Rubber compounds are notoriously difficult to analyse. The rubber may contain a variety of additives including other polymers, which are used to enhance the properties of the rubber matrix, for example, plasticisers, inorganic fillers, carbon black, antidegradants, cure systems, fire retardants and polyvinyl chloride. It is unlikely that more than 90-95% of a complex formulation can be determined by analysis alone. Compounds may contain over 15 different ingredients, some present at very low levels. During vulcanisation chemical reactions occur which may change the nature of the components in a rubber and this must be taken into account. It is evident that a good rubber analyst must have a working knowledge of rubber technology to succeed.
Rubber analysis is used for a variety of purposes such as quality control, reverse engineering (deformulation) and to determine causes of failure.
A wide variety of techniques can be used to discover different facts about a rubber compound. For example, elemental analysis may be required, or a method of measuring cure state.
Many spectroscopic techniques are employed in rubber analysis including infrared spectroscopy, ultraviolet light spectroscopy, NMR spectroscopy, atomic absorption spectroscopy, X-ray fluorescence spectroscopy, chemiluminescence spectroscopy and energy dispersive analysis. Chromatographic methods include gas chromatography-mass spectrometry (GC-MS), high performance liquid chromatography (HPLC), gel permeation chromatography (GPC) and thin layer chromatography (TLC). Thermal techniques include differential scanning calorimetry (DSC), dynamic mechanical thermal analysis (DMTA) and thermogravimetric analysis (TGA).
This review outlines each technique used in rubber analysis and then illustrates which methods are applied to determine which facts. For example, polymer and filler identification, molecular weight determination, elemental analysis and carbon black study methods are all included.
The author has included a worked example of the deformulation of a complex rubber compound. The review also includes useful appendices on international standards, rubber nomenclature and key polymer and ingredient properties.
This text is a good introduction to a very complex subject area and will enable the reader to understand the basic concepts of rubber analysis. It is around twice the size of the normal reviews in this series.
Around 350 abstracts from the Rapra Abstracts database accompany this review, to facilitate further reading. These include core original references together with abstracts from some of the latest papers on rubber analysis.
2. Analytical Techniques
3. Characterisation of Rubber Polymers
4. Determination of the Principal Components in a Rubber Compound
5. Carbon Black
6. Determination of Antidegradants in a Rubber Compound
7. Determination of Cure System Additives and Their Breakdown Products
8. Determination of Miscellaneous Compound Additives
9. Cure State Studies
10. Reverse Engineering and Product Deformulation
11. Surface Blooms and Product Contaminants
12. Analysis of Rubber Latices
13. Failure Diagnosis
APPENDIX 1: Standard Nomenclature System for Rubbers
APPENDIX 2: International Rubber Analysis Standards (ISO)
APPENDIX 3: Glass Transition Temperatures of Rubbers
APPENDIX 4: Maximum Service Temperatures and Relative Stabilities of Different Rubber Types to Various Degradation Agencies
APPENDIX 5: Solubility Parameters of Rubbers and Typical Solvents
APPENDIX 6: Specific Gravities of Rubbers and Compounding Ingredients
Abbreviations and Acronyms
Dr Martin Forrest has worked as a Consultant in the Polymer Analysis Section at Rapra for over thirteen years and has gained experience in the analysis of a wide variety of polymers and polymer products using a range of techniques. He currently holds the position of Principal Consultant and is the main contact at Rapra for projects involving rubber analysis.