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How Do We Carry Our Shopping Home Now? (Part 2)

In part 1 of this two-part series, we examined the environmental impacts of the humble lightweight plastic single-use shopping bag, and argued that simply banning them without providing a sustainable alternative is not a valid long-term solution: the large-scale use of many of the alternatives, such as non-woven polypropylene bags, would also cause environmental damage — in particular, due to the lack of sustainable production and disposal options. Here, in part 2, we’ll speculate on what properties the ideal shopping bag would have, and provide recommendations for shoppers when selecting new bags.

Part II: The ideal shopping bag

In part 1 of this two-part series, we examined the environmental impacts of the humble lightweight plastic single-use shopping bag, and argued that simply banning them without providing a sustainable alternative is not a valid long-term solution: the large-scale use of many of the alternatives, such as non-woven polypropylene bags, would also cause environmental damage — in particular, due to the lack of sustainable production and disposal options. Here, in part 2, we’ll speculate on what properties the ideal shopping bag would have, and provide recommendations for shoppers when selecting new bags.

The circular economy

It is likely that the production, use, and disposal of a truly eco-friendly bag will need to conform to a so-called circular economy system. As opposed to the “take-make-break-discard-repeat” linear material and energy flows that often characterize our current economy, the circular economy model uses restorative and regenerative processes to preserve resources and eliminate waste. Excellent inspiration can be found from natural biological ecosystems, where materials are continuously repurposed and reused, and nothing is wasted.   

It has been predicted that the implementation of such a system across the entire economy would lead not only to a vast reduction in environmental impact, but would deliver significant social and economic benefits as well. For instance, according to estimates made in a 2013 report by the Ellen MacArthur Foundation, the material that the global consumer goods sector sends to landfills/incineration each year actually would have a value, if repurposed, of $2.6 trillion. Considering plastic packaging alone (all packaging, not just bags), the estimated annual loss of value due to 95% of plastic packaging being discarded after a first use is $80–120 billion. It seems the financial rewards awaiting adopters of the circular economy model are significant indeed.

So, how could elements of the circular economy be implemented in the life cycle of shopping bags? Firstly, the use of finite fossil fuels as starting materials for the bags would need to be eliminated. Secondly, the end-of-life disposal would need to return the materials either directly to the Earth (composting) or be otherwise reintroduced into the economy, for instance using closed-loop recycling. Below, we’ll look at two of clean technology products that could be candidates: compostable and highly recyclable plastic bags.

Compostable plastic bags

Compostable materials are a specific subset of biodegradable materials which, can be defined as being “capable of undergoing biological decomposition in a compost site as part of an available program, such that the plastic is not visually distinguishable and breaks down to carbon dioxide, water, inorganic compounds and biomass, at a rate consistent with known compostable materials (e.g. cellulose).” Compostable plastic bags are typically made with renewable materials such as corn or potato starch. They are also naturally suited to transporting food, as residues can simply be allowed to decompose together with the bag. This is in contrast to recycling of regular consumer plastics, where food residues can be problematic. Moreover, compostable bags can be disposed in curbside organic waste collection bins, which are becoming more common due to the increasingly recognized benefits of diverting kitchen organic waste away from regular disposal streams. International standards for compostable plastics are also well-established, which allows for effective regulation against contaminating organic waste streams with bags that don’t have satisfactory composting properties.

One might therefore expect that they could be strong candidates. However – there are challenges. Certified compostable materials need the right conditions (specified by oxygen, heat and moisture levels) to decompose to form compost effectively. These conditions can be reliably provided at commercial composting systems, but not necessarily in home systems. For this reason, composting may not occur satisfactorily outside dedicated facilities, including in home systems, and importantly, in natural land or marine environments. Effective curbside collection and transport to commercial facilities may therefore prove to be a firm pre-requisite.

For single-use compostable bags, it is possible that their cost, which is currently higher than LP bags, may also discourage retailers. In a correspondence with CleanTechnica, Edward Kosior, Managing Director of Nextek, a resource management consultancy firm, points out: With single-use compostable plastics or paper bags, these are substitutes for the disposable plastic bag and the supermarkets realise that they are more expensive than the plastics so they are not keen to promote these.” He also adds: “Environmentally, they perpetuate the throw away culture that got us into this mess.”

This suggests that the technical challenge facing manufacturers of these bags is to make their products robust enough for a large number of reuses, with a maximum renewable content, at low cost, all while ensuring they decompose to compost as soon as exposed to the right conditions. However, a quick Internet search is sufficient to demonstrate that many companies already offer products that appear to be promising. Cotton and paper bags, despite their relatively poor performance in past life cycle assessment (LCA) studies, may also yet play a role if high-volume, sustainable farming practices can be further improved.

Recyclable plastic bags

As we mentioned in part 1 of this series, closed-cycle recycling can preserve more value than other methods. This may prove to be a key advantage for closed-loop recyclable bags over compostable bags. To be truly sustainable, the use of fossil fuels as a feedstock, as has historically been the case for most plastics, must be eliminated. Fortunately, this is already happening on an industrial scale. Plastics such as such as low-density polyethylene (LDPE) and high-density polyethylene (HDPE), can be made from renewable organic materials (such as sugarcane) and can have virtually identical properties to those made with virgin fossil fuels.

An important feature of using renewable organic feedstock for the production of plastic is that the production can be carbon-negative. In other words, the production can actually reduce the amount of carbon dioxide in the atmosphere. For instance, the production of sugarcane-derived, 100% recyclable HDPE has been calculated to absorb 3.09 kg of CO2 from the air for every kg of plastic produced. This figure includes credit for offsetting fossil-fuel generated electricity by co-production of electricity from a by-product of the process. This value only pertains to the manufacture of the feedstock HDPE, and does not include the emissions from using this feedstock to manufacture products (such as shopping bags) or the emissions associated with the end-of-life disposal of these products. However, having a strongly carbon-negative feedstock production is likely a vital step in achieving overall carbon-neutrality for the end product. The overall environmental impact of HDPE produced in this way is shown in the figure below, contrasted with conventional HDPE (made with fossil fuels).

The figure shows that sugarcane HDPE has a lower environmental impact in the categories of climate change — for which it has a negative net carbon footprint — and ecotoxicity. The fossil-fuel-derived plastic is superior in the other categories. It is possible that further research and development could lead to improved performance for the sugarcane HDPE in these categories as well.

As in the case of compostable bags, there appears to be a number of companies that offer bags that are made from more than 50% renewable feedstock, can be effectively recycled, and are of low cost.

Summary

So where does all of that leave us? It is evident that up-to-date LCA studies are required to assess the performance of both currently available and potential next-generation shopping bags, which strive for increasingly improved renewable feedstock content, material properties and sustainable disposal. The ideal shopping bags are likely to have the following characteristics:

Characteristic Justification
High-value products Promotes reduction, re-use, correct disposal, suitable for buy-back schemes
Not lightweight Less easily dispersed into environment
Sustainable production with renewable feedstock Lowered (or eliminated) carbon footprint and other environmental impacts (toxicity, eutrophication, acidification etc.). Maximised renewable feedstock content. No use of finite fossil fuel resources.
Bio-benign Bags that are (despite all preventative measures) dispersed into environment do not harm wildlife or cause release of harmful substances.
Robust, re-usable, easy to maintain/clean Evidence indicates that re-usable bags are preferred to single-use from a sustainability perspective. Re-using extracts the maximum value from the bags.
Conducive to sustainable disposal Recyclable

Highly recyclable, ideally closed-loop. Eliminates the use of materials that can’t be recycled (e.g. multi-layer composites). Sustainability and yield of recycling needs to be continuously improved. Super-recyclability is a long-term goal of the New Plastic Economy. Clearly labeled.

Compostable

Compostability (under a range of conditions) needs to be continuously improved. Clearly labeled.

 

Creating shopping bags that satisfy all of these criteria is certainly a challenge, but, as mentioned earlier, numerous companies are already making progress. It is important to recognize that the responsibility doesn’t only lie with the bag manufacturers. Consumer behavior and infrastructure are also critical. Some comments relating to those are shown below.

Infrastructure

Rather than simply banning LP bags and leaving consumers to choose from a large range of slightly-less-bad options, local governments need to take a more active role in providing real solutions. The bans, or disincentives, could be extended to include all bags that can’t be disposed sustainably in that jurisdiction. Or to keep things simple for regulators, consumers and retailers, governments could introduce legislation to permit only one kind of bag. If any inspiration is needed, one only needs to look to the city of Zurich, which permits only one kind of rubbish bag for non-recyclable waste. The high cost of these city-approved bags, known as Züri-Sacks, and the fines awaiting those who use any other kind of bag, prompts residents to use good recycling and waste avoidance habits to minimize the number of Züri-Sacks they need to purchase. Applied to shopping bags, this approach would enable regulators to be sure of the sustainable production of the bags and have adequate and optimized collection and recycling/composting facilities.

Consumer behavior

Previous LCA analyses clearly show that the number of re-uses is a decisive parameter which can make or break the sustainability of a given bag. It is therefore important to re-use the bags as many times as possible, noting that bags will require periodic cleaning. Some bags are machine-washable. Disposal is also critical. Providing local governments and/or retailers are doing their part by providing adequate disposal services, whether they be buy-back schemes or curbside collection for recycling or composting, it is up to the consumers to use them. When selecting a bag, make sure sustainable, local disposal facilities for that bag exist, and confirm, perhaps using the information provided on the website of bag retailers, that the content of renewably sourced feedstock material is as large as possible.


References:

The circular economy

Compostable plastic bags

  • Definition: Biodegradable and compostable alternatives to conventional plastics, J. H. Song, R. J. Murphy, R. Narayan, G. B. H. Davies, Phil. Trans. R. Soc. B 2009 364 2127-2139; DOI: 10.1098/rstb.2008.0289. Published 14 June 2009.

Recyclable plastic bags

 
 
 
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Written By

has worked in solar energy (the vast majority with solar PV, but also with concentrated solar thermal) since 2008. During his career, he has worked in Germany, Austria, Australia and the USA. He has published 11 peer-reviewed scientific papers on solar energy and established an independent solar cell test facility in Australia, one of only a handful of such labs in the world who are relied upon to certify new breakthroughs in PV technology. Aside from renewable energy, his other interests include sustainable living, the outdoors and classic literature.

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