Commodity Plastics – The ‘Almost’ Everywhere Versatile Thermoplastics

The monomer ethylene (C₂H₄)_n units link to form the polymer polyethylene (or polythene/PE). It is the most used type of thermoplastic with applications such as bottles, food packaging, bubble packaging, industrial liners, and mattress bags. It is projected that the market will be valued at USD 135.87 billion by 2030². It is becoming a highly cost-effective solution owing to recent developments that may replace some costlier alternatives. The most common types of PE are low density (LDPE), medium density (MDPE), and high density (HDPE).

LDPE has a high level of short and long sidechain branching which results in low density and crystallinity while greater flexibility and toughness than HDPE. HDPE is known to exhibit resistance to UV and chemicals. Due to difference in their properties, LDPE is more popular for packaging films and mulch in agriculture.

Polypropylene (PP) is another type of thermoplastic that is produced from the monomer propylene. It shows similar characteristics like PE but is harder and more resistant to heat. PE and PP together belong to the family of polyolefins. It is a light weight, durable polymer with good tensile strength (0.95--1.30 N/mm²). The global market for polypropylene³ is projected to grow from USD 76.00 billion in 2021 to USD 108.57 billion in 2028.

Polypropylene can be processed by multiple processing methods: extrusion blow molding, injection molding, and general-purpose extrusion. It is available as three types: homopolymer, copolymer, and impact copolymer. PP Homopolymer contains propylene monomer in a semicrystalline solid form. The copolymer type is further divided into random copolymers and block copolymers produced by polymerizing of propene and ethane. Propylene homopolymer containing a co-mixed Propylene Random Copolymer phase which has an ethylene content of 45--65% is referred to as PP impact copolymer.

Polypropylene finds great use in packaging, textiles, healthcare, pipes, automotive and electrical applications.

Polystyrene (PS) is another cost-effective, widely produced and used plastic. It is made from the aromatic hydrocarbon styrene. It occurs transparent naturally but with use of colorants and other additives, it is used in electronics, appliances, gardening pots, toys and many other common applications. When copolymerized or blended with other polymers, it is known to provide hardness and rigidity to a many other polymers and rubbers.

While the solid form is hard and brittle, polystyrene is also available as foam (expanded polystyrene [EPS] or extruded polystyrene [XPS]). This lightweight foam finds use in protective packaging, home and appliance insulation, disposable eating utensils. Although polystyrene is resistant to many acids and bases, it can be easily dissolved down in contact with organic solvents such as acetone. Polystyrene is generally considered to be non-biodegradable. However, some recent research has revealed that a common super worm can ‘eat’ polystyrene.

Polyvinyl chloride (PVC) is yet another low-cost polymer exhibiting numerous properties for common applications. It is made by polymerization of monomer vinyl chloride.

According to a recent report⁴, its capacity will register a growth of 16%, increasing from 60.27 mtpa in 2021 to 69.73 mtpa in 2026. PVC is available in two forms: rigid or unplasticized (RPVC or uPVC) and second as flexible.

Apart from its low price, PVC is popular for its resistance to environmental degradation, resistance to chemicals, hardness & tensile strength (rigid PVC).

While the rigid form can be used in pipes, profile applications such as doors and windows, with the use of plasticizers (most popular being phthalates), it can be used in electrical cable insulation, plumbing, flooring where it replaces rubber.

Polyethylene terephthalate (PET) is a naturally transparent and semi-crystalline plastic. It belongs to the family of polyesters. PET is product of the polymerization of ethylene glycol and terephthalic acid. Amongst its properties, stiffness and hardness, good strength, ductility is most prominent. PET is the most widely recycled plastic. Since it is inert, it resists attack by micro-organisms and can be commercially recycled by chemically breaking it down to its component materials to make new PET resin.

PET is used in bottles, bags, containers, packaging films, carpets, microwave containers. It can be processed through vacuum forming, injection molding, compression molding and blow molding. Due to its high strength & lightweight, it is energy efficient and allows for more product to be delivered in less packaging and using less fuel for transport.