Adhesion viscosity effects

In most adhesives, tackifier is the ingredient present in the highest proportion. Tackifying resins are primarily used to reduce adhesive viscosity and adjust the 7g of the adhesive s amorphous matrix phase. Through their effects on the other ingredients and the overall system they can also dramatically affect wet out, hot tack, open time, set speed, and heat resistance. 

Table 4.19 Effect of adhesive viscosity on dispensing and component placement time ...

We investigated the effect on the adhesion strength of shear stresses applied to the adhesive interlayer MDI as a component of Sprut-5M adhesive. An equimolar quantity of butylene glycol was added to MDI to cure it. The shear stresses were created by the torsion of one dolly of standard size relative to another in a special device the adhesive was placed between the dollies. On reaching the prescribed shear stress (due to the increase of the adhesive viscosity) the torsion of the dolly... 

The effect of adhesive penetration also was expressed by the portion of partly or completely filled cells (lumens or rays) in the interphase region. The filled interphase region (FIR) increases only slightly with an increased adhesive viscosity (higher degree of condensation) but not showing significant differences. 

Table 4.19. Effect of Adhesive Viscosity on Dispensing and Component Placement TimeP ...

Aspects of viscosity, elasticity, and morphology have been discussed in general terms by various workers [73-76]. Rheological studies specific to particular polymers include dynamic rheological measurements and capillary rheometry of rubbers [77], capillary rheometry of PP [78], degradation of PP [79], torsion rheometry of PE [80], viscosity effects in blends of PC with styrene-acrylonitrile and acrylonitrile-butadiene-styrene [81], peel adhesion of rubber-based adhesives [82], and the effect of composition of melamine-formaldehyde resins on rheological properties [83]. 

FIGURE 3. Effect of adhesive viscosity on interfacial contact. (From Reference 23.) (a) Low area of interfacial contact resulting from high viscosity of fluid, (b) Lack of voids and high area of interfacial contact resulting from low viscosity of fluid. 

Surface Tension. Interfacial surface tension between fluid and filter media is considered to play a role in the adhesion of blood cells to synthetic fibers. Interfacial tension is a result of the interaction between the surface tension of the fluid and the filter media. Direct experimental evidence has shown that varying this interfacial tension influences the adhesion of blood cells to biomaterials. The viscosity of the blood product is important in the shear forces of the fluid to the attached cells viscosity of a red cell concentrate is at least 500 times that of a platelet concentrate. This has a considerable effect on the shear and flow rates through the filter. The surface stickiness plays a role in the critical shear force for detachment of adhered blood cells. 

Additives. Because of their versatility, imparted via chemical modification, the appHcations of ethyleneimine encompass the entire additive sector. The addition of PEI to PVC plastisols increases the adhesion of the coatings by selective adsorption at the substrate surface (410). PEI derivatives are also used as adhesion promoters in paper coating (411). The adducts formed from fatty alcohol epoxides and PEI are used as dispersants and emulsifiers (412). They are able to control the viscosity of dispersions, and thus faciHtate transport in pipe systems (413). Eatty acid derivatives of PEI are even able to control the viscosity of pigment dispersions (414). The high nitrogen content of PEIs has a flame-retardant effect. This property is used, in combination with phosphoms compounds, for providing wood panels (415), ceUulose (416), or polymer blends (417,418) with a flame-retardant finish. 

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. 

Once the crosslinker is added, it is important to apply the adhesive and dry off the water. Most of the commonly used crosslinkers will react with water over a period of time and lose effectiveness. In some two-component PUD s, the system may increase in viscosity and even gel, giving the user some idea of when the useful life of the crosslinker is approaching its end. In other instances, no viscosity increases or other visible indications signal that the crosslinker has reached the end of its useful life. The improvements in physical properties, solvent resistance, and water resistance normally provided by a crosslinked PUD adhesive would not be fully realized, in this case. 

Fully hydrated potassium ion coordinates about 10-11 molecules of water, whereas sodium coordinates about 16-17 molecules [115]. The ionic mobility of potassium is about 50% greater than that of sodium. In simple terms, this means that more of the water in a potassium-catalyzed resin will be available as free water for viscosity reduction and that movement of water from a glue line into the wood will have less effect in moving the adhesive off of the glue line with it. 

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