Adhesive Specifications

Bell, 1978] Bell, G. I. Models for the specific adhesion of cells to cells. Science. 200 (1978) 618-627... 

Rosin, modified rosins, and derivatives are used in hot-melt adhesives. They are based primarily on ethylene—vinyl acetate copolymers. The rosin derivative is used in approximately a 1 1 1 concentration with the polymer and a wax. The resin provides specific adhesion to the substrates and reduces the viscosity at elevated temperatures, allowing the adhesive to be appHed as a molten material. 

Compounding is quite different for the two systems. The solvent base system is dependent on magnesium oxide and a /-butylphenoHc resin in the formulation to provide specific adhesion, tack, and added strength. Neither of these materials have proven useful in latex adhesive formulations due to colloidal incompatibihty. In addition, 2inc oxide slowly reacts with carboxylated latexes and reduces their tack. Zinc oxide is an acceptable additive to anionic latex, however. Other tackifying resins, such as rosin acids and esters, must be used with anionic latexes to provide sufficient tack and open time. 

The definition is intended to differentiate these adhesives from merely sticky materials like flypaper or materials that may have only substrate specific adhesion. 

Isocyanates can be added to solvent-borne CR adhesive solutions as a two-part adhesive system. This two-part adhesive system is less effective with rubber substrates containing high styrene resin and for butadiene-styrene block (thermoplastic rubber) copolymers. To improve the specific adhesion to those materials, addition of a poly-alpha-methylstyrene resin to solvent-borne CR adhesives is quite effective [76]. An alternative technique is to graft a methacrylate monomer into the polychloroprene [2]. 

Fillers. Fillers are not commonly added to CR adhesives. Calcium carbonate or clay can be primarily added to reduce cost in high-solids CR mastics. Maximum bond strength is obtained using fillers with low particle size (lower than 5 [jim) and intermediate oil absorption (30 g/100 g filler). In general, fillers reduce the specific adhesion and cohesion strength of adhesive films. Although polychloroprene is inherently flame retardant, aluminium trihydrate, zinc borate, antimony trioxide or... 

This chapter first reviews the general structures and properties of silicone polymers. It goes on to describe the crosslinking chemistry and the properties of the crosslinked networks. The promotion of both adhesive and cohesive strength is then discussed. The build up of adhesion and the loss of adhesive strength are explained in the light of the fundamental theories of adhesion. The final section of the chapter illustrates the use of silicones in various adhesion applications and leads to the design of specific adhesive and sealant products. 

A chemical property of silicones is the possibility of building reactivity on the polymer [1,32,33]. This allows the building of cured silicone networks of controlled molecular architectures with specific adhesion properties while maintaining the inherent physical properties of the PDMS chains. The combination of the unique bulk characteristics of the silicone networks, the surface properties of the PDMS segments, and the specificity and controllability of the reactive groups, produces unique materials useful as adhesives, protective encapsulants, coatings and sealants. 

Specialty waxes include polar waxes for more polar adhesive systems. Examples would be castor wax (triglyceride of 12-hydroxy stearic acid) or Paracin wax N- 2 hydroxy ethyl)-12-hydroxy stearamide) which are used in polyester, polyamide, or with high VA EVA copolymer-based systems. Other common polar waxes are maleated polyethylenes, which are used to improve the specific adhesion of polyethylene-based adhesives, and low molecular weight ethylene copolymers with vinyl acetate or acrylic acid, which are used to improve low temperature adhesion. High melting point isotactic polypropylene wax (7 155°C) and highly refined paraffin wax (7,n 83°C) are used where maximum heat resistance is critical. Needless to say, these specialty waxes also command a premium price, ranging from 2 to 5 times that of conventional paraffin wax. 

Adhesion depends on a number of factors. Good adhesion is defined by most customers as substrate failure. The major adhesive manufacturers possess equipment that allows them to make bonds with customer substrates under conditions that closely simulate actual packaging lines. These bonds are peeled either automatically or by hand to gauge adhesion. The most important factors influencing adhesion are the wet-out of the substrate, partieularly by the polymer component of the adhesive system, and the specific adhesion with the substrate. Choice of resin is critical for both. Rosin, rosin esters and terpene phenolics are eommonly added for these purposes in EVA and EnBA-based systems. Adhesion at low temperatures is also influenced by the overall toughness of the system at the test temperature. 

Most moisture-curing liquid adhesives utilize poly(oxypropylene) (PPG) polyols, as shown above. These raw materials produce among the lowest-viscosity prepolymers but may not have sufficient modulus at higher temperatures for some applications. A certain percentage of polyester polyols may also be utilized to boost performance, but these may cause a large increase in viscosity, and so they are more often used in conjunction with polyether polyols to provide a high-performance adhesive with workable viscosities. Poly(butadiene) polyols may be utilized for specific adhesion characteristics. 

Common plasticizers are used to reduce viscosity and to aid adhesion. Most plasticizers commonly utilized in PVC are also used in urethanes. One of the most common plasticizers is diisodecyl phthalate, though many others are used equally effectively. In some cases tackifiers, such as certain esters or terpine phenolics, are utilized to obtain specific adhesion characteristics. 

Condition in which two surfaces are bonded together by interfacial forces caused by valence forces or interlocking forces or both (see mechanical adhesion and specific adhesion). 

Adhesion, specific Adhesion between surfaces whereby valence forces predominate that are similar to those promoting cohesion. 

Adhesion of neutrophils to endothelial cells employs specific adhesive proteins (integrins) located on their surface and also specific receptor proteins in the endothelial cells. (See also the discussion of selectins in Chapter 47.)... 

By virtue of promising preliminary biological results indicating that tri- and tetravalent glycoclusters constitute potent inhibitors of bacterial binding, which fitted particularly well into the CRD of bacterial lectins (especially for mannose-specific adhesion) straightforward syntheses of low-valency glycoclusters were initiated. 

We have found enough exceptions to refrain from predicting that a specific adhesive system, e.g., epoxy or polyester, will always adhere better to a fluorinated or oxfluorinated surface. 

Mieroscopic visualization techniques have also been used to investigate mucus-polymer interactions [36-39]. Transmission electron microscopy was used by Fiebrig et al. [36], whereas different microscopical techniques were used by Lehr et al. [37] for the visualization of mucoadhesive interfaces. Transmission electron microscopy in combination with near-fleld Fourier transform infrared microscopy (FT-IR) has been shown to be suitable for investigating the adhesion-promoting effect of polyethyleneglycol added in a hydrogel [38]. Moreover, scanning force microscopy may be a valuable approaeh to obtain information on mueoadhesion and specific adhesion phenomena [39]. 

Materials. The adhesives and primers used in this study were model and commercial materials that were cured according to conditions appropriate for the specific adhesive chemistry. Adhesives A and B were conventional epoxy/Versamid and epoxy/dlcyandiamlde adhesives, respectively. Adhesives C and D were commercial urethane and epoxy/polyamlde adhesives, respectively. Adhesive E was a conventional two-part epoxy/amldoamlne adhesive. Adhesive F was a vinyl plastlsol adhesive. The adhesive primers used in this study were a urethane crosslinked epoxy electrocoat primer and spray primers based on tall oil modified epoxy ester, and polyesterpolyol/isocyan-ate chemistry. Dicyandlamlde was obtained from Aldrich Chemical Company. Epon 828 was obtained from Shell Chemical Company. 

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