PVC production

Organophosphoms compounds, primarily phosphonic acids, are used as sequestrants, scale inhibitors, deflocculants, or ion-control agents in oil wells, cooling-tower waters, and boiler-feed waters. Organophosphates are also used as plasticizers and flame retardants in plastics and elastomers, which accounted for 22% of PCl consumed. Phosphites, in conjunction with Hquid mixed metals, such as calcium—zinc and barium—cadmium heat stabilizers, function as antioxidants and stabilizer adjutants. In 1992, such phosphoms-based chemicals amounted to slightly more than 6% of all such plastic additives and represented 8500 t of phosphoms. Because PVC production is expected to increase, the use of phosphoms additive should increase 3% aimually through 1999. 

Internal Plasticizers. There has been much dedicated work on the possibiUty of internally plasticized PVC. However, in achieving this by copolymerization significant problems exist (/) the affinity of the growing polymer chain for vinyl chloride rather than a comonomer implies that the incorporation of a comonomer into the chain requites significant pressure (2) since the use of recovered monomer in PVC production is standard practice, contamination of vinyl chloride with comonomer in this respect creates additional problems and (J) the increasing complexity of the reaction can lead to longer reaction times and hence increased costs. Thus, since standard external plasticizers are relatively cheap they are normally preferred. 

The steps involved in the incorporation of a plasticizer into a PVC product can be divided into five distinct stages ... 

Emissions During Processing. During the production of flexible PVC products plasticizers are exposed for up to several minutes to temperatures of - ISO C. The exact conditions depend on the processing technique employed, but it is evident that the loss of plasticizer by evaporation and degradation can be significant. 

In volume terms the most important class of fire retardants are the phosphates. Tritolyl phosphate and trixylyl phosphate are widely used plasticisers which more or less maintain the fire-retarding characteristics of PVC (unlike the phthalates, which reduce the flame resistance of PVC products). Better results are, however, sometimes obtained using halophosphates such as tri(chloroethyl) phosphate, particularly when used in conjunction with antimony oxide, triphenyl stibine or antimony oxychloride. 

Flexible PVC grades account for approximately 50% of PVC production. They go into such items as tablecloths, shower curtains, furniture, automobile upholstery, and wire and cable insulation. 

Over 90% of organotin stabilizers are used in rigid PVC. Table 3 provides details of the estimated quantities of methyl-, butyl-, and octyltin stabilizers used in rigid and flexible PVC applications, whereas Table 4 details the types of applications in which the PVC products are used. 

For the octyltin compounds, the only source of these substances relates to their use as stabilizer compounds in PVC products (including other relevant life cycle stages such as production). Thus, it can be safely assumed that measured levels in the environment relate to this application. 

Methyltin compounds, in addition to being used as stabilizers in PVC products, can also be produced via natural processes in the environment. Thus, as with butyltin compounds, it is not possible to exactly attribute the source of methyltin compounds in the environment. 

Another study (Mersiowsky et al., 1999) also undertook laboratory-scale landfill simulations of PVC products, with leachate and landfill gas as well as PVC degradation analysed. It was found that some of the plasticized PVC products exhibited a partial loss of additives into the leachate. Furthermore, Mersiowsky et al. (2000) also monitored a number of actual landfill... 

DEPA (2001) Phthaiates and organotin compounds in PVC products. Copenhagen, Danish Environmental Protection Agency, 16 August (Journal No. M 7041-0367). 

Matthews, G, PVC Production, Properties and Uses. (1996) Institute of Materials V. 587, Great Britain. 

In the results the emissions of mercury appear to have a very substantial contribution for the human toxicity impact score. These emissions are caused by the coproduction of chlorine and sodium hydroxide by electrolysis using a mercury cell. However, this technique is phased out. Therefore, the process descriptions in the Ecoinvent database do not represent up to date technology. In the Ecoinvent database the process for PVC production, in which chlorine is used as one of the compounds, is an aggregated processes based on, seemingly outdated, data from PlasticsEurope. These outdated data also influence the impacts related to waste treatment by incineration because sodium hydroxide is necessary for the waste incineration process. 

Figure 4. Emulsion PVC production in the new continuous latex reactor train.

It was found that the amount of energy needed for the room fire to cause thermal decomposition of the PVC products in the plenum was larger than that needed to take the room to flashover. Furthermore, if the PVC products did eventually decompose or burn, somehow, they would cause a lethal smoke concentration only significantly later than a lethal (by toxicity) atmosphere had already been created by the fire itself. Thus, the PVC products did not add any significant fire hazard to that caused by the room fire. 

Describe measurements of mass loss rates of various electrical PVC products, by thermoanalytical experiments. 

The fire properties of PVC have been put into perspective recently [4, 5]. They show that PVC is a polymer with a high ignition temperature and low flammability. Furthermore, PVC products are associated with a low rate of heat release as well as little total heat released [4-9]. This will depend, clearly, on the type of product, since plasticised PVC products are obviously more flammable than rigid ones. 

The average rate of mass loss is calculated from the amount of mass lost and the corresponding time period. The calculations in Table I at 573 K represent the average mass loss of isothermal dehydrochlorination. Thus, the values in Table I (3.4 %/min for blue conduit, 2.9 %/min for grey conduit and 2.3 %/min for wire coating) represent a reasonable estimate of the mass loss rate of the PVC products in a fire, at a temperature not exceeding 563 K. 

The heat release rate necessary for flashover was calculated, from the equation given by Quintiere et al. [31]. The series of equations is then solved, with the assumption that the temperature increase for flashover is 500 K (leading to an upper level temperature of TUL 795 K) and the plenum temperature for decomposition of the PVC products is 573 K. The results in Table III show that a much more intense fire is required, in all cases, to cause the PVC products to undergo dehydrochlorination than to take the room to flashover. Thus, the heat released by this fire at flashover is insufficient to dehydrochlorinate the PVC products in the plenum, for any of the scenarios. Therefore, the occupants of the room will succumb before there is an effect due to the plenum PVC products. 

It is of interest to calculate, too the time required for both the fire itself and the thermal decomposition of the plenum PVC products to produce a lethal atmosphere. Table III presents such results for the fire, for heats of combustion of 20 kJ/g and 40 kJ/g, a range typical of most fires. In order to carry out this calculation it is assumed that the smoke is distributed instantaneously throughout the volume being considered, one or four room-plenums. The barriers represented by walls or... 

In order to calculate the "time to lethal concentration" the concentration of smoke (per unit time) is first calculated. Then the total amount of smoke (in concentration per unit time) is calculated from the mass of material (and, in the case of the PVC products, the percentage of the weight of the product that can be volatilised, as seen from the STA results). To the ratio... 

Table III presents the results of calculating the "time to lethal concentration" for each one of the PVC products investigated. The toxic potency values used for all the materials are based on 30 min exposures in the NBS cup furnace toxicity test, in the Non-Flaming mode, the one most relevant to this scenario.

It is clear that the "time to lethal concentration" for the smoke from any of the PVC products in the plenum, in all the six scenarios considered, is much longer than the time required for the fuel in the room itself to cause a lethal concentration in the same scenario. 

Fires starting in a room may eventually get transferred to a plenum above it. However, by the time the effects of such a fire cause PVC products (rigid conduit, ENMT conduit and wire coating) in the plenum to burn, the room has already reached flashover conditions. Furthermore, the smoke generated by the room fire fuel causes much faster toxic concern than that from the PVC products in the plenum. 

Di-n-butyl phthalate (DBP) Diethyl phthalate (DEP) Butyl benzyl phthalate (BBP) Di(2-ethylhexyl) phthalate (DEHP) a a O O y Plasticizers in PVC production. Component in the manufacture of cosmetics, inks, and adhesives - SW levels are near to 10 pg L 1 in rivers, between 0.5-1 pg L 1 and in sea water between 0.005-0.7 pg L-1 - US streams 2.5 pg L 1 (DEHP) and 0.25 pg L"1 (DEP) [4] Fast biodegradation under aerobic conditions. Half-life in water 1-15 days Half-life in soils 7 days -several months [65]... 

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