Sheet-Like Lignin Particles as Multifunctional Fillers in Polypropylene
journal contributionposted on 26.07.2016 by Fenggui Chen, Wanshuang Liu, Seyed Ismail Seyed Shahabadi, Jianwei Xu, Xuehong Lu
Any type of content formally published in an academic journal, usually following a peer-review process.
Lignin is an attractive renewable reinforcing agent for polyolefins and also a promising low-cost antioxidant for polymers. It, however, exhibits poor compatibility with nonpolar polymers. In this work, alkali lignin was freeze-dried to achieve sheet-like morphology and then incorporated into polypropylene (PP) by melt compounding. Owing to the significantly increased interfacial area and improved dispersion, with the addition of only 2 wt % freeze-dried lignin, the PP/lignin composites show much enhanced tensile mechanical properties, including a moderately improved Young’s modulus and almost doubled elongation at break compared with those of neat PP. The enhancements brought by the sheet-like lignin are far more impressive than those achieved with the same amount of as-received lignin. The composites with the freeze-dried lignin also have rough fractured surfaces with fiber pull-out near the interface, revealing a significant toughening effect of the lignin, which can be attributed to the crazing near the interface, and enhanced relaxation in PP-lignin interphase as evidenced by the reduced Tg. Furthermore, the large interfacial area also drastically improves the antioxidant effect of lignin, greatly slowing the UV-induced and thermo-oxidative degradation of PP. After 2 weeks of intense UV exposure, neat PP becomes very brittle with its yield strain reduced to about 37% of its original value, whereas the yield strain of the composite with 2 wt % sheet-like lignin is almost unchanged, demonstrating the excellent free-radical scavenger effect of the lignin.