Adhesives are commonly used in a variety of industries such as housing, furniture, packaging,and upholstery. Volatile organic compounds (VOCs) have been used widely in adhesives for the past half-century, but now that negative health and environmental effects have been uncovered, many organizations are moving to adopt low-VOC adhesives. In particular, it is suspected that VOCs may contribute to air pollution and create low ground-level ozone, also known as smog.

High-performance low-VOC adhesives that are sustainable could be a viable alternative in many industries. Organizations and researchers have been focused on developing and marketing eco-friendly adhesives made from renewable biomass material.

Global pressure to reduce VOC emissions, and rising demand

In North America demand for low-VOC adhesives is expected to increase as regulations about toxic chemicals in chemically cured adhesives increase. After the pandemic slow-down of the economy, the construction industry has been on an upswing and the demand for low-VOC adhesives is expanding. The packaging industry is also increasing its demand for adhesives, with water-based and hot melt adhesives being the main preference in these industries.

Not only is exterior air affected, but indoor air quality can be adversely impacted by VOC emissions. According to WHO Housing and health guidelines, indoor air quality is affected by many factors that include finishing materials that use coatings and adhesives. Some major emitters that have an adverse effect on interior air quality are formaldehyde and benzene as well as tri- and tetrachloroethylene. Notably, construction adhesives are considerable contributors to resulting emissions due to their complex composition.

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The drive for change is occurring at different rates around the world but it is expected to continue to develop throughout many industries. Growth in polyurethane adhesives is likely to increase due to low VOC requirements. Water-borne adhesives will be a large component of the low VOC adhesive market.

Estimated global adhesive market share by end-use industry in 2020 (Data source: Ceresana)

The organizational need to contribute to sustainability and environmental preservation initiatives increases as countries seek to improve air quality and reduce emissions. Some industries are taking steps to switch to sustainable alternatives. With increasing environmental concerns, eco-friendly and sustainable wood composites are being developed. Unfortunately, many wood composites use formaldehyde as a primary bonding component.

Demand is also increasing for lightweight vehicles. As a result, the automotive industry is manufacturing composites and lightweight alloys that cannot always be welded. Instead, adhesives may be used to bond car parts together. Multi-material designs also lead to an increased need for adhesives. Consumers are also interested in environmentally friendly and non-toxic alternatives to conventional products. A 2022 survey of over 1,000 Americans indicated that 66% were willing to pay more for sustainable products.

Sustainable and low-VOC adhesives

Nonetheless, expensive crosslinking agents that release VOCs into the environment and use unsafe mildew-proofing agents continue to be studied and produced. However, some researchers are trying to find more solutions to the VOC and sustainability issue and recent advancements have been made in the field.

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Conventional adhesives that include epoxies, formaldehyde-based resins, and polyurethanes are often derived from petroleum and result in the off-gassing of carcinogenic formaldehyde and other VOCs that contribute to environmental and health problems. Due to the ill health effects of formaldehyde, biomass-derived alternatives are being researched to create biobased adhesives that are both sustainable and non-toxic.

Some materials that have been used to create these eco-friendly adhesives are lignin, tannin, fiber, polysaccharides and protein. In recent studies, high-strength, formaldehyde-free adhesives were made using renewable materials such as camellia and soybean meal, combined with a low epoxy crosslinker. Soy protein is a widely available plant protein but has limited water resistance. Some efforts have been made to improve their performance including cross-linking, chemical denaturation and enzymatic modification.

Soy protein has low bond strength and water resistance, but this can be mitigated through crosslinking and modifying the protein of soybean meal with chemical means. This material can be denatured with agents such as alkali and urea, which causes hydrophobic protein subunits to be exposed and results in increased water resistance.

Soybeans in a field ready for harvest.

In a 2022 study, a camellia meal-based adhesive was used as a bonding agent in plywood, and this eco-friendly alternative performed 93% better than an unmodified adhesive. It also has anti-mildew properties and could effectively substitute formaldehyde resin in terms of strength. Camellia meal is waste produced as a result of camellia oil manufacturing that cannot be used as livestock feed due to biological toxicity.

It would be ideal to use waste products from the production of other materials when creating biomass adhesives as biomass waste products often are inexpensive and easily accessible. Using bio-waste from food-manufacturing processes has been a subject of high interest and would increase the material efficiency of manufacturing. Sustainable adhesives similar to this could be used in wood-based panel industries as a high-performance yet eco-friendly alternative.

Another example of biomass that can be used in adhesives is lignin, a unique biomacromolecule with a 3D network structure and large molecular weight. Lignin-based epoxy prepolymers can create an epoxy resin adhesive that performs well in high humidity and extreme temperatures.

Sustainable hot-melt adhesive (HMA)

There is increasing adoption of polyurethane-based hot melt adhesives (HMAs), which are low-VOC and biodegradable but not necessarily sustainable.

HMAs are solvent-free solids when at room temperature; upon heating they melt and provide adhesion when cooled. Conventional formulas contain a base polymer, a tackifier and a plasticizer. Most commercially available HMAs use petroleum-derived polymers and are not biodegradable. Combining synthetic biodegradable thermoplastics with natural vegetable proteins could be a sustainable solution to hot melt applications without significantly reducing performance.

In a 2019 study, non-renewable bioplastic polycaprolactone (PCL) in a hotmelt adhesive was replaced by 50% biological material without significant strength reductions while still being potentially biodegradable. Soy proteins may be applicable in hot-melt applications as they can be recovered from residual oil cake and have thermo-plastic-like behavior. When combined with pine rosin as a tackifier and castor oil as a plasticizer, soy protein isolates derived from biowaste can be used as a sustainable and biodegradable component.

The need for high-performance alternatives

Low-VOC adhesives that do not compromise on performance are expected to increase in market share as alternatives that do not pose the same health risks are sought. VOC content and sustainability are important aspects to consider and allow individuals and organizations to make informed decisions regarding health and environmental consequences.

References

Barry, C. P., Morose, G. J., Begin, K., Atwater, M., & Hansen, C. J. (2017). The identification and screening of lower toxicity solvents for contact adhesives. International Journal of Adhesion and Adhesives, 78, 174–181. https://doi.org/10.1016/j.ijadhadh.2017.06.022

Kozicki, M., & Guzik, K. (2021). Comparison of VOC Emissions Produced by Different Types of Adhesives Based on Test Chambers. Materials, 14(8), 1924. https://doi.org/10.3390/ma14081924

Tous, L., Ruseckaite, R. A., & Ciannamea, E. M. (2019). Sustainable hot-melt adhesives based on soybean protein isolate and polycaprolactone. Industrial Crops and Products, 135, 153–158. https://doi.org/10.1016/j.indcrop.2019.04.043

Wang, H., Chen, G., Zhang, S., Zhang, W., Wu, H., Li, C., & Xiao, Z. (2022). Camellia meal-based formaldehyde-free adhesive with self-crosslinking, and anti-mildew performance. Industrial Crops and Products, 176, 114280. https://doi.org/10.1016/j.indcrop.2021.114280

Zhang, H., Chen, T., Li, Y., Han, Y., Sun, Y., & Sun, G. (2020). Novel lignin-containing high-performance adhesive for extreme environments. International Journal of Biological Macromolecules, 164, 1832–1839. https://doi.org/10.1016/j.ijbiomac.2020.07.307

Zhang, Y., Zhang, M., Chen, M., Luo, J., Li, X., Gao, Q., & Li, J. (2018). Preparation and characterization of a soy protein-based high-performance adhesive with a hyperbranched cross-linked structure. Chemical Engineering Journal, 354, 1032–1041. https://doi.org/10.1016/j.cej.2018.08.072

About the author

Jody Dascalu is a freelance writer in the technology and engineering niche. She studied in Canada and earned a Bachelor of Engineering degree. Jody has over five years of progressive supply chain work experience and is a business analyst. As an avid reader, she enjoys researching upcoming technologies and is an expert on a variety of topics.