All Biomass and UV Protective Composite Composed of Compatibilized Lignin and Poly (Lactic-acid)

Youngjun Kim,Hee-Won Seo,Jae-Do Nam,Kwang-Jin Kim,Youngkwan Lee,Hanna Sun,Jonghwan Suhr,In-Kyung Park,Sanghoon Kim,Soo-Hyun Kim

doi:10.1038/srep43596

Abstract

Utilization of carbon-neutral biomass became increasingly important due to a desperate need for carbon reduction in the issue of global warming in light of replacing petroleum-based materials. We used lignin, which was an abundant, low cost, and non-food based biomass, for the development of all biomass-based films and composites through reactive compatibilization with poly (lactic-acid) (PLA). Using a facile and practical route, the hydrophilic hydroxyl groups of lignin were acetylated to impose the compatibility with PLA. The solubility parameter of the pristine lignin at 26.3 (J/cm3)0.5 was altered to 20.9 (J/cm3)0.5 by acetylation allowing the good compatibility with PLA at 20.2 (J/cm3)0.5. The improved compatibility of lignin and PLA provided substantially decreased lignin domain size in composites (12.7 μm), which subsequently gave transparent and UV-protection films (visual transmittance at 76% and UV protection factor over 40). The tensile strength and elongation of the developed composite films were increased by 22% and 76%, respectively, and the biobased carbon content was confirmed as 96 ± 3%. The developed PLA/lignin composites provided 100% all-biomass contents and balanced optical and mechanical properties that could broaden its eco-friendly applications in various industries.

Highlights

Using this method, the biobased carbon content of various bioplastics can be accurately evaluated and gives somewhat surprising results
A-LIG is a bright brown dry powder due to the fact that the hydrophilic hydroxyl groups are reduced by the acetylation reaction (Fig. 1D)
The hydroxyl groups of lignin are substituted with acetyl groups, which makes the lignin hydrophobic and soluble in some organic solvents

Summary

Introduction

The biobased carbon content of various bioplastics can be accurately evaluated and gives somewhat surprising results. The UV protection materials include titanium dioxide, zinc oxide and organic UV absorbers such as phenylbenzotriazole and dibenzoylmethances[11] Incorporation of those UV-protection materials into the PLA matrix usually decreases transparency[12] and biobased content in the final products. Natural products such as green coffee oil, extracts of carica papaya, rosa kordesii, helichrysum arenarium, etc. Natural lignin tends to aggregate in polymer composites due to the π-πstacking of its aromatic rings, hydrogen bonding among hydroxyl groups, and poor compatibility with other polymers, which usually impairs the properties of the resulting lignin composites[21,22]. It desirably decreases the hydrogen-bond strength in lignin molecules and subsequently gives a decreased domain size of aggregated lignin when it is mixed with organic polymers

Methods

Results

Conclusion