Adhesion promoters performance

For the evaluation of the diffusion constant D at a time t, the potential difference relative to the potential of the intact, electrolyte-free metal/adhesive interface is fitted with respect to Eq. (22). For the ingress of sodium chloride from an aqueous solution of 0.5 m NaCl into the defect area as shown in Fig. 31.2, a diffusion coefficient of 1 x 10 cm s is calculated, even for highly stable adhesive/metal interfaces modified with an aminosilane adhesion promoter. Performing the diffusion measurement with other metal hahde solutions shows that an effective diffusion coefficient of the hydrated ion-pair, is measured by this method. This could be shown by changing the size of either the hydrated cation or anion, which resulted in a corresponding change in the measured diffusion coefficient (with smaller hydrated ions diffusing faster). 

Fig. 31. 8 Increase in the delamination velocity as a function of mechanical stress in the blister test experiment measured with the HR-SKP comparison of an unmodified epoxy adhesive (as in Fig. 31.2, about 70 p,m thick) and of the adhesive modified with an organosilane adhesion promoter, performed with 0.5 M NaCi as electrolyte.

Compared with vacuum plasma batch processes, the opportunity to apply atmospheric chemical plasma surface treatments to material surfaces on continuous production lines with similar surface cleaning and adhesion promotion performance is economically attractive. 

Hybrid Circuits. The use of parylenes as a hybrid circuit coating is based on much the same rationale as its use in circuit boards. A significant distinction Hes in obtaining adhesion to the ceramic substrate material, the success of which determines the eventual performance of the coated part. Adhesion to the ceramic must be achieved using adhesion promoters, such as the organosilanes. 

The performance of a product where adhesion plays a role is determined both by its adhesive and cohesive properties. In the case of silicones, the promotion of adhesion and cohesion follows different mechanisms [37]. In this context, adhesion promotion deals with the bonding of a silicone phase to the substrate and reinforcement of the interphase region formed at the silicone-substrate interphase. The thickness and clear definition of this interphase is not well known, and in fact depends on many parameters including the surface physico-chemistry of... 

Proper reinforcement of rubber matrix using hllers can be achieved only if there exists adequate adhesion between the hller and the mbber. Rubber-mbber adhesion and rubber-hller adhesion both without and with adhesion promoters have been studied extensively [125-127]. Fiber-matrix adhesion in short fiber-rubber composites is always a field of extensive research. If the fibers are not bonded properly with the rubber matrix, fibers will shde past each other under tension deforming the matrix, thereby reducing the strength properties. In the case of short fiber-reinforced rubber composites, loads are not directly applied to the fibers, but are apphed to the matrix. To obtain a high-performance composite, the load must be effectively transferred to the fibers, which is possible only when the fiber-matrix interphase is sufficiently strong. In addition, the adhesion between the fiber and the matrix should be such that the failure occurs in the matrix rather than at the interphase [92]. 

Control of fiber friction is essential to the processing of fibers, and it is sometimes desirable to modify fiber surfaces for particular end-uses. Most fiber friction modifications are accomplished by coating the fibers with lubricants or finishes. In most cases, these are temporary treatments that are removed in final processing steps before sale of the finished good. In some cases, a more permanent treatment is desired, and chemical reactions are performed to attach different species to the fiber surface, e.g. siliconized slick finishes or rubber adhesion promoters. Polyester s lack of chemical bonding sites can be modified by surface treatments that generate free radicals, such as with corrosive chemicals (e.g. acrylic acid) or by ionic bombardment with plasma treatments. The broken molecular bonds produce more polar sites, thus providing increased surface wettability and reactivity. 

Other additives used to improve the performance of radiant cured adhesives are similar to those that might be found in more conventional adhesives. These include adhesion promoters, fillers, light stabilizers, antioxidants, and plasticizers. 

Most of the raw materials used in large quantities in structural adhesives are used because they are widely available, relatively safe, and inexpensive. Quite often they are made in large quantities for uses other than adhesives and the adhesive manufacturers have taken advantage of supply and price. Few new basic raw materials are being developed specifically for the adhesive industry although the traditional raw materials are being combined in new ways to enhance desired adhesive properties. New initiators, adhesion promoters, primers, and specialty chemicals are being developed for use in small quantities to provide wider application latitude and improved performance. 

Other properties that are heavily influenced by the choice of monomer include cure speed (in general higher functional monomers cure more rapidly), viscosity, and durability of the film. Table 1 lists some monomers, their viscosities, and the properties that they enhance (reprinted with permission from Sartomer). it is important to note several trends on the chart. Cure speed increases with an increase in functionality (all of the recommended monomers in that column are at least trifunctional and several are tetra- or penta-functional). Viscosity also increases as the functionality of the monomer is raised (all of the low viscosity diluents are diacrylates). The adhesion promoting monomers are all di- or mono-functional. Most formulas contain several different monomers and sometimes also oligomers as there is often a balancing act that must be performed when selecting materials that will provide the required performance properties while still maintaining the correct viscosity and surface tension. 

Some of them (adhesives, coatings, foam plastics, and resins) use Mannich bases or their derivatives as structural components of the material, whereas all the listed branehes are concerned with the use of important additives (mainly antioxidants) or auxiliaries such as basic catalysts and accelerators. Specific functions are performed, for instance, by agents improving the adhesion of photopolymerizable paints and by accelerator-modified adhesion promoters for mbber-to-wirc adhesion." ... 

Silylated urethane polymers allow formulators to produce fast-cure construction joint sealants with superior performance properties. The sealant is composed of silylated urethane polymer, plasticiser (e.g. diisodecyl phthalate), fillers (calcium carbonates), fumed silica, adhesion promoter, dehydrating agent, and catalyst (dibutyltin dilaurate). 

A similar mechanism acts in the case of reactive adhesion promoters such as polyurethanes. Here water is a factor, as well as surface functional groups of fillers. The adhesion promoter is exhausted within the bulk of organic material (coating, adhesive, etc.) and unable to perform the task. 

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