Study on phase transition behavior and lamellar orientation of uniaxially stretched poly(L-lactide) / cellulose nanocrystal-graft-poly(D-lactide) blend

摘要

Towards the development of high-performance green composites, the surface functionalized cellulose nanocrystals (CNC) have been widely used as reinforcement along with biopolymer. In our previous work, it has been demonstrated that CNC grafted with PDLA (CNC-g-PDLA) could improve the crystal nucleation density and heat distraction ability of PLLA matrix via the PLLA/PDLA stereocomplex interaction. Herein, to understand the role of CNC-g-PDLA on the deformation behavior of PLLA/CNC-g-PDLA nanocomposites, the melt-quenched PLLA/CNC-g-PDLA nanocomposite was uniaxially stretched at 160 degrees C with various draw ratios. The stretched PLLA/CNC-g-PDLA composites allow us to discriminate the crystal transformation and crystal orientation of three individual components in the composites, that is, (i) PLLA matrix, (ii) PLLA/PDLA stereocomplex existed as interfacial phase, and (iii) CNC reinforcement. The results indicate that PLLA alpha' and PLLA/PDLA stereocomplex crystals ((3c) appear at the initial stage of drawing process. The disordered alpha' transforms to ordered alpha and beta forms gradually with increasing in draw ratio, whereas beta(c)-crystals keep almost unchanged during the whole drawing process. The calculation on orientation function of various crystals suggests that the lamellaes of alpha form have the largest orientation degree along the stretching axis. Meanwhile,CNC nanoparticles and the beta(c) crystals form the nano-dimensional shish kebab structure during stretching and present relatively low orientation. This study provides the physical insight to guide the preparation of high performance PLLA nanocomposites with hierarchical crystal and orientation structure. (C) 2018 Elsevier Ltd. All rights reserved.