Fiber Surface Modification by Steam-Explosion: Sorption Studies With Co-Refined Wood and Polyolefins
Keywords:Sorption, diffusion, reactive processing, wood plastic composites (WPC), moisture
AbstractSteam-explosion was investigated as a reactive processing method to create a modified wood fiber by simultaneously co-refining wood chips and polyolefins (polyethylene and polypropylene). Sorption studies, along with infrared spectroscopy, were utilized to determine changes in physical and chemical properties to assess the degree of modification. From the isotherm sorption studies, it was found that co-steam-exploded wood fiber had reduced weight gain for the swelling region of the isotherm as compared to steam-exploded fiber without polyolefin (normalized by fiber mass). The reduction in weight gain for the co-steam-exploded samples was a function of polyolefin loading and polyolefin type. Additionally, the sorption rate of the fibers was reduced for the co-steam-exploded wood with polypropylene (in oxygen gas-deficient reaction conditions). With polyethylene, however, the rate of sorption increased for the co-steam-exploded mixtures. This phenomenon arose from an increase in the initial diffusion constant for all the materials. Although co-steam-exploded wood and polypropylene had a similar increase in diffusion constants, a difference of polyolefin interaction with wood fiber is attributed to slowing the rate of moisture penetration into the fiber for the iPP sample (in oxygen gas-deficient reaction conditions). The increase in diffusion constant for all co-steam-exploded material indicates modification within the cell wall. The proposed agents for interior cell-wall modification are oxidized polyolefin degradation products that migrate into the cell wall during processing.
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