Avaliação das propriedades do compósito de polipropileno carregado com farinha do bagaço de mandioca

Abstract

The ceaseless search for new materials with small effective cost and at the same time does not cause harm to the environment, make the use of raw materials from renewable sources as one of the most emergent sectors of the last decades. In this sense, the various sources of lignocellulosic fibers are studied by several branches of science. In this work, polypropylene (PP) and cassava bagasse flour (CBF) composites were obtained with the objective of evaluating the influence of CBF on the properties of PP. The composites were prepared using the single-screw extruder first and then the twin-screw extruder. The adopted content of the CBF present in the blends was 0, 5, 10, 15, 20, 25 and 30% (mass/mass). A compatibilizing agent (PP-g-MA) with a fixed rate of 2% (mass/mass) in the 5, 15 and 30% (mass/mass) CBF blends was used to evaluate the properties of the composite due to the improvement of the interfacial adhesion promoted by the compatibilizing agent. In order to obtain the characterization of the material, tensile strength, flexural strength, impact strength, differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), X-ray diffraction (XRD), scanning electron microscopy (SEM) and granulometric analysis were performed. The results obtained from the composites when submitted to the tests of tensile strength, showed that with the incorporation of high levels of CBF to the PP causes an increase in the elastic modulus of the thermoplastic polymer. The incorporation of CBF at any content of the polymer causes a reduction in tensile strength and the 20 and 30% CBF contents caused a reduction in the yield stress. The characterization of the composites by thermogravimetric analysis showed a marked drop in the thermal stability of polypropylene for small CBF contents (up to 15%). With the incorporation of higher CBF contents, above 15%, an increase in thermal stability occurred. In general, the micrographs obtained of the PP/CBF composites showed dispersed starch granules in the polypropylene matrix, and in most cases the observed distribution was not homogeneous. The PP/CBF/PP-g-MA composites, in general, presented superior mechanical properties to that obtained for the composites without the compatibilizing agent, except for the impact strength in which the results obtained were lower than all the others composites analyzed. The flexural modulus for PP/30%CBF/2%PP-g-MA composite showed a substantial increase of 83% over neat polypropylene. The behavior of the cassava bagasse diffractogram obtained in this study is unusual for that described in the literature. This behavior analyzed was related to the severe conditions of industrial drying. The crystallinity index measured for the cassava bagasse was approximately 16%, being in agreement with the range of crystallinity predicted in the literature for this type of material.