Comportamento físico de compósitos polipropileno/atapulgita: um estudo comparativo.

Abstract

A study of the effect of the incorporation of a fibrous clay, attapulgite, on the properties of isotactic polypropylene was carried out. The evaluated properties were: tensile strength, hardness, Vicat softening temperature and a proposed parameter In this work, the degree of apparent crystallinity of the matrix in the composite, gc. "The experimental results showed that the atapulgite, due to its fibrous constitution and good compatibility with polypropylene, presented a relatively good reinforcement level, with small increases in resistance up to about of 15% load and a small decrease in this property with up to 45% load. Comparisons with similar polypropylene composites with glass fiber and polypropylene with mica indicated good prospects of industrial use. The studies showed that the addition of the fillers to the polypropylene increased the hardness and the softening temperature (confer greater thermal and dimensional stability), whereas the degree of crystallinity of the matrix appears to be dependent on the compatibility between the phases, and the charge may act as a heterogeneous nucleating agent (attapulgite and glass fiber) or as a crystallization inhibitor (mica case). Some changes in the employed system were performed aiming to have a larger field of study. The effect of strain rate of the tensile test, activation treatment of attapulgite with hydrochloric acid, addition of polyvinyl alcohol to polypropylene, influence of composition and molding temperature, effect of cooling rate after molding, and the performance of annealing heat treatments in materials molded. The results indicated a strong dependence of the deformation rate on the tensile strength of both composites as the pure polymer, and that the efficiency of atapulgite as reinforcement to polypropylene is higher at lower rates. The treatment with hydrochloric acid gave a greater porosity to the load, increasing the resistance of the composite due to the phenomenon of "mechanical grabbing" and greater adsorption. When present, the polyvinyl alcohol interacts well with the atapulgite, but it weakens the polypropylene because it must form a new phase, not miscible with the matrix. The molding conditions also affected the properties, obtaining better results for the molded composites at 220 ° C and normal cooling at r. Finally, it was observed that the annealing may alter some morphological aspects in the composites and the pure polypropylene, reflecting on the properties of these materials and that the ideal conditions of this treatment may be different in the polypropylene and in the composite with 29% of attapulgite.