Polyolefins staining

Olefin fibers, also called polyolefin fibers, are defined as manufactured fibers in which the fiber-forming substance is a synthetic polymer of at least 85 wt % ethylene, propjiene, or other olefin units (1). Several olefin polymers are capable of forming fibers, but only polypropylene [9003-07-0] (PP) and, to a much lesser extent, polyethylene [9002-88-4] (PE) are of practical importance. Olefin polymers are hydrophobic and resistant to most solvents. These properties impart resistance to staining, but cause the polymers to be essentially undyeable in an unmodified form. 

Some of the most difficult heterophase systems to characterize are those based on hydrocarbon polymers such as mbber-toughened polypropylene or other blends of mbbers and polyolefins. Eecause of its selectivity, RuO staining has been found to be usehil in these cases (221,222,230). Also, OsO staining of the amorphous blend components has been reported after sorption of double-bond-containing molecules such as 1,7-octadiene (231) or styrene (232). In these cases, the solvent is preferentially sorbed into the amorphous phase, and the reaction with OsO renders contrast between the phases. 

The formation and role of hydroperoxide groups, particularly in the early stages of polymer oxidation is well discussed in the introduction to the next chapter and also features in many of the references cited in this chapter. Their detection and quantification is therefore important. Although this can be done directly or implicitly through many of the instrumentation techniques discussed in this chapter, there are several tests that have been developed, some of which are still widely used, that are based more on chemical methods, titration or staining. The majority have been applied to polyolefins, especially polyethylene. 

Conventional bright-field TEM observations of polyolefins often require contrast enhancement, usually by staining with Ru04 or other suitable markers [17]. These accumulate in the amorphous phase, at lamellar surfaces and in cavities, and differential staining can reveal the phase distribution in blends. Staining also hardens the specimens, facilitating preparation of thin sections at room temperature (cryo-sectioning is required for unfixed polyolefins). 

Bitumen. Bitumen is a black thermoplastic obtainable from the refining of crude oil. Its composition is somewhat variable, depending upon the type of crude, and it tends to stain light-coloured substrates. However, the relatively low cost of the material makes it attractive for some applications and it may be compounded with other thermoplastics—like the polyolefins. 

Monohydric phenols, the most applied group of phenolic antioxidants, are changed via phenoxyls into more types of products. The C-C coupling reactions leading to the antioxidation-efficient multinuclear phenols play a favourable role. The formation of quinone methionid compounds which stain polyolefins cannot be avoided in the transformation process. However, these compounds exhibit a retardation effect in thermal oxidation and are able to quench singlet oxygen. The least favourable properties have alkylperoxycyclohexadienones and dioxycyclohexa-dienones, which initiate both the thermal and photochemical oxidation. Products of their subsequent transformations are either inactive or have a weak retardation effect. 

Seip, S.D. Thompson, S.E. Townsend, E.B. Polyolefin additive packages for producing articles with enhanced stain resistance, U.S. Patent 6,777,470, August 17, 2004. 

Stain test This test is based on the afihnity for various fibers toward different dyes. A series of dyes which have known affinity for specific fibers are prepared, and the fiber in question is immersed to check its dye pickup. The morphology of the fiber and its chemical stmcture determine its dyeability and hydrophiUcity. Polyolefin fibers are hydrophobic, and they have very poor dyeability. 

Phenolic Polyolefins, styrenics, and engineering resins PhenoUcs are generally stain resistant and include simple phenoUcs (BHT), various polyphenolics, and bisphenohcs. 

Staining techniques for detecting localised oxidation in HDPE powders and films were reviewed [237]. Optical absorbance following staining with 2,4-dinitrophenylhydrazine (DNPH) can be used as a measure of the aldehyde/ketone content in oxidised polyolefins. SO2 treatment enables regions with high concentrations of hydroperoxides to be clearly distinguished. 

An important staining technique was developed by Kanig [246] for the enhanced contrast of PE, a material that has been a model compound for fundamental polymer studies. Polyethylene crystals cannot be sectioned, nor are they stable in the electron beam, due to radiation damage. The chlorosulfonation procedure cross links, stabilizes, and stains the amorphous material in crystalline polyolefins, permitting ultrathin sectioning and stable EM observation. Chlorosulfonic acid diffuses selectively into the amorphous material in the semicrystalline polymer, increasing the density of the amorphous zone compared with the crystalline material. The treatment stains the surfaces of the... 

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