Structure–property relationships in glass reinforced polyamide, part 2: The effects of average fiber diameter and diameter distribution

Abstract

AbstractWe present the results of an extensive study of the influence of average fiber diameter and the width of the diameter distribution on the performance of injection‐molded glass‐fiber reinforced polyamide 6,6. In the average fiber diameter range from 9 to 18 μm, dry‐as‐molded (DaM) composite unnotched impact and tensile strength decreased significantly. The composite notched impact performance and tensile modulus showed little dependence on fiber diameter. The influence of broadening the fiber diameter distribution by blending glass fiber samples of different average diameter was found to be particularly negative on the level of composite unnotched impact when compared at equal number average diameter. After hydrolysis treatment, the composite tensile strength and modulus exhibited a large drop compared to the DaM results. In contrast, the unnotched impact results became insensitive to fiber diameter after hydrolysis. The average level of unnotched impact after hydrolysis was sufficiently high to show an increase over DaM when the fiber diameter was above 14 μm. Residual fiber length correlated significantly with fiber diameter with a lower average length for thinner fibers. The interfacial shear strength was found to be in the range of 26–34 MPa for DaM composites. There was a highly significant inverse correlation between the DaM interfacial strength and the average fiber diameter. It is shown that results from both tensile and unnotched impact measurements can be brought back to single trend lines by using a Z average value for the average fiber diameter, which is more heavily weighted to the thicker fibers in the distribution. POLYM. COMPOS., 28:331–343, 2007. © 2007 Society of Plastics Engineers