Abstract
Poly(lactic acid) (PLA)/lignin-containing cellulose nanofibrils (L-CNFs) composite films with different lignin contents were produced bythe solution casting method. The effect of the lignin content on the mechanical, thermal, and crystallinity properties, and PLA/LCNFs interfacial adhesion wereinvestigated by tensile tests, thermogravimetric analysis, differential scanning calorimetry (DSC), dynamic mechanical analysis, Fourier transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM). The tensile strength and modulus of the PLA/9-LCNFs (9 wt % lignin LCNFs) composites are 37% and 61% higher than those of pure PLA, respectively. The glass transition temperature (Tg) decreases from 61.2 for pure PLA to 52.6 °C for the PLA/14-LCNFs (14 wt % lignin LCNFs) composite, and the composites have higher thermal stability below 380 °C than pure PLA. The DSC results indicate that the LCNFs, containing different lignin contents, act as a nucleating agent to increase the degree of crystallinity of PLA. The effect of the LCNFs lignin content on the PLA/LCNFs compatibility/adhesion was confirmed by the FTIR, SEM, and Tg results. Increasing the LCNFs lignin content increases the storage modulus of the PLA/LCNFs composites to a maximum for the PLA/9-LCNFs composite. This study shows that the lignin content has a considerable effect on the strength and flexibility of PLA/LCNFs composites.
Highlights
As a renewable bio-based polymer, poly(lactic acid) (PLA) is considered to be a promising alternative to petroleum-based plastics because of its excellent physical properties and thermal process ability [1,2]
The differential scanning calorimetry (DSC) results indicate that the lignin-containing cellulose nano-fibrils (LCNFs), containing different lignin contents, act as a nucleating agent to increase the degree of crystallinity of PLA
We reported that lignin-containing cellulose nano-fibrils (LCNFs) can be dispersed in PLA by the solvent casting technique, and the thermal, mechanical, and crystallization properties of PLA are enhanced [24]
Summary
As a renewable bio-based polymer, poly(lactic acid) (PLA) is considered to be a promising alternative to petroleum-based plastics because of its excellent physical properties and thermal process ability [1,2]. Incorporating nanoparticle fillers as a reinforcing agent has been shown to improve the physical, thermal, and crystallization properties of PLA [5]. Cellulose nanocrystals (CNCs) have attracted academic and industrial interest as a reinforcing agent for PLA composites owing to their excellent strength, biodegradability, high specific surface area, and crystallization [6,7]. The high hydrophilicity of natural CNCs is because of the large amount of hydroxyl groups on their surface, which leads to poor interfacial interactions and compatibility between CNCs and hydrophobic PLA [8,9]. The tendency to form agglomerates upon incorporation into the PLA matrix prevents realization of the full potential of CNCs as a reinforcing phase [10]
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