Polyacetal is used for many mechanical parts because of its high lubricity. Gas injection molding is applied to the processing of plastic parts to obtain good quality and performance. In this study, gas injection molding of polyacetal mechanical parts in a printer roller application was investigated. Two rollers (Design 1, 2) were molded by gas injection molding with several polyacetal. The obtained rollers were evaluated by comparing with those made by the conventional injection molding with the same materials. It was found that the precision of gas injection moldings was better than that of conventional injection molding. This improvement is due to the long uniform gas pressure in the cavity. However the surface roughness was not enough because of the jetting phenomena. We have also investigated the relationship between surface roughness and crystallization time, and it was clear that the material with a good surface roughness could be obtained when the crystallization time of the material was long. Moreover, because metal insertion is not necessary in the case of gas injection molding, polymer recycle is easier than for rollers with metal inserts. This high lights one of the environmental advantages of gas injection molding. These results suggested the possibility of higher precision, reduced cost and improved recycling of polyacetal mechanical parts.

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The thermal stability and recyclability of polycarbonate resin (PC) composites filled with coprecipitated polyhydric phenol/polyethylene glycol (CGP) have been investigated. The composites were evaluated after 4 repeated molding. For the composites containing 0.02wt% polyhydric phenol CGP, the number-average molecular weight (M_n) of PC in the composites, measured by gel permeation chromatography, decreased from 24300 to 22100 after 4 injection molding cycles while the unfilled PC resin control decreased to 21000. These results suggest that the PC molecule depolymerized during the injection molding process due to the thermal energy and stress. On the other hand, we found that the CGP reduced the increase in PC Izod impact strength to 120% that of the neat PC resin. In addition, we studied the effects of the addition of a coprecipitate of polyhydric phenol with polyethylene glycol at levels of 0.02 to 0.03wt%. The glass transition temperatures (T_g) of the composites were evaluated by dynamic viscoelastometry. Using the Fox equation to examine the T_g-M_n^-1 plots of these PC composites, it was observed that these results were different from those expected for particle dispersed PC composites.
These findings suggest that the addition of polyhydric phenol/polyethylene glycol coprecipitation compounds in PC improved the stability of PC. This implies that added coprecipitation compounds may be an effective method in the recycle of PC resin.

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An in-line sensor using near infrared (NIR) spectroscopy was developed for sensing carbon dioxide (CO₂) concentration in molten polymers during the extrusion foaming process. The sensor obtains the CO₂ concentration from the measured NIR absorption spectra. The spectra were acquired in-line through probes equipped at the die of the extruder. The experiments were conducted on three different polymers, polypropylene (PP), low-density polyethylene (LDPE) and polybutylene succinate (PBS), at different flow rates and at different operating temperature. By employing wavelet transforms for analyzing the NIR spectra, the influence of the operating conditions such as operating temperature and flow rate on CO₂ measurement could be eliminated. The regression model derived from the wavelet-treated NIR spectra could successfully estimate the CO₂ concentrations for all three polymers.

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