β-Cyclodextrin-allyl isothiocyanate complex as a natural preservative for strand-based wood composites

Environmental concerns over chemicals used for protecting wood and wood products from biological degradation have prompted the development of natural wood preservatives with lower health risks and prolonged efficacy. In this study, an effective and environmentally friendly method is demonstrated to substantially improve the durability of a strand-based wood composite product by incorporating a natural wood preservative system. Specifically, allyl isothiocyanate (AITC), a mustard oil-based natural biocide, was encapsulated into the cavity of beta-cyclodextrin (beta CD) and the as-prepared beta CD-AITC complex was applied in the strand-based composite manufacturing process to produce a natural-preservative-treated engineered wood panel. The formation of the beta CD-AITC complex was qualitatively confirmed by attenuated total reflection-Fourier transform infrared spectroscopy, and the inclusion yield of AITC was estimated to be 71% by thermogravimetric analysis. The preservative complex was blended with southern pine strands at 0%, 5%, and 10% prior to the application of polymeric methylene diphenyl diisocyanate resin and hot-pressing. The application of the preservative system significantly improved decay resistance against brown-rot fungi, Gloeophyllum trabeum and Postia placenta, by keeping the average mass losses of the treated panels below 7%. The internal bond strengths of the treated panels were maintained above the required level for structural OSB for use in humid conditions specified in the European OSB product standard. This study suggests the beta CD-AITC complex to be a promising alternative to conventional preservatives for the protection of wood composite products.