Increasing Adhesion

There are instances where adhesion can be increased rather than reduced, that is, where silica particles are present not as weak aggregates but as dispersed particles 

It is sometimes not realized that dispersion of substantial proportions of discrete, fully disaggregated particles in a liquid does not appreciably increase the viscosity and does not develop any thixotropy. Thus organosols containing 20-30% SiO, are quite fluid. It is only when particles of colloidal size form a network through the liquid that these thickening ejects are observed. 

The overall behavior of silica cannot be understood until the following variables are considered in turn  

Degree to which particles arc dispersed—to separate particles or aggregates. 

Relative energy of particle-particle contacts versus particle surface-liquid. 

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Tire Cord. Melamine resins are also used to improve the adhesion of mbber to reinforcing cord in tires. Textile cord is normally coated with a latex dip solution composed of a vinylpyridine—styrene—butadiene latex mbber containing resorcinol—formaldehyde resin.. The dip coat is cured prior to use. The dip coat improves the adhesion of the textile cord to mbber. Further improvement in adhesion is provided by adding resorcinol and hexa(methoxymethyl) melamine [3089-11 -0] (HMMM) to the mbber compound which is in contact with the textile cord. The HMMM resin and resorcinol cross-link during mbber vulcanization and cure to form an interpenetrating polymer within the mbber matrix which strengthens or reinforces the mbber and increases adhesion to the textile cord. Brass-coated steel cord is also widely used in tires for reinforcement. Steel belts and bead wire are common apphcations. Again, HMMM resins and resorcinol [108-46-3] are used in the mbber compound which is in contact with the steel cord to reinforce the mbber and increase the adhesion of the mbber to the steel cord. This use of melamine resins is described in the patent Hterature (49). 

Increased flexibility Increased dispersing power Increased water sensitivity Increased adhesion to hydrophobic surfaces... 

Increased water resistance Increased tensile strength Increased block resistance Increased solvent resistance Increased adhesion to hydrophilic surfaces... 

Increase adhesion tension. Maximize surface tension. Minimize contact angle. Alter surfactant concentration or type to maximize adhesion tension and minimize Marangoni effects. Precoat powder with wettahle monolayers, e.g., coatings or steam. Control impurity levels in particle formation. Alter crystal hahit in particle formation. Minimize surface roughness in milhng. 

A very simple tape test was used to demonstrate that a significant increase in adhesion of copper to PS accompanied formation of this complex. Copper films applied to clean PS were easily removed when a tape was pressed against the copper films and then peeled away. However, copper films applied to PS that was treated with an oxygen plasma were never removed by the tape, indicating significantly increased adhesion. 

Other polymers used in the PSA industry include synthetic polyisoprenes and polybutadienes, styrene-butadiene rubbers, butadiene-acrylonitrile rubbers, polychloroprenes, and some polyisobutylenes. With the exception of pure polyisobutylenes, these polymer backbones retain some unsaturation, which makes them susceptible to oxidation and UV degradation. The rubbers require compounding with tackifiers and, if desired, plasticizers or oils to make them tacky. To improve performance and to make them more processible, diene-based polymers are typically compounded with additional stabilizers, chemical crosslinkers, and solvents for coating. Emulsion polymerized styrene butadiene rubbers (SBRs) are a common basis for PSA formulation [121]. The tackified SBR PSAs show improved cohesive strength as the Mooney viscosity and percent bound styrene in the rubber increases. The peel performance typically is best with 24—40% bound styrene in the rubber. To increase adhesion to polar surfaces, carboxylated SBRs have been used for PSA formulation. Blends of SBR and natural rubber are commonly used to improve long-term stability of the adhesives. 

Tackifiers. Resins are generally added to adjust the desired tack. In general, resins must be used with plasticizers to obtain a good balance between tack and cohesive strength. Typical tackifiers are polyterpenes, although hydrocarbon resins and modified rosins and rosin esters can also be used. In some cases, terpene-phenolics or phenol-formaldehyde resins are added to increase adhesion. 

Adhesion promoter. Epoxy silane can be added to increase adhesion to glass (mainly for BR sealants). In certain textile applications, isocyanates can be added to solvent-borne BR cements. 

Although the diffusion mechanism can be seen as mechanical but occurring at molecular dimensions, van der Waals intermolecular interactions and conformational entropic energy provide an additional mechanism that increases adhesion [62]. It is interesting to note the analogy that exists between this mechanism at the molecular level with the adherence, adhesion and viscoelastic deformations concept applied for a macroscopic adhesive. 

The SEM investigation shows that the particle size of the dispersed domain size decreased from 3.3 to 1.1 fxm with the incorporation of 6 wt%, EMA, and this indicates the increased surface area of the dispersed phase morphology. The increase in surface area led to effective compatibilization and is responsible for the increased adhesion strength and tensile impact strength of compatibilized blends. 

Evidently, the critical pressure to cause failure decreases with a stiffer interphase modulus, E, or a reduced interlayer thickness, h, or both. This hypothesis has been tested on several simulation systems, which confirm that increased adhesion is possible with a negative transversal modulus gradient at the material interface. 

The formation of these polar groups contributes increased adhesion. Observation of disappearing vinyl groups in the silane coupling agent and of the formation of polystyrene in the silica by FTIR analysis (Fig. 15) have confirmed the occurrence of a reaction between the polymer and the silane coupling agent [77]. 

In a series of reviews [244-246] the models proposed for the assessment of the effect of fillers on the complex of PCM properties are discussed. Analysis of the models shows that, for a fixed filler content, the strength must be higher in compositions with fillers featuring the absolute adhesion to the matrix than in systems with little or no adhesion. The relative elongation and specific impact strength must, on the contrary, go up with the increasing adhesion. 

Figure 2. (1) Neutrophils circulating passively in blood capillary. (2) Chemoattractants may be detected by the circulating neutrophils, by the endothelial cells lining the lumen, or both in order that the neutrophils become adhesive. This adhesion is mediated by selectins, a group of cell surface proteins. Neutrophils roll on the surface of the endothelial cells and then actively locomote seeking out spaces between the endothelial cells. (3) The adhesive neutrophils begin to squeeze between endothelial cells. (4) Cells move through the extracellular matrix towards the site of infection. Here adhesion is low and may not be necessary for locomotion. (5) At the site of infection, neutrophils become trapped by increased adhesion where they phagocytose bacteria and liberate the contents of their granules. After Lackie (1982,1986).

Lauro C, Catalano M, Trettel F et al (2006) The chemokine CX3CL1 reduces migration and increases adhesion of neurons with mechanisms dependent on the betal integrin subunit. J Immunol 177 7599-7606... 

A cement slurry additive consisting of methylcellulose, melamine-formaldehyde resin, and trioxane has been proposed for better bonding of cement to the casing string [20]. Bisphenol-A epoxide resins, with amine-based curing agents, sand filler, and a mixture of n-butanol and dimethyl benzene as a diluent, have been proposed as additives to increase adhesion properties of cement [572]. 

Small amounts of phosphonium complexone [1560] are sufficient to increase adhesion to the stratal rock. Table 18-4 illustrates an example for plugging solution with Portland cement and phosphonium complexone. Calcium chloride acts as a regulator of the setting time in the suggested composition. More precisely, phosphonium complexone stands for certain chelating phosphorous compounds (e.g., oxyethylidene diphosphonic acid, nitrilo-trimethyl phosphonic acid, sodium tripolyphosphate, or amiphol) [1540]. The mixture is applicable at low temperatures from 20° to 75° C. 

L. V. Palij, V. E. Akhrimenko, A. K. Kuksov, V. M. Medentsev, and V. I. Panov. Plugging solution for oil and gas wells—contains Portland cement, fly ash, sodium or calcium sulphate and additionally hydrosil, to increase adhesion of cement rock to casing string. Patent SU 1802087-A, 1993. 

Keratinization, the sloughing of epithelial cells in the hair follicle, is also a natural process. In acne, however, hyperkem-tinization occurs and causes increased adhesiveness of the sloughed cells. Accumulation of these cells clogs the hair follicle, blocks the flow of sebum, and forms an acne lesion called an open comedo or blackhead. ... 

Oba Y, Lee JW, Ehrlich LA, et al. MIP-lalpha utilizes both CCR1 and CCR5 to induce osteoclast formation and increase adhesion of myeloma cells to marrow stromal cells. Exp Hematol 2005 33(3) 272-278. 

Povidone PVP Water, GI fluids, alcohol, and IPA Care needed in use due to tackiness during drying best used in mixtures to increase adhesion is hydroscopic if used alone... 

Wick T, Kaye N, Jensen W. Unusually large von Willebrand factor multimers increase adhesion of sickle erythrocytes to human endothelial cells under controlled flow. N Engl J Med 1982 337 1584-1590. 

Increase Adhesion Tension Maximize Surface Tension Minimize Contact Angle Determine the critical surfactant concentration to maximize adhesion tension. Control impurity levels in particle formation... 

Chlorobutyl (CIIR) and bromobutyl (BIIR) are modified types containing 1.2% wt of chlorine or bromine, the isoprene unit being the site of halogenation. Introduction of the halogen gives greater cure flexibility, and enhanced cure compatibility in blends with other diene rubbers. It also confers increased adhesion to other rubbers and metals. 

Histamine contributes to the progression of allergic-inflammatory responses by enhancement of the secretion of proinflammatory cytokines like IL-la, IL-1(3, IL-6 as well as chemokines like RANTES or IL-8, both in several cell types and local tissues [26-29]. Endothelial cells express functional HRl and HR2 and increased adhesion molecule expression such as ICAM-1, VCAM-1 and P-selectin was demonstrated by histamine infusion via HRl [30-32]. Histamine regulates the expression of its own receptors on endothelial cells and influences the overall inflammatory reaction [33]. 

Endothelial dysfunction increases adhesiveness and permeability of the endotheMum for platelets and leukocytes. Infiltrations involve monocytes and T cells. Damaged endothelium has procoagulant rather than antico ulant properties. In some cases, the endothelial lining may become partially denuded. 

Hild, D.N. and Schwartz, P. (1992b). Plasma treated ultrahigh strength polyethylene fibers. Part 11. Increased adhesion to poly(methyl methacrylate). J. Adhesion Sci Technol. 6, 897-917. 

For polyamine-cured resin, recycle of presoaked epoxy also increased both impact strength and heat deflection temperature. For polyamide-cured resin, recycle also increased volume resistivity. Pre-soaked recycle dramatically increased adhesion to aluminum, especially in the anhydride system. 

Note 1 A coupling agent increases adhesion between phase domains. 

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