Polyphenolic extracts of Pinus radiata bark and networking mechanisms of additive-accelerated polycondensates

摘要

The use of various chemicals for extracting polyphenolic fractions (tannins) from Pinus radiata bark was examined with the aim of obtaining high yields of high-quality tannins to be used as wood adhesives. Extractions carried out under very highly alkaline conditions (pH > 10.5) gave relatively high yields but also excessive viscosity values even in 30% (w/w) solutions, and this demonstrated their inability to function as wood adhesives. Solutions (30%, w/w) of mildly extracted (pH < 8.3) fractions gave workable viscosity values and were used in a subsequent study. A rapid acceleration effect was observed in these fractions when ammonia was used as a catalyst. Solid-state, cross-polarization/ magic-angle-spinning C-13-NMR of the cured samples showed evidence proving the existence of benzyl amine bridging networks in their hardened state. Simultaneously accelerated copolymerization could be observed in phenol-resorcinol-formaldehyde/P. radiata bark tannin mixtures with the addition of ammonia, as indicated by viscosity measurements. (c) 2006 Wiley Periodicals, Inc.