Antioxidants volatility

Aethanethiol Aethylmercaptan AI3-26618 EINECS 200-837-3 Etantiolo Ethaanthiol Ethanethiol Ethyl hydrosulfide Ethyl mercaptan Ethyl suifhydrate Ethyl thioalcohol Ethylmercaptaan Ethyimerkaptan Etilmerc-aptano HSDB 814 LPG ethyl mercaptan 1010 Mercaptoethane 1-Mercaptoethane NSC 93877 Thio-ethanol Thioethyl alcohol UN236S Used to impart odor to natural gas, in manufacture of pesticides, plastics and antioxidants. Volatile liquid mp = -147,8° bpn 36,1° d = 0,8315 slightly soluble in H2O, more soluble in organic solvents, Alofina S/gma-Aldrich Fine Chem. US. BioChem. 

It has already been mentioned that a large number of components are used for the construction of wood-based furniture. In addition to the compounds described earlier, a large spectrum of volatile organics can be found in emission studies (Salthammer, 1997b). The main sources for formaldehyde (which is not considered here), phenol and acetic acid are substrates such as particle board and MDF. BHT is a common antioxidant. Volatile plasticizers include dimethyl phthalate (DMP), dibutyl phthalate (DBP), as well as esters of adipic acid and sebacic acid. Further important compound groups are amines, siloxanes, carboxylic acids and naphthalenes. The identification of special substances does not only require suitable analytical equipment. Both experience and detailed knowledge of the chemical composition of furniture are also necessary. 

The formation of polymers leads to an increase in viscosity. The various lipids that can leach into the frying oil change the properties and the performance of the frying oil. Colored lipids solubilized in the oil contribute to the darkening. Phospholipids are emulsifiers. Traces of liposoluble metal compounds may act as prooxidants. Liposoluble vitamins and phenolic compounds are antioxidants. Volatile compounds (e.g., from fish or onions) contribute to off-flavors. 

The requirements of flexible polyurethane slabstock foam manufachirers vary due to sensitivity to antioxidant volatility, preference in physical form (liquid or sohd), and degree of anti-scorch protection. As a result of this broad variation in antioxidant performance demands, several alternative antioxidants to BHT are available. AO-2 and AO-3 combine relatively low volatility and good anti-scorch performance with the advantage of a liquid product form. AO-4 and AO-5 have significantly lower volatility than BHT and improved performance. Addition of peroxide scavengers such as DTDTDP and PHOS-1 can further enhance the scorch resistance of the polyurethane foam. 

Solvent extraction followed by gas chromatographic analysis is used to determine paraffin wax antioxidants (qv), ie, butylated hydroxyanisole and butylated hydroxytoluene and other volatile materials. Trace amounts of chlorinated organic compounds, eg, polychlorinated biphenyls, can be deterrnined by using a gas chromatograph with an electron-capture detector (22). 

Many antioxidants ia these classes are volatile to some extent at elevated temperatures and almost all antioxidants are readily extracted from their vulcanizates by the proper solvent. These disadvantages have become more pronounced as performance requirements for mbber products have been iacreased. Higher operating temperatures and the need for improved oxidation resistance under conditions of repeated extraction have accelerated the search for new techniques for polymer stabilization. Carpet backiag, seals, gaskets, and hose are some examples where high temperatures and/or solvent extraction can combine to deplete a mbber product of its antioxidant and thus lead to its oxidative deterioration faster (38,40). 

Introducing long aliphatic chains into a stabilizer molecule decreases volatility and increases solubility in hydrocarbon polymers. This improves performance. However, it also increases the equivalent weight of the active moiety. Di- and polyphenoHc antioxidants combine relatively low equivalent... 

Increasing surface-to-volume ratio increases susceptibiUty to oxidation. Thin film and fiber are much more sensitive to oxidation than thick specimens (26). The effectiveness of an antioxidant for products with high surface-to-volume ratios is deterrnined not only by its inherent activity in a particular polymer, but also by the rate of loss by volatilization. 

To obtain maximum lifetime, the oxidants must not be lost during service. A major potential source of loss is the evaporation of the antioxidant. Evaporation is often observed with BHT (butylated hydroxytoluene), a monomeric phenol, and to avoid evaporation less volatile, higher molecular weight antioxidants are used (i.e. bisphenols). 

For hot melt adhesives there are other considerations as well in choosing an antioxidant. Primary among these are volatility and solubility. Low molecular weight antioxidants (MW <400) should be avoided, for example BHT, as these... 

One key consideration in developing radiation curable adhesive systems is the thermal stability and volatility of any photoinitiators used. These chemicals are designed for liquid systems where these issues do not arise. Few of the commercial photoinitiators have adequate thermal stability at the highest hot melt temperatures (180-200°C) and many are too volatile. Reduced application temperatures and special antioxidant packages are often required. 

A multidimensional system using capillary SEC-GC-MS was used for the rapid identification of various polymer additives, including antioxidants, plasticizers, lubricants, flame retardants, waxes and UV stabilizers (12). This technique could be used for additives having broad functionalities and wide volatility ranges. The determination of the additives in polymers was carried out without performing any extensive manual sample pretreatment. In the first step, microcolumn SEC excludes the polymer matrix from the smaller-molecular-size additives. There is a minimal introduction of the polymer into the capillary GC column. Optimization of the pore sizes of the SEC packings was used to enhance the resolution between the polymer and its additives, and smaller pore sizes could be used to exclude more of the polymer... 

More recently, the same author [41] has described polymer analysis (polymer microstructure, copolymer composition, molecular weight distribution, functional groups, fractionation) together with polymer/additive analysis (separation of polymer and additives, identification of additives, volatiles and catalyst residues) the monograph provides a single source of information on polymer/additive analysis techniques up to 1980. Crompton described practical analytical methods for the determination of classes of additives (by functionality antioxidants, stabilisers, antiozonants, plasticisers, pigments, flame retardants, accelerators, etc.). Mitchell... 

Plasticiser/oil in rubber is usually determined by solvent extraction (ISO 1407) and FTIR identification [57] TGA can usually provide good quantifications of plasticiser contents. Antidegradants in rubber compounds may be determined by HS-GC-MS for volatile species (e.g. BHT, IPPD), but usually solvent extraction is required, followed by GC-MS, HPLC, UV or DP-MS analysis. Since cross-linked rubbers are insoluble, more complex extraction procedures must be carried out. The determination of antioxidants in rubbers by means of HPLC and TLC has been reviewed [58], The TLC technique for antidegradants in rubbers is described in ASTM D 3156 and ISO 4645.2 (1984). Direct probe EIMS was also used to analyse antioxidants (hindered phenols and aromatic amines) in rubber extracts [59]. ISO 11089 (1997) deals with the determination of /V-phenyl-/9-naphthylamine and poly-2,2,4-trimethyl-1,2-dihydroquinoline (TMDQ) as well as other generic types of antiozonants such as IV-alkyl-AL-phenyl-p-phenylenediamines (e.g. IPPD and 6PPD) and A-aryl-AL-aryl-p-phenylenediamines (e.g. DPPD), by means of HPLC. 

As diffusion to the surface of a polymer is one of the limiting steps in extraction, the particle size or film thickness of a sample is also important [278,333,337-340]. With the typical diffusion coefficients of additives in polymers a particle diameter of about 0.3 mm is required for an extraction time of about 1000 s at 40 °C. An exception to this is the extraction of thin films and foams, for which the shortest dimension is small. It is not surprising that no more than 50 % of antioxidants could be extracted from PP pellets as opposed to 90 % recoveries from the same polymer extruded into film [341]. Grinding of the polymer is usually an essential step before extraction. Care should be taken to avoid loss of volatile additives owing to the heat generated in such processes. Therefore, cryogrind-ing is preferred. 

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