EXTERIOR PLYWOOD RESINS FORMULATED FROM PINUS-PINASTER BARK EXTRACTS

Phenol-tannin-formaldehyde resins prepared by copolymerization of resoles and Pinus pinaster bark tannins were used for bonding eucalyptus plywood boards. The dependence of board quality on the formaldehyde/phenol ratio F/P, the overall soda/phenol ratio S/P and the viscosity of the resol was studied using a 2 x 2 x 2 factorial design. The most critical of the variables studied was S/P, the best results being obtained with its lower value. A follow-up study using a lower S/P value confirmed this trend, better results being obtained than with commercial phenolic resins. Moreover, the pine-based resins allowed a press temperature of 160-degrees-C to be used, which further improved board quality.