Controlled coagulation of emulsion polymers

Coagulation of latex particles is most often carried out in the diffusion limited aggregation (DLA) regime where the time for coagulation to take place is on the millisecond timescale. This process produces aggregates of low density, irregular shape, and a broad particle size distributions. When the coagulation is carried out in the reaction limited aggregation (RLA) regime, a coagulation time of about 1–120 sec, the system can be controlled by mixing to yield dense, spheroidal aggregates with a very narrow particle size distribution. The important variables in the RLA process for butyl acrylate/methyl methacrylate (BA/MMA) latexes were found to be mixing intensity, latex copolymer composition, and coagulation temperature. Dried aggregates formed in the RLA process were found to have excellent powder flow properties and low dustiness.     

核壳型聚丙烯酸酯乳液硬挺整理剂的合成与应用研究

以苯乙烯（ST）、甲基丙烯酸甲酯（MMA）、丙烯酸丁酯（BA）为主要原料,采用乳液聚合法,合成了性能稳定的核壳型聚丙烯酸酯硬挺剂。通过红外光谱仪（FT—IR）验证了聚合物的分子结构。对涤纶织物进行硬挺整理,可有效满足实际要求的整理工艺为：硬挺剂600g／L,200℃焙烘1．5min。结果表明,合成的硬挺剂具有优良的硬挺效果,整理后的织物高温不泛黄或泛黄不明显,厚重感明显增加且耐水洗性良好。     

An investigation of fatigue failure prediction of adhesively bonded metal/metal joints

A fracture mechanics-based model for fatigue failure prediction of adhesive joints has been applied in this work. The model is based on the integration of the kinetic law of evolution of defects originated at stress concentrations within the joint. Final failure can be either brittle (fracture toughness-driven) or ductile (tensile/shear strength-driven) depending on the adhesive. The model has been validated against experiments conducted on single-lap shear joints bonded with a structural adhesive. Three different kinds of adhesives, namely a modified methacrylate, a one-part epoxy and a two-part epoxy supplied by Henkel, have been considered and three different overlap lengths have been tested. Fracture toughness and fatigue crack growth properties of the adhesives have been determined with mode I tests. The number of cycles to failure has been successfully predicted in several cases. It is interesting to notice that in the case of joints loaded at the same average shear stress, the shorter the joint, the longer the duration. This fact is also captured by the model.     

Advances in room temperature curing adhesives and sealants—a review

Room temperature curing adhesives and sealants, defined here as those which cure without a mixing process under the influence of substrates or environmentally available reagents such as daylight, oxygen or moisture, include polyurethane, silicone, anaerobic adhesives, cyanoacrylate and certain acrylic types. Advances in cure chemistry, built-in adhesion promotion, and in formulating techniques have created the scope for significant new properties within all the mentioned systems. In addition, development of resins having two (or more) different functionalities, which respond to substrate and or atmospheric cure agents, has created the potential to achieve new advanced performance levels. Examples of these include compositions which give light curing through acrylic functions while having RTV (room temperature vulcanising) silicone resin chemistry polymerising under the influence of atmospheric moisture. The properties can be tailored by molecular design, formulation and choice of cure accelerators.     

可碱溶丙烯酸酯共聚压敏胶乳液的研制

介绍了一种壳核结构丙烯酸酯共聚乳液的制备工艺、性能,该乳液适用于生产可碱溶回收压敏胶带纸及商标纸等。     

Anaerobic Adhesive Cure Mechanism-I

Anaerobic adhesives are single-component acrylic adhesives which cure rapidly at or below room temperature when air is excluded, but they remain in an uncured stage over a long time when they are exposed to an adequate supply of air. Thus, anaerobic adhesives are widely used in retaining compounds for nuts and bolts, in sealants, and for impregnation. Recently, anaerobic adhesives have also been used in electrical and electronic applications because of their fast room temperature cure capability and their convenience.¹     

Dynamic Mechanical Analysis of Amorphous-Phase Organization in Acrylic Polymers

Factors affecting polymer network organization were studied in highly crosslinked acrylics of the type used in dental adhesive resins. The variables tested were comonomer content and processing conditions. BisEMA (2,2,-bis[4-(2-methacryloyloxyethoxy)-phenyl]-propane) and BisEMA + TEGDMA (triethyleneglycol dimethacrylate) were cured with and without 25% comonomer. Comonomers had characteristics that are expected to influence intrachain organization in amorphous phases: TEGDMA, crosslinking; methyl methacrylate (MMA), monomer conversion; isobornyl methacrylate (IBM), low cure shrinkage; tetrahydrofurfuryl methacrylate (THFM), antiplasticization. Dynamic mechanical analysis temperature scans were run at 0.1 Hz 2h or 24h after ambient cure, or 24h postcure after heating at 75° or 125°C. After 24h, tan δ maxima occurred in ranges centering on approximately -30°, 75° and 150°C (T_g). Heating at 125°C nearly eliminated all peaks except T_g, reduced tan δ peaks and increased T_g by 0–14°. T_g increased in the order: TEGDMA>125°C>IBM>MMA>75°C>2h>24h>THFM. The ability to crosslink, and postcure heating at 125°C, were the more important factors found to increase intrachain organization in amine-promoted, unfilled BisEMA resins of the type used in dental sealants, luting cements and bulk-filling resin composite materials.     

淀粉接枝类高吸水树脂的合成研究

以N,N′-亚甲基双丙烯酰胺为交联剂,过硫酸铵为引发剂,用可溶性淀粉与丙烯酸(AA)、丙烯酰胺(AM)为原料采用溶液聚合法合成了新型高吸水树脂.讨论了引发剂用量、交联剂用量、淀粉用量、氮气氛围等因素对树脂吸水性能的影响,确定最佳反应条件为:以AA质量为标准,可溶性淀粉用量为20％,引发剂用量为0.5％,交联剂用量为0.05％,AA中和度为75％,反应温度为65℃,在氮气保护下所得产物在蒸馏水中吸水率最大,达1 059.1 g/g.     

The Evaluation of Alkyl Borane Compounds and Imidazole Borate Complexes as Initiators for Acrylic Adhesives Bonding Low Energy Substrates

Novel amido-borate initiators based on imidazolide bridged borate complexes were developed for acrylic adhesives used to bond low surface energy substrates. The focus of this development was examining the shelf life of the acrylic adhesive system as a function of the molecular architecture of the organoboron curative. The two key molecular features which significantly affect stability are: 1) the chain length of the alkyl groups on the boron atom and 2) arrangement of the imidazolide bridged borate structure. The results show that superior shelf life stability can be attained over the conventional trialkyl borane- and tetraalkyl borate-type initiators when this new family of catalysts (imidazolide borate compounds) is incorporated into the adhesive formulation without any harmful effect on cure speed.     

Electrooptical Light-Management Material: Low-Refractive-Index Adhesives

A prototype pressure-sensitive adhesive that has a low refractive index (<1.36) and is optically clear has been developed (Holguin and Chang, US Patent 6703463, 2002). The refractive index is a key feature in the application of optical polymers, and this pressure-sensitive adhesive is particularly useful for light-transmitting devices. It is a fluoro-substituted mono-acrylate adhesive. Fluoro-polymers are known to have a low refractive index, but typically the fluoro-polymers are not sticky and are opaque because of their crystallinity. The design of this novel fluorosubstituted monoacrylate adhesive polymer is based on the rheological marriage of fluoro-polymers and pressure-sensitive adhesives.