Preparation And Properties Of Poly(lactic Acid)/Acetylated Nanocellulose Crystal Compositesm

Nowadays, exploring and using of the environment-friendly bio-degradable polymer has attracted increasing attention with the aggravation of energy shortage and white pollution. Poly lactic acid (PLA) is nontoxic, bioabsorbable and biocompatible, it has a great potential to replace petroleum-based plastics. However, the product of PLA that acts as current polymer was little because a slow crystallization, brittleness, and low heat resistance limited the wider application of PLA.Natural cellulose is the most abundant biomass resources in nature, and is the most popular biological macromolecular. Nanocrystalline cellulose extracted from natual fiber is nanoscale cellulose, which not only has the features of nanoparticals, but also has some unique strength, which makes it pospective in the industry,In this thesis, the surface morphology and properties of nanocellulose crystal(NCC) extracted from degreasing cotton, microcrystalline cellulose(MCC) Vivapur101and MCC pH101by sulfuric acid hydrolysis were investigated. The results showed that when temperature, time and the ratio of MCC to sulfuric acid were60℃,1h,1/50, respectively. NCC was determined to have diameters in the range of10～20nm and lengths of50～100nm, and the yield of NCC would reach43.7%. The thermalstability of NCC was lower than MCC, but the crystal structure and chemical structure were reserved.Acetylation of NCC by using acetic anhydride was performed in two types of ionic liquids of1-allyl-3-methylimidazolium chloride and l-butyl-3-methylimidazolium tetrafluoroborate, respectively. And the effects of temperature, time and the ratio of NCC to acetic anhydride on the substitution degree and acetyl content of NCC were also studied. The results demonstrated that when temperature, time and the ratio of NCC to acetic anhydride were80℃,2h,7:1, the substitution degree and acetyl content would reach1.12and23.03%, repectively. When1-allyl-3-methylimidazolium chloride was as solvent media, morphology and crystal structure of modified NCC were changed greatly due to its solubility. However, the crystal structure of modified NCC was maintained and crystallinity decreased with increasing the substitution degree when in1-butyl-3-methylimidazolium tetrafluoroborate as solvent media.Nanocomposites of PLA/Modified NCC were prepared by the solution casting method. From SEM images, it can be observed that modified NCC could be dispersed well in PLA. DSC resuits showed that in the non-isothermal crystallization experiment modified NCC was the effective nucleating agent, the addition of it promoted the cold crystallization of PLA/Modified NCC composites and the crystallinity of PLA was increased; and isothermal tests indicated that the multiple melting behaviors of composites became unobvious with increasing the content of modified NCC. Moreover, the higher the crystallization temperature, the more evident the effects of the content of modified NCC on the multiple melting behaviors of composites were. TGA analysis indicated that the composite films filled with modified NCC exhibited improved thermostability as compared to the pure PLA film. The absorption and hydroxylation properties of nanocomposites were also studied. The results showed that as the time increased, they all decreased, and gradually reached a plateau.