Adhesive working time

Attempts to make adhesive formulations by direct reaction of formaldehyde or its equivalent resulted in products that were excessively viscous, and the working time was too short for commercial application (57). It was concluded that formaldehyde, although readily reactive with the tannin molecule, provided much too short linkages to connect the bulky tannin molecules. This problem was circumvented by the preparation of a polymethylolphenol reagent that, when put in solution with the bark extract, formed a combination that was stable for several weeks at room temperature. When heated, the polymethylolphenol and bark extract reacted rapidly to form an infusible resin. Commercial trials were made to produce exterior-grade Douglas-fir plywood. Widespread use of the extracts for this purpose, however, was inhibited by a drop in the price of phenol below what the bark extracts could be manufactured for. (The best extract for adhesive purposes was an ammonia extract of hemlock bark converted to a sodium derivative prior to spray drying, a more costly extraction procedure than simple sodium hydroxide extraction of bark.)... 

Fig. 8. Variation of auto-adhesion work and hydroperoxide concentration of iPP modified by corona discharge with the time of auto-adhesive joint formation...

A probe tack test may be regarded as a mechanical thumb in which a disc or hemisphere of standard material (e.g. brass) is brought into contact with the adhesive surface under a fixed load for a specified dwell time (e.g. 1 s) and then removed at a specified rate. The maximum force of removal is usually taken as the tack value, although sometimes the work or energy of separation is reported. In such a test, it is important to control accurately the variables probe material and finish, probe diameter and shape, load on probe, thickness of adhesive, dwell time, rate of debonding of probe from adhesive, and... 

Working time Period of time during which an adhesive or coating, after mixing with catalyst, solvent or other compounding ingredients, remains suitable for use. 

To make an economical and practical joint, the surface preparation methods must also meet several other requirements. They must be safe to handle and should not be flammable or toxic. They should be inexpensive and provide fast processing times. The prebond processes should be easy to monitor and control in a production situation. In addition, the process should not in itself leave a weak boundary layer. If chemical solutions are used, they should rinse off easily and not continue to react with the surface past the time when the bond is made. The surface preparation process should allow for practical working time between preparation and application of the adhesive or sealant. Finally, the surface provided by the treatment should not change once the assembled joint is made and placed into service. 

Both of the adhesion work of water flooding and microbial flooding decreased, which interpret that the adhesion work of water flooding will decrease when contact with rock for a long time. While the adhesion work of microbial flooding decreased more sharply, this is because abundant... 

The addition of the Booster to the adhesive has little effect on the open or working time, which is the interval between application of adhesive and joint assembly. However, a significantly faster setting results after just 2 h (Fig. 59). 

Lord 310 A/B A non-flammable epoxy, composite adhesive with a working time of 30 - 60 minutes. 

Lord 363 A/B A fast-set epoxy adhesive with a working time of 5 - 7 minutes. 

Lord 406/17 An acrylic adhesive for composite application offering a working time of 6 -10 minutes and fast room temperature bonding. 

Lord 7610 A one part, urethane sealant/adhesive for composites application, offering a working time... 

Manufacturers Comments Family of film adhesives (supported and non-supported). Various areal veights. High mechanical properties. X-ray opaque. Improved work-time. Limited self-extinguishing. 

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