Phenol formaldehyde modification of radiata pine and termite resistance under laboratory testing

Abstract

The development of phenol formaldehyde (PF) resins as a means of impregnating solid wood is one that has been explored for several decades, both in terms of conventional impregnation processing (Impreg) or compressional impregnation (Compreg). However, it is only recently with advances in processing conditions that the method truly affords a means of achieving conventional modification for solid timber. This paper has investigated the modification of radiata pine (Pinus radiata) using PF resin at 22.5% and 30% solids content, with subsequent curing at 150oC under pressure. Samples were tested against Reticulitermes grassei according to EN117 over a period of 8 weeks using no-choice and choice tests. Controls included unmodified blocks and those modified without resin but just water, whilst treated blocks included those subjected to water soaking as well as without. No choice testing realised significantly reduced attack ratings, particularly for higher solid content treatments even following water soaking and 100% termite mortality. Modification with water did not influence level of attack and mortality which indicates it is the resin and not the process that imparts resistance to termite attack. Two-choice termite testing showed low attack for both impregnation treatment levels, with results slightly better for the higher solid contents treatment, whilst triple choice testing further confirmed this. In choice tests, slight attack of resin treated blocks took place, though significant attack of control blocks occurred, even when 100% mortality occurred by the end of the test. This seemed to suggest that ingestion of PF treated wood led to poisoning. Results confirm the potential of PF-treatment of solid wood as a method for minimising risks from subterranean termite attack.