What are plastics and rubbers?
Plastics and rubbers
Plastics and rubber materials are both made from the same families of polymers.
The polymers are mixed with a complex blend of materials known as additives.
Rubbers are elastomers, these are polymers with an elastic property. This elasticity differentiates rubbers from plastics. Elastic means that the material can be stretched and, when released, returns to within at least 90% of its original dimensions and shape within a period of time, at room temperature.
Monomers and polymers
The word polymer comes from the Greek words for "many (poly) parts (-mer)"; monomer means "one part".
Polymers are large molecules that consist of a series of smaller building blocks. Those building blocks are called monomers. Think of a polymer as a chain of monomers linked to each other. The monomers can be simple or they might be more complicated ring-shaped structures containing a dozen or more chemical elements (atoms).
For example, the polymer PVC (polyvinylchloride) is a very long chain of vinylchloride monomers which explains the name poly-vinylchloride: many vinyl-chlorides. The building block monomer is made of two carbon (C) atoms, three hydrogen (H) atoms and one chlorine (Cl) atom, as shown in the diagram above.
Some examples of commonly used polymers and their possible applications are:
- Polypropylene (PP): carpets, furniture upholstery, garden furniture, food packaging;
- Polyethylene low density (LDPE): grocery bags, food packaging, household foils;
- Polyethylene high density (HDPE): detergent bottles, toys, pipes and fittings, helmets;
- Poly(vinyl chloride) (PVC): piping, decking, electric cables, packaging;
- Polystyrene (PS): toys, foam, food packaging, thermal insulation;
- Polytetrafluoroethylene (PTFE, Teflon): non-stick pans, electrical insulation;
- Poly(methyl methacrylate) (PMMA, Lucite, Plexiglas): face shields, skylights;
- Poly(vinyl acetate) (PVAc): paints, adhesives;
- Polychloroprene (Neoprene): wetsuits, laptop sleeves, orthopaedic braces;
Without additives, plastics and rubbers would not work, but with them they can be made safer, cleaner, tougher and more colourful.
The polymers themselves often do not have any desired properties when they are manufactured. Therefore, polymer materials are blended with certain chemicals called additives to create the desired properties in the final plastic or rubber products. Additives are used to make plastic products suitable for specific situations or applications. Examples of additional properties are stiffness or flexibility, UV-resistance, water repellant, flame resistant etc.
During the production of plastics or rubbers a significant amount of additives is mixed with the polymers.
This mixing process of polymers with additives is known as "plastic" or "rubber" compounding.
The percentage of additives in polymer based products depends on the required properties but it can easily be more than 50% of the end product.
Examples of types of additives usually used for making plastics:
- Plasticisers (softeners, phthalates);
- Processing aids;
- Flame retardants;
- Antistatic agents;
- (Enforcement) fillers.
Monomers, polymers and additives are all chemicals. And chemicals may be hazardous or problematic for people, animals and the environment.
Polymers on their own may be safe and not toxic. But polymers may be made from monomers which are often toxic and subject to chemical legislation. During the manufacturing process a 100% conversion of monomer into polymers (polymerisation) is not feasible. This means that the polymer contains a certain amount monomers residues and the hazardous properties of the monomer are then also present in the polymer.
The same is true for additives, these are chemicals that may be hazardous and therefore they are regulated by chemical legislation. Monomers as well as additives in final products may lead to exposure for people and the environment.
For compliance it is essential to know the composition or blend of your materials. Which building blocks, monomers are used for polymerisation and what are their chemical properties. Which chemicals are used during manufacturing and which additives have been applied to give the end product the required properties.
For the chemical risk assessment of materials this is essential information from your supply chain.