Toxicity And Environmental Protection Of PVC

Since early 1970s, PVC has become an environmentalist, safety advocates and mediators of concern and attack targets, the main contents are:

(1) suspected carcinogenic vinyl chloride;

(2) PVC combustion or waste ashes may form dioxins;

(3) the potential toxicity of some additive PVC;

(4) with safety and environmental risks related to various other charges.

Despite this protracted debate, the worldwide demand for PVC is still growing. Industry has responded to these claims by substantially reducing the diffusion of vinyl chloride in a single processing plant, polymerization plant, resin production plant and the general environment. In addition, if it is not eliminated, it is necessary to reduce the dependence on those potentially harmful additives, such as some heavy metal heat stabilizers, by changing the formula. Further, the waste management program has been launched to deal with some of the claims of the PVC activist to clean up the PVC in the name of the environment.

However, it is clear that global PVC sales have been adversely affected by security issues and concerns. This is the most obvious problem in Europe, where the anti PVC movement has succeeded in promoting some restraining legislation. Any estimate of the loss of the global PVC in the traditional application resulting from this is very uncertain.

The special markets with the greatest impact include:

(1) medical devices;

(2) toys and adolescent health care products;

(3) packaging products;

(4) automotive interiors.

The use of PVC in pipes and other long lifecycle construction products is very little influenced by this concern.

A.Tukker in 2001 after a long and thorough investigation and study, using a variety of "from the cradle to the grave" LCA (life cycle assessment) method of PVC chain of life of Swedish assessment concluded that the PVC chain of life in Sweden's ozone layer disappeared, acidification and eutrophication is only some effect, and the influence on global warming smoke, and soil volume share is only 0.15%, so the effect of PVC on the environment is just the chain of life in general. The impact of PVC life chain on environment is mainly the production of two vinyl chloride / vinyl chloride (releasing two chloroethane, vinyl chloride monomer, volatile organic compounds and carbon dioxide) and soil burial (soil burying).

When the PVC implementation of the chain of life improvement plan, is the production of chlorine (mercury), two chloride (Er Eying), manufacturing PVC products, as well as in the use of poisons and waste incineration when (lead, mercury and Er Eying) greatly reduced amount of total emissions in Sweden is equal to or less than 0.15%. Because PVC almost does not release a large number of other toxic substances, it is sure to improve the overall toxicity and environmental protection to Sweden.

Brussels plastics waste management institute has been engaged in an independent development model and standardized European database, completed the research on the ecological balance of packaging and window frames, and concluded that PVC is favorable for environmental protection. Taking the possible alternatives to replace PVC has no advantage in the ecological balance.

At present, pure PVC is now recognized as nontoxic material, even if it is consumed by the human body, it is not digested. The toxicity of PVC mainly comes from the residual vinyl chloride monomer and the added toxic additives.

In 1979, the upper limit of PVC residual vinyl chloride monomer for food packaging was 1 x 10-6, while the limit of vinyl chloride content in food contacted with products was 1 * 10-9. From PVC products monitored 1974 to 1985 years of vinyl chloride content in food packaging shows that due to the improvement of PVC technology, widely used in continuous gas extraction technology, the European PVC manufacturers and processors have no difficulty to reach this requirement. But you don't know what the upper limit 1 * 10-9 will have on consumers.

In the United States, PVC has been widely used as a food packaging material before 1958, so FDA acknowledges that it is a GRAS (generally considered safe) grade material. From 1960s to 70s, the discovery of vinyl chloride monomer caused the AOL (osteolysis, accoosteolysis) and ASL (angiosarcoma, liver cancer) lesion in specific populations. Because of the fear of carcinogens, residual vinyl chloride will enter into packaged foods, BATF (alcohol, tobacco and light weapons authority) forbids the use of rigid PVC bottles. Therefore, in 1975, FDA put forward a proposal (40FR40259) to cancel the status of GRAS material for rigid PVC, and prohibit it to be used for food packaging, but it does not prohibit soft PVC packaging materials from touching food. PVC resin manufacturing technology and plastic industry rapid response, the PVC residual vinyl chloride concentration reduced to very low in a very short period of time, to eliminate the concerns of consumers, but the FDA until 1986 1975 revocation of the proposal, and reaffirmed the safety of PVC food packaging, just to meet the FDA requirements of residual vinyl chloride limit (51FR4173). According to the interpretation of the Delancy regulations, FDA does not think that the extremely small amount of residual vinyl chloride monograph in hard PVC packaging has an impact on the human and environment.

Most of the PVC packaging materials in contact with food are soft, mostly thin film and PVC coating. The security of this kind of packaging is no longer considered a problem by the FDA. But it is necessary to ensure that the plasticizer used is safe.

According to Ficken theory, the diffusion of small molecules from plastic substrate or plastic substrate is carried out according to the relaxation step of local swelling polymer, and the gradient of concentration is established on the wall of pipes and food packaging materials, which provides power for solute movement. The balance rate is migrated the square of time, temperature and concentration of residual function, the main limiting factor is the original concentration. The low limit of concentration is set from the theoretical and practical considerations, which is lower than this, and there is no obvious migration effect. The experiment has confirmed the prediction of the theory. That is, when the concentration of vinyl chloride in hard PVC is less than 1 * 10-6 or more, the concentration in water will be lower than the actual limit of 1 or 2 * 10-9, and the limit of determination is 1 * 10-9 in non-aqueous simulated food solvents. Only when the storage is exaggerated can the migration of less than 1 * 10-6 be seen.

After storing the PVC resin in a closed container for a long time, the concentration of vinyl chloride in the free space will exceed the index proposed by OSHA, that is, 0.5 * 10-6. If a worker enters a silo and a tank used for storage or transportation, it should be ventilated or with a respirator. The warehouses or transport vehicles of the packaged products are slightly better and usually have enough natural ventilation to prevent ultra - standard exposure. However, there are also a large number of packed materials in the closed place, which may also exceed the standard.

Some chloroethylene will be released during the mixing process, especially during the heating and plasticizing stages, which will lose 1/3~2/3 residual vinyl chloride. If there are plasticizers or multiple times of operation at high temperature, more vinyl chloride will be lost. If only one operation, hard particles will be generated and less vinyl chloride will be lost.

In the drinking water pipe, the production factory put forward the standard of product itself, of which the content of vinyl chloride is not more than 10 x 10-6. In fact, the resin is usually less than 10 * 10-6, so it does not need to be tested over the standard after mixing. The pipe and general resin are often far less than 5 * 10-6 in delivery, and only a small amount of residual vinyl chloride is released in the mixing process. Adequate ventilation is needed to control the odor of plasticizers and stabilizers released by dust and heating. When a extruder is used to process a resin with 2 x 10-6 chloroethylene at a 1t/h rate, the release of vinyl chloride is about 1g/h, and the ventilation rate is about 6m/h enough.

#pvc #pvccompound #pipe

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