Green strength development

It is probably obvious at this point that the molecular weight distribution of a resole is an extremely important characteristic. It has major influence on such important performance capabilities as cure speed, viscosity, green strength development (or prepress), assembly time tolerance, required application rates. 

Compatibility of Components. While plasticization of the phenolic component (by solvent or water) appears to give a partial explanation of its tackifying mechanisms, it certainly cannot be the entire explanation for green strength development. Neither solutions of CK-1834 nor dispersions of BKUA-2260 exhibit contact properties by themselves. Their interaction with the other components in the formulation (neoprene or acrylic) must be considered. 

Moist curing of the castable is not required and is detrimental to green strength development with this bond system. It has also been reported that dehydration is easier with this bond that dehydrates between 200°C and 300°C (peak at 255°C). In reality, most castables utilizing this bond do have low permeabiUties because of ultrafine particle additions, such as siUca fume and reactive alumina, so again it is recommended to consult with the castable manufacturer prior to initial heat up of castables based on this bond system. 

The first isostatic pressing technique was described by Madden in a US patent assigned to the Westinghouse Lamp Co. It was developed to overcome the limitations of billets compacted in dies. Madden claimed that isostatically pressed billets were uniformly compacted, devoid of strata, and possessed sufficient green strength to permit handling. 

The preform expands due to relaxation and recovery. The pressure placed on the molded resin exerts three types of changes in the particles of resin. Resin particles undergo plastic deformation and are intermeshed together leading to the development of cohesive or green strength. Particles also deform elastically and experience cold flow underpressure. The air trapped in the space between the resin particles is compressed. Removal of pressure allows the recovery of elastic deformation, which creates a quick snap back of the preform. Overtime, stress relaxation partly reverses the cold flow, and the preform expands. 

Following the extrusion, several alternative flow paths are possible. In most cases, because the pellets from expander-extruders are relatively wet and have low green strength, the discharge is carefully positioned onto a belt dryer, which dries-off excess moisture at minimum mechanical stress while the final binding mechanism is developed (e.g., by recrystallization of dissolved substances, increased viscosity of molasses. 

Green strength (grab)— The ability of an adhesive to hold two surfaces together when first brought into contact and before the adhesive develops its ultimate bonding properties when fully cured. 

Several polymeric green strength promoters have been developed. The green strength promoter with commercial designation Vestenamer 8012 is a polyoctenamer manufactured by Huls [2]. The raw material for this polymer is cyclooctene. In a metathesis polymerization reaction cyclooctene is converted into a polyoctenamer. It was developed as a green strength promoter for tire sidewalls, apexes or bead fillers, and other... 

In adhesive bonding, green strength refers to the first stage of adhesive strength development (although not fully cured) where the operator can first handle the bonded joint without fear of bond failure. 

The development of two new polychloroprene latices, designated Dispercoll C LS-2324 and Dispercoll C LS-2373, which are suitable for the manufacture of waterborne contact adhesives, is reported. Examples are presented of formulations in which blends of these polychloroprene latices are used to optimise initial green strength, contact bond life and heat resistance. 

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