Elastomers, additives Plasticisers

Some more specific polymer chemistry applications for TG-FTIR are solvent and water retention, curing and vulcanisation reactions, isothermal ageing, product stability, identification of base polymer type and additives (plasticisers, mould lubricants, blowing agents, antioxidants, flame retardants, processing aids, etc.) and safety concerns (processing, product safety, product liability, fire hazards) [357]. A wide variety of polymers and elastomers has been studied by TG-FTIR [353,358,359]. The potential applications of an integrated TG-FTIR system were discussed by various authors [346,357]. 

In the rubber field it is not only the polymer that determines the properties of an elastomer, but many accompanying substances, like fillers, pigments, plasticisers, curing agents, antioxidants, stabilisers and processing aids (cf. Table 2.2). With rubbers the possible compositional permutations are numerous. In fact, already within the additive group of CBs there are more than 30 different possible products. 

It is of interest to examine the development of the analytical toolbox for rubber deformulation over the last two decades and the role of emerging technologies (Table 2.9). Bayer technology (1981) for the qualitative and quantitative analysis of rubbers and elastomers consisted of a multitechnique approach comprising extraction (Soxhlet, DIN 53 553), wet chemistry (colour reactions, photometry), electrochemistry (polarography, conductometry), various forms of chromatography (PC, GC, off-line PyGC, TLC), spectroscopy (UV, IR, off-line PylR), and microscopy (OM, SEM, TEM, fluorescence) [10]. Reported applications concerned the identification of plasticisers, fatty acids, stabilisers, antioxidants, vulcanisation accelerators, free/total/bound sulfur, minerals and CB. Monsanto (1983) used direct-probe MS for in situ quantitative analysis of additives and rubber and made use of 31P NMR [69]. 

Various additives show considerable extraction resistance, such as impact modifiers (polyacrylates and polyblends PVC/EVA, PVC/ABS, etc.), highpolymeric processing aids (PMMA-based), elastomers as high-MW plasticisers, reactive flame retardants (e.g. tetrabromobisphenol-A, tetrabromophthalic anhydride, tetrabromophthalate diol, dibromostyrene). Direct measurement of additives by UV and IR spectroscopy of moulded films is particularly useful in analysing for additives that are difficult to extract, although in such cases the calibration of standards may present a problem and interferences from other additives are possible. 

The 8000-MW, ultra-low monol PPG is used particularly in the development of soft, plasticiser-free elastomers [16, 17]. The nse of this high MW, low polydispersity polyol allows for the preparation of low viscosity prepolymers with low isocyanate contents. Initial evalnations of these very soft elastomers showed lower than expected physical properties. The lower properties can be attributed to the very low hard-segment content of these polymers. The lack of hard segment (physical crosslinks) can be compensated for by the incorporation of low levels of chemical crosslinks (triol) [18]. This is accomplished by the addition of a 6000-MW, ultra-low monol triol (Acclaim Polyol 6300) into the polymer matrix. Table 9.7 shows the triol effect on prepolymer viscosities, elastomer processability and physical properties. It shonld be noted that very low levels of crosslinking are needed to improve the elastomer properties. 

In principle a liquid additive can be added to polymers anywhere from the base of the hopper to an add-on mixer at the screw tip. In a few cases such as plasticisers with polyvinylchloride (PVC) polymer powder and hydrocarbon oil with styrene/butadiene thermoplastic elastomer pellets, batch premixing can be used, during which the polymer absorbs the liquid. The dry blend can then be processed by the extruder. 

Continuous processing of filled elastomers by twin-screw extrusion and achievement of viable mixing distribution characteristics present formidable challenges. A thermoplastic elastomer, HyTemp, is plasticised with DOA and filled with ammonium perchlorate powder and additives. It is found that the extruder geometry, the order of ingredient addition and die pressmisation have profoimd effects on the mixing distribution characteristics of the elastomer-based extraded profiles. The mixing distribution characteristics are quantitatively determined by X-ray diffraction techniques. 16 refs. 

Volatile substances such as moisture, plasticisers and other additives. The actual elastomers involved. 

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