Polyvinyl chloride - Processing and structure
Abstract - Widely different procedures for the processing of PVC have proved themselves and have succeeded in practice on the basis of the special physical and chemical properties of PVC. In this connection a distinction must be made between the processing of plasticized PVC and the relatively difficult processing of rigid PVC. A survey of the most important methods of preparation and processing is given here. The special, rather abnormal properties of PVC in comparison with other thermoplastics are partly a result of its characteristic structure. The consequences for preparation and processing must therefore be considered anew. Of course, the globular structure of PVC has an effect on the behaviour of the solid-state material and the melt, too, so that great importance must be attributed to the processes at the particle interface.
The nature of poly (vinyl chloride) crystallinity—the microdomain structure
The microstructure of polyvinyl chloride (PVC) controls much of its processing and property behavior. A model put together from X-ray diffraction and small-angle scattering data, swelling data, and processing data shows that PVC crystallites, of a wide melting range and spaced at 0.01 micron, act as crosslinks in a three-dimensional network. Tie molecules limit swelling by plasticizer. The network prevents strong primary particle interaction at low melt temperatures. At higher temperatures, partial melting and then recrystallization leads to strong ties between particles and a tough product.
A device for uranium series leaching from glass fiber in HEPA filter
For the disposal of a high efficiency particulate air (HEPA) glass filter into the environment, the glass fiber should be leached to lower its radioactive concentration to the clearance level. To derive an optimum method for the removal of uranium series from a HEPA glass fiber, five methods were applied in this study. That is, chemical leaching by a 4.0 M HNO3–0.1 M Ce(IV) solution, chemical leaching by a 5 wt% NaOH solution, chemical leaching by a 0.5 M H2O2–1.0 M Na2CO3 solution, chemical consecutive chemical leaching by a 4.0 M HNO3 solution, and repeated chemical leaching by a 4.0 M HNO3 solution were used to remove the uranium series. The residual radioactivity concentrations of 238U, 235U, 226Ra, and 234Th in glass after leaching for 5 h by the 4.0 M HNO3–0.1 M Ce(IV) solution were 2.1, 0.3, 1.1, and 1.2 Bq/g. The residual radioactivity concentrations of 238U, 235U, 226Ra, and 234Th in glass after leaching for 36 h by 4.0 M HNO3–0.1 M Ce(IV) solution were 76.9, 3.4, 63.7, and 71.9 Bq/g. The residual radioactivity concentrations of 238U, 235U, 226Ra, and 234Th in glass after leaching for 8 h by a 0.5 M H2O2–1.0 M Na2CO3 solution were 8.9, 0.0, 1.91, and 6.4 Bq/g. The residual radioactivity concentrations of 238U, 235U, 226Ra, and 234Th in glass after consecutive leaching for 8 h by the 4.0 M HNO3 solution were 2.08, 0.12, 1.55, and 2.0 Bq/g. The residual radioactivity concentrations of 238U, 235U, 226Ra, and 234Th in glass after three repetitions of leaching for 3 h by the 4.0 M HNO3 solution were 0.02, 0.02, 0.29, and 0.26 Bq/g. Meanwhile, the removal efficiencies of 238U, 235U, 226Ra, and 234Th from the waste solution after its precipitation–filtration treatment with NaOH and alum for reuse of the 4.0 M HNO3 waste solution were 100, 100, 93.3, and 100%.