Impact modification of PP/wood composites: A new approach using hybrid fibers

The impact resistance of polypropylene (PP)/wood composites was improved either by the traditional approach of adding an elastomer or by the use of poly(ethylene terephthalate) (PET) fibers. Composites were prepared with various elastomer and PET fiber contents at a constant wood content of 20 wt% for all hybrid composites. Interfacial adhesion was improved by the addition of a maleic anhydride modified PP (MAPP). The components were homogenized in a twin-screw compounder and injection molded into standard tensile bars. Properties were characterized by tensile and impact testing, while scanning electron microscopy (SEM) was applied for studying the structure. A combination of acoustic emission measurements (AE) and SEM was used to understand local deformation processes, the results showing that the traditional route of impact modification with elastomers does not work in wood reinforced PP, since the simultaneous fracture of large wood particles and the cavitation of the elastomer result in limited fracture toughness. On the other hand, polymeric fibers (PET) increase the impact resistance of rigid PP homopolymer matrices reinforced with wood fibers, because they initiate new local deformation processes. The concept of using polymeric fibers for the impact modification of rigid PP/wood composites is an efficient way to extend the field of application of such reinforced materials

Click chemistry in mesoporous materials: Functionalization of porous silicon rugate filters

In this paper we report the use of the optical properties of porous silicon photonic crystals, combined with the chemical versatility of acetylene-terminated SAMs, to demonstrate the applicability of "click" chemistry to mesoporous materials. Cu(I)-catalyzed alkyne-azide cycloaddition reactions were employed to modify the internal pore surfaces through a two-step hydrosilylation/cycloaddition procedure. A positive outcome of this catalytic process, here performed in a spatially confined environment, was only observed in the presence of a ligand-stabilized Cu(I) species. Detailed characterization using Fourier transform infrared spectroscopy and optical reflectivity measurements demonstrated that the surface acetylenes had reacted in moderate to high yield to afford surfaces exposing chemical functionalities of interest. The porous silicon photonic crystals modified by the two-step strategy, and exposing oligoether moieties, displayed improved resistance toward the nonspecific adsorption of proteins as determined with fluorescently labeled bovine serum albumin. These results demonstrate that "click" immobilization offers a versatile, experimentally simple, and modular approach to produce functionalized porous silicon surfaces for applications as diverse as porous siliconbased sensing devices and implantable biomaterials. © 2008 American Chemical Society