Abstract
This study proposes an innovative solution to flame-retard a sandwich composite made of unsaturated polyester resin, glass fibre skins and polyester nonwoven core material. The strategy uses the core material as flame-retardant carrier, while the resin is also flame-retarded with aluminum trihydroxide (ATH). A screening of the fire-retardant performances of the core materials, covered with different types of phosphorous flame-retardant additives (phosphate, phosphinate, phosphonate), was performed using cone calorimetry. The best candidate was selected and evaluated in the sandwich panel. Great performances were obtained with ammonium polyphosphate (AP422) at 262 g/m2. The core material, when tested alone, did not ignite, and when used in the laminate, improved the fire behaviour by decreasing the peak of heat release rate (pHRR) and the total heat release (THR): the second peak in HRR observed for the references (full glass monolith and sandwich with the untreated core) was suppressed in this case. This improvement is attributed to the interaction occurring between the two FR additives, which leads to the formation of aluminophosphates, as shown using Electron Probe Micro-Analysis (EPMA), X-ray Diffraction (XRD) and solid-state 31P Nuclear Magnetic Resonance (NMR). The influence of the FR add-on on the core, as well as the ATH loading in the matrix, was studied separately to optimize the material performances in terms of smoke and heat release. The best compromise was obtained using AP422 at 182 g/m2 and 160 phr of ATH.
Highlights
Driven by the need to decrease the environmental impact of transportation, fibrereinforced plastics (FRP) are progressively replacing conventional materials such as aluminum or steel in this sector of applications, enabling significant weight savings and reducing energy consumption
Ammonium polyphosphate was selected from different types of phosphorous FR additives as the most efficient option, based on cone calorimeter results
Its use in the sandwich modified the burning behaviour by suppressing the second peak of heat release that was observed for the sandwich made using the untreated core material
Summary
Driven by the need to decrease the environmental impact of transportation, fibrereinforced plastics (FRP) are progressively replacing conventional materials such as aluminum or steel in this sector of applications, enabling significant weight savings and reducing energy consumption. Among the various FRP formulations available on the market, unsaturated polyester resin (UPR)–glass fibre (GF) are widely used due to their high strength-to-weight ratio, high-quality surface finishes and good dimensional stability. The performance of these composites can be improved by the inclusion of a core material in the laminate build-up. A number of different core materials with various properties and costs are available on the market, such as thermoplastic foams, polyurethane foams or honeycomb core material The latter are very efficient in weight reduction while maintaining the stiffness of the laminate
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