writer：Hou-Yong Yu, Heng Zhang, Mei-Li Song, Ying Zhou, Juming Yao, and Qing-Qing Ni
keywords：cellulose nanospheres， cellulose nanocrystals， cellulose nanofibers， 15 polylactic acid nanocomposites， nucleation effect，reinforcing effect
source：期刊
Issue time：2017年
The traditional approach toward improving crystallization rate, mechanical and barrier property of poly(lactic acid) (PLA) is the incorporation of nanocelluloses (NCs). Unfortunately, little study was focused on the influence of differences in NC morphology and dimension on the PLA property enhancement. Here we unveil the preparation of cellulose nanospheres (CNS), rod-like cellulose nanocrystals (CNC), and cellulose nanofibers (CNF) with different aspect ratios by HCOOH/HCl hydrolysis of lyocell fibers, microcrystalline cellulose (MCC) and ginger fibers, respectively. All the NC surfaces were chemically modified by Fischer esterification with hydrophobic formate groups to improve the NC dispersion in PLA matrix. This study systematically compared CNS, CNC, and CNF as reinforcing agents to induce different heterogeneous nucleation and reinforcing effects on the properties of PLA. The incorporation of three NCs can greatly improve PLA crystallization ability, thermal stability and mechanical strength of nanocomposites. At the same NC loading level, the PLA/CNS showed the highest crystallinity (19.8 ± 0.4 %) with smaller spherulite size (33 ± 1.5 μm), indicating CNS with the high specific surface area can induce stronger heterogeneous nucleation effect on the PLA crystallization than CNC and CNF. Instead, compared to PLA, the PLA/CNF nanocomposites gave the largest Young’s modulus increase of 350 %, due to the larger aspect ratio/rigidity of CNF and their interlocking or percolation network caused by filler-matrix interfacial bonds. Furthermore, taking these factors of hydrogen bonding interaction, increased crystallinity and interfacial tortuosity into accounts, the PLA/CNC nanocomposite films showed the best barrier property against water vapor and lowest migration levels in two liquid food simulates (well below 60 mg kg-1 for required overall migration in packaging) than CNS and CNF based films. This comparative study was very beneficial for selecting reasonable nanocelluloses as nucleation/reinforcing agents in robust-barrier packaging biomaterials with outstanding mechanical and thermal performances.