A water resistant hot glue from expired milk proteins
Hello fellow chemists,
in this experiment I present the preparation of a strong, water-proof, hot glue from expired milk proteins.
Introduction
Almost two years ago, I posted an experiment about the precipitation of proteins out of expired milk, giving an example of a food waste valorisation.
Here you can see that post and the relative YT video
Since then though, I have been thinking about a final utilisation of these proteins and complete this project.
After checking some books, manuals, old industrial things I decided to make a glue with those proteins. The glues have been historically made with
animal skins, blood, hide and others suspended, emulsified in aqueous basic media, like lye, lime, caustic soda and so on. Starch glue are known also.
Synthetical glue are instead made with polymers, as polyvynil alcohol but all these substrate have in common the possibilities to make a lot of
hydrogen bonding. Any basic emulsion of a substrate containing many hydrogen bonding donor and acceptor could be a glue.
Additives as mineral salts, or fungicide, soap, perfume are used often. The most simple recipe that I found for a casein-based natural glue is the
following:
casein = 100 kg
water = 250 kg
calcium hydroxide = 30
sodium silicate = 70 kg
I modified it, proportionate it to 10 g of milk proteins, and using 3 g of NaOH in place of sodium silicate. Let's find out.
Procedure
Since the proteins were two years old, and also already in an expired milk, I tested them with a 0.4% ninhydrin aqueous solution, comparing both with
blank and a control triptophan solution, and the proteins gave a positive test, a blue-violet color.
In a 100 ml beaker containing 25 ml of water, 10 g of expired milk proteins are added. The temperature is brought to 70 - 80 C circa on hotplate. To
this 20 ml of 15% NaOH aq. solution is added at once. After a while, the mixture start to have an homogeneous appeareance. Lastly, 3 g of calcium
hydroxide is added at once, and stirring and warming is continued until the volume is reduced to 25 ml circa. Then, the mixture is a skin-colored,
viscous, perfectly homogenous emulsion.
Product test
The glue is tested while still hot. Firstly, on two paper sheets, then two wood pieces. The glue is spread on the surface still hot, then the second
sheet applied, worked a bit and kept pressed with a jar or a flask overnight. Teh day after, the two sheets are teared apart with increasing force.
The paper has not been glued so much. Discarded.
The wood pieces instead have been very strongly and not even a medium force could separate them.
Once cool, the glue solidifies into a paste. But when warmed again, and eventually a bit of water added, it is again ready to use. I store it in a
glass jar.
Conclusion
This experiment has been successful, and I hope you enjoyed to repeat it in your laboratories. Make your own milk glue, and post it the results. I am
looking forward to see what do you got.
Unfortunately I have no photos to show, but as usual I recommend to watch the corresponding YT video.
See you next time,
palico
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