Facile exfoliation method for improving interfacial compatibility in montmorillonite-natural rubber nanocomposites

A novel charge inversion approach

Significance 

Nanoscale fillers have exhibited great potential for use as an efficient alternative to conventional reinforcement fillers like carbon black.  For instance, nanoscale fillers have been widely used to reinforce various polymeric materials such as natural rubber (NR) to enhance their mechanical properties. In particular, layered silicates exhibiting remarkable anisotropy and swelling properties such as montmorillonite (Mt) have attracted significant research attention as promising nanostructured reinforcement for natural rubber. A recent study has reported that in order to achieve a high degree of reinforcement, Mt layers should be exfoliated within the rubber matrix to obtain high surface area and strong interfacial interactions between the two components. However, obtaining high interfacial properties between the rubber matrix and inorganic fillers has remained a research challenge mainly due to lack of appropriate methods for making stable Mt dispersions.

In an effort to address the above challenges, a group of researchers: Dr. Malindu Alwis, and Dr. Upul Ratnayake at Rubber Research Institute of Sri Lanka, in collaboration with Professor Nilwala Kottegoda from the University of Sri Jayewardenepura developed a novel facile exfoliation method for improving interfacial compatibility in montmorillonite-natural rubber nanocomposites. The main aim of their study was to realize a high degree of exfoliation through enhanced compatibility between the two components and high surface area for interactions between the filler and rubber matrix. Their research work is currently published in the journal, Applied Clay Science.

Briefly, the new approach comprised of two main steps: formation of a charge inverted NR latex and coagulation using the exfoliated Mt layers. First, a charge inversion approach involving the NR latex treatment with quaternary ammonium surface-active substance was used to prepare the stable cationic latex of NR. Secondly, the prepared cationic NR latex was directly coagulated using Mt aqueous dispersion to facilitate the formation of Mt-NR nanocomposite comprising exfoliated and intercalated clay mineral layers. Lastly, the feasibility of the method was validated by studying and comparing the interfacial and stress behavior of the un-vulcanized nanocomposite with those prepared by the conventional latex compounding method.

The research team observed the occurrence of exfoliation of Mt platelets within the NR matrix, thus resulting in improved reinforcement. As evidenced by the X-ray diffraction and transmission electron microscopy images, the Mt platelets exhibited a higher degree of exfoliation accompanied by significantly enhanced physicochemical and mechanical properties. This was attribute to the increased computability between the NR latex particles and nanostructured Mt platelets. Furthermore, studies carried out using a combination of Mooney viscosity and green strength measurements revealed that the interfacial interaction between the cation latex and Mt was much improved than that of nanocomposites prepared using conventional latex compounding method.

In summary, the study reported a novel, scalable, and simple method for reinforcing natural rubber with Mt. Results showed that the presented approach was suitable for improving the interfacial compatibility in Mt-natural rubber nanocomposites. Moreover, the un-vulcanized Mt-NR prepared using this method exhibited enhanced mechanical properties, including high strength and stiffness. In a statement to Advances in Engineering, Dr. Upul Ratnayake said that the charge inversion approach is a promising technology for preparing clay-based rubber nanocomposites with improved interfacial compatibility.

About the author

Upul N Ratnayake is the General Manager – Technical and Research & Development in Hayleys Group, Dipped Products PLC, one of the leading glove manufacturing companies in the World. He obtained his PhD in Polymer Technology and Material Engineering from Loughborough University, UK. He started his professional carrier in Rubber Research Institute of Sri Lanka and he has more than 20 years’ of experience in rubber chemistry and technology.

He is one of the starting members of Sri Lanka Institute of Nanotechnology (SLINTEC). Developing polymeric nanocomposites and understanding its reinforcement and functional properties are one of his major areas of research expertise. His major research innovations are developing novel NR and Synthetic latex gloves for different applications.

He has published many indexed journal articles and many national and international patents were awarded to his team, some of which are successfully implemented commercially. He was awarded National Technology Award in 2016 from National Science Foundation, Sri Lanka

About the author

Nilwala Kottegoda is a Professor in Chemistry at University of Sri Jayewardenepura. She obtained a first class BSc Special Degree in Chemistry from University of Peradeniya, Sri Lanka and the Ph.D. in Materials Chemistry from the University of Cambridge, UK. Her on-going research work spans over a wide spectrum of areas; nanotechnology applications in agriculture, value addition to natural minerals, biological pathways for development of novel efficient composites, nanomaterials for water purification, and rubber nanocomposites. She joined Materials Research Group at Rice University, USA in 2018, as a visiting Fulbright fellow.

She is the principal author of several US patents and she has many high indexed journal publications. She was awarded the Third World Academy of Science Young Scientist Award and the National Award for the Best Innovation with Commercial Potential. She was nominated as one of the most innovative women scientists by World Intellectual Organization in 2018.

About the author

Malindu Alwis is a Rubber Technologist whose main interest lies in the fields of nanomaterial synthesis, polymer blends and polymers processing for industrial applications.

He received Bachelor Degree in Chemistry from University of Sri Jayewardenepura, Sri Lanka and completed his Master Degree in Polymer Science Technology in 2014. He received PhD fellowship from National Research Council Sri Lanka and was awarded his PhD in Material Science in 2017.

Dr. Alwis has over 8 years of experience in both research institutes and industries. He started his research career as a Graduate Scientist in Rubber Research Institute, Sri Lanka. Then he worked as a Research Scientist in Sri Lanka Institute of Nanotechnology. He started his professional  career in CAMSO Inc. (Camso is now part of the Michelin Group) as a Senior Rubber Technologist.

Reference

Alwis, G., Kottegoda, N., & Ratnayake, U. N. (2020). Facile exfoliation method for improving interfacial compatibility in montmorillonite-natural rubber nanocomposites: A novel charge inversion approach. Applied Clay Science, 191, 105633.

Go To Applied Clay Science

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