Mechanical Property Enhancement of Semi-Crystalline Polymers by Solid State Rolling

Abstract

Calendering of molten thermoplastics is frequently used to produce sheet materials of uniform thickness. The mechanical and chemical properties of such sheets are those inherent to the basic isotropic material. If semicrystalline polymers are rolled into sheets at temperatures below their melting point, significant molecular orientation takes place. Mechanical property enhancement and improved chemical stability then accompany good thickness control in the oriented sheet. In a series of experiments with high-density polyethylene and polypropylene, tensile moduli and tensile strengths as high as 8.7 GPa and 300 MPa, respectively, have been obtained. Output speeds as high as 20 m/min are easily reached. Chemical and dimensional stability in hot polybutene oil has been demonstrated. Less than 2 percent change in weight, thickness, or length of samples has been observed after 5000 hr exposure in the oil at 100°C. The most critical factors in obtaining and controlling these properties are roll temperature and degree of thickness reduction obtained during rolling. Property control and reproducibility have been shown to be good.