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Doctoral thesis2011Open access

Chemical composition and machinability of selected wood species from Mozambique

Lhate Inácio Arnaldo

Abstract

The objectives of the current work were to carry out a survey on timber sector in Mozambique and to determine chemical, calorific and machinability features of selected species. Mozambican timber sector was described as dominated by selective harvesting practices on a few hardwood species out of 118 species growing in the forest with potential for industrial timber. Selective logging is believed to be due to the demand in both domestic and international markets of traditionally used, and lack of technical data on lesser used species. In order to avert the negative effect of selective logging, this work argued the need to widen the resource base by studying lesser used species. Taking into account stock volumes recorded in the last forest inventory, the lesser used species, Acacia nigrescens Oliv, Icuria dunensis Wieringa, Pseudolachnostylis maprounaefolia Pax, and Sterculia appendiculata K. Schum were selected to assess their chemical, calorific and machinability features. Lesser used species were compared with traditionally used species, namely, Afzelia quanzensis Welwn, Milletia stuhlmannii Taub, Pericopsis angolensis Meeweven, and Pterocarpus angolensis DC, regarding chemical and calorific features. Aiming to get a thorough chemical characterization along radial direction, samples for chemical analyses were taken from sapwood, outer and inner heartwood. Chemical, proximate and ultimate analyses were performed according to standard methods. The contents of carbohydrates, extractive, ash, volatiles and high heating values were in ranges considered normal for tropical species. Contents of lignin and minerals were unexpectedly high in Pseudolachnostylis, reaching 37.51% and 2.2% (wt%, extractive free) on a dry basis, respectively. Based on the determined chemical features, it was concluded that Acacia and Pseudolachnostylis were similar to well-known, whereas Icuria and Sterculia differed from the known species. In ranking of all studied species using fuelwood value index (FVI), Acacia was best ranked, whereas Sterculia was worst ranked. Acacia, Pericopsis, Pseudolachnostylis and Sterculia, considered as lesser used in the study, were subjected to experiments for cutting forces and tool wearing measurements. Density measurements on samples for cutting forces and tool wearing experiments were performed with the aid of a CT scanner. Two different cutting tools 20˚ and 30˚ rake angle were used. Before cutting, the edge radius of the tools was measured. Main cutting force in 90˚-90˚ and 90˚-0˚ cutting directions were measured by piezoelectric gauge. Tool wearing experiments were performed on a shaper using cemented carbide tools for woodworking and fixed cutting conditions. Edge recession and tool wear radius were measured for monitoring tool wearing. Ranking the species using cutting forces only or tool wearing only for machinability recorded different earnings, and for measuring the net effect of machining output variables, this work suggested the Digraph and Matrix Method as an expeditious and integrated method to evaluate the machinability of lesser used species. Based on the calculated indexes, the easiest species to be machined was Sterculia, whereas the most difficult species to be machined was Acacia. Cutting forces earned by Acacia seemed to have been affected by anatomical features not measured in current work.

Keywords

hardwood; wood properties; chemical composition; energy value; mozambique

Published in

Acta Universitatis Agriculturae Sueciae
2011, number: 2011:48ISBN: 978-91-576-7592-7
Publisher: Department of Forest Products, Swedish University of Agricultural Sciences

      SLU Authors

    • Arnaldo lhate, Inácio

      • Department of Forest Products, Swedish University of Agricultural Sciences

    UKÄ Subject classification

    Wood Science

    Permanent link to this page (URI)

    https://res.slu.se/id/publ/34354