Temperature Thermal Deformation Research Articles

The effects of the size and content of potassium titanate whiskers on the properties of PTW/PTFE composites

In this study, the effects of the content and the average diameter of potassium titanate whiskers (PTW) on the mechanical strength, thermal properties, tribological performance and chemical stability of PTW/PTFE (polytetrafluoroethylene) composites were investigated. For the small size PTW at 5 wt%, the tensile strength, elongation at break, notched impact strength, thermal deformation temperature and wear resistance were simultaneously increased by 35.6, 46, 3, 11.1 and 1000% over pure PTFE, respectively. When filler size was increased, the tensile strength, elongation and hardness were decreased, while the wear resistance and thermal deformation temperature were improved. The range of PTW in PTFE for optimal integrative properties is 5–10 wt%, which is similar to the behavior of nanoparticles. SEM analysis shows that, comparing to glass fiber/PTFE composites, the internal structure of PTW/PTFE composites is more uniform and dense.

Study on mechanical properties, thermal stability and crystallization behavior of PET/MMT nanocomposites

PET/montmorillonite (MMT) nanocomposites were prepared via melt-blending and its nano-dispersion morphology was confirmed by X-ray diffraction and transmission electron microscopy. Its non-isothermal crystallization behavior was studied by DSC. It is found that the crystallization rate of PET nanocomposite was increased significantly. The Avrami equation parameters related to crystallization, such as n, Z c and t 1/2, were calculated and analyzed. The thermal property and mechanical property of the composite were studied. When the MMT content was 1%, the composite has a desired comprehensive property. At this composition, the thermal degradation onset temperature and the thermal deformation temperature of PET were increased by 12 and 35 °C, respectively, and the tensile strength of the PET was increased by 25% with slightly increase of the notched impact strength.

Preparation of Exfoliated Polyester/Clay Nanocomposites

Poly(ethylene terephthalate) (PET)/clay nanocomposites are prepared by intercalation of a catalyst precursor and an organic modifier, followed by the polymerization of monomers between the adjacent clay layers. The mechanical properties, thermal deformation temperature, anti-UV-radiation properties, CO2 gas-barrier properties, and clarity of bottles blown from the PET/clay nanocomposites (see Figure) are improved.

Assembly of Well-Aligned Multiwalled Carbon Nanotubes in Confined Polyacrylonitrile Environments: Electrospun Composite Nanofiber Sheets

Highly oriented, large area continuous composite nanofiber sheets made from surface-oxidized multiwalled carbon nanotubes (MWNTs) and polyacrylonitrile (PAN) were successfully developed using electrospinning. The preferred orientation of surface-oxidized MWNTs along the fiber axis was determined with transmission electron microscopy and electron diffraction. The surface morphology and height profile of the composite nanofibers were also investigated using an atomic force microscope in tapping mode. For the first time, it was observed that the orientation of the carbon nanotubes within the nanofibers was much higher than that of the PAN polymer crystal matrix as detected by two-dimensional wide-angle X-ray diffraction experiments. This suggests that not only surface tension and jet elongation but also the slow relaxation of the carbon nanotubes in the nanofibers are determining factors in the orientation of carbon nanotubes. The extensive fine absorption structure detected via UV/vis spectroscopy indicated that charge-transfer complexes formed between the surface-oxidized nanotubes and negatively charged (-CN[triple bond]N:) functional groups in PAN during electrospinning, leading to a strong interfacial bonding between the nanotubes and surrounding polymer chains. As a result of the highly anisotropic orientation and the formation of complexes, the composite nanofiber sheets possessed enhanced electrical conductivity, mechanical properties, thermal deformation temperature, thermal stability, and dimensional stability. The electrical conductivity of the PAN/MWNT composite nanofibers containing 20 wt % nanotubes was enhanced to approximately 1 S/cm. The tensile modulus values of the compressed composite nanofiber sheets were improved significantly to 10.9 and 14.5 GPa along the fiber winding direction at the MWNT loading of 10 and 20 wt %, respectively. The thermal deformation temperature increased with increased MWNT loading. The thermal expansion coefficient of the composite nanofiber sheets was also reduced by more than an order of magnitude to 13 x 10(-6)/ degrees C along the axis of aligned nanofibers containing 20 wt % MWNTs.

Fabrication and characterization of poly(methyl methacrylate) microchannels by in situ polymerization with a novel metal template.

A stainless steel template for the fabrication of plastic microfluidic devices has been developed by photolithography and chemical etching technique. The preparation process of the template is simple, rapid, and low-cost. The cross sectional profiles of raised microchannels on the template are trapezoidal. The surface roughness of the templates was controlled down to 190 nm. The template can be used repeatedly to generate devices reproducibly. The microfluidic devices of poly(methyl methacrylate) (PMMA) were fabricated by in situ polymerization using the templates. The reproducibility of the fabricated microchannel is high and the relative standard deviation is 0.7% by the in situ polymerization approach. Some physical properties of the polymerized microchannels were characterized including the transparency, the thermal deformation temperature, and the dimensional information. Current monitoring was used to evaluate the electroosmotic flow within the microchannels under the electric field strength of 300 V/cm.

Location of Sink-marks on the Surface of Injection-molded Polymer Strips Controlled by the Heat Trasfer

This paper deals with a technique for improving the shape quality of injection-molded polymer products by controlling the heat transfer within the mold. In this paper, the authors tried to find a refined technique for improving the sink-mark problem, and examined the mechanism governing the sink-mark generation on an asymmetrically cooled polystyrene strip from the standpoint of thermal engineering. Sink-marks due to the shrinkage are considered to be controlled by both the cohesion between the molten polymer and the mold wall, as well as the stiffness of the frozen layer which gradually develops within the molded polymer adjacent to the mold wall. Although limited to polystyrene strip, the results obtained in the present study showed that the cohesive power of the molten polymer increases rapidly when the mold wall temperature exceeds the thermal deformation temperature of the polymer, and that the thickness of the frozen layer, which dominates its stiffness, monotonously increases with increasing time elapsed after the shot and decreasing with the mold wall temperature.

ガラスマット強化プラスチックの動的破壊じん性

The dynamic fracture toughness values of glass mat reinforced polyester laminates were compared with the analytical values of dynamic stress intensity factor, and their temperature dependence was discussed using instrumented Charpy test results. The results obtained are as follows:(1) The ratio of dynamic fracture toughness KId to the static one KIS, which was obtained by the finite element method, decreased with time by oscillating around one, when the load increased at a constant rate. The ratio of KId/KIS was between 0.99 and 1.1, when the loading speed was about 0.55kgf/μs and KIS was greater than 30kgf/mm3/2 for EW test specimens, and when the speed was about 0.35kgf/μs and KIS was greater than 20kgf/mm3/2 for FW test specimens. The difference between the dynamic fracture toughness values obtained by the static K-calibration using the maximum load and by the dynamic K-calibration was smaller than the variation of measured values.(2) The dynamic fracture toughness values of EW specimens decreased slowly as the temperature became higher, while those of FW specimens were about constant at temperatures below 60°C. The toughness values of both specimens decreased rapidly as the temperature became higher than the thermal deformation temperature of resin (about 90°C). This temperature dependence of toughness was different from that of specific absorbed energy.