Polypropylene Composites Filled with Steam-Exploded Wood Fibers from Beetle-Killed Loblolly Pine by Compression-Molding

Suzhou Yin, Siqun Wang, Timothy G. Rials, Kevin M. Kit, Marion G. Hansen


Beetle-killed loblolly pine chips were steam-exploded (SE) with a severity factor of 4.8 in a batch reactor into a fibrous mass followed by a sieve step to remove oversize pieces (>16 mesh). The sieved SE fibers (<16 mesh) contained 5%-10% water-soluble materials and were mainly composed of fiber fragments with lignin droplets on their surfaces. Composites were prepared by firstly compounding sieved SE fibers and polypropylene (PP) with or without maleic anhydride grafted polypropylene (MAPP) as a compatibilizer, and then by compression-molding the mixtures at 195°C. The MOE of the composites increased greatly, and the yield stress σy, was decreased slightly by inclusion of 50% SE fibers with no compatibilizer. Addition of 2.5% MAPP improved significantly the flexural properties of the composites, especially the σy which was eventually superior to that of neat PP. DMA and DSC measurements revealed that the SE fibers increased the crystallinity of PP by forming more crystalline fractions around wood fibers or fiber fragments. Addition of MAPP resulted in a reduction in the damping and an increase in the heat of fusion of the PP in the composites, suggesting a stronger interface between the matrix and SE fibers. The better interfacial adhesion was also demonstrated by SEM observations showing fiber breakage occurring on the fractured surfaces of the PP composites with MAPP as a compatibilizer.


Beetle-killed pine;steam explosion;polypropylene composite;compatibilizer;flexural properties

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