Acid-etching pretreatment

Acid etching pretreatment of enamel, such as the use of buffered 50% phosphoric acid solutions, has found clinical applications to bond enamel to restorative materials, sealants and orthodontic brackets (4, ). The etching creates an increased enamel surface area and opens pores into which the resin can flow. Greater porosity of the substrate allows an easier ingress of un-... 

Acid etching pretreatment of dentin prior to application of a resin restorative leaves the collagenous component of this substrate substantially untouched. The collagen at the dentin surface interferes with the mechanical adhesion of the hydroxyapatite, (the inorganic constituent of dentin) to the adhesive. Thus, in contrast to its successful use with enamel, etching pretreatment produces a bond between dentin and restorative resin that is too weak to withstand the forces encountered at the interface under clinical conditions. 

Fig. 1. Effect of outdoor weathering on the strength of epoxy-polyamide/aluminium alloy (chromic-acid etched pretreatment) structural joints [7]. (a) Hot/wet tropical site, (b) Hot/dry desert site.

Original oxide Irom acid etch pretreatment... 

There are numerous metal pretreatment techniques that can be used in addition to solvent degreasing. To obtain metal/polymer systems which exhibit strong initial adhesion it is usually sufficient to wash the metal with a solvent followed by an acid etch or sandblasting technique to remove any weak oxide layers and roughen the surface simultaneously. 

Fig. 5. Effect of outdoor weathering on the strength of aluminum alloy/epoxy-polyamide joints (chromic-sulfuric acid-etch metal surface pretreat-ment)61 (Reprinted from Ref. 61, p. 194, by courtesy of Gordon and Breach...

The outdoor durability of epoxy bonded joints is very dependent on the type of epoxy adhesive, specific formulation, nature of the surface preparation, and specific environmental conditions encountered in service. The data shown in Fig. 15.19, for a two-part room temperature cured polyamide epoxy adhesive with a variety of fillers, illustrates the differences in performance that can occur due to formulation changes. Excellent outdoor durability is provided on aluminum adherends when chromic-sulfuric acid etch or other chemical pretreatments are used. 

Figure 1. AFM image of a phlogopite (001) surface after pretreatment acid etch and rinse. The light gray triangular pits are 1 nm deep, equivalent to one unit cell along [001]. The black pits are deeper, typically between 2 and 20 nm. The scale bar is 1 pm long.

Figure 2. AFM images, approximately 2.5 im on a side, of phlogopite (001) surfaces after pretreatment acid etch and rinse (top), and after pretreatment acid etch, rinse, and 24 hours in DI water equilibrated with air (bottom). Both images are taken from the same area of the same sample, although the bottom image is rotated about 30 counterclockwise from the top image. The scale bars in both images are 0.5 pm long. See text for additional details.

For each alloy studied, the chromic-sulfuric acid etching, Alodining, and anodizing surface pretreatment produced the most durable joints, although the relative order of effectiveness could vary with different alloys. 

Figure 15. XPS carbon Is and oxygen Is photopeaks for pretreated aluminum alloy after acid etch and before bonding (FPL) two failure surfaces following bonding with polysulfone and testing in the wedge configuration (FPL MFS and FPL AFS) and, neat polysulfone (PSF) (38).

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