From Polypropylene to Polystyrene: Decoding Plastic Codes

Not all plastics are created equal—codes 5, 6 and 7 show why some materials recycle easily, while others pose serious challenges.

In the earlier parts of this series, we examined the first set of Resin Identification Codes. Let us now continue our exploration of the remaining codes and their uses.

Code no. 5

This code is assigned to products made from polypropylene (PP). It is a highly versatile polymer, widely known for its durability, chemical resistance, and light weight. Polypropylene is commonly used in food containers and textiles, as well as in automotive parts and medical devices. When exposed to high temperatures, it melts rather than burns; hence, it is classified as a thermoplastic.

PP is easily mouldable and recyclable, and it offers an excellent strength-to-weight ratio. These properties make it an ideal raw material across many industries. In fact, it is the most commonly used thermoplastic in the world. It is extensively used in medical devices such as syringes, medical vials, petri dishes, pill containers, and specimen bottles.

Polypropylene is particularly well-suited to applications that require repeated bending and manipulation without breaking. Examples include hinges on medication pots, lids or caps on shampoo bottles, and various types of plastic bottles and containers. Beyond packaging, PP is also used to manufacture ropes, twine, tape, carpets, upholstery, clothing, and camping equipment. Its waterproof properties make it especially effective for use in the marine sector.

Although polypropylene is recyclable, there are certain limitations. Rigid items, such as containers and bottle caps, are easily accepted for recycling, whereas flexible films made from PP are more difficult to recycle.

Code no. 6

This code is assigned to products made from polystyrene (PS). Polystyrene is a hard and brittle plastic that may be transparent or opaque. It is available in three distinct forms, each used for different applications.

The first type is GPPS (General Purpose Polystyrene). This form is commonly used for disposable items such as cups, cutlery, and food trays. It is also used in rigid packaging, cosmetic boxes, toys, lighting diffusers, and laboratory ware.

The second type is High Impact Polystyrene (HIPS), which is modified to improve toughness and impact resistance. HIPS is widely used in packaging, retail displays, and signage, as well as in consumer electronics, including housings for televisions, computers, and toys. It also finds applications in automotive interiors, such as trims and panels.

The third type is Expanded Polystyrene (EPS). This form is hard and brittle yet extremely lightweight and is more commonly known as 'styrofoam' or 'thermocol'. EPS is generally used as moulded foam packaging for televisions, computers, household appliances, and other fragile goods. It is also commonly found in trays used for meat, fish, and similar products, as well as in egg cartons. In addition, EPS is used to make disposable items such as cups, plates, bowls, lids, and cutlery, and it is also used as an insulating liner in refrigerators and air conditioners.

Technically, polystyrene is 100% recyclable. However, because it is lightweight, bulky, and often contaminated with food residue, recycling it is not economically viable in many regions. The process requires specialised facilities and handling systems, which are not widely available.

Code no. 7

This code is assigned to plastics that do not fall under any of the six categories discussed earlier. It generally includes a broad group labelled as “other” plastics, such as polycarbonates (PC), acrylic, nylon, multilayered composite plastics used in sachets or pouches, and fibreglass composites used in automotive parts, industrial containers, and similar applications.

Polycarbonates are commonly used in products that require strength and impact resistance, such as safety goggles and reusable water bottles. Acrylic, also known as Plexiglas, has a wide range of applications and is frequently used in light fixtures, display units, and packaging windows. Nylon is valued for its strength and flexibility and is typically used in products such as toothbrush bristles, gears, and other mechanical components.

Because of their complex and mixed compositions, plastics classified under Code 7 are generally not recyclable.

Will continue in the next week. Till then, have a nice weekend!

(The author is an environmentalist. Views personal.)