Surface Characterization Techniques applied in heat-treated wood / Utilização de técnicas de caracterização de superfícies em madeiras tratadas termicamente

AUTOR(ES)
DATA DE PUBLICAÇÃO

2009

RESUMO

The main aim of this work was the characterization of changes of properties occurred on the surface and structure of heat-treated wood in response to thermal treatments. In order to cover different types of heat-treated wood, two species were elected as models for two great groups of woods, the so-called hard and soft woods. The samples were thermally treated in temperature range from 100 to 200 C under air atmosphere, and the water contact angle was periodically measured with the sessile drop method during one year. High values of contact angle were observed for the samples after the thermal treatment, reflecting their increased hydrophobicity. Probably, the reason for such increased hydrophobicity is the increase in the crystallinity of the samples, probed by ATR-infrared spectroscopy and X-ray scattering analyses. Even with FTIR analysis showing low-intensity bands, it was possible to distinguish between woods from the two groups, hard and soft woods by using this technique. Measurements of wood shrinkage were also carried out for the samples, with hard wood showing higher values of volumetric shrinkage. Moreover, for thermal treatments at higher temperatures, the volumetric shrinkage of the wood sampes was markedly reduced. During the drying process, the highest and lowest values of volumetric contraction were obtained for Eucalyptus grandis (heartwood) and Araucaria angustifólia (heartwood), respectively. Surprisingly, when treated at higher temperatures the samples from Pinus elliotti showed a small expansion, but Eucalyptus grandis (heartwood) was still the more contractile wood. Also, during the thermal treatment, the loss of mass was evaluated for all the samples. Hard woods exhibited a large reduction of mass in response to the heating in comparison with soft woods, with no exceptions. The CIE Lab system was used to categorize the heat-treated woods. A multivariate data analysis was used to monitor each color parameter, and its dependence on the type of heat treatment. From these analyses, a dendogram was generated, and the samples with almost the same final color were grouped regarding the species and type of treatment.

ASSUNTO(S)

heat treated wood pinheiro pine tecnologia de madeira wood tecnology madeira termorretificada eucalyptus eucalipto

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