Sink or burn marks can appear on injection molded plastics when the air vents in molds become clogged by volatile substances emitted by the molten plastic. The clogging caused by volatiles from PET resin were experimentally reproduced in a glass capillary and the causes of the phenomena were analyzed. When using a nitrogen gas flow, the deposits inside the glass capillary were almost identical with those in the injection molding air vent. The composition of the deposits were as follows; MHET:BHET:B-2:C-2:C-3=87:100:22:66:30 (mold clogs) and 63:100:12:61:21 (glass capillary). The similarity of the compositions is a strong indication that the air vent clog phenomenon was reproduced by the glass capillary experiment using a nitrogen gas flow. A large amount of TA is deposited when air is used instead of nitrogen gas. This is quite different from the deposits accumulated in the injection molding air vent slots. This difference is not unexpected because the short injection time prevents the melted resin from being exposed to air.
The volatility of the main monomers and oligomers that are generated from PET resin in descending order is: TA>BHET>MHET>C-3. On the other hand, the amount of each in PET resin in decreasing order is: C-3>C-2>B-2>BHET>TA>MHET, with the MHET amount being much smaller than BHET. This order is different from that of the mold clogs. The simple monomers (BHET and TA), which are the main volatile substances in PET resin, are conducted in exactly the same manner with PET resin. Though BHET is entirely stable in the nitrogen gas, it changes to MHET in air easily. Therefore, It was concluded that a part of the BHET in the PET resin changed to MHET by the existence of absorbed oxygen within the PET resin and the amount of MHET in volatile substances was comparable with BHET.

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Polymer composites filled with electrical conductive fillers are used in various industrial fields, and some of these materials show a positive temperature coefficient resistivity (PTC). This phenomenon is ascribed to volume expansion of the matrix polymer. By applying the PTC effect, these electrically conductive materials are able to be used as self-temperature control plane heater.
In this study, new type of plane heater, different from ordinary plane heaters, with a rigid network structure filled with conductive fillers was prepared by a new processing method. First of all, the characteristics of the matrix urethane resin such as curing conditions and thermomechanical properties were investigated. This resin mixed with short nickel coated carbon fibers having different fiber lengths or aspect ratios was processed in to thin sheets and cured. The relationship between resistivity and fiber content and the influence of environmental temperature on resistivity of these composites were investigated experimentally. The relationship between heating properties and resistivity of the materials under supplied voltage and also the influence of environmental temperature on heating temperature were also discussed.

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The filler size in polymer composites has experienced a tremendous reduction, especially in nano-composite formulations. The physical properties of polymer composites are also strongly dominated by the dispersion conditions of the filler. In the case of nano-composites, break up of the agglomerated filler is an important factor for improvement of the properties.
In our previous report, the dispersion conditions were explained by using total shear strain [γ·t] as the dominant dispersion parameter, and the optimum mixing conditions for the blending of polycarbonate (PC) and carbon-nanotubes(CNT) were determined.
In this study, break up of agglomerated CNT (analysis of dispersion process) was observed by a visualization analysis of shear flow. CNT was used as the filler in a PC matrix as we reported previously. The minimum shear rate required to break up the agglomerated CNT was defined as “critical shear rate” [γ c]. “Critical shear rate” was observed in two steps of the break up of agglomerated CNT. Dispersion conditions by a visualization analysis of shear flow were explained in terms of total shear strain as performed in the previous report. At the same total shear strains, the shear rate [γ] had a greater effect on the dispersion conditions than the shear rate history time [t] in the PC/CNT material combination.

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