Rubber products, compositional analysis

It is quite clear from Schemes 2.1-2.5 that in rubbers polymer identification and additive analysis are highly interlinked. This is at variance to procedures used in polymer/additive analysis. The methods for qualitative and quantitative analysis of the composition of rubber products are detailed in ASTM D 297 Rubber Products-Chemical Analysis [39]. 

Tyler, W.P. Analysis, composition and structure of rubber and rubber products. Rubber Chem. Technol. 40, 239-270 (1967). 

Recently rubbers have been modified by blending or by chemical reaction to suit specific needs for the product. In these cases, the compositional analysis... 

Despite the above-cited difficulties, TGA-DTGA analysis remains a useful tool for the compositional analysis of rubber vulcanizates. It is a straightforward, reasonably accurate process and is much faster than classical extraction methods. Also, it is an excellent quality control tool for determining possible weighing errors and reproducibility for elastomer batches in a production setting. Thus, TGA-DTGA is the method of choice for compositional determinations for cured and uncured elastomer compounds, as well as for many other polymer compositions. 

This book on natural rubber presents a summary of the present state-of-the-art in the study of these versatile materials. The two volumes cover all the areas related to natural rubber, from its production to composite preparation, the various characterization techniques and life cycle assessment. Chapters in this book deal with both the science of natural rubber - its chemistry, production, engineering properties, and the wide-ranging applications of natural rubber in the modern world, from the manufacture of car tyres to the construction of earthquake protection systems for large buildings. Although there are a number of research publications in this field, to date, no systematic scientific reference book has been published specifically in the area of natural rubber as the main component in systems. We have developed the two volumes by focusing on the important areas of natural rubber materials, the blends, IPNs of natural rubber and natural rubber based composites and nanocomposites their preparation and characterization techniques. The books have also profoundly reviewed various classes of fillers like macro, micro and nano (ID, 2D and 3D) used in natural rubber industries. The applications and the life cycle analysis of these rubber based materials are also highlighted. 

Recently, a group of Indian researchers developed a new elastomer product based on NR/BR blend with reclaim rubber (RR) from ground rubber tires (GRT). The reclaiming was carried out by tetra methyl thiuram disulfide (TMTD) in the presence of spindle oil, a paraffin-based rubber process oil. Thermogravimetric analysis of RR, NR/BR and different NR/BR/RR vulca-nizates was carried out in order to measure the thermal stability of the vulca-nizates. Isothermal ageing test of fresh rubber RR composites showed that the ageing performance of RR containing vulcanizates are superior than that of the fresh rubber vulcanizates, which do not contain any reclaimed rubber. 

Figure 3.20. Compositional analysis of rubber products by TGA styrene-butadiene rubber (courtesey of TA Instruments).

Compositional analysis of polymeric rubber products by TGA has been used for many years to determine the quality and content of various rubber products (Kau 1988 Sircar 1997). A polystyrene butadiene rubber composition is illustrated in Fig. 3.20. The protocol for this analysis includes the following heating rate 20°C/min, 30 mg sample mass, and switching the purge gas from nitrogen to air at 500 °C. The results are illuminating for a 30-min determination of composition 8.4 mass% oil, which evaporates prior to the onset of polymer decomposition just below 400°C 50.4 mass% polymer, whose decomposition is complete by 500 °C, at which point the purge gas is switched to air 36.2 mass% carbon black, taken as the mass loss in air and 5.0 mass% residue, either ash or mineral filler plus ash. 

Techniques based on TG analysis have made it possible to readily and accurately measure the carbon-black content in commercial polymer formulations, such as in rubbers, at levels as far apart as 0.1% and 30%. The typical procedure is shown in Fig. 2.15 (sensitivity of the TG scan is 100 wt.% full scale) for a polyethylene masterbatch formulation, which was initially heated in N2 at a rate of 160°C/min. to about 550°C. Pyrolytic decomposition to gaseous products resulted in a 75% weight loss. After changing to O2 atmosphere the carbon-black is then oxidised [151]. The precision of the determination in the PE/CB masterbatch formulation is about 0.05 to 0.1% carbon (absolute). The TG method is fast, le. 6 min at 160°C/min, as compared to 2 h for ASTM D 1063 [266] without TG, thus providing substantial time savings. The compositional analysis (polymer and CB content) of LDPE has been reported [85] Affolter et al [155] have determined the content of carbon-black in polyolefins (2-3% CB) by TG following ISO 9924-1 and have noticed an inhomogeneous distribution in commercial... 

Rubber Chem. Technol., Rubber Rev. Degradation of Polymers (1962) Analysis, Composition and Structure of Rubber and Rubber Products (1967) Branching in Polymer Chains (1972) Applied Infrared Spectroscopy in the Rubber Industry (1972) Elastomer Blends (1974) Spectroscopy in the Rubber Industry (1976). 

If additional information pertaining to the rubber composition were sought, FTIR analysis of the pyrolysis products would have been performed. Even more detailed analysis can be obtained by gas chromatography (GC) separation of the multiple pyrolysis products followed by mass spectrometric (MS) detection. The gas chromatography-mass spectrometry (GC-MS) method is well suited to deformulation and contaminant analysis. 

It was well known at the turn of the century that rubber has the empirical composition, C5H9. Michael Faraday elucidated its composition in 1826 by careful elementary analysis. His work, an effort of extreme complexity, has been diminished by the years, but it regains its stature when you recall that over thirty years passed before the next major step was performed. In those thirty years rubber was blended, dissolved, and even vulcanized (by Charles Goodyear in 1839), but it was in 1860 that its major chemical component was discovered. This important finding was made by Greville Williams. He named the product of the destructive distillation of rubber, isoprene. 

Rubber industries produce various types of complicated products like tyre, cable, belt, seal, bearings, engine mounts, etc. The products are composed of rubber, plastics, fibre, metal, fillers and many other additives like antioxidants, accelerators, etc. Reverse engineering is a technique by which a rubber technologist can reconstruct the composition of the products based on thermal analysis. Dormagen [178] and Baranwal [179] reconstructed the formulation of a tyre, based on analyses of FTIR, spectra, thermal analysis and high performance liquid chromatography. 

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