Sustainable Materials

Lifecycle Assessment: Measuring Sustainability

Lifecycle assessment (LCA) is the systematic methodology for evaluating the environmental impact of a material or product from raw material extraction through manufacturing, use, and end-of-life disposal or recycling, a scope known as cradle-to-grave. LCA quantifies impacts across multiple categories including global warming potential (kilograms of CO2 equivalent), energy consumption (megajoules), water use, acidification, eutrophication, and toxicity. The results often challenge intuitive assumptions: a lightweight aluminum car body requires far more energy to manufacture than a steel one, but the fuel savings during use can offset the manufacturing energy over the vehicle lifetime.

The embodied energy of a material is the total energy required to extract, process, and deliver it to the point of use. Primary aluminum production requires approximately 170 megajoules per kilogram due to the energy-intensive electrolysis of alumina, while recycled aluminum requires only about 10 megajoules per kilogram, a 94 percent reduction. Steel from scrap in an electric arc furnace consumes roughly 8 megajoules per kilogram, compared to 25 megajoules per kilogram for steel from iron ore in a blast furnace. These enormous differences between primary and recycled material energy make recycling one of the most effective sustainability strategies.

The embodied carbon of materials has become a primary focus as industries work to reduce greenhouse gas emissions. Cement production alone accounts for roughly 8 percent of global CO2 emissions, primarily from the chemical decomposition of limestone (CaCO3 -> CaO + CO2) and the fuel burned to heat kilns to 1,450 degrees Celsius. Steel production contributes about 7 percent of global emissions. Together, these two materials account for more than half of all industrial CO2 emissions, making them critical targets for decarbonization.

Decarbonizing Metals and Cement

Green steel production replaces coal-based blast furnace reduction of iron ore with hydrogen-based direct reduction, where hydrogen gas (H2) rather than carbon monoxide (CO) removes oxygen from iron ore, producing water vapor rather than CO2 as the byproduct. SSAB in Sweden operated the first fossil-free steel pilot plant (HYBRIT) in 2021, and commercial-scale green steel production is expected to ramp up through the 2030s. Electric arc furnace steelmaking powered by renewable electricity already produces steel with 75 percent lower emissions than conventional blast furnace routes, and increasing the proportion of scrap steel in the global mix reduces emissions further.

Low-carbon cement approaches include supplementary cementitious materials (SCMs) that partially replace Portland cement clinker with industrial byproducts. Ground granulated blast furnace slag, coal fly ash, and calcined clay (LC3 cement) can replace 30 to 50 percent of clinker while maintaining adequate strength and durability. Novel cement chemistries including calcium sulfoaluminate cement, magnesium-based cements, and geopolymers achieve significantly lower CO2 emissions than Portland cement. Carbon capture, utilization, and storage (CCUS) applied to cement plants can capture 90 percent or more of the process CO2 emissions, though the economics remain challenging without carbon pricing.

Aluminum decarbonization focuses on powering smelters with renewable electricity (hydropower already supplies over 70 percent of global primary aluminum production) and replacing carbon anodes, which generate CO2 during electrolysis, with inert anodes that produce oxygen instead. Elysis, a joint venture between Rio Tinto and Alcoa, is commercializing inert anode technology that eliminates direct process CO2 emissions from aluminum smelting.

Bio-Based and Biodegradable Materials

Bio-based materials derived from renewable biological resources offer alternatives to fossil-fuel-based materials. Bio-based plastics include polylactic acid (PLA) from corn starch, polyhydroxyalkanoates (PHAs) from bacterial fermentation, and bio-based polyethylene from sugarcane ethanol. Global bio-based plastic production capacity is approximately 2.2 million tonnes, representing about 0.5 percent of total plastic production, but growth rates exceed 20 percent annually for some categories.

Engineered wood products are gaining ground as structural materials that sequester carbon rather than emitting it. Cross-laminated timber (CLT), made from layers of lumber boards glued with alternating grain direction, achieves strength-to-weight ratios competitive with concrete and steel for mid-rise construction. Mass timber buildings up to 25 stories tall have been completed, with the timber storing roughly one tonne of CO2 per cubic meter while displacing emission-intensive concrete and steel. Bamboo, the fastest growing plant on Earth, is being engineered into laminated structural members with mechanical properties comparable to softwood lumber, offering particular advantages in tropical regions where it grows naturally.

Biodegradability must be carefully distinguished from bio-based origin. A material can be bio-based but not biodegradable (bio-based polyethylene is chemically identical to fossil-based polyethylene and persists indefinitely), or biodegradable but not bio-based (some fossil-derived polyesters biodegrade in soil). PHA is both bio-based and biodegradable in soil and marine environments, making it particularly valuable for applications where material leakage into the environment is likely, such as agricultural mulch films and fishing gear.

Recycling and the Circular Economy

The circular economy model replaces the traditional linear take-make-dispose approach with closed-loop systems where materials are continuously recycled, reused, or remanufactured. Metals are inherently recyclable without degradation: aluminum, steel, copper, and precious metals can be recycled indefinitely with no loss of intrinsic properties. Global steel recycling rates exceed 80 percent, and aluminum recycling reaches approximately 70 percent in developed economies. The challenge is contamination from mixed alloy scrap, which limits the use of recycled metal in the highest-specification applications and drives ongoing research in scrap sorting and alloy-tolerant design.

Polymer recycling faces greater challenges because most thermoplastics degrade during mechanical recycling (the polymer chains shorten with each melt-reprocess cycle), mixed plastic waste is difficult and expensive to sort, and thermosets and fiber-reinforced composites cannot be mechanically recycled at all. Chemical recycling technologies, including pyrolysis (thermal decomposition into oils and monomers), solvolysis (dissolving polymers in solvents), and depolymerization (breaking specific polymers back into their constituent monomers), are scaling up to handle plastic waste streams that mechanical recycling cannot address. Enzymatic recycling of PET using engineered enzymes that break the ester bonds at moderate temperatures is approaching commercial scale, producing virgin-quality monomers from post-consumer PET bottles and textiles.

Composite recycling remains one of the most difficult challenges in sustainable materials. Wind turbine blades, typically made of glass fiber reinforced thermoset polyester or epoxy, are being decommissioned in growing numbers as early installations reach end of life. Pyrolysis can recover the glass fibers but at significantly degraded strength (typically 50 percent loss), and the energy required partially offsets the environmental benefit. New thermoplastic composite formulations designed for recyclability and bio-based resins that can be chemically recycled are being developed specifically to address the end-of-life challenge for the next generation of composite structures.

Critical Materials and Resource Security

The transition to clean energy and electrification requires massive quantities of specific materials that face supply constraints. Lithium, cobalt, nickel, and manganese for battery cathodes, rare earth elements for permanent magnets in electric motors and wind turbines, and copper for electrical infrastructure are all classified as critical materials by multiple governments. Lithium demand is projected to increase six-fold by 2030, and cobalt supply is concentrated in the Democratic Republic of Congo with significant ethical concerns regarding mining practices.

Materials science responses include developing alternative battery chemistries that reduce or eliminate critical materials (sodium-ion batteries replacing lithium, lithium iron phosphate cathodes replacing cobalt-containing formulations), improving recycling processes to recover critical materials from end-of-life products, and designing products for easier disassembly and material recovery. Urban mining, the recovery of valuable materials from electronic waste, construction demolition, and industrial residues, is becoming economically competitive with primary mining for some materials as ore grades decline and recycling technology improves.

Designing for Sustainability

Material efficiency reduces environmental impact by using less material to deliver the same function. Topology optimization algorithms design structures that place material only where it is structurally needed, reducing mass by 30 to 60 percent compared to conventional designs while maintaining strength and stiffness requirements. Lightweighting in automotive design, combining high-strength steel, aluminum, and composites to reduce vehicle mass, improves fuel efficiency by approximately 6 to 8 percent for every 10 percent reduction in mass. Thin-film solar cells use less than 1 percent of the semiconductor material required for conventional wafer-based cells, reducing both material cost and embodied energy.

Design for disassembly considers end-of-life recovery from the earliest design stages. Snap-fit connections instead of adhesive bonding, standardized fasteners, labeled material types, and modular construction all facilitate material separation and recycling. The European Union End-of-Life Vehicle Directive requires 95 percent recovery and 85 percent recycling of vehicle mass by weight, driving automotive manufacturers to consider recyclability during material selection and vehicle design. Electronics manufacturers face similar requirements under the WEEE (Waste Electrical and Electronic Equipment) Directive.

Industrial symbiosis turns one industry waste into another raw material. Blast furnace slag from steel production becomes supplementary cementitious material for concrete. Fly ash from coal power plants serves the same purpose. Red mud from aluminum refining, traditionally a problematic waste, is being investigated as a source of iron, scandium, and rare earth elements. These cross-industry material flows reduce both waste disposal costs and primary resource extraction, creating economic incentives aligned with environmental goals. The Kalundborg industrial park in Denmark is the most celebrated example, where a power plant, oil refinery, pharmaceutical factory, and gypsum board manufacturer exchange energy, water, and material streams in a network that has operated for over 50 years.