A 58% (by weight) long glass fiber reinforced (LGF)‐HDPE master batch was blended with a typical blow molding HDPE grade. HDPE composites having between 5% and 20% (by weight) long fiber content were extruded at different processing conditions (extrusion speed, die gap, hang time). The parison swell (diameter and thickness) decreased with increasing fiber content. Although the HDPE exhibited significant shear rate dependence, the LGF/HDPE composites were shear rate insensitive. Both the diameter and weight swell results also indicated very different sagging behavior. The LGF/HDPE parisons did sag as a solid‐body (equal speed at different axial locations) governed by the orientation caused by the flow in the die. Samples taken from blown bottles showed that fiber lengths decreased to 1‐3 mm, from the original 11 mm fiber length fed to the extruder. No significant difference in fiber length distribution was found when samples for different regions of the bottle were analyzed. SEM micrographs corroborate the absence of fiber segregation and clustering or the occurrence of fiber bundles (homogeneous spatial fiber distribution) as well as a preferential fiber orientation with the direction of flow. The blowing step did not change the orientation of the fibers. Five‐percent (5%) and 10% LGF/HDPE composites could be blown with very slight variations to the neat HDPE inflation conditions. However, 20% LGF/HDPE composites could not be consistently inflated. Problems related to blowouts and incomplete weldlines were the major source of problems.
A liquid crystal polymer (LCP) was blended with polyethylene terephthalate (PET) in different concentrations to improve the barrier properties of PET in injection stretch blow molded bottles. The improvement depends on the microstructure developed at various stages of the process. In this work, the emphasis is on the injection molding stage of the preform. The characteristics and number of morphological layers were directly related to the amount and type of LCP in the blend and the location within the preform. It was found that at 10% LCP, three morphological layers were found across the thickness of the part, while at 30% LCP, five morphological layers could be identified. The LCP structure can be classified into four types: droplets, thick rods, thin fibrils and ribbons. Each morphological layer is made up of one or more types of structures. The evolution of one type of structure to another depends on the particular flow regime ongoing at various locations in the mold. This microstructure development, during the flow, was examined in detail.
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