MX2012009641A - Thermoplastic nanocomposite material based on nanocrystalline cellulose (ncc). - Google Patents

Abstract

A green approach for the development of nanocomposite materials comprising nanocrystalline cellulose (NCC) and appropriate vinyl polymers is conceived. The approach deals with the in-situ graft co-polymerization of hydrophobic vinyl monomers, such as vinyl acetate and methyl methacrylate, onto the NCC surface in an aqueous medium. The resulting material is significantly more hydrophobic and thermally stable than the starting NCC. The nanocomposite material can be suspended in appropriate solvents, dried and moulded with other materials using conventional polymer processing techniques to develop yet new materials with new characteristics. These nanocomposites have wide ranging applications from industrial to medical use.

Description

THERMOPLASTIC NANOCOMPUESTO MATERIAL BASED ON NANOCRYSTALLINE CELLULOSE TECHNICAL FIELD This invention relates to a hydrophobic nanocomposite thermoplastic nanocrystalline cellulose (NCC) and a hydrophobic vinyl monomer, and to a process for producing this nanocomposite; the process can be considered as a green process. The nanocomposite is a thermally stable and sustainable biomaterial, which is hydrophobic and compatible with a wide range of synthetic polymers. The nanocomposite material can be suspended in appropriate solvents, and also dried and molded with other materials using conventional polymer processing techniques, to further develop materials with new characteristics. These nanocomposites have a wide range of applications from industrial to medical use.

TECHNICAL BACKGROUND It has been recognized that nanocrystalline cellulose (NCC) can be applied as a reinforcement material in nanocomposites. NCC, a chiral nematic structure of high strength and elastic modulus, is renewable, has a relatively large reactive surface, and is biodegradable. The main obstacles to the application of NCC in the manufacture of composite materials are (1) the dispersion of hydrophilic NCC in polymeric matrices generally hydrophobic and (2) the poor interfacial adhesion between NCC and the polymer. Different proposals have been followed to increase the dispersion of NCC and its interaction with polymer matrices. NCC has been coated with surfactant or chemically modified on its surface.1, 2 The use of surfactants is a fairly simple method but a large amount of surfactant is usually required, which would have a negative impact on the strength of the resulting composite material. On the other hand, the modification of the surface generally involves a reaction with the hydroxyl groups on the NCC surface. Silanes have been used to graft hydrophobic groups on the surface of NCC. Moreover, some polymers with reactive hydroxyl groups, such as PEG, 3 PCL4 and PP.5 have also been used. These modifications can make NCC more hydrophobic and give the NCC reasonable stability in organic solvents. However, these reactions are usually carried out in organic solvents and involve several steps.

Surface graft copolymerization of vinyl monomers on surfaces of polysaccharides, for example cellulose, starch and chitosan, has been extensively investigated.6"8 Methyl methacrylate, methyl acrylate, acrylic acid or vinyl acetate can be used as the monomer of choice Graft polymerization has been reported using different initiation systems, including photoinitiators, UV light,? -radiation, free radical initiators, etc. In these techniques, free radical initiators such as AIBN, iron (ll) -peroxide of hydrogen, potassium persulfate and transition metal ions, have been used extensively Among the initiators of free radicals, the ceric ion (IV) has shown great efficiency in the grafting of vinyl monomers on a number of polysaccharides. for the initiation reaction has been attributed to the formation of a complex with the hydroxyl groups in the polymer, which can be dissociated by transfer of an electron to give free radicals.

BRIEF DESCRIPTION OF THE INVENTION This invention seeks to provide a hydrophobic nanocomposite of nanocrystalline cellulose (NCC) and polymerized hydrophobic vinyl monomer.

This invention also seeks to provide a process for producing a nanocrystalline cellulose hydrophobic nanocomposite (NCC) and polymerized hydrophobic vinyl monomer.

Moreover, this invention seeks to provide a composition comprising a hydrophobic nanocomposite of the invention, combined or mixed with a high molecular weight polymer.

In one aspect of the invention, a hydrophobic nanocomposite of nanocrystalline cellulose (NCC) and monomer is provided vinyl hydrophobic polymer, in which said polymerized vinyl monomer is grafted onto said NCC.

In one aspect of the invention, there is provided a process for producing a nanocrystalline cellulose hydrophobic nanocomposite (NCC) and a hydrophobic polymerized vinyl monomer, which comprises the polymerization of at least one hydrophobic vinyl monomer in the presence of NCC particles.

In another aspect of the invention, there is provided a composition comprising a nanocomposite of the invention, combined or mixed with a high molecular weight polymer.

BRIEF DESCRIPTION OF THE DRAWINGS The invention is illustrated and further explained by reference to the accompanying drawings in which: Figure 1 is an FT-IR of NCC, PVAc-g-NCC and PMMA-g-NCC, which indicates the successful surface grafting of the vinyl monomers on NCC.

Figures 2A, 2B and Table A comprise a 1H NMR of PVAc-g-NCC and PMMA-g-NCC, which indicates the successful surface grafting of the vinyl monomers on NCC.

Figure 3A and Table B comprise a 13C NMR of PMMA-g-NCC, which indicates successful surface grafting of vinyl monomer over NCC.

Figure 4 is a thermogravimetric analysis of NCC, PVAc-g-NCC and P MA-g-NCC.

Figure 5 is a differential scanning calorimetry of NCC, PVAc-g-NCC and PMMA-g-NCC.

Figure 6 shows the contact angle with water of NCC and PMMA-g-NCC, indicating the increased hydrophobicity in the case of the nanocomposite.

Figure 7 shows the percentage of nanocomposite produced for different MMA: NCC ratios in the polymerization mixture.

Figure 8 shows the percentage of nanocomposite produced for different VAc: NCC ratios in the polymerization mixture.

BRIEF DESCRIPTION OF THE PICTURES Table 1: Optimal polymerization conditions for vinyl acetate (VAc) and methyl methacrylate (MMA) with nanocrystalline cellulose (NCC).

Table 2: Size of NCC and PMMA-g-NCC particles in different solvent systems. Graft yields are reported for polymerization with 2% CAN.

DETAILED DESCRIPTION OF THE INVENTION A green proposal for the development of nanocomposite materials comprising nanocrystalline cellulose (NCC) and appropriate vinyl polymers is described. The proposal employs in situ graft copolymerization of hydrophobic vinyl monomers on the surface of NCC in an aqueous medium. The proposal is hereinafter described by reference to two classes of monomers, vinyl acetate and methyl methacrylate, but other hydrophobic vinyl monomers may be employed.

The nanocomposite material is significantly more hydrophobic and thermally stable than the initial NCC. The nanocomposite material can be suspended in appropriate solvents, and also dried and molded with other materials using conventional polymer processing techniques, to further develop materials with new characteristics. These nanocomposites have a wide range of applications from industrial to medical use.

This invention addresses the development of thermoplastic hydrophobic nanocomposites by in situ graft copolymerization of hydrophobic monomers on the surface of nanocrystalline cellulose (NCC). Although any suitable class of hydrophobic vinyl monomer can be used to develop the nanocomposites with NCC, this disclosure focuses on vinyl acetate and methyl methacrylate as the vinyl monomers of choice, by way of illustration of the invention.

Suitable hydrophobic vinyl monomers in particular are those that will polymerize in situ in the presence of NCC, binding to NCC without crosslinking with each other. Acrylates are suitable monomers, but monomers that are likely to crosslink may not be particularly suitable. Molecules that have a mid-range hydrophobicity with respect to NCC are suitable.

The solubility in water of the hydrophobic vinyl monomer is a factor in the selection of the vinyl monomer for polymerization. If it is too high, then the polymer would be soluble in water; if it is too low, then graft polymerization will not occur or will progress with difficulty. The water solubility of methyl methacrylate is 1.5 g / 100 ml, and that of vinyl acetate is 2.5 g / 100 ml. Suitably, the range of solubilities is from about 1.5 to about 3 g / 100 ml, and thus, methyl acrylate having a solubility in water of 3 g / 100 ml and ethyl acrylate having a solubility in water of 1.5 g / 100 ml, are also hydrophobic vinyl monomers suitable for polymerization.

Suitable mixtures of monomers can be used, whereby the polymer chain of the NCC can be a copolymer. Thus, the polymer chains grafted onto the NCC can comprise homopolymer chains of the different monomers of the mixture and also copolymer chains comprising the different monomers of the mixture.

The polymerization is carried out in an aqueous medium. The ability to use an aqueous medium to carry out the polymerization, with the ultimate aim of creating a hydrophobic system, is a particularly interesting aspect of the invention, and also has significant advantageous implications for cost-effective manufacturing, in addition to advantages for the environment (green).

Preferably, the polymerization is carried out in an acidic aqueous medium having a pH of less than 7, and in particular from 1 to 4. The acidic pH is achieved by the addition of an acid such as nitric acid.

The polymerization is suitably carried out at room temperature (about 20 ° C) to 90 ° C for 1 to 24 hours, preferably at a temperature of 40 ° C to 70 ° C for 1 to 4 hours.

Typically, a free radical initiator is used to promote the polymerization, and a terminator is used to terminate the polymerization.

The open olefinic monomer has free bonds at the ends, one of which forms an oxide linkage through a hydroxyl in a NCC crystal, and the other bonds with another monomer to form the polymer chain; thus, the polymer chain will have a terminal bond with the hydroxyl group of NCC.

There can be several polymer chains attached independently to each nanocrystal of NCC through hydroxyl groups in the crystal; whereby a single central crystal has several polymer chains that radiate therefrom.

Although it is possible, it is unlikely that the external terminal free bond of the olefin polymer at the end of the chain can be bound through a hydroxyl in a NCC crystal, due to competing reactions. The external terminal free radical will be terminated mainly by these reactions: - Finished by unused initiator.

- Reaction with another external terminal free radical. There are two possibilities. (1) If the reaction takes place with a free radical in a monomer, then it would be finished. In this case, the polymer chains extend radially from the crystals. - (2) However, if the reaction takes place with a free radical in a polymer chain, then two structures are possible: - (a) If the polymer chains originate from the same crystal, a handle is formed with opposite ends attached to the crystal. - (b) If the polymer chains originate from different crystals, the crystals cross over. Although this is possible, it is probably minimal, it has been found that the grafted NCC is well suspended in an organic solvent, and no aggregates have been detected.

- Transfer to a monomer and start of polymerization, resulting in free ungrafted polymers.

The grafting yield is the ratio between the weight of the modified NCC (i.e., NCC grafted with vinyl) and the weight of the original NCC. For the optimum reaction conditions shown in Table 1 herein, the grafting yields are as follows: 1. For PMMA-g-NCC it is 66.4% at a weight ratio of MMA: NCC = 1: 1 2. For PVAc-g-NCC it is 12.4% at a weight ratio of VAc: NCC = 2: 1.

If the weight ratio of the monomer increases, then the grafting yield, under the same reaction conditions, will also increase. Figures 7 and 8 are graphs that confirm trends for MMA and VAc.

In general, the polymerization proceeds with the grafting of the vinyl monomer onto the NCC, and the polymerization of this monomer with another monomer to form a polymer chain extending from the NCC.

The nanocomposite can be mixed or combined with a high PM polymer, generally ungrafted free polymers will be removed from the nanocomposite before said mixture or combination, but if PMMA is used as a high PM polymer, then it is not necessary to remove the polymers from Free PMMA present in the produced PMMA-g-NCC. On the other hand, if polystyrene is used as a high PM polymer to be mixed with the PMMA-g-NCC, then it is necessary to remove the free PMMA homopolymers.

Suitable high PM polymers have a molecular weight from 20,000 to several million, for example from 20,000 to 5,000,000; Suitable polymers include polymethylmethacrylate, polyvinyl acetate and polystyrene.

In a specific embodiment, the surface graft copolymerization of vinyl acetate (VAc) or methyl methacrylate (MMA) on NCC is carried out according to the following protocol. First the inhibitors in the monomer are removed by a column of inhibitor removal. The suspension of NCC in water is first mixed with VAc or MMA and diluted with deionized water (DI) to the required concentration. The mass ratio of NCC to MMA (or VAc) is adjustable and in this case 1: 2 is used. In the final reaction solution, the concentration of NCC is controlled to be 3% w / w, and the pH of the reaction solution is adjusted to be acidic using for example HN03, and pointing for example to pH = 2. The required amount of a free radical initiator, for example ceric ammonium nitrate (CAN), is dissolved in DI water with the desired amount of HNO3. Then, in both CAN and NCC solutions, nitrogen is bubbled in for 30 minutes, for example. Polymerization begins by adding the CAN solution to the NCC solution, and allowing the reaction to advance for a specific time at a specific temperature. Near the end of the reaction, 100 μ? of hydroquinone (for example, at 1% w / w) to stop the reaction, and the solid is centrifuged at 4,400 rpm for 30 min. The ungrafted poly (vinyl acetate) (PVAc) or poly (methyl methacrylate) (PMMA) is extracted by acetone using, for example, Soxhiet extraction for at least 3 days. Once the extraction is complete, the nanocomposite PMMA-g-NCC or PVAc-g-NCC is dried under vacuum at room temperature overnight. To determine the optimum reaction conditions for the graft surface polymerization, a series of experiments are carried out for vinyl acetate and methyl methacrylate, respectively. The optimal conditions are indicated in table 1.

The ratio between grafted polymer and NCC can vary widely for different monomers, and is also dependent on the amount of monomer added. By way of illustration, for a 1: 1 ratio of MMA: NCC, the ratio of grafted PMMA: NCC is 0.63: 1; for VAc: NCC 2: 1, PVAc grafted: NCC is 0.12: 1.

A variety of acids, including mineral acids such as nitric, hydrochloric and sulfuric acids, as well as organic acids such as acetic acid, are suitable for carrying out the polymerization reaction.

EXAMPLES EXAMPLE 1 Nanocomposites were prepared according to the protocol mentioned above. Evidence of successful surface copolymerization of vinyl monomers on NCC, that is, the determination of whether PVAc or PMMA are grafted onto NCC, is carried out using Fourier transform infrared (FT-IR) and / or magnetic resonance nuclear (NMR). In Figure 1, after graft copolymerization, two peaks are particularly evident compared to the original NCC. The peak in 1. 734 cm "1 is the vibration of C = 0 and the peak in 1241 cm" 1 corresponds to the vibration of C-0 in the ester group, respectively. The occurrence of the graft of PVAc and PMMA is further confirmed by 1H NMR. In Figures 2A, 2B and Table A for PVAc-g-NCC, the peak "a" at 1755 indicates the protons of -CH2-, and the peak "c" (from 1.9-1.97) indicates the protons of -CH3, whereas the peak "b" in 4.78 indicates the proton of -CH-.9 In the NMR spectrum for PMMA-g-NCC, the peak "b" (0.84 and 1.02) indicates the protons of methyl on carbon, in so much so that the peak "c" (3.6) indicates the protons of methyl on oxygen. The peak "a" at 1.81 indicates the protons of -CH2-.10 In addition to NMR in solution, 13C NMR was made in the solid state in the sample of PMMA-g-NCC, to provide a conclusive proof of successful surface grafting on NCC . As is evident in Figure 3A and Table B, all specific peaks can be assigned according to the literature.11, 12 TABLE A TABLE B EXAMPLE 2 The particle size of NCC and PMMA-g-NCC can be detected using a high-definition particle size analyzer (eg a Zetesizer), which measures the hydrodynamic diameter of an equivalent sphere. NCC is suspended in water, while PMMA-g-NCC is suspended in either chloroform or tetrahydrofuran (THF). The size of PMMA-g-NCC, shown in Table 2, can be changed with different polymerization models. If MMA: NCC 1: 1 is used, the product can not be suspended in solvent, which means that there is not enough MMA grafted on the NCC to be able to suspend it in a suitable organic solvent. On the other hand, if less initiator amount is used, the resulting PMMA-g-NCC will be larger than in cases where more initiator amount is used. This is explained by the fact that more initiator amount would make the PMMA chain shorter, which will result in a smaller particle size of PMMA-g-NCC. Finally, PMMA-g-NCC tends to be smaller in THF than in chloroform. Table 2 also indicates the graft yield for 2 conditions, confirming an efficient and successful graft.

EXAMPLE 3 The thermogravimetric data (TG), presented in Figure 4, demonstrate that both PVAc-g-NCC and PMMA-g-NCC are more thermally stable than the original NCC. This indicates that it would be possible to process these nanocomposites using conventional polymer processing techniques, for example extrusion. In Figure 5, differential scanning calorimetry (DSC) data illustrates that there is no detectable slope change for PVAc-g-NCC, however for PMMA-g-NCC there is an obvious slope change to around 100 ° C, which is the Tg for PMMA. This is probably because the amount of grafted PVAc is not high enough to be detected by DSC. However for NCC, the slope changes by over 160 ° C, and the probable reason for this is that at temperatures above 160 ° C the NCC starts to degrade, so that there is an exothermic response in the DSC curve. The TG curve for NCC in Figure 4 confirms that the degradation of NCC begins at just above 160 ° C.

EXAMPLE 4 The contact angle measurement with water is used to determine the surface hydrophobicity of both NCC and PMMA-g-NCC. Figure 6 shows that the contact angle with water of the nanocomposite PMMA-g-NCC increased to more than double the value for the original NCC, indicating an increased hydrophobicity of the new nanocomposite material.

TABLE 1 Optimal polymerization conditions for vinyl acetate (VAc) and methyl methacrylate (MMA) with nanocrystalline cellulose (NCC).

Temperature Time [HN03] Dosage of the initiator (° C) (hours) (M) (% by weight on NCC surface) MMA 50 3 0.01 2 VAc 65 3 0.01 2 TABLE 2 Size of NCC and PMMA-g-NCC particles in different systems of solvents. Graft yields are reported for polymerization with 2% CAN.

NCC MMA Samples: NCC MMA: NCC MMA: NCC MMA: NCC 1: 1 2: 1 2: 1 2: 1 2% CAN 2% CAN 5% CAN 5% CAN Solvent Water THF THF THF Chloroform Size 45.5 ± 1.2 Not good 205.9 ± 18.2 126.3 ± 1.1 160.8 (nm) suspended Performance N / A 63.2 77.3 of graft References: 1 . Samir, M .; Alloin, F .; Dufresne, A., Review of recent research into cellulosic whiskers, their properties and their application in nanocomposite field. Biomacromolecules 2005, 6, (2), 612-626. 2. Lima, M. M. D .; Borsali, R., Rodlike cellulose microcrystals: Structure, properties, and applications. Macromolecular Rapid Communications 2004, 25, (7), 771-787. 3. Araki, J .; Wada, M. Kuga, S., Steric stabilization of a cellulose microcrystal suspension by poly (ethylene glycol) grafting. Langmuir 2001, 17, (1), 21-27. 4. Habibi, Y .; Dufresne, A., Highly filled bionanocomposites from functionalized polysaccharide nanocrystals. Biomacromolecules 2008, 9, (7), 1974-1980. 5. Ljungberg, N .; Bonini, C; Bortolussi, F .; Boisson, C; Heux, L .; Cavaille, J. Y., New nanocomposite materials reinforced with cellulose whiskers in atactic polypropylene: Effect of surface and dispersion characteristics. Biomacromolecules 2005, 6, (5), 2732-2739. 6. Bhattacharya, A .; Misra, B. N., Grafting: a versatile means to modify polymers - Techniques, factors and applications. Progress in Polymer Science 2004, 29, (8), 767-814. 7. Don, T. M .; King, C. F .; Chiu, W. Y., Synthesis and properties of chitosan-modified poly (vinyl acétate). Journal of Applied Polymer Science 2002, 86, (12), 3057-3063. 8. The M.; Don, T. M .; Liu, Y. H .; Chiu, W. Y., Graft polymerization of vinyl acétate onto granular starch: Comparison on the potassium persulfate and ceric ammonium nitrate system. Journal of Applied Polymer Science 2006, 102, (3), 3017-3027. 9. Chen, F .; Cheng, Z. P .; Zhu, J .; Zhang, W .; Zhu, X. L, Synthesis of poly (vinyl acétate) with fluorescence via a combination of RAFT / MADIX and "click" chemistry. European Polymer Journal 2008, 44, (6), 1789-1795. 10. Lee, H. F .; Kuo, S. W .; Huang, C. F. Lu, J. S .; Chan, S. C; Wang, C. F .; Chang, F. C, Hydrogen-bonding interactions mediated the phase behavior of an A-B / C block copolymer / homopolymer blend comprising poly (methyl methacrylate-b-vinylpyrrolidone) and poly (vinylphenol). Macromolecules 2006, 39, (16), 5458-5465. 1 1. Kristensen, J. H .; Bampos, N .; Duer, M., Solid state C-13 CP MAS NMR study of molecular motions and interactions of urea adsorbed on cotton cellulose. Physical Chemistry Chemical Physics 2004, 6, (12), 3175-3183. 12. Kuo, S. W .; Chang, F. C, Miscibility and hydrogen bonding in blends of poly (vinylphenol-co-methyl methacrylate) with poly (ethylene oxide). Macromolecules 2001, 34, (12), 4089-4097.

Claims (1)

1. NOVELTY OF THE INVENTION CLAIMS 1. A process for producing a hydrophobic nanocomposite of nanocrystalline cellulose (NCC) and a hydrophobic polymerized vinyl monomer, comprising the polymerization of at least one hydrophobic vinyl monomer in the presence of NCC particles in an aqueous medium. 2. - The process according to claim 1, further characterized in that said aqueous medium is acidic. 3. - The process according to claim 2, further characterized in that said aqueous medium has a pH of 1 to 4. 4. - The process according to any of claims 1 to 3, further characterized in that said polymerization is carried out at room temperature (around 20 ° C) up to 90 ° C for 1 to 24 hours. 5. - The process according to claim 4, further characterized in that said polymerization is carried out at a temperature of 40 ° C to 70 ° C for 1 to 4 hours. 6. - The process according to any of claims 1 to 5, further characterized in that said polymerization is carried out in the presence of a free radical initiator. 7. - The process of compliance with any of the claims 1 to 6, further characterized in that said polymerization comprises grafting the vinyl monomer onto the NCC, and polymerizing said monomer to form a polymer extending from the NCC. 8. - The process according to any of claims 1 to 7, further characterized in that it additionally comprises, after completion of said polymerization, the extraction of the free polymer from said vinyl monomer and the recovery of the hydrophobic nanocomposite. 9. - The process according to any of claims 1 to 8, further characterized in that said hydrophobic vinyl monomer is one having a solubility in water of about 1.5 to about 3 g / 100 ml. 10. - The process according to any of claims 1 to 8, further characterized in that said vinyl monomer is selected from vinyl acetate, methyl methacrylate, methyl acrylate, ethyl acrylate and mixtures thereof. 1 1 - A nanocomposite hydrophobic nanocrystalline cellulose (NCC) and polymerized hydrophobic vinyl monomer, wherein said polymerized vinyl monomer is grafted onto said NCC. 12 -. 12 - The hydrophobic nanocomposite according to claim 1, further characterized in that said vinyl monomer is one having a solubility in water of about 1.5 to about 3 g / 100 ml. 13. - The hydrophobic nanocomposite according to claim 1, further characterized in that said vinyl monomer is selected from vinyl acetate, methyl methacrylate, methyl acrylate, ethyl acrylate and mixtures thereof. 14. The hydrophobic nanocomposite according to any of claims 11 to 13, further characterized in that said vinyl monomer is grafted to said NCC by an oxide linkage through a hydroxyl in the NCC and an open olefinic bond of the vinyl monomer. 15. - The hydrophobic nanocomposite according to any of claims 11 to 14, further characterized in that said polymerized vinyl monomer is a homopolymer. 16. - The hydrophobic nanocomposite according to any of claims 11 to 14, further characterized in that said polymerized vinyl monomer is a copolymer. 17. - A composition comprising a nanocomposite of any of claims 1 to 16, combined or mixed with a high molecular weight polymer. 18 -. 18 - The composition according to claim 17, further characterized in that said high molecular weight polymer is selected from the group consisting of polymethylmethacrylate, polyvinylacetate and polystyrene. 19. - The composition according to claim 17, further characterized in that said vinyl monomer is selected from vinyl acetate, methyl methacrylate, methyl acrylate, ethyl acrylate and mixtures thereof.