Resistance to chemical treatment

Prions (section 2.2.7) are generally considered to be the infectious agents most resistant to chemical disinfectants and sterilization processes strictly speaking, however, they are not microorganisms because they have no cellular structure nor do they contain nucleic acids. Of the conventional microorganisms, bacterial spores are the most resistant to chemical treatment. The majority of antimicrobial... 

Melamine resins were introduced about ten years after the Beetle molding compound. They were very similar to those based on urea but had superior quaHties. Henkel in Germany was issued a patent for a melamine resin in 1936 (7). Melamine resins rapidly supplanted urea resins and were soon used in molding, laminating, and bonding formulations, as well as for textile and paper treatments. The remarkable stabiHty of the symmetrical triazine ring made these products resistant to chemical change once the resin had been cured to the insoluble, cross-linked state. 

Bacterial spores are the most resistant of all microbial forms to chemical treatment. The majority of antimicrobial agents have no useful sporicidal action, with the exception of the aldehydes, halogens and peroxygen compounds. Such chemicals are sometimes used as an alternative to physical methods for sterilization ofheat sensitive equipment. In these circumstances, correct usage of the agent is of paramount importance since safety margins are lower in comparison with physical methods of sterilization (Chapter 20). 

High-alumina cement is a rapid-hardening cement made from bauxite and limestone. It is comparatively resistant to chemical attack. Milling retards the setting of aluminous cement [1582]. On the other hand, setting accelerators such as lithium carbonate increase their effect by this treatment. 

Like many other fluoropolymers, Nafion is quite resistant to chemical attack, but the presence of its strong perfluorosulfonic acid groups imparts many of its desirable properties as a proton exchange membrane. Fine dispersions (sometimes incorrectly called solutions) can be generated with alcohol/water treatments. Such dispersions are often critical for the generation of the catalyst electrode structure and the MEAs. Films prepared by simply drying these dispersions are often called recast Nafion, and it is often not realized that its morphology and physical behavior are much different from those of the extruded, more crystalline form. 

Preliminary structural studies of cutin and suberin breakdown involved examination of 13C NMR spectra for insoluble residues that were resistant to chemical depolymerization. In cutin samples, flexible CH2 moieties in particular were removed by such treatments, but CHOCOR crosslinks and polysaccharide impurities were retained preferentially. A concomitant narrowing of NMR spectral lines suggested that the treatments produced more homogeneous polyester structures in both cases. Our current studies of cu-ticular breakdown also employ selective depolymerization strategies with appropriate enzymes (1,28). 

Chlorosulfonated polyethylene A product obtained by treatment of polyethylene by chlorine and sulfur dioxide. It is an elastomer highly resistant to chemicals and ozone. 

A large proportion of the chlorine added to wastewater is consumed in oxidizing organic materials other than phenolic con-pounds. Thus, for example, in the work of Thompson and Dust cited above, the wastewater COD content averaged 20,400 mg/liter before and 10,400 mg/1 after treatment with chlorine at a rate of 2 g/liter. However, the OOD was further reduced to only 10,250 mg/liter upon the addition of 10 g/liter of additional chlorine. This result suggests that a portion of the organic content of the wastewater was resistant to chemical oxidation, as indicated above for phenolic compounds. 

Azari and Feeney (8) found metal-free ovotransferrin to be much less resistant to chemical modification and to inactivation of the metalbinding capacity by chemical treatment than was the metal ovotransferrin. 

Dimethyldichlorosilane. Because dimethyldichlorosilane has been polymerized to a silicone polymer on cotton fabrics to impart stain and water resistance and can be applied as a vapor, this agent was examined as a possible consolidant. This treatment also improves fabric hand, resistance to chemicals and weathering, resistance to abrasion (by reducing friction), and reduces the tensile strength loss when resin finishes are applied all factors that should make the material a desirable and effective consolidant. The reactions involved are as follows ... 

Polymeric fibers are popular for reinforcing concrete matrices because of their low density (more number of fibers for a prescribed volume fraction), high tensile strength, ease of dispersion, relative resistance to chemicals, and relatively low cost compared to other kinds of fibers. Polypropylene and polyolefin fibers are typically hydrophobic, resulting in a relatively poor bond with concrete matrices compared to some other types of fibers. Treatment of polypropylene with an aqueous dispersion of colloidal alumina or silica and chlorinated polypropylene enhances the affinity of these fibers toward cement particles. Treatment of polypropylene fibers with a surface-active agent provides better dispersion of the fibers and a stronger bond between cement and fiber. The earlier attempts at surface treatments of polypropylene fibers have had only limited success and have not been commercially attractive. 

One of the most efficient methods for rapid generation of highly crosslinked polymers is by exposing multifunctional monomers to UV radiation in the presence of a photoinitiator. A liquid resin can be transformed within a fraction of a second into a solid polymer that is very resistant to chemical, heat and mechanical treatments. A review of UV curing of polymers is presented by Decker (1989). ... 

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