On the occurrence of network interpenetration in the wood-isocyanate adhesive interphase

This paper discusses the chemistry and morphology of the wood-isocyanate adhesive bondline in reference to polymeric methylenebis(phenylisocyanate), pMDI. The typically low molecular weight of pMDI may cause swelling of the wood substrate prior to resin polymerization. These circumstances could lead to an interphase morphology that resembles an interpenetrating polymer network, IPN. In order to test this hypothesis, experiments were performed to determine if liquid pMDI swells and plasticizes yellow poplar (Liriodendron tulipifera) wood. It was found that liquid pMDI caused little or no plasticization of yellow poplar wood under the conditions studied. Consequently, the interphase morphology in these samples had little or no network interpenetration. The topic of network interpenetration in the wood-adhesive interphase needs additional study because of the potential utility for improving bondline durability. (C) 1998 Elsevier Science Ltd. All rights reserved.