Cellular Structure And Electrical Conductivities Of Microcellular ABS/Carbon Fiber Composites

In this dissertation,acrylonitrile-butadiene-styrene（ABS）/carbon fiber（CF）composite foams were prepared via batch foaming or microcellular injection molding（MIM）.The formation mechanisms of cellular structure were investigated by combining the rheological properties of the composites and the solubility CO₂in the composites,and the relationship between the cellular structure and electrical conductivity of MIM parts was investigated.The dynamic shear and elongational rheological properties of the ABS and ABS/CF composites with four CF contents（5,10,15 and 20 wt%）were studied by using dynamic rheometer and capillary rheometer,respectively.The storage modulus（G′）and complex viscosity（η*）of the ABS/CF composites in the low frequency region were enhanced by CF and the largest increase was achieved for the ABS/CF composite with 20 wt%CF.The apparent viscosity and melt strength of the ABS/CF composites were higher than those of the ABS and were increased with the increase of the CF content.The melt strength was increased from 5.7m N for the ABS to 30.3 m N for the ABS/CF with 20 wt%CF.The ABS/CF composite foams were prepared via batch foaming process.The effects of CF content,foaming temperature,saturation pressure and depressurization rate on cellular structure were studied.The ABS/CF composite foams with bi-modal cell structure were achieved.The large and small cells were formed by the CF and the PB phase in ABS matrix used as nucleating agents,respectively.The average diameter and density of the large and small cells were decreased and increased with the increase of the CF content,respectively.As for the ABS/CF composite foam with 10 wt%CF,the smallest average diameter and highest density of large and small cells were achieved at the foaming temperature of 70℃.At a saturation pressure range of 6–10 MPa,the average diameter and density of large and small cells were decreased and increased with the rise of saturation pressure,respectively.As further increasing the saturation pressure to 12 MPa,there was almost no change in the average diameter and density.The cell diameter and its uniformity of small cells were largely affected by depressurization rate（0.05 and 20 MPa/s）.Compared to conventional injection molding（CIM）,the electrical conductivities of the ABS/CF composites was enhanced by MIM,and the electrical conductivity of the ABS/CF composite foams with 15 wt%CF was increased by 17 times.The highest electrical conductivity was achieved for the sample near the gate of the MIM ABS/CF composite part with 15 wt%CF molded at the shot size of 26.5 cm³.The electrical conductivities of the samples near the gate of the MIM ABS/CF composite part with 15 wt%CF were enhanced with the increase of injection speed,gas content and melt temperature.The electrical conductivitise of three samples from near the gate location to end location were gradually increased.The main factors that affected the electrical conductivities of MIM ABS/CF composite parts were cellular structure,thickness of each layer（skin,transition and core layer）and the orientation and contact degree of CF through thickness direction.