TAGS: Waterborne Adhesives
University of Manchester scientists have produced synthetic spider silk to create new biodegradable glue alternative. The scientists found that their homemade synthetic spider silk glue, as well as the commercially available adhesives works without being environmentally harmful.
The glue was made by coaxing harmless bacteria to produce spider silk in addition to their normal proteins. The bacteria could then be fed sugar and nutrients to produce the spider silk glue through fermentation. The process is similar to the fermentation of beer but with spider silk glue being made instead of alcohol.
Spider Glue Stronger than Commercially Available Specialty Glass Glue
The spider silk glue was found to be especially good at sticking glass together with an initial adhesive strength rating of 6.28MPa (Megapascals), when compared with a commercial specialty glass glue has a strength of 11.9MPa. The new breakthrough opens the door to a range of sustainable alternatives to an industry which is worth billions of dollars annually.
Dr Aled Roberts from the Manchester Institute of Biotechnology who led the research said: “
We found evidence that the mechanism of adhesion was due to unfolding of the protein and reorganisation into a dense hydrogen-bonded structure rich in what are known as ‘β-sheets’."
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This was interesting because natural spider silk has been shown to undergo a similar transformation into a β-sheet rich structure as spiders spin their silk – and is understood to be what makes spider silk so strong and tough. Kevlar® also gets its strength from a densely hydrogen-bonded network,” added Roberts.
Unfolding and Reorganization of Protein – Mechanism of Adhesion
Natural proteins were commonly used as glues before synthetic adhesives were developed. Collagen (from animal hooves), casein (from cheese) and gluten (from grain) were all used as glues before we developed chemical synthesis methods to make adhesives from crude oil.
“
We found evidence that the mechanism of adhesion was due to unfolding of the protein and reorganization into a dense hydrogen-bonded structure rich in what are known as ‘β-sheets’. This was interesting because natural spider silk has been shown to undergo a similar transformation into a β-sheet rich structure as spiders spin their silk – and is understood to be what makes spider silk so strong and tough,” said Roberts.
Protein-based Glue Replaced by Synthetic Alternatives
Today, protein-based glues have been almost completely displaced by synthetic alternatives, which are produced on a vast scale with the global market totaling UDS 41 billion in 2010. This industrial process from oil contributes significantly to global emissions of greenhouse gasses and volatile organic compounds (VOCs) so alternatives are required.
The findings should help with the design and formulation of other protein-based adhesives which, with further optimization, could compete with commercial crude-oil derived adhesives and give us renewable, biodegradable and green glues as we had in the past.
Water-based Biodegradable Non-Toxic Glue
Many organisms produce specialized proteins specifically for adhesion. Mussels produce a strong protein-based glue that allows them to stick to slippery rocks in rough inter-tidal zones. Spiders also produce tough silk-based glues which they use to capture fast-moving insects in their webs.
As the world transitions away from fossil fuels and towards a renewable future, there is a growing need to replace CO
2-intensive crude-oil derived adhesives with greener alternatives. One option could be to return to return to protein-based glues, who’s properties could be designed and optimized using the tools of synthetic biology.
Unlike synthetic crude-oil derived adhesives, these protein-based glues would be water-based, non-toxic, biodegradable and environmentally non-persistent. They would also be grown under benign conditions (ambient temperatures and pressures) and could be produced through fossil-fuel free, green synthesis routes – via processes similar to the fermentation of beer.
Source: University of Manchester