Rubbers, additives Volatiles

Macaione et al [235] have used TG for the characterisation of SBR, BR and NR in mono-, di-, or triblend rubber systems and carbon-filled rubber composites and determined the percentage of highly volatile organics, elastomer(s), carbon-black, and inorganic residue for each sample. Lochmiiller et al [194] applied factor analytical methods to evaluate TG results of a series of rubber blends and mixtures composed of chloroprene rubber, NBR, and common rubber additives. TG and measurements of toluene extractable matter of cured siloxane rubbers thermally aged in inert gas atmosphere at 80° C showed a build-up of low-MW fragments in the rubber network with age [244]. 

There are many temporary protectives on the market and it would be impracticable to describe them individually. However, they may be classified according to the type of film formed, i.e. soft film, hard film and oil film the soft film may be further sub-divided into solvent-deposited thin film, hot-dip thick film, smearing and slushing types. All these types are removable with common petroleum solvents. There are also strippable types based on plastics (deposited by hot dipping or from solvents) or rubber latex (deposited from emulsions) these do not adhere to the metal surfaces and are removed by peeling. In addition there are volatile corrosion inhibitors (V.C.I.) consisting of substances, the vapour from which inhibits corrosion of ferrous metals. 

Alternative approaches consist in heat extraction by means of thermal analysis, thermal volatilisation and (laser) desorption techniques, or pyrolysis. In most cases mass spectrometric detection modes are used. Early MS work has focused on thermal desorption of the additives from the bulk polymer, followed by electron impact ionisation (El) [98,100], Cl [100,107] and field ionisation (FI) [100]. These methods are limited in that the polymer additives must be both stable and volatile at the higher temperatures, which is not always the case since many additives are thermally labile. More recently, soft ionisation methods have been applied to the analysis of additives from bulk polymeric material. These ionisation methods include FAB [100] and LD [97,108], which may provide qualitative information with minimal sample pretreatment. A comparison with FAB [97] has shown that LD Fourier transform ion cyclotron resonance (LD-FTTCR) is superior for polymer additive identification by giving less molecular ion fragmentation. While PyGC-MS is a much-used tool for the analysis of rubber compounds (both for the characterisation of the polymer and additives), as shown in Section 2.2, its usefulness for the in situ in-polymer additive analysis is equally acknowledged. 

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. 

Small Quantities. Wear Viton rubber gloves,16 laboratory coat, and eye protection. Work in the fume hood. For each 0.05 mol (3.8 g, 3.0 mL) of carbon disulfide to be destroyed, use 670 mL of sodium hypochlorite (bleach) or a mixture of 55 g of 65% calcium hypochlorite in 220 mL of water. Place the hypochlorite in flask equipped with dropping funnel, stirrer, and thermometer, and add the carbon disulfide dropwise such that the reaction temperature is maintained between 20 and 30°C (to avoid volatilizing of the carbon disulfide). When addition is complete, continue stirring for 2 hours or until a clear, homogeneous solution remains (perhaps containing traces of oily by-products). The reaction mixture can be washed into the drain.18... 

Despite the relatively low percentage content of extractives (Table II), they very often influence wood properties and thus play a role in utilization. Advantages accrue from the presence of colored and volatile extractives which provide esthetic values. Some of the phenolic compounds provide resistance to insect and fungal attack. Other extractives provide useful products. From tall oil, products such as turpentine, rosin and fatty acids are produced. In addition, tannins, camphor, gum arabic, natural rubber and flavonoids are some of the many products from extractives. 

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