Epoxy adhesives parameters

TABLE 3.8 Effect of Various Formulation Parameters on the Flexibility of an Epoxy Adhesive... 

The common surface preparation treatment for epoxy resins is to wipe with solvent, mechanical abrasion, and final solvent cleaning. Epoxy parts can be most easily bonded with an epoxy adhesive similar to the material being bonded. Urethanes, cyanoacrylates, and thermosetting acrylics have also been used when certain properties or processing parameters are required. 

Bisphenol A is used as a raw material to make polycarbonate and epoxy adhesives and can coatings. It is also used in flame-retardants, in unsaturated polyesters and in polyacrylate resins. Many foodstuff containers are made of these resins, including containers for oven and microwave cooking. Recent studies have shown that bisphenol type compounds have both mutagenic and cytotoxic properties [84]. Nerin et al. developed a fast screening method based on SPME and HPLC with fluorescence detection suitable for the analysis of several bisphenol derivatives and their degradation products in aqueous canned foods such as tuna, olives and corn [85]. The best results were obtained with carbowax and PDMS/DVB fibers. The detection limits were between 0.7 and 2.4ngmL while RSDs were between 14 and 32%. After the extraction parameters were optimized, the method was applied to... 

One-part epoxy adhesives generally need to be kept frozen and allowed to come to room temperature before use. In this case, the pot life is the time where the adhesive is workable at the ambient. With two-part systems, the epoxy resin and hardeners are mixed just before use and the pot life is taken from that time. Any change in parameters such as viscosity, skin-over, or loss of bond strength may be... 

In addition to the strength of adhesives under impact, also the properties related to dynamic deformabdity are of interest. Sato and Ikegami (2000) have studied the cases of lap joints and scarf joints subjected to axial impact loads. Preliminarily, they have measured the attenuation of the axial-strain waves in a special specimen of epoxy adhesive, manulactured (by molding the adhesive resin) as a cylinder of length 900 mm and diameter 20 mm. From these results the complex compliance of the material was obtained and, in turn, used to identify the parameters of a five-element Voigt model of viscoelasticity. These material data have been introduced in the finite element simulation of the impact tests on the joints. The joints used in... 

Despite all precautions, urethanes can be used most effectively within certain thermal and oxidation limits. Outside these parameters, other adhesives, such as certain epoxies, cyanate esters, and other high-temperature adhesives, should be considered. 

The theory has been examined by measuring the ratio K,c/Klcs as a function of j/g, as shown in Fig. 17. The theoretical lines have been fitted to the experimental points by choosing suitable values of the critical distance, c, which is the only fitting parameter. The agreement between theory and experiment has been found to be equally good for many different epoxy polymers cured with many different hardeners, both unmodified 44- 45,51), rubber-modified 45) and containing glass particles 22) and even, under certain circumstances, for structural adhesive joints S3). Values of critical stress, ct,c, and distance, c, for various epoxy materials, obtained from bulk and... 

Note that good wetting is necessary for bond formation. However, it is not the sole criterion for a strong adhesive joint. Several other important parameters, as noted in the sections that follow, strongly affect the adhesive strength of epoxy systems. 

It should also be emphasized that the epoxy resins are only building blocks in the development of epoxy-based adhesives. The formulation will ultimately involve one or more epoxy resins curing agents modifiers, such as plasticizers, flexibilizers, accelerators, stabilizers, and flow control agents and fillers. In general, flexibility can be controlled by the parameters shown in Table 3.8. 

The adhesive properties of epoxy resins coupled with their dielectric behavior have made them attractive to the electronic industry. The evaluation of thermally cured rubber modified epoxy thermosets has been the subject of recent studies (1, 2), which dealt with the dependence of morphology on the curing parameters, e.g., catalyst, cure schedule, time of gelation, etc. This work utilizes one of the new series of photocationic initiators (PCI) developed by Crivello, et al (3) which are presently commercially available. These onium salts initiate the reaction by absorbing the actinic radiation, generating radicals and producing a protonic acid. The radicals can lead to polymerization of olefinic moieties (4) while the acid initiates the polymerization of the epoxy groups (3). 

---