Polycarbonate yield sensitivity

It was pointed out earlier that photosensitivity may be realized not only by the inclusion of dyes in a polymer matrix, but also by means of multilayered system production. For TPA dispersed in a polycarbonate, sensitized by a thin layer of vacuum-deposited amorphous selenium, the quantum yield was equal to 0.7 at the electric field strength 6 x 10s V cm-1 [308]. The photoinjection efficiency of holes into polymer was equal to the efficiency in pure selenium. The spectra of the quantum efficiency is shown in Fig. 54. 

Polycarbonates are processed at very elevated temperatures (>300 °C) so that hydrolysis of the carbonate linkage to yield carbon dioxide and a phenol end group can occur if the polymer is not rigorously dried (residual water <0.02 wt.%). Complex chemistry can follow (Scheirs, 2000), resulting in the formation of low-molar-mass species and darkening of the polymer in addition to chain scission. The degradation is very sensitive to trace acidic or basic impurities, and it has been noted that in blends (e.g. PC/ABS) there may be initiation of the degradation by impurities in the ABS (Cook et al, 1996). 

One common stress concentrator is a notch, since polycarbonate is very notch-sensitive. For example, a polycarbonate resin bar that has a notch with a 0.254-mm (0.010-in) radius will break with yield under lower forces when bent in the center compared to an unnotched bar. The material is not brittle however, the notch concentrates stress to a value above the typical 66.2-MPa (9600-psi) flexural strength of polycarbonate, and it breaks more easily. The sharper radius concentrates the deformation across a... 

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