Based on a new expansion technology for oriented polyvinyl chloride (PVC-O) pipes, the stress distribution in pipe wall during expansion and the efficiency of the heating process are analyzed theoretically. According to the results of theoretical calculation, the optimal parameter and strength variation for different expansion ratios are studied experimentally. Theoretical calculation results show that the hoop stress and radial stress in pipe wall are near-linearly distributed, and they are approximately equal. The heating efficiency is gotten by heat transfer calculations for different oil bath temperatures and heating times. After expansion, the intensity and Young's modulus are increased but elongation at break is reduced. All the variations in properties enlarge along with the raise of expansion ratio. Fine appearance and high-strength PVC-O pipe can be achieved by optimizing the expansion parameter.
The properties of the polymer nanocomposites (PNCs), consisting low density polyethylene (LDPE) and magnesium oxide nanoparticles (MgO-NPs), were systematically discussed in this paper. The shear mixing time and MgO concentration were considered as the two factors affecting the dispersion state, which was found to be effective to change the crystallinity and the mechanical performance of MgO/LDPE PNCs. A reduction in the dynamic shear viscosity was observed when the concentration of MgO-NPs at a relative low level, which was also dominant by the dispersion states of MgO-NPs. Evident enhancement of the static yield stress was revealed only by introducing a minute amount of MgO-NPs (0.25 wt %). Meanwhile, the elastic and loss modulus were also found to be dependent on the dispersion state of MgO-NPs. A positive increase in dielectric permittivity was identified by uniaxial stretching the MgO/LDPE PNCs strips owing to the orientation enhancement of internal microstructure. V C 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 43038.
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