Siloxane-Brominated Polycarbonate Flame Retardant Composition
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Solution Overview
Problem
Current polycarbonate materials used in aircraft and transportation applications do not adequately meet stringent flammability safety standards, particularly in terms of smoke density and heat release rates, and lack improved melt flow, UV stability, and light transmission properties.
Innovation Solution
A polycarbonate composition comprising a poly(siloxane-carbonate) derived from dihydroxy aromatic units and polysiloxane bisphenols, combined with a brominated polycarbonate containing 2,2',6,6'-tetrabromo-4,4'-isopropylidenediphenol units, optimized to provide at least 0.3 wt% siloxane and 7.8 wt% bromine, achieving low smoke density and heat release rates, while maintaining transparency and impact strength.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If conventional flame retardant polycarbonates are used to meet flammability standards, then smoke density and heat release rates are reduced, but melt flow and UV stability deteriorate
Solution Approach 1:
The patent uses a composite material system consisting of poly(siloxane-carbonate) copolymer combined with brominated polycarbonate. The siloxane component provides improved melt flow and UV stability, while the brominated polycarbonate contributes flame retardancy. This composite approach allows simultaneous achievement of low smoke density and good processability without sacrificing either property.
Solution Approach 2:
The patent modifies the chemical composition parameters by incorporating siloxane units (0.1-10 mole%) into the polycarbonate backbone and adding brominated components (7.8-14 wt% bromine). These parameter changes enable the material to achieve both low smoke density during combustion and improved melt flow during processing, resolving the contradiction between flame safety and manufacturability.
2Object-affected harmful factors
If flame retardant additives are incorporated to reduce heat release rates, then flammability safety is improved, but material transparency and impact strength deteriorate
Solution Approach 1:
The patent employs a composite system where poly(siloxane-carbonate) provides structural integrity and impact resistance, while brominated polycarbonate provides flame retardancy. The siloxane backbone maintains material toughness and transparency, preventing the typical degradation of mechanical properties associated with flame retardant additives.
Solution Approach 2:
The patent achieves flame retardancy through localized bromine content (7.8-14 wt%) distributed within the polycarbonate matrix, rather than throughout the entire molecular structure. This localized approach allows the bulk material to retain its inherent toughness and transparency while providing sufficient flame safety through the brominated regions.
3Object-affected harmful factors
If brominated polycarbonates are used to achieve low smoke density, then flammability safety is improved, but UV stability and color stability deteriorate
Solution Approach 1:
The patent combines poly(siloxane-carbonate) with inherent UV stability with brominated polycarbonate to create a composite where the siloxane component protects the brominated regions from UV degradation. The siloxane backbone acts as a stabilizing matrix that prevents color shifting and degradation while allowing the brominated portions to provide flame safety.
Solution Approach 2:
The poly(siloxane-carbonate) copolymer serves as an intermediary protective matrix that shields the brominated polycarbonate from UV exposure. The siloxane units absorb and dissipate UV energy, preventing direct UV attack on the brominated aromatic rings, thereby maintaining color stability and preventing degradation while preserving the flame retardant properties.
Data Source
AI summary
A composition comprising: a first polycarbonate comprising a poly(siloxane-carbonate); a second polycarbonate different from the first polycarbonate; and optionally, a third polycarbonate different from the first and second polycarbonate; wherein the first polycarbonate is present in an amount effective to provide the siloxane units of in the first polycarbonate in an amount of at least 0.3 wt%, and the second polycarbonate is present in an amount effective to provide the bromine of the second polycarbonate in an amount of at least 7.8 wt%; and further wherein an article molded from the composition has an OSU integrated 2 minute heat release test value of less than 65 kW-min/m2 and a peak heat release rate of less than 65 kW/m2, and an E662 smoke test Dmax value of less than 200.