Study On The Fabrication And Properties Of Polylactic Acid/Cellulose Nanocrystals Composites

Polylactic acid?PLA?has been widely concerned owing to its good physical and chemical properties,excellent biocompatibility and biodegradability.Because of its excellent mechanical properties,it can be widely used in the fields of packaging,plastic tableware,construction and automobile,and is expected to become a substitute of traditional petroleum-based polymer.However,the large-scale commercial application of PLA is limited by its inherent disadvantages,such as low crystallization rate and poor toughness.In the process of using,the lower crystallization rate leads to the inevitable loss of mechanical properties,and the poor toughness greatly limits the use of PLA.Nanocellulose has the advantages of biodegradation,biocompatibility,good mechanical properties and low cost.It can be used as nano filler to improve the inherent shortcomings of PLA.In this paper,cellulose nanocrystals grafted with different optical properties polylactic acid segments?CNCs-PLLA and CNCs-PDLA?and cellulose nanocrystals grafted with flexible segments?CNCs-PCLLA-PDLA?were prepared by surface modification of cellulose nanocrystals.The properties of its composites were studied.CNCs-PLLA and CNCs-PDLA were prepared by melt in situ polymerization of CNCs and L-lactic acid or D-lactic acid.The nanocomposites were prepared by mixing the obtained nanocomposites with commercial PLA.The crystallization and mechanical properties of the composites were characterized by DSC,POM,XRD and tensile test.The results showed that CNCs-PLLA and CNCs-PDLA can significantly improve the crystallization rate and tensile properties of PLA.Meanwhile,the CNCs-PDLA can improve the properties of the composite more effectively.Compared with neat PLA,the crystallinity of the nanocomposites containing 10%CNCs-PDLA was increased by 86.7%under the condition of slow cooling(5°C min^-1)and 879%under the condition of rapid cooling(25°C min^-1).And the nanocomposites with 5%CNCs-PDLA exhibited both high crystallinity and improved mechanical properties.Compared with the neat PLA,the tensile strength of nanocomposites with 5%CNCs-PDLA content was apparently enhanced by 32.6%,reaching79.53 MPa and the crystallinity of the nanocomposites was improved by 72.3%under the condition of slow cooling(5°C min^-1).CNCs-PCLLA-PDLA were prepared by ring opening polymerization?ROP?of?-caprolactone,L-lactide and D-lactide on the surface of CNCs.The flexible segments composed of polycaprolactone and polylactic acid were grafted onto the surface of CNCs.Nano fillers were mixed with commercial PLA by solvent method to prepare nanocomposites.The results showed that the tensile strength of the composite with 6%CNCs-PCLLA-PDLA was equivalent to that of neat PLA,and the elongation at break has been improved significantly?85.9%?,which proved that this method can enhance the toughness of the composite without losing the tensile strength.