Estabilização dimensional por meio do tratamento térmico e seus efeitos sobre as propriedades de painéis de partículas orientadas (OSB)

Wood is a hygroscopic material and therefore vary its dimensions in contact with moisture. Beyond the hygroscopic nature, reconstituied wood panels also are unstable because of the compression stress during the pressing stage. These stresses are released when the panel contacts the moisture, causing dimensional variations. In view of this, the improvement of the dimensional stability has been a great area of study, with several methods already available for this purpose. The oriented strandboard (OSB) is a type of structural panel that also presents dimensional instability. The main competitor of OSB panels is plywood , mainly because they are much more stable panels. The methods considered for the dimensional stabilization of OSB panels are not applied industrially, either because of the costs involved or due to operational and technical limitations. Thus, it is important to develop methods that provide the improvement of the dimensional stability of OSB panels and at the same time are viable both economically and operationally. The present work had as main objective to propose a method for the improvement of the dimensional stability of OSB, and specifically, to evaluate the efficiency of this method in reducing the dimensional variations, analyzing any possible alterations related to its properties, and finally to study the operational and economic viability of the method. OSB Panels supplied by the a manufacturer were submitted to thermal treatment, in a laboratorial press. Two temperatures (190°C and 220°C) and three times (12, 16, 20 minutes) (a total of six treatments) had been analyzed. Physical, mechanical, colorimetric and chemical properties of the treated panels were analysed, and the results were compared with the properties of untreated panels. The operational viability of the treatment was also analyzed, including cost and economic indicators such as internal rate of return (IRR), net present value (NPV) and cost-benefit index (CBI). The results indicated that treatment improved the dimensional stability, reduced the thickness swelling up to 50%, and the water absorption up to 33%, in comparison with the non-treated panels. The mechanical properties had been affected only partially, with reduction of the maximum force and modulus of rupture up to 23%. Other mechanical properties had not been affected by the thermal treatment. The color of the panels was slighy modified, while among the chemical properties, only hemicelulose (mainly galactose) was significantly affected. A more detailed analysis demonstrated that the temperature of treatment was the most important factor in the alterations of the properties, while that the time factor was significant mainly for the physical properties. Amongst the evaluated treatments, it was recommended the lower temperature for a longer period (190°C, 20 ') and higher temperature in shorter time (220°C, 12 ') because of their superior dimensional stability and similar properties if compared to untreated panels. The method revealed to be viable, with impact in the production cost not superior to 5%. Additionally, all the economic variables (IRR, NPV, CBI) had demonstrated the economic viability of the proposed thermal treatment. Key-words: oriented strandboard, thermal treatment, dimensional stability, investment analysis.