Post chlorination

The process of post-chlorinating PVC was carried out during World War II in order to obtain polymers soluble in low-cost solvents and which could therefore be used for fibres and lacquers. The derivate was generally prepared by passing chlorine through a solution of PVC in tetrachloroethane at between 50°C and 100°C. Solvents for the product included methylene dichloride, butyl acetate and acetone. These materials were of limited value because of their poor colour, poor light stability, shock brittleness and comparatively low softening point. 

In the 1960s materials became available which are said to have been obtained by chlorination at lower temperatures. In one process the reaction is carried out photochemically in aqueous dispersion in the presence of a swelling agent such as chloroform. At low temperatures and in the presence of excess chlorine the halogen adds to the carbon atom that does not already have an attached chlorine. The product is therefore effectively identical with a hypothetical copolymer of vinyl chloride and symmetrical dichloroethylene. An increase in the amount of post-chlorination increases the melt viscosity and the transition temperature. Typical commercial materials have a chlorine content of about 66-67% (c.f. 56.8% for PVC) with a Tg of about 110% (c.f. approx. 80°C for PVC). 

Commercial PVC is atactic and has a relatively high Tm (173 0, which is 100 C lower than that of /7-PVC. Because of weak linkages and the presence of some unsaturation, commercial PVC tends to discolor and decompose at normal processing temperatures. More-stable polymers are obtained by the addition of stabilizers or by post-chlorination. Because of the presence of the chlorine pendant group, unplasticized PVC has a higher coefficient of friction than hdpe. 

Chlorination is the most widely used disinfecting or sterilizing process. Where daily water requirements arc not large, it is common practice to use a hypochlorite, but for large plants liquefied chlorine gas is used. Chlorination may be practiced before filtration (prechlorination), after filtration (post-chlorination), or both before and after. 

However, a 50 percent reduction in both chemicals was obtained in post-chlorination treatments of the same waste. 

Post-chlorinated polyvinyl chloride (cPVC) is a material which offers a combination of mechanical strength, temperature and corrosion resistance and low installation costs, that meets a variety of process uses. This comprehensive article describes cPVC s key properties in detail and highlights the various industries and applications for the polymer, particularly pipes and fittings. 

Choisy-le-Roi, France [8 ] Surface water Seine River Ozonation (1) Coagulation/flocculation Sedimentation Sand filtration GAC filtration Ozonation (2) Post chlorination Removal of taste Removal of organics which might form toxic chloro-compounds during post chlorination Two columns Contact time 15 miri. Vol per filter 117 m Filter velocity 9 m/hr Organics removal improved by 40%... 

The heat resistance of polyvinyl chloride was also improved by post chlorination, the ductility of polyethylene was Improved by increasing the molecular weight and the usefulness of polystyrene was Increased by copolymerization with acrylonitrile. Nevertheless, in spite of improvement in performance, resulting from these modifications, most general purpose plastics were under engineered for many applications. 

When only post-chlorination is to be employed the points just considered can be very satisfactory. The trend in recent years toward free chlorination, however, can adversely influence the effectiveness of activated carbon at those points. When pre-chlorination would cause the formation of chlorinated compounds that are adsorbed... 

Since most water treatment plants practice pre- and post-chlorination, an attempt was made to determine the influence of various doses of chlorine on parathion and paraoxon and to study how pH affects the chlorine—insecticide oxidation reaction. Chlorine dioxide was tested under the same environmental conditions as chlorine to compare their oxidative capacities. 

Chlorinated Poly(Vinyl Chloride). Post-chlorinated PVC combines the advantageous properties of PVC, e.g., good chemical and weather resistance with good solubility in most conventional solvents. Its importance has, however, continually decreased in the paints sector. 

Halogens can also be incorporated into the polymeric chain by post-chlorination or -bromination. 

The major benefit of post-chlorination of PVC is the dramatic rise in glass transition temperature as chlorine is added to the molecule. It has been observed that the Tg of chlorinated PVC increases from about 82°C for the starting PVC (chlorine content 57 percent) to about 100°C at 62 to 63 percent chlorine, to above 120°C at about 67 percent chlorine content (146). Fukawa(147)hasdemonstrated thattheTgofa PVC resin, converted to CPVC, follows the relationship ... 

Poly(vinyl chloride) is soluble in few solvents (tetrahydrofuran, cyclohexanone, etc.). An acetone-soluble polymerizate can be obtained by extensive post-chlorination of the PVC and this product contains 63-64% chlorine. Chlorinated PVC s are used as adhesives, lacquer bases, and industrial fibers. The chlorination occurs in solution at 60-100°C or in the gel state at 50°C. In the gel-state chlorination, PVC is swollen with chlorohydrocarbons and irradiated in aqueous suspension with UV light. Since CH2 groups are more easily chlorinated than CHCl groups, the polymer contains approximately equal proportions of- CHCl—CHCl and -f H2—CHCl groups. At an equal chlorine content, the PVC that was chlorinated as a gel possesses a higher glass-transition temperature, probably because of the stronger block copolymer character. 

PE CE Post-chlorinated poly(vinyl chloride) (fiber) BASF, Germany... 

Post chlorinated elastomeric copolymer from isobutene and isoprene... 

The resin identified in this book as chlorinated PVC is ordinarily termed perchlorovinyl in the USSR this is a post-chlorinated polyvinyl chloride with 64-65% chlorine content. This resin may also be identified as chlorovinyl in the USSR. 

Chlorinated polyvinyl chloride (CPVC) n. A PVC resin modified by post-chlorination. A series of such resins, known as Hi-Temp Geon , is available from B F Goodrich Ghemical Co. Compared to conventional rigid PVC, CPVC withstands service temperatures 20-30°C higher, is stronger, and... 

PE CE n. Post-chlorinated vinyl chloride polymer. The post-chlorination process increases chlorine content form 57 to 64%. The resulting polymer is soluble in... 

The chlorine content (chlorine content PVC 56 wt%) can be increased by post-chlorination (post-chlorinated PVC PVC-C). The chlorine content of poly(vinylidene chloride) is ca. 73 wt%. 

Depending on the conditions used, various products may be obtained by the post-chlorination of poly(vinyl chloride). Two types of product are made commercially, one by chlorination at low temperature and one by chlorination at high temperature. 

In the event of a spill or leak involving chlorine, persons not wearing protective equipment and fully-encapsulating, vapor-protective clothing should be restricted from contaminated areas until cleanup has been completed. Figure 2-6 shows a posted chlorine leak evacuation procedure. The following steps should be undertaken following a spill or leak ... 

Liquid aluminum sulfate storage and sign, 34 2-5 Carbon dioxide warning sign and detector, 36 2-6 Posted chlorine evacuation procedure, 38 2-7 Breathing apparatus, 39... 

---