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To recycle the “bad” protein food by reproducing glue
Have you even thrown some food because it becomes “bad”? Do you think it really waste money? Do you want to make them become useful again? If you do, our experiment will show you how to do and everything about it.
Heater, measuring cylinder ï¿½2(250ml&50ml),
pH paper,beakerï¿½2(300ml&500ml),glass rod, spoon
skim milk, vinegar
The sticking properties of different proteins in daily food are being investigated in our experiment. Casein in dairy products and textured soy protein (TSP) in soybean products are abstracted out by precipitation in acid. The samples are then neutralized by carbonate and undergo a series of stress tests to compare the strength of our reproduced protein glues with commercial products.
The basic principle of the sticking properties of protein glues is the ionic attractions and the Van der Walls’ attractive force generated by the protein molecules. Protein molecules are highly folded, resulting in a great contact surface area and exposure of the hydrophobic bonds. When two surfaces of substances like wood or paper are held together by protein, linkages are formed in between the molecules, and the two surfaces are stick together and are difficult to separate.
We expect the result the casein in milk and textured soy protein in soybean milk have comparable sticking strength as starch contained in commercial glue. The significant advantage of the production of our protein glues is that proteins in expired food can be recycled and reused to make the useful glue. The glue produced is also not toxic or harmful to the environment.
1)The history of glue
The earliest evidence of use of glue can still be observed in the cave paintings made by Neanderthal ancestors in Lascaux, France. These early artists wanted their work to last and mixed glue with the paint they used to help the colors resist the moisture of the cave walls. Egyptian artifacts unearthed in their tombs show many uses of glues; perhaps the most striking are the veneers and inlays in wood furniture, which was made using glue as early as 3,000 B.C. The Egyptians also used glue to produce papyrus. Greek and Roman artists used glues extensively; mosaic floors and tiled walls and baths are still intact after thousands of years.
Around 1750, the first glue or adhesive patent was issued in Britain. The glue was made from fish. Patents were then rapidly issued for adhesives using natural rubber, animal bones, fish, starch, milk protein or casein. As we can see from ancient and medieval records, fish glue was both a common and important adhesive for many special applications; adapted by artists, it was used from the time of ancient Egypt to twentieth-century France, in painting media, coatings and grounds, in the gilding of illuminated manuscripts, and in pastel fixatives.
2)Theory of milk glue
Casein is the principal protein found in cow milk (about 3%) from which it has been extracted commercially for most of the 20th century. It is responsible for the white, opaque appearance of milk in which it is combined with calcium and phosphorus as clusters of casein molecules, called micelles.
The major uses of casein until the 1960s were in technical, non-food applications such as adhesives for wood, in paper coating, leather finishing and in synthetic fibers, as well as plastics for buttons, buckles etc.
The first step in making acid-precipitated casein is acidification. Mineral acids or organic acids can add to the skim milk; or the milk is allowed to sour, in which case lactic acid, produced by fermentation of lactose, is the effective precipitant. The precipitated curd is then drained, washed, press to remove water, milled, drill, and ground. Solutions of casein in alkalis (with enough of the protein to give a suitable viscosity) can be used as glue.
Such glue compares favorably in strength with animal glue on drying the protein forms numerous hydrogen bonds with the cellulose in paper and with itself, so it can stick woods together, but it is not water-resistant. Resistance to water can be imparted to casein glue, however, by modifying the simple formula of casein in alkali; these improved casein glues are widely useful in industry. Prepared casein glues are sold in the form of dry mixtures, which need only the addition of water before use.
They are commonly composed of casein, lime, and a number of alkaline salts. Various chemicals have been used to improve the resistance to water, and many colloidal materials with adhesive properties can be mixed with casein to modify the properties of the resulting glues. It has thus been possible to adapt casein glues to a variety of specialized applications. These glues are used in the woodworking industry, in gluing paper, and in many other fields.
ï¿½Preparation of milk glue
1) 250cm3 of milk and 50cm3 of vinegar (about 5% ethanoic acid) were added into a beaker.
2) The mixture was heated slowly and stirred continuously until curds were observed. (Caution: Heater is very hot, temperature of mixture should not be more than 60ï¿½C)
3) Curds were allowed to settle to the bottom for about 10 minutes.
4) The heated mixture was filtered.
5) The curds were squeezed to remove liquid.
6) The curds were washed with little volume of water and squeezed again.
7) The curds were stirred with solid sodium hydrogencarbonate (NaHCO3) gradually and monitored pH by pH paper until pH became slightly alkali.
ï¿½Testing of adhere strength of glue
1) The glues were used to stick two plywood together, a the plywood at downside , with contact surface of 20 cm2
2) Two samples were made for each glue and one sample of starch glue was made as control.
3) The stack plywood was pressed by 0.8kg mass and allowed to dry at dry place for 2 days .
4) The plywood was set above the ground.
5) 0.5 kg Test mass was added gently each time until the masses drop.
6) The maximum mass of the glues that can afforded were recorded.
7) The plywood was cut into 4, which contact surface was decreased 4 times, and the above tests were repeated.