| Learning Aims: |
|
| Materials: |
|
| Suggestions for use: |
|
From the selected products containing synthetic polymers, choose the two of them. Determine your requirements on these products (functional– incombustibility, strength, hardness, brittleness …; economic – low price, distribution options, …; aesthetic – possibility of colouration, processing into a desired shape, workability, …; health – no side effects). On the basis of the information obtained from the units 2 and 3 and possibly from the Internet and from the related literature, try to find a polymer appropriate for your application. Justify your choice. Refer both to positives and negatives of your choice: Application 1: Surface of pan Material requirements: Temperature resistance, resistance to chemicals, non - sticky, good thermal conductivity, no occurrence of toxic products throughout degradation. Selected polymer: PTFE – polytetrafluorothylene Justification: PTFE is thermally very resistant (degrades above 250 °C, up to 250 °C there was no release of toxic vapours), which is above the usual temperature of pan surface (around 200 °C) suitable for frying. PTFE is also self - lubricating, which means that its surface is non - sticky. Due to this, fried foods do not “stick“ to the pan surface, do not bake in but they bake evenly. This allows a low consumption of fat and oil (and healthier, less fatty meals). PTFE is also very resistant to acids, alkali, salts, and solvents even at higher temperatures; therefore it will not degrade due to the effects of e.g. acids or acidic substances in the food or dissolve in oil with a consequent deterioration of fried foods. The properties can be further improved by supplying additives, e.g. glass particles, which improve thermal conductivity and ensure a better thermal distribution within the pan. The price of PTFE is however many times higher than in the case of other polymers or also alternative materials (metals). Nevertheless, considering the fact that the alternatives are only a few and also have their disadvantages, it is evident that the higher price of the product, due to its advantages offered by the manufacturer, will be accepted. The amount of the material used will not also be so high to raise the price of the product above a reasonable level. A disadvantage could be the fact that the temperature of the pan could be, when the product is treated unsuitably, higher than 300 °C. Therefore it will be necessary to ensure (instructions for customers, choice of appropriate complaint terms, qualitative detection of temperature) a proper use of the product and avoidance of polymer degradation and damage. An evident disadvantage of PTFE is an improper wear resistance; the pan surface should therefore be appropriately treated; when working with it do not use metal items with sharp points.
Application 2: Packaging material, e.g. yogurt cup Selected polymer: PP – polypropylene
Material requirements: The selected polymer must not release toxic substances or react with preserved food. Because of transportation, the selected polymer must be reasonably strong, further it must be easy to process to enable a formation of any shape (because the product should be easy to sell). Packaging must not release its contents. An important requirement as for packaging will be its price, which should not exceed the price of the product. Temperature resistance is not important because the existence of the product at higher temperatures is not supposed (this will lead to damage of the packed product). On the contrary, a reasonable (i.e. lower) temperature of processing enables easy forming of polymer into a desired shape at reasonable energy costs. Justification: There is a wide range of polymers; almost all of them have the required properties. Improper will undoubtedly be formaldehyde resins and aminoplastics (they can release toxic products). PTFE or PC is however eliminated due to a higher price; the cheapest polymers of appropriate properties are PE (indeed the cheapest) or PP. For PP speaks its higher strength.
Discuss your choices with other groups. Try to oppose the choices of other groups. Discussion can be over the properties, acceptability of price, aesthetic qualities of the product, etc |