Innovation in poly(vinyl acetate) water resistant D3 glues used in wood industry

Poly(vinyl acetate) (PVAc) water-resistant glues used in the wood industry and belonging to the class of durability D3 show high resistance to both water and heat compared to the usual PVAc-based ther- moplastic products. In conventionally synthesised adhesives this is attained by means of cross-linking (although limited) of the linear polymer chains and moreover by using inorganic salts, such as alumi- nium chloride. The paper illustrates the limits of these products and presents the prospects in the chemistry of industrial-grade D3-class PVAc adhesives. More in detail, it is shown how the individual roles of both cross-linking agent and aluminium chloride contribute to the occurrence of recurring inconveniences characterising conventional PVAc-D3 glues, which include formaldehyde release during time (mostly related to the curing agent), glueline colouring and indirect staining of wood (both are mostly evident in selected wood species, in the presence of either heat or UV irradiation), acidic pH, and equipment cor- rosion (related to the presence of aluminium chloride). Understanding those mechanisms has constituted the basis for the development of newly synthe- sised PVAc-D3 glues, whose characterisation is expressly reported in the present work. Such systems have shown good adhesion to wood surfaces and have exhibited neither corrosive nor chromatic alteration evidences, as well as absence of formaldehyde emissions. All these occurrences were verified by specific tests, such as corrosion on steel, measurements of the formaldehyde content of the dispersion, and emissions from panel boards, and glueline exposure to both temperature and UV irradiation after application in selected wood species.