Polystyrene mechanical behavior

Since the compliance is essentially the inverse of the modulus, it is not surprising that the same four regions of mechanical behavior show up again here. The data for polystyrene is more fully developed, so we shall examine if. 

The mechanical properties of Shell Kraton 102 were determined in tensile creep and stress relaxation. Below 15°C the temperature dependence is described by a WLF equation. Here the polystyrene domains act as inert filler. Above 15°C the temperature dependence reflects added contributions from the polystyrene domains. The shift factors, after the WLF contribution, obeyed Arrhenius equations (AHa = 35 and 39 kcal/mole). From plots of the creep data shifted according to the WLF equation, the added compliance could be obtained and its temperature dependence determined independently. It obeyed an Arrhenius equation ( AHa = 37 kcal/mole). Plots of the compliances derived from the relaxation measurements after conversion to creep data gave the same activation energy. Thus, the compliances are additive in determining the mechanical behavior. 

A good dispersion of rubber particles appears to favor the nucleation and growth of a large number of thick crazes uniformly distributed in the polystyrene matrix. This is believed to be an efficient source of energy absorption for the material under mechanical loading. The concepts of stress field overlap and critical volume of stress concentration zone for craze initiation were introduced to explain the observed mechanical behavior of HIPS. 

Similar stress-strain curves have been obtained for polystyrene crazes. However, these results do not necessarily reveal the real mechanical behavior of the craze. The removal of the solvent from samples will cause shrinkage and have a significant plasticizing effect on the craze fibrils. This has to... 

The relative amounts of the two monomers used in the synthesis determine the relative size of the two blocks or the composition of (BAB)X. This in turn determines whether mechanical behavior resembles that of thermoplastics or thermoplastic elastomers. The greater the polystyrene content, the greater the initial modulus and yield point of the block copolymer. Overall composition thus tends to dominate the parameters discussed above. At a given level of polystyrene the... 

As shown above (Section 8.4), the IPN s prepared from polybutadiene/ polystyrene combinations are much tougher than the corresponding graft copolymers (Curtius et a/., 1972). More recently, the mechanical behavior of the IPN s and semi-IPN s was compared (Donatelli et u/., 1974ft) (see Figure 8.27). While all materials exhibited a yield point, the (full) IPN exhibited slightly better mechanical properties than the semi-IPN of the first kind, and much better properties than the semi-IPN of the second kind. The IPN s exhibited Charpy impact strengths of 5-6 ft-lb/in. of notch. 

Antich P, Vazquez A, Mondragonb I et al (2006) Mechanical behavior of high impact polystyrene reinforced with short sisal fibers. Compos A 37 139-150... 

The papers read showed that, for application at low temperatures down to 4 K, the most critical properties of nonmetallic materials are their flexibility and resultant mechanical behavior, their coefficients of thermal expansion as compared with that of the inorganic materials with which they are combined, and their thermal conductivity. At present, the leading pol3nneric materials for low-temperature applications are epoxy resins, polypropylene, and polyimide strips and films, and polystyrene and polyurethane based foams. The leading fibers for reinforcement are glass, graphite, boron, and organic polyaramid. 

N. Devia-Manjarres, Synthesis and Characterization of Simultaneous Interpenetrating Networks Based on Castor Oil Elastomers and Polystyrene, Diss. Abstr. Int. B 39(8), 3972 (1979). Castor oil-polyester/PS SIN. Synthesis, morphology, mechanical behavior. Ph.D thesis. 

A. A. Donatelli, L. H. Sperling, and D. A. Thomas, Interpenetrating Polymer Networks Based on SBR/PS. 2. Influence of Synthetic Detail and Morphology on Mechanical Behavior, Macromolecules 9(4), 676 (1976). SBR/Polystyrene IPN. Mechanical Properties. 

S. C. Kim, D. Klempner, K. C. Frisch, H. L. Frisch, and H. Ghiradella, Polyurethane-Polystyrene Interpenetrating Polymer Networks, Polym. Eng. Sci. 15(5), 339 (1975). Polystyrene/polyurethane SINs. Phase Separation. Tg and mechanical behavior. 

Copolymers of Styrene and Divinj benzene, Rubber Chem. Tech. 40, 476 (1967). Homo-IPNs of polystyrene and polystyrene. Swelling and mechanical behavior. 

L. H. Sperling and D. W. Friedman, Synthesis and Mechanical Behavior of Interpenetrating Polymer Networks Poly(ethyl acrylate) and Polystyrene, J. Polym. Sci. A-2 7, 425 (1969). Synthesis of sequential IPNs. Modulus-temperature behavior. Modulus-composition behavior. 

L. H. Sperling, J. A. Manson, G. M. Yenwo, N. Devia-Manjarres, J. Pulido, and A. Conde, Novel Plastics and Elastomers from Castor Oil Based IPN s A Review of an International Program, in Polymer Alloys, D. Klempner and K. C. Frisch, eds.. Plenum, New York (1977). Castor oil-urethane/polystyrene sequential IPNs. Synthesis, morphology, and mechanical behavior. Fatigue behavior. 

The quantity RllM Y is Rg in A, a measure of chain stiffness. For example, polycarbonate, with (RpM y = 0.457, is stiffer than polystyrene, which has a value of 0.275. The importance of these quantities lies in their relation to physical and mechanical behavior. Both melt and solution viscosities depend directly on the radius of gyration of the polymer and on the chain s capability of being deformed. The theory of the random coU (Section 5.3), strongly supported by these measurements, is used in rubber elasticity theory (Chapter 9) and many mechanical and relaxation calculations. 

Figure 8.29 Dynamic mechanical behavior of polystyrene-Wocfc-polybutadiene-Woc/f-polystyrene, a function of the styrene-butadiene mole ratio (123,124).

The relaxation behavior of partially crystalline systems is complex and different from amorphous polymers. Observations give the general impression that, in comparison to amorphous systems, partially crystalline samples are much less uniform in behavior. Many of the systems exhibit peculiarities and these can dominate the viscoelastic properties. This is not the place to explore this large field in the necessary depth, which would mean we would have to discuss separately the mechanical behavior of polyethylene, poly(ethylene terephtha-late), polypropylene, it-polystyrene, poly(tetrafluoroethylene) etc. What can be done for illustration is to pick out one instructive example and we select polyethylene. 

Styrene decreases the viscosity of SPS significantly relative to atactic polystyrene and offsets that effect. From a practical standpoint, the dynamic mechanical behavior of SPS reveals that SPS softens appreciably at its glass transition temperature, thus to maintain mechanical strength up to the melting point, the polymer needs to be reinforced. 

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