Cellulose Nanoparticles-Reinforced Optically Transparent Polymer Composite Materials

Cellulose nanoparticles (CNP) have been widely used in various fields as a new type of nanomaterials due to its high transparency, high purity, high crystallinity, high strength and high young’s modulus. The addition of CNP as reinforced material into the natural transparent polymer matrix not only can effectively improve the strength, crystallinity and thermal properties of the material, but also can keep the transparency of the material. Researches about CNP as reinforced material at domestic and abroad have obtained many achievements. However, the researches on optical transparent polymer matrix reinforced by CNP is still in initial stage at present. In addition, how to obtain the cellulose nanoparticles-reinforced composites has not been solved yet.CNP were prepared from microcrystalline cellulose using two concentration levels of sulfuric acid (i.e.,48wt%and64wt%) followed by high-pressure homogenization in this paper. The produced CNP was designated as CNP-48and CNP-64, respectively. Polymethylmethacrylate (PMMA) composites reinforced with CNP-48and CNP-64were prepared through solvent exchange and solution casting. The aim of this study are to investigate the effects of acid concentration and CNP amount on CNP/PMMA composites. The properties of CNP and CNP/PMMA composites were analysis by transmission electron microscopy, wide-angle X-ray diffraction analysis, differential scanning calorimetry analysis and so on.The main results are as following:(1)Effects of CNP on the transparency of the composites:the results showed that the acid concentration had little effects on the chemical structure of CNP, but it affect the particle size of CNP, the size of CNP-64are smaller than that of CNP-48.The CNP/PMMA suspension containing20wt%CNP showed good optical transparency. The transparency of CNP/PMMA composites reduced with the increase of the addition of CNP. CNP/PMMA-64showed higher optical transparency than CNP/PMMA-48; when the addition of CNP was same.(2) Effects on the crystallinity of composites; the results showed that the crystallinity of composites increases gradually with the increase of CNP, and the crystallinity of CNP/PMMA-48containing15wt%and20wt%CNP-48increased to20.8%and20.8%respectively, of CNP-48adding amount of CNP/PMMA treated increased to20.8and20.8respectively, indicating significant reinforcement from CNP.(3) Effects on the heat-resisting properties of composites, the results showed that the glass transition temperatures and the maximum melting temperature of two composites increase with the addition of CNP. The glass transition temperatures of CNP/PMMA-48and CNP/PMMA-64containing20wt%CNP-48and CNP-64increase10℃and20℃respectively. The maximum melting temperature of two kinds of composites increase approximately40℃.In this study, the thermal stability of composites is best when the level of CNP is20%is best.(4) Effects on the thermal expansion properties of composites, the results indicatedthat when compared with the pure PMMA the coefficient of thermal expansion (CTE) of CNP/PMMA-48and CNP/PMMA-64containing10%wt CNP reduce by5.5×10-5and3.9×10-5/℃respectively. The CTE of CNP/PMMA-64was slightly lower than that of CNP/PMMA-48. The addition of CNP significantly reduced the CTE of the two composites.(5) Effects on the mechanical properties of composites, the results showed that the mechanical properties of composites enhance strongely at high temperature with the addition of CNP. CNP/PMMA-64have a higher storage modulus than CNP/PMMA-48, especially when the loading level of CNP is very high. The static young’s modulus and tensile strength of the two composites were higher than pure PMMA. The tensile properties of pomposities increased with the addition of CNP. The effects of CNP on young’s modulus of composites is more obvious than the tensile strength.