Electron microscopic and chemical study of degraded Pinus radiata wood from a marine pile

Abstract

During an inspection of marine piles, 12 years after installation, severe degradation was noted on one of them in the vicinity of a corroded eyebolt. The wood was dark brown in colour and tended to crumble easily. Wood fragments were examined by light microscopy and scanning and transmission electron microscopy and were also analyzed for carbohydrates and lignin. Light microscopy indicated numerous cracks in tracheid walls resulting in delamination at the middle lamella – S1 and S1–S2 boundaries and also in fractures across the tracheid wall. Chemical analysis showed extensive loss of both hemicellulose and cellulose. Observations with polarized light microscopy supported the data from chemical analysis on cellulose degradation, indicating a loss of crystallinity. Although presence of microbial flora in the lumen of wood cells was revealed by scanning electron microscopy, transmission electron microscopy showed only occasional soft rot decay zones in the S2 layer. The degradation of Pinus radiata wood from this sample appears to have been caused primarily by brown rot attack and (or) iron corrosion products, soft rot attack playing a minor role. Key words: Pinus radiata wood, marine pile, wood cell wall degradation, electron microscopy.