Estudo de compósitos poliuretânicos reforçados com fibras de Malva

Abstract

In Brazil, it is possible to find a great diversity of lignocellulosic fibers with different chemical, physical and mechanical properties capable of raising the resistance of the polymers acting as reinforcement in polymer matrix. In this work, composites were produced using as a matrix the polyurethane resin based on castor oil reinforced with malva fibers. This native fiber is typical of the Amazon region, easily found and still under studied. Composites with 30, 50 and 70% mauve fiber (in mass) were prepared without and with treatment (with sodium lignosulfonate, LS, in an ultrasonic bath for 1 h). The behavior of these malva fibers inserted in the polyurethane matrix of castor oil (PU-OM) were evaluated for physico-chemical and mechanical properties. The techniques of chemical characterization of fibers (untreated and treated) and X-ray diffraction (XRD) (for fibers), Thermogravimetry (TGA / DTG), Differential scanning calorimetry (DSC) (DSC), IR spectroscopy, mechanical impact test, water absorption and finally Optical Microscopy (OM) to investigate the fracture region of the composites after impact test. The chemical analyzes showed that after treatment of the fibers with LS, the total lignin Klason content increased by 3%. In addition, the peak in the DTG curve after 470 °C, corresponding to lignin, had a significant increase in intensity (about 30%). X-ray results showed that despite the decrease in cellulose content in the fibers (from 59 to 53%) there was no change in the crystallinity index (maintained at approximately 68%). The mechanical impact test showed that the impact resistance increased significantly with the increase of the percentage of fiber introduced in the composites. The treatment with LS / ultrasonic had its proven efficiency in the composites of 70% of fiber whose results of resistance stood out from the others. The water absorption test showed that 70% fiber composites generally absorbed more water as a function of time, due to the greater presence of fibers, consequently more polar groups, when compared to the others. In general, the results were promising, as it allowed the substitution of synthetic materials (PU) by renewable materials, fibers, manoma oil and LS treatment.