Cellulose fiber reinforced polyvinyl alcohol composites

Abstract

1. A method of making a composite material, the method comprising the steps of providing a mixture of polyvinyl alcohol and a fibrous or non-fibrous cellulosic material; heating the mixture to a temperature of 190°C or greater; reacting the mixture to form a composite mixture; and cooling the mixture to form an isotropic solid composite material.

Description

[Technical Field]

[0001] The present invention relates to composite materials comprising polyvinyl alcohol and cellulosic fibers, the manufacture of the composites and products comprising or including the composites. [Background technology]

[0002] Polyvinyl alcohol is generally produced by the hydrolysis of polyvinyl acetate. Polyvinyl alcohol produced by partial or complete hydrolysis of homopolymer polyvinyl acetate is called homopolymer polyvinyl alcohol. The degree of hydrolysis determines the properties of the resulting polymer. Copolymer polyvinyl alcohol or homopolymer polyvinyl alcohol with a low degree of hydrolysis (LD) is easy to process but has poor mechanical and chemical properties. Homopolymer polyvinyl alcohol with a high degree of hydrolysis (HD), for example, 85% or more, has excellent properties but cannot be processed without degradation under conditions using equipment used to produce other polymers, such as polyolefins. The present invention specifically relates to polyvinyl alcohol produced by the hydrolysis of homopolymer polyvinyl acetate.

[0003] Highly hydrolyzed polyvinyl alcohol, with a degree of hydrolysis greater than 70%, decomposes before reaching its melting point of about 250°C, as do many carbohydrates. This makes it difficult to melt process. For this reason, highly hydrolyzed polymers are generally processed as aqueous solutions. Partially hydrolyzed polyvinyl alcohol is more easily melt processed.

[0004] A significant difference between highly hydrolyzed (high hydrolysis, HD) and partially hydrolyzed (low hydrolysis, LD) polyvinyl alcohol is the degree and quality of crystalline order due to differences in chain structure. Polyvinyl alcohol with less than 2% unhydrolyzed acetate groups can readily crystallize to form strongly hydrogen-bonded crystalline domains. These crystalline domains have essentially the same structure as found in polyethylene. This may be due to the small size of the hydroxyl groups. However, due to hydrogen bonding, the melting point of highly hydrolyzed polyvinyl alcohol is approximately 150°C higher than that of polyethylene.

[0005] Polyols have been used as plasticizers, but the efficient production of plasticized polyvinyl alcohol with a high degree of hydrolysis has been difficult to achieve.

[0006] WO 2017 / 046361 discloses a method for producing plasticized polyvinyl alcohol having a degree of hydrolysis of 98% by weight or more. Summary of the Invention [Means for solving the problem]

[0007] According to a first aspect of the present invention, a method for producing a composite material comprises the steps of: providing a mixture of polyvinyl alcohol and a fibrous or non-fibrous cellulosic material; heating the mixture to a temperature of 190°C or greater; reacting the mixture to form a composite mixture; allowing the mixture to cool to form an isotropic solid composite material; Includes:

[0008] According to a second aspect of the present invention, a composite material comprises an isotropic reaction product of polyvinyl alcohol and a fibrous or non-fibrous cellulosic material, wherein the amount of cellulosic material ranges from about 0.1 wt % to about 50 wt % of the total weight of the composition. DETAILED DESCRIPTION OF THE INVENTION

[0009] The polyvinyl alcohol may be a homopolymer polyvinyl alcohol.

[0010] The composite material may be distinguished from a simple mixture or blend in which the polyvinyl alcohol and cellulose components remain substantially unchanged. In embodiments, cellulose fibers or non-fibrous cellulose particles are no longer observed after reaction with polyvinyl alcohol, resulting in an isotropic composite material.

[0011] A homogeneous composite is obtained in which there are no longer any distinct domains containing cellulose. The structure of the composite can be determined using scanning electron microscopy.

[0012] Cellulosic materials include fibrous or non-fibrous cellulose, for example, cellulose in granular or powder form.

[0013] The cellulosic material may be selected from the group consisting of cellulose pulp, unbleached cellulose pulp, enzyme-treated cellulose pulp, chemically treated cellulose pulp, microfibrillated and nanofibrillated cellulose, modified cellulose (including methylcellulose, hydroxypropylcellulose, ethylcellulose) and mixtures thereof.

[0014] Cellulose esters, such as cellulose acetate, are not used.

[0015] The composite may exhibit a variety of advantageous properties that cannot be achieved using the unreacted mixture of the two components.

[0016] Composite materials can be produced by controlled heating of a mixture of polyvinyl alcohol and cellulosic material. To this end, the polyvinyl alcohol must be heat-processable under the conditions necessary for reaction with the cellulose.

[0017] A minimum temperature in the range of 190°C to 240°C, for example in the range of 205°C to 215°C, may be used.

[0018] The reaction is preferably carried out in the absence of a solvent.

[0019] The reaction may be carried out by passing the mixture through an extruder maintained at a temperature of 190° C. to 240° C. A constant rotor speed may be used.

[0020] The polyvinyl alcohol is a homopolymer polyvinyl alcohol having a degree of hydrolysis of 65% to 98% by weight or more and a molecular weight in the range of 4,000 to 20,000; a plasticizer selected from the group consisting of diglycerol, triglycerol, fructose, ribose, xylose, D-mannitol, triacetin, pentaerythritol, dipentaerythritol, methylpentanediol, 1,2-propanediol, 1,4-butanediol, 2-hydroxy-1,3-propanediol, 3-methyl-1,3-butanediol, 3,3-dimethyl-1,2-butanediol, polyethylene glycol 300, polyethylene glycol 400, alkoxylated polyethylene glycol, caprolactam, tricyclic trimethylolpropane formal, rosin esters, erucamide, and mixtures thereof; an optional stabilizer selected from the group consisting of sodium stearate, potassium oleate, sodium benzoate, calcium stearate, dimethyl, propionic acid, and mixtures thereof; The polyvinyl alcohol composition may include:

[0021] The degree of hydrolysis may be between 65% and 98% by weight, such as between 67% and 85% by weight, alternatively between 86% and 93% by weight, such as between 94% and 98% by weight.

[0022] The polyvinyl alcohol composition may have a melt flow index (MFI) of 5 to 50, such as 10 to 35, e.g., 10 to 15 g / 10 min. The melt flow index referred to herein is determined at 230°C using a 10 kg weight by conventional techniques.

[0023] The polyvinyl alcohol may have a molecular weight in the range of 4,000 to 20,000, such as 4,000 to 15,000, for example 4,000 to 9,000, alternatively 12,000 to 20,000. Molecular weights referred to herein are weight average molecular weights and may be measured using conventional liquid chromatography techniques.

[0024] The polyvinyl alcohol composition is preferably stable at the temperatures at which it is melted and extruded. Polyvinyl alcohols without the plasticizers and stabilizers disclosed herein, especially homopolymers with a high degree of hydrolysis, tend to decompose at the temperatures required for reaction with cellulose, for example, by melting and extrusion processing.

[0025] The stabilized polyvinyl alcohol polymers used in the present invention may be produced using the methods disclosed in WO 2022 / 008516 and WO 2022 / 008521, the disclosures of which are incorporated herein by reference for all purposes.

[0026] The polyvinyl alcohol composition is introducing into a mixing reactor a polyvinyl alcohol polymer comprising a homopolymer polyvinyl alcohol or a blend thereof having a degree of hydrolysis ranging from 65% by weight to 98% by weight or greater, The mixing reactor includes a blending chamber having a first inlet, a first outlet, and at least two interengaging components extending between the first inlet and the first outlet, the components configured to apply a shear force to the polymer while the polymer is conveyed by the components from the inlet through the reaction zone to the outlet; one or more second inlets located downstream of the first inlet for introducing reactants, including processing aids, plasticizers, and reaction stabilizers, into the chamber to form a reaction mixture; The plasticizer is selected from the group disclosed above, the reaction stabilizer, when present, is selected from the group consisting of sodium stearate, potassium oleate, sodium benzoate, calcium stearate, dimethylpropionic acid, and mixtures thereof; the blending chamber includes a plurality of heating zones configured to subject the mixture to a temperature profile in which the temperature increases from the inlet to the outlet; a second outlet located between the reaction zone and the first outlet configured to allow removal of a processing aid from the chamber; reacting the treating agent, plasticizer, and polymer in a reaction zone to form a plasticized polymer; passing the plasticized polymer through a first outlet; It can be made by a method comprising:

[0027] The use of a reactive mixing device, typically an extruder according to the present invention, allows the processing aids and plasticizers to react with the polyvinyl alcohol or blend thereof without polymer degradation, followed by removal of all or most of the processing aids through a second outlet to obtain a plasticized polyvinyl alcohol or blend thereof, which provides a polyvinyl alcohol composition suitable for reaction with cellulosic materials according to the present invention.

[0028] The use of a reactive stabilizer can advantageously reduce the degree of degradation during melt processing to form the composites of the present invention. This allows homopolymer polyvinyl alcohols with a high degree of hydrolysis, for example, 88% by weight or greater, to be processed to form fibers, pellets, or other forms suitable for reaction with cellulose. The reactive stabilizer can be used in an amount of about 0.1% to about 5% by weight, for example, about 0.1% to about 3% by weight, for example, 0.1% to about 1.5% by weight, for example, about 0.2% to about 0.5% by weight, for example, about 0.25% by weight.

[0029] The reactive stabilizers of the present invention can reduce the degree of polymer degradation during processing. Homopolymer polyvinyl alcohol has been difficult to process due to its decomposition at the required high temperatures. This susceptibility to degradation has led to the use of polyvinyl alcohol copolymers with consequently reduced engineering properties. The degree of degradation can be determined by UV spectral analysis of the amount of conjugation present in the polymer. Sodium benzoate has been found to be particularly effective.

[0030] The use of homopolymer polyvinyl alcohol is particularly advantageous. Homopolymer polyvinyl alcohol is produced by hydrolysis of homopolymer polyvinyl acetate, and the degree of hydrolysis is 65% by weight or more in embodiments of the present invention. For example, as disclosed in U.S. Patent Application Publication No. 2005 / 001348 (Kohnen), polyvinyl alcohol copolymers produced by hydrolysis of polyvinyl acetate copolymers have inferior properties compared to homopolymer polyvinyl alcohol. Composites formed from homopolymer polyvinyl alcohol and cellulose according to the present invention can exhibit advantageous properties, such as high tensile strength and flexibility.

[0031] Polyvinyl alcohol may be produced by hydrolysis of the homopolymer polyvinyl acetate, the degree of hydrolysis being in the range of from 65% to 98% by weight, such as from 67% to 85% by weight, for example from 86% to 93% by weight, for example from 94% to 98% by weight.

[0032] A blend of two or more polyvinyl alcohol polymers may be used, for example, a blend of two polyvinyl alcohol polymers having a relatively high molecular weight and a relatively low molecular weight, respectively.

[0033] Blends of polyvinyl alcohols with the same molecular weight and different degrees of hydrolysis can be combined. By mixing different polyvinyl alcohol grades together, it is possible to improve the properties of the resulting polymer, such as melt strength. The blend of polymers with different molecular weights used is selected depending on the physical properties required in the final product. This may require the use of materials with different molecular weights. The use of polymers with three or more different molecular weights may be advantageous. The use of a polymer with a single molecular weight is not excluded.

[0034] The use of a blend can allow for control of the viscosity of the polymer. The selection of a stabilizer according to the present invention allows for the use of a blend with a desired viscosity without compromising other properties. Alternatively, the use of a blend can allow for the use of polyvinyl alcohol containing one or more stabilizers while maintaining viscosity or other properties to allow for pellet or film production.

[0035] The processing aid is preferably water. Alternatively, the processing aid may comprise a mixture of water and one or more hydroxyl compounds having a boiling point below the boiling point or melting point of the plasticizer. For cost and environmental reasons, the use of water is preferred.

[0036] In one embodiment, the plasticizer may be selected from the group consisting of diglycerol, triglycerol, xylose, D-mannitol, triacetin, dipentaerythritol, 1,4-butanediol, 3,3-dimethyl-1,2-butanediol, and caprolactam.

[0037] Binary mixtures of plasticizers may be advantageous.

[0038] The total amount of plasticizer in the formulation can be from about 15% to about 30% by weight.

[0039] In one embodiment, the cellulose may include unbleached pulp fibers.

[0040] The amount of unbleached pulp fibers can range from about 0.1% to about 50% by weight, preferably from about 10% to about 40% by weight.

[0041] In one embodiment, the cellulose may include enzyme-modified cellulose microfibers or nanofibers. The amount of enzyme-modified cellulose microfibers or nanofibers may range from about 0.1 to about 30% by weight, preferably from about 5 to 20% by weight.

[0042] According to a further aspect of the present invention there is provided an article of manufacture comprising an isotropic reaction product of a heat-processable homopolymer polyvinyl alcohol having a degree of hydrolysis of 65% by weight or greater and cellulose, the article being capable of being produced according to the second aspect of the present invention.

[0043] The composites of the present invention exhibit advantageous properties. Composites containing cellulose, e.g., unbleached cellulose pulp fibers, and polyvinyl alcohol can be stronger and exhibit higher tensile strength and lower ductility compared to the corresponding unfilled polyvinyl alcohol. They can also be less brittle. Increasing the amount of unbleached cellulose pulp fibers can increase the tensile strength and tensile modulus of the composite, allowing for unexpectedly high values ​​to be achieved, compared to the individual components and physical mixtures of the individual components.

[0044] The composites of the present invention can be used to make heat-processable pellets that can be processed by extrusion to form, for example, films, fibers, and rigid thermoformed products such as food trays, bottles, and other containers. Unreacted cellulosic products are not heat-processable, for example, by extrusion or film coating.

[0045] The composites of the present invention can be applied to a substrate as a coating by melt extrusion. Cellulosic substrates such as paper or composite board can be coated.

[0046] According to a further aspect of the present invention there is provided a thermoformable pellet consisting of or comprising a composite according to the previous aspect of the present invention.

[0047] Composites containing unbleached cellulose pulp fibers can change the intermolecular and intramolecular structure of polyvinyl alcohol, affecting both the crystallization and physical behavior of the composite. The addition of unbleached cellulose pulp fibers can significantly increase the glass transition temperature. Without wishing to be bound by theory, this may indicate that the fibers limit the segmental mobility of the polymer chains due to bonding interactions between the fibers and the polymer chains. The enthalpy, melting, and crystallization temperature can increase, indicating an increase in the crystallinity of the polyvinyl alcohol. This may be due to the pulp fibers acting as a nucleating agent for the polyvinyl alcohol, increasing the crystallinity and crystal size.

[0048] Percentages and other amounts referred to herein are by weight unless otherwise specified and are selected from any range to add up to 100%.

[0049] The present invention is further illustrated by examples, but not in a limiting sense. [Example]

[0050] Example 1 The following table shows the properties of composites containing polyvinyl alcohol (PVOH) with 0%, 10%, 20% and 30% by weight of unbleached cellulose pulp fibers.

[0051] [Table 1]

[0052] Example 2 The table below shows a comparison between composites containing polyvinyl alcohol (PVOH) with and without fibers, polylactic acid (PLA) with and without fibers, and polypropylene (PP) with and without cellulose fibers.

[0053] [Table 2]

[0054] The properties of the composite of the present invention were superior to those of polypropylene. The composite containing PLA did not exhibit good barrier properties. The polyvinyl alcohol used had the following properties:

[0055] [Table 3]

[0056] The composites of the present invention can be used to produce environmentally sustainable multifunctional packaging materials. These materials can provide advantageous thermal and mechanical properties, including barrier, antimicrobial, antioxidant, and UV-blocking properties. The composites can also be utilized in the production of engineering components, such as automotive and aerospace parts.

[0057] Example 3 Pulp Preparation Dried cellulose pulp (92% dry solids Nordic Paper UKP, an unbleached softwood kraft pulp derived from pine and spruce from Sweden) was comminuted by passing it through a twin-screw extruder at 50°C and 150 rpm. The extruder was open-fronted and had screws without mixing segments. The resulting powder was a homogeneous pulp powder with a dry content of 95% by weight and a decomposition temperature of 250°C.

[0058] Example 4 Extrusion of polyvinyl alcohol-cellulose pulp composites Mixtures containing blends of 50% by weight of polyvinyl alcohol with a degree of hydrolysis of 98% by weight and a molecular weight of 160,000, 50% by weight of polyvinyl alcohol with a degree of hydrolysis of 94% by weight and a molecular weight of 55,000, and 0, 10, 20, and 30% by weight of unbleached pulp fiber were prepared. These components were added to a feed hopper and processed by extrusion through a Lab Tech LTE-20-48 co-rotating twin-screw extruder with a screw diameter of 20 mm and a length / depth ratio of 48. The feed rate was 50 g / min. The nominal speed was 200 rpm. Twelve consecutive heating zones were maintained at the following temperatures (°C): 90, 90, 70, 190, 190, 190, 200, 200, 210, 215, 220, 230, 230, 220, and 200°C.

[0059] After exiting the die zone, the material was run onto a conveyor at 9.2 rpm and cooled with a fan.

[0060] Example 5 Testing of cellulose pulp / polyvinyl alcohol composites The pellets obtained from the previous examples were injection molded in a BOY 25 E VH injection molding machine to obtain samples for tensile and impact testing. Injection was performed using the following temperature profile and a mold temperature of 20°C: Five heating zones were maintained at 215, 225, 225, 190, and 180°C, respectively. Injection was performed at 1200 bar and 10 cm 3 Set it to / s.

[0061] Tensile tests were performed using procedures based on ISO 527.

[0062] Samples were conditioned at 25°C and 50% humidity for at least 72 hours prior to testing. Tensile modulus, strength at break, and strain at break were measured using an MTS Flex Test 60 Controlled Hydraulic Actuator at an initial rate of 1 mm / min, which was increased to 50 mm / min after 0.5% strain. Data was collected using MTS SERIES 793 Controlled Software at a rate of 500 Hz.

[0063] The impact test procedure was performed using a notched Charpy impact test on a Zwick / Roell HIT 5P Impact Tester using a 5J Pendulum, which measures the toughness of a material under impact loading by the deformation required to fracture the sample.

[0064] Differential scanning calorimetry (DSC) was performed according to the ISO 11357-3:2018 procedure. DSC measurements were obtained on a Mettler-Toledo DSC822e calorimeter. Tests were performed at 50 mL / min. -1 The experiment was carried out under a nitrogen atmosphere with a flow rate of 1000 kJ / min. A quantity of 4 mg of each sample was placed in a standard aluminum crucible (40 μL). The temperature program was 98°C. -1 Thermogravimetric analysis (TGA) was based on ASTM E2550 procedures. TGA measurements were obtained using a Mettler-Toledo 851 instrument. Tests were run at 50 mL / min. -1 The experiment was carried out under a nitrogen atmosphere with a flow rate of 1000 kJ / min. Each sample was placed in a ceramic cup with an amount of 8 mg. The temperature program was 10°C / min. -1 The temperature was set at 30° C. to 400° C. The results are shown in Table 3.

[0065] [Table 4]

[0066] Example 6 Enzymatic cellulose nanofiber (CNF) reinforcement production Refined pulp with a 4 wt% pulp consistency was treated with an enzyme cocktail from Novonzyme in a sulfate buffer solution at pH 7.2 for 2 hours at 50° C. Examples of pretreated pulp with a 2 wt% fiber consistency were homogenized using a high-pressure fluidizer, Microfluidiser-110 EH (Microfluidics Corp., USA), by passing it through a 200 / 100 μM chamber at 1700 bar.

[0067] The properties of the treated fibers were as follows:

[0068] [Table 5]

[0069] Comparative Example 7 Composite Manufacturing A comparative example was carried out using dispersion at 70°C followed by film casting.

[0070] Polyvinyl alcohol pellets were dissolved in water at 70°C with stirring to obtain a 10 wt% suspension. 2 wt% cellulose nanofibers were heated to 70°C and mixed with the polyvinyl alcohol solution with stirring at 500 rpm for 2 hours to obtain composites containing 5 wt%, 10 wt%, and 20 wt% cellulose nanofibers. The samples were sonicated using an Ultra Turuz to remove fiber agglomerates and obtain a uniform dispersion. The samples were vacuum degassed after sonication to remove air bubbles.

[0071] The suspension was transferred to a square Petri dish and kept at room temperature. A transparent film measuring 22.5 cm was obtained with an average thickness of 431±51 μm and a weight of approximately 23 g.

[0072] The films were cut, dried and compounded in a HAAKE Mini Lab II counter-rotating twin screw extruder at 220° C. and 100 rpm to obtain pellets of the composite.

[0073] Pellet samples were pressed to a thickness of 0.4 mm at 220°C with a force of 25 kN using a Servitec Polystat 200 T Laboratory Hot Press. The compounded samples were cut into seven strips with dimensions of 45 x 6 mm. The samples were reconditioned at 50% humidity and 23°C for at least 30 hours before testing. Tensile modulus, strength, strain at break, and tensile E absorption were measured using an MTS tensile strength machine at a rate of 3 ml / min and an initial gap between the holders of 30 mm.

[0074] Dynamic scanning calorimetry (DSC) according to ISO 11357-3:2018. Live DSC measurements were obtained on a Mettler-Toledo DSC 822e calorimeter. Tests were run at 50 mL / min. -1 The experiment was carried out under a nitrogen atmosphere with a flow rate of 1000 kJ / min. 4 mg of each sample was placed in a standard aluminum crucible (40 μL). The temperature program was as follows: -1 ) set to: a) Heating stage from -10℃ to 200℃ b) Isothermal step at 200°C for 1 minute c) Cooling from 200℃ to -10℃ d) an isothermal step at -10°C for 1 minute e) Heating stage from -10℃ to 400℃.

[0075] Thermogravimetric analysis (TGA) was performed according to ASTM E2550. TGA measurements were obtained on a Mettler-Toledo 851. Tests were run on a 50 mL min -1 The experiment was carried out under a nitrogen atmosphere with a flow rate of 1000 kJ / min. 8 mg of each sample was placed in a ceramic cup. The temperature program was 10°C / min. -1 The temperature was set to 30℃ to 400℃.

[0076] The method of the present invention resulted in composites with improved tensile strength and modulus, but reduced elongation and toughness compared to the composites from Method 1. The addition of enzymatic cellulose nanofibers to polyvinyl alcohol resulted in stronger and stiffer composites, but strain and toughness were reduced compared to pure polyvinyl alcohol. A clear correlation between cellulose nanofiber content, tensile strength, and modulus was observed during compounding. The two compounds achieved the highest values ​​for composites containing 20 wt% cellulose nanofiber. The addition of cellulose nanofibers increased the glass transition temperature, which may indicate that the fibers restricted the segmental mobility of the polymer chains during the reaction. Compounding by extrusion resulted in a decrease in crystallinity and melting and crystallization temperatures when the cellulose nanofiber content exceeded 5 wt%. This may indicate that the cellulose nanofibers hinder the crystallization of polyvinyl alcohol or cause polymer chain degradation. Extrusion was performed at 220°C. The results are summarized in the table below.

[0077] [Table 6]

[0078] Example 8 Further compositions were investigated: The polyvinyl alcohol used was partially hydrolyzed with low molecular weight and a degree of hydrolysis between 67% and 89% as follows:

[0079] [Table 7]

[0080] The plasticizers used are listed below: Water was used as a processing aid and sodium benzoate was used as a stabilizer.

[0081] [Table 8]

[0082] The following formulations were prepared using various commercially available cellulose products.

[0083] [Table 9]

[0084] [Table 10]

[0085] [Table 11]

[0086] [Table 12]

[0087] [Table 13]

[0088] result Thermal analysis, including differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA), was used to investigate the thermal stability of the composites, and the melting and recrystallization temperatures of the polymers were observed. The crystallinity (%) was calculated and estimated by DSC.

[0089] TGA analysis of cellulose samples was performed to determine the thermal stability of pure cellulose before blending with PVOH. Cellulose types 3 and 4 showed the highest thermal stability.

[0090] According to DSC, TGA analysis and torque stabilizer (batch mixer), it was concluded that PVOH / cellulose was suitable for compounding and some of these compounds were suitable for scale-up.

[0091] TGA analysis showed that after the addition of cellulose, the PVOH polymer still exhibited thermal stability up to at least 230°C.

[0092] DSC analysis demonstrated the thermal stability of the composites.

[0093] Changing the plasticizer from dipentaerythritol to ε-caprolactone was effective in lowering the melting peak and recrystallization temperature, as shown in the table below.

[0094] [Table 14]

[0095] Batch mixer testing showed that compounding was smooth. After the maximum peak, the torque reached a steady level, with no signs of degradation or incompatibility. The addition of cellulose also increased the maximum torque, confirming that more energy was required for compounding due to the presence of cellulose. The polymer was mixed at a constant rotor speed while the torque was recorded as a function of time. The results showed that the polymer experienced thermomechanical hysteresis under mixing. When the polymer was introduced into the mixing chamber, the torque increased due to the energy required to melt and compound the polymer. The torque then decreased and reached a steady state.

[0096] A single peak was observed in the cellulose / PVOH composite blend, indicating that a single reaction occurred. No cross-linking or degradation occurred during the residence time required to process the polymer. There was no indication of incompatibility between the polymers.

[0097] The addition of cellulose increased the maximum torque, confirming that more force and energy was required for compounding due to the presence of cellulose. It was concluded that the resulting PVOH / cellulose composites had higher strength than unreacted PVOH.

[0098] TGA and DSC measurements showed that the composite exhibited thermal stability. The higher temperature stability above 230 °C is significant because both individual unreacted polymers exhibit lower stability under these temperature conditions. This indicates a persistent interaction between the polymers. This was confirmed by SCM analysis, which showed that individual original polymer domains were not present in the composite. This was also indicated by the difference in crystallization shown by DSC analysis.

Claims

1. 1. A method for producing a composite material, comprising: providing a mixture of polyvinyl alcohol and a fibrous or non-fibrous cellulosic material; heating the mixture to a temperature of 190°C or greater; reacting the mixture to form a composite mixture; cooling the mixture to form an isotropic solid composite material; A method comprising:

2. The method of claim 1 , wherein the polyvinyl alcohol is a homopolymer polyvinyl alcohol.

3. 3. The method of claim 1 or 2, wherein the cellulose material is fibrous, granular or powdered cellulose.

4. 4. The method according to any one of claims 1 to 3, wherein the cellulose material is selected from the group consisting of unbleached cellulose pulp, enzyme-treated cellulose pulp, chemically treated cellulose pulp, microfibrillated and nanofibrillated cellulose, modified cellulose, methylcellulose, hydroxypropylcellulose, ethylcellulose, and mixtures thereof.

5. 5. The method according to any one of claims 1 to 4, wherein the polyvinyl alcohol has a degree of hydrolysis of 65% to 98% by weight or more.

6. 6. The method of claim 5, wherein the polyvinyl alcohol has a degree of hydrolysis of 67% to 85% by weight or more.

7. 6. The method of claim 5, wherein the polyvinyl alcohol has a degree of hydrolysis of 94% to 98% by weight or more.

8. The polyvinyl alcohol comprises a homopolymer polyvinyl alcohol having a degree of hydrolysis of 70% to 98% by weight or more and a molecular weight in the range of 20,000 to 140,000; a plasticizer selected from the group consisting of diglycerol, triglycerol, fructose, ribose, xylose, D-mannitol, triacetin, pentaerythritol, dipentaerythritol, methylpentanediol, 1,2-propanediol, 1,4-butanediol, 2-hydroxy-1,3-propanediol, 3-methyl-1,3-butanediol, 3,3-dimethyl-1,2-butanediol, polyethylene glycol 300, polyethylene glycol 400, alkoxylated polyethylene glycol, caprolactam, tricyclic trimethylolpropane formal, rosin esters, erucamide, and mixtures thereof; a stabilizer selected from the group consisting of sodium stearate, potassium oleate, sodium benzoate, calcium stearate, dimethyl, propionic acid and mixtures thereof; The method according to any one of claims 1 to 7, comprising:

9. 9. The method according to any one of claims 1 to 8, wherein the polyvinyl alcohol composition has a melt flow index (MFI) in the range of 5 to 50, preferably 10 to 35, more preferably 10 to 15 g / 10 min.

10. 10. The method of any one of claims 1 to 9, wherein the polyvinyl alcohol has a molecular weight in the range of 4,000 to 20,000.

11. 11. The method of any one of claims 1 to 10, wherein the polyvinyl alcohol has a molecular weight in the range of 4,000 to 15,000.

12. 12. The method of any one of claims 1 to 11, wherein the polyvinyl alcohol has a molecular weight in the range of 4,000 to 9,000.

13. 13. The method of any one of claims 1 to 12, wherein the polyvinyl alcohol has a molecular weight in the range of 12,000 to 20,000.

14. A method according to any one of claims 1 to 13, wherein the mixture is heated to a temperature in the range of from 190°C to 240°C.

15. The method of any one of claims 1 to 14, wherein the mixture is heated to a temperature in the range of 205°C to 215°C.

16. A method according to any one of claims 1 to 15, wherein the mixture is heated by passage through an extruder.

17. A composite material according to any one of claims 1 to 16, wherein the cellulosic material is fibrous cellulose.

18. 18. The method of any one of claims 1 to 17, wherein the polyvinyl alcohol is a blend of two or more homopolymer polyvinyl alcohols.

19. A composite material comprising an isotropic reaction product of polyvinyl alcohol and a cellulosic material in an amount of 0.1% to 50% by weight of the total weight of said composite material.

20. A composite material comprising an isotropic reaction product of polyvinyl alcohol and a cellulosic material made by the method of any one of claims 1 to 18.

21. 21. A heat treatable pellet consisting of or comprising the composite material of claim 20.

22. 22. A heat-treatable pellet comprising the composite material of claim 21 together with fillers or other additives.

23. 21. A substrate having a coating, the coating comprising a composite material according to claim 19 or 20.

Images