Study On The Interface Regulation And Properties Of Polylactide /Cellulose Nanocrystal Composites

Adding modified cellulose nanocrystals(CNC)to poly(L-lactide)(PLLA)is an important method to improve the performance of PLA.The low thermal stability of the CNCand its poor interfacial interaction with the matrix PLA are the key factors affecting the PLA nanocomposites.We explored the improvement methods from the two aspects of the surface chemical structure and interfacial stereocomplex(sc-PLA).We hydrolyzing cotton linters to prepare CNC.The preparation and properties of surface grafted CNC(CNC-g),the mechanism of the thermal stability of CNC-g,construction of sc-PLA and its effect on thermal properties and crystallization properties of composites,the effect of different interface on the rheological properties and aggregate structure of composites were investigated.In order to investigate the effect of ionic groups and PLA grafting on the thermal stability of CNC,we prepared the sulfonated CNC(SCNC)and phosphorylated CNC(PCNC)by sulfuric acid and phosphoric acid hydrolysis of cotton linters.And the,adjusting the mass ratio of D-lactide(DLA)to CNC to prepare the modified CNC(CNC-g)with different grafting density.It is found that the surface ionic groups of SCNC-g and PCNC-g were removed with the increase of grafting density;the crystal structure of CNC-g changes with the difference of ionic groups;the thermal stability of PCNC-g were increased with the increased grafting density,while that of SCNC-g showed the opposite change.PCNC-g and SCNC-g with similar grafting content were added to poly(L-lactide)(PLLA)to prepare composites,and the effects of sc-PLA on the crystallization and thermal properties of the composites were investigated.Studies have shown that SCNCg with large surface graft segment length has the ability to form sc-PLA,PCNC-g with small surface graft segment length cannot form sc-PLA;initial thermal degradation of PLLA/SCNC-g composite The temperature is about 30 °C higher than PLLA/PCNC-g;the relative crystallinity of the high-filled PLLA/SCNC-g sample is about twice as high as the high-filled PLLA/PCNC-g,and the former has a half-crystallization time of about half of the latter.We added surface-grafted poly(L-lactide)and poly(D-lactide)filler particles(CNCg-PLLA and CNC-g-PDLA)to PLLA to prepare composite materials,and studied the difference in interface effects on the rheological properties and aggregate structure of composites.Impact.Studies have shown that the crystallization performance of the sample with CNC-g-PDLA is worse than that of the sample with CNC-g-PLLA;the storage modulus,loss modulus and complex viscosity of the sample added with CNCg-PDLA are higher than those of CNC-g-PLLA.