Two-Step Surface Modification of Chemically Resistant Polymers: Blend Formation and Subsequent Chemistry1

Area of Science:

• Materials Science
• Polymer Chemistry
• Surface Science

Background:

• Fluoropolymers like PTFE, PCTFE, and FEP exhibit excellent chemical resistance but poor surface wettability.
• Surface modification is crucial for improving the adhesion and functionality of fluoropolymer materials.
• Supercritical fluid (SCF) technology offers an environmentally friendly approach for material processing.

Purpose of the Study:

• To investigate the efficacy of supercritical fluid carbon dioxide (SCF-CO2) processing for modifying the surface properties of fluoropolymers.
• To develop a two-step surface modification strategy for enhancing fluoropolymer wettability.
• To assess the impact of SCF-CO2 based polymerization and subsequent sulfonation on surface composition and wettability.

Main Methods:

• Utilized supercritical fluid (SCF) carbon dioxide to swell fluoropolymer substrates (PTFE, PCTFE, FEP).
• Performed in-situ free radical polymerization of styrene within the SCF-swollen substrates to form blends or semi-interpenetrating networks.
• Conducted heterogeneous sulfonation of the incorporated polystyrene to alter surface chemistry.
• Analyzed surface composition using X-ray photoelectron spectroscopy (XPS).
• Measured surface wettability via water contact angle (WCA) measurements.

Main Results:

• Successfully modified the surfaces of PTFE, PCTFE, and FEP using the two-step SCF-CO2 based procedure.
• X-ray photoelectron spectroscopy confirmed the presence of modified polymer layers on the fluoropolymer surfaces.
• Water contact angle measurements showed significantly decreased advancing and receding angles for all treated fluoropolymer samples.
• The modified surfaces exhibited increased wettability compared to the pristine fluoropolymers.

Conclusions:

• Supercritical fluid carbon dioxide processing provides an effective route for the surface modification of challenging fluoropolymer substrates.
• The two-step approach, involving SCF-mediated polymerization and subsequent sulfonation, successfully enhances the surface wettability of fluoropolymers.
• The improved wettability indicates potential for enhanced adhesion and compatibility in composite materials or for further surface functionalization applications.