Laboratory moisture-curing

The vast majority of reactive hot melts are moisture-curing urethane adhesives. Radiation (UV/EB) curable adhesives have been explored in the laboratory since the mid-1970s, but are only recently beginning to gain significant market penetration, particularly for PSA applications. The formulation and properties of these two classes of adhesives are discussed below. 

A substantial effort in our laboratory has been directed toward the synthesis and characterization of acetylene-terminated (AT) matrix resins. The most significant feature and driving force for the effort is that the thermal induced addition reaction provides a moisture Insensitive cured product. This technology offers a wide variety of thermoset resins for various high temperature applications. Backbone structural design for use temperature capabilities, processing characteristics and mechanical performance has demonstrated the versatility of the AT type systems. 

During the course of this program, experimental studies were conducted to identify a number of polymer types in formulations which can be cured via radiation for adhesive applications. Performance studies were also made to determine endurance to exposures of various environmental conditions including moisture, solvents and high temperature aging. Data have been developed on a number of good candidate materials from both commercially available products and laboratory experimental... 

A substantial effort in this laboratory has been directed toward the synthesis and characterization of acetylene terminated oligomers for use as addition-curable, moisture-resistant, thermoset systems. Early work on the acetylene-terminated phenylquinoxalines demonstrated the moisture insensitivity of the product generated from the thermal cure. Studies of various difunctional acetylene-terminated monomers has demonstrated that the polymerization is a free radical propogation of the acetylene moiety to a linear conjugated polyene. 

Process NMR is used for chemicals (free/bound moisture, viscosity, activity, loading efficiency in powders, catalysts, liquids, detergents, pigments) and polymers (density, crystallinity, rubber and copolymer content, dispersion of fillers, melt properties, finish content, extent of cure and cross-linking, content of solubles, plasticisers, moisture, etc.). Process NMR is fully operational in the polymer industry, both as on-line units [202] which provide virtually continuous process feedback control as well as off-line and laboratory units for checks of the various processes [198]. The use of NMR for advanced process control has reduced the need for frequent wet tests, has reduced off-spec materials and has improved product transition times. 

Prismoidal specimens of 70 x 70 x 280 mm were formed in the laboratory. The vibration time was chosen to ensure maximum compaction factor for each mix. If this was less than 0.05%, the specimen was rejected. The samples were cured at air moisture of 95-98% and temperature of 18-22 C. for 28 days, then isolated from environmental water exchange prior to testing at 1-year age. Such conditions ensured a degree of consistency of mechanical properties for all samples tested. 

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