Sustainability and environmental impact of plastic

Plastics, more technically referred to as polymers, are a class of materials that can be engineered to assume a broad range of physical properties. Commercial plastics play a leading role in many sectors, from medicine to energy, because the low cost, ease of processing, and customizability are attractive. The low cost of plastics has led to numerous problems in their disposal; current environmental problems include the Pacific garbage patch, infiltration of microplastics into waterways, and leaching of plastic additives from landfills.

The Pacific garbage patch is not one, but many large aggregates of waste plastic floating in the oceans. Circular ocean currents, known as gyres, cause the floating rubbish to collect into dense, island-like structure that cover many square kilometres. The rubbish can ensnare marine animals and may be ingested, causing deformities and death. Whilst the degradation of petroleum-based polymer is very slow, the breakup of plastic into smaller particles occurs, allowing the plastics to spread more widely. Recent efforts to remove plastics from the oceans include The Ocean Cleanup, which harnesses natural recirculation flows within gyres to move particulates into capture nets. In addition to removing plastic debris, marine researchers, like Charles Moore, advocate developing stronger policies to prevent plastic trash from entering the oceans.

 

Petroleum vs bio-sourced polymers

Many commodity plastics are synthesized using petrochemicals, e.g., polyethylene, polypropylene, and polystyrene. They are extremely inexpensive because they are made from the hydrocarbon byproducts of catalytic cracking. Polymers that only contain carbon and hydrogen atoms are known as polyolefins and generally derive from petrochemicals. These polymers require centuries to degrade; consequently, they comprise a major contributor to environmental pollution.

Conductive polymers are an example of high-value resins produced from petrochemicals. In order to conduct electrons, the polymer backbone must be conjugated, meaning that single and double bonds alternate regularly along the length of the backbone. The feedstock materials required to produce a conjugated structure are presently only available from petrochemical sources. Advances in conductive polymer devices, like solar cells, transistors, batteries, and supercapacitors, have the potential to level the technological playing field across economic barriers, and represent a relatively low-volume demand on petroleum resources.

Biosourced polymers derive from plant and animal materials; examples include chitosan, carageenan, alginate, cellulose, and polylactic acid. Although polylactic acid is made from plants, like corn, the carbon footprint may be high because production relies upon petroleum-intensive farming practices to generate the feedstock. Biodegradable polymers are those that degrade under ambient conditions of temperature and humidity. Clearly, ambient conditions vary significantly across locations; there is presently no standardized certification for biodegradable plastics. Compostable materials degrade under specific composting conditions, which often involve higher than ambient heat and the addition of specialized microbes. Not all biosourced polymers are biodegradable, and not all biodegradable polymers come from biological sources. The term biopolymer may be used to generalize any polymer that is either biosourced, biodegradable, or compostable.

Recycling

Although recycling keeps billions of tons of plastic out of the landfill each year, plastics are fundamentally difficult to recycle because they must be separated by chemical species. Large-scale plastics manufacturing is a commercial reality, so it is the job of today’s polymer scientists to direct the course of research towards increasingly sustainable materials and processing methods.