Enhancement of Interface between Lignocellulosic Fibers and Polypropylene Matrix via the Structure Alteration of Lignin at Elevated Temperatures.

Zhen Dong,Na Li,Bomou Ma,Chongwen Yu,Qixia Liu,Aixue Dong,Teye Chu

doi:10.3390/ma13235428

Zhen Dong, Na Li + Show 5 more

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https://doi.org/10.3390/ma13235428

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Abstract

This paper investigated the feasibility of enhancing the interface between lignocellulosic fibers and a polypropylene matrix via structure alteration of lignin at elevated temperatures. Alkali treatment can remove gum substances from lignocellulose fibers effectively at elevated temperatures but easily causes damages to fiber strength. In previous studies on directional delignification of lignocellulosic fibers, loss of fiber strength is avoided but condensation and degradation of lignin are accelerated. So far, few reports have been available on the effect of lignin structures on the interface between fibers and a matrix. In this study, jute fibers with different lignin structures are produced at 100 and 130 °C for reinforcing a polypropylene matrix. The interface between the fibers and matrix is analyzed. The result shows that decrease in aliphatic hydroxyl concentration by 9.5% at 130 °C from 3 to 5 h contributes to a 14.2% decrease in the surface energy of jute fibers. Meanwhile, the polydispersity index of lignin decreases from 1.21 to 1.15. Centralized distribution of lignin molecule-weight and reduction in fiber surface energy improves the interface between the fibers and matrix, which manifests as a 30.8% increase in the impact strength of the composites. Similar improvement is not observed in the composites reinforced with jute fibers at 100 °C, due to the absence of lignin-structure changes. This paper provides a new strategy to improve the interface between lignocellulose fibers and a hydrophobic matrix.

Highlights

Lignocellulosic fibers are widely used to reinforce polymer matrices but are limited in high performance applications due to their hydrophilic nature [1]
When treatment time exceeds 3 h, the lignin content of jute fibers at 130 C remains constant at 7.6%, 1, lignin content in both the two fibers shows a gradual decrease with time increasing from 0 to 3 h
Aliphatic hydroxyl concentration decreases by 9.5% from 3 to 5 h, which results in a 14.2% reduction in the surface energy of jute fibers

Summary

Introduction

Lignocellulosic fibers are widely used to reinforce polymer matrices but are limited in high performance applications due to their hydrophilic nature [1]. Most natural lignocellulosic fibers have moisture regain as high as 12.6% due to existence of hydrophilic gum substances. It is reported that jute fibers have 12–13 wt % of lignin, 13.6–20.4 wt % of hemicellulose and 0.2 wt % of pectin [3]. These hydrophilic substances may destroy the interface between the fibers and hydrophobic matrix, resulting in composites with limited mechanical properties.

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