FOOD PACKAGING: PACKAGING AND THE ENVIRONMENT
Diagram
Biodegradable and compostable packaging: breaking down, and breaking down in compost
Biodegradable packaging
Microbes can break the material down over time into natural substances, in soil, water or compost, but no set place or set time is fixed by the word alone.
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Compostable packaging
The material breaks down in a composting system, under the heat, moisture and microbes of composting, and leaves no harmful residue.
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The difference
Every compostable pack is biodegradable, but not every biodegradable pack is compostable. Compostable adds a place, a system and a result.
Figure 1: Breaking down by microbes compared with breaking down in a composting system. Drawn in our own style from Pilla (ed.), Handbook of Bioplastics and Biocomposites Engineering Applications, Wiley, 2011, and Robertson, Food Packaging: Principles and Practice, 2nd ed., CRC Press, 2005. Note: the comparison is drawn from chapters on biobased materials and on packaging and the environment, not from a single head to head passage.
Introduction
Biodegradable packaging and compostable packaging are two words that are often used as if they meant the same thing, but they do not. Biodegradable means that microbes can break the material down over time into natural substances. Compostable means that the material breaks down in a composting system, under the heat, moisture and microbes of composting, and that it leaves no harmful residue behind.
The core difference is place and proof: biodegradable says only that breakdown by microbes is possible, while compostable says that breakdown happens in compost, within a composting system. Every compostable pack is biodegradable, but a biodegradable pack may break down far too slowly, or only in some places, to count as compostable.
Quick comparison
Table 1: Biodegradable packaging compared with compostable packaging
| Aspect | Biodegradable packaging | Compostable packaging |
|---|---|---|
| Meaning | Microbes can break it down over time | Breaks down in a composting system |
| Place of breakdown | Not fixed: soil, water or compost | In compost, home or industrial |
| Time limit | No set time fixed by the word alone | Within the time of the composting system |
| Conditions needed | Microbes, moisture and time | Heat, moisture, air and microbes of composting |
| Residue left | Natural substances in principle | Compost, with no harmful residue |
| All compostable is biodegradable | Not the question: it is the wider word | Yes, every compostable pack is biodegradable |
| All biodegradable is compostable | No, many biodegradable packs are not compostable | The narrower word: it must pass composting |
| Materials | Some biobased plastics, some fossil based plastics | PLA, starch based plastics, PHBV blends and similar |
| Labelling | The word alone gives no time or place | Must state the composting system it suits |
| Food example | A bag that breaks down slowly in soil | A compostable cup or wrapper for food waste collection |
Scientific explanation
Definition
Biodegradable packaging is packaging made of a material that can be broken down by microbes into natural substances. Compostable packaging is packaging made of a material that breaks down in a composting system into compost, with no harmful residue.
Working principle
Microbes attack the polymer chains of a biodegradable material and break them into smaller pieces, and then into carbon dioxide, water and biomass, given moisture, warmth and time. In composting, the heat of the compost pile, the moisture and the large numbers of microbes speed that breakdown, so a compostable material is broken down within the composting cycle. A material can be biodegradable in soil over a long time yet still fail in compost, because it breaks down too slowly or leaves pieces behind.
Apparatus
The books name no single apparatus for this comparison. Composting is checked in a composting system, home or industrial, and breakdown is checked by seeing whether the material disappears and whether the compost that results is free of visible pieces and harmful residues.
Measurement procedure
The books read name no specific compostability standard number and no set time limit, so no standard number or time limit is given in this article. In practice a compostable claim is checked by putting the material through a composting test and checking how much of it breaks down, how fast, and what the compost contains. A buyer should look for the composting system named on the pack, rather than trusting the word compostable on its own.
Factors affecting readings
The result depends on temperature, moisture, air and the microbes present, so the same pack can break down fast in a hot industrial compost pile and hardly at all in cold soil or in water. It also depends on the thickness of the pack and on the polymer used. A thick piece breaks down more slowly than a thin film of the same material.
Formulas and calculations
The books read give no formula for biodegradable against compostable packaging, and they give no standard number or set time limit for compostability. No formula, standard number or time limit is given here, because the sources read do not give one. The distinction is qualitative: biodegradable means microbes can break it down, and compostable means it breaks down in a composting system and leaves compost with no harmful residue.
Industrial applications
- Biodegradable packaging: bags and wraps that break down in soil over time, where a long breakdown time is acceptable.
- Biodegradable packaging: mulch films in farming, where the film breaks down in the field after use.
- Compostable packaging: cups, cutlery and wrappers collected with food waste for industrial composting.
- Compostable packaging: food waste bags that go into the compost bin with the food waste.
- Compostable packaging: PLA and starch based packs for takeaway food, where the pack and the leftovers are composted together.
Advantages and limitations
- Biodegradable packaging, advantage: breaks down by microbes instead of lasting in the environment like ordinary plastic.
- Biodegradable packaging, limitation: the word alone fixes no time and no place, so breakdown can be very slow and may not happen in a given place.
- Compostable packaging, advantage: breaks down in compost and returns to the soil as compost, with no harmful residue.
- Compostable packaging, limitation: it needs a composting system to work, and it does not break down well in soil, in water, or in landfill.
FAQ
Is compostable packaging always biodegradable?
Yes. A material that breaks down in compost is broken down by microbes, so it is biodegradable too.
Is biodegradable packaging always compostable?
No. A biodegradable pack may break down too slowly, or only in some places, to count as compostable.
What standard proves a pack is compostable?
The books read name no specific compostability standard number and no set time limit, so none is given here. A buyer should look for the composting system and the certifier named on the pack.
Will a compostable cup break down in my garden?
Not necessarily. Home compost is cooler and slower than industrial compost, so a pack made for industrial composting may not break down in a garden heap.
Does biodegradable mean the pack disappears quickly?
No. Biodegradable only means microbes can break it down. Without the right warmth, moisture and microbes, it can last a long time.
References and further reading
- Fellows, P., Food Processing Technology: Principles and Practice, Woodhead Publishing (FTN book on disk).
- Pilla, S. (ed.), Handbook of Bioplastics and Biocomposites Engineering Applications, Wiley, 2011 (Google Books page read: Biobased Materials in Food Packaging Applications, p. 121, and Biobased and Biodegradable PHBV-Based Polymer Blends, p. 373).
- Robertson, G. L., Food Packaging: Principles and Practice, 2nd ed., CRC Press, 2005 (Google Books page read: Food Packaging and the Environment, p. 503).
