Ganesh Gopal T.M.
PMDI (Polymeric diphenylmethane diisocyanate) resins cannot be used for plywood, as these resins, after spreading on veneer will lose -NCO by reacting with moisture in air and wood. In this study for plywood manufacturing, the –NCO group is blocked using phenol and imidazole and the cost of the resin is reduced by mixing with phenol-cardanol formaldehyde resin. The FTIR (Fourier Transform Infrared) studies confirm NCO blocking. For phenol blocked PMDI resin studied using DSC (Differential Scanning Calorimetry) analysis the deblocking of NCO group started at 160o C. For imidazole blocked PMDI resin, even though the deblocking of NCO group started at 125oC, curing is only achieved at a pressing temperature of 170-180oC. For getting Boiling Water Resistant (BWR) grade as per IS-848:2006-Specification for Synthetic Resin Adhesive for plywood, a press temperature of 180oC is required. The addition of DBTL (Dibutyltin dilaurate) catalyst to phenol blocked PMDI resin improved the bond strength of plywood. The Phenol cardanol formaldehyde resin combined with phenol blocked PMDI resins, when used to make BWR grade plywood has confirmed to Boiling Water Proof (BWP) grade plywood as per IS-848:2006.
