Glassy polymers polycarbonate

Figure 5. Correlation of the apparent solubility at 20 atm and 35 °C with the critical temperatures of various penetrants in a number of glassy polymers polycarbonate,...

This relationship graphic interpretation for amorphous glassy polymers -polycarbonate (PC) and polyarylate (PAr) - is adduced in Fig. 1.1. Since at r = r (T ) (where T, T and are testing, glass transition and melting temperatures, accordingly) AG =0[10 11], then from the Eq. (1.1) it follows, that at the indicated temperatures cluster structure full decay (9, = 0) should be occurred or transition to thermodynamically equilibrium structure. 

FIGURE 1.1 The dependence of clusters relative fraction j, on absolute value of specific Gibbs function of nonequilibrium phase transition AG" for amorphous glassy polymers -polycarbonate (1) and polyarylate (2) [3],... 

The authors of Refs. [7, 8] considered the typical amorphous glassy polymer (polycarbonate) structure change within the frameworks of solid body synergetics. 

The process of blending with another glassy polymer to raise the heat distortion temperature is not restricted to polycarbonate, and the polysulphones are obvious candidates because of their higher Tg. One blend has been offered (Arylon T by USS Chemicals) which has a higher softening point than the ABS-polycarbonates. 

Kambour, R. P. and Gruner, C. L., Effects of polar group incorporation on crazing of glassy polymers styrene-acrylonitrile copolymer and a bisphenol polycarbonate, J. Polym. Sci., Polym. Phys. Ed., 16, 703 (1978). 

This was originally a very slow batch process, because of the need to dissolve gaseous CO2 in solid glassy polymers such as polycarbonate and polystyrene. The low diffusivity meant that the time taken was many hours. The foam was formed when there was a phase change from the glassy to the melt state. In recent developments of the process, supercritical CO2 (for temperatures >31 °C, and pressures >7.2 MPa) is... 

The density or its reciprocal, the specific volume, is a commonly used property for polymeric materials. The specific volume is often plotted as a function of pressure and temperature in what is known as a pvT diagram. A typical pvT diagram for an unfilled and filled amorphous polymer is shown, using polycarbonate as an example, in Figs. 2.10 and 2.11 The two slopes in the curves represent the specific volume of the melt and of the glassy amorphous polycarbonate, separated by the glass transition temperature. 

The criteria (Eqs. 11 and 12) are similar and are derived from studies on materials that are elastic at initiation of crazing, while more ductile materials like polycarbonate show a more pronounced sensitivity to the hydrostatic tension. This has been found experimentally by Ishikawa and coworkers [1, 27] for notched specimens of polycarbonate. Crazing appears ahead of the notch root, at the intersection of well-developed shear bands. From a slip fine field analysis, the tip of the plastic zone corresponds to the location of the maximum hydrostatic stress. This has been confirmed by Lai and Van der Giessen [8] with a more realistic material constitutive law. Therefore, Ishikawa and coworkers [1,27] suggested the use of a criterion for initiation based on a critical hydrostatic stress. Such a stress state condition can be expressed by Eq. 11 with erg = 0 and I r = B°/A°. Thus, the criterion (Eq. 11) can be considered general enough to describe craze initiation in many glassy polymers. For the case of polycarbonate, a similar criterion is proposed in [28] as... 

Glassy polymers with highercohesiveness, like polycarbonate and cross-linked epoxies, preferentially exhibit shear yielding [7], and some materials, such as rubber-modified polypropylene, can either craze or shear yield, depending on the deformation conditions [8]. Application of a stress imparts energy to a body which... 

For ionomer samples with high ion content (more than 6 mol %), it is noted that fewer crazes are formed, and the direction of some of these is not perpendicular to the stress axis (Fig. 26a). Also, bifurcation of crazes is observed (Fig. 26b). In addition to these anomalies in craze structure, some shear character, such as localized shear deformation, also appears (Fig. 27a). For comparison, a TEM micrograph taken for a polycarbonate (PC) sample under the same experimental conditions is shown in Fig. 27b. PC is known to deform by shear deformation at room temperature In Fig. 27b, it is seen that shear bands are formed at approx. 45° to the stress direction. Similar structural features, although in smaller degree, are seen for ionomer samples with high ion content (Fig. 27a). Also, in these samples interactions between crazes and shear bands are noted (for example. Fig. 26a). Interaction effects have also been observed in other glassy polymers... 

Glassy polymer-diluent mixtures deformed in a temperature range close to are susceptible to exhibit a cavitational mode of plasticity at hi stresses and strains. Activation of this mechanism in mixtures of polycarbonate with esters of the phthalic acid results in extensive fibrillation and stress whitening of the material. There is strong evidence that the diluent plays an important role in enhancing chain slippage, which is required for the formation of craze fibrils. One of the most fundamental problems which is still unsolved is the elucidation of the molecular mechanism by which diluents become active. 

The fracture process is investigated for two glassy polymers polymethyl methacrylate (PMMA) and polycarbonate (PC) which are generally thou t to show a brittle and a ductile response respectively and thus selected to illustrate the method. These materials consist of commercial sheets (from Goodfellow) of 10 mm thickness which ensures plane strain conditions for both materials. Caution about plane strain conditions concerns primarily PC which is prone to develop plasticity and a 10 mm thickness appears reasonable according to analysis of the influence of the thickness on its toughness found in [6, 7]. 

J. S. Royal and J. M. Torkelson, Photochromic and fluorescent probe studies in glassy polymer matrices. 5. Effects of physical aging on bisphenol-A polycarbonate and poly(vinyl acetate) as sensed by a size distribution of photochromic probes, Macromolecules 25, 4792-4796 (1992). 

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