Synthesis Mechanism of an Environment-Friendly Sodium Lignosulfonate/Chitosan Medium-Density Fiberboard Adhesive and Response of Bonding Performance to Synthesis Mechanism.

Xiaodi Ji,Li Zhu,Minghui Guo,Wenxin Du,Hongbin Wang

doi:10.3390/ma13245697

Abstract

Environment-friendly medium-density fiberboards (MDFs) prepared using sodium lignosulfonate/chitosan adhesives (L/C) show potential in environment-friendly wood-based panel application. However, the synthesis mechanism of this adhesive and the relationships between synthesis mechanism and bonding performance were not discussed in depth. Herein, the synthesis mechanism of L/C was explored in detail based on characterizations of L/C with different mass ratios of sodium lignosulfonate to chitosan by Fourier-transform infrared spectroscopy, thermogravimetric analysis, and X-ray diffraction. For L/C with different mass ratios of sodium lignosulfonate to chitosan, the corresponding bonding performance was also determined based on characterizations of mechanical and dimensional performance of MDFs. Results showed a 3D network structure of L/C formed through the hydrogen linkages among hydroxyl groups in sodium lignosulfonate and hydroxyl and amino groups in chitosan, amide linkages resulted from reaction between carbonyl groups in sodium lignosulfonate and amino groups in chitosan, and sulfonamide linkages originated from reaction between sulfonic groups in sodium lignosulfonate and amino groups in chitosan. The mechanical performance of MDF was closely related to the 3D network and amino groups of L/C, while the dimensional performance of MDF was negatively affected by sodium lignosulfonate. The MDFs with 1:3 and 1:2 mass ratios of sodium lignosulfonate to chitosan showed superior mechanical properties and comparable dimensional performance with a commercial panel.

Highlights

Traditional medium-density fiberboards (MDFs) on the market are prepared mainly using formaldehyde-containing adhesives, which causes harm to humans and the environment and further hinders the high-end applications of MDF [1]
Polymeric network formed in because of hydrogen linkages among hydroxyl groups in sodium polymeric network formed in lignosulfonate/chitosan adhesives (L/C) because of hydrogen linkages among hydroxyl groups in sodium lignosulfonate and hydroxyl and amino groups in chitosan, amide linkages resulted from reaction lignosulfonate and hydroxyl and amino groups in chitosan, amide linkages resulted from reaction between carbonyl groups in sodium lignosulfonate and amino groups in chitosan, and sulfonamide linkages originated from reaction between sulfonic groups in sodium lignosulfonate and amino groups in chitosan
The mechanical performance of MDFs was closely related to the 3D network and remaining amino groups, while the addition of sodium lignosulfonate negatively affected the dimensional property of MDFs

Summary

Introduction

Traditional medium-density fiberboards (MDFs) on the market are prepared mainly using formaldehyde-containing adhesives, which causes harm to humans and the environment and further hinders the high-end applications of MDF [1]. These formaldehyde-containing adhesives are made synthetically from non-renewable and non-replenishable petrochemical resources. With the depletion of petrochemical resources, the deterioration of raw materials for synthetic resin has been becoming an issue of concern In contrast to these synthetic adhesives, biopolymer-based MDF adhesives, such as soy protein [2], wheat protein, [3] and starch [4], have gained more attention in Materials 2020, 13, 5697; doi:10.3390/ma13245697 www.mdpi.com/journal/materials. Chitosan has been recognized world-wide as a potential biopolymer-based wood adhesive, because of its non-toxicity and renewability, which is of great interest to both industries and consumers [6]

Methods

Results

Conclusion