2012 Volume 48 Issue 7 Pages 222-228
To develop novel adhesives that can bond wood species with poor bonding capacity to each other, five kinds of polyvinylalcohol (PVA) samples with different degrees of saponification were prepared. The storage stability of the aqueous solutions, dispersibility of the oily components, and adhesion performance of the wood were examined. The following conclusions were drawn. Because perfectly saponified PVA contains many hydrophilic groups and has a tendency to crystallize, the viscosity of an aqueous solution increases quickly, and the solution readily turns into a gel. Thus, the storage stability is poor. By blending PVA that is rich in hydrophobic groups with the perfectly saponified PVA, the increase in viscosity was suppressed. An increasing number of hydrophobic groups in the PVA sample corresponded to improved dispersibility of 4,4'-diphenylmethane diisocyanate (pMDI) and oily components of Chamaecyparis in the aqueous solutions. A comparison between two polymer systems containing similar amounts of hydrophobic groups showed that the dispersibility of oily components in aqueous solutions of the blended system was better than that in solutions of the non-blended system. The adhesion performance of wood specimens coated with essential oils of Chamaecyparis was examined using these adhesives. There was no significant difference between the adhesion performance of the blended system and that of the non-blended system when pMDI was not added to the adhesive. When pMDI was added to the adhesive, the adhesion performance of the blended system was better than that of the non-blended system. By blending PVA samples with various degrees of saponification and using them as adhesives, the adhesive performances of wood with poor bonding capacity can be greatly improved.
