Chapter 10 Conclusions and Future Scope Abstract A brief account of the major conclusions drawn from the present study on the chlorobutyl rubber nanocomposites is summarised in this chapter. Scope for the future investigations and possible applications are also mentioned.
10.1 Conclusions From the above discussion it is evident that chlorobutyl rubber nanocomposites are promising materials since they exhibit excellent mechanical, gas barrier, solvent resistance and good thermal resistance. Though works have been done earlier in the field of elastomeric nanocomposites, there has not been much contribution in the area of chlorobutyl rubber. Not much systematic study has been carried out in the barrier properties of layered silicate filled chlorobutyl rubber nanocomposites. So the present work fills the aforementioned gap in the area of rubber nanocomposites. The study was carried out by preparing nanocomposites using different types of fillers like titanium dioxide, nano calcium phosphate and three different varieties of layered silicates (cloisite 15 A, cloisite 10A, cloisite 20 A). The layered silicates differed from each other with respect to their organic modification, surfactant concentration, d spacing etc. The work also envisages the outline of the development of a novel route towards the preparation of chlorobutyl rubber nanocomposites which is indeed a hybrid of solution mixing and melt mixing. It was found that the layered silicates at very low loadings (5 phr) could give the reinforcement given by traditional fillers like titanium dioxide at higher loadings. This improves the processability of rubber nanocomposites since the major difficulty in preparing the rubber nanocomposites include the addition of filler in high loadings. The mechanical properties at very low filler loadings (5 phr) correspond to the enhanced interaction between the filler and the chlorobutyl rubber matrix due to intercalation and exfoliation of the layered silicates. The use of different clays with varying d spacing has helped to identify the apt layered silicate for the chlorobutyl rubber matrix and also paved way for the tailoring of the properties of the nanocomposites. It is clearly substantiated by the study that with the increase in the d spacing of the layered silicates the efficiency of intercalation/exfoliation is increased and the property enhancement is obtained beyond prediction. This exactly justifies for the superior performance of cloisite 15 A. Cloisite 15 A as well as 10 A are effective materials as fillers in the chlorobutyl
rubber matrix for the decrease in the gas permeation properties. Cloisite 15 A excels in almost all the properties shown by the nanocomposites when compared to the other two layered silicate moieties. Another important feature of the layered silicate which governs the property of the nanocomposites is the nature of the organic modifier as well as the cation exchange capacity of the layered silicate used. The properties shown by cloisite 20 A is found to be less than the other two varieties of layered silicates. The study also helps in the comparison of the nature of the different fillers like nano calcium phosphate, titanium dioxide and layered silicates and has helped in understanding the difference in the behavior of various fillers in the matrix. The dynamic mechanical analysis shows the decrease in the tan delta peaks with the increase in filler loading which substantiates the use of chlorobutyl rubber nanocomposites as effective damping materials. Moreover the layered silicate reinforced nanocomposites exhibit superior transport properties like resistance to the penetration of chemicals which make them an important component in the fabrication of chemical protective clothing. The permeation of the gases in the nanocomposite systems have been evaluated using nitrogen, carbon dioxide, oxygen and helium. The enhanced gas barrier properties exhibited by these materials enable them to be used as barrier materials in a variety of industrial as well as advanced applications. The working times calculated throw light into the effectiveness of the material to be used as potential VOC barrier membranes. The enhancement in thermal properties of the layered silicate nanocomposites make them suitable for moderately high temperature applications. Nevertheless at very high temperatures the alkyl ammonium surfactant in the layered silicate undergoes thermal degradation and hence limits the high temperature applications of chlorobutyl rubber nanocomposites. The evaluation of the dielectric characteristics of the nanocomposites show that the maximum dielectric permittivity is exhibited at higher frequencies and higher filler loadings. Higher loadings of layered silicate increase the conductivities of the nanocomposite systems at higher frequencies which can be attributed to the formation of percolation structure. Thus we have
positively contributed to the field of polymer nanocomposites by fabricating a new variety of barrier membrane which has high efficiency. 10.2 Discussion including future plans for investigation The presence of organically modified nanoclay in the chlorobutyl matrix causes considerable enhancement in many properties including mechanical, transport and gas barrier. It is also understood that the performance of a nanocomposite depends to a great extend on the type of and the concentration of the organic modifier used. The family of isobutylene isoprene rubbers is well differentiated to include general purpose types for cost sensitive applications and specialty products for more demanding service conditions. 10.2.1 Synergism of nanoclay and nanotubes in CIIR Nevertheless a detailed examination of the literature reveals that the presence of carbon nanotubes also enhances the properties of rubber matrices to a great extend. In future it would be interesting to undertake a study on the synergistic effect of nanoclay and carbon nanotubes in the halo butyl rubber matrix so that the anomaly in thermal properties observed in the case of clay reinforced rubber nanocomposites can be solved. Moreover since the nanotubes exhibit superior mechanical properties it is possible that the presence of these two reinforcing fillers would definitely contribute to the mechanical property enhancement of the rubber matrix. The barrier properties of chlorobutyl rubber nanocomposites are highly superior by the inclusion of clay alone. The synergism of carbon nanotubes and nanoclay would definitely make the chlorobutyl rubber matrix impermeable. 10.2.2 Thermal property enhancement using organic modifications other than alkyl ammonium salts. One of the major drawbacks in the use of alkyl ammonium salts as modifiers in rubber systems is that the end product will not be thermally stable at very high temperatures. In such cases the end product can be used only for medium temperature based applications. In order to tailor the properties and make the system
susceptible to very high temperatures the organic modification can be carried out using stibonium salts, phosphonium salts, POSS etc. 10.3 Applications Polymer nanocomposites are recognized as one of the most promising research areas in polymer science and technology in the 21st century. While the reinforcement aspects are a major part of the nanocomposite investigations reported in the literature, many other variants and property enhancements are under active study and in some cases commercialization. The advantages of nanoscale particle incorporation can lead to a myriad of application possibilities where the analogous larger scale particle incorporation would not yield the sufficient property profile for utilization. These areas include barrier properties, membrane separation, UV screens, flammability resistance, polymer blend compatibilization, electrical conductivity, impact modification, and biomedical applications. The nano concept is highly relevant and more advantageous for rubber composites, and nano reinforcement has been proved to be an extremely effective and necessary way for rubber application. Rubber-layered silicate nanocomposites are the foremost members of such nanocomposites which have exhibited great promise for industrial applications due to their ability to display synergistically advanced properties with relatively small amounts of clay loading. Rubber nanocomposites prepared with nano silica has lead to big advantages for the tyre users: increased security (better wet grip), reduced fuel consumption (rolling resistance) with a wear resistance similar to that of carbon black compounds and also a decrease in the rolling noise, this has clearly resulted, although by a cost increase, to new requirements for reinforcement, the real challenge is to go outside what is called the magic triangle that holds rolling resistance, wet grip, and wear linked together, meaning that improving one property lead to the worsening of the other.
Fig 10.1. Impermeable lining with chlorobutyl rubber nanocomposites Butyl rubber nanocomposites are used in a wide range of applications, such as tyres, curing bladders, air springs, drug cap sealants, gas pipe coating, gaskets, military attires, and sporting goods. Due to the decreased permeability for gases and water, as well as for hydrocarbons, they have a wide range of applications in packaging and automotive industries One of the most important applications of rubber nanocomposites is in the chemical protective clothing (CPC). Figure 10.2 The use of butyl rubber in pharmaceutical stoppers and CPC
They are highly stable against aggressive chemicals and can also be implemented in corrosive protective coatings. In high temperature areas because of good thermal stability and flame retardancy rubber nanocomposites are more attractive and promising than other conventional materials. These materials have a good perspective of application for the near future in daily life. CURRICULUM VITAE Name : SARITHA A. Permanent Address : Choorakunnathu, Daffodils
Kuttapuzha Near Marthoma College Thiruvalla RS PO Kerala. Pin: 689111 Educational Qualifications : M Sc Research experience : Seven years research experience in micro and nano filled synthetic rubbers. Research interests : Polymer micro and nanocomposites, nanoparticle preparation and characterisation, polymer membranes, gas barrier and solvent transport properties.
Instrumental skills Hands on experience on two roll mill, UTM, Mooney viscometer, densitometer, internal mixer, impact tester, hardness tester,hydraulic press, Elasograph, Plastimeter, XRD, Scanning Electron Micrograph, Transmission Electron Micrograph, cryosectioning of rubber samples for TEM, Atomic Force Microscope, Differential Scanning Calorimeter, IR spectrometer, Thermogravimetric Analyser etc. Familiar with Microsoft Office, Data analysis and Technical Graphics software- Origin, Chemical structure drawing softwares - Chem Window, Chem sketch. Conferences / Seminars attended/papers presented 1. Saritha A., Kuruvilla Joseph, Sabu Thomas Mechanical properties of Titanium dioxide filled Chlorobutyl vulcanizates at the National Conference on Thermo physical properties, organized by the Thermo physical Society of India on September 20-22, 2007 2. Saritha A., Kuruvilla Joseph, Sabu Thomas Tensile properties of Chlorobutyl nano clay composites at the International Conference on Natural polymers ICNP, organized by the institute of Macromolecular Science and Engineering on November 19-21,2007 3. Saritha A., Kuruvilla Joseph, Sabu Thomas Mechanical and barrier properties of chlorobutyl rubber nanocomposites with varying filler size and morphology at the International Conference on blends and composites, ICBC 2008, September 22-24, 2008, Kottayam, Kerala. 4. Saritha A., Kuruvilla Joseph, Sabu Thomas Comparative study on the mechanical properties of chlorobutyl rubber nanocomposites with varying
filler size and morphology at the at the NANO-09 National Seminar organized by S.N college, Chengannur on 17-18 th March 2009. 5. Saritha A., Kuruvilla Joseph, Sabu Thomas on Barrier properties clay reinforced chlorobutyl rubber nanocomposites in the International Conference on nanostructured materials and nanocomposites ICNM-2009, on April 6-8, 2009, Kottayam, Kerala. 6. Saritha A., Kuruvilla Joseph, Physical and mechanical properties of high performance rubber nanocomposites at the National Conference on advanced materials, NCAM -2009 organised by PSN college of Engineering, Tirunelveli on August 25-27, 2009. 7. Saritha A., Kuruvilla Joseph, Sabu Thomas Thermophysical properties of chlorobutyl rubber vulcanizates at the International Conference on recycling and reuse of materials, ICRM -09,July 17-19, 2009 Kottayam, Kerala. 8. Saritha A., Kuruvilla Joseph, Sabu Thomas Chlorobutyl rubber nanocomposites as effective gas barrier materials in the International Conference on Polymer processing, ICPPC-2010 at Mahatma Gandhi University, Kottayam on January 15, 2010. 9. Saritha A., Kuruvilla Joseph, Chlorobutyl rubber nanocomposites as effective barrier materials, in the International Conference on Advances in polymer technology, APT, on 26-27 February, 2010 at CUSAT. 10. Saritha A., Kuruvilla Joseph, Sabu Thomas Novel route towards the synthesis of chlorobutyl nanocomposites using solvent interaction parameters, in the International Conference on Recent Trends in Material Science and Technology, ICMST, on 29-31, October 2010 at the Indian Institute of Space science and Technology, ISRO, Trivandrum. 11. Saritha A., Kuruvilla Joseph, Sabu Thomas Tailoring of chlorobutyl rubber nanocomposites for advanced applications in the National
Conference, RANCER at Kongu Engineering college, on February 18-19, 2011 12. Saritha A., Kuruvilla Joseph, High performance rubber nanocomposites in the Iternational Conference on nanostructured materials and nanocomposites ICNM-09 on April 6-8,2009, Kottayam, Kerala. 13. Saritha A., Kuruvilla Joseph, K. Jayanarayan Recent advances in polymer based micro and nanocomposites in the International Conference on innovative technologies, ICIT -09 on June 18-19, 2009. Papers published in International journals 1. Design, development and testing of rubber nanocomposites, Key Engineering Materials, Vol. 425, 61-93, 2010. 2. Mechanical and Thermophysical properties of TiO 2 filled chlorobutyl composites, Polymer Composites, Volume 32, Issue 10, pages 1681 1687, 2011. 3. Role of surfactant type and modifier concentration in tailoring the properties of chlrobutyl rubber organoclay nanocomposites, Journal of Applied Polymer Science, Volume 124, Issue 6, pages 4590 4597, 15 2012 4. Chlorobutyl rubber nanocomposites as effective VOC and gas barrier materials, Composites Part A, 43, 864-870, 2012. Book Chapters 1. Book chapter in Trends in composite materials and their design by Saritha A., Kuruvilla Joseph & Sabu Thomas, edited by Mohamed A. Taha, Ahmed M. El-Sabbagh and Iman M. Taha and published by Trans Tech Publications, Switzerland, 2010.