Polyurethane (PU) foam is widely used to provide softness and comfort when padding is needed for furniture, packaging, insulation, or other consumer goods, like the headphones I am wearing now. Finding more sustainable alternative solutions is challenging, as foams must be highly resilient and able to withstand years, if not decades, of daily use. In this first of a series of articles looking at potential replacements for PU foams, I take a look at what researchers and innovative companies are doing with lignin.
Lignin is the second most abundant organic material on earth, second only to cellulose, it accounts for up to a quarter of the weight of wood. This organic polymer is removed during most papermaking processes but retained as a bulking agent when making cardboard or newsprint. Lignin is water and UV-resistant and is a natural binding agent making it an ideal candidate for developing bio-based chemicals and bioplastics. In addition, lignin is fire-resistant, durable, lightweight, and, importantly, can be recyclable and biodegradable.
As with most bio-based materials, the structure of lignin can vary significantly so consistency remains a challenge. Also scaling production and driving down costs is essential to compete in the mass market for PU foams. Despite these challenges, researchers from industry and academia are experimenting with foams using lignin.
At Washington State University research team has created an environmentally friendly preparation of lignin that can substitute 20% of the fossil fuel-based chemicals used to create PU foam. The team developed an environmentally friendly solvent that can be used to separate high-quality homogenous lignin from pine. The university is now looking for commercial partners to develop the product.
The Fraunhofer Institute for Wood Research is financing a project to develop recyclable lightweight furniture using lignin-based foams. The project aims to develop flexible foams with a lignin content of at least 80%. In addition, leather alternatives are being developed, to achieve 100% bio-based materials with a lignin content of 70% or more.
The most common source of industrial lignin is black liquor, a byproduct of the papermaking process. It is often burned but lignin can be extracted with potential application to make foams. Michigan Technological University has a team of researchers looking at how to extract lignin with more homogeneous characteristics so it can be used as an input for other applications including the creation of foams.
While these projects are still in the laboratory at least one organisation has succeeded in producing commercial quantities of lignin-based plastics. While foams are not currently among their offerings, Lignin Industries manufactures Renol which is 100% bio-based, made from lignin and oils. Renol can be blended at up to 40% with traditional ABS or up to 70% with polypropylene to reduce CO2 impacts.
These projects demonstrate that lignin offers promising potential as a substitute for PU in foams, however, commercial quantities are not currently available. In this next article in this series, I will look at other alternatives to PU to create foam.
See also:
Rethinking Foam: Greener Solutions for Furniture & Footwear
Reimagining Upholstery: Foam Without Compromise
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