Quantitation, additives Plasticisers

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]. 

Applications The general applications of XRD comprise routine phase identification, quantitative analysis, compositional studies of crystalline solid compounds, texture and residual stress analysis, high-and low-temperature studies, low-angle analysis, films, etc. Single-crystal X-ray diffraction has been used for detailed structural analysis of many pure polymer additives (antioxidants, flame retardants, plasticisers, fillers, pigments and dyes, etc.) and for conformational analysis. A variety of analytical techniques are used to identify and classify different crystal polymorphs, notably XRD, microscopy, DSC, FTIR and NIRS. A comprehensive review of the analytical techniques employed for the analysis of polymorphs has been compiled [324]. The Rietveld method has been used to model a mineral-filled PPS compound [325]. 

Whereas the use of conventional fast atom bombardment (FAB) in the analysis of polymer/additive extracts has been reported (see Section 6.2.4), the need for a glycerol (or other polar) matrix might render FAB-MS analysis of a dissolved polymer/additive system rather unattractive (high chemical background, high level of matrix-, solvent- and polymer-related ions, complicated spectra). Yet, in selected cases the method has proved quite successful. Lay and Miller [53] have developed an alternative method to the use of sample extraction, cleanup, followed by GC in the quantitative analysis of PVC/DEHP with plasticiser levels as typically found in consumer products (ca. 30 %). The method relied on addition of the internal standard didecylphthalate (DDP) to a THF solution of the PVC sample with FAB-MS quantitation based on the relative signal levels of the [MH]+ ions of DEHP and DDP obtained from full-scan spectra, and on the use of a calibration curve (intensity ratio m/z 391/447 vs. mg DEHP/mg DDP). No FAB-matrix was added. No ions associated with the bulk of the PVC polymer were observed. It was... 

Quantitatively, the basic use of NMR is to determine the composition of a mixture in terms of the fraction of each species present from the relative intensities of peaks from each component. The components may be different chains in a polymer blend, different monomer units in a copolymer, or a polymer and an additive, for example in a polymer/plasticiser or polymer/ stabiliser system. 

Griddle [43] has described a column chromatographic procedure for the identification and semi-quantitative determination of plasticisers in PVC. In this procedure the plasticiser is first Soxhlet extracted from 1 to 2 gram of PVC sample using anhydrous diethyl ether. Ether is then evaporated from the extract and residual traces of PVC precipitated by the addition of 2 ml of absolute ethanol. Following filtration of any polymer, the ethanol is finally evaporated off to provide a PVC free plasticiser extract. 

IR spectroscopy may be used for detection of plasticisers in soft PVC cables [75], but does not distinguish clearly between the many possible di-alkylphthalates. With the advent of difference spectroscopy, identification of a plasticiser in a polymer no longer requires isolation of the additive. Identification can readily be made without separation if the polymer is known and a plasticiser-free spectrum is available. This was illustrated for di-2-ethylhexylsebacate in an acrylonitrile-butadiene copolymer [76]. IR can sometimes quantify plasticisers in solid plastic compositions without the need for extraction or dissolution steps. FTIR difference spectroscopy has also been used for quantitative analysis. Another example of difference spectroscopy is the case of two plastic films which differed in printability [77]. Difference mid-IR spectra of the surfaces of the two films in the 1600-1300 cm region revealed a stearate (and eventually a free acid, at 1720 cm ). Surface properties of... 

PVAc has been determined according to equation Tg = 18.4 - 6.77C + 0.2197C (plasticiser content C in % validity range 0-12.5% correlation coefficient 0.9986) [85]. Whereas further chlorinating (PVCC) increases Tg from approximately 86°C towards 100°C, it can be lowered to almost any value by addition of plasticisers (-40° to +90°C), as indeed is true also for PVAc. When the additive concentration in a resin exceeds a few weight percent, it is often possible to assay the additive calorimetri-cally without extracting it. If the additive is incompatible with the resin, it can be detected in a separate crystalline or glassy phase by either its Tm or Tg and measured quantitatively from A7/f determinations at Tin or Acp measurements at Tg. When an additive is soluble in a polymer, its concentration can be estimated from shifts in Tm or Tg of the resin. Once a master curve of Tg V5. plasticiser concentration has been prepared for a particular PVC composition, it can be used to determine the amount of plasticiser in an unknown formulation of the particular plasticiser, e.g. PVC/DIDP (cfr. Fig. 2.1) [27]. For PVC/DOP a linear relationship from zero to 45 wt.% plasticiser has been reported [86]. DSC was also used in miscibility studies of erucamide and PA 12 [87]. 

With TG it is also possible to determine glass fibres in polymer systems. Fava [261] recorded TG/DTG curves of PP filled with carbonate and fibreglass. TG is an ideal analytical tool for the control of the glass fibre content in composite materials. Since the glass fibre is thermally inert, there is no problem resolving the weight from the resin (by simple subtraction from 100%). Gibbons [151] has analysed additives such as plasticisers, antioxidants, fillers, and reinforcements for PAll, PE, PP and epoxy resins both qualitatively and quantitatively by DSC and thermomechanical analysis. Fig-... 

Quantitative analytical schemes (using calibration curves, internal standardisation) have been devised for selected (copolymeric) systems [540]. An example is the determination of the composition of styrene-methacrylate by PyGC [603]. Qther applications include the quantification of rubber components [604,605], cellulose esters [606], isocyanate components of polyurethanes [607], nylon [608], plasticisers [609], aliphatic sulfur-containing additives [4]. Standardisation for quantitative analysis based on PyGC data requires careful choice of reference polymers. Use of an internal standard may improve the precision when the concentration of a single polymeric component of a blend or copolymer is calculated on the basis of PyGC data [610]. 

Relatively few studies have been made on the feasibility of quantitative FAB analysis. Riley et al. [217] have described a quantification procedure to monitor the paint additive Tinuvin 770 in two coating systems (acrylic melamine and a hydroxy ester melamine). Tinuvin 770 proved to be well suited for FAB analysis in coating extracts on glycerol basis using an internal standardisation procedure. Lay et al. [218] have developed a FAB-MS method for the quantitative analysis of plasticisers (DEHP, including any isomeric dioctyl phthalates) in baby PVC pacifiers that does not require sample extraction, clean-up, or chromatographic separation. A reference material, didecylphthalate (DDP), was added to a solution of the PVC sample in THF as an internal standard. Quantitation was based on the relative... 

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