Influence of moisture content on the thermophysical properties of tropical wood species

International audienc

Investigation of green-glued laminated timber from the Congo Basin: durability, mechanical strength and variability trends of the bondlines

The development of glulam may give complementary, added-value to an important part of the timber production in the Congo Basin. Nevertheless, the high humidity in which these timbers operate may cause problems such as cracks and severe deformations if they are not suitably bonded. Moreover, there is a lack of knowledge concerning the refined design of the bondlines of glulam assembling from the Congo Basin hardwoods. We investigated the durability, mechanical strength, and variability features of the bondlines, manufactured under higher moisture conditions. Eight hardwood species with very different properties were selected. A one-component polyurethane adhesive was used. Industrial gluing parameters were kept constant. Delamination, shear tests and analysis of bondlines thickness were carried out. Multivariate analysis and a goodness-of-fit test of the strength variability of the bondlines were performed. Optimum bondlines thicknesses were obtained. Their durability exhibited satisfactory trends up to a density of 750 kg/m3. The behaviour of the bondlines can operate in three homogeneous groups. In each of them, the variability of the shear strength can be properly modelled using a 3-parameter Weibull probability. Wood failure trends were in accordance with several international requirements. The density value of 750 kg/m3 appeared as critical for the compatibility between the shear strength, the durability and the bondlinesthickness. The overall results showed the ability of several tropical timber species to be valorised in green-glulam applications. Moreover, the findings unlock new trends concerning a reliable and safe design of tropical glulam as a structural wood-based product

Influence of water content on the mechanical and chemical properties of tropical wood species

This paper aims to study the mechanical behavior and surface chemistry in relationship with moisture content of Iroko (Milicia excelsa), Bilinga (Nauclea diderrichii), and Tali (Erythrophleum suaveolens). Mechanical characterization was done experimentally using tensile and bending tests. Chemical semi quantitative analysis of the wood at 10%, 15%, 20% and 30% of moisture content was investigated using attenuated total reflectance Fourier transform infrared spectroscopy. The main chemical functions involved by the presence of water were identified as well as the other functional groups. The ratio between lignin and carbohydrates was estimated for all the wood species. The results indicated a negative correlation in the relation between moisture content and mechanical properties. Tali had the higher bending strength while Iroko had the lowest value. The average percentage change rate of the Young’s moduli induced by 1% of moisture content changes, especially between 10% and 20%, varied with the wood species: 1.69% in Tali, 1.65% in Bilinga and 2.54% in Iroko approximately. The infrared spectra obtained differed among species. The results also showed that Iroko contained higher lignin and were the least sustainable according to mechanical properties. The bands at 3340 cm−1 and 1635 cm−1 were more impacted by moisture content. Keywords: Tropical wood, Chemical component, Strength, Moisture content, ATR-FTI