The rheological and mechanical properties of composites of two crystalline polymers, high density polyethylene (HDPE) and poly-propylene (PP), and two liquid crystalline low molecular weight additives, tere-phthal-bis-(4-n-butylaniline) (TBBA) and p-p'-azoxyanisol (PAA), have been studied. An experimental investigation has been carried out to verify whether the rigid rob type additives can enhance the orientation of the matrix polymers.
The rhological and mechanical properties of the composites were measured for various additive concentrations, 1, 3, 5, 10 and 15 weight percents. The composites were prepared by mixing the polymers and the additives with a roller mixer.
Good compatibilities between the matrix polymers and the additives were observed by a differential scanning calorimetry for additive concentrations less than 10 weight percents. The rheological properties of the composites showed that the additives behave as plasticizer decreasing shear viscosities and dynamic moduli in melt state. In order to elucidate the effects of the xliquid crystalline additives upon the orientation and crystallinity of the matrix polymers during processing, yield tensile strengths and the degrees of orientation angle for specimens prepared both by extrusion and by injection molding were measured with a Instron tensile tester and a X-ray diffractometer. The experiments reveal that the yield strengths and the degrees of orientation of the specimens for the additive concentrations of 1, 3 and 5 weight percents are greater than those of pure polymers and show a maximum in the vicinity of 3 weight percent.
These results showed that the rigid-rod type low molecular weight additives can be used as molecular fillers with plasticizing effects for crystalline polymers.
