Abstract
In this study, the effect of lignin esterification with fatty acid chloride on the properties of lignin and lignin/poly(lactic acid) (PLA) composites was investigated. Lignocellulose (Pinus densiflora S. et Z.) was treated using a deep eutectic solvent (DES) with choline chloride (ChCl)/lactic acid (LA). From the DES-soluble fraction, DES-lignin (DL) was isolated by a regeneration process. Lignin esterification was conducted with palmitoyl chloride (PC). As the PC loading increased for DL esterification, the Mw of esterified DL (EDL) was increased, and the glass transition temperature (Tg) was decreased. In DL or EDL/PLA composite films, it was observed that EDL/PLA had cleaner and smoother morphological characteristics than DL/PLA. The addition of DL or EDL in a PLA matrix resulted in a deterioration of tensile properties as compared with neat PLA. The EDL/PLA composite film had a higher tensile strength and elastic modulus than the DL/PLA composite film. DL esterification decreased water absorption with lower water diffusion coefficients. The effect of lignin esterification on improving the compatibility of lignin and PLA was demonstrated. These results are expected to contribute to the development of high-strength lignin composites.
Highlights
Lignin is the most abundant aromatic biopolymer on earth and accounts for 20–40% of lignocellulose
Lignin is mainly produced from black liquor, which is a by-product of the pulping process through a regeneration process by precipitation [8]
Lignocellulose (Pinus densiflora S. et Z.) with a lignin content of 31.4% was used as the raw material for lignin isolation
Summary
Lignin is the most abundant aromatic biopolymer on earth and accounts for 20–40% of lignocellulose It consists of three basic structural phenylpropane units: p-coumaryl alcohol, coniferyl alcohol, and sinapyl alcohol [1,2]. Phenylpropane units are randomly cross-linked by linkages of β-O-4, β-5, β-β, and others [1,2] It has some advantages including biodegradability, biocompatibility, nontoxicity, low density, high carbon content, thermal resistance and oxidation resistance [1,2,3]. During the regeneration of lignin, the depolymerized lignin fragments are recondensed [9,10], which can lead to the formation of recalcitrant condensed units and structural heterogeneity [11] These heterogeneous structures and characteristics can limit its potential for further application in bioplastics
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