Emm 16 Marks

UNIT 1-16 MARKS

15..(a)(i).Explain the following terms with respect .to poIYI:De~. 1. Mechanical behaior  !. "hermal behaio#r $. Electrical behaio#r. behaio#r. 1. Mechanical behaviour % molten pol&mer is amorpho#s an' possesses ran'om chain orientation. I f the molec#les are linear their str#ct#re ma& be compare' with that of a ball of cotton. "his str#ct#re of the molec#les at higher  temperat#res temperat#res can be presere' at lower temperat#res thro#gh a #ench in fig. "ension on s#ch a mass pro'#ces most ofthe initial 'eformation an' improes the alignment of the molec#les .%s a res#lt the stressstrain relationsh ips are not Ii*e those of metals beca#se the mo'#l#s of  elasticit& is increase' when the stress is applie' 'irectl& against the pol&mer chain after alignment has occ#rre' Deformation of linear pol&mers. (a) "hermal an' 'eformation treatments. (b)+omparatie (b)+omparatie stress,strain relationships. -"he n#mbers in (b) correspon' to the str#ct#res in-a "he stress,strain stress,strain relation behaio#rs shown in fig. /#ggest means where b& pol&mers hae their properties enhance'. 0or example the 'rawing process which is #se' in ma*ing artificial fibers proi'es an a''e' benefit of increase' strength "hro#gh molec#lar orientation. f co#rse the strength at right angles to the axis of the 'rawn fiber wo#l' be exceptionall& wea* in the absence of cross lin*ing beca#se 2onl& an'erwaals bon's are operat3~e fort#natel& fort#natel& we neer loa' a fiber in that 'irection4 howeerthe problem is real in a plastic film or sheet. "he pro'#ction of plastic film re#ires the sim#ltaneo#s 'rawing of the pro'#ct in two 'irections at same time. "his is achiee' thro#gh blowing proce'#res or thro#gh roiling operations which increase the wi'th as the length is increase'. (linear) an' thermosetting pol&mer pol&merss 'iffer in that Thermal behaviour "hermoplastic (linear) thermoplastic pol&mers pol&mers act#all& melt an' lose all semblance of cr&stallinit& at high temperat#res temperat#res .f#rther more thermosetting plastics after the completion of pol&meriation can eent#all& lose strength if the& are expose' to high temperat#res  beca#se 'egra'ation 'egra'ation occ#rs. "he most critical effect of increase' temperat#re is an increase' . rate of chemical reaction. "he temperat#re temperat#re is an increase' rate of  chemical reaction ."he temperat#re at which pol&mers become highl& s#sceptible to chemical reaction correspon's closel& to the temperat#re at which mechanical strength 'rops off ."his is below the melting temperat#re in linear pol&mers. an' correspon's to start of 'egra'ation in framewor* pol&mers Electrical behaviour "here is consi'erable #se ofplastics in electrical ins#lation. 6lastics hae obio#s a'antages .s#ch as their abilit& when the& are applie' on wire as #npol&merie' or partiall& pol&merie' li#i' to forma #niform coating which can then b & pol&merie' in  place. /ome plastics len' themseles to film formation4 these are partic#larl& #sef#l as electrical materials. %wi'e choice of flexible or rigi'  plastics is aai aai lab Ie. UNIT 5-16 MARKS

1. (a) (ii).What are the special properties of plastics that make them suitable for engineering applications. PROPERTE! "#$ "PP%&"TO#! "PP%&"TO#! O' !OME TERMOP%"!T&! /ome of the important thermoplastics. thermoplastics. their tra'e names properties an' t&pical applications are gien in "able "able 0ollowing are some comments abo#t seeral thermoplastics liste' in "able

7&'rocarbon 6lastics "he ma8or h&'rocarbon thermoplatic pol&mers are polð&lene pol&prop&lene pol&prop&lene an' pol&st&rene.

6olð&lene (6E) 6olð&lene. also *nown commonl& as pol&rhene is ma'e b& the pol&merisation of ethene i.e. eth&lene (CHt~CH). "he properties an' application of 6E ar& oer wi'e ranges 6ol&th&lene is ma'e from petrole#m or nat#ral gas fee' stoc*s 'epen'ing 911 the molec#lar weight the metho' of man#fact#re an' 'ifferences in str#ct#re an' 'ensit&.

6ol&prop&lene (66) 6ol&prop&lene is forme' from the monomer propene i.e. prop&lene (CH,=CH-CK) It is similar to high,'ensit& polð&lene (76E) b#t its mechanical properties ma*e it more s#itable for mo#l'e'  parts than polð&lene.

+haracteristics of 66s I. "he& are stiffer har'er an' often stronger than polð&lene2s. !. "he& hae excellent fatig#e resistance an' a higher #se temperat#re. $. "he& are lighter in weight . "he& hae goo' chemical an' thermal resistance. ;#t the& hae poor resistance. 5. "he& are relatiel& low cost to #ltra,iolet light.

6ol&st&rene (6/) 6ol&st&rene is ma'e from eth&l,benene. It acco#nts for abo#t !9< of all thermoplastics in commercial #se.

+haracteristics of pol&st&renes 1. They are low cost brittle glass&: transparent pol&mers.  !. "he& are eas& to process4 hae excellent mol' abilit&. $. "he& hae goo' 'imensional stabilit& Polvinl chlori*e (P+&)

6ol&in&l chlori'es(6=+)isma'eb& pol&merisationof the monomer in&lchlori'e (+7 2>+7+I). 6=+ is one of the most wi'el& #se' plastics in terms of ol#me produced. "&pical applications of 6=+ incl#'e pipes. ales fittings floor tiles wire ins#lations to&s phonograph recor's in&l a#tomobile roofs etc. Polurethanes (P,R)

6ol&#rethane is a famil& name gien to a series of pol&mers that are pro'#ce' b& the reaction between aromatic'i,isoc&anates an' low molec#lar weight pol&mer molec#les. Depen'ing on the 'egree of form#lation. the #rethanes behae as thermosetting pol&mers thermoplastic pol&mers. or elastomers. PROPERTE! "#$ %66?r+%"I~/ O' !OME TER!ETMOT#- P%"!T&! /ome of the important thermosetting plastics. their tra'e names. properties an' t&pical applications are

gien "able 0ollowing are somecommentsabo#tseeral thermosettingplastics liste' in "able Phenolics

6henolics also *nown as ;a*elites are the ol'est famil& of thermosetting plastics. "he most important  phenolic materials is the pol&formal'eh&'es. 1. Polformal*eh*e (P')

6henolics are base' on phenol an' formal'eh&'e that2s wh& the& are also terme' as phenol foormalal'eh&'es (60). "mino'ormal*eh*e Materials

"hese thermoset high pol&mers contain an amino gro#p (,@7A) con'ense' with al'eh&'es. "he most important of amino,formal'eh&'e pol&mers are #rea formal'eh&'e an' melamine formal'eh&'e. 1. ,rea formal*eh*e (,') Brea formal'eh&'eis pro'#ce'b&con'ensing #rea monomerswith formal'eh&'e. !. Melamine formal'eh&'e (M0) Melamine formal'eh&'e is pro'#ce' b& con'ensing melamine monomerswith formal'eh&'e. +haracteristics of M0s : "he general properties of Inelamine formal'eh&'e(M0) materials are similar to those of #rea formal'eh&'e (B0) materials. ;#t the M0s hae a better resistance to heat an' can be #se' at temperat#res of #pto C5+. 6ol&#rethanes (6B)

6ol&#rethane is a fami Iy name gien to a series of pol&mers that are pro'#ce' b& the reaction between aromatic 'i,isoc&anates an' low molec#lar weight pol&mer molec#les. Depen'ing on the 'egree of form#larion the #rethanes behae as thermosetting pol&mers thermoplastic pol&mers or elastomers