Poly stress-strain behaviour

Stress-strain behaviour of poly(methyl methacrylate) is shown in Fig. 13.65 at various temperatures. At low temperatures the polymer behaves brittle (at this rate of deformation) and at high temperatures ductile. At 40 °C a transition from brittle to ductile... 

Cail, J.J., Stepto, R.F.T. and Ward, I.M. (2007) Experimental studies and molecular modelling of the stress-optical and stress-strain behaviour of poly(ethylene terephthalate). Part 111 Measurement and quantitative modelling of birefringence-strain, stress-strain and stress-optical properties. Polymer, 48, 1379. 

Fig. 5.24 Variation of the stress-strain behaviour of poly (methyl methacrylate) with temperature (after Andrews).

The mechanical and thermal properties of a range of poly(ethylene)/po-ly(ethylene propylene) (PE/PEP) copolymers with different architectures have been compared [2]. The tensile stress-strain properties of PE-PEP-PE and PEP-PE-PEP triblocks and a PE-PEP diblock are similar to each other at high PE content. This is because the mechanical properties are determined predominantly by the behaviour of the more continuous PE phase. For lower PE contents there are major differences in the mechanical properties of polymers with different architectures, that form a cubic-packed sphere phase. PE-PEP-PE triblocks were found to be thermoplastic elastomers, whereas PEP-PE-PEP triblocks behaved like particulate filled rubber. The difference was proposed to result from bridging of PE domains across spheres in PE-PEP-PE triblocks, which acted as physical crosslinks due to anchorage of the PE blocks in the semicrystalline domains. No such arrangement is possible for the PEP-PE-PEP or PE-PEP copolymers [2]. 

Figure 5. Tensile behaviour to point of ftacture for 85% kraft lignin-based thermoplastic blends with poly(vinyl acetate) in presence of diethyleneglycol dibenzoate (1.6%) and indene (0.8%). Stress-strain a-e curves determined for material test pieces at strain rate of 4.5 x 10" sec" graphical data from reference 1.

Generally large yield stress effects were dominant in the nematic melts, but they were strongly pre-history dependent. A three region flow curve for 15 mol % modified poly(pheny1-1,4-phenylene terephthalate) was probably due to a not completely molten system. Dynamic viscosity measurements showed strong pseudoplastic behaviour. Strain and time dependence phenomena were not observed. 

Boneva D, Balt Calleja F J, Fakirov S, Apostolov A A and Krumova M (1998) Microhardness under strain 3. Microhardness behaviour during stress-induced polymorphic transition in blends of poly(butylene terephthalate) and its block copolymers, J Appl Polym Sci 69 2271-2276. 

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