Halogenated and Non-Halogenated Flame Retardant Additives in Polypropylene (PP) Homopolymer for Battery Applications

Abstract

The paper describes how to make PP homopolymer flame retardant through the use of halogenated and halogen-free additives. The paper attempts to capture the intricacies involved in compounding recipe development, physical and mechanical properties and performance aspects during injection moulding of the final article. In a nutshell, the paper describes the end user's experience of flame retardant additives in PP homopolymer from concept to product. The present work was directed towards compound development and the characterization of physical, mechanical, flammability performance and performance during the injection moulding of PP homopolymer. The application identified was injection mouldable battery boxes for applications in the telecom sector. PP compounds were prepared from halogen-based and halogen-free flame retardant (FR) additives, designed to meet V0 at 3.2 mm thickness as per the UL94 test protocol. Flame retardant polypropylene; (FR-PP) is used for “back-up” batteries. These are used in telecommunications and railway units and supply energy immediately in the case of an interruption of normal power supply. The batteries contain sulphuric acid as electrolyte. Experimental work was undertaken to develop FR-PP compounds and investigate the effect of FR additives on critical properties. The effect of FR-additives on the heat sealing properties of battery containers was also investigated. The results show that halogenated FR additives can contribute to the excellent acid resistance of PP. Use of non-halogenated FR additives in PP resulted in compounds having densities close to 1.0 g/cm3, at identical loadings to those used with halogenated FR additives. In comparison, FR-PP compounds based on halogenated FR additives gave densities close to 1.2 g/cm3. The data obtained from this investigation show that both types of FR/PP compounds are suitable for battery box applications made by injection moulding.