Flax fibres modified with a natural plant agent used as a reinforcement for the polylactide-based biocomposites

Abstract

The purpose of this study was to create "green" biocomposite consisting of natural components which will exhibit biocidal properties against microorganisms and would have positive effect on mechanical properties. The authors assumed that the application of natural plant compound will reduce the hydrophilicity of natural fibres. Polylactide (PLA) biocomposites containing flax (Linum usitatissimum) fibres (20 wt%) were prepared by extrusion and injection molding processes. The samples containing fibres modified with the tannic acid (TA) used as biocidal and crosslinking agent as well as the control samples (with non-modified fibres) were prepared. The TA-treatment effects on the mechanical and structural properties of the biocomposites were studied using dynamic mechanical analysis (DMA) and tensile tests, differential scanning calorimetry (DSC), and thermogravimetry (TG). The flax fibres and biocomposites were examined with scanning electron microscopy (SEM): the analysis of samples fractures was performed in order to evaluate the influence of TA modification on interfacial adhesion properties. We investigated the biocidal and wettability properties of the materials. Application of the TA-modified fibres led to the deterioration of mechanical properties. TA decreased interphase adhesion and led to plasticization of PLA phase in the biocomposite. The migration of TA into PLA matrix caused its volume plasticization which lowered stiffness of the biocomposites with modified fibres. According to the thermal studies, the higher degradation temperature (Td = 352.72 ºC) of materials containing modified fibres has been noted. Moreover, the hydrophobic (Θw = 91.82) and biocidal (against Escherichia coli and Staphylococcus aureus) properties of the TA-treated biocomposites have been observed. The modification of the biocomposites plant reinforcements with a natural agent is an eco-friendly method that allows to change its properties in a safe way. However, it should be conducted with caution and consideration of the intended use of the finished material.