Antiozonants, analysis

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. 

At Goodyear laser-desorption MS has been used for direct analysis of rubber additives (e.g. antioxidants, antiozonants, vulcanising agents, processing oils, silica fillers, etc.), in situ at the surface of an elastomeric vulcanisate [74,75]. 

Brack [81] has illustrated the analysis of antioxidants in a CB-free vulcanisate of unknown composition according to Scheme 2.7. Some components detected by off-line TD-GC-MS (cyclohexylamine, aniline and benzothiazole) were clearly indicative of the CBS accelerator other TD components were identified as the antioxidants BHT, 6PPD, Vulcanox BKF and the antiozonant Vulkazon AFS. In the methanol extract also the stabiliser ODPA was identified. The presence of an aromatic oil was clearly derived from the GC-MS spectra of the thermal and methanol extracts. The procedure is very similar to that of Scheme 2.3. 

ASTM Standard D 3156-81, Thin-layer Chromatographic Analysis of Antidegradants (Stabilizers, Antioxidants and Antiozonants) in Raw and Vulcanized Rubbers, Annual Book of ASTM Standards, ASTM, Philadelphia, PA (1990). 

FAB has been used to analyse additives in (un) vulcanised elastomer systems [92,94] and FAB matrices have been developed which permit the direct analysis of mixtures of elastomer additives without chromatographic separation. The T-156 triblend vulcanised elastomer additives poly-TMDQ (AO), CTP (retarder), HPPD (antiozonant), and TMTD, OBTS, MBT and A,lV-diisopropyl-2-benzothiazylsulfenamide (accelerators) were studied in three matrix solutions (glycerol, oleic acid, and NPOE) [94]. The thiuram class of accelerators were least successful. Mixture analysis of complex rubber vulcanisates without chromatographic separation was demonstrated. The differentiation of matrix ions from sample ions was enhanced by use of high-resolution acquisition. 

FD-MS is also an effective analytical method for direct analysis of many rubber and plastic additives. Lattimer and Welch [113,114] showed that FD-MS gives excellent molecular ion spectra for a variety of polymer additives, including rubber accelerators (dithiocar-bamates, guanidines, benzothiazyl, and thiuram derivatives), antioxidants (hindered phenols, aromatic amines), p-phcnylenediamine-based antiozonants, processing oils and phthalate plasticisers. Alkylphenol ethoxylate surfactants have been characterised by FD-MS [115]. Jack-son et al. [116] analysed some plastic additives (hindered phenol AOs and benzotriazole UVA) by FD-MS. Reaction products of a p-phenylenediaminc antiozonant and d.v-9-lricoscnc (a model olefin) were assessed by FD-MS [117],... 

In later papers in this series, there was more emphasis on direct analysis of the rubber or plastic material by field ionizationJ Figure 6.15 is the total ion current (TIC) vs. time (or temperature) profile for a diene rubber compoimd. ° The sample was heated in e direct probe from 50-750°C, with FI-MS. There are two distinct regions in which TIC maxima are observed. The first occurs between 50-400°C and largely represents the evaporation of organic additives from the rubber (Figure 6.16). Additives in the rubber include fatty acid (MW 256,284), a p-phenylenediamine antiozonant (MW 332),... 

Jackson, A. T., Jennings, K. R., and Scrivens, J. H., Analysis of a fivepolymer additives by means of high energy mass spectrometry and tandem mass spectrometry. Rapid Commun. Mass Spectrom., 10,1449, 1996. Lattimer, R. P., Layer, R. W., and Rhee, C. K., Mechanisms of antiozonant protection Antiozonant-rubber reactions during ozone exposure. Rubber Chem. Technol, 57, 1023, 1984. 

This technique has found limited applications in polymer additive analysis in plastics and rubbers. These include aromatic amines and antiozonants in rubber extracts [2, 50-62], and di-laurylthiodipropionate in polymer extracts [56]. 

The analysis of vulcanisates was reviewed by Burger [116] and Aulder [117]. Aulder examined the various methods that had been used for the determination of antioxidants, antiozonants and accelerators with special emphasis on paper chromatography. He evaluated and developed the methods of Miksch and Prolss [118] and Zijp [114], and refined parts of their methods. 

Lattimer and co-workers [25] have applied mass spectrometry (MS) to the determination of antioxidants and antiozonants in rubber vulcanisates. Direct thermal desorption was used with three different ionisation methods [electron impact (El), chemical ionisation (Cl), field ionisation (FI)]. The vulcanisates were also examined by direct fast atom bombardment mass spectrometry (FAB-MS) as a means for surface desorption/ionisation. Rubber extracts were examined directly by these four ionisation methods. Of the various vaporisation/ionisation methods, it appears that field ionisation is the most efficient for identifying organic additives in the rubber vulcanisates. Other ionisation methods may be required, however, for detection of specific types of additives. There was no clear advantage for direct analysis as compared to extract analysis. Antiozonants examined include aromatic amines and a hindered bisphenol. These compounds could be identified quite readily by either extraction or direct analysis and by use of any vaporisation/ionisation method. 

Laser desorption MS has been used for direct analysis of rubber additives, in situ at the surface of elastomeric vulcanisates [201,202]. For example, the technique was used to analyse a sample of truck tyre that displayed premature sidewall cracking. By using a single laser pulse, the molecular ions of several intact molecular species (AOs, antiozonants and a production impurity of an additive) were observed on the rubber surface. Also McClennen et al. [203] have used controlled laser energy to desorb organic additives from a rubber vulcanisate. 

Lykke et al. [177,262] have used L MS (ToF-MS, FTMS) in resonant and non-resonant mode for the molecular analysis of complex materials, including polymer/additive systems. Different wavelengths for the post-ionisation step (near-UV, far-UV, VUV) permit selectivity that provides important additional information on the chemical constitution of these complex materials. LDI techniques render more accessible analysis of complex materials such as polymers and rubbers containing a wide variety of additives and pigments. Lykke et al [218] also compared laser desorption, laser desorption/post-ionisation and laser ionisation in both direct and extract analysis of three vulcanised rubbers (natural rubber, SBR and poly(c/5 -butadiene)). Desorption (532, 308, 266 nm)/post-ionisation (355, 308, 266, 248, 213, 118 nm) was carried out with various lasers. Desorption (308 nm)/post-ionisation (355 nm) with REMPI detection allows preferential detection of various additives (antiozonant HPPD, m/z 268, 211, 183, 169 antioxidant poly-TMDQ, m/z 346, 311) over the ubiquitous hydrocarbons in a rubber (Fig. 3.13). 

Protivova and Pospisil have reported on the behaviour of some amine antioxidants and antiozonants and some model substances (phenols, aromatic hydrocarbons and amines) during gel permeation chromatography and have applied this technique (method 47) to the analysis of rubber extracts. 

Antioxidants and antiozonants examined include aromatic amines (HPPD, DOPPD, DODPA and poly-TMDQ) and a hindered bisphenol (AO 425). These compounds could be identified quite readily by either extraction or direct analysis and by use of any vaporization/ionization method. 

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