (NMP) and dihydrolevoglucosenone (Cyrene).

[0027] In another embodiment of the invention, a thermoplastic composite of cellulose pulp modified by reactive extrusion with anhydrides is described, in which the fibers of the treated cellulose pulp present a better dispersion characteristic in relation to an untreated pulp, and, furthermore, have a degree of defibrillation controlled by the extrusion conditions in the reaction phase with ASA and also, but to a lesser extent, during composting with the thermoplastic matrix.

[0028] Therefore, the present invention relates to a new and inventive process for preparing thermoplastic composite materials and to a thermoplastic composite obtained from said process, in which said process consists of modifying the cellulose pulp via reactive extrusion in the presence of an aprotic solvent that has the capacity to swell the cellulose.

[0029] The thermoplastic composite presents an increased modulus of elasticity, good dispersion characteristics, as well as improved mechanical properties in relation to the synthetic thermoplastic polymer, in which the cellulose present in the composite acts as a reinforcing agent in the thermoplastic matrix.

[0030] Furthermore, the process of the present invention uses reduced amounts of anhydride and swelling agent in relation to processes known in the state of the art, in addition to allow the optimization of the washing process with a smaller number of steps or solvents in all phases of the process. BRIEF DESCRIPTION OF THE FIGURES

[0031] To assist in identifying the main characteristics of the process of preparing a thermoplastic composite and the thermoplastic composite obtained from said process, some figures are presented to which reference is made, as follows:

[0032] FIG. 1 is a flowchart illustrating the process of preparing a thermoplastic composite material from bleached Kraft eucalyptus pulp modified via reactive extrusion (REX) with anhydrides.

[0033] FIG. 2 is a representative image of bleached Kraft Eucalyptus pulp modified with alkenyl succinic anhydride (ASA) via REX.

[0034] FIGS. 3A-3C show optical micrograph images of bleached Kraft eucalyptus pulp modified with ASA.

[0035] FIG. 4A is a representative image of a composite injection molded specimen with bleached Kraft eucalyptus pulp modified via the conventional method with excess ASA.

[0036] FIG. 4B is a representative image of a composite injection molded specimen with modified bleached eucalyptus Kraft pulp under reactive extrusion (REX) conditions with reduced amounts of ASA, solvents, and other reagents.

[0037] FIG. 5A is an illustrative image of a 0.5 mm thick thin film pressed from the specimen in FIG. 4A without prior filtration, i.e., with bleached Kraft eucalyptus pulp modified via the conventional method with excess ASA.

[0038] FIG. 5B is an illustrative image of a 0.5 mm thick thin film pressed from the specimen in FIG. 4B without prior filtration, i.e., with bleached Kraft eucalyptus pulp modified under reactive extrusion (REX) conditions with reduced amounts of ASA, solvents and other reagents. DETAILED DESCRIPTION OF THE INVENTION

[0039] In particular, composite materials represent the union or combination of two different materials with the aim of forming a new material with characteristics and properties specific to the materials used.

[0040] Despite the known difficulty related to the incompatibility of hydrophilic compounds (cellulose) with hydrophobic compounds (thermoplastic polymers), the inventors of the present invention were unexpectedly able to obtain a method that can be employed to prepare a thermoplastic composite with better dispersion characteristics, which can be observed from pressed films with 0.5 mm thickness where the reduction of agglomerates in test specimens with modified pulp via the conventional method with excess ASA in relation to test specimens with modified pulp under reactive extrusion (REX) conditions with reduced amounts of ASA, solvents and other reagents indicates good dispersion, and better processing, in addition to more desirable mechanical properties of specific polymers and ensure the use of a smaller amount of alkenyl succinic anhydride (ASA) and also of the swelling agent (NMP).

[0041] Furthermore, the process of the present invention also provides for the optimization of the washing process, with a smaller number of steps or solvents in all phases of the process.

[0042] The terms “treated pulp”, “treated cellulose pulp”, “modified pulp” and “modified cellulose pulp” are interchangeable and should be understood as cellulose pulp that has undergone a treatment, in which the cellulose fibers have been modified, so that the composite obtained from the processes of the present invention presents better dispersion and processing characteristics.

[0043] Cellulose fiber is selected from the group consisting of cellulose pulp, microfibrillated cellulose (MFC) and nanofibrillated cellulose (NFC), originating from hardwood (short fiber) such as eucalyptus or softwood (long fiber) such as pine.

[0044] Similarly, the terms “pulp treatment”, “fiber treatment”, “pulp modification”, “fiber modification” and “cellulose modification” are also interchangeable and should be understood as the process of treating cellulose pulp, in which the cellulose fibers are modified through their coating, in order to improve the dispersion of the fibers in the polymer matrix.

[0045] The present invention relates to a process for preparing a thermoplastic composite from modified cellulose pulp via reactive extrusion (REX) with long-chain anhydrides, and to a thermoplastic composite prepared from said process.

[0046] The process involves modifying cellulose into chemical pulp, microfibrillated cellulose (MFC) or nanofibrillated cellulose (NFC) via reactive extrusion (REX) in the presence of a aprotic solvent with the swelling capacity of cellulose for the preparation of thermoplastic composite materials that present good dispersion characteristics, as well as improved mechanical properties in relation to the thermoplastic polymer, and its subsequent use as reinforcement in composites with thermoplastic resin.

[0047] Specifically, the aforementioned thermoplastic composite presents good dispersion characteristics of cellulose fibers, better mechanical properties, increased modulus of elasticity, in addition to presenting processing benefits in relation to the synthetic thermoplastic polymer, while at the same time reducing the amount of swelling solvent and aprotic solvent used.

[0048] As indicated herein, the prior art already presents thermoplastic composites of cellulose pulp. However, it fails to reveal or suggest an environmentally friendly product, in which the cellulose pulp (or microfibrillated cellulose (MFC) or nanofibrillated cellulose (NFC)) is modified via a reactive extrusion process with anhydrides in the presence of a small amount of an aprotic solvent with the cellulose swelling capacity, thus allowing for better dispersion of the cellulose fibers in the polymer matrix.

[0049] Surprisingly, the inventors of the present application have developed a process for preparing a thermoplastic composite that combines bleached Kraft eucalyptus cellulose pulp, i.e., a highly hydrophilic component, with a thermoplastic polymer, a hydrophobic component, without the problems of incompatibility and difficulty in dispersion known in the state of the art, and with an optimization of the washing process through the reduction in the number of steps or solvents in all phases of the process.

[0050] The treatment of cellulose pulp via reactive extrusion with alkenyl succinic anhydride (ASA) provides the modification of cellulose fibers by coating them with a low polarity material, such as a polymer, allowing a good dispersion characteristic of the fibers in the polymer matrix, while reducing the amount of swelling solvent used.

[0051] Thus, the process of preparing thermoplastic composite from modified cellulose pulp via reactive extrusion (REX) with ASA allows obtaining a product with good mechanical properties for later use as reinforcement in thermoplastic matrix.

[0052] In particular, a process for preparing composites of cellulose fibers and thermoplastic polymers is disclosed, in which the cellulose fiber in the form of pulp, microfibrillated cellulose or nanofibrillated cellulose is initially treated directly by exchanging the water in the pulp for isopropanol, followed by filtration and pressing, addition of N-methyl-2-pyrrolidone (NMP) or dihydrolevoglucosenone (Cyrene) as a swelling agent and reactive extrusion of the thermoplastic polymer matrix with alkenyl succinic anhydride (ASA), in which a high dispersion of the fibers is achieved, together with a decrease in the amount of swelling solvent.

[0053] This process uses a raw material from a renewable source as reinforcement, which guarantees an environmentally friendly character of the process of the present invention in relation to processes already existing in the state of the art and which make use of a non-renewable raw material, such as, for example, glass fibers, talc, among others.

[0054] In a first embodiment, the process for preparing thermoplastic composite from modified cellulose pulp via reactive extrusion with anhydrides comprises the following steps: a) dewatering the wet pulp, microfibrillated cellulose (MFC) or nanofibrillated cellulose (NFC) by pressing and filtration; b) adding isopropanol or another water-miscible and easily removable solvent; c) pressing and filtering the mixture to eliminate excess liquid; d) repeating the process of adding isopropanol, pressing and filtration at least twice more; e) adding an aprotic solvent to the resulting material until the cellulose / aprotic solvent ratio is 1:1 by mass or greater; f) evaporating the isopropanol in a vessel with stirring under a nitrogen flow and applying a vacuum; g) obtaining a composition with 50% pulp in aprotic solvent and a residual water in relation to cellulose of less than 5%; h) add ASA anhydride and K2CO3 in the molar ratio ASA / K2CO3 1:1 (mol / ml);i) extrude the material from step h) generating a modified pulp with partially defibrillated ASA; j) disperse the resulting product in pressed and filtered ethanol; k) carry out the same process with a diluted solution of 1% acetic acid, water and isopropanol; l) dewater and dry the resulting product; m) process and compost the material obtained in step I) to incorporate the thermoplastic polymer; and; n) obtain a composite material with excellent fiber dispersion.

[0055] In some embodiments, the aprotic solvent is selected from the group consisting of N-methyl-2-pyrrolidone (NMP) and dihydrolevoglucosenone (Cyrene). Preferably, the aprotic solvent is N-methyl-2-pyrrolidone (NMP).

[0056] Optionally, a compatibilizer is used in step m). Preferably, the compatibilizer is from the class of polypropylene copolymers functionalized with maleic anhydride with an acidity of 37-45 mg KOH / g corresponding to 8-12% maleic anhydride, such as, for example, Lycocene 6452. Compatibilizing agents with other maleic anhydride contents, including copolymers with styrene, acrylate and ethylene, can also be used, since they have the same function.

[0057] Other examples of compatibilizers are: Orevac CA 100(PP-g-MA), Synthomer G-3015, Epolene E25, E-43 and E-43P, Orevac 18732 RBP, among others.

[0058] In some embodiments, the wet pulp, microfibrillated cellulose (MFC), or nanofibrillated cellulose (NFC) from step a) has a solids content of at least 10%, originating from hardwood such as eucalyptus or softwood such as pine. In preferred embodiments, the solids content of the wet pulp, MFC, or NFC is in the range of 10 to 15%. More preferably, the solids content of the wet pulp or NFC is 15%.

[0059] In some embodiments, the wet cellulose pulp is a chemical or semi-chemical pulp, bleached or unbleached, mechanical pulp, thermomechanical pulp, chemical-thermomechanical pulp, enzymatic pulp, among others. Preferably, the wet cellulose pulp is a bleached eucalyptus Kraft pulp.

[0060] In some embodiments, the wet pulp, microfibrillated cellulose (MFC) or nanofibrillated cellulose (NFC), is dewatered by pressing and filtration until the solids content is between 10% and 50%. Preferably, these materials are obtained from wet Kraft pulp of bleached eucalyptus pulp.

[0061] In some embodiments, isopropanol or another water-miscible and easily removable solvent is added to the dewatered pulp, wherein the other solvent may be selected from the group consisting of ethanol, methanol, n-butanol, acetone, etc.

[0062] The mixture is then pressed and filtered to eliminate excess liquid, until it preferably reaches a solids content of at least 25% and so that the resulting mixture has a liquid phase with a water content of around 40% or less.

[0063] The process should be repeated several times, preferably two more times, so that several cycles of isopropanol addition and pressing / filtration are performed. The final pulp with a solids content of 25% should have a water content in its liquid phase of less than 10%. An aprotic solvent is then added to the resulting material as a swelling agent in step e) until the cellulose / aprotic solvent ratio is 1:1 by mass or greater. Preferably, the aprotic solvent is N-methyl-2-pyrrolidone (NMP).

[0064] In some embodiments, the material from step e) is then subjected to evaporation of the isopropanol in a vessel with agitation such as a ribo-blender or similar under a flow of nitrogen and application of a vacuum to eliminate the isopropanol and drag away the residual water, so that in the end it results in a composition with 50% pulp in NMP and a residual water in relation to the cellulose of less than 5% (step g)).

[0065] In some embodiments, the material from step g) is then added with alkynyl succinic anhydride (ASA) and potassium carbonate (K2CO3) in a 1:1 (mol / mol) molar ratio of ASA / K2CO3.

[0066] The material from step h) is then extruded in an extruder, such as a twin screw, CP Farrel, etc., at room temperature or at temperatures in the range of 50 to 120 °C.

[0067] The resulting product in step j) is dispersed in ethanol, in a material / ethanol ratio of 1:5, being pressed and filtered. Then, the same process is carried out in step k) with a diluted solution of 1% acetic acid, water and isopropanol in a cellulose / isopropanol ratio of 1:2.

[0068] In some embodiments, the product resulting from step k) is drained and dried in a dryer with counterflow of hot air at temperatures below 90 °C.

[0069] The material resulting from step I) appears as a flocculate that can be easily broken down into smaller particles.

[0070] After the treated pulp dries, the fibers are dispersed.

[0071] In some embodiments, the material obtained after drying step i) is subjected to a processing step, in which the material is added in step m) via the main funnel together with a thermoplastic polymer or by means of a side-feeder type doser in a twin-screw extruder for incorporating the thermoplastic polymer to produce a composite with excellent fiber dispersion.

[0072] In some embodiments, the thermoplastic polymer of step m) is a polyolefin. In preferred embodiments, the polyolefin is selected from the group consisting of high-density polyethylene (HDPE), low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), polypropylene (PP), and copolymers of propylene and ethylene.

[0073] In preferred embodiments, processing is carried out in a twin-screw extruder with a granulation system in the head to generate the composite material with excellent dispersion of the cellulosic fibers.

[0074] According to the present invention, the process consists of modifying cellulose pulp (or microfibrillated cellulose (MFC), or nanofibrillated cellulose (NFC)), never dried, with low water content, via reactive extrusion (REX) with anhydrides and its subsequent direct use as reinforcement in a thermoplastic matrix.

[0075] Another embodiment of the present invention relates to a thermoplastic composite obtained from the modification of cellulose pulp through a reactive extrusion process with alkenyl succinic anhydride (ASA).

[0076] The thermoplastic composite of cellulose pulp modified via REX with ASA is a composite of cellulose fiber in a polymer matrix, in which the cellulose fiber is a cellulose pulp, microfibrillated cellulose (MFC) or nanofibrillated cellulose (NFC) that acts as a reinforcing agent, that is, it is related to mechanical properties of thermoplastic polymers.

[0077] The starting material for obtaining the thermoplastic composite is eucalyptus pulp obtained by the Kraft process, bleached but never dried, which has a solids content of at least 10%.

[0078] Coating cellulose fibers with low-polarity materials such as polymers allows for improved dispersion of the fibers in the polymer matrix.

[0079] Furthermore, the modification of cellulose pulp via the reactive extrusion process with ASA also allows a reduction in the amount of swelling solvent and aprotic solvent used, with a consequent optimization of the washing process through the reduction in the amount of steps or solvents in all phases of the process.

[0080] The process proposed by this application represents a reduction in the use of anhydrides (ASA) of 5.3 times in relation to state-of-the-art processes, indicated by the increase in the initial cellulose mass / ASA mass ratio from 1.4 to 7.4, in addition to a reduction in the amount of swelling agent (NMP) of 50%.

[0081] Thus, the thermoplastic composite of cellulose pulp modified via reactive extrusion presents improvements in mechanical properties in relation to synthetic polymers.

[0082] Specifically, the REX-modified cellulose pulp thermoplastic composite with anhydride exhibits improved elastic modulus, tensile strength, and elongation at break compared to a synthetic polymer. EXAMPLES

[0083] The following examples, described in detail, serve to illustrate embodiments of the present invention without, however, having a limiting character to the scope of protection thereof. Example 1 - Process for preparing thermoplastic composite from cellulose pulp modified via REX with anhydrides Cellulose pulp preparation - water removal through solvent exchange

[0084] The process consists of modifying never-dried Kraft eucalyptus pulp with low water content, via reactive extrusion (REX) with alkenyl succinic anhydride (ASA) and its subsequent direct use as reinforcement in a thermoplastic matrix.

[0085] In the process, the wet bleached eucalyptus Kraft pulp, microfibrillated cellulose or nanofibrillated eucalyptus cellulose (with a solids content (ST) of 10 - 15%) is dewatered by pressing and vacuum-assisted filtration until it reaches a solids content of between 25% and 30%.

[0086] To this material (dewatered pulp containing 51.66g of dry pulp), 267 mL (or 210g) of isopropyl alcohol (isopropanol) is then added in order to obtain a water content in the liquid phase mixture of approximately 40%. This mixture was filtered / pressed using a vacuum to remove excess liquid until reaching a solids content between 25% and 30%.

[0087] The same amount of isopropanol was added again to this material, followed by filtration / pressing. A third cycle of isopropanol addition and subsequent filtration / pressing was performed to achieve a final residual water content of approximately 6%.

[0088] Then, N-methyl-2-pyrrolidone (NMP) was added and mixed with the pulp in the same mass quantity as cellulose (dry basis), in order to obtain a mixture with 50% cellulose and 50% NMP. The isopropanol contained in the mixture was then evaporated under an air flow and heated to 50°C. of ASA-modified cellulose succinic) via extrusion

[0089] To 116 g of cellulose pulp with NMP (51.7 g of solids), obtained previously, 7 g of alkenyl succinic anhydride (ASA) diluted in 4.3 g of NMP, 2.2 g of potassium carbonate (CaCOs) was added.

[0090] This mixture was fed into a twin-screw extruder with a free outlet at the head. The reaction occurred with the extruder at room temperature (heating elements turned off) and with a screw rotation of 200 rpm.

[0091] Optionally, after chemical modification, the modified pulp can undergo thorough washing with ethanol, aqueous acetic acid solution (1% v / v) and distilled water, or it can be washed with ethanol alone.

[0092] The pulp thus modified is partially defibrillated. Figures 3A-3C obtained by optical microscopy show the appearance of the pulp after processing. Preparation of ASA-polymer modified pulp composite

[0093] ASA-modified pulp dried in an oven at 60°C (48.5 g of dry modified pulp) was mixed with 207.5 g of high-density polyethylene (HDPE) (HC 7260 / Braskem) and 10.8 g of maleic anhydride-grafted polypropylene (PP-g-MA) (LICOCENE® PP MA 6452 / Clariant) and 2.7 g of calcium carbonate (CaCOs), generating a formulation with 18% modified pulp, 4% PP-g-MA, 1% CaCO3 and 77% HDPE.

[0094] The mixture was processed in a twin screw extruder with a temperature profile from the feeding zone to the die of: 130, 130, 130, 135, 140 and 140 °C with a screw rotation of 200 rpm and with the material fed through the dosing funnel.

[0095] The material obtained in the form of noodles was granulated. The granulated composite obtained was oven-dried at 70°C for injection into Type 1 tensile test specimens (ASTM format) in a Battenfeld injection molding machine, type Plus 35 / 75 Unilog B2, under the following conditions: temperature of 160°C, injection pressure of 90 bar, and mold temperature of 40°C. Example 2 - Mechanical Properties Test Results in Tensile

[0096] After completing the development of exemplary formulations of HDPE composites with cellulose pulp modified via reactive extrusion (REX) with alkenyl succinic anhydride (ASA), tensile mechanical properties tests were performed in accordance with ASTM D638 or equivalent to evaluate and compare the results obtained for the thermoplastic composites of cellulose pulp modified by reactive extrusion with anhydrides to the results obtained for the synthetic thermoplastic polymer.

[0097] The specimens were tested on a universal testing machine with a 5 kN load cell and a tensile speed of 10 mm / min. Five specimens were tested to obtain an average of the measured properties.

[0098] Table 1 below illustrates the results of the mechanical properties of the tested samples of the synthetic polymer and of the exemplary formulations of thermoplastic composites with pulps treated via REX with ASA, specifically in relation to the elastic modulus (GPa), tensile strength (MPa) and elongation at break (%) of each of these samples. Table 1: Mechanical properties in tension

[0099] It is understood that when a parameter range is given, all whole numbers and ranges within that range, as well as tenths and hundredths, are also given by the modalities. For example, "5-10%" includes 5%, 6%, 7%, 8%, 9%, and 10%; 5.0%, 5.1%, 5.2%, 9, 8%, 9.9%, and 10.0%; and 5.00%, 5.01%, 5.02%, 9.98%, 9.99%, and 10.00%; as well as, for example, 6-9%, 5.1%-9.9%, and 5.01%-9.99%. Similarly, when a list is presented, unless otherwise indicated, it should be understood that each individual element of that list and each combination of components of that list is a separate modality. For example, “1, 2, 3, 4 and 5” includes, among numerous modalities, 1; 2; 3; 1 and 2; 3 and 5; 1, 3 and 5; and 1, 2, 4 and 5.

[0100] It should be understood that the embodiments described above are merely illustrative and that various modifications may be made by a person skilled in the art to them without departing from the scope of the present invention. Consequently, the present invention should not be considered limited to the exemplary embodiments described in this application. Furthermore, the present disclosure may include subject matter not currently claimed but which may be claimed in the future in combination with or separately from the features claimed herein.

Claims

CLAIMS 1. Process for preparing thermoplastic composite from modified cellulose pulp via reactive extrusion (REX) with anhydrides, characterized by the fact that it comprises the following steps: a) dewatering the wet pulp, microfibrillated cellulose (MFC) or nanofibrillated cellulose (NFC) by pressing and filtration; b) adding isopropanol or another solvent miscible in water and easily removed; c) pressing and filtering the mixture to eliminate excess liquid; d) repeating the process of adding isopropanol, pressing and filtration at least twice more; e) adding an aprotic solvent to the resulting material until the cellulose / aprotic solvent ratio is 1:1 by mass or greater; f) evaporating the isopropanol in a vessel with stirring under a nitrogen flow and application of vacuum; g) obtaining a composition with 50% pulp in aprotic solvent and a residual water in relation to cellulose of less than 5%; h) add ASA anhydride and K2CO3 in the molar ratio ASA / K2CO3 1:1 (mol / ml);i) extrude the material from step h) generating a modified pulp with partially defibrillated ASA; j) disperse the resulting product in pressed and filtered ethanol; k) carry out the same process with a diluted solution of 1% acetic acid, water and isopropanol; l) dewater and dry the resulting product; m) process and compost the material obtained in step I) to incorporate the thermoplastic polymer; en) obtain a composite material with excellent fiber dispersion.; 2. Process according to claim 1, characterized in that the aprotic solvent is selected from the group consisting of N-methyl-2-pyrrolidone (NMP) and dihydrolevoglucosenone.

3. Process according to claim 1 or 2, characterized in that a compatibilizer is used in step m).

4. Process according to any one of claims 1 to 3, characterized in that the wet pulp, microfibrillated cellulose (MFC) or nanofibrillated cellulose (NFC) of step a) has a solids content of at least 10%.

5. Process according to any one of claims 1 to 4, characterized in that the solids content after pressing and filtration in step a) is between 10% and 50%.

6. Process according to claim 5, characterized in that the solids content after pressing and filtration in step c) is at least 25%, and in which the resulting mixture has a liquid phase with a water content of the order of 40% or less.

7. Process according to any one of claims 1 to 6, characterized in that in step i), the material is extruded in an extruder.

8. Process according to claim 7, characterized in that the extruder is a twin screw extruder.

9. Process according to any one of claims 1 to 8, characterized in that the extrusion is carried out at room temperature or at temperatures in the range of 50 2 C to 120 2 W.

10. Process according to any one of claims 1 to 9, characterized in that the product resulting from step j) is dispersed in ethanol in a material / ethanol ratio of 1:

5.

11. Process according to any one of claims 1 to 10, characterized in that the dewatering and drying step I) is carried out in a dryer with counterflow of hot air.

12. Process according to any one of claims 1 to 11, characterized in that the material resulting from step I) is in the form of a flocculate.

13. Process according to any one of claims 1 to 12, characterized in that the cellulose fibers are dispersed after step I) of dewatering and drying the pulp treated via reactive extrusion with anhydride.

14. Process according to any one of claims 1 to 13, characterized in that the thermoplastic polymer of step m) is a polyolefin selected from the group consisting of high-density polyethylene (HDPE), low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), polypropylene (PP) and copolymers of ethylene and propylene.

15. Process according to any one of claims 1 to 14, characterized in that it further comprises an additional processing step after step m).

16. Process according to claim 15, characterized in that the processing is carried out in an extruder.

17. Thermoplastic composite obtained by the process as defined in any one of claims 1 to 16, characterized in that it comprises a thermoplastic polymer and cellulose fiber modified with anhydrides.

18. Thermoplastic composite characterized by the fact that it is obtained by the process as defined in any one of claims 1 to 16.

19. Thermoplastic composite according to claim 17 or 18, characterized in that it further comprises a compatibilizer.

20. Thermoplastic composite according to any one of claims 17 to 19, characterized in that the cellulose fiber is selected from the group consisting of cellulose pulp, microfibrillated cellulose (MFC) and nanofibrillated cellulose (NFC).

21. Thermoplastic composite according to any one of claims 17 to 20, characterized in that the synthetic thermoplastic polymer is a polyolefin selected from the group consisting of high-density polyethylene (HDPE), low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), polypropylene (PP) and copolymers of ethylene and propylene.

22. Thermoplastic composite according to any one of claims 17 to 21, characterized in that it presents improved dispersion of the cellulosic fibers in relation to a synthetic thermoplastic polymer.

23. Thermoplastic composite according to any one of claims 17 to 22, characterized in that it also presents improved mechanical properties in relation to a synthetic polymer.

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