In this study, we developed a thin-walled bar-flow cavity mold (cavity thickness: 0.5mm) in order to understand the influence of residual gas inside the cavity on the flow length and appearance during ultra high-speed injection molding of polypropylene (PP) and liquid crystal polymer (LCP). Both the resin flow and the internal gas pressure were simultaneously measured. The results of the effects of gas-venting on the flow length and blister generation of the LCP and PP molded part are summarized as follows:
1) The flow length of PP and LCP molded samples increased with increasing screw injection speed (injection rate), but the flow length did not differ between natural exhaust (with gasvent) and forced exhaust (with vacuum-pumping).
2) After heat treatment, numerous blisters were found in the LCP molded samples during high injection rates under natural exhaust, but not under forced exhaust even at ultra high-speed.
3) The results suggested that blisters generated from residual gases trapped in the resin due to the jetting phenomenon inside the sprue during ultra high-speed filling.

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In this study, we investigated the correlation between the flow-front velocity and gas pressure inside the cavity during ultra high-speed filling under different gas-vent conditions and sprue volumes using polypropylene and a thin bar-flow cavity mold with a thickness of 0.5mm. The results are summarized as below.
(1) In the case of normal exhaust (with gas-vent) and forced exhaust (with vacuum-pumping), the resin completely filled the cavity, but without gas-vents, the flow front velocity dropped and led to incomplete filling. In addition, the gas pressure in the cavity exceeded 4MPa.
(2) With a reduced volume sprue of about 40% the normal volume, the peak gas pressure inside the cavity dropped, the speed of the resin in the runner increased (about 30%), and the flow front advance velocity in the cavity also increased (about 35%). It was also found that the flow length increased by about 10%, indicating that a decrease in the sprue volume contributed to increasing flow length.

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The establishment of recycling systems and the reduction of various fiber wastes are strongly required to create a truly recycling society. In recent years, antibacterial functionality in products such as household articles have become widely used because of the rising demand for cleanliness and comfort in our lives. Therefore the amount of antibacterial waste fibers is expected to increase in the near future. With this trend in mind, this paper focuses on the use of PET fiber waste containing antibacterial agents in producing useful PET fiber reinforced PP thermoplastic composites.
The PET waste fibers containing antibacterial agents were cut into 50mm lengths and mixed with a PP web by using a carding machine to make PET/PP webs with 0-70 weight percent of PET fiber (W_f). Samples were compression molded at a molding temperature between 180∼250°C. The antibacterial and the mechanical properties of the PET/PP composites were evaluated.
The results of antibacterial tests showed that the antibacterial activity of the composites increased with increasing W_f. The composites with large W_f showed high antibacterial activity at short times. The bending strength of composites with W_f=10∼40% was larger than that of the neat PP matrix, and showed a maximum value at W_f=40% of about 1.6 times that of the neat PP matrix. The Izod impact value also increased notably with increasing W_f. It was concluded that the molding system devised here was an effective method for the recycle of PET fiber waste containing antibacterial agents in composite materials.

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