Seth M. Kirk

Flame surface modification of polypropylene film

Contact-angle measurements, the ASTM standard wetting test for polyolefin films, and X-ray photoelectron spectroscopy (XPS or ESCA) were used to characterize flame-treated polypropylene (PP) films. Two combustion models, STANJAN and PREMIX, were then used to determine the chemical and physical properties of the flames used to treat the PP films. Both the flame equivalence ratio and the position of the PP film in the flame are important variables in determining the extent of oxidation and improvement in wettability obtained by flame treating. The optimal equivalence ratio for the flame treatment of PP is 0.93, while the optimal luminous flame-to-film distance is 0-2 mm. Modeling of the combustion processes occurring in the flame provides evidence that the extent of treatment correlates closely with the concentrations of H, O, and OH radicals present in the flame. The extent of surface modification of the flame-treated PP does not appear to correlate with either the flame temperature or the concentraion of ...

Contact angle measurements on oxidized polymer surfaces containing water-soluble species

Advancing and receding contact angle measurements on polymer surfaces can be performed using a number of different methods. Ballistic deposition is a new method for both rapidly and accurately measuring the receding contact angle of water. In the ballistic deposition method, a pulsed stream of 0.15-μL water droplets is impinged upon a surface. The water spreads across the surface and then coalesces into a single 1.8-μL drop. High-speed video imaging shows that, on most surfaces, the water retracts from previously wetted material, thereby forming receding contact angles that agree with the receding angles measured by the Wilhelmy plate technique. The ballistic deposition method measures the receding angle within one second after the water first contacts the surface. This rapid measurement enables the investigation of polymer surface properties that are not easily probed by other wettability measurement methods. For example, meaningful contact angles of water can be obtained on the water-soluble low-molecular-weight oxidized materials (LMWOM) formed by the corona and flame treatment of polypropylene (PP) films. Use of the ballistic deposition method allows for a characterization of the wetting properties and an estimation of the surface energy components of LMWOM itself. Both corona- and flame-generated LMWOM have significant contact angle hysteresis, almost all of which is accounted for by the non-dispersive (polar) component of the surface rather than by the dispersive component. Surface heterogeneity is thus associated primarily with the oxidized functionalities added to the PP by the corona and flame treatments.

Fluorination of polypropylene by remote inductively coupled plasmas sustained in Ar/F 2 and Ar/NF 3 gas mixtures

The surface energy and adhesion properties of commodity polymers such as polypropylene (PP) can be modified by functionalization of the surface by plasma-generated radicals and ions. For example affixing fluorine to the surface in a low temperature plasma lowers surface energy and increases hydrophobicity. The F atoms produced in the plasma both abstract H atoms from and adhere to the surface. In such plasma fluorination, the surface is also subject to energetic ion and photon fluxes. Another strategy is the use of a remote plasma to produce a flow of fluorine radicals which are injected into a reactor where the PP sheets are processed. For example, a remote inductively coupled plasma (TCP) sustained in mixtures containing F2 or NF3 produces plumes of F and NFX radicals which functionalize the PP. In these systems, the PP is subject to only neutral species and so may have different surface properties than PP immersed in a plasma.

Consequences of Ion and Photon Fluxes on the Low-Pressure Plasma Fluorination of Polypropylene

Summary form only given. The surface energy and adhesion properties of commodity polymers such as polypropylene (PP) can be controlled by functionalization of the surface layers in plasmas. Affixing fluorine lowers surface energy and increases hydrophobicity. One such fluorination process is the immersion of PP sheets in a low pressure, capacitively coupled discharge sustained in F2 containing gas mixtures wherein F atoms both abstract H atoms from and adhere to the surface. In these plasmas, the PP is subject to both energetic ion and photon fluxes. In this talk, the consequences of ion and photon bombardment during low-pressure plasma fluorination of PP will be discussed with results from computational and experimental investigations. PP was treated on a mewing web in low pressure (< a few Torr) capacitively coupled plasmas sustained in gas mixtures containing F2. The fractional coverage of surface resident groups (CH, CF, CF2, CF3) was measured using FSCA. Plasma and surface processes on the moving web were simulated using a 2-dimensional plasma hydrodynamics and surface chemistry model. In the surface reaction mechanism, apart from a hierarchy of reactions beginning with H abstraction by F atoms and followed by passivation by F and F2, ion (sputtering, scission) and photon (H abstraction, scission) activated processes are included. Ion sputtering rates were determined by TRIM while rates of photon activation processes were parameterized. Comparisons will be made between the model and experiments for surface coverages of =CH and =CFn. Preliminary results have shown that the surface coverage of =CH is a sensitive function of ion energy, a consequence of sputtering of previously fluorinated sites and the slow re-fluorination of underlying sites that are sterically hindered.