Effects of low and high molecular weight of phenol-formaldehyde (PF) on the properties of strand boards from kiri wood (Paulownia tomentosa)

Abstract

ABSTRACT Kiri (Paulownia tomentosa) wood is a promising material for lightweight strand boards (SBs); however, kiri SBs have displayed a limited dimensional stability. The aim of this study was to evaluate the possibility of using low molecular weight (LMW) phenol-formaldehyde (PF) resin not only as an adhesive but also as a treatment (impregnating) agent to manufacture SBs. SBs from kiri wood were manufactured with densities of 400 kg m−3 and 500 kg m−3. PF resin with low and high molecular weight as well as its 50-50% mixture was studied at two adhesive formulation contents of 10% and 20% related to the strand mass. At 400 kg m−3 density, internal bond strength (IB), screw withdrawal resistance (SWR) and thickness swelling (TS) of SBs containing LMW PF were significantly higher than those of HMW PF at 10% adhesive content and the differences slightly decreased as the adhesive content increased to 20%. At 500 kg m−3 density, IB, TS and SWR of SBs were considerably enhanced by LMW PF at both adhesive contents. We concluded that using LMW PF may cause higher strength and dimensional stability, at least, when the strand material and the SBs exhibits very low density, which is highly compressed during SBs manufacturing.