Know Your Plastics Series: Polyvinyl Chloride.

PVC: Resins, products and recycle code

Following polyethylene and polypropylene, polyvinyl chloride (PVC) is the third most widely used worldwide. In construction, PVC is fast replacing traditional building materials such as rubber, clay, wood, concrete, glass and metal.

The first preparation of PVC was in 1935 by a French chemist, Henri Victor Regnault but was patented in 1912 by a German chemist, Freidrich Heinrich August Klatte. The first commercial production was done in 1926 by Waldo Lunsbury Semon while working for the US Company, B. F. Goodrich. The product of his work is what is known as plasticized PVC today.

Polyvinyl chloride is a thermoplastic that is generally white in colour, brittle, solid, odourless and quite popular. Available in pellets and powder form, its versatility cuts across numerous applications such as:

Applications of PVC

- water pipes (drinking, waste, irrigation, industrial)

- garden hoses

- roofing and flooring

- Cables

- Children toys

- door and window frames

- credit cards

- healthcare (blood bags, intravenous (IV) bags, feeding tubes, artificial skin)

- shower curtains

- raincoats

- shrink wrap (most common packaging material in the world)

- automobile fittings (mud flaps, sun visors, interior panels and underbody coating)

- Sports venue seats, flooring, roofs, piping, wiring as well as sporting equipment.

Components of PVC

The primary ingredients in PVC are salt and oil.

Surprising?!

In layman’s terms, one may refer to the chlorine obtained from saltwater and the ethylene obtained from petroleum as salt and oil. For PVC, these two organic ingredients undergo several chemical processes that create the vinyl chloride monomers that are eventually linked to produce PVC resin, the standard base for vinyl compounds.

The other essential ingredients in a PVC formulation include:

- Primary plasticiser

- Secondary plasticizer

- Stabilisers (heat and light)

- Lubricants

- Fillers

- Pigments

- Special additives (where necessary)

Depending on the intended properties in a PVC sample, PVC resin is combined with the other ingredients to get a vinyl compound. The formulation used will determine if the PVC will be rigid, flexible or blended; its colour, durability, reaction to UV conditions and other characteristics.

Types of PVC Resin

Based on the polymerisation method used during production, there are four types of PVC resin:

1. Bulk Polymerised PVC: This resin is the purest form of PVC because emulsifying or suspending agents are not involved. Here, plasticisers are mixed with PVC powder to form a paste-like resin used in spraying, coating or dipping. They are produced primarily for transparent applications, but recent developments in suspension resin technology are steadily replacing the bulk polymerised PVC.

2. Suspension Grade PVC: Production involves polymerising Vinyl Chloride monomer droplets while suspended in water. Depending on the suspension agents and polymerisation catalysts used, the structure of suspension grade PVCs may be rigid or porous:

- Porous structure: This suspension grade PVC has a coarser particle size that allows more quantities of plasticiser to be absorbed. Plasticised PVCs make footwear, cables and soft calendared sheeting and films.

- Rigid structure: These PVCs are unplasticised and are useful in high volume, rigid applications such as PVC pipes, ducting, windows and sidings.

Rigid PVCs are the most common type available, with their particle size ranging from 50-250 microns.

3. Copolymer PVC: Comonomers (Vinyl acetate and Vinyl Chloride) are copolymerised to produce a unique range of resin properties known as Copolymer of Vinyl Chloride and Vinyl Acetate AKA PVAc.

- PVAc is used for floor tiles especially, the Vinyl Asbestos variant. Usually, it functions as a binder and not the main ingredient. For instance, floor tiles are a combination of 84% fillers such as calcium carbonate or asbestos (though asbestos is now on the blacklist) and 16% of copolymer and other additives.

One advantage of this copolymer PVC or PVAc is the high melt viscosity that allows it to coat inert fillers at a high level.

- PVAc solvents are the top choice for vinyl printing inks and solvent cement.

4. Emulsion Grade PVC: Also known as paste grade resin, its production process is similar to that of the powdered milk-an emulsion of PVC in water is spray-dried, producing a very fine-particle PVC that is mainly in plastisols.

Plastisol is the general name for PVC particles suspended in plasticisers; they are the most common moulding liquid thermoplastic usually used for tool handles and medical supplies. Other properties include:

- They have compact structures that do not absorb a large amount of plasticiser at room temperature. When temperatures rise to between 160 and 180 degrees during curing, the resin can absorb more plasticisers.

- It contains emulsifying chemicals and catalysts that reduce its purity and clarity levels compared to the suspension or the bulk polymerised types.

- The electrical properties are lower than those of suspension resin compounds

- It is more expensive than the suspension resin because it requires a lot more energy to produce.

The most common application of paste grade resin is in wide-width, cushion vinyl flooring.

Types of PVC Pipes

PVC is well known for its usefulness in pipes used for transporting water for residential, industrial, irrigation and drainage purposes. The success of PVC in these applications requires the presence of specific properties. The result? Multiple pipe variants.

The top four variants of PVC pipes are:

1. PVC-U pipes – Otherwise known as rigid PVC, PVC-U is most commonly used in pipes and fittings for transporting drinking water and wastewater. The U in PVC-U represents unplasticised, which means it does not contain the solvent called a plasticiser. When added to PVC, plasticiser reduces brittleness thereby, making it more flexible. PVC-U is light, affordable, durable, easy to handle and recyclable.

2. PVC-O pipes - This is PVC that undergoes a molecularly oriented process that essentially produces a layered structure that heightens its corrosion resistance. Other properties include unique strength, stiffness, flexibility, hydraulic capacity and durability. These make PVC-O a perfect high-pressure pipe for irrigation, drinking water and sewer pumping mains..

3. C-PVC pipes – The C in C-PVC stands for Chlorinated. Bearing similar characteristics with PVC-U, the difference is that the chlorination in C-PVC accommodates a wide range of temperatures than PVC-U. Highly resistant to corrosion, C-PVC pipes are engineered to transport drinking water in residential and commercial construction. Chlorinated Polyvinyl Chloride is also known as perochlorovinyl.

PVC-Hi pipes – High Impact PVC pipes are used primarily in transporting natural gas. The high volatility of this product requires that every PVC-Hi product meets a multitude of international standards and regulations to certify that it has long-term strength and can withstand very high pressures. To meet the requirements for durability and resistance to external blows, conventional PVC pipes are a combination of modifier and a mixture of compounds.

Benefits of PVCs

1. Versatile – The properties of PVC (in both rigid and flexible forms) allows for a higher degree of freedom especially, when designing products and solutions for replacement or refurbishing purposes. From window frames to water systems, interior designs and scaffolding billboards, PVC is a preferred material.

2. Compatibility with additives – PVC structure and chemical make up allows for different substances known as additives to mix easily with PVC. These additives improve qualities in the PVC product such as colour, elasticity, flexibility, resistance to fire, microbes, mist and impact.

3. Durable – Resistant to chemical rot, corrosion, weathering and other forms of degradation, PVC is the prime pick for many outdoor products that require a medium to long term life span. Compared to other piping materials, PVC is engineered to have a higher resistance to stress, shock, abrasion and the effects of atmospheric oxygen. These features make it so durable that it can last up to 100 years in use and storage

4. Lightweight and strength – With their lightweight and abrasion resistance, PVCs possess technical toughness and mechanical strength which, is crucial in building and construction.

5. For specialised packaging - The properties of high clarity and no taint to food makes PVC suitable for special packages.6. Excellent dialectic strength – PVC can resist a great deal of electric field strength. PVC does not conduct electricity so, it works in insulation applications such as sheathing of low voltage residential cables, switch boxes, insulation tape and communication cables. This feature is further enhanced when the PVC is fire-resistant.

7. Cost-effective – Generally, PVC pipes are cheaper to purchase and maintain. As long as piping lasts decades without the need for a replacement, that is money saved. Its durability, life span and low maintenance provide the great cost-performance advantage for which PVC is known.

8. Ease of installation – The lightweight reduces any difficulty in manual handling so PVC is easily cut, shaped and joined, even with simple hand tools.

9. Safe for public health – As the most researched and thoroughly tested plastic, PVC is certified non-toxic by international safety and health standards. Engineered especially to move drinking water PVCs design restricts contaminants and bacteria breeding.

10. Environmentally friendly – Producing PVC requires less energy and resources so, it is low-carbon plastic.

- Production is not dependent on only non-renewables of crude oil or natural gas. This capability is why many refer to PVC as sustainable plastic.

- The lightweight means less transportation energy is required.

11. Recyclable - Usually, PVC pipes are 100% recyclable and are recyclable up to seven times without affecting their properties. Recycling protects the environment (each kilo of recycled PVC saves two kilos of carbon dioxide) and provides jobs that boost local economies.

12. Fire-resistant - PVC, like every other organic material (wood), will burn in the presence of fire. However, burning will stop when the fire source ceases. This unique, self-extinguishing property is due to the chlorine content in PVC that makes catching fire difficult; the material will char and not burst into flames. This ability also implies that the heat production of PVC is relatively low.

13. Good chemical stability – PVC properties are not significantly affected when used in environments with different chemicals.

14. Protection and security – Items wrapped in PVC shrink wrap are not only aesthetically tidy; it is protected from possible tampering and damage when in transit.

Dangers

1. In a large building fire, PVC will burn and release thick, black, toxic substances into the air, such as carbon monoxide (CO), which is a silent killer because it has no smell.

- Burning PVC also emits hydrochloric acid (HCL), which is irritating when inhaled.

These toxins are traceable to health conditions such as cancer, asthma and foetal development issues etc.

2. There are growing concerns about the chemical composition of PVC that releases certain by-products during the production and even decomposition. Some researchers believe the high sodium content in PVC potentially poses an environmental and health hazard.

3. It is not suitable for medium to high voltage cables.

4. It has poor heat stability which, makes it a poor conductor of heat.

5. Over time, PVC properties may change due to the migration of plasticisers.

PVC and Sustainability

Sustainable development is the development that meets the needs of the present without compromising the ability of future generations to meet their own needs."

The business of PVC not only provides economic sustainability by providing numerous jobs across the value chain, but its inherent properties also contribute to the social and environmental sustainability of our planet.

For instance, as a 100% recyclable material, PVC increases material efficiency by limiting waste and conserving scarce resources.

The lightweight property of PVC products also impacts ecosystems by reducing the possibility of accidents during installation.