Engineering Chemistry S Datta

452 ENGINEERING CHEMISTRY
properties like extreme toughness, high softening point (350°C), high chemical resistance, low
coefficient of friction and waxy touch, good mechanical and electrical properties. Due to all
these qualities, the polymeric material can be machined. It softens at about 350°C, hence at
this high temperature it can be moulded applying high pressure.
Uses. It can be used for insulating motor, transformers, cables, wires etc. Non-stick
cookware coatings are made of TEFLON. It can also be used for making gaskets, pump parts,
tank linings, pipes and tubes for chemical industry, non-lubricating bearings and to make
non-reactive coating.
Polyurethane
(i)
O
(ii) CH —CH —CH
3 2 2
OH –
CH 3
CH 3
CH 3
HOCH—CH —O—CH —CH—O—CH CHOH
2 2 2
Poly(oxypropylene) glycol
Polyurethanes are a varied range of crosslinked polymers made from two liquids—a
polyol and an isocynate.
Properties. It can be foamed like polystyrene but unlike thermocoal, is soft, spongy known
as ‘U-foam’. It has low thermal conductivity. Its greatest advantage lies in the fact that it can
be made where they are needed without any complex machinery—the two liquid ingredients
can be mixed and moulded.
Uses. It is used as insulating material in refrigerators. Due to its spongy nature, it is
used for making pillows and matresses. A coating of polyurethane is applied over leather,
which improves the appearance and quality of the leather and hence the bags made of these
look attractive and the shoes feel comfortable. It is also used to make chairs etc.
Nylon-66
Polyamides are synthetic polymers, having recurring amide groups, which have a structure
similar to that of polypeptides. Nylon belonging to this class is used for making fibres.