CL20FunctionalMaterials0290769

CONE CALORIMETER TESTING OF UL-94V RATED

PLASTICS:

EFFECTS OF HEAT FLUX AND SAMPLE THICKNESS

Authors:

Alexander B. Morgan

University of Dayton Research Institute

Nonmetallic Materials Division

Advanced Polymers Group

Dayton, OH 45469-0160

Matthew Bundy

National Institute of Standards and Technology

Building and Fire Research Laboratory

Fire Research Division

Gaithersburg, MD 20899

Abstract

Cone calorimeter continues to be an extensively used tool for studying the flammability of materials, especially flame retarded plastics. Over the course of a NIST project designed to look at the bench scale and full scale performance of UL-94V rated plastics (some data of which was presented at Fire and Materials 2005), a large volume of cone calorimeter data was collected, the results of which are still being analyzed. This paper studies the effects of cone calorimeter heat flux and sample thickness on material heat release rate, and offers some statistical analysis on cone calorimeter measurements.

Materials reported in the paper include high impact polystyrene, polycarbonate, polypropylene, poly(vinyl chloride), poly(acrylonitrile-butadiene-styrene), and polycarbonate/poly(acrylonitrile-butadiene-styrene) blends at UL-94 V-0, V-1, V-2, and “no rating” classifications. Different types of flame retardant mechanism (brominated, non-halogenated, phosphorus) are included in this study as well, but the exact chemical formulations are not reported due to the commercial nature of the materials tested. The cone calorimeter results found overall that not all materials with the same UL-94V rating give the same heat release rate, as this measurement was very polymer and flame-retardant system dependent.

Variations in heat flux and sample thickness showed some very interesting heat release rate phenomena. Some materials had lower heat release rates and longer time to ignition at low heat fluxes, which changed to very different heat release rate curve shapes at higher heat fluxes. Sometimes this was polymer chemistry dependent, but in other cases the flame retardant type was responsible for the observed changes. Sample thickness experiments showed in most cases, going to a thinner sample results in lower peak HRR and total HR, but not always. Some materials which were UL-94 V-0 rated at 3.2mm thickness, but only V-2 at 1.6mm, showed higher peak HRR at 1.6mm thickness than at 3.2mm thickness in the cone calorimeter at 50 kW/m2. This phenomena hints that the cone calorimeter may be able to determine when a

material will be UL-94V rated throughout several thicknesses, and when it is only robust enough to provide UL-94V level of flame retardancy in thick samples.

Finally, statistical analysis of the combined cone calorimeter data collected at 30, 50, and 90 kW/m2 is presented in this paper in a quantitative attempt to correlate cone calorimeter data to UL-94V rating. It was found that some aggregate measurements (such as average heat release rate divided by time to ignition) gave reasonable correlation to UL-94V rating, but that this finding was not universal. In short, the results were best within a polymer class, and not universal to all polymers or flame retardant mechanisms.