A simple method for the assessment of molecular orientation in transparent plastics mouldings

A simple practical method for assessing the principal birefringences of a transparent or translucent moulding as a function of depth has been developed. The results obtained on a number of poly(ethylene terephthalate) and polycarbonate mouldings have been used to characterise and quantify the optical anisotropy and hence the molecular orientation or residual stresses. The results are largely free from the distorting effects of optical dispersion of birefringence and specimen preparation. They highlight the hazards of estimating stresses or orientation from the observation of an unprepared moulding between crossed polars. They also agree with the published data on the distribution of birefringence through injection moulded plaques.