Presentation on theme: "Characterization, applications"— Presentation transcript:
1 Characterization, applications CHAPTER 15Characterization, applicationsand processing of Polymers
2 Mechanical Characteristics of Polymers v.sensitive to TEMPERATURESTRAIN RATEENVIRONMENT(presence of water, O2, solvents)Stress at which fracture occursModulus of Elasticity =Tensile modulus = modulusFor polymers: 7 MPa- 4GPaMetals: GPa
3 Three typical types of stress strain curves are found for polymers Polymers can experience elongationsup to 1000%Metals typically 100% maximum.
5 Effect of TemperaturePMMATensile modulusElongationStrength
6 Effect of Molecular weight Constant FACTORS INFLUENCING MECHANICAL PROPERTIES OF POLYMERSExtensive chain entanglement or significant molecular bonding= increase in modulus and strengthEffect of Molecular weightConstantTS = TS – AMnTensile strength at infinite molecular weightTS increases with increase in molecular weight, WHY????Increasing chain entanglement
7 DEGREE OF CRYSTALLINITY Important since affects extent of intermolecular secondary bondingTensile modulus increases with increase in degree of crystallinityAs crystallinity increases polymer more brittle
8 CRYSTALLIZATIONOccurs by nucleation and growth of ordered and aligned chainfolded layers from random and tangled molecules in the melt.
9 Tm - occurs in crystalline polymers MELTING POINT Tm and GLASS TRANSITION TEMPERATURE TgTm - occurs in crystalline polymersTg - occurs in amorphous and semi-crystalline polymers
10 From ordered to disordered state. MELTING POINTFrom ordered to disordered state.Requires rotation and movement of ordered moleculesCHAIN STIFFNESSControlled by ease of rotation about chemical bonds along he chainDouble bond chains and aromatic groups reduces chain flexibility increases TmSize and type of side group affect chain rotational freedom and flexibilityTm increases with increase in Molecular weight (chain length).Why is there a range of Tm rather than a single temperature???
11 e.g. Polypropylene (Tm = 175 oC), Polyethylene(Tm = 115 oC) Polyethylene MERPolypropylene MERHHHH- C – C -- C – C -HHH- C -HHHLarger side groupTg affected in similar way to Tm
14 Repeatable and reversible THERMOPLASTIC AND THERMOSETTING POLYMERSClassification according to mechanical response at elevated temperaturesTHEMOPLASTICTHEMOSETRepeatable and reversibleprocessesHeating = harden polymer cross-linkingSecondary bonding decreases with increasedTemp. due to increased molecular motion10-50% of mers x-linkedMOST LINEAR & SLIGHTLY BRANCHEDPOLYMERSX-lined and network polymerse.g. Epoxy
15 If plastic is x-linked and used above Tg = good elastomer POLYMER TYPESPLASTICS- ELASTOMERS (RUBBERS)- FIBERS, COATINGS, ADHESIVE,FOAMS, FILMS.If plastic is x-linked and used above Tg = good elastomerPLASTICSMajority of polymerse.g. Polyethylene, Polypropylene, PVC, Polystyrene, fluorocarbons, epoxies,polyesters.Brittle and flexible, linear , branched, thermoplastic, thermosetting etc.Fluorocarbons = low coeff. Of friction, extremely resistant o chemical attack Used as coating in cookware.Optical applications = PMMA, polystyrene