Aqueous Fluoropolymer Dispersion Stability via Nonionic Surfactant
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Solution Overview
Problem
Aqueous polytetrafluoroethylene-based fluororesin dispersions lack mechanical and storage stability due to high viscosity and sludge formation when fluorinated surfactants are removed, and existing methods fail to produce stable dispersions without fluorinated surfactants.
Innovation Solution
An aqueous fluoropolymer dispersion with a core-shell structure is created through emulsion polymerization, using a monomer composition of 99.999 to 98 mole percent tetrafluoroethylene and 0.001 to 2 mole percent hexafluoropropylene, with a nonfluorinated nonionic surfactant content of 2 to 15% by mass, and a fluorinated surfactant content below 50 ppm, achieving good mechanical and storage stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If fluorinated surfactant is removed from aqueous fluororesin dispersion, then environmental safety and product purity are improved, but mechanical stability and storage stability deteriorate
Solution Approach 1:
A nonionic surfactant is introduced as an intermediary substance to replace the fluorinated surfactant. This nonionic surfactant mediates between the fluororesin particles and the aqueous medium, providing steric stabilization through its molecular structure that prevents particle aggregation and maintains dispersion stability without the harmful effects of fluorinated surfactants
Solution Approach 2:
The invention changes the chemical composition parameters by controlling the monomer ratio (99.999 to 98 mole percent TFE and 0.001 to 2 mole percent modifier monomer) and adjusting the nonionic surfactant content (2 to 15% by mass relative to fluoropolymer). These parameter changes create a core-shell structure with specific surface properties that enable stability without fluorinated surfactants
2Object-generated harmful factors
If fluorinated surfactant is removed from aqueous fluororesin dispersion, then environmental safety and product purity are improved, but storage stability deteriorates due to sludge formation
Solution Approach 1:
The nonionic surfactant acts as a protective intermediary that prevents direct interaction between fluororesin particles during storage. Its amphiphilic structure provides a steric barrier that keeps particles separated and prevents the formation of sludge and aggregates over time, ensuring long-term storage stability
Solution Approach 2:
The core-shell structure is prepared in advance with the nonionic surfactant incorporated into the shell during emulsion polymerization. This preliminary structuring provides pre-established stability mechanisms that prevent particle aggregation and sludge formation during subsequent storage, rather than attempting to stabilize the dispersion after particle formation
3Productivity
If fluororesin concentration is increased, then application efficiency is improved, but viscosity increases making handling difficult
Solution Approach 1:
The nonionic surfactant serves as a lubricating intermediary between fluororesin particles, reducing interparticle friction and preventing aggregation even at high concentrations. This mediation allows the dispersion to maintain low viscosity and good flow properties while containing high levels of fluororesin solids
Solution Approach 2:
The invention optimizes the nonionic surfactant concentration parameter (2 to 15% by mass relative to fluoropolymer) to achieve the right balance between particle stabilization and viscosity control. This parameter optimization enables high fluororesin content while maintaining ease of application
Data Source
AI summary
The present invention provides an aqueous fluoropolymer dispersion having good mechanical characteristics and storage stability and containing substantially no fluorinated surfactant. The present invention is related to an aqueous fluoropolymer dispersion comprising a dispersed fluoropolymer particle with an average primary particle diameter of 50 to 400 nm, a surface layer of the dispersed fluoropolymer particle being obtained by emulsion polymerization of a monomer composition consisting of 99.999 to 98 mole percent of tetrafluoroethylene and 0.001 to 2 mole percent of a modifier monomer, a fluorinated surfactant content being not higher than 50 ppm, a fluoropolymer content being 20 to 75% by mass, and a nonfluorinated nonionic surfactant content being 2 to 15% by mass relative to 100% by mass of the fluoropolymer.