Preparation and characterization of coffee hull fiber for reinforcing application in thermoplastic composites

Nowadays, there is an increasing concern toward substituting the scarce wood fibers with alternative lignocellulosic fibers that originate from crop residue to reinforce biocomposites. In this paper, the potential application of coffee hull (CH) of the reinforced polyethylene (PE) matrix composites was studied for the first time. Experiments of composite that enhanced with CH on mechanical properties, hydroscopicity, thermogravimetric analysis, fiber treatment, and microstructures were tested in this study. The PE matrix was reinforced with varying volume fractions of CH and was studied. The results show that incorporation of coffee hull markedly improved the mechanical properties of the reinforced high-density polyethylene (HDPE) matrix composites. Micrographs show a strong interfacial adhesion between the CH fiber particles. This property may be the main reason for the stability between composites. At the same time this work investigated the effect of different treatments on the mechanical properties and water absorption behavior of composites. The fiber surface treatments were done using active chemicals such as calcium hydroxide (Ca(OH)₂), silane coupling agent (SCA), maleic anhydride grafted polypropylene (MA-g-PP), stearic acid (SA), ethylene bis stearamide (EBS) and the combination (MA-g-PP, SA, EBS). The results show that (Ca(OH)₂)treatment is the best way to improve its properties. Probably because attributed to removal of surface active functional groups (-OH) from the CH fiber and induction of hydrophobicity that in turn improved the compatibility with the polymer matrix. As a result, the use of coffee hull in composites could have great significance for the industry.