Crystallization Behavior And Controllable Performance Of Poly(Lactic Acid)/Nanocellulose Whiskers Composites

Exploring and using of the environmentally friendly, abundant in source, and non-petroleum-based polymers is very urgent with the growing environmental awareness and the worry about the exhausted the petroleum resources. In this work,bionanocomposites of Poly lactic acid(PLA)/ nanocellulose crystal(NCC) were prepared, and the effects of contents and the degree of substitution(DS) of NCC on thermostability, mechanical properties, and degradation behaior of nanocomposites were investigated, which can provide the experiment data for controlling the properties of nanocomposites.Nanocellulose crystal(NCC) with different sizes were extracted from microcrystalline cellulose(MCC) Vivapur 101 by sulfuric acid hydrolysis. And modification of NCC by using acetic anhydride was performed in ionic liquids of1-butyl-3-methylimidazolium tetrafluoroborate. And NCC with different DS were obtained, which proved the feasibility of this green modification method. Effects of content and DS of NCC on the thermostability of PLA/ NCC nanocomposites were performed by thermogravimetric analysis(TGA). It is found that the thermostability of the nanocomposites is lower than that of PLA. But with the modified NCC content increasing, the thermostability of the nanocomposites first increased then decreased.DS of NCC has almost no significant effect on the thermostability of PLA/NCC composites. The thermostability of nanocomposites with lower content of modified NCC can be improved by annealing. However, the thermostability for the nanocomposites containing NCC with different DS changed a little after annealing.The results for mechanical testing showed that the tensile strength and Young’s modulus of PLA can be enhanced in a certain extent after adding the modified NCC.Generally speaking, with content of modified NCC increasing the tensile strength of the PLA/NCC(DS=2.45) nanocomposites first increased then decreased. And the Young’s modulus of the nanocomposites with different compositions are all higher than that of PLA. However, the elongation at break of the nanocomposites decreased with the increasing modified NCC. The tensile strength and Young’s modulus of thenanocomposites containing the NCC with modification are higher than that of the nanocomposites containing the NCC without modification. But the elongation at break for the two has almost no difference.The results for PLA/NCC(DS=2.45) nanocomposites after degradation indicated that the degradation rate sped up with conten of modified NCC increasing. The degradation rate of the nanocomposites containing the NCC with modification are obviously lower than that of the nanocomposites containing the NCC without modification. Before degradation, the crystallinity for the nanocomposites increased with increasing the DS of NCC, which indicated that the modified NCC promoted the crystallization of the nanocomposites as a nucleation agent. The crystallinity for the nanocomposites with different modified NCC content has no obvious difference before degradation. The crystallinity for the nanocomposites first increased then decresed with increasing degradation time during degradation. The results of SEM revealed that spherulites, lamellae and holes and pits in the film were observed in ture during degradation. Moreover, the degradation morphology can reflect the degradation rate of the nanocomposites in a certain extent.The above results show that the properties for the PLA/NCC nanocomposites such as the mechanical properties and degradation rate can be controlled in a certain extent by changing the content and DS of NCC.