Abstract
Post-harvest crop residues are an interesting raw material for the production of composite materials. However, their surface often contains waxy and siliceous substances, which can cause adhesion problems. Therefore, various surface pre-treatment methods have been developed to increase the surface tension of these particles and hence to improve adhesive adhesion. The influence of hydrothermal, chemical, plasma and enzymatic treatment was investigated. The aim of the paper is to evaluate the effect of pre-treatments of post-harvest crop residues on the nature of joint failure and adhesive dispersion on the particles. The evaluation is based on microscopic analysis of particles obtained from the rupture area after internal bonding tests. The nature of bond failure and adhesive dispersion on the particle surface is evaluated. The results show a clear influence of material pre-treatment on the failure bond of the bond and, to a large extent, correlate with the mechanical properties of composites published in previous studies. The most suitable treatment appears to be a plasma treatment at a properly adjusted intensity. Conversely, the unsuitable treatment was alkaline, which, although it increased adhesion, deteriorated the overall mechanical properties. Hydrothermal treatment could be also considered as an industrially suitable method.
Highlights
Composites made of natural materials have many advantages over composites based on glass, carbon, polypropylene and other synthetic fibers
The results revealed that proteins and lignin released at elevated temperature and pressure were beneficial in forming new covalent bonds and showed better performance at higher temperatures
It showed that a thermal extract from wheat straw can be used as an adhesive
Summary
Composites made of natural materials have many advantages over composites based on glass, carbon, polypropylene and other synthetic fibers. The results showed that mould growth significantly influenced the weight loss of dry matter (about 15% for 100% hemp and 30% for 100% flax mat) and a decrease in tensile modulus of the tested natural fiber non-wovens and composites (about 33% for hemp-based composites and 43% for flax-based composites). The effect depended both on the type and length of the fibers and on the exposure and time conditions [6]. This article further summarizes the comprehensive results from previous research and observes the developed materials from the microstructure perspective
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