Science - June 1, 2017

Bioplastics: fact and fiction

Text:
Tessa Louwerens
2

Bioplastics have a ‘green’ image. But in reality they are not a miracle cure for litter and other environmental problems. The truth lies – as always – somewhere in the middle, shows a review of the facts produced by Wageningen researchers.

photo Guy Ackermans

More and more big companies such as Coca-Cola are investing in bioplastic as a sustainable alternative to traditional plastics made from fossil fuels. But there is quite a lot of uncertainty about bioplastics. Are they always more environmentally friendly? Are they the solution to the plastic soup in the ocean? Which garbage bin do they belong in? This confusion has made it difficult for companies to switch to these materials. To provide a bit more clarity, Wageningen Food & Biobased Research reviewed all the research on bioplastics, at the behest of the Netherlands Enterprise Agency (RVO). This resulted in the report Biobased and biodegradable plastics – Facts and figures. ‘A lot has been written on this subject but the evidence is often missing,’ says researcher Christiaan Bolck. ‘In our report we line up the scientific facts and everyone who wants to say or write something about this kind of plastic can refer to it.’

Oil price

The study by Bolck and his colleagues included the market for bioplastics. In 2015, the production capacity for biobased and biodegradable plastic (see box) was approximately one percent of the total global production. This proportion is expected to go up. Bolck: ‘Generally, biobased and biodegradable plastics are more expensive, but there are already several examples of competitive products and if more of those are produced, the price will go down.  Besides, the price of fossil fuels depends on the price of oil, which tends to fluctuate more than the price of biomass.’

Biobased and biodegradable plastic is currently used for food packaging, disposable cups and cutlery, carrier bags and agricultural materials, among other things. The best way to use the plastic depends on its qualities. Its permeability for water vapour makes a biobased PLA unsuitable for bottles, but could be an advantage in ‘breathable’ packaging for fruit or vegetables.

Plastic soup

Nor is biodegradable plastic a panacea for the ‘plastic soup’ of plastic litter that ends up in the sea, says Bolck. Because even if plastic is biodegradable, it does not necessarily break down quickly. The speed at which it disappears depends on the material and the environment. Bolck: ‘There are biodegradable plastics which break down completely within a few months, but in that time a seagull can already suffocate on a plastic bag.’ So the litter problem is not solved at a blow with bioplastics.

Most biobased and biodegradable plastics can be recycled mechanically in the same way as conventional plastics. But with the exception of recycled PET bottles, many recycled plastics are not 100 percent pure, making them unsuitable as food packaging for food safety reasons. Bolck: ‘It is technically possible to distinguish between different types of plastic, including the various types of biobased and biodegradable plastics. But in practice it has proven difficult to separate them 100 percent.’ Recycled plastic is therefore always a mix of different types of plastic.

18-ACH foto bioplastic komkommers.jpg

Biodegradable plastics can also be composted. That means that the consumer can dispose of them with the organic waste. But then it does need to be clear what is biodegradable plastic and what isn’t. At the moment about one percent of household waste consists of non-compostable plastic. Bolck: ‘Dutch waste disposal workers are afraid there will be more non-biodegradable plastic in the organic waste because consumers can’t tell plastics apart. So they are reluctant to accept biodegradable packaging, apart from the compostable bags for organic waste.’ This problem should be solved by clear pictograms which show which bin the packaging should go into.

Farmland

Generally speaking, the production of biobased plastic relies less on non-renewable resources. Instead, it makes use of raw materials such as sugar, starch and waste products such as beet pulp. The use of edible materials for generating energy or manufacturing plastics is controversial. Bolck: But you can’t just condemn outright all uses of edible products for other things than food. It gives farmers more security, for instance, because they can sell their crops for other purposes.’

Currently, 0.2 percent of farmland worldwide is used to grow raw materials for bioplastics. ‘If we substituted bioplastics for all our petroleum-based plastics, we would need about five percent of all the biomass harvested annually,’ says Bolck. But this seems to him an improbable scenario, because alternative materials sourced from garbage and waste flows from agriculture will be used as well.

Greenhouse gas

The environmental impact of the production of bioplastic is not easy to determine. ‘It is sometimes claimed that just as much CO2  is emitted in the production of biobased plastics as in that of petrobased plastics, and that it is therefore not necessarily better for the environment,’ says Bolck. ‘But our report shows that in most cases smaller amounts of greenhouse gases, including CO2, are released in the production of biobased plastics.’ On the other hand: ‘If you look at negative environmental effects that are specific to agriculture, such as eutrophication and acidification, you’ll find that biobased plastics contribute more to them than petrobased plastics,’ says Bolck. This is because farmland is used to produce bioplastics.

According to Bolck, it is difficult to generalize about the environmental impact of plastics because so much depends on the kind of plastic in question. ‘You cannot simply say that all conventional plastics are bad for the environment, any more than you can say that all biobased plastics are good for the environment. The truth is more complex.’


Biobased or biodegradable

‘Bioplastic’ is actually a confusing blanket term. It gets used to denote biodegradable plastic, which dissolves into the environment, as well as for biobased plastic, which is made out of biomass. These are two different characteristics, however, which sometimes go together and sometimes do not. There are biobased plastics which do not break down in the environment, and biodegradable plastics which are petroleum-based.

Petrobased Partially biobased Biobased
Non-biodegradable PE, PP, PET, PS, pvc Bio-PET, PTT Bio-PE
Biodegradable PBAT, PB (A), PCL Blends based on starch PLA, PHA, cellophane

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