Kuruma Malkappa
@csirnano.co.za
Postdoctoral Researcher
CSIR-Pretoria, National center for Nanostructured Materials
EDUCATION
Ph. D Polymer Material Science
RESEARCH INTERESTS
Polymer synthesis and structure-property analysis, synthesis of various nanomaterials, surface modifications, polymer nanocomposites, polymer formulation and melt processing, polymer nanofibers and blends, super hydrophobic and super hydrophilic materials, especially polyurethanes, water dispersible polyurethanes, emulsion polymerizations for coating and painting, also for fire retardant, adhesives, textiles, antibacterial, biodegradable, biological and packaging applications.
Scopus Publications
Scopus Publications
Cheera Prasad, Nawal Madkhali, Seong-Geun Jeong, Kuruma Malkappa, Hyeong Yeol Choi, and V. Govinda
Elsevier BV
Nawal Madkhali, Cheera Prasad, K. Malkappa, Hyeong Yeol Choi, V. Govinda, Indra Bahadur, and R.A. Abumousa
Elsevier BV
Kuruma Malkappa, Jayita Bandyopadhyay, Vincent Ojijo, and Suprakas Sinha Ray
Wiley
Reza Salehiyan, Mohammadreza Nofar, Kuruma Malkappa, and Suprakas Sinha Ray
Wiley
Kuruma Malkappa, Reza Salehiyan, and Suprakas Sinha Ray
Wiley
Copyright: 2020 Wiley. Due to copyright restrictions, the attached PDF file only contains the abstract of the full text item. For access to the full text item, please consult the publisher's website. The definitive version of the work is published in Macromolecular Materials and Engineering, pp 14
Kuruma Malkappa, Jayita Bandyopadhyay, and Suprakas Sinha Ray
American Chemical Society (ACS)
To obtain polyamide 6 (PA6) composites with improved flame retardancy and thermomechanical properties, highly cross-linked supramolecular poly(cyclotriphosphazene)-functionalized α-zirconium phosphate (f-ZrP) nanoplatelets were synthesized and melt-blended with PA6 in a twin-screw extruder. The performance enhancements of composites were investigated through measuring the dynamic mechanical property and observing cone calorimeter data, toxic gas evolution, and UL-94 rating. The thermomechanical performance of PA6 was increased by 37.2% after composite formation with f-ZrP. As for the fire retardancy performance, compared to neat PA6, the composite containing 10 wt % f-ZrP showed 41.7 and 30.4% decrease in the peak heat and total heat release rates, respectively, and the UL-94 rating of the composite was V-0. Moreover, the thermogravimetric analysis combined with infrared spectroscopy revealed that the addition of f-ZrP to the PA6 led to decrease in the evolution of the volatile compounds and toxic gases, with the formation of highly cross-linked P–N-containing dense char with microspheres, providing a strong barrier to the inhibition of the heat and flammable volatile components transferring between the flame zone area and substrate during the combustion test. Finally, based on the obtained results, the possible mechanisms for improved mechanical and fire retardancy properties of the composites were proposed.
Kuruma Malkappa and Suprakas Sinha Ray
American Chemical Society (ACS)
A novel halogen-free highly cross-linked supramolecular poly(cyclotriphosphazene-co-4,4′-sulfonyl diphenol) (PZS)-functionalized melamine cyanurate (MCA) (MCA@PZS) hybrid nanosheet fire-retardant (FR) was synthesized and thoroughly characterized using scanning electron microscopy, Fourier-transform infrared (FTIR), X-ray diffraction, and X-ray photoelectron spectroscopy analyses. The polyamide 6 (PA6) composites comprising MCA, PZS, and the MCA@PZS hybrids were prepared via the melt-blending technique. The thermogravimetric analysis combined with FTIR and mass spectroscopy revealed that during thermal degradation, the PA6/MCA@PZS composites released less toxic gases and small organic volatile compounds than the neat PA6 and composites containing MCA or PZS solely. Moreover, compared to neat PA6, the PA6 composite with a 5 wt % MCA@PZS hybrid exhibited enhanced fire retardation properties, with a 29.4 and 32.1% decrease in the peak heat and total heat release rates, respectively. Besides, the PA6 composites with MCA@PZS-5% content achieved a V-0 rating in the UL-94 test. Finally, based on the obtained results from gaseous and condensed phases, the possible mechanism responsible for improved FR properties of the PA6/MCA@PZS composites was proposed.
Billa Narasimha Rao, Kuruma Malkappa, Nagendra Kumar, and Tushar Jana
Elsevier BV
Abstract In this work, iron containing hydroxyl terminated polybutadiene (Fe-HTPB) based binder cum burn rate catalyst has been developed without altering the crucial physical properties of HTPB. Ferrocene, the source of Fe in the Fe-HTPB, has been grafted at the terminal carbons of HTPB to ensure no alternation in microstructure of HTPB which in turn helped in retaining physical properties of pristine HTPB. The structure and the presence of ferrocene as the end cap groups of the Fe-HTPB were confirmed by solid-state NMR and MALDI-TOF-MS analysis. Control over the viscosity and Fe content of the Fe-HTPB was achieved by varying the grafting reaction recipes and conditions. The Fe content, as measured by inductively coupled plasma - atomic emission spectroscopy (ICP-AES) in the Fe-HTPB varied from 0.06% to 0.165% (by weight) and found to be responsible for increasing viscosity of Fe-HTPB from 5857 mPa S to 11,890 mPa S. Non aluminized composite solid propellants (CSPs) with 86% (wt%) ammonium perchlorate loading were prepared using Fe-HTPB as a binder for studying the burn rate efficiency. Burn rates of CSPs made from Fe-HTPB binders were found to be enhanced by ∼125% compared to CSPs of pristine HTPB. At 40 bar pressure, the burn rate of CSPs made from Fe-HTPB and pristine HTPB binders are 20.56 and 9.07 mm/s burn rate, respectively. In addition, all the CSPs made from Fe-HTPB were found to be very stable as their pressure index is less than 0.5.
Kuruma Malkappa, Suprakas Sinha Ray, and Neeraj Kumar
Wiley
Copyright: 2018 Wiley. Due to copyright restrictions, the attached PDF file only contains the abstract of the fulltext version. For access to the published article, please consult the publisher's website: https://onlinelibrary.wiley.com/doi/full/10.1002/mame.201800562
Kuruma Malkappa, Jayita Bandyopadhyay, and Suprakas Ray
MDPI AG
Polylactide (PLA) is one of the most widely used organic bio-degradable polymers. However, it has poor flame retardancy characteristics. To address this disadvantage, we performed melt-blending of PLA with intumescent flame retardants (IFRs; melamine phosphate and pentaerythritol) in the presence of organically modified montmorillonite (OMMT), which resulted in nanobiocomposites with excellent intumescent char formation and improved flame retardant characteristics. Triphenyl benzyl phosphonium (OMMT-1)- and tributyl hexadecyl phosphonium (OMMT-2)-modified MMTs were used in this study. Thermogravimetric analysis in combination with Fourier transform infrared spectroscopy showed that these nanocomposites release a smaller amount of toxic gases during thermal degradation than unmodified PLA. Melt-rheological behaviors supported the conclusions drawn from the cone calorimeter data and char structure of the various nanobiocomposites. Moreover, the characteristic of the surfactant used for the modification of MMT played a crucial role in controlling the fire properties of the composites. For example, the nanocomposite containing 5 wt.% OMMT-1 showed significantly improved fire properties with a 47% and 68% decrease in peak heat and total heat release rates, respectively, as compared with those of unmodified PLA. In summary, melt-blending of PLA, IFR, and OMMT has potential in the development of high-performance PLA-based sustainable materials.
Kuruma Malkappa, Billa Narasimha Rao, Gandham Suresh, Ch. Venkata Ramana, and Tushar Jana
Springer Science and Business Media LLC
AbstractWe report an in-situ synthetic strategy to prepare water dispersible polyurethane (WDPU) from an organic/inorganic hybrid nanocolloids in which the organic component is dinitrobenzene-modified hydroxyl-terminated polybutadiene (HTPB-DNB)-based polyurethane and the inorganic part is TiO2 (core)–SiO2 (shell) nanoparticles. The shape, size, and polydispersity of the hybrid nanocolloids are determined using microscopic and light scattering studies and are found to be slightly dependent on the loading of core–shell nanofillers. FT-IR and solid-state NMR studies prove the presence of the interaction between the carbonyl functionality of the urethane linkage and the SiO2 present in the shell part of the particles, and this interaction is found to be the driving force for the formation of stable nanocolloids. The films, obtained from the nanocolloids of WDPU upon curing, display better thermal and mechanical properties, and also, these properties increase with increasing loading of nanofillers. Higher tensile strength and Young modulus are obtained in WDPU nanocolloids films compared to pristine WDPU films. The antibacterial activity of WDPU nanocolloids was studied on Staphylococcus aureus (Gram-stain-positive bacterium) and Escherichia coli (Gram-stain-negative bacterium) displayed significantly higher zone of inhibition in both the cases, indicating the potential use of these nanocolloids in antibacterial coating.
Graphical Abstractᅟ
Kuruma Malkappa, Billa Narasimha Rao, and Tushar Jana
Elsevier BV
Abstract In this article, we report preparation and studies of water dispersible polyurethane (WDPU) nanocomposite which has high hydrophobic characteristics with contact angle greater than 100° and strong thermo-mechanical properties. An in-situ method is developed for synthesizing the WDPU nanocomposites where hydroxyl terminated polybutadiene (HTPB) functionalized at the terminal carbon atoms with dinitrobenzene (DNB), named as HTPB-DNB, is the diol source for the polyurethane chain, two types of organically modified clays namely Cloisite-30B and dimethyl sulfoxide (DMSO) intercalated Kaolinite (OKao) are the nanofillers and an ionic diol co-monomer e.g. dimethylol propionic acid (DMPA) is used to incorporate the ionic characteristics in the polymer chain to ensure the water dispersibility of the resulting nanocomposites. Microscopy and light scattering studies prove the formation particles of 100–200 nm size, and the particles size and the polydispersity of WDPU nanocomposites vary as the loading and type of clay are altered. In depth analysis of 13C CP-MAS NMR spectra using full width half maxima (FWHM) of carbonyl carbon peak of PU chains reveals the interactions between the polyurethane and organoclay that helped in preparing stable WDPU nanocomposites. Structural analysis of nanocomposites reveal the formation of intercalated morphology till 3 wt% loading of Closite-30B and exfoliated structure for higher loading whereas aggregated structure in case of OKao nanocomposites. Thermo-mechanical and tensile behaviour of resulting nanocomposites are largely influenced by the clay type and loading which can be attributed as the consequence of the different morphology and structure of nanocomposites. The surface hydrophobicity of nanocomposite films is determined by measuring the contact angle which increases with increasing clay loading and all samples show contact angle greater than 100° attributing good hydrophobic surface of nanocomposites.
Billa Narasimha Rao, P. Jaya Prakash Yadav, Kuruma Malkappa, Tushar Jana, and P.U. Sastry
Elsevier BV
Abstract In the present work, we have examined the role of triazine based functional moieties namely cyanuric chloride (CYC), 2-chloro-4, 6-bis (dimethylamino)-1, 3, 5-triazine (CBDT) and 1-chloro-3, 5-diazido-2, 4, 6-triazine (CDT), which are attached to the terminal carbons of hydroxyl terminated polybutadiene (HTPB), on the structure-property of polyurethanes (PUs). Triazine attached HTPB, called as modified HTPB, was polymerized with varieties of diisocyanates and the resulting PUs were further cured at 70 °C for 5 days to prepare the free-standing elastic PU films. Thorough spectroscopic studies (FT-IR and 13 C CP-MAS solid state NMR) of PU films could not identify any hydrogen bonding interactions between urethane bonds and triazine rings present in the soft segment (HTPB segment) of PU but revealed the presence of favorable electrostatic interaction between them because of the electron rich nature of triazine and the presence of polar substituents on the triazine ring. An in-depth small angle X-ray scattering study along with morphological study carried out by scanning electron microscopy confirmed that the interaction between urethane and triazine is the driving force for the formation of nanometer size mass fractals of hard segment domains (HSD) in the triazine attached HTPB-PU. Tensile strength and mechanical stability of modified HTPB-PU was found to be better than the native HTPB-PU owing to the formation of HSD. The current study also revealed the influence of nature and position of substituents in the triazine ring on the properties of modified PUs. The electron donating dimethyl amine groups of CBDT and segregation of PU chain were responsible for the strong photoluminescence of HTPB-CBDT-PU film compared to all other modified HTPB-PUs.
Kuruma Malkappa and Tushar Jana
American Chemical Society (ACS)
Preparation of stable, free-standing elastic film with hydrophobic surface from water-dispersible polyurethanes (WDPUs) is a challenging task. Here, we have prepared WDPUs from polybutadiene-based diols and the resulting PU films are satisfying the requisites. Two types of diols, namely, hydroxyl-terminated polybutadiene (HTPB) and terminal-functionalized HTPB with dinitrobenzene (DNB) [HTPB-DNB], were used to make WDPUs and the effects of diol structures were investigated. The synthesized WDPUs displayed particle morphology with size in the range of ∼130–270 nm and more than 1 year storage stability. WDPUs yielded stable and free-standing films upon curing and the resulting films showed high thermal and mechanical stabilities. The contact angle of the films is in the range of ∼80–100°, attributing the hydrophobic nature of the surface. Hard segment content of the PU varied from 30 to 40% (by weight) to tune the properties of WDPUs and the resulting films.
Kuruma Malkappa and Tushar Jana
American Chemical Society (ACS)
Chemical modifications of hydroxyl terminated polybutadiene (HTPB) with hydrogen bond forming functionalities were used as tactics to improve both tensile strength and elongation of polyurethanes (PUs) simultaneously. PUs were prepared using various diisocyanates with modified HTPB in which dinitrobenzene (DNB) groups are attached to terminal carbon atoms. The spectroscopic studies revealed the presence of an additional hydrogen bonding network between DNB and the urethane backbone which resulted into supramolecular cross-linking and was found to be responsible for significant improvement in mechanical properties of HTPB-DNB-PUs. Also, substantial improvement of elongation at break was observed in the case of HTPB-DNB-PUs. Small angle X-ray scattering (SAXS) and thermodynamical studies indicated a strong segmental mixing between the hard and soft segments of HTPB-DNB-PUs. Growth of partial crystalline character in HTPB-DNB-PUs was believed to be responsible for “fibrous-assembly” morphology. In summary, m...
Mousumi Hazarika, Kuruma Malkappa, and Tushar Jana
Wiley
The influence of sulfonation reaction time, temperature and the parent polystyrene (PS) particle size on the degree of sulfonation (DS), ion exchange capacity (IEC), morphology and glass transition temperature (Tg) of sulfonated polystyrene (SPS) particles was investigated. A longer reaction time (ca 2 h) at 40 °C and a smaller particle size resulted in SPS particles with a high DS. It was found that a larger PS particle size did not readily yield SPS particles with a high DS even with a longer reaction time. Contrary to the popular belief in the literature that a higher DS ensures a high IEC, we observed that the proportionality of IEC to DS is primarily controlled by the SPS particle size. Larger IEC values were obtained for larger particles rather than smaller ones despite their similar DS, owing to the presence of strong interactions between − SO3H groups within the particles in the latter case which restricts the availability of free H+ for ion exchange. The SPS particles displayed a core-shell morphology in which the outer shell appeared because of sulfonation on the PS. The DS value and the SPS particle size significantly influenced the shell thickness and thereby the morphology of the SPS particles. Copyright © 2012 Society of Chemical Industry