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

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 13C‐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.