Biobased But Not Biodegradable

Today it is almost impossible to read a food magazine or browse a food conference program without coming across the word sustainable, often followed by the word packaging. In its simplest sense, sustainable means “to maintain or keep going continuously,” and it has been used in connection with forest management for over a century (Robertson, 2009). According to the U.S. Environmental Protection Agency, “sustainability, or sustainable development, is the ability to achieve continuing economic prosperity while protecting the natural systems of the planet and providing a high quality of life for its people.” Implicit in this definition is the reality that consumption of resources must match their rate of renewal, and the use of nonrenewable resources, including metals, and plastics from fossil carbon sources such as crude oil and natural gas, is unsustainable. This has led to the current focus on renewable, biobased plastics.

Sustainable Packaging
Although sustainable packaging is widely discussed at conferences and in the packaging media, many in the packaging industry are confused. In 2005, the U.S.-based Sustainable Packaging Coalition defined sustainable packaging by listing eight criteria that blended broad sustainability objectives with business considerations and strategies to address the environmental concerns related to the life cycle of packaging. (See www.sustainablepackaging.org.) One of the coalition’s criteria is that sustainable packaging is sourced, manufactured, transported, and recycled using renewable energy, which means that there is no sustainable packaging on the market today.

The European Organisation for Packaging and the Environment (EUROPEN) believes it makes much more sense to talk about packaging and sustainability rather than sustainable packaging, which, according to that group, cannot be an end in itself.

The Consumer Goods Forum, a global industry network that brings together the CEOs and senior management of over 650 retailers, manufacturers, service providers, and other stakeholders across 70 countries, published the Global Protocol on Packaging Sustainability in 2011 to provide a common language with which to discuss and assess the relative sustainability of packaging. This so-called common language consists, not in a definition of sustainable packaging, but in a framework and a measurement system. To confuse things even further, a recent book by Verghese et al. (2012) was entitled Packaging for Sustainability.

A recent report by PricewaterhouseCoopers (2012) in the United Kingdom concluded that sustainable packaging as a term is no longer relevant today, and is too broad a term to be useful at a practical level as no one can come up with a single meaningful definition. Instead, the report stated that sustainable packaging has been substituted with a more balanced view of efficient packaging characterized by minimum resources, minimizing product waste, transport and display efficiency, and effective after-use disposal and recycling.

Consumer Confusion
From the preceding discussion, it is clear that trying to reconcile “sustainable packaging” and “packaging and sustainability” is difficult if not impossible and is more than simply an exercise in semantics. How can the fast-moving consumer goods industry expect the public to understand what they are doing to become more sustainable when the language and metrics are so confusing? Reaching a broad consensus on what may constitute sustainable packaging would provide the packaging industry with a platform from which to influence regulation as well as customer and consumer attitudes and expectations. Because consumers are confused, the possibility exists for unscrupulous companies to market packages as “sustainable” when they are not and mislead consumers. The latest Federal Trade Commission Green Guide (2012) omits any mention of sustainable under environmental claims.

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Biobased Packaging Materials
Biobased packaging materials are defined as materials derived primarily from annually renewable sources. This definition excludes paper-based materials because, although obviously biobased, trees generally have renewal times of 25–65 years (Robertson, 2013). The current interest in sustainability and the desire for renewable resources is driving development of biobased packaging materials.

Why is biodegradation popular? To many consumers, biodegradation appears “natural;” it is what nature does, so it must be good. The public also believes that biodegradable packaging will solve the solid waste problem plus the litter problem. Other advocates suggest that composting will reduce the quantity of waste going to landfills.

To realize the benefits of biodegradable plastics, municipal composting facilities must be available. However, few cities have such facilities or the capacity to collect green waste separately. This is a major drawback to the expansion of biodegradable plastics. The biggest benefit of composting is avoidance of methane production in landfills from anaerobic biodegradation.

Petrochemical-based plastics when incinerated (or when they biodegrade in some cases) release CO₂ that was fixed millions of years ago. By reviewing the biological carbon cycle, Narayan (2012) showed that replacing petrochemical carbon with biobased carbon in plastics intrinsically offers a zero material carbon footprint value proposition. However, despite its popularity among members of the public, carbon footprint is only one environmental consideration.

Although nature produces 170 billion metric tons (t) per year of biomass by photosynthesis, only 3.5% of these compounds are used by humans for food and nonfood purposes. Biomass carbohydrates account for 75% of this biomass and are the most abundant renewable resources available; they are currently viewed as a feedstock for the so-called “green” chemistry of the future.

However, the promise of compostable packaging is not, as once proposed, a reduction in landfill volume, but is actually a technology to enhance the collection of food waste and food-contaminated packaging to enable diversion of these materials from landfill to composting or anaerobic digestion facilities (Kolstad et al., 2012). The ability to divert food wastes from landfill would result in a reduction in methane generation. Disposal of biobased biodegradable materials in landfills as opposed to anaerobic digestion is not recommended because under anaerobic conditions they biodegrade to form methane, and most landfills capture only a small fraction of the methane created.

Are biobased, biodegradable packaging materials the best option? Converting a solid material into a gas via composting or biodegradation should only be a last resort. It is much better to capture the embodied energy and material for reuse through recycling, or to recover the energy through incineration. Composting a biobased packaging material after a single use is a wasteful approach and is not sustainable. Biobased but not biodegradable is the way forward to sustainable packaging.

Biobased Plastics
Biobased plastics are derived from biobased materials and may (or may not) be biodegradable because biodegradability depends not on the origin of the raw materials but on their chemical composition. Plastics can be classified into four types with respect to whether or not they are biodegradable and the source of the feedstock used to make them. These four types are 1) biobased and biodegradable; 2) petrochemical-based and biodegradable; 3) biobased but not biodegradable; and 4) conventional petrochemical-based plastics (Figure 1).

1) Biobased and biodegradable. Thermoplastic starch (TPS) typically consists of 70% starch plus plasticizers (glycerine and polyols), fillers, and polycaprolactone (PCL) or poly(vinyl alcohol) (PVOH) (petrochemicalbased). TPS packages normally retain the hydrophilic characteristics of starch and readily degrade in home composters. They are suitable for low-moisture products such as confectionery and biscuit trays. However, TPS is not really a viable alternative to most petrochemical- based plastics although nanoclays can be added to improve properties.

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Polylactic acid (PLA) is a linear, aliphatic polyester synthesized from lactic acid monomers. In the United States, the starting material to produce lactic acid is genetically modified corn, while in Europe, sugar beets are used. In Thailand, sugarcane and tapioca are used. The major application of PLA in food packaging is as a rigid bottle or tub although it also finds some use as a film. The biggest problem is its high water vapor transmission rate.

Polyhydroxyalkanoates (PHAs) are microbial polyesters that are produced by many bacterial species as intracellular particles that act as energy and carbon reserves. The bacteria Cupriavidus necator ferments sugars to a random copolymer of hydroxybutyrate (HB) and hydroxyvalerate (HV). PHAs have high performance properties including excellent strength and toughness, as well as resistance to heat and hot liquids.

2) Petrochemical-based and biodegradable. A considerable number of plastics have been available for many years including PCL, PVOH, poly(butylene adipate-co-terephthalate) (PBAT), poly(butylene succinate) (PBS) and more recently poly(propylene carbonate) (PPC) and polyglycolic acid (PGA). The quantities used for food packaging are very small.

3) Biobased but not biodegradable. Bioethylene can be produced by the catalytic dehydration of bioethanol, produced by the fermentation of carbohydrates, followed by normal polymerization to produce polyethylene (PE) as shown in Figure 2.

 It is not biodegradable and has the same properties, processing, and performance as PE made from natural gas or oil feedstocks. The major producers are in Brazil and use sugar from cane as the starting material. Current applications by multinationals include yogurt cups (Danone), fruit juice bottles (Odwalla), and plastic caps and closures for aseptic paperboard cartons (Tetra Pak).

In May 2009, The Coca-Cola Co. announced the release of a PET PlantBottle™ made from a blend of petrochemical-based material [terephthalic acid (TA)] and up to 30% plant-based material (ethylene glycol (EG) from molasses), resulting in a 25% reduction in carbon emissions.

Coca-Cola and H.J. Heinz have a strategic partnership that enables Heinz to produce its ketchup bottles using Coca-Cola’s PlantBottle™ packaging; Volvic will also use PlantBottle™.

In 2011, Coca-Cola announced multimillion-dollar investments in two innovation companies that have technology solutions for producing biobased TA: Virent, which can produce para-xylene (BioFormPX™) from a wide variety of feedstocks, including sugarcane, corn, and woody biomass and convert this to TA; and Gevo, whose Integrated Fermentation Technology^® (GIFT^®) converts biomass into isobutanol that can be used to make para-xylene and then TA. The company also invested in Avantium, which has developed 100% biobased bottles made of polyethylene furanoate (PEF). Avantium’s patented technology (YXY) converts biomass into furanics building blocks such as 2,5-furan dicarboxylic acid (FDCA) that can replace TA and be polymerized with EG to PEF (Figure 3). PEF has superior barrier properties compared to PET with a 10 times better O₂ barrier, a four times better CO₂ barrier, and twice as good water vapor barrier; it also has more attractive thermal properties with a higher glass transition temperature of 86°C (Avantium, 2013). The first commercial-scale plant will be operational in 2019.

In March 2011, PepsiCo unveiled plans for a bioPET bottle made from switch grass, pine bark, corn husks, and other materials to be piloted in 2012. The company plans to ultimately use orange peels, oat hulls, potato scraps, and other leftovers from its food business but has not yet announced from where they will source TA or their pilot plant results.

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Are Biobased Plastics Sustainable? This is a key question, but given the lack of agreement on what sustainable packaging is, one must turn to life cycle analyses and assess the environmental impacts.

Liptow and Tillman (2012) found that PE from sugarcane used significantly less fossil fuels but more total primary energy and contributed more to acidification and eutrophication than petrochemical-based PE. It has the potential to significantly reduce greenhouse gas emissions. If effects of land use change are ignored, the sugarcane route is the better one with respect to global warming and the use of nonrenewable resources. However, converting rain forests for food-crop-based bioproducts creates a “carbon debt” by releasing from nine to 170 times more CO₂ than the annual greenhouse gas reductions from bioplastics displacing petrochemical-based plastics.

In a comprehensive analysis, Weiss et al. (2012) addressed the environmental impacts of biobased materials in a meta-analysis of 44 life cycle analysis studies. They found that biobased materials save primary energy and greenhouse gas emissions but may increase eutrophication and stratospheric ozone depletion. Most impacts are caused by the application of fertilizers and pesticides during industrial biomass cultivation. Loss of biodiversity, soil carbon depletion, soil erosion, deforestation, as well as greenhouse gas emissions from indirect land use change, were not quantified in the life cycle analyses.

Eerhart et al. (2012) reported that production of PEF can reduce nonrenewable energy use by 40–50% and greenhouse gas emissions by 45–55% compared to PET on a cradle-to-grave basis as shown in Figure 4. These reductions are higher than for other biobased plastics such as PLA or bioPE. Given that annual global production of PET bottles is around 15 million t, substitution by PEF could save 440–520 petajoules (PJ) of nonrenewable energy use and reduce greenhouse gases by 20–35 t of carbon dioxide equivalents (CO₂e). Greenhouse gases could be reduced further by a switch to lignocellulose feedstocks, but more research is required.

Hottle et al. (2013) compared standard database results for three biobased polymers (PLA, PHA, and TPS) with five common petrochemical- based polymers. Biobased polymers, coming out of a relatively new industry, exhibited similar impacts compared to petrochemical-based plastics. Studies that included the end-of-life reported much higher global warming potential results than those that limited the scope to resin or granule production. Including end-of-life in the life cycle analysis provides more comprehensive results for biopolymers, but simultaneously introduces greater amounts of uncertainty and variability. Little life-cycle data is available on the impacts of different manners of disposal, and thus it will be critical for future sustainability assessments of biobased polymers to include accurate end-of-life impacts.

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In the authors’ view, none of the biobased plastics currently in commercial use or under development are fully sustainable. They caution that when deciding to substitute conventional petrochemical-based plastics with biobased plastics, it is important to understand the flow of these materials and their adverse impacts in all parts of their life cycles in order to select a material that is more sustainable.

Yates & Barlow (2013) reviewed existing life cycle analyses on PLA, PHA, and TPS. Although reductions in nonrenewable energy use and global warming potential can be achieved, there are higher impacts in other categories. Definitive conclusions were difficult to draw although the studies reviewed suggested that these biopolymers may not necessarily be more environmentally friendly than the petrochemical-based polymers they could replace.

While the internationally agreed life cycle analysis standards provide generic recommendations on how to evaluate the environmental impacts of products and services, they do not address details that are specifically relevant for the life cycles of biobased materials. In particular, according to Pawelzik et al. (2013), treatment of biogenic carbon storage is critical for quantifying the greenhouse gas emissions of biobased materials in comparison with petrochemical-based materials but is lacking from present life cycle analyses.

Global production of petrochemical-based plastics is around 250 million t/ year, of which plastic packaging is 100 million t/year. Biobased plastics production has grown from 80,000 t in 2005 to 1.2 million t in 2011 with an estimated production of 5.8 million t in 2016. Strongest growth will be led by biobased, nonbiodegradable bioplastics such as bioPE and bioPET, which are dubbed “drop-in” solutions as they can be readily substituted in-line for petrochemicalbased plastics and recycled alongside their conventional counterparts. BioPET already accounts for 40% of the global bioplastics production capacity.

Biobased but not biodegradable? To return to the question posed by the title of this article, the answer is most certainly yes. Despite uncertainty over what sustainable packaging really is, the large food multinationals have spoken and opted for biobased but not biodegradable plastics. This fact should be noted by smaller companies contemplating switching to biobased, biodegradable packaging, and those researching biodegradable packaging materials.

Gordon L. Robertson, Ph.D., a Professional Member of IFT, is an adjunct Professor at the University of Queensland and Principal Consultant at Food•Packaging•Environment , 6066 Lugano Drive, Hope Island, QLD 4212, Australia ([email protected]).

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