The scope of the present paper is to study the effect of adding a novel coupling agent, polybutadiene isocyanate (PBNCO), on the mechanical properties of hardwood aspen fiber/polypropylene (PP) composites. The resulting properties were compared to those obtained with the most commonly used coupling agent, maleic anhydride modified polypropylene (MAPP). In this study, we determined a value of 24.75 MPa for the tensile strength of pure PP and 22 MPa for the composite containing 30 or 40wt% unmodified fibers. These results indicate that wood fiber behaves merely as filler when incorporated into PP and no reinforcing effect was observed in this case. This occurs because of the chemical incompatibility between the thermoplastic PP and the polar fiber, resulting in low interfacial adhesion. However, it was verified that addition of 3% MAPP and 5% PBNCO to this formulation produced composites with better performance, since the tensile and impact properties were increased up to 30 MPa and 22 J/m2, respectively. This behavior can be attributed to the enhanced interfacial bond between reinforcing fibers and polymer matrix modified MAPP and PBNCO treatments, play a significant role in improving the mechanical properties of the composites. The increase in mechanical properties demonstrated that PBNCO is an effective coupling agent for wood fiber/PP composites.
Fracto-emission is the emission of particles (e.g., electrons, ions, ground state and excited neutrals, and photons) during and following fracture. We have found that during fracture in vacuum of adhesive bonds and crystalline materials involving large amounts of charge separation on the surface the emission of charged particles, excited neutrals, light, and radio waves occurs with unique and revealing time dependencies. In this paper we report simultaneous fractoemission measurements on several systems. We interpret the results in terms of a conceptual model involving the following steps: (1) charge separation due to fracture, (2) desorption of gases from the material into the crack tip, (3) a gas discharge in the crack, (4) energetic bombardment of the freshly created crack walls, and (5) thermally stimulated electron emission, accompanied by electron stimulated desorption of ions and excited neutrals. In addition to evidence from fracture experiments, we present results from studies of electron bombardment of a polymer surface.
The goal of this study was to investigate the use of old newsprint (ONP) fiber as raw material for laboratory made medium density fiberboard (MDF). Effect of ONP fiber mixed with virgin aspen (Populus deltoides) fiber and the press time (3, 4, and 5 min) on the properties of MDF panels were determined. Panels were produced using aspen fibers in surface layer and combination of aspen fibers and ONP fibers in core layer. Physical (thickness swelling) and mechanical properties of the panels were determined according to the procedure of EN standards. This study showed reduction in bending strength and internal bond strength of the panels as ONP fiber was loaded from 35 to 70% in core layer. Thickness swelling of MDF panels was drastically increased with addition of ONP fiber to the panels' furnishes. Based on the findings of this study, it appears that ONP can be considered as a potentially suitable raw material for manufacturing MDF products without having any significant adverse influence on the panel properties.
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