Variação do ângulo microfibrilar e do conteúdo de lignina na parede celular das fibras da madeira de clones de Eucalyptus grandis × Eucalyptus urophylla

Abstract

Various properties of wood of Eucalyptus grown in Brazil for cellulose production have been evaluated. Besides, various studies were performed from the year 2000 addressing about the importance of microfibril angle to describe another properties of both wood and pulp. However, there are no reports about the microfibril angle variation in different layers of the secondary cell wall in those woods so far. In this study, we aimed to investigate the microfibril angle variation, as well as the lignin content in the cell wall of fibers of three wood clones of Eucalyptus grandis ×Eucalyptus urophylla. These parameters were associated with anatomical features, and physical and mechanical properties. Samples of three erect trees per clone of those planted in Vale do Rio Doce were collected in three points established from the medulla to trunk bark. We evaluated fiber morphology, basic density, dimensional instability, parallel compression for fibers, lignin content, and microfibril angle. For the same collection points, we also prepared ultra-thin sections for transmission electron microscopy. In addition, fine sections obtained on microtome were used for observation of lignin distribution across the cell wall, using fluorescence microscopy. According to results we could conclude the following: i) anatomical, chemical, physical, and mechanical features ranged according to reports found in the literature; ii) regarding the content of lignin, there was no common radial trend for both three clones; iii) higher brightness intensities were found in the corner of cells and middle lamella, indicating greater content of lignin in these regions when compared to that found in other layers; iv) the average microfibril angle ranged from 7.6º to 8.3º, and there was a tendency for decrease of MFA from the medulla to bark for all clones; v) the relation between MFA with another wood properties was found to be stronger for wood density, tangential contraction and mechanical properties; and vi) the transmission electron microscopy allowed to differentiate the S2 layer from the others. The microfibril angles ranged within the same layer, either for S1, S2 or S3. The MFA of S2 layer was equal to 6.7º; and the transition layer from S1 to S2 was equal to 49.4º in the inner position of the CNB007 clone. The middle wood of trunk of the CNB010 clone showed MFA equal to 74.5º in the S3 layer, 3.0° in the S2 layer, and the transition layer from S1 to S2 equal to 6.0º.