Making plastics – from crude oil to plastic pellets

Plastic processing equipment and transformation of pellets into usable products

Forming usable plastic products, for instance, bottles, hoses, or toys, is executed using various processes: compounding, forming, thermoforming, extrusion and molding. Compounding is the first step – mixing liquids with other ingredients according to the desired recipe in conventional stirred tanks. Other essential plastic processing equipment includes two types of mixers; the workhorse mixer, which applies heat and pressure simultaneously, and the Banbury mixer which reminds of a robust dough mixer with two interrupted spiral rotors.

The next step is forming plastics into various shapes by melting, shaping, and solidifying. Extrusion and molding processes create finished or semi-finished products. During extrusion, the melted polymer is continuously forced through an orifice in an extruder for products such as sheets, tubing, and grocery bags. Various types of molding rely on molds to create the desired shape.

To illustrate, rotational molding produces large, hollow products such as kayaks. On the contrary, blow molding is used for small hollow pieces – bottles or fuel tanks. With compression molding, plastic parts can replace metal in the automotive industry. Finally, the most common type, injection molding, has virtually limitless uses with a large production capacity.

Any further heating would result in burning. For this reason, thermosets are not recycling-friendly. Further categorization is between amorphous, also known as shapeless, material and semi-crystalline material. While the former gradually softens when exposed to heat, the latter maintains its shape until a certain temperature point, when it rapidly becomes liquid. Finally, according to their monomer composition, plastics can be classified as homopolymers, made of a single type of monomer, or, on the contrary, copolymers.

Bioplastics, biodegradable plastics and recycled plastics – ecological alternatives?