Polysiloxane Core-Shell Impact Modifier for Low Temperature PVDF Blends
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Solution Overview
Problem
Vinylidene fluoride-containing polymers, such as PVDF-HFP copolymers, do not meet the low temperature impact requirements below -40°C, and traditional core-shell impact modifiers compromise their excellent properties like weathering and flame resistance.
Innovation Solution
Blending vinylidene fluoride-containing polymers with core-shell impact modifiers having a polysiloxane core and an acrylate shell maintains clarity, weathering, chemical, and flame resistance while reducing the ductile-brittle transition temperature.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If traditional core-shell impact modifiers (MBS with butadiene cores or all-acrylic) are added to vinylidene fluoride-containing polymers to improve low temperature impact performance, then the ductile-brittle transition temperature is reduced, but weathering resistance, oxidation resistance, and flame retardancy are compromised
Solution Approach 1:
The patent uses a composite core-shell impact modifier where the core is made of polysiloxane (providing low temperature flexibility) and the shell is made of fluorinated polymer (providing weathering and flame resistance). This composite structure allows the impact modifier to simultaneously improve low temperature impact performance while maintaining the excellent weathering and flame retardant properties of the PVDF matrix.
Solution Approach 2:
The impact modifier is designed with different properties in different parts: the core provides low glass transition temperature for cold weather flexibility, while the shell provides chemical resistance and flame retardancy. This local differentiation of properties allows each component to fulfill its specific function without compromising the overall performance.
2Temperature
If hexafluoropropylene is copolymerized with vinylidene fluoride to improve ductility and low temperature performance, then the ductile-brittle transition temperature is reduced to some extent, but the transition temperature remains above -40°C and low temperature impact requirements are not met
Solution Approach 1:
The patent changes the glass transition temperature parameter of the impact modifier core to below -60°C (using polysiloxane), which is significantly lower than the PVDF matrix. This large temperature difference allows the rubbery core to remain flexible at very low temperatures, enabling the composite material to meet the -40°C low temperature impact requirements.
Data Source
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AI summary
The invention relates to blends containing polymers of vinylidene fluoride, having low ductile-brittle transition temperatures and having excellent low temperature impact properties while maintaining the positive aspects of unmodified vinylidene fluoride-containing polymers. The blends of this invention are produced by adding a core-shell impact modifier (CSIM) comprised of a polysiloxane core and a shell compatible with vinylidene fluoride-containing polymer. The blends are further characterized by the presence of a heterogeneous copolymer composition comprised of two or more distinct phases and/or at least one flame and smoke suppressant. The preparation of these new blends can be done by conventional thermoplastic compounding techniques such as twin screw compounding; alternatively, the CSIM can be introduced earlier, such as in the latex. The unique properties of the new blends make them useful in end-use applications where those properties provide performance advantages, such as in wires & cables and in oil and gas applications.