Effect of nucleating agents and pigments on crystallisation, morphology, and mechanical properties of polypropylene

Polypropylene is increasingly being used for the thermoforming of food packaging. Compared with amorphous materials, such as polystyrene, it is much more difficult to process and within the industry it is generally poorly understood. In the present study the effects of pigments and nucleating agent on the crystallisation, morphology, and mechanical properties of an un-nucleated isotactic polypropylene (iPP) have been investigated. Results were compared with those obtained for a grade of iPP containing a proprietary nucleating agent. Quinacridone red pigment was found to be almost as efficient a nucleating agent as a standard nucleating agent, Millad 3988, and both of these were superior in performance to the iPP containing the proprietary agent. The white pigment (White PE MB) was found to be a nucleating agent for β-crystals. Young's modulus and yield stress increased with increasing crystallinity and increasing α-crystal content. Elongation at break increased with increasing β content.