Question

1. If nothing sticks to Teflon, how does it stick to pans? 2. Which of the following has highest crosslinks? Thermoplastic, elastomer, or thermoset? 3. Crosslinking is an endothermic or exothermic process? 4. Which has higher chemical resistance, dimensional stability, density and shrinkage, thermoplastics or thermosets? 5. What is resoles and what is novolacs? 6. How can we distinguish if a plastic is elastomer or not? 7. What is vulcanization?

Answer 1

Teflon is also known as Polytetra- 10 fluoroethylene (PTFE). It is very Slippery due to presence of electro- negative fluorine atoms. Fluorine atoms repeal almost all other material ther by preventing Teflon from adhering. When teflon sticks to pan it is a Physical bond and not chemical bond we can consider it in same way as we have seen of ice get Stuck to ice-tray. So, we do a Process called sintering where Teiflon. is heated to a high temperature but below its boiling point. It is then pressed firmly to the surface and finally let out to Cool down to. room temperature:

& order of Crosslink :- Thermoset > Elastomer Thermoplastic Thermoset have intense cross-link that result in 3-D network. This repult in more rigidity, hardness and a higher Melting point. Ex-Bakelites Elastomers are loosely Cross-linked. This result in flexibility and elasticity. Ex- Natural Rubber. Thermoplastic on the other hand are not cross-linked. This enable them to be reshaped once molded Ex-PVC. (polyvinyl chloride): 2. Cross-linking reactions are AH <o. exothermic.

Go Higher chemical resistance - Thermosets. 15) Higher dimensional stability - Thermosets ii) Higher density - Thermosets. ir) Higher shrinkage - Thermosets s Resoles : - It is a 2 Step process. done in basic environment and having higher formaldehyde relative to. Phenol. O-CH₂-OH PH. Kl+HO OH Phenol Ć -OH . Glycol OH CH-OH -CH₂-OH 애 -OH 0

Novolacs: - It is a 2 step process carried out in acidic environment and having lesser formaldehyde compared to phenol .. .OH. LOH SO +HO 8.5. choth OH + H Corthor ortho) Elastomers, commonly known as Rubber have great capacity for large elastic deformation under an applied stress. In other word, they can be stretched over 100% of their original length with no permanent deformation.

Vulcanization is a chemical process by which physical properties. of natural or synthetic rubber are improved by heating rubber with sulphur. It form cross-link between long chain molecules. Temperature of about 140-180°C is used and is heated in presence of sulphur and zinc oxide.. This and reduces deformation . process the risk increases elasticity of plastic