Are bioplastics the solution to plastic waste?

Caroline Wood asks whether bioplastics are the solution to tackle plastic waste. 

Can you imagine a world without plastic? Despite their relatively recent invention, plastics are now ubiquitous in every area of our lives from healthcare to homewares and from food to fashion. This has brought many unquestionable benefits, such as replacing materials made from animal products and allowing unprecedented levels of hygiene and food preservation. But it’s clear we urgently need a new materials revolution because the unique selling point of plastics - it’s sheer durability and indestructible nature – has resulted in an unsustainable waste crisis. Globally, only 14% of plastic packaging is thought to be collected for recycling,^[1] with the rest being incinerated, landfilled or entering the environment. Suddenly we have woken up to the scale at which plastic waste is penetrating our oceans, our soils and even our bodies. Challenges such as these, however, are catalysts for innovation and the search is on for alternative materials that match plastic in performance without burdening the environment. Right now, one of the hottest topics in the materials world is bioplastics.

A wide range of natural materials are being investigated for potential new bioplastics Image courtesy of Green Lab

What exactly is a bioplastic? Is it a plastic made from natural materials? Or a plastic that can biodegrade, i.e. it breaks down harmlessly in the environment without leaving toxic traces? Slightly confusingly, the answer is either, or both.^[2] Conventional plastics are manufactured from chemicals in fossil fuels during a process that is both energy-intense and a major source of green-house gas emissions. Given the increasing concern about climate change, there is growing pressure to move away from these ‘oil-based’ plastics. Alternative bioplastics already exist that are wholly or partly derived from natural materials: these are also known as ‘bio-based’ plastics. Many bio-based plastics can biodegrade, although this typically requires an industrial composting facility. Other bio-based plastics do not degrade but can act as functional replacements for conventional plastics (so-called ‘drop in’ bioplastics) and can be recycled. One example is bio-based polyethylene terephthalate (PET) which can replace oil-based PET currently used to make drinks bottles. Coca-Cola’s ‘Plant Bottle’ for instance, is made partially from bio-based PET derived from sugar cane residue, yet is fully recyclable in PET recycling streams. Confusingly, bioplastics also include oil-based plastics that can biodegrade, for instance polybutyrate adipate terephthalate (PBAT), used in flexible packaging such as compostable shopping bags.  

One of the most widely-used bioplastics is polylactic acid (PLA), made from fermented plant starch such as corn, sugarcane or sugar beet pulp. Since it is both plant-derived and biodegradable, it is becoming increasingly popular for ‘sustainable’ takeaway containers for food and drink. However, within the plastic packaging industry, PLA often provokes a ‘marmite’ reaction. On the one hand, it is seen as a solution to packaging waste that is contaminated with food residue, which cannot be recycled. But if a meal is served in a PLA container, both the packaging and the food waste can be disposed of together and sent to a composting facility. Across the UK certain tourist attractions, canteens, hotels and airports are using this system as a ‘zero-waste’ approach to out-of-home catering.

Whilst the theory sounds great, in practice this can be difficult to achieve. PLA will only biodegrade under the high temperatures of an industrial composter (50-60°C), but since it can look identical to conventional plastics, it is often not recognised at these facilities and removed. Meanwhile, the recycling industry are concerned that if PLA is disposed of in a plastics recycling bin, it could contaminate recycling streams for conventional plastics, lowering the quality of the end product. Due to the low amount of PLA in the system, this is unlikely to be an issue at present although this could change if the market expanded rapidly. PLA can be recycled like conventional plastics and has a distinct infra-red signature that would allow it to be sorted by the optical scanners used in recycling plants. But it only becomes economically viable to do this if significant amounts of material are collected.

There is another problem inherent with PLA (and other bio-based plastics derived from crops). If they were to replace all conventional plastics, this could put pressure on land and other resources needed to produce food. One solution could be to move plastics production from the land to the sea. Skipping Rocks Lab, based in London, have developed a seaweed-based material that could replace flexible food packaging that is often difficult to recycle. The material, made from sodium alginate and calcium chloride, decomposes within 6 weeks even outside an industrial facility and is also edible. It has already been trialled by the food takeaway business Just Eat to replace sauce sachets and this year helped reduce the London Marathon’s colossal use of plastic water bottles in the form of 30,000 biodegradable drinks capsules handed out to the runners.

Although seaweed-based packaging sounds promising, it raises the question as to how many acres of the ocean surface we would need to farm enough seaweed for all our needs. But there is also interest in using ‘waste’ resources from existing industries. One example is chitin: a polymer found in mushrooms and the exoskeleton of insects and crustaceans. This can be chemically converted into chitosan: a biodegradable material which has been demonstrated to show antimicrobial properties.^[3] Globally, chitin is available in abundance: an estimated 50,000 tonnes of mushroom waste are generated in Europe each week^[4] and chitin is a by-product of prawn, crab and lobster farms. Insect farming may soon become another source of chitin since EU regulations changed to allow insects to be used as feed for fish farms. Even the fish themselves can be a valuable source of material polymers: Marinatex, for instance, is a recently-developed translucent film made from fish skin and scales.

Besides animal industries, crop waste offers many under-utilised resources for plastic alternatives. At a basic level, this includes banana and palm leaves that can be pressed or moulded to make plates and bowls. New material sources include polymers based on cutin: a waxy compound that forms the protective coating on leaves and tomato skins. A collaboration between Heinz, a leading producer of tomato ketchup, and the Ford Motor Company is currently investigating the potential of cutin-based polymers to use in vehicle manufacturing. Meanwhile, the Mandin Collective produces a range of bowls, plates and containers using orange peel collected from commercial juice sellers. The peel is dried and ground then combined with an organic glue to form a paste which is pressed into moulds and left to set.

Using locally-produced, abundantly available waste materials offers the chance to move plastic production from large corporations to community ventures. This is the goal of the Materiom project, an open source database of bioplastic recipes that anyone in the world can access

Workshops such as this one hosted by Green Lab, London, give everyone the chance to try making a bioplastic Image courtesy of Green Lab

and contribute to. The focus is on using ‘locally abundant biomass’ to make materials ‘that nourish local economies and ecologies.’ Since many of the recipes only require simple ingredients, you could even have a go yourself, or use them as the inspiration for a school project or educational activity. For those with more commercial ambitions, open innovation labs such as Green Lab (based in London) provide access to facilities to experiment and prototype with bio-plastics. Developing new materials is no longer a preserve of big industries: anyone with a feasible idea for a plastic alternative can now explore its potential.

Nevertheless, bioplastics will need to overcome a number of challenges before they can become mainstream. Sourcing enough organic matter from food industries typically requires changing existing supply chains and working closely with manufacturers. Secondly, for the final price to be comparable with existing plastics, the production process must be scalable to the point that the economics are favourable. Besides this, there are also concerns that novel materials may present new food-safety issues. Chitin, for instance, could be an issue for people with shellfish allergies, whilst products containing wheat gluten could affect those with coeliac disease. Clearly, more research is needed into the potential for compounds in new packaging materials to migrate into and affect the food product.

Perhaps the greatest danger is that bioplastics may take our focus off the real issue: we have become a single-use society where packaging is typically used once then thrown away. The most efficient way to reduce packaging waste is simply to reuse packaging or not use it in the first place. Already, innovators and entrepreneurs are leading the way, including new pack formats; zero-packaging shops and reuse schemes for takeaway meal containers. Whilst the creativity driving new bioplastics is wonderful, we shouldn’t use it as an excuse to plunder our planet’s resources for uses that last merely minutes.

Caroline Wood is a PhD student at the University of Sheffield, studying parasitic weeds that infect food crops. Outside her lab work she enjoys taking part in public engagement initiatives, including through the Sheffield Branch of the British Science Association. She ultimately hopes to have a career in science policy. You can learn more about her by following her on Twitter (@sciencedestiny) or by reading her blog.

References