The role of extractives and lignin for the durability of three hardwood species grown in Mozambique

Abstract

The present study is aimed at assessing separately the role of extractives and lignin content for the natural durability of three tropical hardwoods growing in Mozambique, namely: ntholo (Pseudolachnostylis maprounaefolia Pax), metil (Sterculia appendiculata K.Schum) and neem (Azadirachta indica). The experiment consisted of exposing wood samples to fungal attack under three treatments, namely: untreated, a set of samples from which extractives were removed and a set of samples from which lignin were removed. Thereafter, all specimens from each treatment were exposed against wood destroying fungi such as b rown rot (Postia placenta and Gloeophyllum trabeum), white rot (Trametes versicolor and Pycnoporus sanguineus) and soft rot (Chaetomium globusum and Phialophora mutabilis) under controlled environment. In general as expressed by mass loss, all species suffered more decay after removal of extractives and lignin. The results show that untreated wood samples of ntholo were relatively more durable showing lower mass loss percentages: 0.26 - 2.63%. Untreated wood samples of neem: 0.74 - 15.77%. The most perishable of untreated samples was metil with higher mass loss against all fungi types: 8.44 - 29.78%. After removal of extractives ntholo increased mass loss: 2.17 - 4.22%. The decay also increased for neem: 1.93 - 18.19%. Metil showed similar percentages as in untreated wood: 8.66-26.58%. After delignification all species experienced severe decay as described by mass loss. Ntholo: 14.47 - 44.43%. Neem: 15.43 -62.82%. Metil: 5.57 – 51.58% Regarding to extractives, ntholo had the highest extractives content (3.95%). Metil (1.11%) and neem (1%) had similar content. Apparently both lignin and extractives seem to play key role against fungal attack especially for ntholo and neem