Effect of Particle Size of Additives on the Flammability and Mechanical Properties of Intumescent Flame Retarded Polypropylene Compounds

Katalin Bocz,Tamás Krain,György Marosi

doi:10.1155/2015/493710

Abstract

The effect of particle size reduction of the components of a common intumescent flame retardant system, consisting of pentaerythritol (PER) and ammonium polyphosphate (APP) in a weight ratio of 1 to 2, was investigated on the flammability and mechanical performance of flame retarded polypropylene (PP) compounds. Additives of reduced particle size were obtained by ball milling. In the case of PER, the significant reduction of particle size resulted in inferior flame retardant and mechanical performance, while the systems containing milled APP noticeably outperformed the reference intumescent system containing as-received additives. The beneficial effect of the particle size reduction of APP is explained by the better distribution of the particles in the polymer matrix and by the modified degradation mechanism which results in the formation of an effectively protecting carbonaceous foam accompanied with improved mechanical resistance. Nevertheless, 10% higher tensile strength was measured for the flame retarded PP compound when as-received APP was substituted by milled APP.

Highlights

In parallel with the continually increasing use of plastics, the issue of fire safety has come to the forefront
It was concluded that the particle size of the flame retardant additives has a significant impact on both the flammability and mechanical performance of intumescent flame retarded compounds
Depending on the particle size and the distribution of the two flame retardant components (PER and ammonium polyphosphate (APP)) in the polymer matrix their reaction pathway and degradation mechanism may change; carbonaceous chars of different composition and structure can be obtained from the PER/APP system, significantly differing in flame retarding performance

Summary

Introduction

In parallel with the continually increasing use of plastics, the issue of fire safety has come to the forefront. Among the commercially available halogen-free flame retardants, the so called intumescent flame retardant (IFR) systems have gained increasing interest due to their low toxicity and smoke production in fire accidents. The fire retardant mechanism of IFRs involves the formation of an expanded charred foam layer on the polymer surface, which acts as a heat insulator, limiting the heat transfer from the heat source to the polymer and the mass transfer from the polymer [5,6,7]. The intumescent formulations are composed of three main ingredients: acid source, char forming agent, and blowing agent [8]. Xia et al [10]

Methods

Results

Conclusion