Resistência de linha de solda em moldados por injeção de compósitos de polipropileno com talcos e fibra de vidro.
Sena Neto, Alfredo Rodrigues de
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The presence of weld lines in injection moulded reinforced thermoplastics contributes towards substantial reduction in mechanical properties, due to unfavourable orientation of the reinforcement in the weak plane of the weldline. However, published literature presents controversial data on the influence of glass fiber and lamellar talc on the weldline strength. Therefore, tensile mechanical properties of injection moulded polypropylene copolymer (PPcopol) composites with short glass fiber and three different grades of talc (medium, fine and ultrafine size) were investigated in presence and absence of weldline. PPcopol composites with 10, 20, 30 and 40 wt. % of filler were compounded in a co-rotating twin-screw extruder and tensile test specimens were injection moulded without and with butt weldlines. The DSC measured increase in the degree of percentage crystallinity of the thermoplastic matrix with talc content, contributed to a slight increase in tensile strength of talc-filled composites only in mouldings without weldlines. The tensile properties of mouldings with weldline were superior in talc-filled composites than in glass fiber (GF) reinforced composites, indicating clearly the pronounced debilitating effect of higher GF aspect ratio in comparison to the lower aspect ratio of talc lamellae. The depreciation in tensile modulus and strength of the moulded composites with weldline increases with filler volume fraction and is greater in glass fiberreinforced composites than in talc-filled composites. The particle size differences of the three grades of talc used in this work had minor influence on the weldline tensile properties, probably due to the nearly similar values of aspect ratio of lamellae of these talcs. These results on weldline tensile properties of PP composites were corroborated with scanning electron microscopy analysis of the preferential fiber/talc orientation patterns in the weldline region of moulded tensile specimen with and without weldline.