Plastics of the future
Plastics are used everywhere in our life. They are made into everything from spoons to electronics covers, and countless other things in between. Plastics are so useful because they are cheap, mechanically strong, light in weight, pliable and can be shaped into pretty much any form. Plastics have been used for nearly 200 hundred years and have replaced other more traditional materials such as metals and wood in many applications. They are considered as one of the most fantastic inventions in human history. But we are now realising they are not really that fantastic.
What is wrong with plastics?
Our reliance on plastics is causing environmental pollution on a grand scale. As we have been generating more and more plastics, we are seeing growing amounts of plastic waste which is now being well documented. The advent of ‘single use’ disposable items had once been the very height of modern convenience has now become the poster product for humans’ impact on our environment.
A recent study has shown that “As of 2015, approximately 6300 Mt of plastic waste had been generated, around 9% of which had been recycled, 12% was incinerated, and 79% was accumulated in landfills or the natural environment. If current production and waste management trends continue, roughly 12,000 Mt of plastic waste will be in landfills or in the natural environment by 2050.” Many millions of tons enter our oceans every year. Scientists have found “about 80,000 tonnes of buoyant plastic currently in the GPGP [Great Pacific Garbage Patch] … around the weight of 500 jumbo jets.”
Since January 2018, the media has reported plastic wastes issues much more frequently. This upturn in interest came in the wake of television series like Blue Planet II which filmed the extent to which plastics were impacting on marine ecosystems. It also coincided with China banning plastic waste imports. Before that, the UK had been shipping up to 500,000 tonnes of plastic every year for recycling in China. The end of such a trade means we have to deal with plastic wastes ourselves here, which is a huge burden. There is the same issue in many other developed countries such as the USA, Canada and Australia. Prime Minister Theresa May has pledged to eliminate all avoidable plastic waste in Britain by 2042, which shows the commitment, but also the scale of the challenge.
Toxins and fossil fuels
As we understand plastics better we are beginning to discover some of the health risks associated with some of the additives we put into them or the unreacted substances left in them. Ingredients like phthalates in cling film are toxic, and BPA in hard clear polycarbonate a hormone disruptor.
As a planet we are reliant on plastic components in everything in our everyday life – machines, cars, computers, phones – everything. Even if we give up the single use plastics, like straws and polystyrene coffee cups, we will still need it in more durable items.
Plastics are produced from crude oil (a fossil fuel) through chemical reactions. About 8% of global oil production is used for plastics. While this is not a big proportion, fossil fuels are non-renewable, non-sustainable resources and one day, we will run out of them. We have to find alternatives to these traditional plastics, and we need to find ways to produce plastics from renewable resources.
What are plastics of the future?
In 2017, the Ellen MacArthur Foundation proposed three strategies to transform the global plastic packaging market, which are: 1) fundamental redesign and innovation, 2) reuse and 3) recycling with radically improved economics and quality.
Regarding the first strategy, an important way could be to develop new plastics from renewable resources instead of fossil fuels.
A Nature article has reviewed potential renewable sources such as carbon dioxide, plant or vegetable oils, and carbohydrates (e.g., sugar) which could be used to produce sustainable plastics. Sustainable plastics made from components of plants and animals (or bio-resources) can be called bioplastics.
Two stars of the bioplastics world that have received the most attention are PLA (polylactide) and PHA (polyhydroxyalkanoate). PLA is a compostable bioplastic made from the sugars from fermented starch (e.g., corn and cassava), sugarcane or sugar beet. “Compostable” means the plastic can break down into simpler chemical compounds in composting facilities with controlled conditions (e.g., added nutrients and certain temperature). Plants absorb carbon dioxide from the atmosphere during growth, which means reduced or even neutral carbon footprint for using such a bioplastic. They present material characteristics similar to those of PE (used in films and packaging) and PS (used in foam cups and cutlery). On the other hand, PHA is produced by microorganisms (bacteria) from organic matters like sugar or lipids. These organic matters are nutrients to bacteria and then PHA grows in the bodies of bacteria. Wastewater usually is rich of such nutrients so can be used as a resource to produced PHA. PHA is biodegradable, which means it can break down by bacteria or other living organisms in the natural environment without causing pollution; so it can be used for food packaging. PHA is also harmless to living tissue, which means it can also be used to produce biomedical materials such as sutures, bone plates and tissue scaffolds.
Crabs and beans
Besides bioplastics that are produced from simple organic matters, there are also bioplastics that are directly obtained from plants and animals. These naturally-existing plastics include biomass (e.g., starch and cellulose), protein, and chitin. Biomass can be found everywhere on the Earth and can be from agricultural bioproducts or wastes. Proteins can be from soy, zein, whey and gelatin. These proteins may be produced excessively as food or need to be separated from food due to allergies of some people. The excess in the system could be used as a resource. Also chitin is the main component of shrimp/crap shells. According to a Nature comment, “every year, some 6 million to 8 million tonnes of waste crab, shrimp and lobster shells are produced globally”. This could be an important source for bioplastic production. A simple chemical reaction converts it into chitosan, which has natural antimicrobial and antifungal functions. This makes chitosan bioplastic very suitable for biomedical applications where germs need to be killed.
Having said all this, there are still great challenges to produce bioplastic materials cost-effectively from the engineering perspective. The material properties of PLA and PHA still need to be tailored to meet various application need but natural products such as cellulose, starch, protein and chitosan are less easy to shape and adhere together to form new solids that are as mechanically strong as traditional plastics.
So there is still a lot of research ongoing to explore the chemistry and engineering aspects for working with these bioplastics. For example, we are working on engineering processes based on conventional plastic processing equipment to produce bioplastic items for diverse applications. We are also designing bioplastic materials with desired properties and functions by adding nanomaterials (materials in the form of very small particles) derived from natural resources such as biomass and clay.
If we can find safe and environmentally friendly bioplastics to replace traditional plastics for high-volume applications like packaging, foams and disposable items, we can reduce the carbon footprint of production, produce minimal plastic waste and create products which are better for humans to use. If these bioplastic materials are used for biomedical applications, we envision less pain and better recovery of patients. With the development and use of bioplastics, we are closer to a sustainable future.
21 May 2019
Dr Fengwei (David) Xie is a Marie Skłodowska-Curie Individual Fellow at the International Institute for Nanocomposites Manufacturing, WMG, University of Warwick.
His research focuses on exploring the mechanisms behind the relationship between processing, structure and properties of materials particularly based on “green” polymers. He is interested in developing sustainable materials for better health and a sustainable future.
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