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

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 ( y , 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 σ y 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.