Expandable Graphite as a Multifunctional Flame-Retarding Additive for Highly Filled Thermal Conductive Polymer Formulations

Abstract

Expandable graphite (EG) and graphite (G) were assessed as multifunctional additives improving both flame retardancy and thermal conductivity in highly filled, thermal conductive polymeric materials based on polyamide 6 (PA6). Fire testing was conducted using modern UL-94, LOI and cone calorimeter test setups. It is demonstrated that thermal conductivity can significantly influence the time to ignition, although offering little fire resistance once ignited even in highly filled systems. Thus, for PA6 formulations containing solely 70 wt.% G, the peak heat release rate (pHRR) measured in cone calorimeter tests was 193 kW/m², whereas PA6 formulations containing 20 wt.% EG/50 wt.% G did not exhibit a measurable heat development. Particular attention was paid to effect separation between thermal conductivity and residue formation. Good thermal conductivity properties are proven to be particularly effective in test scenarios where the heat impact is comparatively low and the testing environment provides good heat dissipation and convective cooling possibilities. For candle-like ignition scenarios (e.g., LOI), filling levels of >50 wt.% (G or EG/G) are shown to be sufficient to suppress ignition exclusively by thermal conductivity. V0 classifications in UL-94 vertical burning tests were achieved for PA6 formulations containing ≥70 wt.% G, ≥25 wt.% EG and ≥20 wt.% EG/25 wt.% G.

The Impact of β-Radiation Crosslinking on Flammability Properties of PA6 Modified by Commercially Available Flame-Retardant Additives

“…The following chapter focuses on differences in the fire behavior found for flame-retardant non- and β-RC PA6 formulations. All flame-retardant additives tested are commercially available and have been extensively studied in the literature (MC [ 46 , 47 , 78 ], EG [ 50 , 51 , 52 , 79 ], AlPi [ 74 , 75 ], and IFR [ 80 ]). Thus, where appropriate, literature for further information is presented.…”

“…In the case of expandable graphite, a high thermal conductivity provides an improved heat distortion effect, which has a positive effect on LOI testing results. A corresponding study addressing this issue can be found in [ 79 ]. β-RC formulations containing EG showed a comparable LOI development.…”

The Effect of Intumescent Coating Containing Expandable Graphite onto Spruce Wood

“…EG has not only the flame-retardant effect but also has minimal smoke production and low toxicity [25][26][27]. In addition to its properties as a flame retardant, EG also has good thermal and electrical conductivity, high strength, and stiffness [28,29]. These properties make it a universal material that can be used in a wide range of applications, e.g., flame retardant, conductive additive, absorbent, covering product, graphene precursor, and graphite foils.…”

“…These properties make it a universal material that can be used in a wide range of applications, e.g., flame retardant, conductive additive, absorbent, covering product, graphene precursor, and graphite foils. Therefore, EG can be used in various fields including fire protection of wood, and the flame-retardant property of the composite of wood and EG improved as the total heat release rate (HRR) decreased [17,18,29]. The Bochemit Antiflash, based on boric acid and 2-aminoethanol, acts mainly chemically; its usage is limited (due to ammonia gas).…”

Significant Improvement of Thermal Conductivity of Polyamide 6/Boron Nitride Composites by Adding a Small Amount of Stearic Acid

“…Polyamide 6 (PA6) is increasingly utilized in various industrial applications, such as aerospace, automotive, and electronics, due to its corrosion resistance, high specific strength, and good formability [2]. Unfortunately, the thermal conductivity of PA6 is only 0.3 W m −1 K −1 [3], which limits its application in thermal conductive electronic components. Preparing filled PA6-based composites is a beneficial approach to improving the thermal conductivity of PA6.…”