Thermal stabilisers, analysis

For samples that meet the solubility requirements of the SEC approach, analyses were also reported for additives in polymers such as PVC and PS [28,29]. Direct SEC analysis of PVC additives such as plasticisers and thermal stabilisers in dissolution mode has been described [28,30,31 ]. In the analysis of a dissolved PS sample using a SEC column of narrow pore size, the group of additives was separated on a normal-phase column after elution of the polymer peak [21]. Column-loading capacity of HPSEC for the analysis of additives, their degradation products and any other low-MW compounds present in plastics has been evaluated for PS/HMBT, PVC/TNPP and PVC/TETO (glyceryl tri[l-14C] epoxyoleate) [31]. It was shown that HPSEC can be used to separate low-MW compounds from relatively large amounts of polymers without serious loss of resolution of the additives the technique has also been used for the group analysis of chlorohydrin transformation products of the TETO model compound [32]. 

FTIR spectroscopy, the rate of increase of the concentration of degradation products was monitored as the parameter determining polymer degradation. Significantly better stability was expressly confirmed by the statistical analysis of the results for the film containing Mg(OH)2 as thermal stabiliser. The presented results confirmed that a good stabiliser must effectively eliminate acidic compounds in PVA melt to avoid degradation reactions. 

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. 

While additive analysis of polyamides is usually carried out by dissolution in HFIP and hydrolysis in 6N HC1, polyphthalamides (PPAs) are quite insoluble in many solvents and very resistant to hydrolysis. The highly thermally stable PPAs can be adequately hydrolysed by means of high pressure microwave acid digestion (at 140-180 °C) in 10 mL Teflon vessels. This procedure allows simultaneous analysis of polymer composition and additives [643]. Also the polymer, oligomer and additive composition of polycarbonates can be examined after hydrolysis. However, it is necessary to optimise the reaction conditions in order to avoid degradation of bisphenol A. In the procedures for the analysis of dialkyltin stabilisers in PVC, described by Udris [644], in some instances the methods can be put on a quantitative basis, e.g. the GC determination of alcohols produced by hydrolysis of ester groups. 

David et al. [184] have shown that cool on-column injection and the use of deactivated thermally stable columns in CGC-FID and CGC-F1D-MS for quantitative determination of additives (antistatics, antifogging agents, UV and light stabilisers, antioxidants, etc.) in mixtures prevents thermal degradation of high-MW compounds. Perkins et al. [101] have reported development of an analysis method for 100 ppm polymer additives in a 500 p,L SEC fraction in DCM by means of at-column GC (total elution time 27 min repeatability 3-7 %). Requirements for the method were (i) on-line (ii) use of whole fraction (LVI) and (iii) determination of high-MW compounds (1200 Da) at low concentrations. Difficult matrix introduction (DMI) and selective extraction can be used for GC analysis of silicone oil contamination in paints and other complex analytical problems. 

Relatively few descriptions of direct mass spectral analysis of plastics compounds have appeared in the literature. In a rather early report, additives in PP compounds were thermally desorbed into a heated reservoir inlet for mass spectral analysis [58]. It was found that numerous stabilisers could be identified via 80 eV EI-MS. Thermal, desorption of additives via direct probe introduction of PP compounds was described in a later report [59]. A more recent paper considered the mass spectral analysis of both rubber and plastic compounds. This report was an overview, without much detail. Analysis of additives in PP compounds via direct thermal desorption CI-MS has also been described [45]. 

Schwartz and co-workers [97] used isothermal differential thermal analysis to study the diffusion of Irganox 1330 (1,3,5 tris (3,5 di-tor -butyl-4-hydroxyl benzyl) mesitylene) in extruded sheets of isotactic polypropylene (iPP). Studies were conducted over the temperature range 80-120 °C. The measurements showed a clear relation between oxidation induction time and oxidation maximum time [both determined by isothermal dynamic thermal analysis (DTA)] and the concentration of stabiliser. It was possible to calculate the diffusion coefficients and the activation energy of diffusion of Irganox 1330 in iPP by measuring the oxidation maximum times across stacks of iPP sheets. 

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