Jiazhen Sun

Modification of polytetrafluoroethylene by radiation—1. Improvement in high temperature properties and radiation stability

Polytetrafluoroethylene (PTFE) has never been reported to form a network structure when subjected to high energy radiation. Results obtained in this work indicates that when irradiation is performed under 330-340-degrees-C in vacuo PTFE can be crosslinked

Radiation crosslinking of polytetrafluoroethylene

Abstract Polytetrafluoroethylene (PTFE) is considered to be a typical radiation degradative polymer. In this work the polymer was crosslinked by means of radiation at 335 ± 5°C under vacuum. Crosslinked PTFE showed a great improvement in high temperature properties and radiation stability.

Effects of zeolites on the pyrolysis of polypropylene

Abstract With the intention of understanding chemical recycling of waste polymers, various kinds of zeolites were used as catalysts in the pyrolysis of polypropylene (PP). The effects of zeolites on the degradation temperature and pyrolyzed products of PP were studied. It was found that the degradation temperature of PP strongly depended on the type of zeolite used and the amount added. One type of HY zeolite (320HOA) was shown to be a very effective catalyst. Pyrolysis products, which were identified by using a coupled gas-chromatograph-mass-spectrometer, were also affected by the addition of zeolites. Some zeolites did not change the structure of the products but narrowed the product distribution to a smaller molecule region, while the HY zeolite led to hydrocarbons concentrated at those containing 4–9 carbons. Furthermore, some new compounds with cyclic structures were found in the presence of the HY zeolite.

The compatibility and morphology of chitosan-poly (ethylene oxide) blends

Abstract Thermal behavior and morphology of blends prepared by solution casting of mixtures of chitosan and poly(ethylene oxide) were studied by means of differential scanning calorimetry (DSC) and scanning electron microscopy (SEM). The preliminary results indicate that both melting point and crystallinity depend on the composition of the blends, and that they exhibit minimum values when the blend contains 50% chitosan. From the prediction of melting point depression analysis, the compatibility of the blends shows a transition at this specific composition. This conclusion was further confirmed by observation of the morphology.

Effect of irradiation on pyrolysis of polypropylene in the presence of zeolites

For recycling of waste polymers, the degradation behavior of PP was studied with a combination of radiolysis and thermolysis methods. The results revealed that thermal degradation temperature of PP was significantly reduced when PP was irradiated in the presence of a zeolite. The irradiation-induced temperature reduction depended on the zeolite structure and composition, as well as on the morphology of the mixture. Identification of pyrolysis products indicated that, in the absence of zeolite, irradiation resulted only in a change of the product distribution but no formation of new compounds. In the presence of zeolite, however, a series of oxidized products were formed. In addition, the pyrolysis could be performed at a much lower temperature.

Thermal, mechanical and ionic conductive behaviour of gamma-radiation induced PEO/PVDF(SIN)-LiClO4 polymer electrolyte system

An effort has been made to modify the mechanical behaviour of our previously reported gel-type gamma-radiation crosslinked polyethylene oxide (PEO)-LiClO4 polymer electrolyte. A highly polar and gamma-radiation crosslinkable crystalline polymer, polyvinylidene fluoride (PVDF), was selected to blend with PEO and then subjected to gamma-irradiation in order to make an simultaneous interpenetrating network (SIN), which was used as a polymer host to impart stiffness to the plasticized system. Experimental results have shown that the presence of PVDF in the system, through gamma-radiation induced SIN formation, could not only give a rather high mechanical modulus of 10(7) Pa at ambient temperature, but also maintain the room temperature ionic conductivity at a high level (greater than 10(-4) S/cm). DSC, DMA and conductivity measurement techniques were used to examine the effects of blending, gamma-irradiation and plasticization on the variations of glass transition and melting endotherm, on the appearance of high elastic plateau and on the temperature dependence of ionic conductivity: In addition, it was found that, in contrast with the unplasticized system, the ionic conductivity mechanism of this gel-type electrolyte seems to conform to the Arrhenius model, suggesting that, as a result of the high degree of plasticization, the polymer chains act mainly as the skeleton of the networks or polymer cages to immobilize the liquid electrolyte solution, whereas the ionic species migrate as if they were in a liquid medium

Radiation-induced crystal defects in PTFE

Changes induced in the crystal structure of PTFE by irradiation at different temperatures have been investigated. In the dose and temperature range examined, the density of PTFE was observed to increase continuously with increasing dose due to the radiation-induced increase in crystallinity, while after post-irradiation annealing at 380-degrees-C, the density was observed to increase for samples irradiated at 20-degrees-C, and to begin to decrease after a certain dose for samples irradiated at 150 and 200-degrees-C. On the basis of the observation of radiation-induced separation of the melting peak of PTFE and its stability relative to the change in the rate of heating, the observed decrease in density was explained as being due to the radiation-induced crosslinking and/or branching inhibiting the process of crystallization and existing in the crystalline region as defects.

XPS studies of radiation-induced structural changes in polyvinylidene fluoride

Abstract In this work the radiation-induced structural changes in PVDF were studied using XPS. It was found that for PVDF irradiated at 150°C, double bonds were formed mainly through the further dehydrofluorination of crosslinked and/or branched molecules, whereas for samples irradiated at 20°C the dehydrofluorination of macromolecular radicals to form stable polyene radicals is the main source of unsaturated structures.

RADIATION-INDUCED CROSSLINKING OF CHLOROTRIFLUOROETHYLENE-ETHYLENE COPOLYMERS

Abstract Copolymer of chlorotrifluoroethylene and ethylene (abbr. as F-30) is an alternative copolymer. Irradiated F-30 at certain condition it crosslinks readily. Thus, the mechanical properties of crosslinked F-30 are improved remarkedly. The molecular weight of F-30 has not been reported before. We determine the stress-strain relationship of F-30 at the temperature above its melting point, and find out the crosslinking G value of F-30. We also determine the dose of gelation of crosslinked F-30. From the obtained data, we can calculate the weight of F-30. This method may also be applied to other fluoro-polymers. The sol-gel relation of the crosslinked F-30, F-46, F-406 and F-2406 are determined, and the results are treated according to theoretical relationship of Charlesby-Pinner and Chen-Liu-Tang.

Radiation stability of PTFE irradiated under various conditions

As a typical example of a polymer degraded by radiation, the radiation stability of PTFE was observed to depend upon irradiation conditions. Increases in irradiation temperature and crystallinity were found to increase its radiation stability whereas increase in the concentration of oxygen in the system over a certain range was observed to have little effect on radiation-induced reactions of PTFE as measured by changes in number-average molecular weight, melting temperature and crystallinity.