Adhesion to porous substrates

Thickeners added to an adhesive will raise viscosity and permit dilution with water. This reduces the total solids of the adhesive and thus lowers its (wet) cost. Thickeners release water slowly, and when combined with lower solids, they also slow the setting (prolong open time) of the adhesive. Thickeners such as polyvinyl alcohol, starch, and hydroxy ethyl cellulose will improve adhesion to porous substrates by reducing penetration of an emulsion into the substrate and decreasing the likelihood of a starved joint. ... 

Many of the features of the adsorption theory of adhesion, just discussed, can be traced back to McBain and Hopkins classical work in the 1920s, where they are referred to it as specific adhesion (McBain and Hopkins 1925 Packham 1998, 2002 2003). They also described mechanical adhesion to porous substrates, such as wood, unglazed porcelain, pumice, and charcoal. They regarded it as obvious that a good joint must result whenever a strong continuous film of partly embedded adhesive is formed in situ. This is, in essence, the mechanical theory of adhesion. 

The second category was concerned with adhesion to porous or microfibrous surfaces on metals. Aluminium may be anodised to form an oxide surface comprising pores of diameter of tens of nanometers. Electroforming and chemical oxidation can be used to produce microfibrous or needle-like coatings on metals, including copper, steel and titanium. The substrate topography was demonstrated to play an vital part in adhesion to these surfaces [45-48]. 

Despite the high specific surface areas, the amount of accessible catalyst remains low due to the limited thickness of the porous catalytic layer dictated by considerations such as the adhesion to the substrate. The susceptibility of the fine channels to blockage with solid impurities or deposits formed in the reaction, together with the problems of integrating connections with the external macroenvironments and ensuring uniform gas distribution between the individual channels, a prerequisite for numbering up, represent further questions that have to be resolved for the industrial application of microreactors to become practicable. 

Amidoamines exhibit very good adhesion characteristics, particularly to porous substrates such as concrete and wood. They also cure extremely well under humid conditions. They are much less corrosive than aliphatic amines and provide less skin irritation. 

While a static load test is the commonly accepted procedure, in practice many variations in areas and weights are used, to compensate for the various qualities of adhesive evaluated, so that the test results will fall into a similar time frame, so it becomes difficult to compare different adhesive systems from accumulated data. It has the disadvantage of giving variable results for the same adhesive system, and is essentially a pass/ fail test, as many products remain in place at the end of the test period. Experience has shown that the shear properties of pressure-sensitive adhesives to porous and nonporous substrates can be quite different, and each must be judged on its own merits. 

In a simple approach, monomers of the guest polymer are first impregnated into a preformed porous silicate film, and subsequently polymerization is initiated either by a free radical initiator (UV, peroxides), by thermal treatment, or by electrochemical means. On the positive side, this procedure is favorable for the incorporation of linear polymers in silicates, but on the downside, some of the major advantages of composites, such as biocompatibility and adhesion to the substrate, are lost. The polymerization of organic moieties within the interconnected pores of the organic material can be carried out by two general methods that are addressed in the following text. 

Clays and other fillers impart stiffness to adhesive films. Clays reduce the penetration of adhesives into porous substrates. Large-particle clays are better able to control penetration and also impart more rapid setting speed. A highly plastic clay, bentonite, makes adhesives thixotropic—fluid under high shear, thicker upon application. A study has been made of the effect of various fillers on the adhesive properties of polyvinyl acetate. 

These resins were somewhat brittle. They bonded well to porous substrates but found limited application unless modified by compounding in order to improve flexibility and adhesion to nonporous surfaces. For example, blending of solid thermoplastic resins with the reactive polyamides resulted in hot melt adhesives which bonded well to metals and other substrates, and also had improved flexibility. 

Generally, gas evolution is deliberately suppressed during the electrochemical metal deposition process to enhance the qualities of deposits such as their compactness and adhesion to the substrate. Thus, the potentid for the creation of highly-porous stmetures by gas evolution during electrochemical deposition of metals has not attracted much attention. 

Coating Processes and Adhesion to Porous and Non-Porous Substrates... 

Uses Defoamer for aq. formulations, printing inks, adhesives, industrial maintenance coatings, wood coatings, latex dipping bath formulations Features Esp. suitable for applic. to porous substrates silicone-free Properties Tan liq. self-emulsiflable in water sp.gr. 0.912 vise. < 600 cps vapor pressure 10 mm Hg (21 C) m.p. -7 C pour pt. < 2 C flash pt. (PMCC) HOC VOC 4.8% 100% act. 

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