Effect of Treatment on Plastic Surfaces

The increase in surface energy of plastic occurs through the surface oxidation of the polymer chains 

Cleaning, or removal of contamination, including process oils, dirt, waxes, mold release agent, and exuded plasticizer, is an important change that occurs as a result of surface treatment. Methods involving chemicals such as solvent cleaning and etching, if not properly used, can leave behind a residue that may interfere with adhesive bond formation. Clean surfaces must be protected because of rapid reacquisition of contamination from the ambient atmosphere. 

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These data indicate that the polymethylmethacrylate (PMMA) surface was basic and that chlorinated polyvinylchloride (CPVC) and polyvinyl flouride (PVF) were both acidic and basic. Polypropylene was nonpolar, but corona treatment led to formation of acidic and basic sites. Another example of the effect of treatments on the surface of a plastic is shown in Table 6 (49). The surface activity of PVF was increased by plasma treatment, whereas corona treatment... 

Figure 11.63. The effect of treatment time on surface free energy of PVC plasticized with 10 phr of epoxidized soybean oil and 40 phr of di-(2-e1hylhexyl) phthalate and 40 phr of poly(ethylene-co-vinyl ace-tate-eo-carbon monoxide). [Data from Audic J-L Poncin-Epaillard F Reyx D Brosse J-C, J. Appl. Polym. Sci., 79, No.8, 22nd Feb.2001, p.1384-93.]...

The effect of corona discharge treatment on the surface physico-chemistry of PP and PET films has been investigated using surface energy measurements from contact angles, XPS and AFM. The information gathered from these techniques, in addition to practical adhesion measurements, has enabled identification of the dominant mechanisms of adhesion of silicones to these plastic films. The physisorption mechanism and the mechanism of mechanical interlocking are not the cause of... 

Fluorination of polyethylene surfaces leads to an increase in the surface energy, some degree of cross-linking and a reduction of the free volume of the polymer. All of these effects impart on the surface of the polymer a barrier that is very impermeable to hydrocarbon solvents. A blow-moulding process, in which a low concentration of fluorine in nitrogen is used as the blow-moulding gas, is used for the production of plastic fuel tanks for the automotive industry (Airopak , Air Products) [51]. Post-treatment of hydrocarbon surfaces with fluorine is an alternative technology and techniques for the surface fluorination of natural and synthetic rubber have been described [52]. 

The interface between plastic and wood fibres strongly influences the mechanical properties of a plastic/wood fibre composite. A means for evaluating the effectiveness of surface treatment on the wood fibres in the PVC/wood fibre composites is presented that investigated the adhesion between PVC and laminated wood veneers. Wood veneers were first treated with gamma-aminopropyltriethoxysilane, dichlorodiethylsilane, phthalic anhydride, and maleated PP for surface modification. The chemical modification made on the wood surfaces was then characterised by different complementary surface analytical techniques X-ray photoelectron spectroscopy and surface tension measurements. 63 refs. 

An effective solvent for plastics objects may be required as a component of an adhesion or repair treatment where the edges to be joined require etching or softening. By contrast, a poorly effective solvent for plastic may be sought as a component of a cleaning treatment where the soil is dissolved while the original plastic surface remains undamaged. In addition, selection of an effective and appropriate solvent may also depend on its evaporation rate, environmental or health and safety considerations. 

For many industrial applications of plastics that are dependent on adhesive bonding, cold gas plasma surface treatment has rapidly become the preferred industrial process. Plasma surface treatment, which is conducted in a vacuum environment, affords an opportunity to minimize or eliminate the barriers to adhesion through three distinct effects (1) removal of surface contaminants and weakly bound polymer layers, (2) enhancement of wettability through incorporation of functional or polar groups that facilitate spontaneous spreading of the adhesive or matrix resin, and (3) formation of functional groups on the surface that permit covalent bonding between the substrate and the adhesive or matrix resin. Since plasma treatment is a process of surface modification, the bulk properties of the material are retained. The nature of the process also allows precise control of the process parameters and ensures repeatability of the process in industrial applications. Finally, several studies have demonstrated that these surface modifications can be achieved with minimum impact on the environment. 

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