LAUSR

Abstract This study investigated the effect of R-value (the ratio of -NCO to -OH) and addition content of blocked polyurethane prepolymer (BPUP) on the properties of melamine-urea-formaldehyde (MUF) particleboards made from high-moisture particles (25 wt%). Eight types of particleboards (A, B, C, D, E, F, G, H/D, I) were made with various BPUP contents (0, 4, 6, 8, 10 wt%) and R values (R=3, R=4, R=5, R=6). The dimensional stability and mechanical properties of the particleboards were improved by adding BPUP to MUF resin. With the increase in R-value and BPUP concentration, particleboards showed relatively better dimensional stability and mechanical properties. Best results were obtained with Board H (92:8, R=5) with thickness swelling of 13.1% and water uptake of 25.7%. The recording statistics in Board H have identified an optimum internal bond strength value of 0.83 MPa, which was 59.6% higher than Board F (96:4, R=5) and 159.4% higher than only MUF bonded particleboard. It was also found that increasing R-value and the proportion of additional BPUP showed positive effects on the flexural properties of MUF particleboards. Besides, the function relationship among mechanical properties was obtained to investigate correlation between thickness swelling (TS) and internal bond strength (IB), modulus of elasticity (MOE) and modulus of rupture (MOR).