BLOG
Performance Will Be Deciding Factor for Success of Sustainable Adhesives
After at least three decades of development in bio-based and sustainable adhesives, for many applications they still fall short. What would it take to completely phase out solvent-based, petrochemical-derived adhesives and mainstream sustainable alternatives?
Commonly used adhesives today are still based on non-biodegradable polymers derived from petrochemical sources. Although bio-based and sustainable alternatives have been on the market for decades, they still come with trade-offs. It can be a struggle to find sustainable adhesives for your product that meet your requirements in strength and durability and are available at the required scale and price point.
For certain applications, water- and bio-based adhesives are already the standard. ‘We have never worked with solvent-based adhesives,’ says Julian Heusser, CTO of Swiss adhesives manufacturer Alfa Klebstoffe. The company pioneered water-based, one-component adhesives with instant tack for bonding of foams and other materials. Until recently all their Simalfa products, primarily used in the mattrass and upholstery industries, still contained chlorine. ‘We have now gone a step further and developed this chlorine-free technology,’ Heusser says.
Water- and bio-based adhesives started replacing solvent-based solutions three decades ago, initially in the packaging and paper industries. Improvements in performance characteristics in the 2000s made them more suitable for a wider range of applications, first in industries like construction and after the introduction of the Polyurethane Dispersions (PUDs) class of water-based adhesives also in automotive, aerospace, textiles and footwear. In recent years sustainable adhesives have become more mainstream, with accelerated adoption in electronics and structural applications.
Fundamental research has been going on everywhere to shift the paradigm to completely new adhesives systems. A team from Purdue University in the United States in September 2023 proposed an adhesives system in scientific journal Nature based on epoxidized soy oil, malic acid and tannic acid that would be competitive in performance with current industrial products, achieving adhesion between metal substrates up to around 18 Mpa and in some cases beating the performance of a classic epoxy. All components of the system would be biomass-derived, low cost and widely available.
Until those kinds of systems reach the market in commercial products, end-users will often stay hesitant to ditch their trusted solvent-based, petrochemical-derived adhesives for sustainable alternatives. The bar for performance characteristics in many applications and markets is high. Applications in automotive, aerospace, defense and construction generally require structural bonding and the ability to withstand exposure to heat, moisture, chemicals and mechanical stress. Manufacturing processes like high-speed production lines may require strong initial tack and quick curing that alternative adhesives are often still unable to deliver.
Adhesive products succeed or fail based on performance. Being bio-based or sustainable is just a bonus. A company like Spanish thermoplastic polyurethanes (TPU) specialist Merquinsa is well aware of this. TPU is produced from diisocyanates and polyols that are generally derived from petrochemical sources. They are unloved, but versatile and the reliable default solution for many applications. Merquinsa was in 2012 acquired by American chemical manufacturer Lubrizol, owned by Warren Buffett’s Berkshire Hathaway that has a strong focus on sustainability. Over the last decade the company, now rebranded under Lubrizol, has invested heavily in solvent-free and bio-based solutions, but without compromising on performance.
When Lubrizol in May 2024 announced Pearlbond Eco, the latest addition to their bio-based thermoplastic polyurethane (TPU) adhesives portfolio, the press release emphasized the high thermoplasticity of the new product and the fact that it can be processed by extrusion, unlike other previously available bio-based hot melt adhesives. The impact on manufacturing processes is a major deciding factor in mainstreaming adoption of sustainable adhesives. Would using alternative adhesives require changes and investments in new mixing, dispensing and curing systems? Would it slow down production with longer curing times and inconsistent results?
The search for sustainable adhesives that don’t compromise on performance offers great opportunities for formulators. A lot of innovation is happening in bio-based or non-toxic hot melt, epoxy and acrylic adhesives. Another area of innovation is mono-materials, where the adhesives have basically the same chemistry as the substrates they are bonding, making the product more recyclable. The focus in sustainability in recent years has shifted from biodegrability to circular economy, increasing the importance of debonding as a requirement for next-generation adhesives. Formulators are now looking to not only equal the performance of traditional adhesives, but beat them and be more versatile.
JOIN US AT ADHESIVES & BONDING EXPO EUROPE, STUTTGART, GERMANY, 3-5 DECEMBER
Julien Heusser (SIMALFA), Bárbara Galisteo Almirón (Lubrizol) and Helena Cheminet (Bostik) will discuss how to overcome limitations and expand performance of sustainable adhesives on a panel at the next Adhesives & Bonding Expo, December 3-5 in Stuttgart. Find out more about our conference here.