3.1. Purification and chemical comp

3.1. Purification and chemical composition
A diluted alkali treatment was performed to solubilize the lignin, pectins, hemicelluloses and proteins (Dufresne et al., 1997), while the bleaching was applied to remove the lignin residues (de Rodriguez et al., 2006). The yield of purification was 46% (by dry mass). Fig. 1 shows the physical aspect of the SH before and after purification (TSH). Visually, a white colored TSH was obtained, indicating that a great part of the initial non-cellulosic compo- nents were removed by purification process, consequently TSH have higher cellulose content than SH.
The contents of the cellulose were 48.2 ± 2.1% and 84.6 ± 4.0%, of the hemicelluloses were 24.0 ± 3.0% and 11.2 ± 4.0%, and lignin were 5.78 ± 1.06% and 3.67 ± 0.33%, for SH and TSH, respectively. The values found for the main constituents of SH are in agreement with literature data (Ipharraguerre and Clark, 2003; Zambom et al., 2001).
The sum of the percentage of cellulose, hemicelluloses and lignin to the SH corresponds to 78.0% of the total dry matter, showing that there are other components in SH (e.g. protein, extractives and ash). As showed above, after the purification, the cellulose content sig- nificantly increased, while the hemicelluloses content was reduced to approximately half of the original, and the lignin content was reduced to approximately two-third of the original.
The sum of the percentage of cellulose, hemicelluloses and lignin to the TSH corresponds to 99.5% of the total dry matter, there- fore the purification not only removed hemicelluloses and lignin but also other components such as proteins, extractives and ash. The purification process was effective so the composition of TSH is suitable for the extraction of whiskers. It was verified that the percentage of mass consumption of the main components of the SH due to the purification process was 19.3, 78.3 and 56.0% for