Reaction Kinetics Behavior of Phenol Formaldehyde Wood Adhesives by Differential Thermal Analysis and Its Application

Phenol formaldehyde (PF) adhesive resins are frequently used in the wood industry. It is important to understand the relationship of their hardening kinetics. A differential scanning calorimeter (DSC) was used to investigate the thermal properties of PF adhesives for wooden cement molds and container liners. All specimens demonstrated a single exothermic peak from the results of DSC. Peak temperatures rose with an increasing heating rate. According to ASTM method E698, logarithmic values of the heating rate were linearly correlated with reciprocal peak temperatures, and correlations fit well with the Arrhenius equation. Polymerization kinetics parameters were measured as follows. Respective values for the activation energies of the cement molds and container liners with PF, were 90.64 and 145.2 kJ mole-1 ; logarithmic values for Arrhenius frequency factors were 11.07 and 18.33 ; half-life temperatures at 60 min were 90.9 and 101.2℃.
For Taiwania PF-glue-lam and PF container liners, viscoelastic properties, like E' (modulus of elasticity), E" (modulus of viscosity), and tan δ (mechanical damping), were determined by scanning using a multi-frequency method specified by ASTM D-4065-95. Time-temperature superimposing software based on the Williams-Landel-Ferry (WLF) equation was applied to obtain the logarithmic relationship between the angular frequency and the modulus of elasticity, modulus of viscosity, and mechanical damping. Hence, mechanical properties after long-term usage and changes in viscoelastic properties were subject to various low and ultra-high frequency stimulations. Analysis of E', E", and tan δ measurements under 0.1~33 Hz and 50~200°C demonstrated that E' values decreased with increasing temperature. Over 180°C, thermal degradation accelerated the softening, causing the E" and tan δ values to sharply increase.