Ultra-high Molecular Weight PVDF Melt Strength and Processability
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Solution Overview
Problem
Commercial polyvinylidene fluoride (PVDF) polymers have limitations such as low melt strength, poor impact resistance, and low elongation at yield point, making them unsuitable for producing highly oriented fibers or films, and they lack sufficient gel strength for fast gel extrusion processes and battery applications.
Innovation Solution
Development of ultra-high molecular weight polyvinylidene fluoride with a solution viscosity greater than 35 Pa-s in 10% NMP at 20°C, achieved through emulsion polymerization, exhibiting unique properties like high elongation at yield point, excellent clarity, and high gel strength.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If PVDF molecular weight is increased, then melt strength is improved, but drawdown ratio decreases
Solution Approach 1:
The patent applies parameter changes by dramatically increasing the molecular weight of PVDF beyond conventional limits (achieved solution viscosity >35 Pa-s in 10% NMP at 20°C, corresponding to ultra-high molecular weight). This parameter change resolves the contradiction by achieving exceptional melt strength while maintaining processability through controlled emulsion polymerization, producing materials with both high strength and acceptable drawdown characteristics.
2Strength
If crosslinking is used to increase melt strength, then melt strength is improved, but processability decreases and gel content increases
Solution Approach 1:
The patent extracts the crosslinking step from the processing sequence by achieving the desired melt strength through ultra-high molecular weight linear chains alone. This eliminates the need for post-polymerization crosslinking, thereby maintaining excellent processability and avoiding high gel content while still achieving superior melt strength through the inherent molecular weight effects.
3Ease of manufacture
If conventional PVDF is used, then processability is maintained, but impact resistance and elongation at yield point are insufficient
Solution Approach 1:
The patent applies parameter changes by increasing PVDF molecular weight to ultra-high levels, which fundamentally alters the material's mechanical properties. This produces exceptional impact resistance and elongation at yield point (>100% in some embodiments) while maintaining processability through the emulsion polymerization route, resolving the contradiction between conventional processability and enhanced mechanical performance.
4Quantity of substance
If emulsion polymerization is used to make high molecular weight PVDF, then molecular weight is increased, but solution viscosity remains limited compared to ultra-high molecular weight requirements
Solution Approach 1:
The patent applies parameter changes by optimizing emulsion polymerization conditions to achieve ultra-high molecular weights with solution viscosity exceeding 35 Pa-s in 10% NMP at 20°C. This represents a significant parameter change from conventional emulsion PVDF, achieved through controlled polymerization that minimizes chain termination and maximizes chain growth, producing materials with both high molecular weight and exceptional solution viscosity.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The ultra-high molecular weight PVDF demonstrates unexpected properties including lower melting temperature, reduced crystallinity, superb impact resistance, and high clarity, enabling its use in producing highly oriented fibers, high-impact articles, and as a binder in Li-ion batteries, while also improving melt strength when blended with other polymers.
Implementation Method 1
having a solution viscosity of greater than 35 Pa-s in 10% n-methyl pyrrolidone (NMP) at 20° C.
Implementation Method 2
high gel strength, and excellent impact strength
Data Source
AI summary
The invention relates to a polyvinylidene fluoride polymer having an ultra-high molecular weight, and unexpected physical properties. The ultra-high molecular weight polymer is clear, has a lower melting point, reduced crystallinity, excellent impact resistance, and a high elongation at the yield point. The ultra-high molecular weight polyvinylidene fluoride can be alone, or blended with other polymers, in final applications and articles.