Rubber 433 Vulcanisation

Antioxidants may be assessed in a variety of ways. For screening and for fundamental studies the induction period and rate of oxidation of petroleum fractions with and without antioxidants present provide useful model systems. Since the effect of oxidation differs from polymer to polymer it is important to evaluate the efficacy of the antioxidant with respect to some property seriously affected by oxidation. Thus for polyethylene it is common to study changes in flow properties and in power factor in polypropylene, flow properties and tendency to embrittlement in natural rubber vulcanisates, changes in tensile strength and tear strength. 

Rubber vulcanised-determination of adhesion to, and corrosion of, metals Corrosion of metals and alloys determination of dezincification resistance of brass Sulphur dioxide test with general condensation of moisture... 

Table 2.7 lists techniques used to characterise carbon-blacks. Analysis of CB in rubber vulcanisates requires recovery of CB by digestion of the matrix followed by filtration, or by nonoxidative pyrolysis. Dispersion of CB within rubber products is usually assessed by the Cabot dispersion test, or by means of TEM. Kruse [46] has reviewed rubber microscopy, including the determination of the microstructure of CB in rubber compounds and vulcanisates and their qualitative and quantitative determination. Analysis of free CB features measurements of (i) particulate and aggregate size (SEM, TEM, XRD, AFM, STM) (ii) total surface area according to the BET method (ISO 4652), iodine adsorption (ISO 1304) or cetyltrimethylammonium bromide (CTAB) adsorption (ASTM D 3765) and (iii) external surface area, according to the dibutylphthalate (DBP) test (ASTM D 2414). TGA is an excellent technique for the quantification of CB in rubbers. However, it is very limited in being able to distinguish the different types of... 

Applications Shake-flask extraction nowadays finds only limited application in polymer/additive analysis. Carlson et al. [108] used this technique to extract antioxidants from rubber vulcanisates for identification purposes (NMR, IR, MS). Wrist-action shaking at room temperature was also used as the sample preparation step for the UV and IR determination of Ionol CP, Santonox R and oleamide extracted from pelletised polyethylene using different solvents [78]. BHT could be extracted in 98 % yield from powdered PP by shaking at room temperature for 30 min with carbon disulfide. 

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]. 

In a study on the identification of organic additives in rubber vulcanisates using mass spectrometry, Lattimer et al. [22] used direct thermal desorption with three different ionisation methods El, Cl and FI. Also, rubber extracts were examinated directly by four ionisation methods (El, Cl, FD and FAB). The authors did not report a clear advantage for direct analysis as compared to analysis after extraction. Direct analysis was a little faster, but the extraction methods were considered to be more versatile. 

Salmona et al. [66] used El and CIMS to identify benzothiazole derivatives leached into injections by rubber plunger seals from disposable syringes. One of the compounds was used as a rubber vulcanisation accelerator, and four others were formed during syringe sterilisation with ethylene oxide. Applications of hyphenated chemical impact mass-spectrometric techniques are described elsewhere GC-MS (Section 7.3.1.2), for polar and nonpolar volatile organics, SFC-MS (Section 13.2.2) and TLC-MS (Section 7.3.5.4). 

FAB has been used to analyse additives in (un) vulcanised elastomer systems [92,94] and FAB matrices have been developed which permit the direct analysis of mixtures of elastomer additives without chromatographic separation. The T-156 triblend vulcanised elastomer additives poly-TMDQ (AO), CTP (retarder), HPPD (antiozonant), and TMTD, OBTS, MBT and A,lV-diisopropyl-2-benzothiazylsulfenamide (accelerators) were studied in three matrix solutions (glycerol, oleic acid, and NPOE) [94]. The thiuram class of accelerators were least successful. Mixture analysis of complex rubber vulcanisates without chromatographic separation was demonstrated. The differentiation of matrix ions from sample ions was enhanced by use of high-resolution acquisition. 

FD-MS by itself provides only limited chemical information. Lattimer et al. [92] have also compared the analysis of extracted rubber vulcanisates by means of FD-MS and FAB-MS, using the aforementioned EI/FD/FT/FAB ion source. The systems investigated were neoprene/DOPPD, EPDM/(DOP, PBNA, paraffin wax), neoprene-SBR blend/(DOP, DOPPD, TDBHI). Certain compounds were observed by FD but not by FAB (wax, oil, isocyanurate antioxidant TDBHI). In FAB conditions some polymer additives suppress... 

Analysis of solid matter, in particular of rubber vulcanisates, is a classical application of DP-MS [263]. 

Table 6.40 Optimal methods for detection of organic additives in carbon-black-filled rubber vulcanisates...

Sodium chlorite reacts very violently with organic compounds of divalent sulfur, or with free sulfur (which may ignite), even in presence of water. Contact of the chlorite with rubber vulcanised with sulfur or a divalent sulfur compound should therefore be avoided [1]. Application of factorial design techniques to experimental planning gave specific conditions for the safe oxidation of organic sulfides to sulfoxides using sodium chlorite or calcium hypochlorite [2],... 

Organic compounds having four alkyl groups attached to nitrogen. A quaternary ammonium salt is employed in reversing the electric charge on natural rubber latex quaternary ammonium dithiocarbamates are ultra-accelerators for rubber vulcanisation. 

The reduction in stress which takes place in a test strip of rubber held at constant elongation. Stress relaxation measurements are used in the study of the ageing of rubber vulcanisates, the degradation of the network structure resulting in a reduction of the tension. 

This is the ratio of the rates of vulcanisation at two temperatures 10 °C (or 18 °F) apart. For rubber vulcanisation the coefficient is approximately 2 but it varies slightly with the temperature, the type of compound and the accelerator. 

This is the percentage increase in volume attained by immersing a vulcanised sample of rubber in a specified solvent. Volume swelling measurements are useful in determining the resistance of rubbers to solvents, but are also of value in measuring the crosslink densities of rubber vulcanisates. 

The degree of moisture present affects the properties of the silicone rubber vulcanisate. Moisture levels also determine the ease with which the filler is incorporated into the silicone rubber. Low moisture levels improve the final physical properties but definitely detract from the incorporation speed of the silica filler. 

Consideration is given to the toxicity of nitrosamines formed during rubber vulcanisation in the presence of certain accelerators, the mechanisms by which they are formed, and French, German and European Union regulations relating to nitrosamines in the workplace atmosphere and in rubber products. Methods used in the sampling and analysis of nitrosamines are also described. 6 refs. 

MORPHOLOGY AND PHYSICAL PROPERTIES OF CLOSED CELL MICROCELLULAR ETHYLENE-PROPYLENE-DIENE TERPOLYMER(EPDM) RUBBER VULCANISATES - EFFECT OF SILICA FILLER AND BLOWING AGENT Guriy a K C Tripathy D K Indian Institute of Technology... 

Attempts to use selenium either in place of or in conjunction with sulphur in the vulcanisation of rubber do not appear to be completely successful,2 although it is claimed that rubber vulcanised with sulphur and selenium in the presence of an organic accelerator exhibits enhanced rigidity and resistance to abrasion.3 The incorporation of powdered selenium in ordinary rubber for vulcanisation by sulphur is said to provide crystalline selenium nuclei which induce the internal crystallisation of any superfluous sulphur and so prevent the undesirable surface crystallisation (or bloom ). The effect is attributed to the isomor-plious character of selenium and sulphur. 

Figure 7.14. Damping curve fora rubber vulcanisate.

Compression moulding of rubbers is not essentially different from that of thermosets. The starting material is a blend of a rubber, vulcanisation ingredients and... 

These samples were tested as a whitening pigment.15 The Ti02 jacket was calculated to be 2 nm. This material was used as a new activator for rubber vulcanisation, substituting ZnO and establishing better mechanical characteristics. 

The technology of sulfur vulcanisation of unsaturated elastomers has evolved since Goodyear s invention in 1839. Scientific studies into the chemistry of sulfur vulcanisation started to appear in the late 1950s (for reviews see References [14-18]). Two experimental approaches can be distinguished the analysis of rubber vulcanisates themselves and the so-called low-molecular-weight model studies. 

Patel, D. K., Shah, K. H and Krishnan, V., A new class of protective agents for general purpose rubber vulcanisates, in lOih Prog. Paper and Rubber Conf. 127, 97S , Chem. Abstr. 93, 16938.3, 1980. 

Dimethylomine and Derivatives Dimethylomine, (H3C)2NH, mw 45.08, N 31.07%, col gas at RT and liq at below 7° sp gr 0.680 at 0°/4, fr p —92.2° extremely flammable and hazardous causes bums sol in w, ale eth. Can be prepd by passing a mixture of ammonia with vapors of methanol over a catalyst, such as silica gel. Has been used in agricultural herbicides and fungicides, synthetic textiles, fiber solvents, rubber vulcanising accelerators and in missile fuels (Refs 1, 2. 4)... 

One of the applications of pyrolytic techniques in the study of rubber vulcanisates is the evaluation of crossiinking density [10, 11]. Pyrolytic data can be correlated with total crosslinking density. Pyrolysis results can be used based on the generation of individual compounds or using the whole set of results. An excellent correlation has been obtained, for example, between the crosslinking density and a canonical variate function obtained from the whole pyrolysis data set [5]. The results from such a study are illustrated in Figure 7.2.1. 

Carbon disulfide (1) reacts with aniline and potassium hydroxide in boiling ethanol to yield syw-diphenylthiourea (8) (Scheme 5), which is used as a rubber vulcanisation accelerator (see Chapter 11, p. 219). 

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