Adhesion surface modification

Carbon fibers are used as reinforcement material in composites, the mechanical properties of which are dependent upon the matrix/fiber adhesion. Surface modification such as dry or wet oxidation of die carbon fibers may be used to improve those characteristics [3]. 

The literature shows that it is possible to improve the properfies of the adhesive joint by surface treatment of the fibres to increase interfacial strength (Luo and Van Ooij, 2002 Holme, 1999). Oxidation prebond treatments are currently the most widely used. Plasma treatments offer some advantages and are becoming more popular. They have the potential to increase the surface functional groups and thereby increase the number of chemical bonds between the treated fibre and the adhesives. Surface modification of textile fibre is stdl an area under active study and more techniques may emerge in the near future. 

Biomaterials with Low Thrombogenicity. Poly(ethylene oxide) exhibits extraordinary inertness toward most proteins and biological macromolecules. The polymer is therefore used in bulk and surface modification of biomaterials to develop antithrombogenic surfaces for blood contacting materials. Such modified surfaces result in reduced concentrations of ceU adhesion and protein adsorption when compared to the nonmodifted surfaces. 

Patterns of ordered molecular islands surrounded by disordered molecules are common in Langmuir layers, where even in zero surface pressure molecules self-organize at the air—water interface. The difference between the two systems is that in SAMs of trichlorosilanes the island is comprised of polymerized surfactants, and therefore the mobihty of individual molecules is restricted. This lack of mobihty is probably the principal reason why SAMs of alkyltrichlorosilanes are less ordered than, for example, fatty acids on AgO, or thiols on gold. The coupling of polymerization and surface anchoring is a primary source of the reproducibihty problems. Small differences in water content and in surface Si—OH group concentration may result in a significant difference in monolayer quahty. Alkyl silanes remain, however, ideal materials for surface modification and functionalization apphcations, eg, as adhesion promoters (166—168) and boundary lubricants (169—171). 

Organic titanates perform three important functions for a variety of iadustrial appHcations. These are (/) catalysis, especially polyesterification and olefin polymerization (2) polymer cross-linking to enhance performance properties and (J) Surface modification for adhesion, lubricity, or pigment dispersion. 

Lucie, S., Kovacevic, V., Packham, D.E., Bogner, A., Gerzina, A., Stearate-modified calcium carbonate fillers and their effect on the properties of polyvinyl acetate, composites. Proc. 2nd Int. Symp. Polymer Surface Modification Relevance to Adhesion, Newark, NJ, 24-26 May, 1999. 

K. L. Mittal, Polymer Surface Modification Relevance to adhesion, VSP, Utrecht, Netherlands, 1996. 

Rebenne, H. E., and Bhat, D. G., Effect of Diffusion Interface on Adhesion and Machining Performance of TiN-Coated Silicon-Nitride Cutting Tools, Proc. ThirdInt. Conf. on Surface Modification Technologies, Neuchatel, Switzerland (Aug., 1989)... 

Price C, Waters MGJ, Williams DW, Lewis MAO, and Stickler D. Surface modification of an experimental silicone rubber aimed at reducing initial candidal adhesion. J Biomed Met Res, 2002, 63, 122-128. 

Fluoroelastomers Novikova et al. [32] reported unproved physico-mechanical properties of fluoro mbbers by reinforcement with chopped polyamide fibers. Other fiber reinforcements are covered by Grinblat et al. [33]. Watson and Francis [34] described the use of aramid (Kevlar) as short fiber reinforcement for vulcanized fluoroelastomer along with polychloroprene mbber and a co-polyester TPE in terms of improvement in the wear properties of the composites. Rubber diaphragms, made up of fluorosilicone mbbers, can be reinforced using aramid fiber in order to impart better mechanical properties to the composite, though surface modification of the fiber is needed to improve the adhesion between fluorosUicone mbber and the fiber [35]. Bhattacharya et al. [36] studied the crack growth resistance of fluoroelastomer vulcanizates filled with Kevlar fiber. 

Styrene-butadiene-styrene (SBS) block copolymers are adequate raw materials to produce thermoplastic mbbers (TRs). SBS contains butadiene—soft and elastic—and styrene— hard and tough—domains. Because the styrene domains act as cross-links, vulcanization is not necessary to provide dimensional stability. TRs generally contain polystyrene (to impart hardness), plasticizers, fillers, and antioxidants processing oils can also be added. Due to their nature, TR soles show low surface energy, and to reach proper adhesion a surface modification is always needed. 

Acidification of chloramine T with sulfuric acid produces the formation of dichloramine T (DCT) and hypochlorous acid (HCIO), species which react with C=C bonds of the butadiene units. The effectiveness of the treatment is ascribed to the introduction of chlorine and oxygen moieties on the mbber surface. A decrease in the pH of the chloramine T aqueous solutions produced more extended surface modifications and improved adhesion properties in the joints produced with waterborne polyurethane adhesive (Figure 27.9). The adhesive strength obtained is slightly lower than that obtained for the rubber treated with 3 wt% TCI/MEK, and its increases as the pH of the chloramine T solution decreases (Figure 27.9). A cohesive failure in the rubber is generally obtained. 

Several environment-friendly surface preparation for the treatment of mbber soles with radiations have been recently studied. These treatments are clean (no chemicals or reactions by-products are produced) and fast, and furthermore online bonding at shoe factory can be produced, so the future trend in surface modification of substrates in shoe industry will be likely directed to the industrial application of those treatments. Corona discharge, low-pressure RF gas plasma, and ultraviolet (UV) treatments have been successfully used at laboratory scale to improve the adhesion of several sole materials in shoe industry. Recently, surface modification of SBR and TR by UV radiation has been industrially demonstrated in shoe industry... 

Treatment of TR with UV radiation has been shown to be successful in increasing its adhesion to polyurethane adhesive. A low-pressure mercury vapor lamp (main emission at 254 nm power = 20 mW/cm ) has been used. The UV treatment of TR improves the wettabUity, produces the formation of C—O, C=0, and COO moieties, and ablation is also produced. The extended UV treatment produces greater surface modifications, as well as the incorporation of nitrogen moieties at the surface. Peel strength values increase after UV treatment of TR, in a greater extent by increasing the treatment time. 

The treatment of SBR with fumaric acid solutions avoids the migration of antiadherent moieties to the surface and the treatment with TCI solutions is effective to enhance the adhesion of several mbbers to polyurethane adhesive. Therefore, the combined use of mixtures of TCI and FA solutions should be more effective in improving the adhesion of difficult to bond SBR. The wettability of SBR is improved by treatment with 3 wt% TCI/EA followed by treatment with 0.5 wt% FA/EtOH (3 wt% TCI-0.5 wt% FA), with 0.5 wt% FA/EtOH followed by treatment with 3 wt% TCI/EA (0.5 wt% FA-3 wt% TCI), or with TCI + FA mixtures.However, the extent of the surface modifications produced and the adhesive strength of adhesive joints are mainly due to chlorination with TCI/EA. 

Femandez-Garcfa J.C., Orgiles-Barcelo, and A.C., Martm-Martmez J.M., 1991, Halogenation of styrene-butadiene rubber to improve its adhesion to polyurethanes, J. Adhes. Sci Technol, 5, 1065-1080. Oldfield D. and Symes T.E.F., 1983, Surface modification of elastomers for bonding, J. Adhes., 16, 77-96. Pastor-Bias M.M., Ferrandiz-Gomez T.P., and Martm-Martmez J.M., 2000, Chlorination of vulcanized styrene-butadiene rubber using solutions of trichloroisocyanuric acid in different solvents, J. Adhes. Sci. Technol, 14, 561-581. 

FIGURE 31.9 Change in the peel strength and radiation dose of ethylene-propylene-diene monomer (EPDM)/EPDM joint [Eo/y Eo/yl EPDM/natural mbber (NR)/EPDM joint [Eo/y NR Eo/yl and EPDM/Al joint [Eo/y Al]. (From Sen Majumder, P. and Bhowmick, A.K., in Polymer Surface Modification Relevance to Adhesion, Vol. It, Mittal, K.L., Ed., VSP, Utrecht, The Netherlands, 2000,425. With permission.)... 

The reason for surface modification of a polymer is in most cases a wish to improve wettability and adhesion towards more hydrophilic materials. Both adhesion and wettability are interfacial phenomena. 

The common polymers are composed of a small number of elements whose XP spectra are simple (generally C Is plus one or two peaks from Ols, Nls, FIs and Cl 2s, 2p). Common contaminants contain additional elements such as S, P, Si, A1 and heavy metals, and the presence of these elements, even in low concentrations, can be detected very easily. Polymer surface modification is an area in which XPS has been fruitfully applied, notably in the study of commercial pretreatments aimed at improving wettability and general adhesion characteristics. 

Surface Modifications. Basic photopolymer chemistry is also being used for the surface modification of films, textiles fibers, and many other organic-based materials (104). Some of the novel applications of photopolymer technology to surface modification include the design of cell repellent treatments and in photografting of various chemical functionality onto the surface of materials to improve color retention, enhance the adhesion of antistatic chemicals or to improve staining resistance. 

In a previous section, the effect of plasma on PVA surface for pervaporation processes was also mentioned. In fact, plasma treatment is a surface-modification method to control the hydrophilicity-hydrophobicity balance of polymer materials in order to optimize their properties in various domains, such as adhesion, biocompatibility and membrane-separation techniques. Non-porous PVA membranes were prepared by the cast-evaporating method and covered with an allyl alcohol or acrylic acid plasma-polymerized layer the effect of plasma treatment on the increase of PVA membrane surface hydrophobicity was checked [37].The allyl alcohol plasma layer was weakly crosslinked, in contrast to the acrylic acid layer. The best results for the dehydration of ethanol were obtained using allyl alcohol treatment. The selectivity of treated membrane (H20 wt% in the pervaporate in the range 83-92 and a water selectivity, aH2o, of 250 at 25 °C) is higher than that of the non-treated one (aH2o = 19) as well as that of the acrylic acid treated membrane (aH2o = 22). 

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