Plastic waste poses a huge environmental challenge. We produce them in huge volumes, and they do not degrade easily resulting in substantial environmental pollution. This is particularly a concern for the marine environments where most of these plastics end up resulting in harm to the marine environment.
Plastic is a non-biodegradable substance and, according to the U.S. Environmental Protection Agency (EPA), Americans generate about 34 million tons of plastic waste every year, but only a mere 8% of that amount is recycled annually.
The problem is that plastic does not biodegrade. In fact, it’s extremely difficult for most plastics to degrade at all. According to the U.S. Environmental Protection Agency (EPA), Americans generate about 34 million tons of plastic waste every year, but only a mere 8% of that amount is recycled annually. That means over 90% of each year’s total plastic production ends up in our landfills where it remains indefinitely—often leaching toxic chemicals into the soil and groundwater beneath them over time—or floating out there on the ocean currents where it breaks down into smaller pieces but never truly disappears and sometimes even comes back to us when fishes consume them and we, in turn, consume the fishes.
Plastic pollution has been called one of our “greatest environmental challenges” because it has come to be so ubiquitous within our modern society that we barely notice its existence anymore until we see images like those taken by photographer Charles Moore after he sailed through an area known as “The Great Pacific Garbage Patch.” The discovery was shocking enough for him when he first viewed his photographs after returning home from his journey: hundreds upon hundreds of miles worth of plastic trash floating around in this one section alone!
Recycling plastic is one of the ways to combat this challenge and reduce the amount of plastic waste that ends up in landfills and our waterways.
In this article, I will discuss the different types of plastic and the process for recycling them.
Types of Plastic
The first step in recycling plastic is sorting it into different types based on their chemical composition (for example, PETE or HDPE). Each type of plastic has its own unique properties: some degrade easily while others have longer lifespans; some melt at lower temperatures than others; some are stronger than others. Once these materials are sorted into separate bins they can be recycled into new products or melted down for raw material again. The types and characteristics of the different types of plastics are summarised in the table below.
| Type of plastic | Identification | General properties | Common uses |
| Polyethylene terephthalate (PET/PETE) |  |
Clear
Hard Tough Barrier to gas and water Resistance to heat Resistance to grease/oil |
Mineral water bottles
2 litre soda bottles Cooking oil bottles Powder detergent jars Fibre for clothing Fibre for carpets Strapping Peanut butter jars |
| High density polyethylene (HDPE) |  |
Barrier to water
Chemical resistance Hard to semi-flexible Strong Soft waxy surface Low cost Permeable to gas Natural milky white colour |
Jerry cans
Shopping bags Film Milk packaging Toys Buckets Rigid pipes Crates Bottle caps |
| Polyvinyl chloride (PVC) |  |
Transparent
Hard, rigid (flexible when plasticised) Good chemical resistance Long term stability Electrical insulation Low gas permeability |
Pipes and fittings
Carpet backing Window frames Water, shampoo and vegetable oil bottles Credit cards Wire and cable sheathing Floor coverings Shoe soles and uppers |
| Low density polyethylene (LDPE) |  |
Tough
Flexible Waxy surface Soft – scratches easily Good transparency Low melting point Stable electrical properties Moisture barrier |
Agricultural films
Refuse sacks Packaging films Foams Bubble wrap Flexible bottles Wire and cable applications |
| Polypropylene (PP) |  |
Excellent chemical resistance
High melting point Hard, but flexible Waxy surface Translucent Strong |
Yoghurt containers
Potato crisp bags Drinking straws Medicine bottles Crates, Plant pots Car battery cases Heavy gauge woven bags |
| Polystyrene (PS) |  |
Clear to opaque
Glassy surface Rigid Hard Brittle High clarity Affected by fats and solvents |
Packaging pellets Yoghurt containers
Fast food trays disposable cutlery Coat hangers |
| Other plastics |  |
Mostly not available in sufficient quantities for recycling |
Plastic Recycling Process
1. Collection
As the first step in recycling plastic, setting up an efficient collection system of waste plastic is key. A constant supply of raw materials to the recycling facilities is important for improving the efficiency of the recycling facility. Collection of waste plastic may already happen through the activities of scavengers, middlemen and traders. It is possible to integrate this into more centralised systems to ensure optimal collection of recyclable plastic waste. Another option is to cooperate with the municipality to get involved in collection schemes accompanied with a public awareness campaign. In this way the public can be informed about the advantages of plastic recycling.
2. Storage
Plastic is light in weight but occupies a considerable amount of space for storage due to the volume. A plastic recycling facility needs quite a large storage space in order to store all collected waste items, processed materials and finished products. Plastic waste items, especially bottles, have a large volume and therefore a large storage place is necessary.
3. Sorting and identification
Plastics sorting operations may be carried out manually or automatically, using appropriate means of identification. The more accurate and efficient the means of identification, sorting and separation, the better the quality of the recovered product obtained. Pneumatic separation systems use the weight and volume of the different types of plastics to separate them. More recently, infrared technology is used to scan, identify and separate the different types of plastics.
4. Baling
After collecting and sorting the plastic material, the option exists to sell the material to (other) processing units. If so, it is important to compact the waste to improve handling and save costs during transport, especially when transportation distances are considerable.
5. Washing and Drying
If not sold on, the next step is to clean the plastic if it is dirty. The main cleaning steps are:
- Draining of remaining fluids from plastic containers/bottles.
- Rough cleaning of plastic containers and other pieces of plastic.
- Removing paper, plastic or metal stickers.
- In the case of PET bottles removing caps which are made of a different type of plastic.
- Intensive washing in cold or hot water with the addition of detergents or caustic soda.
- The wastewater can be reused by installing a simple wastewater treatment system like a sedimentation basin
6. Shredding
Shredding is suitable for smaller pieces. A typical shredder has a series of rotating blades driven by an electric motor, some form of grid for size grading and a collection bin. Materials are fed into the shredder via a hopper which is sited above the blade rotor. The product of shredding is a pile of coarse irregularly shaped plastic flakes which can then be further processed.
7. Agglomeration
Clean film sheet is processed in an agglomerator. The agglomerator consists of a vertical drum with a set of fast moving blades in the bottom. The agglomerator chops the sheets into thin film flakes. Due to the cutting and friction energy of the process, the flakes are heated until they start to melt and form crumbs or agglomerate. This will increase the bulk density of the material which is now fit to be fed directly into the extruder for manufacturing of new plastic products.
8. Pelletizing
For many purposes, it is recommended to convert plastic flakes or agglomerate (crumbs) into pellets before processing. The plastic pieces are fed into the extruder, heated and then forced through a die to form a plastic spaghetti which can then be cooled in a water bath before being chopped into pellets.
After pelletization, the plastic is ready to re-enter the supply chain as raw material for producing new plastic products. There are several ways to produce new plastic products from pellets. Here are a few of the production processes to make new plastic products.
- Extrusion
The extrusion process used for manufacturing new products is similar to that outlined above except that the product is usually in the form of a continuous ‘tube’ of plastic such as piping or hose.
The reclaimed plastic is forced along the heated tube by an Archimedes screw and the plastic polymer is shaped around a die. The die is designed to give the required dimensions to the product and can be interchanged.
- Injection moulding
The first stage of this manufacturing process is identical to that of extrusion, but then the plastic polymer emerges through a nozzle into a split mould. The quantity of polymer being forced out is carefully controlled, usually by moving the screw forward in the heated barrel. A series of moulds would be used to allow continual production while cooling takes place. This type of production technique is used to produce moulded products such as plates, bowls, buckets, etc.
- Blow moulding
Here, the spiral screw forces the plasticised polymer through a die. A short piece of tube, or ‘parison’ is then enclosed between a split die – which is the final shape of the product – and compressed air is used to expand the parison until it fills the mould and achieves its required shape. This manufacturing technique is used for manufacturing closed vessels such as bottles and other containers.
- Film blowing
Film blowing is a process used to manufacture such items as garbage bags. It is a technically more complex process than the others described so far and requires high-quality raw material input. The process involves blowing compressed air into a thin tube of polymer to expand it to the point where it becomes a thin film tube. One end can then be sealed, and the bag or sack is formed. Sheet plastic can also be manufactured using a variation of the process described.
Conclusion
Plastic waste is ubiquitous. We use them every day but if not recycled, they can harm the environment for a prolonged period of time since they do not degrade easily. I have described the different types of plastic products we use and the process for recycling them. I hope you found that insightful.
You can contribute by ensuring that the plastic waste you generate is segregated and deposited in a recycling bin or station near you. The key takeaway here is that if we want to make a difference in our world, we need to start by recycling plastic waste into something useful. If every person on earth recycled just one plastic bottle every day, we could save up to 1/3 of all plastics produced annually. It really does take only one person to make a difference!