Plastic Recycling in Chemistry

« What Methods Are Used? »

Plastics are widely used as packaging materials, insulators, components in various machines and devices, and as coating agents. Unfortunately, their widespread use has led to increasing environmental concerns as they are now frequently found in the environment.  Recycling offers a potential solution—but not all chemical recycling methods are equally environmentally friendly. The following provides an overview of chemical processes used to recover value from plastic waste.

Type and Composition of Plastic Waste

The choice of recycling method depends on the physical characteristics of the material and the degree of contamination or  interaction with other substances. Plastics fall into three main categories: thermoplastics, thermosets, and elastomers. Thermoplastics, such as PVC, polyethylene, and polypropylene, soften when heated and can be reshaped and reused once cooled.

These materials can only be recycled by chemically breaking down the molecular bonds in their polymer chains. This process known as solvolysis. Elastomers, which behave like rubber, also decompose at high temperatures. However, they can still be recycled in shredded form, for example, as filler in bitumen applications.

The degree of mixing significantly affects the recycling process. Homogeneous plastic waste is easiest to recycle. When different types of plastics are mixed, combined with other materials, or contaminated, extensive sorting and separation steps are often necessary—especially in the case of collected packaging waste, composites, and coated components. Surface coatings, commonly used to enhance the performance of plastic parts, often interfere with recycling and must be removed in advance.

Types of Recovery Processes

There are three main categories of recovery for plastics within sustainable chemical practices: mechanical recycling, chemical (feedstock) recycling, and energy recovery.

• Mechanical recycling preserves the base material. The plastic is cleaned and reprocessed—using dry, wet, or solvent-based techniques—so that it can be reused. These methods are primarily physical and mechanical.
• Chemical recycling (also called feedstock recycling) uses chemical reactions to break down plastics into raw materials, which can then be used to make new products.
• Energy recovery is not considered a recycling method in the strict sense of chemistry. In this process, plastic waste is incinerated to generate energy.

Chemical Recycling Methods

The most common chemical recycling methods are liquefaction (oil recovery), solvolysis, gasification, and pyrolysis. These often require pre-treatment steps to remove contaminants, such as separating multi-layer materials (e.g., beverage cartons, coated films) or stripping surface coatings. Eco-friendly paint stripping agents are available for these tasks.

Liquefaction (Oil Recovery)

In this process, plastics are converted into oily substances through thermal or catalytic reactions, which requires well-sorted plastic waste. The reaction typically occurs in stirred tank reactors at temperatures up to 750°F (400°C). As the plastic liquefies, gaseous by-products and wax-like residues are separated from the resulting oil.

After purification and distillation, the recovered oil can be used as diesel fuel or as a chemical feedstock.

Solvolysis

Solvolysis breaks down the polymer chains in plastics using special solvents. The reaction may be aided by elevated temperatures and is primarily used for recycling thermosets. It yields the original building blocks of the plastic, which are then separated from the solvent.

The solvents are usually reused in a closed-loop system. Depending on the input material, valuable raw components can be recovered from the decomposed polymers.

Gasification

Gasification is conducted at temperatures of up to 2,900°F (1,600°C) and pressures up to 2,175 psi (150 bar) with limited oxygen supply. This oxygen does not support combustion but facilitates the reaction between carbon and oxygen. The process produces a synthetic gas (syngas) composed of carbon monoxide and hydrogen. Before further use, impurities must be removed. Syngas serves as a raw material for a wide range of chemical products, including GTL (gas-to-liquid) oil, which is used in surface treatment applications.

Pyrolysis

Pyrolysis involves the thermal decomposition of plastic waste in the absence of oxygen at temperatures between 300–1,300°F (150–700°C). One of the oldest known pyrolysis methods is the production of charcoal in kilns. Modern pyrolysis of plastics yields solid, liquid, and gaseous products, which can be processed into valuable chemical precursors.

Comparing Recycling Methods

Chemical plastic recycling requires a high amount of energy as well as extensive pre- and post-treatment steps involving additional auxiliary substances. For this reason, material recycling—which reuses materials without chemical changes—is given priority. When this is not feasible, energy recovery is often the more sustainable option. Under certain conditions, however, chemical recycling methods can still be advantageous. They allow harmful substances to be removed from the material cycle and can supply the chemical industry with valuable raw materials.

This is especially true when larger quantities of homogeneous plastic waste from one or similarly composed materials are available. Research is actively working to improve plastic recycling methods, gradually making this form of plastic recovery more prominent in the future.

Regulatory Considerations

This is particularly true when large quantities of homogeneous plastic waste are available from a single or similar source. In the United States, recycling operations must comply with EPA regulations under the Resource Conservation and Recovery Act (RCRA), which governs how facilities manage hazardous and non-hazardous solid waste. Ongoing research is actively improving chemical recycling methods, making them an increasingly viable part of future waste management strategies.