The utilization of bamboo charcoal enhances wood plastic composites with excellent mechanical and thermal properties

Highlights

• Bamboo charcoal (BC) was used as reinforcing filler of wood-plastic composites.

• BC could have strong interfacial interaction in the wood-plastic composites (WPCs).

• The BC-WPC composites displayed lower water absorption properties.

• The BC-WPC composites displayed higher flexural, tensile and thermal properties.

Abstract

In order to enhance the mechanical properties and thermal properties of wood plastic composites (WPCs), bamboo charcoal (BC) was used as reinforcing filler of WPC, and a series of BC-WPC composites were prepared. The effect of BC and water treatment on water absorptions, morphologies, mechanical properties, the effect of water treatment on mechanical properties and thermal properties of the composites were investigated. The results showed that BC could have strong interfacial interaction in the WPC. The water resistance, flexural properties, tensile properties and thermal properties of BC-WPC were higher than WPC. The flexural and tensile properties were reduced and the impact strength was increased after water treatment. The presence of BC resists the influence of water absorption on composites mechanical properties.

Introduction

Wood has played a vital role in the social, economic and environmental development of human history. However, increasing demand for the limited forest resources in various applications has led to the shortage in wood supply. Thus, there is an urgent need to look for new materials as alternatives or substitutes of wood [1]. Among them, wood plastic composites (WPCs), manufactured products composed of woody materials and thermosetting/thermoplastic resins, are the potential materials since they are low-cost, biodegradable, renewable, and eco friendly [2], [3], [4]. WPC are initially used for decking and non-structural building applications, but now they have been extensively developed for a wider range of applications, including buildings and constructions, automotives and gardening and outdoor products. However, one of the lethal weaknesses of WPC is their poor mechanical properties, due to the weak interface between wood flour and polymer matrix [5], [6], [7], [8]. On the other hand, wood flour (WF), one of the components of WPC, contains cellulose, hemicellulose and lignin, in which the hydroxyl groups build a large amount of hydrogen bonds between the macromolecules of the wood polymers [9]. The hydroxyl groups could form new hydrogen bonds with water molecules, which induce the water absorption, fiber swelling and creation of micro-cracks in the sample, resulting in debonding fibers and degradation of interface of fiber-matrix.

In order to improve the mechanical properties and water resistant of WPC, various approaches have been carried out. Some of them are concentrated on processing the WF, such as acetylation [10], silane treatment [11], heat treatment [7], and treatment with sodium hydroxide [12]. Besides, the incorporation of nanoparticles as reinforcing filler is another method for improving the overall properties of lignocellulosic-thermoplastic composites, such as silica nanopowder [8] and montmorillonite [13]. However, these methods have their own weaknesses, such as complicated processing processes and easy aggregation of nanoparticles which caused poor dispersion in polymer matrix and limited increase in overall properties of composites.

Bamboo charcoal (BC) can be produced from the widespread fast-growing speed and short growth period moso bamboo plants in China. The bamboo and bamboo residues can be transformed to BC at a high temperature under nitrogen atmosphere, which is a mature technology used in China [14]. In recent years, BC has attached great attention in many fields, such as supplier of negative ions, warming effect of far infrared rays, water purifying power of microbes, humidity regulator, oxidization prevention, and a rich source of minerals [15], [16], [17]. BC has countless small holes lengthwise and crosswise. The number of holes, mineral constituent and absorption efficiency of BC are about 5 times, 8 times and 10 times as many as those of wood charcoal [18]. A good deal of holes in BC might be able to stronger interface between filler and polymer matrix, because polymer chains could get into these holes when the polymer has good liquidity. Up to now, no published reports are available regarding the effect of BC on the mechanical properties, water resistant and thermal properties of WPC.

BC powder contains many pores and gaps in its structure and low-density polyethylene (LDPE) have good liquidity. Therefore, incorporation of BC with LDPE would lead to a better interfacial adhesion between matrix and filler. The objective of this research was to investigate the effects of BC on water absorption, thermal properties and mechanical properties of WPC, and the effects of water absorption on mechanical properties of bamboo charcoal-wood plastic composites (BC-WPC).