The use of adhesives has long been intertwined with our everyday lives, with one of the earliest use cases dating to circa 200,000 years ago in the form of tar-hafted stone tools. Today, adhesives are ubiquitous – found in packaging, automobile, aerospace, construction, medical, and consumer industries – and dominated by companies like Henkel, 3M, Huntsman, DowDuPont, Sika, H.B. Fuller, BASF, and Pidilite.
Four technology areas within adhesives have received the most interest from industry: pressure-sensitive, self-healing, low-temperature, and zero-formaldehyde adhesives. In this insight, we conducted a preliminary survey of these areas based on our interviews with start-ups and publicly available information. We also detail other adhesives like reactive hot melt, fluid-activatable, bio-inspired, and those capable of joining mixed substrates to address emerging areas of innovation in these technologies, as well as to showcase emerging startups.
Self-healing adhesives can automatically repair inflicted damage without external intervention. Two main mechanisms exist, the first relying on encapsulation/injected media that releases healing material upon cleavage, and the second relying on intrinsic bonding and chemistries of the adhesive to drive self-healing. However, micro-encapsulation inadvertently weakens adhesives and introduces processing challenges, and the scale of development for intrinsically self-healing adhesives has been limited. Both methods have limited functionality and have not been successfully deployed other than protection from superficial scratches.
While groups have focused more on coatings than adhesives, there is a strong research interest in self-healing adhesives. At the academic level, the State Key Laboratory of Solid Lubrication of the Lanzhou Institute of Chemical Physics, the Ministry of Education Key Laboratory for the Green Preparation and Application of Functional Materials of Hubei University, and the University of Chinese Academy of Sciences (“Inorganic adhesives for robust, self-healing, superhydrophobic surfaces“); the East China University of Science and Technology and the China and Shanghai Urban Transport Design Institute (“Strong and efficient self-healing adhesives based on dynamic quaternization cross-links“); TU Delft and M2i; and Fundación Cidetec are all groups concentrating on novel self-healing adhesives.
Pressure-sensitive adhesives (PSA)
PSAs form bonds with the substrate upon application of pressure. They are viscoelastic, exhibiting both liquid and solid properties, and do not require additional stimuli (such as exposure to chemicals, moisture, or ultraviolet [UV] rays) to bond. Factors affecting the bond strength include molecular forces such as van der Waals, and substrate surface energy, smoothness, or cleanliness. PSAs can form temporary or permanent bonds and are easy to employ. Common examples include 3M’s Post-it notes and Scotch tape; electrical, masking, medical, and sealing tapes; labels, automotive trim, and glue dots.
The PSA space is dominated by incumbent companies like 3M, Henkel, BASF, Huntsman, DowDuPont, Sika, and Pidilite. Additional examples include the National Starch and Chemical Company’s (now Ingredion) PSA for vinyl facestocks, and Cheil Industries’ (now Samsung) PSA to prevent light leakage of thin-film transistor liquid crystal displays (TFT LCDs). Lux identified little start-up or academic innovation in this space.
Zero-formaldehyde adhesives demonstrate adhesion without releasing formaldehydes during the curing process and service life. These adhesives don’t contain chemicals like urea-formaldehyde and melamine formaldehyde, and are typically soy-based. Zero-formaldehyde adhesives usually serve the wood industry in products like plywood and particle board. The value proposition of zero-formaldehyde adhesives is based on their contribution to indoor well-being, as well as their ability to gain credit from green building standards.
Innovators in zero-formaldehyde adhesives either improve performance of the incumbent soy-based solutions or use new technologies as alternatives to soy-based technologies. One example is Ningbo Institute of Materials Technology and Engineering, Chinese Academy of Sciences that developed soy-based wood adhesives with improved water resistance at a lower price than similar technology by its competitors. As another example, Cambond developed algae-based adhesives for woodwork with a comparable performance to soy-based adhesives – by doing this, the company converts wide algae (a widespread pollutant) to a value-added product.
Adhesives that cure or operate under low temperature
Low temperatures, especially below freezing, negatively impact performance as many adhesives will crack or de-bond from their substrate. Multiple companies have existing adhesive products able to operate at freezing temperatures; most of these products are epoxy-based. Example companies include large players like Henkel, and smaller groups like Master Bond. These adhesives usually cure at ambient temperature and operate at low-temperatures.
Compared to the above, adhesives able to cure at low temperatures are less common. Adhesives cure slowly at low temperatures and may not be able to completely cure or perform as designed. A handful of small and medium-size companies have developed adhesives with low curing temperatures, providing application flexibility for end users. One such company is Hilti, with its epoxy-based adhesive that can cure at -5 °C. Another example is Simpson Strong-Tie, with an acrylic adhesive that can cure at -10 °C. Both adhesive products from these two companies serve concrete substrates.
NuLabel Technologies, a U.S.-based company, developed fluid-activatable adhesive technology for attaching paper labels onto plastic and glass substrates. This adhesive is pre-applied on labels and dry to touch, and can be activated by water-based and glue-free spray. Compared with conventional PSAs, this technology claims to eliminate the need for nonstick liner backing on labels and messy wet glue, while achieving higher peel and shear strength. NuLabel claims that its technology can reduce downtime in the labeling process by half and realize the lowest label price in the industry.
Reactive hot-melt adhesives
The field of reactive hot-melt adhesives is crowded with active companies like Henkel, Covestro, H.B. Fuller, DowDuPont, BASF, Huntsman, Jowat Adhesives, and Bühnen. These adhesives are typically based on reactive polyurethanes and reactive polyolefins. Although developers claim some differentiation in product formulations, performance and functions among these are very similar. We expect existing developers to turn to added functionality, such as self-healing, or use novel bio-based materials as a way to differentiate their products.
Emulating gecko feet, the U.S.-based Nanogriptech produces a dry, high-friction adhesive. The micro-structured adhesive relies on van der Waals forces from an array of micron-scale fibrillar structures for its performance, rather than chemical adhesion. The company molds its surface pattern onto sheets of polymer film or fabric using a batch process, producing a material that is washable, reusable, and creates an airtight seal. The technology is also residue-free and claims “commodity-like” prices; however, it is still in an earlier stage of development.
Companies like 3M, Henkel, Sika, and Huntsman continue to dominate this space with adhesives that can join mixed media like wood, plastics, glass, or metals. For engineering applications, these technologies are typically based on epoxies, polyurethanes, or methacrylates. This field also includes household glues like polyvinyl acetate (PVA)/craft glue, cyanoacrylates/super glue, and silicone adhesives. Innovation in this space could include adhesives that are able to join more novel materials together, provide enhanced functionality, or offer ease of processing for high-volume production of multi-material structures. One example includes the Beijing University of Aeronautics and Astronautics’ paper on a heat-resistant organic matrix adhesive for hydrophobic silica aerogels composites and 1Cr18Ni9Ti steel bonding.
With this broad assessment of the adhesives space, it is clear that medium- and large-size companies dominate the market with established products. Interesting but early-stage innovations exist – emerging from the incumbents’ own research and development centers, academic groups, institutes, or start-ups– but have a long developmental road ahead. Start-ups are also scarce in this space, as it is difficult to prove product performance and build successful sales channels with limited resources.
Though the field of adhesives is entrenched with mainstay groups and technologies, readers should be aware that there are both clear demands for specific functions, as well as novel technologies that lack a clear market pull. Readers can view this as an opportunity to use their industry access to help innovative groups match these new functions and properties to unmet needs and be proactive in an industry that is often reactive.
By: Cecilia Gee and Jerrold Wang