Mixed-resin systems

Apparently the performance of the liquid ion exchanger is loosely analogous to that of the CSIRO mixed resin system used for brackish water desalination [3. The basis of this process is a mixture of solid weakly basic and weakly acid resins, which absorb salt at a low temperature and release it at a higher one, the analogy being seen in the fact that the mixture absorbs salt and is regenerated with water. There are, however, substantial differences between the two systems, mainly as regards the media in which the ions are absorbed. Whereas in the CSIRO method ions are absorbed by an... 

It is necessary to mix resin formulations for a number of applications e.g. sizes, prepreg, pultrusion and filament winding. To check the mixed resin system, a number of tests can be undertaken. 

Monofunctional aliphatic glycidyl ethers, eg, based on / -butanol or mixed Cg—alcohols, are used exclusively as reactive diluents to reduce viscosities of epoxy resin systems. Some loss of desirable cured properties results from the lowered functionality of the systems. 

As already indicated, ion exchange resins are osmotic systems which swell owing to solvent being drawn into the resin. Where mixed solvent systems are used the possibility of preferential osmosis occurs and it has been shown that strongly acid cation and strongly basic anion resin phases tend to be predominantly aqueous with the ambient solution predominantly organic. This effect (preferential water sorption by the resin) increases as the dielectric constant of the organic solvent decreases. 

Bis(indolyl)nitroethanes are obtained readily in 7-10 min in high yields (70-86%) on fine TLC-grade silica gel (5-40 pm) by Michael reaction of 3-(2 -nitrovinyl) indole with indoles. The same reaction reported requires 8-14 h for completion at room temperature [77]. Several functionalized resins have been prepared from Merrifield resin via a MW-assisted procedure that utilized mixed solvent system to facilitate the swelling of resins and coupling with microwaves [78], These resins can function as solid supports or polymeric scavengers in solid phase synthesis. 

These chiral catalysts have also been linked to polymeric resins (Equation (7)) for multiple use/reuse without significant loss in enantiocontrol (Fig. 15.2) [40, 41]. Both No-vasyn and Merrifield resins proved effective, and mixed hgand systems with enhanced electronic and steric characteristics could be produced by this methodology [41]. 

The/flc-ClRe(CO)3(4,7-Ph2-phen) complex has been demonstrated to be a useful spectroscopic probe in the curing of photosensitive epoxy-based materials [100], Emission spectra obtained from a 0.05-mm thickness film of a mixed epoxy system of bisphenol-A/novalac resin (Interz, SU8) and diglycidyl ether of bisphenol-A (DGEBA) containing cation-generating triarylsulfonium hexafluo-roantimonate salts as photoinitiators (Union Carbide, Cryacure UVI-6974) and... 

Figure 25 (a) Emission spectra at 293 K of/ac-ClRe(CO)3(4.7-Ph2-phcn) in the mixed epoxy system of bisphenol-A/novalac and DGEBA resin (0.05-mm thin film) containing a triarylsulfonium hexafluoroantimonate photoinitiator as a function of UV-irradiation time (A) 0 s, (B) 15 s, (C) 30 s, and (D) 60 s. The emission spectra are uncorrected for photomultiplier response and vertically displaced for clarity. Excitation wavelength is 420 nm in each case, (b) Plot of emission intensity at the MLCT band maximum of /ac-ClRe(CO)3(4,7-Ph2-phen) as a function of UV-irradiation time. (From Ref. 100.)... 

Reactivity can also be increased by externally heating the epoxy formulation to a preselected curing temperature. Epoxy resin reactions roughly obey Arrhenius law that for every 10°C rise in temperature, the reaction rate doubles. Certain epoxy resin systems must be heated for any reaction to take place at all. This is beneficial in that these latent adhesive formulations are one-component products that do not require metering or mixing yet have long, practical shelf lives. 

To aid in dispersing, mixing, and wetting of components in the resin system at the formulation stage... 

Fillers may be added to low-viscosity resins by conventional sigma-blade mixer or the same type of equipment used for mixing paint systems. Three roll mills are generally employed for more viscous systems to obtain thorough wetting of the filler by the resin matrix. 

Colorants are typically defined as pigments and dyes that, when added to plastics, define a specific color. The subject of colorants has been discussed in numerous books and papers. However, in the context of this chapter, a dye is defined as a substance that is soluble in the resin system and produces color only by the absorption of light and no scattering of light. Pigments are not soluble in the resin system and therefore must be mixed into the resin by one of many dispersion processes. Factors such as pigment particle size and ease of mixing or dispersion directly influence their... 

Fig. 7. Rates of salt uptake by weak electrolyte resin systems. (A) mixed bed of De-Addite G and Zeo-Karb 226 (300-1200 pm) (B) mixed bed of De-Acidite G and Z Karb 226 (10-20 pm) (C) mixed bed of Amberlite IRA-93 and Zeo-Karb 226 (300-1200 pm) (D) snake-cage resin from Amberlite IRA-93 and poly(acrylic acid) (300-1200 pm)...

However, for many potential uses such as boiler feed water it is too contamined, so that a polishing unit is also required. In the manufacture of ammonium nitrate or sulfate, a mixed-bed resin system can be used to polish the partially demineralized condensate. However, poUshing of... 

Another example of the use of expandable powder involves the use of polystyrene powder. The powder is mixed with a liquid-matrix-resin system, such as epoxy. The exotherm of the curing epoxy resin expands the expandable polystyrene powder to form a syntactic foam. 

The two basic deionizer configurations are the two-bed and mixed-bed. Two-bed deionizers have separate vessels for the cation and anion resins. In mixed-bed deionizers, the anion and cation resins are blended in a single vessel. Generally, mixed-bed systems produce higher-quahty water but have a lower total capacity compared with two-bed systems. Figures 3 and 4 are schematics of typical ion exchange demineralization processes. 

In a batch reactor of the type described above it is desirable to reduce or eliminate film diffusion by vigorous mixing of the suspension. If mixing is sufficiently vigorous, particle diffusion may be reduced or eliminated as well. Kressman and Kitchener (1949) showed that mixing was optimum at a stirring speed of 1000 to 1100 rpm for ion exchange in the synthetic resin system. 

Sec-butyl alcohol offered some promise with the trimellitic alkyd and the epoxy ester vehicles, judging from the preliminary phase of the investigation. Further work is needed to establish this fact. An approach involving mixed solvent systems is suggested. With the acrylic resin, the solution properties and deposition characteristics were poor. Isopropyl alcohol offered some promise with the alkyd and the acrylic resin, but further tests are needed to determine its ultimate utility. Diacetone alcohol may be of value with the alkyd and the acrylic. With these resins it... 

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