The composition and microstructure of a blend of bisphenol‐A polycarbonate (PC) and poly (butylene terephthalate) (PBT) have been established by a variety of physical methods. The composition was established by solvent extraction and infra‐red spectrophotometry, while the microstructure was determined by these and the additional methods of differential scanning calorimetry and dynamic mechanical thermal analysis. The PBT retained its crystallinity in the commercial blend, (Xenoy CL‐100), but blending reduced the main glass‐rubber transition of the PC from 147°C to approximately 100°C. Conditioning of the blend at high temperatures resulted in progressive transesterification: 3 minutes at 240°C gave a small but significant effect, while 30 minutes at 270°C yielded large changes in the structure. These findings are important in respect of processing the material, and the limitations which might be incurred in plant recycling of scrap.

Improved products can be obtained from sheet molding compounds (SMC) if due regard is given to the geometry of the molding charge relative to the product shape. For example, it is possible to position designed charge shapes in the mold to produce moldings without weld‐lines and without substantially altering the initial fiber orientation of the SMC matrix. This paper describes theoretical and experimental work which has developed a charge shape calculation procedure for molding two‐dimensional SMC components weld‐line free without substantially altering the SMC‐matrix glass fiber orientation. The two main parts of the work are; (i) The theoretical development of a charge shape calculation procedure for molding symmetrical and unsymmetrical plaques. This includes a mathematical description of the compression flow process, which is used to determine flow front development from mold‐cavity pressure and velocity distributions. (ii) The results of experimental work which test the mathematical description of the compression flow process, and charge shape calculation procedure. These results include mold pressure measurements from an instrumented mold, fiber distribution and orientation measurements, and SMC‐material tensile strength properties.

This paper presents a theoretical and experimental analysis of the rheological behavior of sheet molding compound (SMC). The work analyses the squeeze flow in a parallel plate plastometer of SMC discs which contain 25 percent of fiber glass by weight. This method of flow characterization gives a good insight into the basic rheological behavior of SMC for the compression molding process when producing flat parts. The theoretical analysis applies to thickened and matured SMC at room temperature. The analysis treats SMC as a viscoelastic material having an equation of state with viscous, elastic and yield elements. The time variation of compressive force when squeezing SMC discs between two parallel plates (one fixed and one mobile) has been derived from the equation of state. The values of the viscous, elastic and yield parameters were determined by using a least squares method of curve fitting to the experimental results. There are two aspects to the reported experimental work. One aspect is concerned with showing that the three element model for the equation of state provides a realistic mathematical basis for characterizing the rheological behavior of SMC at room temperature. The other shows how the parallel plate plastometer can be used to give data which characterize SMC flow behavior under conditions similar to those of the actual compression molding process.

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The paper puts forward a system of magnitudes for characterizing the optical properties of polymeric materials or, in general, inhomogeneous media.Two categories of magnitudes can be distinguished: those which depend on the average value of the molecular parameters (describing refraction phenomena) and those which depend on the degree of inhomogeneity of the medium (describing scattering properties). The characteristics in the second category are subsumed under the headings `transparency' and `light transfer'. The magnitudes thought appropriate are defined and discussed. The experimental methods for the determination of the transparency and transfer properties are also presented.