Determinations thermal stabilisers

As in the preceding section, the polymers to be bonded were PVC, ABS, and the thermoplastic polyester blend Xenoy. In addition microscope slide glass was also studied. Surfaces of these materials have been shown to be capable of widely differing acid-base interactions. The PVC was an unplasticised polymer (MW = 54,000 g/mol) from Synergistic Chemicals, Inc. It contained 5 phr of Advastab TM-821SP thermal stabiliser. The ABS (Cycolac AR 3501), was a moulding grade, commercial product of GE Plastics, Inc. The same source supplied the Xenoy blend the exact composition of this material was not determined. 

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. 

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. 

Many methods have been proposed and are used to study the thermal stability of propellants and to ensure the absence of possible autocatalysed decompositions during storage. None are sufficiently reliable to merit individual description. In practice, stabilisers are added, the usual being diphenylamine for nitrocellulose powders and symmetrical diethyl diphenyl urea (carbamate or centralite) for double base propellants. Provided a reasonable proportion of stabiliser remains, the propellant can be assumed to be free from the possibility of autocatalytic decomposition. The best test of stability is therefore a chemical determination of the stabiliser present. 

The isothermal thermal stability determination. Isothermal mass/time curves of non-stabilised PP powder samples were measured during 1000 minutes at temperatures between 160°C and 280°C. The PP TGA samples (about 10 mg.) were flushed with nitrogen during one hour at 30°C before the experiment was started. 

Hence, the Td(o)-value of pure (non-stabilised) PP is about 190°C. It is also clear that the small amounts of oligomers present in these samples do not hamper a proper Td(o)-value determination. This Td(o)-value of 190°C increases to about 240°C due to the addition of the stabiliser system (ionol and irganox). The activity of this stabiliser system is not only temperature but also in time limited. Figure 2.5 shows that this stabiliser system stays active (at 250°C) for about 1000 minutes i.e. long enough to withstand the thermal treatments during all different PP processing procedures. 

DSC and TG can be used to determine the thermal/oxidative stability of PP, PE and their blends. The oxidation induction time (OIT) and the oxidation temperature (T j ) provide relatively, rapid information about the total amount of effective antioxidants in the reprocessed resin, which is important to establish the need for re-stabilisation or upgrade of the resins. 

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