Abstract
Valorization of side streams offers novel types of raw materials to complement or replace synthetic and food-based alternatives in materials science, increasing profitability and decreasing the environmental impacts of biorefineries. Lignocellulose biomass contains lignin and carbohydrates that are covalently linked into lignin-carbohydrate complexes (LCCs). In biomass fractionation processes, these complexes are conventionally considered as waste, which hinders the biomass fractionation process, and they may solubilize into aqueous effluents. This study presents how LCCs, derived from pulp mill effluent, can be turned into valuable biopolymers for industrial polymer film applications. Free-standing composite films containing hydroxyethyl cellulose (HEC) and LCCs with varying molar mass, charge density and lignin/hemicellulose ratio were prepared to study the effect of LCC amount on mechanical properties and oxygen permeability. Increasing the LCC content increased the yield point and Young’s modulus of the films. Breaking strain measurements revealed a non-linear correlation with the LCC concentration for the samples with higher lignin than hemicellulose content. The addition of LCC enhanced oxygen barrier properties of HEC films significantly even at high relative humidity. The present research demonstrates how a currently underutilized fraction of the biorefinery side stream has the potential to be valorized as a biopolymer in industrial applications, for example as a barrier film for paper and board packaging.
Highlights
Lignin-carbohydrate complexes (LCCs) are biopolymers consisting of covalently bound lignin and carbohydrate moieties
Pullulan was used for the molar mass calibration because standards made of LCCs were not commercially available and pullulan has been used for the molar mass determination of similar water soluble LCC previously (Abbadessa et al, 2018)
It should be noted that the chemical composition of pullulan differs significantly from the studied LCC, and the measured molar mass values are only estimates used for qualitative comparison of the size of the different polymers studied in this work and should not be taken as exact values
Summary
Lignin-carbohydrate complexes (LCCs) are biopolymers consisting of covalently bound lignin and carbohydrate moieties. They are formed during the biosynthesis of plant cell walls, and their function in natural systems is to enhance the mechanical strength of plants (Zhang et al, 2020). The chemical structures of LCCs vary depending on the wood source and type of the refinery process. Their chemical and physical properties are not well understood (Zhao et al, 2020). The covalent bonds between lignin and carbohydrate moieties have been studied by 1H, 13C and 2D NMR spectroscopies, and the main linkages identified are phenyl
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