| MadSci Network: Chemistry |
Glue is a very specific form of adhesive, generated from the collagen or "connective tissue" found in animal by-products, such as bone and hide. In essence, you make glue by boiling up the various bits and extracting the degraded collagen protein. (Without using animal bits, this can be done by denaturing - with vinegar - the proteins in milk.) Different starting materials produce glues of different chemical properties, such as pH. The acidity or basicity is a function of the protein itself. Breaking the protein down gets you lots of little amino acid fragments - not singular amino acids but small poly-peptides of several hundred amino acid residues. The ability of glue to bond depends upon the collective interaction of all of these fragments and the formation cross-links and hydrogen bonds. Each amino acid has a characteristic pH. This is a consequence of both the acid and basic portions of the polypeptide. It will decide the buffering capacity of the amino acid residues. On a very practical level, a glue with a high acidity will set more slowly and not be very water soluble. A glue that is basic will foam and have a short shelf-life (basic conditions dissolve proteins). Neutral glues are the best as they combine quick drying properties with a good life time. Remember that glue is protein and protein is food for molds and mildew. But the over-riding condition for different manufacturers is their source material - which ultimately determines pH. For more information, check out: http://sul-server-2.stanford.edu/don/dt/dt1560.html
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