What is PVC?
Plastics are also called synthetic resins and are broadly classified into two categories: thermosetting resins and thermoplastic resins.
The thermosetting resins include phenolic resin and melamine resin, which are thermally hardened and never become soft again. Thermoplastic resins include PVC, polyethylene (PE), polystyrene (PS) and polypropylene (PP), which can be re-softened by heating.
Usually, thermoplastics are supplied in the form of pelletised material (compounds) with additives (antioxidants, etc.) already blended in it. However, PVC resin is often supplied in powder form and long term storage is possible since the material is resistant to oxidation and degradation. Various additives and pigments are added to PVC during the processing stage, and the blend is then converted into PVC products.
PVC is sometimes known as ‘Vinyl’ in Europe and predominantly so in North America. In Europe, ‘Vinyl’ usually refers to certain specific flexible applications, such as flooring, decorative sheets and artificial leather.
PVC is a thermoplastic made of 57% chlorine (derived from industrial grade salt) and 43% carbon (derived predominantly from oil / gas via ethylene). It is less dependent than other polymers on crude oil or natural gas, which are non-renewable, and hence can be regarded as a natural resource saving plastic, in contrast to plastics such as PE, PP, PET and PS, which are totally dependent on oil or gas. This chlorine gives to PVC excellent fire resistance.
How is PVC made?
The chemical process for making PVC involves taking the monomer, and linking these monomer molecules together in the polymerisation chain. The process formed is called polymers (which are also called macromolecules).
This is the case for PVC, which is made from vinyl chloride monomer through polymerisation. Polymers such as PVC, which are manufactured from monomers through polymerisation, are solid and chemically stable substances, therefore do not affect human health or the environment negatively. VCM, which is the raw material for PVC, is a gas at ambient temperature but is usually stored in liquid form under pressure. Ethylene and chlorine are raw materials for PVC. Upstream industries are those that provide these materials and include producers of basic petrochemicals, which supply ethylene, and chlorine.
By thermal cracking of naphtha or natural gas, the basic petrochemical industry manufactures ethylene and propylene, etc. Naphtha is mainly supplied from the petroleum refinery industry, which uses crude oil as raw material. The chlor-alkali industry produces caustic soda, chlorine and hydrogen via electrolysis using industrial grade salt as main raw material.
At a first stage in the PVC production process ethylene and chlorine are combined to produce an intermediate product called ethylene dichloride; this is then transformed into vinyl chloride, the basic building block of polyvinyl chloride or PVC. The process of `polymerisation’ links together the vinyl chloride molecules to form chains of PVC. The PVC produced in this way is in the form of a white powder. This is not used alone, but blended with other ingredients to give formulations for a wide range of products.
Most commodity plastics have carbon and hydrogen as their main component elements. PVC differs by containing chlorine (around 57 per cent by weight) as well as carbon and hydrogen. The presence of chlorine in the molecule makes PVC particularly versatile because it makes it compatible with a wide range of other materials. The chlorine content also helps to make PVC flame retardant. It can also be used as a `marker’ to distinguish PVC in automatic sorting systems for plastics recycling. PVC formulations can be shaped by a variety of techniques and, using very little energy, made into the final product form. PVC polymer is chemically stable, neutral and non-toxic. PVC formulations have a wide range of applications including the most sensitive, such as medical equipment, plus construction, automotive and electrical cabling.
Fire Retarding Properties
PVC has inherently superior fire retarding properties due to its chlorine content, even in the absence of fire retardants. For example, the ignition temperature of PVC is as high as 455°C, and is a material with less risk for fire incidents since it is not ignited easily.
Furthermore, the heat released in burning is considerably lower with PVC, when compared with those for PE and PP. PVC therefore contributes much less to spreading fire to nearby materials even while burning.
We also offer PVC grades with special fire retardant treatment, to further enhance this property.
Therefore, PVC is very suitable for safety reasons in products close to people’s daily lives, as well as truck trailer tarps.
Under normal conditions of use, the factor most strongly influencing the durability of a material is resistance to oxidation by atmospheric oxygen. PVC, having the molecular structure where the chlorine atom is bound to every other carbon chain, is highly resistant to oxidative reactions, and maintains its performance for a long time, making it perfect for truck trailer tarps.
Other general purpose plastics with structures made up only of carbon and hydrogen are more susceptible to deterioration by oxidation in extended use conditions (such as, for example, through repeated recycling).