Polymers and rubber

Many of the remarks made in the previous section concerning fibres can be applied to the analysis of plastics. Some polymers are soluble in organic solvents and samples may be prepared for direct aspiration into a flame in this way, e.g. MIBK is a suitable solvent for polyesters, polystyrene, polysiloxanes, cellulose acetate and butyrate dimethyl formamide for polyacrylonitrile, dimethyl acetamide for polycarbonates and polyvinyl chloride cyclohexanone for polyvinyl chloride and polyvinyl acetate formic acid for polyamides and methanol for polyethers. These organic solutions may alternatively be injected into a graphite furnace. Otherwise, polymers may be wet or dry ashed and the resultant ash dissolved in acid. An approach which is attracting increasing interest is the direct insertion of solid samples into a graphite furnace. 

Oliver [190] recommends the dissolution of the polymer if possible (see above) but in other cases a wet ashing procedure was used. The sample was heated with 2—3 ml of concentrated sulphuric acid and then hydrogen peroxide added drop-wise until the organic matter was destroyed. Twenty elements were determined in a 2% solution of polymer. Polymers may be dispersed in an organic solvent and trace metals removed by leaching with an appropriate aqueous solution, preferably the procedure should be repeated more than once to ensure complete extraction. To determine antimony in fire-retardant polypropylene, the sample was dispersed in xylene and extracted with 6M hydrochloric acid under reflux [191]. The filtered acid layer was combined with two further extracts prior to aspiration into the air/acetylene flame and measurement at 217.6 nm. Martinie and Schilt [45] reported that nylon would dissolve completely in perchloric/nitric acid digestion but potentially explosive problems were encountered in the dissolution of Amberlite resins and rubber. 

Price [67] reported a method for the dissolution of polyvinyl chloride 

Extractable metals in plastics (e.g. those used as kitchen utensils) can be determined following a suitable acid leach. Cadmium has been determined in this way using either an ethanol/acetic acid/water (10 + 3 4- 87) or diethyl ether/4% acetic acid extractant [192]. The extract was evaporated to dryness and redissolved in 1M nitric acid prior to aspiration into an air/acetylene flame and measured at 228.8 nm. 

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The radiation and temperature dependent mechanical properties of viscoelastic materials (modulus and loss) are of great interest throughout the plastics, polymer, and rubber from initial design to routine production. There are a number of laboratory research instruments are available to determine these properties. All these hardness tests conducted on polymeric materials involve the penetration of the sample under consideration by loaded spheres or other geometric shapes [1]. Most of these tests are to some extent arbitrary because the penetration of an indenter into viscoelastic material increases with time. For example, standard durometer test (the "Shore A") is widely used to measure the static "hardness" or resistance to indentation. However, it does not measure basic material properties, and its results depend on the specimen geometry (it is difficult to make available the identity of the initial position of the devices on cylinder or spherical surfaces while measuring) and test conditions, and some arbitrary time must be selected to compare different materials. 

Table 10.4 Resistance of Selected Polymers and Rubbers to Various Chemicals...

TABLE 10.5 Gas Permeability Constants (10 P) at 25°C for Polymers and Rubbers The gas permeability constant P is defined as... 

An extensive new Section 10 is devoted to polymers, rubbers, fats, oils, and waxes. A discussion of polymers and rubbers is followed by the formulas and key properties of plastic materials. Eor each member and type of the plastic families there is a tabulation of their physical, electrical, mechanical, and thermal properties and characteristics. A similar treatment is accorded the various types of rubber materials. Chemical resistance and gas permeability constants are also given for rubbers and plastics. The section concludes with various constants of fats, oils, and waxes. 

A comparison of these predicted values of E with the measured values plotted in the bar-chart of Fig. 3.5 shows that, for metals and ceramics, the values of E we calculate are about right the bond-stretching idea explains the stiffness of these solids. We can be happy that we can explain the moduli of these classes of solid. But a paradox remains there exists a whole range of polymers and rubbers which have moduli which are lower - by up to a factor of 100- than the lowest we have calculated. Why is this What determines the moduli of these floppy polymers if it is not the springs between the atoms We shall explain this under our next heading. 

As an example, a compact high-throughput turbulent flow reactor/mixer/heat exchanger was used for various applications, including polymer and rubber manufacture [50]. Further applications refer to emulsification and intensified heat exchange. 

Infrared spectroscopy is a major tool for polymer and rubber identification [11,12]. Infrared analysis usually suffices for identification of the plastic material provided absence of complications by interferences from heavy loadings of additives, such as pigments or fillers. As additives can impede the unambiguous assignment of a plastic, it is frequently necessary to separate the plastic from the additives. For example, heavily plasticised PVC may contain up to 60% of a plasticiser, which needs to be removed prior to attempted identification of the polymer. Also an ester plasticiser contained in a nitrile rubber may obscure identification of the polymer. Because typical rubber compounds only contain some 50% polymer direct FUR analysis rarely provides a definitive answer. It is usually necessary first... 

Applications Although Soxtec combines the best qualities of reflux and Soxhlet extractions up to now fairly little evidence has been reported concerning the efficacy of this system for polymer and rubber analysis. Nevertheless, it appears that oligomers and other reaction residues, softeners, antioxidants (e.g. BHT) and several other additives used to modify polymers are easily extracted from PVC, PP, PE, PS, rubber and many other polymeric materials. Also, some leading international plastic, rubber and packaging companies have made Soxtec an integral part of their quality control routines. Some application examples where Soxtec has proved successful are [148] ... 

Applications Conventional TLC was the most successful separation technique in the 1960s and early 1970s for identification of components in plastics. Amos [409] has published a comprehensive review on the use of TLC for various additive types (antioxidants, stabilisers, plasticisers, curing agents, antistatic agents, peroxides) in polymers and rubber vulcanisates (1973 status). More recently, Freitag [429] has reviewed TLC applications in additive analysis. TLC has been extensively applied to the determination of additives in polymer extracts [444,445]. 

Applications A limited number of papers refer to the use of AAS in relation to polymer/additive deformulation. Elemental analysis of polymers and rubbers by AAS may be carried out after dissolution in an organic solvent (Table 8.21), after oxidative wet digestion (Table 8.12), after dry ashing (Table 8.22) or directly in the solid state (Table 8.23). 

Polymers and Rubbers. In R.A. Meyers (Ed.), Encyclopedia of Analytical Chemistry, Wiley, Chichester, 2002. 

J.M. Chalmers and N.J. Everall, Qualitative and quantitative analysis of plastics, polymers and rubbers by vibrational spectroscopy. In N.J. Everall, J.M. Chalmers and P.R. Griffiths (Eds.), Vibrational Spectroscopy of Polymers Principles and Practice, Wiley, Chichester, 2007, pp. 1-67. 

Gas chromatography (GC) and mass spectrometry (MS) can be coupled to the TGA instrument for online identification of the evolved gases during heating pyrolysis-GC/MS is a popular technique for the evaluation of the mechanism and the kinetics of thermal decomposition of polymers and rubbers. Moreover, it allows a reliable detection and (semi)quantitative analysis of volatile additives present in an unknown polymer sample. 

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