Abstract
As polypropylene (PP) has no charring ability on its own due to the lack of hydroxyl functional groups, the flame retardant system needs the addition of carbonizing agent in a relatively great amount. Ammonium-polyphosphate (APP), a conventional flame retardant additive was modified by microencapsulation with a sorbitol-based bioepoxy resin shell to create an intumescent flame retardant system with enhanced charring ability for PP. The flame retardant efficiency of the microencapsulated additive, which contains all the components needed in an effective intumescent flame retardant system, was evaluated in PP matrix at different loadings.When compared to the physical mixture of the component, the microencapsuated form of APP (MCAPP) was found to have improved flame retardant efficiency in PP. The LOI values of the MCAPP containing PP samples increased by 8–11 V/V% besides achieved V-0 classification according to the UL94 test. During cone calorimeter tests, the burning intensity was reduced (peak of heat release rate decreased by 20–35% and shifted in time), increased amount of charred residue was obtained, and based on the calculated Flame Retardancy Index (FRI) “Excellent” fire performance was achieved when MCAPP was used. The improved flame retardant performance is attributed to the effective interaction between the APP core and the readily available carbonizing shell, which promoted the formation of increased amount of char accompanied with improved heat protecting and barrier efficiency.
Highlights
Polypropylene (PP) is a widely used polymer in our daily life due to its excellent chemical resistance and mechanical properties, combined with the fact that it can be processed through many converting methods [1, 2]
Ammonium-polyphosphate (APP), a conventional flame retardant additive was modified by microencapsulation with a sorbitol-based bioepoxy resin shell to create an intumescent flame retardant system with enhanced charring ability for PP
The Limiting Oxygen Index (LOI) values of the microencapsuated form of APP (MCAPP) containing PP samples increased by 8–11 V/V% besides achieved V-0 classification according to the UL94 test
Summary
Polypropylene (PP) is a widely used polymer in our daily life due to its excellent chemical resistance and mechanical properties, combined with the fact that it can be processed through many converting methods [1, 2]. Even though its self-ignition temperature is relatively high (570 °C), during its relatively smokefree combustion the polypropylene burns rapidly and completely due to its aliphatic chemical structure [3]. Under flash pyrolysis at 520 °C, the breaking of chains was observed, and the hydrogen content of the formed gaseous products was tested. They concluded that the flammability of PP highly depends on the amount of volatile unsaturated gases, as these "fuellike" compounds can further enhance the spread of flames. In the cool flame combustion test at 350 °C toxic gases formed as the result of the imperfect burning of polypropylene [7]
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