By the end of this topic, you should be able to...
explain how biomaterials are a key part of a circular economy and can be used by designers to design out waste.
Guiding Question
How do material properties and classifications aid material selection for a specified manufacturing process?
💡 Did You Know? In 2013, a packaging company called Ecovative Design shipped its first commercial order of protective packaging — the kind of moulded foam that cradles electronics inside a cardboard box. It looked identical to expanded polystyrene. It performed identically under impact. But bury it in your garden after use and within 45 days it had completely disappeared into the soil, feeding microorganisms and leaving no residue detectable at the molecular level. It was made from mycelium — the root structure of fungi — grown around agricultural waste husks. The fossil-fuel-derived alternative it replaced takes 500 years to decompose, produces toxic combustion products if incinerated, and costs the ocean an estimated 8 million tonnes of contamination annually. The designer's material choice, at the moment of specification, determined which of those two futures happened. Biodegradable materials do not just solve an end-of-life problem — they fundamentally redefine what end of life means.
Biodegradable Materials — What They Are and How They Behave
The Problem They Solve
Conventional synthetic polymers — polyethylene, polypropylene, polystyrene, PET — are derived from fossil fuels and are chemically engineered for permanence. Their polymer chains resist biological attack. That permanence is exactly what made them commercially successful — and exactly what makes them an environmental catastrophe at end of life (Andrady & Neal, 2009).
The global polymer industry produces approximately 400 million tonnes of plastic annually. Of this, around 40% is single-use packaging — used once for minutes or hours, and then persisting in the environment for centuries (Andrady & Neal, 2009).
Biodegradable materials are selected precisely to break this permanence. Their polymer chains are designed — either through biological synthesis or chemical engineering — to be recognised and metabolised by microbial enzymes. End of life is not disposal. It is return.
Principal Biodegradable Material Types
1. Polylactic Acid (PLA)
PLA is currently the most commercially available biodegradable polymer. It is produced by fermenting plant-derived sugars — corn starch, sugarcane, cassava — into lactic acid monomers, which are then polymerised (Callister & Rethwisch, 2018).
Properties:
Tensile strength: 50–70 MPa — comparable to polystyrene
Processable on standard injection moulding, thermoforming, and FDM 3D printing equipment
Clear, rigid, and printable — making it suitable for food packaging
Critical limitation: PLA requires industrial composting conditions — sustained temperatures above 55°C — to biodegrade within a commercially useful timeframe of 60–90 days. In ambient soil, ocean, or domestic compost, PLA degrades extremely slowly and may persist for years (Mohanty, Misra & Drzal, 2005).
Design implication: A designer selecting PLA must simultaneously design the end-of-life system — PLA packaging is only genuinely biodegradable if industrial composting infrastructure exists at the point of disposal. Without it, PLA in landfill behaves similarly to conventional plastic (McDonough & Braungart, 2002).
2. Polyhydroxyalkanoates (PHA)
PHAs are a family of polyesters synthesised directly inside bacterial cells. Bacteria — typically Cupriavidus necator — are fed on carbon-rich organic matter such as agricultural waste, food waste, or methane. The bacteria accumulate PHA granules internally as an energy store. These are then extracted, purified, and processed into pellets for moulding (Mohanty, Misra & Drzal, 2005).
Properties:
Biodegrades in soil, freshwater, and — critically — marine environments
Mechanical properties tunable by varying the bacterial feedstock — ranging from rigid crystalline to flexible elastomeric forms
Does not require industrial composting infrastructure
Key advantage over PLA: Marine biodegradability. PHA is one of the very few polymers certified to biodegrade in open ocean conditions — making it uniquely suitable for applications where leakage into marine environments is a realistic end-of-life scenario, such as fishing equipment, marine packaging, and agricultural films (Mohanty, Misra & Drzal, 2005).
Current limitation: Production cost remains 3–5× higher than commodity plastics — driven by the cost of bacterial fermentation at scale. Industrial investment in waste-fed bioreactors is progressively reducing this gap (Callister & Rethwisch, 2018).
3. Starch-Based Polymers
Thermoplastic starch (TPS) is produced by disrupting the granular structure of native starch — from potato, maize, or wheat — using heat, pressure, and plasticisers such as glycerol or water. The result is a mouldable thermoplastic with full biodegradability in domestic composting conditions (Mohanty, Misra & Drzal, 2005).
Properties:
Fully biodegrades in ambient soil and domestic compost
Very low cost — feedstock is an agricultural commodity
High moisture sensitivity — degrades in humid service environments, limiting packaging applications
Design application: Starch-based polymers are widely used for loose-fill packaging peanuts, single-use cutlery, and agricultural mulch films — applications where the service life is short and the disposal route involves soil contact. The moisture sensitivity, a weakness in other contexts, becomes an advantage in agricultural applications where the film should disintegrate after crop growth is complete (Mohanty, Misra & Drzal, 2005).
4. Mycelium Composites
Mycelium composites represent a fundamentally different approach — the material is not synthesised chemically but grown biologically. Agricultural waste — corn husks, hemp hurds, cotton burrs — is inoculated with fungal spores. The mycelium grows through the substrate over 5–7 days, binding it into a dense, rigid composite. Growth is arrested by heat treatment, and the form is determined entirely by the mould geometry (Jones et al., 2020).
Properties:
Compressive strength comparable to expanded polystyrene (EPS)
Fully compostable in domestic conditions within 45 days
Fire resistant without chemical additives
Production requires no petrochemical inputs and runs at ambient temperature — dramatically lower embodied energy than EPS production
Commercial application: Ecovative Design's Mushroom® Packaging is used by Dell, IKEA, and Sealed Air Corporation as a direct substitute for EPS protective packaging. At end of consumer use, the packaging is placed in home compost or garden soil and fully biodegrades within weeks (Jones et al., 2020).
5. Natural Fibre Biocomposites
Combining plant fibres — flax, hemp, jute, bamboo, kenaf — with biodegradable polymer matrices such as PLA produces fully biodegradable composite materials with structural properties approaching those of GFRP at significantly lower environmental cost (Mohanty, Misra & Drzal, 2005).
Design application: The automotive industry — notably Mercedes-Benz, BMW, and Toyota — uses natural fibre composites in interior door panels, trunk liners, and dashboard substrates. Flax-PLA composites provide stiffness, dimensional stability, and impact resistance while remaining fully compostable at end of vehicle life, avoiding the landfill fate of conventional glass-fibre interior components (Mohanty, Misra & Drzal, 2005).
Biomaterials, Circular Economy, and Designing Out Waste
The Linear Model and Its Failure
The conventional model of material use follows a linear trajectory:
In this model, material value enters the economy once and exits permanently. Every tonne of packaging polymer manufactured from crude oil is — within weeks — either landfilled, incinerated, or released into the environment. The material, the energy used to produce it, and the carbon embedded in it are all permanently lost (Ellen MacArthur Foundation, 2013).
This is not a waste management failure. It is a design failure. The material was specified without a viable end-of-life pathway. The waste was built into the design from the moment of material selection (McDonough & Braungart, 2002).
The Circular Economy Model
The Ellen MacArthur Foundation's circular economy framework restructures material flows into two closed loops (Ellen MacArthur Foundation, 2013):
The Biological Cycle:
Organic materials — food, natural fibres, biodegradable polymers — flow through the economy and, at end of use, are returned to the biosphere as nutrients through composting, anaerobic digestion, or natural biodegradation. The material does not leave the system — it re-enters it as soil fertility, biogas, or biological feedstock for the next generation of products.
The Technical Cycle:
Durable synthetic materials — metals, conventional polymers, electronics — flow through the economy and, at end of use, are recovered through reuse, remanufacturing, or recycling. Material value is preserved within the industrial system.
The critical design insight is that biodegradable materials belong in the biological cycle — and a designer who selects them must simultaneously design the entire biological cycle pathway, not merely the material itself (Ellen MacArthur Foundation, 2013).
Cradle to Cradle — The Design Framework
McDonough and Braungart's Cradle to Cradle framework (2002) provides the design methodology through which circular economy principles are operationalised:
Every material in every product must be designated as either:
A biological nutrient — a material that can safely re-enter biological cycles after use. It must be non-toxic, biodegradable, and capable of being composted or anaerobically digested without contaminating soil or water.
A technical nutrient — a material that cannot safely enter biological cycles but can be safely recovered and reused in industrial processes indefinitely without quality loss.
The framework explicitly condemns monstrous hybrids — products that combine biological and technical nutrients in ways that make neither recoverable. A paper coffee cup laminated with polyethylene is the canonical example: the paper is a biological nutrient, the PE is a technical nutrient, but the lamination makes both unrecoverable — the cup goes to landfill because it can be neither composted nor recycled (McDonough & Braungart, 2002).
A PLA-lined paper cup — where the lining is PLA rather than PE — is only marginally better if the composting infrastructure does not exist. The design intent is sound only if the entire system — material, product, collection, and return pathway — is designed simultaneously.
How Designers Use Biomaterials to Design Out Waste
McDonough and Braungart (2002) and the Ellen MacArthur Foundation (2013) identify five specific design strategies through which biomaterials eliminate waste at the design stage:
Eliminate Toxic Inputs
Conventional plastics frequently contain additives — plasticisers, flame retardants, colorants, stabilisers — that render them toxic to biological systems and prevent safe composting even when the base polymer would otherwise biodegrade. Designing with unmodified biopolymers or ensuring all additives are certified non-toxic at the material specification stage eliminates chemical contamination of the biological cycle (McDonough & Braungart, 2002).
Example: Ecovative's mycelium packaging contains no synthetic additives whatsoever. When composted, the only outputs are water, CO₂, and fungal biomass — both inert and beneficial to soil biology (Jones et al., 2020).
Match Material Longevity to Product Service Life
One of the most fundamental mismatches in conventional design is specifying an immortal material — polystyrene, HDPE — for a disposable application. The material's designed service life is minutes. Its actual environmental persistence is centuries. The mismatch between these two timescales is the physical definition of waste (Ashby, 2011).
Designing out waste requires matching the material's degradation timescale to the product's intended service life. A starch-based agricultural mulch film is designed to persist for precisely one growing season — and then biodegrade into the soil it was protecting. The biodegradation is the end-of-life function. There is nothing to collect, process, or dispose of (Mohanty, Misra & Drzal, 2005).
Design for the Biological Cycle with Infrastructure Clarity
Selecting a biodegradable material is not sufficient — the designer must specify the correct biodegradation pathway and ensure that pathway exists in the target market (Ellen MacArthur Foundation, 2013).
This requires the designer to:
Establish whether industrial composting infrastructure exists in the deployment geography
Design labelling and communication that directs end users to the correct disposal route
Consider whether ambient biodegradation — in soil or water — is a sufficient pathway where composting infrastructure is absent
Select PHA over PLA in contexts where marine leakage is a realistic risk
The absence of this systems thinking is why substantial quantities of PLA packaging currently end up in landfill or contaminate recycling streams — the material was selected correctly, but the biological cycle was not designed (McDonough & Braungart, 2002).
Use Renewable, Carbon-Neutral Feedstocks
Biodegradable materials derived from biological feedstocks close the carbon cycle as well as the material cycle. The CO₂ released during biodegradation is the same CO₂ that was fixed by the plant during growth — net atmospheric addition is zero, provided land use and agricultural practices are managed responsibly (Mohanty, Misra & Drzal, 2005).
This contrasts directly with fossil fuel-derived polymers, where carbon sequestered over millions of years is released irreversibly into the contemporary atmosphere upon incineration or degradation — a one-way carbon transfer with no closing cycle (Andrady & Neal, 2009).
Design implication: LCA of the material's entire feedstock-to-decomposition pathway must be conducted at the design stage. PLA from deforestation-derived corn is not carbon-neutral. PHA from food waste bioreactors is actively carbon-negative — the feedstock carbon was already in the contemporary atmosphere as food waste methane (Mohanty, Misra & Drzal, 2005).
Design Products as Biological Nutrients, Not Components
The highest expression of designing out waste is to conceive the entire product as a input to the next biological cycle — not merely as something that will eventually degrade, but as something whose degradation actively improves the environment it degrades into.
Example: Worn Again Technologies and several sportswear designers are developing running shoes in which the midsole, upper, and bonding adhesives are all PHA-based. At end of wear life — typically 500–800 km — the entire shoe is compostable in industrial facilities. The composted output is used as soil amendment in agricultural applications. The shoe was not just designed to create no waste — it was designed to be the next cycle's soil fertility input (Ellen MacArthur Foundation, 2013).
The Designer's Decision Framework
When specifying a material for any product with a finite use phase, the designer must answer four questions at the point of material selection:
What is the actual service life required? — Match material longevity to this, not beyond it.
What is the realistic end-of-life pathway in the target market? — Industrial compost, domestic compost, soil contact, marine environment?
Is the material and all its additives safe for that biological cycle? — Toxic additives disqualify biological cycle membership.
Has the collection, processing, and return infrastructure been designed alongside the material? — A biological nutrient without a biological cycle is still waste.
These four questions operationalise the circular economy at the level of individual design decisions. Every specification of a biodegradable material that cannot answer all four questions affirmatively is — by definition — not designing out waste (Ellen MacArthur Foundation, 2013; McDonough & Braungart, 2002).
Comparison of Key Biodegradable Materials
Material | Feedstock | BiodegradationPathway | Timescale | Key Application | Key Limitation |
|---|---|---|---|---|---|
PLA | Plant starch (corn, sugarcane) | Industrial composting only | 60–90 days (industrial) | Food packaging, 3D printing | Requires industrial composting infrastructure |
PHA | Bacterial fermentation of organic waste | Soil, freshwater, marine | Weeks to months | Marine packaging, medical devices | High production cost |
Thermoplasticstarch | Potato, corn, wheat starch | Domestic compost, soil | 4–6 weeks | Loose-fill packaging, mulch film | High moisture sensitivity |
Mycelium composite | Agricultural waste + fungal growth | Domestic compost, soil | 45 days | Protective packaging, insulation | Limited mechanical strength range |
Natural fibre biocomposite | Flax, hemp, jute + PLA matrix | Industrial composting | 60–90 days | Automotive interiors, structural panels | Matrix composting infrastructure required |
Key Vocabulary
Pull these terms out. Learn the definition. Use them precisely in responses — examiners award marks for correct technical language.
Term | Definition |
|---|---|
Biodegradable material | A material capable of being decomposed by bacteria, fungi, or other living organisms into natural substances such as water, carbon dioxide, and biomass, under defined environmental conditions within a defined timeframe (Mohanty, Misra & Drzal, 2005) |
Biopolymer | A polymer derived from biological sources — renewable plant or animal feedstocks — as opposed to fossil fuel-derived feedstocks (Mohanty, Misra & Drzal, 2005) |
PLA (Polylactic acid) | A biodegradable thermoplastic polyester derived from fermented plant starch — typically corn or sugarcane — that degrades under industrial composting conditions (Callister & Rethwisch, 2018) |
PHA (Polyhydroxyalkanoate) | A family of biodegradable polyesters synthesised directly by bacteria fed on organic carbon sources — capable of degrading in soil, freshwater, and marine environments (Mohanty, Misra & Drzal, 2005) |
Mycelium composite | A material formed by the growth of fungal mycelium through agricultural waste substrate — producing a lightweight, mouldable, fully compostable structural material (Jones et al., 2020) |
Circular economy | An economic model in which materials and products are kept in use for as long as possible, and at the end of each service life are returned as nutrients to either biological or technical cycles — eliminating the concept of waste (Ellen MacArthur Foundation, 2013) |
Biological cycle | The circular economy pathway for organic materials — consumable products decompose back into the biosphere as nutrients through composting or anaerobic digestion (Ellen MacArthur Foundation, 2013) |
Technical cycle | The circular economy pathway for durable materials — products and components are recovered through reuse, remanufacturing, or recycling, retaining their material value in the economy (Ellen MacArthur Foundation, 2013) |
Cradle to cradle | A design philosophy in which every material in a product is designated as either a biological nutrient — safely returned to natural cycles — or a technical nutrient — safely recovered for reuse in industry (McDonough & Braungart, 2002) |
Cradle to grave | The conventional linear model of material use — extract, manufacture, use, dispose — in which material value is permanently lost at end of life (McDonough & Braungart, 2002) |
Design out waste | The deliberate elimination of waste through design decisions — material selection, product architecture, and end-of-life planning made at the design stage so that waste never arises in the first place (Ellen MacArthur Foundation, 2013) |
Industrial composting | A managed high-temperature biological decomposition process achieving temperatures of 55–70°C — required by materials such as PLA that do not biodegrade adequately in domestic composting or open environments (Mohanty, Misra & Drzal, 2005) |
Life cycle assessment (LCA) | A systematic analysis of the environmental impacts of a product across its entire life cycle — from raw material extraction through manufacture, use, and end-of-life disposal (Ashby, 2011) |
Feedstock | The raw material input from which a product or material is produced — biodegradable materials use renewable biological feedstocks rather than finite fossil fuel feedstocks (Callister & Rethwisch, 2018) |
Linear economy | The dominant 20th-century model of production: take a resource, make a product, dispose of it — a model that generates waste and depletes finite resources at both ends (Ellen MacArthur Foundation, 2013) |
Practice Questions
Question 1 — Command Term: State
State two biodegradable materials that could be used as alternatives to expanded polystyrene (EPS) in protective packaging applications.
What this requires: Direct, concise answer — material names only. No explanation needed.
Question 2 — Command Term: Describe
Describe the biological cycle within the circular economy model and explain how biodegradable materials participate in it.
What this requires: State what the biological cycle is, identify its inputs and outputs, and describe how biodegradable materials re-enter it at end of life. No evaluation required — accurate description of the cycle and the material's role within it.
Question 3 — Command Term: Explain
Explain the difference between a cradle to grave and a cradle to cradle approach to material use in product design. Use a named biodegradable material in your response.
What this requires:Â Define both models, contrast the end-of-life outcomes, and illustrate the difference using a specific material example with its specific end-of-life pathway.
Question 4 — Command Term: Explain
Explain why selecting PLAÂ for food packaging does not automatically constitute designing for a circular economy, even though PLA is a biodegradable material.
What this requires: Identify the specific limitation of PLA — industrial composting dependency — and link this to the broader principle that biodegradable material selection must be accompanied by end-of-life pathway design. Reference infrastructure, labelling, and market geography as relevant factors.
Question 5 — Command Term: Compare
Compare PLAÂ and PHAÂ as biodegradable materials for use in single-use food packaging, considering their properties, biodegradation pathways, and suitability for different disposal contexts.
What this requires: Direct criterion-by-criterion comparison — feedstock, mechanical properties, biodegradation conditions, environmental risk profile. Do not describe each separately. Reach a conclusion about relative suitability for a specified disposal context.
Question 6 — Command Term: Evaluate
Evaluate the claim that designers, not consumers or waste management systems, are primarily responsible for eliminating plastic waste through material selection and product design decisions.
What this requires: The highest-demand command term. Present a sustained, evidence-based argument — supporting the claim with reference to design out waste principles, material selection logic, and cradle to cradle philosophy; critically examining limitations — consumer behaviour, infrastructure investment, cost barriers, regulatory absence. Reach a justified conclusion. Do not list — argue.
Sources
Andrady, A.L. and Neal, M.A. (2009). 'Applications and societal benefits of plastics', Philosophical Transactions of the Royal Society B: Biological Sciences, 364(1526), pp. 1977–1984.
Ashby, M.F. (2011). Materials Selection in Mechanical Design. 4th edn. Butterworth-Heinemann, Oxford.
Callister, W.D. and Rethwisch, D.G. (2018). Materials Science and Engineering: An Introduction. 10th edn. Wiley, New York.
Ellen MacArthur Foundation (2013). Towards the Circular Economy: Economic and Business Rationale for an Accelerated Transition. Ellen MacArthur Foundation, Cowes. Available at: www.ellenmacarthurfoundation.org/assets/downloads/publications/Ellen-MacArthur-Foundation-Towards-the-Circular-Economy-vol.1.pdf
Jones, M., Mautner, A., Luenco, S., Bismarck, A. and John, S. (2020). 'Engineered mycelium composite structures as substitute for expanded polystyrene in packaging applications', Materials and Design, 185, 108397.
McDonough, W. and Braungart, M. (2002). Cradle to Cradle: Remaking the Way We Make Things. North Point Press, New York.
Mohanty, A.K., Misra, M. and Drzal, L.T. (eds.) (2005). Natural Fibers, Biopolymers, and Biocomposites. CRC Press, Boca Raton.
International Baccalaureate Organization (2024). Design Technology Guide: Diploma Programme. First Assessment 2027. IBO, Geneva.
Linking Questions
Why is a good understanding of material properties important when designing structural systems? (A3.2)
When do the physical properties of materials restrict the ability to use certain prototyping techniques? (A2.2)
How do the properties of a material influence the choice of manufacturing techniques for a product? (A4.1)
How can the characteristics of a material limit the effectiveness of modelling and prototyping as designs are developed? (B2.2)
How important is an understanding of the mechanical properties of a material when considering structural and mechanical systems, and their applications? (A3.2, A3.3, B3.2, B3.3)
Which classifications of properties are important when developing electronic systems and their applications? (A3.4, B3.4)
How could the continued development of biodegradable materials influence designers’ ability to address aspects of design for sustainability and design for a circular economy? (C2.1, C2.2)
Why is a thorough understanding of materials key for effective product analysis and evaluation of products? (C3.1)
How do design decisions related to the properties of materials and components impact a product’s life-cycle analysis? (C3.2)