Chapa de media densidade (MDF) fabricada com poliuretana mono-componente derivada de oleo de mamona - caracterização por metodo destrutivo e por ultra-som / Medium density fiberboard manufactured with polyurethane derived from castor oil - characterization of destructive and nondestructive testing

AUTOR(ES)
DATA DE PUBLICAÇÃO

2003

RESUMO

While employing low cost reforestation lumber, the technologies of the fabrication of fiber plates denominated ?Medium Density Fiberboard? (MDF) offer to several industrial sectors the opportunity to aggregate worth to species with little or no commercial interest, opening to them the possibility of promising profitable investments. However, the phenolic resins used in the production of MDF plates are well-known pollutants to the environment and therefore harmful to the human beings in such a way that environmentally friendly alternatives have been eagerly sought. According to that, the present work has been aimed to evaluate the physical, chemical and mechanical properties of MDF manufactured with Polyurethane Adhesive (PU) derived from Castor Oil, due to the low toxicity and to the non-polluting characteristics of the resulting adhesive. The characterization of the plates has been accomplished with the help of Steinkamp BP7 ultrasonic equipment using 45 kHz transducers and the physical and mechanical tests recommended by Euro MDF Board - EMB. The work has been developed along three distinct phases. Initially a better understanding of the characteristics of the polyurethane adhesive derived from castor oil has been acquired. It has been learnt that the adhesive exhibits the main characteristic of a monocomponent synthesis, stabilized by air humidity. During that phase, plates with 5% and 10% of polyurethane adhesive have been manufactured, called Adhesive PU3070 in this work, corresponding to 30% of solids and 70% of solvents. The properties of the plates manufactured with this synthesis have been determined and it has been found that although they have met EMB demands, the strong exhalation of solvent has ruled out its usage for MDF manufacture. As for the second phase, fiber plates have been produced with a new synthesis, called Adhesive PU7030, that is, 70% of solids and 30% of solvents. Again mechanical properties have satisfied EMB regulations. However, during the tests, it has been noticed that in order to control the quality of the final product, a fine adjusting to the values of some important Variables in the manufacture process, such as humidity level, temperature and pressing pressure, would be necessary. Accordingly, in the last phase, using Pinus caribea as fiber material, three experimental conditions have been elaborated, one for each controlled Variable, and repeated again for Eucalyptus gandis. Resulting from the adjusting of the variables, it has been observed that during the manufacture process, plates using much less adhesive than the former standards still have satisfied EMB demands fully, with advantages of a significant decrease in the pressing temperature and the corresponding energy savings. The characterization of the plates using non-destructive tests has been an important feature of the present work. Measurements have been performed in the plates by means of ultrasound equipment, using exponential as well as plane face transducers. From the readings, the propagation times of the ultrasonic waves have been evaluated, allowing to the determination of the propagation velocity of the ultrasonic waves through the material and consequently its dynamic parameters, which have been correlated to the mechanical properties of the plates, by means of a suitable statistic model. It has been concluded from the results that non-destructive test methods could as well be employed for the characterization of the physical and mechanical properties of the plates

ASSUNTO(S)

wood products fibras poliuretanas non-destructive testing composite materials polyurethanes madeira - produtos testes não-destrutivos fibers fibrous composites

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