Flame treating

The dimensional stability of low density, water blown rigid PU foams for pour-in-place thermal insulation applications was improved by the use of a phthalic anhydride based polyester polyol containing a dispersed cell opening agent. The foam systems obtained allowed some of the carbon dioxide to be released through the cell windows immediately after filling of the cavity, and to be rapidly replaced by air. Studies were made of the flowability, density, open cell content, dimensional stability, mechanical properties, thermal conductivity and adhesion (particularly to flame treated PE) of these foams. These properties were examined in comparison with those of HCFC-141b blown foams. 21 refs. 

In the first study of its kind, second harmonic generation has been used to study potential induced reconstruction on Au(lll) and Au(100) by Kolb and coworkers [156]. These surfaces have been known to reconstruct in UHY when they are clean [153, 157], Surface reconstruction occurs when the surface atoms of a solid rearrange themselves in a structure different from that expected from simple termination of the bulk lattice. Various studies by cyclic voltammetry, electroreflectance spectroscopy and ex situ electron diffraction have suggested that flame-treated crystals form stable reconstructions in solution. Unfortunately, due to the lack of in situ probes, very little direct evidence for this reconstruction has been available. 

Some of the commonly used techniques for measuring contact angle [215, 216, 217] are the sessile drop method, captive bubble method and Wilhelmy plate method. These techniques have been extensively used and well documented for characterisation of modified PE surfaces [218, 219, 220, 221, 222, 223, 224, 225, 226, 227, 228, 229, 230] for various applications. Whitesides et al. [231 ] studied the wetting of flame-treated polyethylene film having ionisable organic acids and bases at the polymer-water interface. The effect of the size of substituted alkyl groups in amide and ester moieties on the surface hydrophilicity was also studied [232]. The biocompatibility of the polyethylene film surface modified with various water-soluble polymers was evaluated using the same technique [233]. The surface properties of hy-perbranched polymers have been very recently reported [234]. 

Estimate if separation occurs between coating and substrate in the case where flame-treated polypropylene film, coated with vinylidene chloride/methyl acrylate copolymer is immersed in a solution of sodium n-dodecyl sulphate (concentration 0.5%). The data of polymer, coating and liquid are the following (determined in separate... 

A surface analysis technique that has the potential to detect structural chemical changes in polymer surfaces, including low-molecular weight material formation, is static SIMS. Its capabilities for characterizing polymers by virtue of their fingerprint spectrum nave been amply demonstrated in recent years (5 6). The technique is more surface sensitive than XPS and can detect structural differences, even in hydrocarbons (7). It is, therefore, highly complementary to XPS. Nevertheless, only very few applications to the study of modified polymer surfaces have been published. Among these are reports on SIMS analysis of flame-treated polypropylene and plasma-fluorinated polyolefin surfaces (8 9). 

Recent surface force measurements revealed a similar trend (20). Comparing steam-treated to flame-treated silica sheets using site-dissociation/site-binding model, a decrease in silanol surface sites and apparent decrease in average pKa was observed upon heat treatment. Furthermore, a repulsive force other than double-layer and van der Waals forces was observed 15 A from the surface. This repulsion was attributed to hydration of the surface and was found to be independent of surface treatment and electrolyte concentration. In Bums treatment, an arbitrary plane of shear was introduced to provide a best model fit (l 3). A value of 9 A from the surface for the plane of shear was determined from electro-osmosis measurements. 

Fig. 3.77 TM-AFM height images of (a) an untreated polypropylene web, (b) a flame-treated PP film and (c) a corona treated PP film. Reproduced with permission from [162]. Copyright 2003. Plenum Publishing...

A second relevant example is the surface oxidation of polyolefins, such as LDPE, which is carried out frequently for thick specimens using an oxidizing flame treatment. For instance, while untreated LDPE surfaces are non-polar and thus fairly hydrophobic, flame-treated LDPE possesses a much higher surface energy and therefore improve the binding of these surfaces with other substances, such as adhesives, printing inks, paints, and various metal surfaces. 

Force Titrations of Flame-Treated LDPE Sample Preparation Flame-treatment [29]... 

LDPE films are flame-treated (50x, lOOx, and 200x) according to hands-on example 35. 

In such surface treated samples, the surface ionization state can be analyzed by calculating the average pull-off forces from FV scans on various flame treated samples as a function of the solution pH. Thus, FV data are captured for different... 

The FV data acquired are analyzed as sketched in the examples above. The pull-off force values for each f-d curve are estimated and a histogram of forces for each pH and treatment condition is calculated. In Fig. 4.11 some normalized force titration curves (average pull-off force as a reference of value at pH 4 versus pH) on flame treated LDPE are shown. These titration curves display a typical sigmoidal shape, while the untreated polymer exhibited by contrast an almost constant pull-off force over the entire pH range. 

Fig. 4.11 Normalized force titration curves showing the adhesive force between hydroxyl functionalized tips and flame treated LDPE films as a function of the solution pH. The average pull-off force at pH 4 was set as a reference for each sample. The solid lines have been added as guides to the eye. (a) Untreated LDPE. (b) LDPE flame-treated 50 times, (c) LDPE treated 100 times, (d) LDPE treated 200 times. Reproduced with permission from [29]. Copyright 2007. Elsevier...

On the other hand, for a given electrolyte, the distribution of the adsorption states up to 0.8 V vs. RHE depends on the degree of the surface order of the platinum single crystal. Adsorption states at higher potentials are related to the presence of wide two-dimensional ordered (100) domains [11,62]. The maximum development of these states was obtained after cooling a flame-treated sample in an oxygen-free atmosphere [3,11,62,63]. 

Physical characteristics (size, dimensions, whether flame treated, etc.). 

Searby and Rochwerger [9] developed a model describing the effect of an acoustic field on the stability of a laminar, premixed flame, treated as a thin interface between two fluids of different densities and under the influence of a periodic gravitational field. Their model is an extension of the work by Markstein [8] and is consistent with the more recent flame theory of Clavin and Garcia-Ybarra [16]. Bychkov [17] later solved the problem analytically, presenting the following linear equation for the perturbation amplitude, /, of a flame under the influence of an acoustic field [17] ... 

Figure 13.4.4 First cyclic voltammograms of flame treated platinum of different orientations in O.5MH2SO4 at 50mV/s. Positive potentials are plotted to the right, and anodic currents up. Compare these to the voltammogram of a polycrystalline electrode. Figure...

Roles of Flame and Surface Chemistry in Flame Treating.463... 

The experimental setup mirrors that used in the process of industrial flame treating. The setup consists of a mounted 25 cm diameter roller (the impingement surface) that is driven by a variable-speed drive train allowing for rotational speeds between 0 and 7 Hz, translating to a roller rotational velocity of 0 to 5.5 meters per second (m/s). The roller is chilled to approximately 400 K to prevent any thermal damage that could occur due to the presence of the flame and to prevent the buildup of condensation on the roller surface. The burner is oriented beneath the roller, parallel to the face of the roller. The vertical separation distance or gap between the roller and the burner can be varied along with the horizontal positioning of the burner in relation to the roller. 

Eigure 22.8 shows a plot of ESCA O/C atomic ratios and the contact angles of water on flame-treated polypropylene as a function of the equivalence ratio, where the equivalence ratio (9) is defined as ... 

The surface chemisfry of flame-freafed polypropylene closely correlates wifh fhe weffabilify of the surface. Figure 22.8 also shows fhe ESCA O/C atomic ratio of flame-freafed polypropylene as a function of fhe equivalence ratio. The amounf of surface oxidation generated by the flame follows fhe same trend as the wettability. The maximum O/C ratio of 0.18 is obtained at q) = 0.92 - 0.94. Within this range, the gas phase concentrations of surface oxidizers in fhe flame are high. This surface oxidation is fhe reason for the improved wettability and adhesion properties of flame-treated polypropylene. A detailed discussion of the flame and surface chemistry involved in surface freafing is presented in Section 22.4. 

Wilhelmy advancing force data for flame-treated polypropylene. To generate this data, a scratch was made directly above a downstream primer port while a second downstream primer port located 5 mm away from the scratch was also plugged. 

Laning on flame-treated polypropylene is a small, but significant, nonuniformity in the extent of surface oxidation and wettability that is superimposed upon a much larger average increase in oxidation and wettability. 

Park, J., Lyons, C. S., Strobel, M., Ulsh, M., Kinsinger, M. L, and Prokosch, M. J. "Characterization of Non-Uniform Wettability on Flame-Treated Polypropylene-Film Surfaces." Journal of Adhesion Science and Technology 17 (2003) 643-53. 

Stroud, C., and Branch, M. C. "Modeling of the Surface Oxidation of Flame Treated Polypropylene Film." Combustion Science and Technology 179 (2007) 2091-2105. 

Why are HDPE bottles often flame-treated What does flame-treating do ... 

---