Adhesives general properties

Table 14.6 is only indicative of general properties, and the latest developments of specific manufacturers of self-adhesive tapes may show advances on these. 

The general properties of cured and uncured epoxy resins are reviewed in Chap. 3. The chemical structures of the resin and curing agent will determine these physical properties. They will also determine, to a great extent, the surface chemistry and adhesion properties of the final product. 

The highest-MW DGEBA epoxy resins are termed phenoxy resins. They are highly linear molecules that are used primarily as thermoplastic coating resins. However, they can be blended with lower-MW epoxy resins for the improvement of specific properties such as flexibility, impact and fatigue resistance, and thermal cycling. Phenoxy resins are sometimes used alone as a thermoplastic hot melt adhesive generally in film form. 

Figure 15.22 shows the long-term effect of a heat cured one-part epoxy adhesive to various chemical environments. As can be seen, the temperature of the immersion medium is a significant factor in the aging properties of the adhesive. As the temperature increases, the adhesive generally adsorbs more fluid, and the degradation rate increases. 

Since epoxy adhesive formulation represents a surprisingly broad area of technology, a road map to the use of this book may be valuable. Chapters 1 through 3 discuss the synthesis of raw materials, epoxy chemistry in general, and the physical and chemical properties that are important for an epoxy adhesive. These properties are important during the three primary phases or conditions of an adhesive (1) uncured, (2) during cure, and (3) fully cured. 

Major advantages Ease of fabrication, clarity with Dame retard ancy. moderate dissipation (power) factor Low shrinkage, excellent adhesion Good general properties, low cost... 

Note Material bonded, aluminum alloy sheet, 0.5 mm pretreatment, pickling method cure, 300 °F, 20 min base resins, Versamid resin 115 epoxy 60 40 . These same tables. Including Table VIII, illustrate the general property ranges to expect from epoxy-polyamide adhesives under defined cure and testing conditions (42). ... 

When diamond films are deposited chi non-diamond substrates, stresses may be generated in the films due to lattice mismatch and/or differences in thermal expansion coefiBcients between diamond and the substrate materials.In addition, lateral variations in the grain size, density, or impurities incorporated during growth may also lead to stresses, which may be either tensile or compressive. The stresses are known to generally build up with increasing film thickness, and will influence diamond-substrate adhesion and properties of diamond films. ... 

The wide variety of grades available provides for an extremely diverse array of properties that can be developed for butyl rubber adhesives and sealants. However, the following general properties apply to varying degrees. 

In general, properties such as colour, natural durability and dimensional stability of thermal treated wood differ from those of untreated wood. Depending on the duration and the power of the process, thermally treated wood shows improved rot-resistance properties and also demonstrates increased resistance to both fungi and climatic influences.To warrant the natural durability it must be ensured, however, that the TMT products have no contact to the ground. Furthermore, its dimensional stability can be improved as well as its adhesion property against hydrophobic materials. 

Thin polymer films are generally obtained by solution casting, in many applications, such as paints, varnishes, or adhesives. The properties of polymer films obtained from a solution differ from the original bulk properties, and this effect can have some significant consequences on the expected behavior of the final film. 

The water-based component is the main adhesive component in EPI adhesives. Generally, it consists of water, poly(vinyl alcohol) (PVA), one or more water-based emulsions, filler(s) and a number of additives such as defoamers, dispersing agents and biocides [1, 4, 5, 8, 9]. As with traditional thermosetting and thermoplastic wood adhesives, properties such as viscosity and solids content vary with the intended application. In the European market the typical viscosities are 2000-8000 mPa s at 25°C and the solids content is normally 50% or more. The adhesives are normally neutral with a pH in the range of 6-8 [3]. The storage stability of the EPI adhesive component is typically half a year when stored at a temperature between 10 and 30°C. 

For wood-based panels, European standards are focused on general properties of end-products. The only standard really linked to adhesion is EN 314-1 (2005) [1] which defines a test method for evaluation of the bonding quality of plywood panels. 

Adhesives generally react to radiation in much the same manner as the plastics or elastomers from which they are derived. Generally, those containing aromatic compounds show good resistance to radiation. Fillers and reinforcing materials improve the radiation stability of these products substantially, while also improving other properties. 

The test programme was necessary because of lack of a reliable joint data. For example, there are very limited data on the behaviour of laminated joints. Also, adhesive manufacturers are generally not able to provide those adhesive mechanical properties required in the design process. 

Adhesive test methods and their test results are related to but are not the same as other polymer property tests described in this handbook. In general, adhesive property tests are ultimate properties measured at the failure load of an adhesive joint. Adhesive joint properties are certainly related to adhesion (vide supra) but are primarily due to the physical properties of the adhesive and the physical properties of the adherends. In addition, the design of the adhesive joint has a major effect on the measured strength. Indeed, a properly designed adhesive joint will always lead to failure of the adherend. In addition, adhesive joint properties are as temperature- and rate-dependent as the properties of the polymers used to make the adhesive. Unfortunately, in many cases in the literature, the rate of test is not described. In this chapter, the type of adherend or backing will be described, if at all possible. 

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