Oxyfluorinated surface

Polypropylene has been oxyfluorinated using a gas mixture consisting of fluorine, nitrogen, and water. When cured with mortar slurry, oxyfluorinated surfaces had 20% greater shear bond strength than fluorinated surfaces. 

The surface activation method, especially the gas mixture used, determines the chemistry of the surface and can thus promote the adhesion properties with epoxy adhesives. The following example illustrates the importance of the correct activation gas mixture. As is clearly illustrated by Table 16.6, oxyfluorination induces better adhesive properties than fluorination on PE with Pro-Struct 30/71. 

The lap shear test involves measuring the adhesive shear strength between two surface fluorinated polyolefin sheet tokens that are adhesively secured with a reinforcement resin. The tokens are individually reinforced with steel backing plates to eliminate flexural distortion in the shear joint. Lap shear tests carried out with various reinforcing polyester-type resins, contrasting fluorination and oxyfluorination as surface treatment, are shown in Table 16.8. 

From the above it can be deduced that, in general, oxyfluorinated PP surfaces give slightly improved adhesion over oxyfluorinated HDPE surfaces. This can be attributed to the greater ease with which PP forms the acyl fluoride functionality during treatment.28... 

Our experience indicates that fluorination generally results in decreased adhesion strength compared to oxyfluorination (see Tables 16.6 and 16.8). This is in contrast to reported findings in the literature where epoxy adhesives were used.7,29 This discrepancy can be attributed to the surface energy implications of the increased acyl fluoride to the C—H—F functionalkation ratio (compare Figures 16.3 and 16.4). However, as indicated by our data, certain resin formula-... 

A typical oxyfluorination treatment that is sufficient to activate polyolefin surfaces with respect to polyester adhesion includes the following ... 

Figure 16.4. Effect of oxyFluorination time on the surface tension of PE (10% F2/O2, 30°C, constant of 20 cm /min).

Oxyfluorination of polypropylene was previously done by Hruska [1], and the material was used as an oxidative surface treatment method in electrophotography. 

Surface oxyfluorination was also performed on poly(methyl methacrylate) by Jolet [4] as a method for manufacturing the outer panel of craze-resistant windows. 

For flat samples, the extent of surface modification reactions can be conveniently followed. For the iPP films analyzed in Sect. 3.5 in Chap. 3, the roughness variations due to surface modification were minimal. Thus, crosstalk in the force analysis shown in Fig. 4.8a (acquired using unmodified Si3N4 tips in ethanol) subsequent to oxyfluorination is minimized. 

In these experiments, individual f-d curves were recorded at various locations of each film using the same tip (i.e., the tip radius is assumed to remain constant). Subsequently, the pull-off forces were evaluated off-line and were plotted in a histogram. The pull-off forces were observed to increase with the extent of oxyfluorination and the concomitant increase in surface energy (shown as values of surface tension). Using different tip functionalities and media on oxidized iPP and... 

Fig. 4.8 (a) Histograms of pull-off force values obtained with an unmodified Si3N4 tip on untreated and oxyfluorinated iPP films in ethanol. The total surface free energy y of the polymer film is shown, (b) Mean values of pull-off force measured with COOH-terminated tips on modified polyolefin surfaces (iPP, isotactic polypropylene LDPE, low-density polyethylene) in ethanol (top) and with OH-terminated tips on oxyfluorinated iPP in water (pH 3.8, bottom) as a function of cos 0 (contact angle measured with water). (Reprinted in part/adapted with permission from [26, 27]. Copyright 1998, 2000, American Chemical Society.)... 

SX Park, S.Y. Song, J.S. Shin, XM. Rhee, Effeet of surface oxyfluorination on the dyeability of polyethylene film. J. Colloid Interlace Sd. 283, 190-195 (2005)... 

Hruska, Z. Lepot, X. (2000). Ageing of oxyfluorinated polypropylene surface Evolution of the acid-base surface characterisitics with time. /. Fluor. Chem., Vol. 105, pp. 87-93, ISSN 0022-1139. 

In recent years, controlled surface oxyfluorination has been investigated as an interesting industrial alternative. In comparison with other surface modification techniques, fluorine atoms penetrate the material surfaces to relatively great depths, the extent of which depends upon treatment conditions. In this work, the effects of the oxyfluorination for MWNTs on the surface functional groups and Pt catalyst deposition are investigated. 

This result may lead to improve electrochemical properties of Pt/MWNTs due to the increase of specific polarity and the H-bonding of the MWNTs. However, after a specific reaction time, oxyfluorination hardly influence, change of surface functional groups of MWNTs, due to the disappearance of free radical. 

For the analysis of polar polymer films, the correlation between pull-off forces and surface free energies can be utilized (see section Normal Forces). lonizable fimctional groups, such as carboxylic acid groups in oxyfluorinated isotactic PP... 

Thus by contact angle measurements using three different liquids (L), of which two must be polar, with known y Y and y values, the ys", Ys and ys of any solid (S) can, in principle, be determined. The value of yl must be known or determined independently [108]. The apolar component of the surface tension of solids (yj" ) can be determined by contact angle measurements using strictly apolar liquids for which yL = y These surface tension components can be related to experimentally determined pull-off forces between chemically modified AFM tips and an oxyfluorinated isotactic polypropylene surface in CFM approaches [110]. It was observed that the pull-off force measured with carboxylic acid tips in ethanol depended hnearly on the basic term of the surface tension (y,") on the modified polymer surface. 

Fig. 24 Force titration of an untreated iPP (top, left) and three oxyfluorinated iPP films using OH-terminated SFM tips. The total surface tension values are indicated. The error bars correspond to the standard deviation of the average value calculated from the corresponding histograms. (Reprinted with permission from [58]. Copyright 2000 American Chemical Society)...

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