Adhesive formulations bulk properties

Basically, there are two major considerations when one is formulating or selecting adhesives or sealants for low-temperature applications. The first is the effect of the low temperature on the bulk properties of the polymer, and the second is the effect of thermal cycling and resulting internal stresses on the joint interface. 

The determination of a fundamental or bulk property, such as viscosity, hardness, or settling rate, is usually simpler and more reproducible than end-use tests. However, a correlation between fundamental properties and the results of end-use testing is very difficult. Fundamental property tests are usually employed to assess the consistency of the incoming raw materials, adhesive formulation, or substrates. Often fundamental property testing is done after there is a failure or unexplained occurrence to determine if a change in the incoming material may be the possible culprit. 

Table IV. Bulk Properties of Adhesive B Formulations Containing 5 phr of Toughener...

As intended by the adhesive formulation, no parasitic side reactions such as formation of urea, new uretdione, isocyanurate, biuret, or allophanate are detected for the bulk and for thick films on Al, Cu, and Au (dpu>l pm cf Figs. 6.3, 6.7). Even ultrathin PU films on Au correspond to bulk properties to a very good approximation (Fig. 6.8), which is a recommendation for films on Au as references with respect to effects in the interphase on different metals. 

The adhesion behaviour of urethanes depends not only on their composition but also on the contribution of physico-chemical factors, in particular on the surface properties of urethanes. Two specific aspects of surface behaviour are considered in this chapter, which is arranged in three sections the first concerns the ability of some polymers, including PU to adopt a variety of surface structures or orientations, as dictated by preparation conditions and the medium in contact with the urethane polymer. The ability to undergo surface restructuring is a factor in the well documented difference between surface and bulk properties of all polymers. A second aspect of surface behavior, exerting major influence on the adhesion of urethanes to a variety of plastics or glass, is the acid-base interaction between the adhesive polymer and the substrate. Acid-base interactions are a subject of discussion in the second section of this chapter. Finally, the role of silane modifiers in affecting the adhesion behavior of defined urethane adhesive formulations is considered. 

While pressure sensitive adhesive performance at various temperatures can be determined by practical tests, as described above, it is also possible to predict the temperature performance of pressure sensitive adhesives. The polymers used in pressure sensitive adhesives will have a variety of glass transition temperatures (Tg), and for a pressure sensitive adhesive to be effective, the formulated mass must have a Tg of between 50°C and 70°C below the temperature at which the adhesive is to be used. At the same time, however, the Tg cannot be so low that the adhesive mass is so soft that it fails cohesively even at room temperature. A variety of analytical techniques used to determine the Tg of the adhesive mass include Differential Scanning Calorimetry (DSC), Differential Thermal Analysis (DTA), and Dynamic Mechanical Analysis (DMA). Of these, the most commonly used method is DMA. DMA will measure the bulk properties of the adhesive mass, which will include the base polymer and any additives in it. It does not take into consideration any interfacial relationships between the adhesive and the surfaces to which it is bonded. 

The bulk physical properties of the polymers of the 2-cyanoacryhc esters appear in Table 2. AH of these polymers are soluble in /V-methy1pyrro1idinone, /V,/V-dimethy1foTm amide, and nitromethane. The adhesive bonding properties of typical formulated adhesives are Hsted in Table 3. 

In this reaction, no by-products are evolved, and the crosslinking reactions occur within the bulk of the material. A typical hydrosilylation crosslinking system is depicted in Scheme 11, where n and y can vary depending on the required viscosity of the uncured formulation and the final targeted properties of the cured adhesive. 

CAS 12001-26-2 EINECS/ELINCS 310-127-6 Uses Filler for paint formulations, foundry coatings, adhesives, sealants Properties 81% on 325 mesh, 98% on 200 mesh bulk dens. 10.3 oil absorp. 40... 

Chem. Descrip. Zinc borate CAS 1332-07-6 EINECS/ELINCS 215-566-6 Uses Flame retardant, smoke suppressant for plastisols, coatings for cellulosics, textiles, and adhesives synergist in PVC and halogenated polyester formulations, and in elastomers, thermoplastic elastomers, polyamides, and polyolefins strong char promoter Properties Wh. free-flowing powd., nonhygroscopic 6 p avg. particle size 99.9% < 30 p sol. 0.5 g/100 ml water sp.gr. 2.50 bulk dens. 18.1 Ib/ff oil absorp. 39 ref. index 1.48 Zb -237 [Great Lakes]... 

While the bulk of any cyanoacrylate formulation consists of monomer, a large number of modifiers have been used to impart desired properties to the composition. These include stabilizers, inhibitors, thickeners, plasticizers, dyes or colorants, adhesion promoters, and others. Each of these classes of modifier will be dealt with in subsequent parts of this chapter. Because of the variety of modifiers, and the variety of applications for cyanoacrylates, a bewildering number of cyanoacrylate adhesives are now commercially available. These can be generally divided into the following classifications adhesives of different viscosities and cure rates, adhesives based on different monomers, adhesives for the bonding of metal, plastic, rubber, or wood, various types of improved performance adhesives, i.e., heat, moisture, or impact resistant, and adhesives for bonding low surface... 

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