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

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.

High-Quality Natural Fibers from Cotton Stalk Bark via Limited Alkali Penetration and Simultaneous Accelerated Temperature Rise

“…Moreover, the intramolecular and intermolecular ether bonds are not easily broken under mild conditions [15]. Therefore, only small amounts of lignin in the lignocellulosic fibers can be dissolved at 100 • C or lower temperatures [16]. As the temperature increases to 150 • C or higher, the lignin macromolecules are degraded efficiently.…”

Determination of the lignin content of flax fiber with the acetyl bromide-ultraviolet visible spectrophotometry method

“…Jonasson et al 20 studied the effect of different lignin contents on the oxidative nanofibrillation of wood cell walls and found that wood with high lignin content was more easily fibrillated than wood with low lignin content. Dong et al 21 showed that the changes of lignin in lignocellulosic fibers would definitely affect adhesion between fibers and polymer matrix. Therefore, a quick and accurate method for lignin content testing of flax fiber is of great importance.…”

“…Dong et al. 21 showed that the changes of lignin in lignocellulosic fibers would definitely affect adhesion between fibers and polymer matrix. Therefore, a quick and accurate method for lignin content testing of flax fiber is of great importance.…”