Plasticising solvents

Ion-selective electrodes (ISEs) with sensor membranes based on sensor molecules plus suitable plasticising solvent mediators are best fabricated with such components physically entangled in a thin poly(vinyl chloride) (PVC) membrane. 

Adipic acid Nylon 66, esters, polyurethane resins Fibres, resins, plasticisers, solvents, lubricants Niu etal., 2002... 

Eluted material almost always includes unwanted extraneous matter co-extracted from the paper or thin-layer chromatogram. Thus it is advisable to use the eluent from a blank area as a reference solution. Contamination from plasticisers, solvents, and dirty glassware can also be a serious problem when a spectrum has to be obtained from a few micrograms of a compound. Even momentary contact of dry adsorbent with plastic tubing can remove appreciable quantities of plasticisers. Hence the following precautions should be taken ... 

Synthesis of organic esters, which are used as perfumes, flavours, pharmaceuticals, plasticisers, solvents and intermediates, by esterification can be performed using either mineral acids or solid acid catalysts... 

In dense polymers, the self-diffusion of small plasticising solvent molecules has been measured PGSE methods [105]. For polymers above the glass-transition temperature, it is common to model the solvent diffusion using the free volume theory as modified for polymer systems by Fujita [122] and by Vrentas and Duda [123]. For solvent diffusion in dense polymers below Tg, an alternative model has been given by Frisch and Stern [124]. 

Large amounts of plastic are produced and used in various spheres of human activity, which are ultimately discarded as pollutants containing residues such as plasticisers, solvents and harmful products which can migrate out of the materials. Therefore, the toxicological properties of plastics can be characterised as migratory or derivatives formed under the influence of the environment. Plastics contain many additives which alter its properties and it is important to know the level of these constituents to regulate by maximum concentrations allowable in the plastic [2-6]. 

Usually, both crystalline and amorphous phases are present in polymer electrolytes. Since only amorphous phases present high conductivity, plasticiser solvents are usually added to enhance the amorphous phase and thus the ionic conductivity. Here, propylene carbonate (PC), EC,y-butyrolactone (y-BL) and their binary mixtures are usually used as plasticiser solvents. Hie stereo structures of the polymer matrix molecules are given in Fig. 12.3, including linear, comb, crossing, star, hyper-branched and comb crosslinking. 

The above treatment has considered plasticisers as a special sort of solvent and has enabled broad predictions to be made about which plasticisers will be compatible with which polymer. It has not, however, explained the mechanism by which plasticisers become effective. 

It was pointed out in Chapter 5 that plasticisers were essentially non-volatile solvents. Consequently they were required to have solubility parameters close to that of the polymer and a molecular weight of at least 300. If the polymer or the plasticisers had a tendency to crystallise then there would need to be some sort of specific interaction between the polymer and the plasticiser. Tables 5.4 and 5.6 gave some figures for the solubility parameters of polymers and plasticisers. 

As explained in Chapter 5, these materials are essentially non-volatile solvents for PVC. Because of their molecular size they have a very low rate of diffusion into PVC at room temperature but at temperatures of about 150°C molecular mixing can occur in a short period to give products of flexibility varying according to the type and amount of plasticiser added. 

All PVC plasticisers have a solubility parameter similar to that of PVC. It appears that differences between liquids in their plasticising behaviour is due to differences in the degree of interaction between polymer and plasticiser. Thus such phosphates as tritolyl phosphate, which have a high degree of interaction, gel rapidly with polymer, are more difficult to extract with solvents and give compounds with the highest brittle point. Liquids such as dioctyl adipate, with the lowest interaction with polymer, have the converse effect whilst the phthalates, which are intermediate in their degree of interaction, are the best allround materials. 

Nitration of cellulose followed by plasticisation of the product with camphor has the effect of reducing the orderly close packing of the cellulose molecules. Hence whereas cellulose is insoluble in solvents, except in certain cases where there is chemical reaction, celluloid is soluble in solvents such as acetone and amyl acetate. In addition the camphor present may be dissolved out by chloroform and similar solvents which do not dissolve the cellulose nitrate. 

The hydrohalide is usually prepared by passing hydrogen chloride into a solution of masticated high-grade raw rubber in benzene at 10°C for about six hours. Excess acid is then neutralised and plasticisers and stabilisers are added. The benzene is removed by steam distillation and the product washed and dried. Alternatively the solution is cast on to a polychloroprene rubber belt, leaving a tough film after evaporation of the solvent. 

Variation in the details of the solvent processes will produce different grades of shellac. For example, when cold alcohol is used, lac wax which is associated with the resin remains insoluble and a shellac is obtained free from wax. Thermally processed shellacs were greatly favoured for gramophone records as they were free from residual solvent and also contained a small quantity of lac wax which proved a useful plasticiser. 

Chlorinated rubber is soluble in aromatic solvents, and paints made from it dry by solvent evaporation alone. In contrast to the vinyls, there is less difficulty in formulating systems that are suitable for brush application. It has excellent resistance to a wide range of chemicals and to water, but as it is extremely brittle it needs to be plasticised. To preserve chemical resistance it is necessary to use inert plasticisers such as chlorinated paraffin wax. Due to the presence of ozone depleting solvents, chlorinated rubber coatings are being phased out and largely replaced by vinyl acrylic coatings which have very similar performance and can be formulated from lower aromatic or aliphatic solvents. 

Two of these types are lacquers, giving quick drying to the dust-free state at ambient temperature, but at the expense of lower film build. Nitrocellulose-based lacquers are preferred in some European countries and acrylic lacquers in North America. Nitrocellulose is plasticised with nondrying alkyds, polyester and liquid plasticiser. Acrylics are plasticised internally by use of plasticising monomers with methyl methacrylate and by solvent plasticiser. Acrylics give better durability and nitrocellulose gives easier application. 

P.V.C. plastisols P.V.C. plastisols are liquids which contain little or no solvent/diluent. They consist of a blend of polyvinyl chloride (p.v.c.) resins, plasticisers, stabilisers, viscosity depressants, pigments and sometimes fillers. 

Being slightly crystalline, there are few good solvents, the best known of which are nitrobenzene, cyclohexanone and tetrahydrofuran. When mixed with certain non-volatile solvents such as some phthalates, adipates and phosphates, flexible materials are obtained and which are referred to as plasticised p. v.c. 

Plasticiser/oil in rubber is usually determined by solvent extraction (ISO 1407) and FTIR identification [57] TGA can usually provide good quantifications of plasticiser contents. Antidegradants in rubber compounds may be determined by HS-GC-MS for volatile species (e.g. BHT, IPPD), but usually solvent extraction is required, followed by GC-MS, HPLC, UV or DP-MS analysis. Since cross-linked rubbers are insoluble, more complex extraction procedures must be carried out. The determination of antioxidants in rubbers by means of HPLC and TLC has been reviewed [58], The TLC technique for antidegradants in rubbers is described in ASTM D 3156 and ISO 4645.2 (1984). Direct probe EIMS was also used to analyse antioxidants (hindered phenols and aromatic amines) in rubber extracts [59]. ISO 11089 (1997) deals with the determination of /V-phenyl-/9-naphthylamine and poly-2,2,4-trimethyl-1,2-dihydroquinoline (TMDQ) as well as other generic types of antiozonants such as IV-alkyl-AL-phenyl-p-phenylenediamines (e.g. IPPD and 6PPD) and A-aryl-AL-aryl-p-phenylenediamines (e.g. DPPD), by means of HPLC. 

Contaminated solvents and glassware are a very well known problem in analysis involving extraction. The major problem in the use of solvents is contamination with plasticisers, especially DEHP. After sample extraction usually enrichment of the analytes is required prior to the analysis. 

---