Plastic world¶
Learn the ins & outs of plastic
What is plastic¶
The word plastic is in our mouth day in & day out, but what does it really mean? The word itself is derived from the Greek (plastikos) meaning “capable of being shaped or moulded” and refers to their malleability during manufacture, that allows plastic to be cast, pressed, or extruded into a variety of shapes—like films, fibres, plates, tubes, bottles and much more.
Plastics are synthetic chemicals extracted mainly from petroleum and made of hydrocarbons (chains of hydrogen and carbon atoms). Most plastics are polymers, long molecules made up of many repetitions of a basic molecule called a monomer. This structure makes plastic particularly durable and long lasting.
Due to their relatively low cost, ease of manufacture and versatility, plastics are used in an enormous and expanding range of products, from shampoos (micro beads) to space rockets. Plastic ubiquitousness (it’s everywhere!) is causing serious environmental concerns regarding its slow decomposition rate (recent studies say 500 years) due to its strong bonding molecules. Think it this way, all plastics ever used from your parents and grandparents are still around today and will pollute the planet for another four centuries.
Most plastics contain other organic or inorganic compounds blended in called additives to improve performance or reduce production costs. The amount of additives ranges widely depending on the application and plastic type.
A bit of history¶
The development of plastics has evolved from natural plastic materials to completely synthetic molecules (e.g., epoxy, PVC). Parkesine (nitrocellu- lose) is considered the first man-made plastic (1856). After World War I, improvements in chemical technology led to an explosion of new plastics, with mass production beginning in the 1940s and 1950s. World War II lead to greater research and development into plastic and the discovery of many new plastic types with different properties and applications. As the war ended, these new plastics made their way into society through a multitude of consumer goods.
Thermoset & thermoharders¶
There are two main categories in the world of plastics: thermoplastics and thermosetting. Thermoplastics are the plastics that can be recycled. Thermoplastics can be melted back into liquid and moulded multiple times. Think of this as butter, butter that can be melted and cooled many times and take various shapes. Thankfully, thermoplastics make up to 90% of global production.
Thermosets can melt and take shape only once; after they have solidified, they stay solid forever. In the thermosetting process, a chemical reaction occurs that is irreversible. Thermoset is similar to bread where once the final state is achieved, any additional heat would lead to burning. No recycling is possible for this plastic. Bummer! As you might have guessed already, we will focus exclusively on thermoplastics. From now on when we write “plastic” we will refer to thermoplastics.
Plastic types¶
Plastic (thermoplastics) are further grouped in seven different subcategories often referred to as plastic types. Each plastic type has its specific chemical composition, properties and applications and is given a specific number, called SPI code to differentiate between them. Today, most manufacturers should follow this coding system and place the SPI code on their products, usually moulded at the bottom of the product.
Knowing what plastic type you’re working with is crucial when working with Precious Plastic. This will tell you its melting temperature so that you can set your Precious Plastic machines at the correct temperature and run a smooth recycling process.
The different plastic types are:
PET (polyethylene terephthalate)
This is a very strong plastic that can be easily recognised for its transpar- ent look. All beverage bottles containing your favourite sodas are PET. This plastic is also used in many other products like jars, combs, bags, tote bags, carpets and ropes. Items made from this plastic are commonly recycled. Most recently, PET is often recycled into yarns to make clothes. This plastic is a bit more complex to work with, we advise to start with other plastics.
HDPE (high-density polyethylene)
This plastic is often used for food or drink containers. Items made from this plastic include containers for milk, motor oil, shampoos, soap bottles, detergents, and bleaches. Many toys are also made from this plastic. This plastic works very well with Precious Plastic.
PVC (polyvinyl chloride)
This is toxic and we do not work with it. PVC is most commonly found in plumbing pipes and releases chloride when heated up. Do not use with Precious Plastic.
LDPE (low-density polyethylene)
Plastic wrap, sandwich bags, squeezable bottles, and plastic grocery bags all are made from LDPE. Usually, LDPE is not recycled from the industry but works rather good with Precious Plastic.
PP (polypropylene)
This is one of the most commonly available plastic on the market. This type of plastic is strong and can usually withstand higher temperatures. Among many other application, it is consistently used for products that get in contact with food and drink (Tupperware, yoghurt boxes, syrup bottles etc..). PP works very well with Precious Plastic.
PS (polystyrene)
PS is most commonly known as Styrofoam. PS can be recycled, but not efficiently; recycling it takes a lot of energy, which means that few places accept it. Disposable coffee cups, plastic food boxes, plastic cutlery and packing foam are made from PS. Very good to work with Precious Plastic.
Other (Mix)
This code is used to identify other types of plastic that are not defined by the other six codes. ABS, Acrylic or Polycarbonate are included in this category and can me more difficult to recycle. Precious Plastic can work with some of this.
Mixing plastic¶
Different plastic types should never be mixed together when working with Precious Plastic as this will make it impossible to recycle them again. Mixing plastics would end their cycle. Moreover, when different types of plastics are melted together they tend to phase-separate, like oil and water, and set in layers resulting in structural weakness and lower quality products.