SAE TECHNICAL PAPER SERIES 2002-01-1318 Intumescent Thermoplastic Elastomer Fire Shield Material Ismat A. Abu-Isa Delphi Research Labs SAE 2002 World Congress Detroit, Michigan March 4-7, 2002 400 Commonwealth Drive, Warrendale, PA 15096-0001 U.S.A. Tel: (724) 776-4841 Fax: (724) 776-5760 The appearance of this ISSN code at the bottom of this page indicates SAE’s consent that copies of the paper may be made for personal or internal use of specific clients. This consent is given on the condition, however, that the copier pay a per article copy fee through the Copyright Clearance Center, Inc. Operations Center, 222 Rosewood Drive, Danvers, MA 01923 for copying beyond that permitted by Sections 107 or 108 of the U.S. Copyright Law. This consent does not extend to other kinds of copying such as copying for general distribution, for advertising or promotional purposes, for creating new collective works, or for resale. 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Persons wishing to submit papers to be considered for presentation or publication through SAE should send the manuscript or a 300 word abstract of a proposed manuscript to: Secretary, Engineering Meetings Board, SAE. Printed in USA 2002-01-1318 Intumescent Thermoplastic Elastomer Fire Shield Material Ismat A. Abu-Isa Delphi Research Labs Copyright © 2002 Society of Automotive Engineers, Inc. ABSTRACT mechanical strength so that it will not break or crumble by disturbances that sometimes occur during fires. The intumescent material described in this paper Some degree of mechanical strength will insure physical expands under high heat or fire conditions to form an integrity during fire and effectiveness as a barrier. insulating sponge. Its composition is based on a blend of high-density polyethylene and chlorinated The intumescent material presented in this report could polyethylene. The material is processed using normal be used to replace existing plastic parts in cars, or as a plastic techniques. Tensile properties, heat aging, fluid cover layer or shield to protect other plastic parts. aging, and thermal properties have been evaluated and Similarly, it can be used to manufacture components for are presented. Fire testing using a 1000 °C Bunsen other industries, such as transportation, shipping, burner as a source, showed that the material does not industrial buildings, residential buildings, office and drip or burn through, even after 30 minutes of exposure. home furniture. In the market place most commercial Prototype fire shields made of the intumescent material grades of intumescent materials are available either in have been tested on fuel tanks, bulkheads, and wheel the form of coatings [1, 2] or paper-like composite well covers. In all cases the intumescent material products [3]. provided excellent protection. Similar applications are identified for airplanes, motorcycles, industrial and EXPERIMENTAL residential buildings. The material is recyclable and can be made from recycled polymers. A - OVERALL COMPOSITION OF THE INTUMESCENT MATERIAL INTRODUCTION The intumescent material is based on high-density polyethylene as the hard phase of the thermoplastic Thermoplastic elastomers are a family of materials that elastomer and chlorinated polyethylene and/or silicone have the properties of elastomers, but can be processed rubber as the soft phase. The composition also contains as plastics. Being elastomeric they have the desirable fillers, thermal stabilizers, fire retardant additives, properties of flexibility, impact resistance, shock blowing agents and char forming additives [4]. All absorption, and sound and vibration reduction. They can ingredients were used as received except that some be formed by compression molding, injection molding, were dried in an oven before processing. extrusion, vacuum forming and blow molding. Thermoplastic elastomers are recyclable, allowing in- B - MIXING THE COMPOSITION plant scrap generated during processing to be chopped up and used to make parts. An intumescent material In the laboratory, the melt mixing of compositions was made of thermoplastic elastomer would then provide fire conducted using two techniques: a two-roll heated mill, shielding and would be easily made into parts for and a Brabender extruder having a mixing screw with a automotive and other industrial and residential length to diameter ratio of 20 to 1. In addition to applications. laboratory mixing, 8000 lb. batches of the material were compounded in the plant using a 3.5-inch diameter Intumescent materials expand and char when exposed single screw extruder having an L/D ratio of 11. to fire and form a heat resistant spongy barrier that will reduce the transfer of heat to neighboring objects and reduce the progress of fires. It is desirable that this thermally stables spongy structure have some C - PROCESSING OF THE COMPOSITION modulation is achieved by imposing a sine wave input on the underlying constant rate. Applying Fourier Extrusion, compression molding, injection molding, and transform analysis on the output signal from the MDSC, vacuum forming were used to process the intumescent one is able to discern between thermodynamically material in order to make samples for laboratory testing reversible changes and non-reversible kinetic changes and to form prototypes for in-service field testing. as the polymer is being heated. The reversing heat flow is used as a direct measurement for heat capacity. This D – MECHANICAL PROPERTIES TEST is of primary interest to the work in this report since heat PROCEDURES capacity and thermal conductivity are related properties [6]. The tensile properties of compression molded and injection molded samples of intumescent material were Typically, a polymer sample in pellet form weighing obtained using ASTM D638 procedures. The tear approximately 10 mg was placed in an aluminum pan properties of the samples were obtained using and hermetically sealed. The pan containing the sample procedures outlined in ASTM D624. The flexural was then placed in the MDSC nitrogen-purged cell. The properties were determined per ASTM D790 sample was allowed to equilibrate at -60°C for five procedures. minutes, before starting programmed heating at 5°C per minute to 350°C. During the run, modulation of +/- 0.5°C E – CHEMICAL RESISTANCE TEST PROCEDURES was programmed at time intervals of 40 seconds. MDSC measurements were used to determine the The chemical resistance of the intumescent material to melting temperature (Tm), the glass transition automotive fluids was investigated per GM engineering ∆ temperature (Tg), heat of fusion ( Hf) and the heat test specification 2217M. In separate experiments, capacity (Cp) of the different Intumescent material samples were immersed in water, 5% by weight salt formulations. water, engine coolant, premium diesel fuel, hydraulic brake fluid, windshield washer solution, and automatic G – FLAMMABILITY APPARATUS FOR MEASURING transmission fluid, for four hours at 25°C. The degree of INTUMESCENCE swell by the fluids and the tear strength of the material, before and after exposure were measured. The intumescent flammability test apparatus is shown in Figure 1. It consists of a three walled chamber having a F – THERMAL ANALYSIS left side wall, a back wall, and a right side wall. Each wall is a steel plate 229 mm high, 127 mm wide, and 1 Thermal gravimetric analysis (TGA), differential mm thick. A 152 mm x 152 mm x 1mm steel plate was scanning calorimetry (DSC), and thermal conductivity employed as a roof member. The intumescent material measurements were carried out using procedures test sample is affixed to the lower surface of the roof previously developed for investigating thermal and plate for exposure to flame. Six thermocouples were flammability properties of automotive polymers [5-8]. welded on the topside of the plate to monitor High-resolution TGA measurements were conducted temperatures during the flammability test. Flame using the TA Instrument 2100 module. These analyses temperatures were measured using a thermocouple were carried out using 13 to 15 mg samples. The placed through the back wall at a location corresponding samples were heated from 25 to 1000°C using a linear to the blue flame region of the burner. A 165-mm tall heating rate of 50°C /min., and a resolution factor of Bunsen burner was used as the flame source. The four. All runs were conducted in nitrogen or air flame height above the burner was 60 mm, and was atmospheres at a flow rate of 50 ml /min. Decomposition adjusted so that the tip of the inner blue cone of the temperature, weight loss percent and weight loss rate flame touched the surface of the intumescent material. were determined for each decomposition peak. The Burning tests were carried out for 30 minute. amount of residue left after heating the sample to 900°C was also determined. RESULTS AND DISCUSSION DSC measurements were used to quantitatively DEVELOPMENT OF THE INTUMESCENT MATERIAL: determine thermal events. The apparatus used was the modulated DSC manufactured by TA Instrument (MDSC The base resin is a thermoplastic elastomer consisting 2920). The technique is relatively new. Conventional of polyethylene and chlorinated polyethylene and/or DSC is a device for measuring the heat flow into and out silicone rubber.