TEXTILES NANO EXPERIMENT 1 MAKING AND INVESTIGATING CASEIN PLASTIC GUIDE Experiment 1: Making and Investigating Casein Plastic Guide Part A: Making Casein Plastic Introduction Casein is a phosphoprotein found in fresh milk. It is also used in the manufacture of adhesives, binders, protective coatings, plastics (e.g. knife handles and knitting needles), fabrics, food additives and many other products. Bodybuilders use powdered casein as a slow-digesting source of amino acids. These experiments were adapted from Rickard G. et al. 2006. Science Dimensions 4, Pearson Education, Australia. Aim To make casein plastic. Materials  full cream milk  vinegar  Bunsen burner  heat-proof mat  tripod  gauze mat  100mL measuring cylinder  two 250mL beakers  thermometer  stirring rod  elastic band  coarse cloth for straining  paper towel  assorted moulds (bottle tops, chocolate trays)  fine sandpaper  tongs 1 Experiment 1: Making and Investigating Casein Plastic Guide Method: 1. Place 100ml of milk in a 250mL beaker and heat gently to 50°C. Do not overheat. 2. Add 10mL vinegar and stir with a stirring rod. The milk should curdle forming white lumps of curds (casein) and a yellowish liquid called whey. 3. Place the coarse cloth in a funnel and strain the curds and whey into another beaker. 4. Squeeze the cloth to remove as much liquid as you can 5. Empty the curd onto paper towel and pat dry. 6. Press casein into a mould and leave to dry in the sun. 7. After 1 to 2 days, remove from mould and polish with sandpaper. Discussion: 1. Describe your casein plastic. Answer: Casein is hard, off white colour, opaque. 2. Casein is a protein. What is a protein? Are there any other proteins found in milk? Answer: A protein is a polymer made up of amino acids. Other proteins found in milk include enzymes, alpha-lactalbumin and betalactoglobin. 3. When the casein was allowed to dry it forms a polymer. What is a polymer? Give at least 5 examples of other polymers (2 must be biological molecules). Answer: A polymer is a giant molecule made up of repeating units called monomers. Examples of polymers include; DNA, starch, cellulose, hair, wool, as well as all the synthetic polymers investigated in part B. 4. Research the toothpaste product ‘Recaldent’. How do Nanotechnologists use casein to create the active ingredient in this product? Answer: Recaldent is an Australian invention added to toothpaste. It repairs damaged teeth by promoting calcium absorption. Nanotechnologists at the CSIRO use casein phosphopeptides (amorphous calcium phosphate) to strengthen the tooth by delivering calcium and phosphate the building blocks of tooth enamel. More information can be found at www.foodscience.csiro.au/recaldent.htm 2 Experiment 1: Making and Investigating Casein Plastic Guide Part B: Investigating the Properties of Plastics Aim To test a variety of plastics and look at their properties. Introduction Plastics are made up of polymers, which are very large molecules made from repeating units called monomers. Chemists describe polymers according to their plastic properties. Polymers can be either thermoplastic or thermosetting polymers. Thermoplastic polymers are soft, stretchy and they soften and melt when heated. Thermosetting polymers are hard and rigid. They char when heated leaving a black carbon residue. In this part of the experiment, the teacher should carry out the flame test as a demonstration. The effect of flame component should be performed in a fume hood. Students should then be encouraged to conduct the remaining tests under supervision, e.g. examine, feel, scratch, and float the plastic samples themselves. Please take the appropriate safety precautions when preparing acids and solvents. Gloves, labcoats and safety glasses should be worn. Materials and Equipment  Labelled samples of plastics (casein - prepared in Part A, polythene, polystyrene, PVC, Perspex, nylon,  fireproof mat  scissors  turpentine  nail polish remover  dilute HCl  250mL beaker  Tongs  Bunsen burner in fume hood (teacher demonstration only). Method 1. Observe and record the results of the flame test carried out by your teacher. 2. Carry out each remaining test as demonstrated by your teacher Discussion 1. What is the difference between thermoplastic and thermosetting plastic? 3 Answer: Experiment 1: Making and Investigating Casein Plastic Guide Thermoplastic polymers are soft and melt when heated, thermosetting polymers are rigid and char (blacken) when heated. 2. Classify your plastics as thermoplastic or thermosetting polymers. Answer: Only casein was a thermosetting polymer. 3. Do any plastics sink in water? What does this indicate about their density? Answer: This indicates that the plastic is very dense and the molecules are very close together. In order to sink, the plastic must be denser than water. Perspex and Casein should sink. 4. Why must the burning of plastics be done in the fume hood? What does PVC produce when burnt? Answer: The burning was done in a fume hood because plastics release toxic chemicals when heated. PVC produces chlorine gas. Conclusion Briefly summarise Part A and Part B and write some concluding comments. Comments will vary, but students should conclude that casein plastic can be made quite simply in the laboratory, and its properties compared to other readily available plastics. Results: Note - some of the results will vary depending upon which version of the polymer used. For example, different answers will be recorded for Polystyrene depending if a foam version or a solid version of the polymer is utilised. Items such as whether it feels waxy may elicit several responses as students will give subjective answers. 4