Characterisation and fractioning of Tectona grandis bark in view of its valorisation as a biorefinery raw-material

Abstract

The anatomy and chemical composition of Tectona grandis bark from mature trees in East Timor are described as well as the characterisation of fractionation by grinding and granulometric separation.Teak bark is composed of secondary phloem, periderm and a narrow rhytidome that included various periderms with phloem tissues between them. The layer of phellem cells in each periderm was thin. The phloem showed an orderly stratification with tangential bands of fibres in concentric rings that alternated with thin bands of axial parenchyma and sieve tube elements. Abundant prismatic calcium oxalate crystals were present.The bark fractured easily into clean particles. The yield of fines was low and 64.4% of the particles were over 2mm.The mean chemical composition of teak bark was: ash 18.5%, total extractives 10.7%, lignin 20.0% and suberin 1.9%. The polysaccharides, corresponding to approximately 47%, showed a predominance of glucose (60.3% of total neutral monosaccharides) and an important content of xylose (20.0%). The content of rhamnose was also comparatively high (4.9%). The content of soluble phenolics was 1.6%. Ash elemental composition showed the predominance of calcium, representing about 93% of the total inorganics, followed by potassium (4.8%) and magnesium (1.9%).Extractives were present preferentially in the fines, with about 30% more extractives than the coarse fraction. Lignin content and monosaccharide composition were similar in the different bark fractions. A difference between fractions was found in relation to suberin content which was lower in the fines: 0.6% and 3.5% in the fine and medium fractions, respectively.