Henkel and LIKAT are researching new, bio-based and ‘debondable’ adhesives.
In the BIOVIN project, the Leibniz Institute for Catalysis (LIKAT) and Henkel produced new synthetic building blocks for innovative, bio-based adhesives that can be de-adhered on the basis of carbohydrates and vegetable oils. Such reversible bonds would greatly enhance the ease of repair and recyclability of electronic products or household appliances, for example.
The researchers also obtained interesting secondary results, particularly with the development of a new, highly selective catalytic process for the production of divinyl ethers. The project was funded by the Federal Ministry of Food and Agriculture (BMEL) through the project management organisation Fachagentur Nachwachsende Rohstoffe e. V. (FNR).
In the Biovin project, new diols and polyols were successfully produced in high yields and at low cost from commercially available, bio-based platform chemicals. The researchers pursued two approaches with these intermediate products: firstly, they tested the polyols as reactive components in polyurethane adhesives. The resulting polyester polyols were characterised by similar properties and key figures to comparable petrochemical compounds.
On the other hand, the diols and polyols were processed into new, bio-based, multifunctional divinyl ethers (DVE). To this end, the LIKAT developed a catalytic synthesis method that makes it possible to convert almost any bio-based polyol or phenol into a vinyl ether. With a yield of up to 98 per cent and significantly less formation of unwanted by-products, the process is more selective, efficient and environmentally friendly than the most important commercial process to date. There is still a need for research in the search for an efficient and cost-effective catalyst.
Targeted ‘debonding’
The researchers used the vinyl ethers to produce new adhesive formulations that could be an alternative to the commercially very successful acrylate systems. It was found that they have similar curing behaviour, but adhere less well to metals and better to plastics. Further advantages included their lower toxicity, more pleasant odour and the fact that they are derived from renewable raw material sources.
In addition, DVE provided the basis for adhesives that could be specifically ‘de-glued’ by heat, light or acid. Such cleavable compounds could enable the recycling of electronic and household appliances and support the circular economy. In the Biovin project, a total of 14 different prepolymers were produced from DVE and commercially available, bio-based dicarboxylic acids for this purpose. Additives or catalysts and, for the most part, solvents were not needed. Debonding was achieved under mild experimental conditions by both thermal and chemical cleavage, as verified by spectroscopic investigations. Even though there is still a need for further optimisation, the prepolymers developed already show enormous potential for new, recycling-friendly adhesive systems.
Henkel sees property advantages in the vinyl ether-based polymers produced from Biovin that are suitable for the development of marketable adhesive products. The company is currently conducting various prototype tests to achieve adaptations to a wider range of materials. If the results of these tests continue to be positive, Henkel will then approach specialised suppliers who can produce selected vinyl ethers from biomass on a commercial scale.
