Influences of Mold Fungi Colonization on Wheat Straw–Polypropylene Composites

Abstract

Abstract Wheat straw–polypropylene (PP) composites were formed by mixing compression molding to evaluate the susceptibility to mold fungi colonization. The surface morphology, water absorption, Fourier transform infrared spectroscopy (FT-IR), and color variation of the wheat straw–PP composites were investigated before and after colonization with five kinds of mold fungi (after 1, 2, 3, and 4 wk). Macromorphologic and micromorphologic observations indicated fungal colonization was not obvious during the first week, and the wheat straw was perfectly encapsulated in the PP matrix. The original cracks became small holes when the outer wheat straw at the top surface was degraded after fungal colonization for 2 weeks. Consequently, the inner wheat straw was exposed to the fungal environment, and fungal colonization increased. Similar change trends were obtained through FT-IR spectra and color-change analyses. Some characteristic peak ratios in the FT-IR spectra were calculated to investigate the relative degradation rate. Results showed that the fungi used in this study preferentially degraded hemicellulose, followed by lignin, and then cellulose. The carbonyl and lignin indices were used to illustrate the loss in wheat straw mass during the process of colonization. The carbonyl index showed good correlation with the color change. A similar conclusion was obtained for the lignin index. The correlation analyses suggest color change has a close relationship to the process of degradation in wheat straw.