Packaging - biobased, biodegradable, and Compostable - shedding light on the confusion

Gordon Robertson FNZIFST

Introduction

The term biobased means derived from biomass, and biobased packaging materials are defined as materials derived primarily from annually renewable sources, thus excluding paper-based materials because, although obviously biobased, trees generally have renewal times of 25–65 years. The current interest in sustainability and the desire for renewable resources is driving development of biobased packaging materials. The term biobased is frequently used as a synonym of renewable, and while this is true in most cases, the term renewable refers to a material that is composed of biomass and can be continually replenished.

Figure 1. Four categories of plastics depending on whether or not they are biodegradable and the source of the feedstock used to make them

Biobased plastics

The term bioplastic is used rather loosely to describe both biodegradable plastics and biobased plastics that may or may not be biodegradable, leading to confusion. To avoid any confusion the term ‘bioplastic’ should be qualified to indicate the precise source or properties of the polymer concerned. Biobased plastics are derived from biomass such as organic waste material or crops grown specifically for the purpose and tend to be more expensive than those based on fossil fuels.

Classification of Plastics

Plastics can be classified into four categories depending on whether or not they are biodegradable and according to the source of the feedstock used to make them. These categories are

1) biobased and biodegradable 2) petrochemical-based and biodegradable 3) biobased but not biodegradable 4) conventional petrochemical-based plastics (Figure 1).

The biobased and biodegradable category includes thermoplastic starch (TPS) that retains the hydrophilic characteristics of starch and is suitable for low-moisture foods. TPS is not really a viable alternative to most petrochemical-based plastics but the packs readily degrade in home composters. Polylactic acid (PLA) is synthesised from lactic acid monomers derived from genetically modified corn, sugar beets, sugarcane or tapioca. The biggest problem with PLA is its high water vapor transmission rate. It can only biodegrade in industrial composters where the temperature exceeds 58°C.

Polyhydroxyalkanoates (PHAs) are microbial polyesters that are produced by many bacterial species as intracellular particles that act as energy and carbon reserves. PHAs have high performance properties including excellent strength and toughness, as well as resistance to heat and hot liquids but are usually too expensive to be used for food packaging.

The petrochemical-based and biodegradable category includes a considerable number of plastics that have been available for many years including PCL, PVOH, PBAT, PBS and more recently PPC and PGA. The quantities used for food packaging are very small. (See glossary on pg 29)

The biobased but not biodegradable category includes several common plastics used for food packaging. Bioethylene can be produced by the catalytic dehydration of bioethanol, produced by the fermentation of carbohydrates, followed by normal polymerisation to produce polyethylene (PE). 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.

BioPET can be produced from terephthalic acid (TA) and ethylene glycol (EG) from molasses. Several routes are available to produce TA from a wide variety of feedstocks including sugarcane, corn, and woody biomass via isobutanol and para-xylene. 100% biobased bottles can be made from the new plastic polyethylene furanoate (PEF) using Avantium’s patented technology that converts biomass into furanics

The term bioplastic is used rather loosely to describe both biodegradable plastics and biobased plastics that may or may not be biodegradable, leading to confusion

Figure 2. Global biobased plastics production in 2019. Source: www.european-bioplastics.org/market/

building blocks such as 2,5-furan dicarboxylic acid (FDCA) that can replace TA and be polymerised with EG to PEF. DuPont has taken a similar approach using FDME (the methyl ester of FDCA) to produce polytrimethylene furandicarboxylate (PTF) through polymerisation with bioPDO (1,3-propanediol).

What is most exciting about these two new polyesters is that, in addition to being biobased, they have greatly improved thermal and mechanical properties compared to PET. For example, their barrier properties are up to 5 times greater resulting in longer shelf lives and/ or lightweighting potential.

Global production

Global plastic packaging production is about 100 million tonnes/ year. Biobased plastics production has grown from 80,000 tonnes in 2005 to 1.2 million tonnes in 2011 and 2.11 million tonnes in 2019 (Figure 2), about 2% of total plastic packaging production. Of this total, 1.17 million tonnes were biodegradable and 0.94 million tonnes non-biodegradable. By 2024 global production is expected to reach 2.43 million tonnes. Strongest growth will be led by biobased, non-biodegradable bioplastics such as bioPE and bioPET, which are dubbed “drop-in” solutions as they can be readily substituted in-line for petrochemical-based plastics and recycled alongside their conventional counterparts.

Biodegradation

Biodegradable is a generic term that indicates a material is biologically available for microbial decomposition, with no detail on breakdown products, time or extent of degradation or end environments. Biodegradation is the partial or complete breakdown of a material as a result of microbial action (enzyme secretion and within-cell processes), ultimately into CO 2

. Biodegradation can take place in many environments, including soils, compost sites, water treatment facilities, anaerobic digestors, and marine environments. Biodegradability depends not on the origin of the raw materials but on their chemical composition. The extent to which a biodegradable plastic will break down is dependent on the surrounding environment. Humidity, temperature or concentrations of microorganisms vary in different environments, resulting in different biodegradation rates.

Compostable

This is a specific term which describes a polymer that has been independently certified as meeting the relevant performance standards. For packaging to be called compostable it must biologically decompose and disintegrate in a composting system (under either commercial or home composting conditions) to set levels within a defined period of time. The compost must also meet specific quality criteria relating to ecotoxicity and other characteristics. The biggest benefit of composting is avoidance of methane production from anaerobic biodegradation should the material end up in a landfill.

A disadvantage of the more widespread adoption of biodegradable

plastics is the need to separate them from the non-biodegradable waste streams for plastic recycling to avoid compromising the quality of the final product. There is also some limited evidence to suggest that labelling a product as biodegradable will result in a greater inclination to litter on the part of the public.

Testing

New Zealand does not have standards for biodegradable or compostable plastics but accepts Australian Standards AS 4736 (biodegradable materials suitable for commercial composting) and AS 5810 (biodegradable plastics suitable for home composting). Other recognised standards defining industrial compostability in which temperatures are expected to reach >60°C include ASTM 6400 (USA), EN 13432 (European) and ISO 17088 (International). AS 4736 is similar to EN 13432 and requires that at least 90% of the organic matter is converted into CO 2 within 6 months, and that no more than 30% of the residue is retained by a 2mm mesh sieve after 3 months composting. The test conditions for the home composting standard AS 5810 specify a lower composting temperature of 25±5°C.

One challenge is that biodegradation tests carried out in artificial environments lack transferability to real conditions and, therefore, highlight the necessity of environmentally authentic and relevant fieldtesting conditions. At a laboratory level, the biodegradation rate is expected to be a function of the surface area of the tested sample, and the higher the surface area, the higher the biodegradation rate, all other environmental conditions being equal.

The Australian Competition and Consumer Commission has noted that 100% biodegradable is an absolute claim that usually means ‘entirely’ or ‘totally’, and describing a product as ‘100% biodegradable’ indicates that the whole of the product will biodegrade in the same way and over the same time period—and that is not likely.

The Australasian Bioplastics Association (ABA) offers a verification programme for individuals or companies that wish to have their claims of conformance to the Australian Standard verified. The seedling logo

Figure 3. Australasian Bioplastics Association seedling logo for industrially compostable bioplastics that meet AS 4736

Figure 4. Australasian Bioplastics Association seedling logo for home compostable bioplastics that meet AS 5810

(Figure 3) is a symbol that the product’s claims of biodegradability and compostability as per AS4736 have been verified; the home compostable verification logo (Figure 4) applies to AS 5810. The seedling logo is a registered trademark owned by European Bioplastics and administered by the ABA in New Zealand and Australia. However, packaging certified as compostable to AS 4736 will not necessarily compost at every commercial composting facility, as not all facilities operate at an appropriate level to cope with these materials.

Environmental impacts

A meta-analysis of 44 life cycle analysis (LCA) studies found 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 fertilisers 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 LCAs.

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 and the litter problem. Other advocates suggest that composting will reduce the quantity of waste going to landfills but to realize the benefits of biodegradable plastics, municipal composting facilities must be available. However, today few cities have such facilities or the capacity to collect green waste separately and this is a major drawback to the expansion of biodegradable plastics.

According to the Australian Packaging Covenant Organisation, biodegradable and compostable materials should only be used in preference to other materials when they achieve the best outcomes and can be recovered through widely available recycling or organics recovery services. In some cases, LCA may be necessary to identify the most suitable recovery system to achieve the highest potential environmental value. A long-term goal is for compostable packaging to be accepted in kerbside organics collections by the majority of councils, particularly where both food and garden organics are being collected for composting. In the short to medium term, priorities include commercial and away-from-home collection systems.

Although a polymer may be marketed as biodegradable, this may only apply to a limited range of environmental conditions which are probably not encountered in the natural environment, leading to misunderstandings and confusion as to what constitutes biodegradability. For example, some items such as plastic shopping bags may be labelled as ‘biodegradable’ but it is quite possible that they will only degrade appreciably in an industrial composter. Such polymers will not ‘biodegrade’ in domestic compost bins or if left to litter the environment, and this lack of clarity may lead to behaviours that result in a greater degree of littering.

Conclusions

Are biobased, biodegradable packaging materials the best option?

Few have the mechanical and barrier properties required for food packaging. 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. Composting a biobased, biodegradable 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.

Dr. Gordon Robertson, FNZIFST is a food packaging consultant and Adjunct Professor at the University of Queensland. gordonlrobertson@gmail.com

June/July 2020