Since the invention of cellophane by Swiss chemist Jacques E. Brandenberger in 1900, soft polymeric (plastic) films have revolutionalised food packaging.
Plastic films can act as barriers against gases and moisture, allowing careful regulation of the humidity and gas content of the environment the food is stored in. Additionally, they are commonly transparent and thereby still allow customers to see the produce. Thus, soft plastic films both extend the shelf life of food products and also help to make the shopping experience more convenient for the consumer.
When potatoes - the most wasted food in the UK - are packaged in a plastic covering, it has been shown that they retain freshness and quality for at least 10 days longer than non-packaged potatoes. Similarly, the shelf life of certain meat products can be extended from 3 to 21 days when a plastic covering is used.
Soft plastic films clearly have a role to play in maximizing freshness of food and minimizing food waste.
It is estimated that the UK produces about 1.2 million tonnes of plastic film waste per year. Perhaps unsurprisingly, especially in the light of the current political focus on the global climate, it has become ever more important to consider disposal of these film-based packaging materials once they reach the end of their useful lives.
Currently only 13% of UK local authorities have separate kerbside collection of plastic films. This means that, at the moment, the majority of household plastic film must be put into general waste and will usually end up going to landfill or incineration. Perhaps as a consequence of that, soft plastic films currently have a “bad wrap” when it comes to the environment. But is this justified?
Can we just recycle it all?
The way in which we dispose of products depends on their make-up. A ‘one-size-fits-all’ approach to recycling of plastic films seems unlikely at least partly because the films can be made using a variety of polymers. Common polymers include polyethylene and polypropylene, and polyvinyl chloride (PVC) found in the ubiquitous “cling film wrap”.
It is typically possible to recycle these materials in some way, although some inherently present more challenges than others. Recycling PVC, for example, has to take into account a relatively high level of additives and the chlorine content. In addition, soft polymeric films often cannot be processed in the same way as rigid plastics at the recycling centre. In contrast to heavier, rigid plastics, soft plastics can cause processing machinery at recycling plants to become blocked. It can be problematic and inefficient for businesses to stop their sorting machinery in order to remove blockages caused by plastic films.
To prevent this from happening films typically are collected separately from rigid plastics.
Some recycling schemes based on this premise already exist. Many large supermarkets have recycling schemes for plastic bags. One supermarket, Co-op, has launched a trial in 50 of its stores in southern England, of an in-store recycling initiative for all flexible plastics not currently recycled by local authorities (including polyethylene-free films). Under this system, the disposible film waste that is collected is sorted and, where possible, used for making waste disposal bin liners for Co-op stores.
Another company focused on difficult-to-recycle plastics is TerraCycle® (see my recent blog Circular economy: rethinking composite plastic packaging). TerraCycle® run a range of programs for recycling products such as bread bags. Once collected, the bags are shredded, then melted down, and finally turned into a useable raw format like pellets or powder. This raw format can then be converted into new plastic products. One downside is that the original plastic is downcycled (is turned into a plastic having lower quality than the original).
There are also some recycling options that to avoid the need to separate different kinds of soft plastics. For example, a liquid hydrocarbon feedstock for use in the manufacture of new polymers can be prepared by converting mixtures of plastic waste materials into a multifunctional tar oil by heating in a process called pyrolysis. One company that is active in this area are Recycling Technologies®. Recycling Technologies® have also developed a method for converting mixed plastic waste into an oil for fuel as described in their recently granted European patent EP 2 956 524 B1. Recently, Tesco® PLC announced a partnership with Recycling Technologies® to collect a range of difficult-to recycle soft plastics like film and bags in 10 of its stores near Bristol and Swindon.
Can we make biodegradable films instead?
The development of biodegradable films is being explored by various parties. I have already explored the pros and cons of compostable packaging in my blog Compostable packaging – let’s break it down. From a practical perspective, biodegradable films are unlikely to gain wide traction in the food packaging industry unless they share some of the impressive qualities (and, to at least some degree, cost) of the currently-available soft polymeric films. As a consequence, the challenge being faced is not only the provision of a material which can biodegrade at the end of its useful lifetime, but also which has, for example, the outstanding barrier properties of polyethylene. As a material, cellophane is actually biodegradable; however, it is highly permeable to water vapour and so would ultimately not maintain current standards in relation to shelf-life of foodstuffs.
Starch-based films are currently receiving a lot of attention as possible biodegradable alternatives to conventional polymer films. These materials are made using the starch found in plants such as corn, potatoes or wheat and usually able to be composted in industrial composting conditions.
Italian company Novamont® have developed “Mater-Bi®” compostable resins, which are proposed for use in packaging applications such as as bags, pouches and sealing films. Importantly, this material has good barrier properties for specific applications, such as improved moisture vapour breathability in comparison to traditional plastic films. As a further benefit, Mater-Bi® can be blown on equipment used for so-called conventional plastics, which means there is no need for new and specialist equipment. As shown by patent application WO 2020/216803 A1, one recent area of focus for Novamont is the development of starch-based biodegradable films with improved tensile strength at break. This is important for food packaging applications, such as in potato bags.
Australian firm Plantic Technologies™ have focused attention on packaging materials based on high amylose starch derived from corn. They have a range of flexible barrier packaging materials, which can be used to produce pouches from a variety of food products and which display good gas barrier performance. According to WO 2020172722 A1, Plantic Technologies™ have developed high viscosity starch compositions, which can be extruded to produce films with low haze, high strength and high gas barrier properties.
What does the future look like?
Despite their ubiquity and utility in food packaging, the recycling of plastic films remains a challenge. However, a range of new approaches are being developed to tackle plastic film waste, including recycling schemes and specifically-designed recycling processes, as well as the development of new biodegradable materials and especially starch-based films. Between them, we hope they will reduce – and one day eliminate – plastic film waste that ends up in landfill.
