Bioplastics

Our story about plastics and pollution would not be complete without some mention of bioplastics. These offer some advantages in decreasing our carbon footprint through the use of renewable plant materials rather than from fossil fuel stocks. These plant materials include, wood chips, food waste, cornstalks, and sugar cane, among others. 

This is similar in concept to the use of these same kinds of products to produce energy. Although a good idea in concept, efforts to produce energy from biomass of all types – wood chips, brewery mash, plant materials - have not come to promising commercial ends. The biomass required to produce energy is excessive relative to the amount of energy it yields, especially if one includes the cost of fuel, water, fertilizer, and transportation necessary to grow and harvest the biomass and then bring it to the factory where plastics are synthesized. 

There were attempts to make materials from plant sources in the late 19th and early 20th centuries, but these ended as petroleum-based raw materials became available at very low cost and with economies of scale. These economics created the plastic industry in the mid 20th century which developed in parallel with other industries that use petroleum based raw materials. Interest in bioplastics began in the early 21st as it became clear that plastic pollution was destroying the earth. (See my earlier blogs on plastics for an overview.) Global production of biopolymers of all types is about 4 million metric tons annually, according to an article by Mitchell Waldrop published recently in the Proceedings of the National Academy of Sciences (https://doi.org/10.1073/pnas.2103183118). Bioplastics currently account for around 1% of the >360 million tons of plastics produced annually - although they have an annual growth rate of 20-30%. This is unlikely to change quickly because of the low cost of petroleum – even with the uncertainties of oil pricing and the advent of more economical alternative energy – and the economies of scale that make petroplastic inexpensive. 

Despite the early commercial uncertainties of bioplastics, there have been technical and developmental advances in the past decade. The most important is the use of polylactic acid (PLA), which is a thermoplastic polymer produced by the condensation of lactic acid. It has become popular since it now is produced economically from renewable sources – the most common being cornstalks, sugar cane, and sugar beets. In 2010, PLA had the second highest consumption volume of any bioplastic but commodity status has eluded it because of several physical and processing issues. These are being worked on vigorously by academic and industrial groups and it is relatively certain that PLA has a good commercial future. 

At this time, PLA is the most widely used plastic filament in 3D printing. PLA bioplastics are used in a broad range of other established markets, like fresh food packaging, organic waste bags, food service ware, tea bags, durable consumer products, toys, and N95 face masks. PLA also can be used as a decomposable packaging material, and either cast, injection-molded, or spun. Cups and bags have been made from it. In the form of a film, it shrinks upon heating, allowing it to be used to shrink-wrap packages. It is useful for producing loose-fill packaging, compost bags, food packaging, and disposable tableware. Since PLA degrades into lactic acid, which is readily metabolized by most living things, it is used in medical implants such as screws, plates, mesh, etc. It breaks down in the body in 6 months – 2 years, depending upon the nature of the polymer. 

This polymer will biodegrade slowly when temperatures are not high. In 25C seawater, PLA showed no degradation over a year. This also makes landfill disposal a problem. However, under industrial composting conditions it will degrade in about 30 days into water, carbon dioxide, and compost. This has made it an attractive alternate to other non-biodegradable plastics. PLA also can be incinerated without releasing any toxic chemicals and recycled into new PLA products. It also is degraded by some bacteria. These characteristics make PLA a strong contender to replace many fossil fuel plastics in the relatively near future. 

Although we have fouled the earth and its oceans with plastic waste, there is some hope. The environmental movement is pushing back against petrochemicals, and the advent of biopolymers makes it appear that we may be able to slowly replace petroplastics with biodegradable alternatives. Biopolymer plastics is a rapidly growing and much needed industry.