Mechanism of Strength Improvement of Foamed Plastics Having Fine Cell

Abstract

The influence of cell size on tensile fracture strength of foamed plastics is examined in this study. Foamed specimens having various cell sizes with the same foaming magnification are molded. The tensile fracture strength of foamed plastics is measured and the relationship between the cell size and tensile fracture strength is discussed. It is found that the tensile fracture strength of foamed polyethyleneterephthalate and polypropylene which are crystalline resins increases with decrease in cell size more than the strength presumed from the foam magnification. The decrease in cell size results in an increase in cell density. An increase in cell surface area causes molecular orientation thereby effecting strength improvement.