Packaging
Biobased, biodegradable and compostable packaging – 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.
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
Figure 1. Four categories of plastics depending on whether or not they are biodegradable and the source of the feedstock used to make them 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
June/July 2020
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