MX2012009336A - Nanocomposite biomaterials of nanocrystalline cellulose (ncc) and polylactic acid (pla). - Google Patents

Abstract

A new approach is conceived for the development of sustainable biomaterials comprising nanocrystalline cellulose (NCC) and polylactic acid (PLA) nanocomposites. The invention deals with advancing a method based on in situ ring opening polymerization of L-lactide in the presence of NCC particles to form NCC-PLA supramolecular nanocomposite materials. This material is hydrophobic and compatible with a wide range of synthetic and natural polymers. NCC-PLA nanocomposites have enhanced functionality (e.g. gas barrier), rheological and mechanical performance, as well as dimensional stability (i.e. less hygroexpansivity) relative to PLA. They are made from entirely renewable resources, and are potentially biocompatible as well as recyclable. NCC-PLA supramolecular nanocomposites can be suspended in most organic solvents or dried to form a solid substance. They can be processed using conventional polymer processing techniques to develop 3-dimensional structures, or spun into fibres, yarns or filaments.

Description

BIOMATERIALS NANOCOMPUESTOS DE CELLULOSA NANOCRYSTALLINE AND POLYLACTIC ACID TECHNICAL FIELD This invention relates to a nanocrystalline cellulose nanocomposite (NCC) and polylactic acid (PLA), and a process for producing said nanocomposite. The nanocomposite is a thermally stable and sustainable biomaterial that is hydrophobic and compatible with a wide range of synthetic and natural polymers. NCC-PLA nanocomposites have improved mechanical performance and dimensional stability (ie, less hygroscopicity) relative to PLA, are potentially biocompatible, recyclable and are made with completely renewable resources. NCC-PLA nanocomposites can be suspended in many organic solvents or dried to form a solid substrate that can be processed using conventional polymer processing techniques to develop three-dimensional structures.

BACKGROUND OF THE INVENTION The 20th century was characterized, among many other things, as the century of plastics. It is impossible to imagine the current world without plastics Products range from baby bottles to packaging materials for aircraft components. Although polyolefins have been the basis for almost all commercial plastic development, there have also been doubts about their long-term applications, due to concerns about recycling, health and environmental responsibility, for example, the need to use blocks of chemical construction, such as bisphenol A (BPA), in the manufacture of polycarbonate plastics and epoxy resins.

In response, important efforts were made to develop bioplastics and biomaterials made with renewable resources. Nanocrystalline cellulose (NCC) is highly crystalline cellulose that is extracted from wood or non-wood biomass. Polylactic acid (PLA) is a thermoplastic aliphatic polyester that is constituted by building blocks of lactic acid (2-hydroxypropionic acid). PLA is derived from renewable plant sources, such as starch and sugar, and has potential applications in medicine, engineering and in the packaging of food and beverages. The degradation of PLA can be achieved by means of the hydrolysis of the ester bonds without the need for an enzymatic treatment. However, PLA has certain limitations compared to polyolefins, particularly during processing, which has severely limited its use. The PLA is essentially hygroscopic and has a low thermal resistance. Nano-scale reinforcement can be used to improve the rheological, mechanical and physical properties of polymers, improving also its processability, functionality and performance in the final use. The NCC can function as a high performance reinforcement thanks to its large specific surface area, its high strength and its high surface reactivity. To achieve the above two critical conditions are required: (i) an excellent dispersion of the NCC in the polymer matrix, and (ii) a perfect compatibility between the two, to produce an excellent interfacial mechanics in different environments.

Studies have shown that NCC can be used to increase the storage modulus of some nanocomposites in order of magnitude above the glass transition temperature of the matrix [1-3]. By forming a NCC compound with PLA, it is possible to make a biomaterial, made entirely of renewable resources, with satisfactory properties. However, because NCC is hydrophilic and PLA is hydrophobic, compatibility becomes a critical and difficult problem. Published results have indicated that it is practically impossible to prepare NCC-PLA nanocomposites, forming compounds directly with PLA and NCC [4]. -8] unmodified, or only physically modified using surfactants or polymer compatibilizers. A more recent study showed that dispersion of NCC in a PLA matrix can be improved by grafting NCC with polycaprolactone (PCL) [9]. However, the aggregation of the nanoparticles in said system continued to be observed, and the improvement in the mechanical properties of the resulting nanocomposite was limited.

BRIEF DESCRIPTION OF THE INVENTION The present invention seeks to provide a nanocomposite of nanocrystalline cellulose (NCC) and polylactic acid (PLA).

This invention also seeks to provide a process for producing a nanocomposite of nanocrystalline cellulose (NCC) and polylactic acid (PLA).

Additionally, the present invention seeks to provide a composition comprising a nanocomposite of the invention, which is composed or mixed with high molecular weight PLA.

In one aspect of the invention, there is provided a nanocomposite of nanocrystalline cellulose (NCC) and polylactic acid (PLA) wherein said PLA is grafted onto said NCC.

In another aspect of the invention, there is provided a process for producing a nanocomposite of nanocrystalline cellulose (NCC) and polylactic acid (PLA) comprising ring opening polymerization of L-lactide in the presence of NCC particles, in a medium not watery In yet another aspect of the invention, there is provided a composition comprising a nanocomposite of the invention, which is compounded or mixed with a polymer selected from PLA, poly (hydroxybutyrate), PHB or poly (hydroxyalkanoate), PHA; for example high molecular weight PLA.

The last compounding or mixing can be done, for example, by co-extrusion, injection molding or other polymer processing techniques.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1: is a flow diagram of the process for in-situ graft copolymerization of L-lactide with NCC.

Figure 2: is a solid state 13C nuclear magnetic resonance (NMR) spectrum of nanocomposites of NCC, PLA and NCC-PLA. The peaks for the nanocomposite sample coincide with the individual peaks for NCC and PLA indicating a successful synthesis using the in situ ring opening polymerization of L-lactide in the presence of NCC.

Figure 3: is a graph of the differential scanning calorimetric responses of nanocomposite films of PLA and NCC-PLA. The nanocomposite films exhibit significantly improved crystallization relative to PLA, indicating improved structural integrity, thermal stability and dimensional stability. In effect, the NCC can help overcome problems related to PLA processing and conversion. (Tg = glass transition temperature, Tc = crystallization temperature, Tm = melting temperature) Figure 4: is a graph of the storage module against temperature, indicating the dynamic mechanical response of set films of PLA, compared to films set with different weight ratios of compatibilized NCC. The increased load of NCC represents an improved softening of the final product, indicating a higher crystallinity. The compatibilized NCC, or supramolecular material of NCC-PLA prepared according to this invention, was mixed by film setting with commercial grade PLA.

Figure 5: is a graph of the storage module against temperature, indicating the dynamic mechanical response of nanocomposite films of PLA and NCC-PLA prepared by means of a process different from those shown in figure 4. These samples are they compose by co-extrusion and then are compression molded to form films. The rapid cooling characterizes this process, and the PLA is completely amorphous. The increased load of NCC is evidence of the ability to improve the crystallinity, and therefore the mechanical response of the final product.

DETAILED DESCRIPTION OF THE INVENTION This invention provides a new approach for the development of sustainable and thermally stable biomaterials, comprising nanocomposites of nanocrystalline cellulose (NCC) and polylactic acid (PLA). The novel approach employs in situ ring opening porlimerization of NCC particles with L-lactide to form nanocomposite materials.

NCC-PLA. The resulting material is hydrophobic and compatible with a wide range of synthetic and natural polymers. NCC-PLA nanocomposites have improved mechanical performance and dimensional stability (ie, less hygroscopicity) relative to PLA. They are potentially biocompatible, recyclable and made from completely renewable resources. They can be suspended in most organic solvents or dried to form a solid substrate that can be processed using conventional polymer processing techniques to develop three-dimensional structures.

Nanocrystalline cellulose (NCC) is extracted as a colloidal suspension by the acid hydrolysis of typically chemical wood pulps, but other cellulosic materials can be used, such as bacteria, marine animals that contain cellulose (eg, marine tunicate), or cotton. The NCC is made up of cellulose, a linear polymer of ß (1? 4) linked D-glucose units, whose chains have the same to form crystalline and amorphous domains.

The NCC obtained through the hydrolytic extraction has a degree of polymerization (DP for its acronym in English) in the scale of 90 < DP = 1 10, and from 3.7-6.7 sulphate groups per 100 anhydroglucose units. The NCC comprises crystallites whose physical dimension varies between 5-10 nm in cross section and 20-100 nm in length, depending on the raw material used in the extraction. These charged crystallites can be suspended in water, or other solvents if they are properly derived, or can be self-assemble to form solid materials by means of air drying, sprinkling or freezing. When dry, the NCC forms an agglomeration of bar-like parallelepiped structures, which have cross sections in the nanometer scale (5-20 nm), while their lengths are an order of magnitude larger (100-1000 nm) giving as result high aspect ratios. The NCC is also characterized by a high crystallinity (> 80%, and most likely between 85 and 97%) reaching the theoretical limit of the cellulose chains. The hydrogen bond between the cellulose chains can stabilize the local structure in the NCC, and plays an important role in the formation of crystalline domains. The crystallinity, defined as the crystalline fraction of the sample, has a strong influence on the physical and chemical behavior of the NCC. For example, the crystallinity of the NCC has a direct influence on the accessibility to the chemical properties of derivation, swelling and binding of water.

The nanocomposite of the invention is hydrophobic and has improved molding characteristics, thermomechanical and gas barrier properties, as compared to the PLA formed by ring opening polymerization of L-lactide in the absence of NCC.

In the process of in situ polymerization by which a PLA graft is formed in NCC, it is initiated by the hydroxyl groups in the NCC, or it can be partially initiated by hydroxyl groups in the NCC and partially by an added initiator that provides a source of hydroxyl groups for the polymerization, for example an alcohol, alcohols suitable for the polymerization system include benzyl alcohol and 1-docecanol.

The NCC in the nanocomposite maintains the crystalline characteristics of the original NCC before grafting. However, the crystalline characteristics of the PLA, when formed in compound or mixed with a NCC-PLA nanocomposite material (ie, PLA grafted in NCC), are modified by the NCC and the PLA nanocomposite reaches a further grade. high in crystallinity than PLA formed by L-lactide ring opening polymerization in the absence of NCC (ie, the PLA of origin). The crystalline state of grafted PLA, and subsequently of composite or mixed materials, is more stable than that of the PLA of origin.

The open-ring lactone has carboxyl and hydroxyl end groups; a hydroxyl of an open ring unit forms an ester bond with a carboxylic acid of another open ring unit in the formation of the polymer chain, a chemical bond or linkage is formed with the NCC between a terminal carboxylic acid group of a chain of polymer and a hydroxyl of NCC, thus forming an ester linkage. In this way a single bond is formed between each individual polymer chain and the NCC. In other words, the end of the grafted PLA chain binds with the NCC through a single ester linkage formed during the polymerization process. In principle, the hydroxyl groups in the NCC can act as initiators for the polymerization of lactide.

The nanocomposite would have several or a plurality of polymer chains linked independently with each nanocrystal of the NCC; that is, each NCC crystal would form a structure comprising a central crystal or several polymers or a plurality of chains radiating therefrom. In this way the modified NCC becomes dispersible in chloroform, which is a good solvent for PLA.

The degree of monomer conversion and the molecular weight of the free PLA homopolymer generated during the in situ polymerization reaction depend on the reaction conditions, specifically, the dose of monomer being used and the concentration of NCC in the medium of reaction. In general, both the degree of monomer conversion, defined as the ratio of the total mass of the grafted and free PLA to that of the L-lactide monomer used, as well as the molecular weight of the resulting NCC-PLA composite, increase as non-linear with the increase of the monomer dosage and the concentration of NCC.

For example, if the mass ratio of monomer to NCC is kept constant, from 30 to 1, that is, the mass of the monomer of L-lactide is 30 times that of the NCC, but the concentration of NCC in the solvent (per example, DMSO) increases from 1.5 g / 100 ml to 2.5 g / 100 ml, while all other conditions remain the same, the degree of monomer conversion, the number average molecular weight (MW number), and the average molecular weight by weight (PM peSo) of the NCC-PLA nanocomposite material will increase from 12.7%, 1561, and 1989 to 44.8%, 5532, and 19803, respectively.

Especially ring opening polymerization is carried out under anhydrous conditions. Typically the concentration of NCC in the non-aqueous reaction medium can vary from 1 to 10 g / 100 mL, preferably from 1.5 to 5 g / 100 mL, and that of L-lactide from 5 to 50 times the mass of the NCC starting, and preferably 15 to 30 times.

Normally the nanocomposite, after intensive washing to remove the free homopolymer and the unreacted chemicals, will have a PLA grafting yield, defined as the ratio of the mass of the grafted PLA to that of the NCC, which will generally vary from 30 % to more than 90%, but more generally in approximately 85%. In other words, the mass of the PLA in the resulting nanocomposite will be multiplied by 85% by the mass of the starting NCC.

In particular, the polymerization is carried out in an organic solvent, for example dimethyl sulfoxide (DMSO). In addition, the medium for the in-situ polymerization reaction may be, but is not limited to, alcohols (eg, methanol), amides (eg, dimethylformamide), amines (eg, pyridine), esters (eg, ethyl acetate), ethers (e.g., 1,4-dioxane), glycol ethers (e.g., 2-butoxyethanol), halogenated solvents (e.g., chloroform), hydrocarbon solvents (e.g., toluene), and ketones (e.g. for example, acetone).

The in situ polymerization of L-lactide in the presence of NCC leads to the formation of PLA with various chain lengths. A part of this PLA is grafted into the NCC, namely, in general 30 to 90%, and typically 85%, as indicated above. What remains is the homopolymer of free PLA and unreacted monomers. The purification, etc. it can remove the unreacted PLA monomer and also the free PLA homopolymer.

Therefore, the polymerization is followed by a recovery step of the nanocomposite from the non-aqueous medium. In particular, this recovery step may comprise precipitating the nanocomposite from the non-aqueous medium, and purifying the resulting precipitate by means of dialysis and / or centrifugation. Normally the mass of the free PLA homopolymer generated during the reaction varies from 2 to 15 times the mass of the starting NCC. This depends strongly on the reaction conditions of the polymerization. But it has been found that it may be advantageous to retain some of the free PLA homopolymer, to help facilitate good dispersion of the nanocomposite in the subsequent processing of the nanocomposite, and to ensure a good interface (i.e. good compatibility). At this stage it is not possible to quantify how much free PLA homopolymer is needed. It has been seen that the free homopolymer produced in this way has the advantage of ensuring: (i) the uniform dispersion of the compound in any processed product, and (ii) a good interface with the resin used in the subsequent processing of the polymer, which normally is, but is not limited to, PLA.

The ring opening polymerization is carried out at an elevated temperature, usually from about 100 ° C to about 150 ° C, especially about 130 ° C, and generally for a period of 1 to 20 hours, especially about 15 to 20 hours.

Conveniently the ring opening polymerization is carried out in the presence of a catalyst, typically a metal carboxylate catalyst, other catalysts include metal oxides, and metal alkoxides, for example, carboxylates, oxides, and tin, zinc, and aluminum alkoxides .

The NCC-PLA nanocomposite thus produced is a hydrophobic supramolecular material that can be dispersed in a suitable solvent or dried. For example, it can potentially be used as it is, or it can be derived further for use as an excipient for the delivery and delivery of drugs. It can also be used in combinations mixed with PLA and / or other biopolymers such as poly (hydroxybutyrate), PHB, or poly (hydroxyalkanoate), PHA, using conventional polymer processing techniques, for example, coextrusion, blow molding, injection molding or compression, to produce films and / or three-dimensional moldable products for packaging and other industrial applications. It can also be made in an emulsion and spinning by spinning or electing, to form fibers and / or yarns for textiles, and engineering applications.

Thus, the nanocomposite of the invention can potentially be used in a wide variety of industrial and medical applications, for example, but not limited to, packaging, automotive, structural, drug delivery and delivery, tissue engineering, scaffolding to develop new systems for medical and / or industrial applications.

The NCC-PLA nanocomposite of the invention is a supramolecular material that can be suspended in a suitable solvent, or can be dried and potentially used as is, or can be further derivatized for use as an excipient for the delivery and delivery of drugs.

The composition of the invention comprising a nanocomposite of the invention, which is formed in compound or mixed with a polymer, such as PLA and / or other biopolymers such as poly (hydroxybutyrate), PHB, or poly (hydroxyalkanoate), PHA, for example, using conventional polymer processing techniques, for example, coextrusion, blow molding, injection or compression molding, can produce films and / or three-dimensional moldable products for packaging and other industrial applications.

The latter composition can also be made as an emulsion and can be spun by fusion or by electronic spinning into fibers and / or yarns for textiles and engineering applications.

The preparation of the NCC-PLA nanocomposites according to the invention is described in the form of a procedure in Figure 1. The central step is the in situ ring opening polymerization of L-lactide in the presence of nanocrystalline cellulose (NCC) in a suitable organic medium.

Before the ring opening polymerization, it is necessary to exchange the dispersion medium, if the NCC, as is normally the case, is suspended in water. After the polymerization, it is necessary to purify the product, for example, using dialysis against water and washing it with methanol and, if necessary, with acetone. The methanol is used to remove any unreacted monomer and catalyst, while the acetone is used to dissolve the free PLA homopolymer in the system, ie, the PLA not grafted in NCC. A detailed description of the polymerization process is given below. 1. Typically NCC is produced as a suspension of nanoparticles in water, in a variable concentration, for example of 4.39% w / w, and for the purpose of the present invention, the suspension of NCC is subjected to titration at a neutral pH with a NaOH solution. The exchange of the suspension medium, of water to a suitable organic solvent, for example, dimethyl sulfoxide (DMSO, typically> 99.6%) is carried out by slowly pouring and stirring a desired volume of DMSO, for example 10 ml, into a required mass of NCC, for example, 30 g of NCC in water suspension. The mixture is then stirred for another reasonable period, for example 5 minutes, to allow the water in the DMSO to mix thoroughly. The water in the system is removed by distillation in a rotary evaporator (for example, the BUCHI, Rotavapor R-200) in two steps. In the first step, a distillation temperature of 83 ° C is chosen and the vacuum is adjusted to 720 Torr. At the end of the first step, the volume of the condensed liquid in the collector is kept constant. In the second step, the vacuum increases to 740 Torr to distill -20 mL of DMSO. 2. The steps for the exchange of the dispersion medium described above can be replaced by directly dissolving the lyophilized or dispersible NCC by spray drying (pH neutral) in DMSO. The dissolution process can be facilitated using ultrasound. The container is then sealed to prevent the DMSO from absorbing moisture, and the contents are preferably stirred overnight, or more if necessary. 3. To the suspension of NCC / DMSO in a sealed flask, the following is added: (i) a suitable mass, for example, 39.5 g of L-lactide (typical purity> 98%), (ii) 0.4 g of a suitable catalyst, for example, Tin (II) 2-ethylhexanoate (Sn (oct) 2, ~95%), and (iii) 0.2 g of benzyl alcohol (anhydrous, 99.8%), which is useful for improving dispersion of NCC , particularly with a high dosage of lactide. After stirring it for a reasonable period, for example 5 minutes, the suspension is sonicated for 2 minutes using a sonicator (for example, the Fisher Sonic Dismembrator, Model 300). Finally, the trace amount of residual water in the system is eliminated, passing the suspension through a 250 ml separating funnel filled with 60 g of molecular sieves (3 A, 8-12 mesh), activated at 320 ° C. for at least 3 hours in advance. After the dry suspension of NCC / DMSO is drip directly from the funnel to a 3-necked 500-ml flask Oven-dried, equipped with a mechanical stirrer. To prevent the DMSO from absorbing moisture, both the separatory funnel and the flask are kept in a nitrogen atmosphere during the polymerization process. 4. The ring-opening polymerization is carried out by impregnating the sealed flask in an oil bath at 130 ° C for 17 hours. During the reaction, the suspension is stirred using a magnetic or mechanical stirrer at 200-500 rpm. After the reaction, the resulting product is a clear suspension with a light brown color. 5. The NCC-PLA nanocomposite is precipitated from DMSO, slowly pouring the product into water, with a rapid stirring at a ratio of 3: 1 (water / product). Purification then proceeds, whereby the product is dialysed, for example, in dialysis tubes (suggested molecular weight cutoff, MWCO = 12000-14,000) against running water for at least 4 days, and / or the white precipitate it is subjected to centrifugation at 4,400 rpm for a reasonable time, for example 20 minutes, using a suitable centrifuge system (for example IEC Centra® MP4, Rotor 224). After decanting, the product is redispersed in methanol (>99.8%) by re-stirring and centrifuging. This cycle of centrifugation-decantation repeats a reasonable number of repetitions, for example three times, to wash out all the impurities. Finally, the washed product is dried under vacuum for a reasonable period, for example, overnight. 6. A visual comparison of the suspensions of the pristine supramolecular nanocomposite material of NCC and NCC-PLA in chloroform indicates the perfect dispersibility of the latter in an organic solvent, also indicating the hydrophobicity of the NCC-PLA nanocomposites.

EXAMPLE 1 The NCC-PLA nanocomposite materials prepared with the use of the in situ polymerization approach described in this invention produce particles having a typical hydrodynamic diameter of an equivalent sphere (determined by a Zetasizer) equal to 60.2 ± 0.9 nm ( dispersed in D SO). The nanocomposite materials are perfectly dispersed in the typical organic solvents, indicating excellent hydrophobicity. The mass ratio of the grafted polymer to that of the NCC is usually > 80% Nuclear magnetic resonance (NMR) of 13C in solid state confirms successful synthesis, as described in figure 2.

EXAMPLE 2 The physical, mechanical and barrier properties of polymers or polymeric compounds depend on the solid state morphology and the crystallinity of the material, and the processing of these composite materials can significantly impact these properties. The NCC-PLA composite material described in this invention can be processed with the use of techniques for polymer processing (eg, film setting, extrusion / blow molding, injection or compression molding, fiber spinning , etc.) to produce films, fibers, filaments and, in general, any three-dimensional object. Figure 3 shows the differential scanning calorimetric responses of NCC-PLA nanocomposite films containing 5.3% w / w of NCC. These nanocomposite films significantly improve structural and thermal stability, as well as lower hygroscopicity, compared to net PLA films. This unique behavior is the result of the ability of the NCC to initiate a controllable crystallization in the amorphous PLA, while maintaining the structure of the NCC in an undisturbed state. The small and imperfect PLA crystals successively change to more stable crystals, by means of fusion and recrystallization (as indicated by the two fusion peaks for the NCC-PLA nanocomposites of Figure 3). This is more evident from the data of the dynamic mechanical analysis that is represented in figure 4, where it is indicated how the supramolecular material of NCC-PLA prepared according to the invention works, that is, the NCC compatibilizada, to improve the softening behavior of the PLA as the NCC load increases. There is an order of magnitude of increase in mechanical response, measured, for example, by the module storage, from 41 Pa for net PLA at 480 MPa at 50 ° C to 5% p / p NCC load. If the processing of the material changes from slow cooling (Figure 4), where it is allowed to increase the crystallinity to a higher magnitude, to rapid cooling (Figure 5), the NCC continues to work to improve the crystallinity of the resulting composite product, despite slower speed, since in this case the PLA is completely amorphous. The difference in the magnitude of improvement is mainly due to the different processing techniques. But both examples, Figure 4 and Figure 5, clearly indicate the role that the NCC plays in improving the crystallinity of the final product, regardless of the processing technique used.

An increased crystallinity is preferable for molded articles for which thermal stability is important. In addition, NCC-PLA nanocomposites exhibit a distinctive viscoelastic behavior with a positive impact on processing and functionality. These capabilities result in improved processing, conversion and mechanical performance capability of the resulting objects that contain NCC-PLA nanocomposite materials.

The nanocomposite of the invention can be incorporated in a mixture or compound with a high molecular weight PLA polymer, for example, a PLA polymer having a molecular weight of 20,000 to 1,000,000, by coextrusion, setting or other conventional techniques of mixed or compound formation, and the presence of the nanocomposite gives as a result a significantly reinforced PLA.

The molecular weight of the grafted PLA was determined by two indirect methods in this particular case. (1) An experiment of control to polymerize a lactide in PLA using the exact focus for prepare NCC-PLA nanocomposites, but without NCC. The polymer obtained It was analyzed using GPC. (2) The second approach was to collect the free PLA homopolymer from the NCC-preparation procedure PLA, and then characterize it using 1H NMR. The molecular weight was calculated according to the relationship of the extreme groups to the repeating units in the Principal structure. The number average molecular weights (PM number) in specific examples varied between 890 and 6000, depending on the conditions of the polymerization reaction, indicating that normally the Grafted PLA has a short chain length. By balancing the conditions I of reaction, theoretically it is possible to allow longer chains to grow of PLA, and in this way PLA grafted, high molecular weight is produced, in NCC.

References: [1] V. Favier, G R. Canova, J.Y. Cavaille, H. Chanzy, A Dufresne, C. Gauthier, Polym. Adv. Technol. 6 (1995) 351. [2] V. Favier, G.R. Canova, S.C. Shrivastava, J.Y. Cavaille Polym. Eng. Sci. 37 (1997) 1732. [3] J.R. Capadona, K. Shanmuganathan, D.J. Tyler, S.J.

Rowan, C. Weder, Science 319 (2008) 1370. [4] K. Oksman, A.P. Mathew, D. Bondeson, I. Kvien, Compos. Sci. Technol. 66 (2006) 2776. [5] L. Petersson, I. Kvien, K. Oksman, Compos. Sci. Technol. 67 (2007) 2535. [6] D. Bondeson, K. Oksman, Compos. A 38 (2007) 2486. [7] D. Bondeson, K. Oksman, Compos. Interviews 14 (2007) 617. [8] A.P. Mathew, A. Chakraborty, K. Oksman, M. Sain, The structure and mechanical properties of cellulose nanocomposites prepared by twin screw extrusion, in Cellulose nanocomposites-processing, characterization and properties, K. Oksman, M. Sain, American Chemical Society, 2006, p. 1 14. [9] N. Lin, G. Chen, J. Huang, A. Dufresne, P.R. Chang, J. Appl. Polym. Sci. 1 13 (2009) 3417.

Claims (21)

NOVELTY OF THE INVENTION CLAIMS

1. - A process for producing a nanocrystalline cellulose nanocomposite (NCC) and polylactic acid (PLA) comprising the ring-opening polymerization of L-lactide in the presence of NCC particles, in a non-aqueous medium.

2 - . 2 - The process according to claim 1, further characterized in that said ring opening polymerization is carried out under anhydrous conditions.

3. The method according to claim 1 or 2, further characterized in that it also comprises a step of recovering said nanocomposite from said non-aqueous medium.

4. - The process according to any of claims 1 to 3, further characterized in that said ring opening polymerization is carried out in an organic solvent.

5. - The process according to claim 4, further characterized in that said organic solvent is dimethyl sulfoxide.

6. - The method according to claim 3, further characterized in that said recovery comprises precipitating said nanocomposite from said non-aqueous medium, and purifying the resulting precipitate by means of dialysis.

7. - The process according to any of claims 1 to 6, further characterized in that said ring opening polymerization is carried out at an elevated temperature in the presence of a catalyst.

8. - The method according to claim 7, further characterized in that said elevated temperature is from about 100 ° C to about 150 ° C.

9. - The method according to claim 8, further characterized in that said ring opening polymerization is carried out at said elevated temperature for a period of 1 to 20 hours.

10. - The method according to claim 9, further characterized in that said period is from 15 to 20 hours.

11. - The method according to any of claims 1 to 10, further characterized in that said ring opening polymerization is carried out in the presence of an initiator for said ring opening polymerization, said initiator having an alcohol group.

12. - The method according to claim 3, further characterized in that at least a portion of the homopolymer of Free PLA produced in ring opening polymerization is retained with the recovered nanocomposite as a processing aid.

13. - A nanocomposite of nanocrystalline cellulose (NCC) and polyalactic acid (PLA) in which said PLA is grafted in said NCC.

14. - The nanocomposite according to claim 13, further characterized in that the NCC nanocrystals of the compound have several or a plurality of polymer chains that are independently linked thereto and are irradiated therefrom.

15. - The nanocomposite according to claim 13 or 14, further characterized in that it has a PLA grafting yield of 30% to more than 90%.

16. - The nanocomposite according to claim 15, further characterized in that said grafting yield is about 85%.

17 -. 17 - A composition comprising a nanocomposite as claimed in any of claims 13 to 16, which is compounded or mixed using extrusion, injection or compression molding with a polymer selected from PLA, poly (hydroxybutyrate) (PHB) or poly (hydroxyalkanoate) (PHA).

18 -. 18 - The composition according to claim 17, further characterized in that said polymer is PLA of high molecular weight.

19. - The composition according to claim 18, further characterized in that said PLA has a molecular weight of 20,000 a 1, 000,000.

20. - The composition according to any of claims 17 to 19, further characterized in that it has the form of a three-dimensional moldable film or product for packaging and other industrial applications.

21. - The composition according to any of claims 17 to 19, further characterized in that it has the form of emulsion, fibers or threads spun by melting or electronically for the textile application and in engineering.