Natural rubber, thermal analysis

Figure 10.31 TG and DTG curves of a natural rubber-butadiene rubber blend. (Reproduced with permission from T. Hatakeyama and F.X. Quinn, Thermal Analysis Fundamentals and Applications to Polymer Science, 2nd ed., John Wiley Sons Ltd, Chichester. 1999 John Wiley Sons Ltd.)...

Mixtures, formulated blends, or copolymers usually provide distinctive pyrolysis fragments that enable qualitative and quantitative analysis of the components to be undertaken, e.g., natural rubber (isoprene, dipentene), butadiene rubber (butadiene, vinylcyclo-hexene), styrene-butadiene rubber (butadiene, vinyl-cyclohexene, styrene). Pyrolyses are performed at a temperature that maximizes the production of a characteristic fragment, perhaps following stepped pyrolysis for unknown samples, and components are quantified by comparison with a calibration graph from pure standards. Different yields of products from mixed homopolymers and from copolymers of similar constitution may be found owing to different thermal stabilities. Appropriate copolymers should thus be used as standards and mass balance should be assessed to allow for nonvolatile additives. The amount of polymer within a matrix (e.g., 0.5%... 

Mathew, A.P., Packirisamy, S., Thomas, S. Studies on the thermal stability of natural rubber/polystyrene interpenetrating polymer networks thermogravimetric analysis. Polym. Degrad. Stab. 72, 423 39 (2001)... 

Natural rubber-CaC03 nanocomposites Modified CaC03 addition into NR sulfur vulcanizing Calorimetry and thermogravimetric analysis for physical, thermooxidative aging and thermal degradation property assessment microstructure analysis [96]... 

THERMAL ANALYSIS OF NATURAL RUBBER HEVEA BRASILIENSIS LATEX... 

Thiraphattaraphun and coworkers also reported the thermal transition phenomena of the natural rubber-gru/i -methyl methacrylic acid obtained by the dynamic mechanical thermal analysis method. In the transition region, increasing the temperature resulted in a decrease in the storage modulus due to the increase in the chain stiffness of the polymer. Increasing the amount of... 

Natural rubber based-blends and IPNs have been developed to improve the physical and chemical properties of conventional natural rubber for applications in many industrial products. They can provide different materials that express various improved properties by blending with several types of polymer such as thermoplastics, thermosets, synthetic rubbers, and biopolymers, and may also adding some compatibilizers. However, the level of these blends also directly affects their mechanical and viscoelastic properties. The mechanical properties of these polymer blended materials can be determined by several mechanical instruments such as tensile machine and Shore durometer. In addition, the viscoelastic properties can mostly be determined by some thermal analyser such as dynamic mechanical thermal analysis and dynamic mechanical analysis to provide the glass transition temperature values of polymer blends. For most of these natural rubber blends and IPNs, increasing the level of polymer and compatibilizer blends resulted in an increase of the mechanical properties until reached an optimum level, and then their values decreased. On the other hand, the viscoelastic behaviours mainly depended on the intermolecular forces of each material blend that can be used to investigate the miscibility of them. Therefore, the natural rubber blends and IPNs with different components should be specifically investigated in their mechanical and viscoelastic properties to obtain the optimum blended materials for use in several applications. 

Table 2.5 summarises the main applications of thermal analysis and combined techniques for polymeric materials. Of these, thermomechanical analysis (TMA) and dynamic mechanical analysis (DMA) provide only physical properties of a very specific nature and yield very little chemical information. DMA was used to study the interaction of fillers with rubber host systems [40]. Thermomechanical analysis (TMA) measures the dimensional changes of a sample as a function of temperature. Relevant applications are reported for on-line TMA-MS cfr. Chp. 2.1.5) uTMA offers opportunities cfr. Chp. 2.1.6.1). The primary TA techniques for certifying product quality are DSC and TG (Table 2.6). Specific tests for which these techniques are used in quality testing vary depending upon the type of material and industry. Applications of modulated temperature programme are (i) study of kinetics (ii) AC calorimetry (Hi) separation of sample responses (in conjunction with deconvolution algorithms) and (iv) microthermal analysis.

MBT in vulcanisates semiquantitatively. The accelerator zinc-A-dimethyldithiocarbamate (ZDMC) cannot be detected by PyGC-MS analysis at 550 C in the unfragmented state because of its low thermal stability [502]. However, ZDMC in vulcanised natural rubber (NR) could unambiguously be identified by DI-MS on the basis of the peak spectrum of the molecular mass trace m/z 304 (Pig. 2.37). 

Gorman [971] has described thermal desorption of volatile additives from rubber. The quantitative analysis of 2,2,4-trimethyl-1,2-dihydroquinoline (TMQ) in natural rubber by means of TD-GC-MS has been reported [1018a]. Off-line TD-GC-MS at 180°C of a 75/25 SBR/BR vulcanisate showed t-butylamine, CS2 and benzothiazole, indicative of the vulcanisation accelerator Vulkacit NZ (TBBS) [1019]. Analysis of seals for hydrocarbons and silicon-containing components by means of direct thermal desorption outperforms previous methods based on cyclohexane extraction and headspace techniques [1020]. 

Sircar and co-workers [8] compared experimental and data from the literature for the Tg of some common elastomers determined by different thermal analysis techniques, including DSC, TMTA, DMTA, dielectric analysis and thermally stimulated current methods. Elastomers examined include natural rubber, styrene-butadiene rubber, polyisoprene, polybutadiene, polychloroprene, nitrile rubber, ethylene-propylene diene terpolymer and butyl rubber. Tg values obtained by DSC, TMA and DMTA were compared. Experimental variables and sample details, which should be included along with Tg data were described, and the use of Tg as an indication of low temperature properties was discussed. 

An interesting nonequilibrium eiqieriment involves cutting the steel spring and rubber band in an extended, strained state. Both will naturally snap quickly back to their equilibrium, unstrained state. What are the thermal effects The steel spring loses the stored potential energy and since it does no work, it must heat up as required 1 the loss of work of expansion. The rubber band, in contrast, has the same internal ener in the extended and contracted states — i.e., if there is no work done on contraction there is no change in temperature. This distinct difference between energy and entropy elasticity has important consequences for thermal analysis, and one could predict valuable applications for the stretch calorimeter mentioned in the discussion of Fig. 4.30. 

Dan and co-workers [47] in their investigation of the structure and stability of chlorinated natural rubbers (CNR) applied high-resolution Py-GC-MS coupled with FTIR and thermal analysis techniques. 

Dan and co-workers [8] studied the structures and thermal and thermo-oxidative stabilities of the gel and chlorinated natural rubber from latex. The polymers were analysed by chemical analysis, high-resolution pyrolysis-gas chromatography-mass spectroscopy (HR-Py-GC-MS) coupled with Fourier-transform infrared spectroscopy, and thermal analysis techniques [dynamic thermal analysis and thermogravimetric analysis (TGA)]. 

Thermal analysis techniques will continue to play a vital role in assisting polymer scientists in all of their endeavours fundamental characterisation work and failure diagnosis studies the development of better polymers, polymer blends and compoimds the addressing of pressing current environmental concerns, such as the recycling of used tyres and the polymer components of electrical devices and the substitution of renewable raw materials (e.g. fibres such as hemp and natural rubber) for synthetic materials derived from petroleum products. 

The effect is examined of tetramethyl thiuram disulphide (TMTD) on the heat ageing and oxidation of clay-filled NR, with reference to the plasticity retention index of NR, using thermal analysis and scanning electron microscopy test methods. The results showed that heat and oxygen resistant properties could be obtained when the clay-filled natural rubber compound was cured by semi-effective or effective curing systems, with 1.5 phr or 3.0 phr of TMTD. 3 refs. 

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