Effect of Ammonium Pentaborate on Cure Kinetics of Phenol Formaldehyde Resin in Presence of Wood

In order to investigate the applicability of ammonium pentaborate (APB) as additivein wood-based composites, the effects of APB and wood together on cure kinetics ofphenol formaldehyde (PF) resin were analyzed by using both dynamic andisothermal differential scanning calorimetry (DSC). ASTM E698-79 and model freetechnique were used to analyze dynamic DSC data, while the isothermal DSC curingkinetic parameters were obtained via the nth-order model technique. The resultsshowed that both poplar and Masson pine had little influence on the apparentactivation energy of PF resin, while APB slightly reduced it by increasing the pH valueof APB/wood mixtures. Both poplar and poplar/APB reduced the reaction enthalpy,dramatically. The activation energy dependence on the degree of conversion indicatedthat poplar and APB together accelerate the addition reactions at the early stage of PFresin curing process, but delay the condensation reactions at the later stage. Theearlier acceleration is contributed to the phase change from continuous to dispersed,and the latter is the result of a predominantly diffusion control. The isothermal DSCanalysis confirmed the dynamic DSC result that mixing of wood and/or APBaccelerates the curing reaction rate at lower temperature range. In other words, itimproves the addition reaction of curing process and at the same time, the reactionorders of all specimens are not changed either.