The world's construction industry consumes about about 10000000 tons of plastic annually, accounting for 1/4 of the world's total plastic output, ranking first in the use of plastics. Plastics have been listed in the four major building materials with cement, steel and wood. The rapid development of building materials, in addition to the excellent performance of the product itself, is also in the protection of human ecological environment awareness and national protection of forest resources, land resources and water resources policy. The popularization and application of building plastics, although by the design, production departments and the user's attention, but at the same time, we can not ignore the production and use of PVC in the environment and human health damage.
In recent decades, PVC has been the focus of debate. There are different views on the effects of PVC on human health and environment from the perspectives of science, technology and economy. On the basis of science, a comprehensive analysis of the life cycle of PVC, as well as its various environmental problems, including the impact on human health.
(Poly vinyl chloride) (PVC) is a kind of polymeric material (or resin), which is made up of monomer vinyl chloride (VCM) which has been repeatedly stacked by molecular formula CH2-CHCI. In addition to chlorine, PVC and polyethylene have the same structure, chlorine in PVC accounted for 57% of pure polymerization resin, 35% chlorine from potassium chloride analysis of potassium.
Pure PVC is a granular material, high mechanical hardness, anti climate change, good waterproof, anti chemical properties and study of electrical insulating materials. However, due to the relative instability of heat and light, heating and ultraviolet light lead to the loss of chlorine in hydrogen chloride (HCL), which can be avoided by adding stabilizers. The stabilizers are usually composed of metal salts such as lead, barium, calcium, cadmium or organotin compounds.
The mechanical properties of the PVC by low molecular weight compounds in the polymer matrix to change. The substance added is called a plasticizer. This plasticity material is an organic salt, mainly by two formic acid and oxalic acid salt. The main applications are rigid PVC (total dosage of 2/3) and flexible PVC (total amount of 1/3).
二. Production process of PVC compounds
PVC has two main production process, suspension polymer VCM (80%) and emulsion polymers (10%): from vinyl and chloride or vinyl and hydrogen chloride production VCM is a closed process of industrial production, emissions of chlorine, ethylene, vinyl chloride, HCL, VCM and chlorinated by-products including dioxin. Can be discharged into the work environment and the external environment such as air and water, some of these chemicals are harmful substances.
The original PVC must add some additives called PVC compounds before they are processed into the final product. PVC is a thermoplastic material, that is, by heating, melting can form many shapes. After cooling, the material displays its original characteristics. Using this principle, the use of a large number of different methods to PVC transformation, such as extrusion, injection moulding, blow wheel pressure, shape, form, shape and rotating heat film etc..
But during the synthesis and further transformation, some emissions of harmful substances so that workers exposed, synthesis of PVC powder and additives (in the form of powder or liquid) is usually carried out in closed equipment, workers in the mixer by the synthesis of contact, long time exposure will cause damage to human health.
PVC is overheated in the process of heating and cooling, and there are some risks of degradation of compounds, among which HCL is the most important one. Although it is rare, it has some negative effects on the environment.
三. Range and type of additives:
The most important type of additives is stabilizers, which need to scientifically analyze their risk characteristics and risks to human health and the environment, especially containing heavy metals such as lead, cadmium and plasticizers, such as phthalates.
(1) lead stabilizer
Lead salt stabilizer is a kind of heat stabilizer for plastics with low price and excellent performance. It is widely used in PVC products. But since lead is heavy metals and harmful to human health, from the health and environmental protection considerations, since 2000, Norway, Finland, Sweden, Denmark and the United Kingdom and other European countries have adopted the action of disable lead salt stabilizer. At present, the lead pollution found in PVC plastic water pipe mainly comes from the lead salt which is widely used in PVC plastic water supply pipe. The heavy metal lead in the pipe will precipitate in the pipeline, and directly lead to the pollution of drinking water. At present, the plastic water supply pipe containing lead salt has been listed as the main material for the prohibition of lead in the world, and the Construction Department of the state and Beijing has stipulated that from April 1, 2005 this year, PVC plastic pipes and fittings which restrict the use of lead salt as stabilizer are restricted. By October 1, 2005 this year, it will be stopped within the prescribed scope. If leaded plastic water pipes are used, the lead pollution in the water will be directly caused.
Various colors of some families and public places decoration are widely used in heavy metal containing paints and coatings, a variety of room decoration, automobile exhaust near the highway into the room in residential ventilation, and even some waste gas from the factory into the interior, may cause the lead pollution in indoor air. At present, there are some PVC plastic materials in interior decoration materials, such as PVC doors and windows materials, kitchen and bathroom ceiling materials and so on. Experts predict that with the further understanding of lead salt pollution, other PVC products using lead salt as stabilizer are also faced with