ECO-Adhesive from Modified Natural Rubber for Wood Applications

Abstract

Both commercial entities and the government have expressed interest in safe and environ-mentally friendly adhesives, ECO-adhesives, containing no volatile harmful or toxic chemicals. In the wood industries, currently common adhesives such as urea formaldehyde (UF), phenol formaldehyde (PF) release formaldehyde vapors that are a human health concern, with unpleasant odor. We examined the potential of modified natural rubber latexes (MNRL) for use as ECO-adhesives. Three latex types were used, namely epoxidized natural rubber (ENR), liquid natural rubber (LNR), and NR/PMMA blend. The MNRL was characterized by FT-IR, NMR, and GPC. The proportion of tackifying agent to the dry weight of latex was varied in the range 0 to 60 phr. It was found that the MNRL uniformly mixed in the latex form. All MNRL adhesives would have passed the Thai standard for rubber-based adhesives, based on their: total solids content (TSC), pH, viscosity, shear strength, and emissions of formaldehyde. Up to 30% fraction of tackifying agent, tack and shear strength increased with its content. Compared to a commercial UF adhesive, the MNRL had lower emissions of formaldehyde vapors, lower shear strength, but higher TSC, and higher viscosity. In summary, for select wood applications with moderate bond shear demands, these new rubber based adhesives could provide a health conscious and non-toxic alternative, with the further advantage of low odor.