Low-Pressure H2, NH3 Microwave Plasma Treatment of Polytetrafluoroethylene (PTFE) Powders: Chemical, Thermal and Wettability Analysis

Abstract

Functionalization of Polytetrafluoroethylene (PTFE) powders of ~6 μm particle size is carried out using low-pressure 2.45 GHz H2, NH3 microwave plasmas for various durations (2.5, 10 h) to chemically modify their surface and alter their surface energy. The X-ray Photoelectron Spectroscopy (XPS) analyses reveal that plasma treatment leads to significant defluorination (F/C atomic ratio of 1.13 and 1.30 for 10 h NH3 and H2 plasma treatments, respectively vs. 1.86 for pristine PTFE), along with the incorporation of functional polar moieties on the surface, resulting in enhanced wettability. Analysis of temperature dependent XPS revealed a loss of surface moieties above 200 °C, however, the functional groups are not completely removable even at higher temperatures (>300 °C), thus enabling the use of plasma treated PTFE powders as potential tribological fillers in high temperature engineering polymers. Ageing studies carried over a period of 12 months revealed that while the surface changes degenerate over time, again, they are not completely reversible. These functionalised PTFE powders can be further used for applications into smart, high performance materials such as tribological fillers for engineering polymers and bio-medical, bio-material applications.

Plasma treatment of polymer powders – from laboratory research to industrial application

“…X‐ray photoelectron spectroscopy (XPS) is widely used to analyze the powder's atomic surface composition and enables the identification of introduced functional groups . Fourier‐transform infrared spectroscopy (FTIR) and attenuated total reflectance infrared spectroscopy (ATR‐IR) are used to probe samples up to a depth of about 4–5 μm . Time of flight secondary ion mass spectroscopy (TOF‐SIMS) is utilized to evaluate the uniformity of plasma‐deposited polymer coatings by detecting sputtered ions and fragments.…”

“…Differential scanning calorimetry (DSC) and thermal gravimetric analysis (TGA) are applied to study the thermal properties of the plasma‐treated polymer powders. Rheology provides information about the polymer viscosity, crosslinking, melting index, and the behavior under dynamic load.…”

“…To achieve an optimal plasma treatment, the best ratio between the powder filling quantity, size of the plasma reactor, treatment time, and powder‐gas mixing needs to be (experimentally) determined . Additionally, the storage time and conditions (i.e., temperature, light, storage dispersed in water or in ambient air) of treated powder after plasma exposure influence the final state of the plasma‐treated surfaces.…”

Peptide with endothelial cell affinity and antiplatelet adhesion property to improve hemocompatibility of blood‐contacting biomaterials

“…Instead, the O/C atomic ratio is apparently related to the decrease in the contact angle (Figure and Table ). We presume that partial oxidation of the surfaces occurred during handling, transport, and preparation for XPS analysis . The presence of functional polar groups on the ePTFE molecule can lower its surface energy and improve wettability.…”

A Spectroscopic Study on Argon-Ammonia Water Gaseous Plasma Super-hydrophilizing Polytetrafluoroethylene

“…Furthermore, based on PTFE surface chemical analysis after NH 3 plasma treatment, in addition to the -C-F groups, many new polar groups (e.g., -NH 2 , -OH, -COOH, -CO-NH 2 ) and cross links are The larger the number of polar groups (e.g., -OH, COOH) bound at the polymer film surface, the greater the wettability of the surface after plasma treatment. The dependence of the adhesive strength on the type of functional groups is in the order COOH > OH ≫ NH 2 > CH 2 , and for the peel strength measurements of an Ar plasma copolymerpolypropylene system, the maximum adhesion (650 N m -1 ) was measured at 27 OH groups per 100 C atoms, which was substantially higher than the peel strength for the allyl alcohol homopolymer [12].…”