Pankaj Tambe

Effect of sodium alginate modification of graphene (by ‘anion-π’ type of interaction) on the mechanical and thermal properties of polyvinyl alcohol (PVA) nanocomposites

Layered aligned dispersion of graphene in graphene/polyvinyl alcohol (PVA) nanocomposites is prepared in the form of films through simple solution processing route. The results indicate that there exist an interfacial interaction between PVA and graphene because of hydrogen bonding. This is responsible for the change in structure of PVA (such as decrease in the level of crystallization) and exhibiting ductile PVA nanocomposite film with improved tensile modulus, tensile strength, and thermal stability. Moreover, to improve the mechanical properties of PVA nanocomposites, graphene is successfully modified using a non-covalent modifier, sodium alginate (SA) and there exist an ‘anion-π’ type of interaction in between SA and graphene. The modification results in finer dispersion of the graphene in PVA/SA-m-graphene nanocomposites. In addition, there exist a hydrogen bonding in between PVA and SA. This has resulted in the remarkable improvement in mechanical properties of PVA/SA-m-graphene nanocomposites as compared to pure PVA and PVA/graphene nanocomposites. The increase in mechanical properties of PVA/SA-m-graphene nanocomposites is achieved through better load transfer from graphene to polymer matrix, despite decrease in crystallinity of PVA. Improvement in tensile modulus and tensile strength is highest at 0.5 wt.% of SA-modified graphene in PVA/SA-m-graphene nanocomposites because of finer dispersion of graphene and is 62 and 40% higher than that of pure PVA. Addition of SA-modified graphene also improves the thermal stability of PVA/SA-m-graphene nanocomposites remarkably as compared to unmodified graphene PVA nanocomposites.

EMI shielding effectiveness of graphene decorated with graphene quantum dots and silver nanoparticles reinforced PVDF nanocomposites

Abstract Graphene decorated with graphene quantum dots (G-D-GQDs) have been successfully synthesized using solvothermal cutting of graphene oxide. The incorporation of G-D-GQDs in polyvinyledene fluoride (PVDF) matrix shows the total EMI shielding effectiveness (SET) of 31 dB at 8 GHz. The main mechanism of high EMI shielding effectiveness is reflection and absorption of EM radiation. The high absorption of EM radiation is due to tunneling of electrons from GQDs. Further, decoration of G-D-GQDs with conducting Ag nanoparticles (G-D-GQDsAg) enhances the SET value to 43 dB at 8 GHz of PVDF/G-D-GQDsAg nanocomposite, due to increase in electrical conductivity of PVDF/G-D-GQDsAg nanocomposite and enhanced dispersion of G-D-GQDsAg in PVDF matrix. The incorporation of G-D-GQDs and G-D-GQDsAg in PVDF matrix also increases the thermal stability and crystallinity of PVDF. The increase in thermal stability and crystallinity are more for PVDF/G-D-GQDsAg nanocomposite as compare to PVDF/G-D-GQDs nanocomposite, due to better dispersion of G-D-GQDsAg in PVDF matrix. Thus, PVDF/G-D-GQDsAg nanocomposite having high SET value can shield 99.9% of electromagnetic radiation in X-band range, which make it suitable for EMI shielding application for consumer electronic equipment’s.

Effect of non-ionic surfactant assisted modification of hexagonal boron nitride nanoplatelets on the mechanical and thermal properties of epoxy nanocomposites

Hexagonal boron nitride (hBN) nanoplatelets have attracted considerable interest recently. In this work, hBN nanoplatelets have been prepared using chemical exfoliation route. The exfoliation of hBN nanoplatelets takes place along the (0 0 2) plane without destroying the crystal structure. The hBN nanoplatelets are modified using polyvinylpyrrolidone (PVP), a non-ionic surfactant in order to achieve finer dispersion of hBN nanoplatelets in ethyl alcohol, and subsequently in the epoxy matrix. The enhanced dispersion of hBN nanoplatelets achieved using PVP is due to the adsorption of PVP over the hBN nanoplatelets, and PVP miscibility with epoxy resin in an uncured state. Due to the finer dispersion of hBN nanoplatelets in the epoxy matrix, the flexural properties are higher as compared to pure epoxy. PVP assisted dispersed hBN nanoplatelets reinforced with epoxy nanocomposites have higher flexural properties as compared to pure hBN nanoplatelets-reinforced epoxy nanocomposites. The enhanced dispersion of hBN nanoplatelets using PVA also limits the decrease in glass transition temperature (Tg). Further, thermal stability of the epoxy increase with an addition of PVP modified and unmodified hBN nanoplatelets in the epoxy matrix as compared to pure epoxy. Fractography studies reveal that addition of PVP modified and unmodified hBN nanoplatelets in the epoxy matrix depict rough surface with many small facets due to resistance offered by the dispersed nanoplatelets.

Thermodynamic approach to enhance the dispersion of graphene in epoxy matrix and its effect on mechanical and thermal properties of epoxy nanocomposites

Abstract Graphene-reinforced polymer nanocomposites are under intense investigation in recent years. In this work, graphene nanosheets have been prepared using chemical reduction method of graphene oxide. Graphene-reinforced epoxy nanocomposites show an enhancement in mechanical and thermal properties at 0.05 wt.% of graphene in epoxy matrix. Modification of graphene with polyvinylpyrrolidone (PVP) shows the significant enhancement in mechanical and thermal properties of epoxy nanocomposites. PVP-modified graphene nanosheets reduces the gap of enthalpic and entropic penalties and facilitates improved dispersion of graphene in epoxy matrix. In addition, enhanced dispersion of PVP-modified graphene in epoxy matrix results in better load transfer across graphene–epoxy interface. Glass transition temperature (Tg) of PVP-modified graphene epoxy nanocomposites increases as compared to pure epoxy because there exist an interaction between epoxy and PVP. Fractography study reveals the localized ductile fracture.

Predictive modelling of surface roughness and kerf widths in abrasive water jet cutting of Kevlar composites using neural network

Abrasive water jet cutting (AWJC) is one of the important non-traditional machining processes used for cutting of difficult-to-cut materials and intricate profiles. Cutting of Kevlar fibre reinforced polymer composites is a complex process, making it difficult to model, predict and improve the cut surface quality. This paper presents a detailed approach of the usage and effectiveness of a back-propagation neural network (NN) for modelling and prediction of three cut surface characteristics namely top kerf width, bottom kerf width and surface roughness (Ra) in AWJC of aerospace grade Kevlar-epoxy composites. Statistically designed full factorial experiments based on three process parameters [water jet pressure (WJP), abrasive flow rate (AFR) and quality level (QL)] at three levels each were conducted to generate the NN training database. The results demonstrate that the NN model was able to successfully model and predict the two kerf widths and surface roughness closely matching the experimental results.

Influence of halloysite nanotubes (HNTs) on morphology, crystallization, mechanical and thermal behaviour of PP/ABS blends and its composites in presence and absence of dual compatibilizer

Abstract Halloysite nanotubes (HNTs) filled 80/20 (wt/wt) polypropylene (PP)/acrylonitrile butadiene styrene (ABS) blends and its composites in presence and absence of dual compatibilizer (polypropylene grafted maleic anhydride (PP-g-MA), and styrene-ethylene, butylene-styrene triblock copolymer grafted with maleic anhydrite (SEBS-g-MA)) have been prepared using twin screw extruder followed by injection moulding. Significant refinements in dispersed ABS droplets diameter and interparticle distance between dispersed ABS droplets were observed in case of HNTs filled 80/20 (wt/wt) PP/ABS blends and its composites in presence of PP-g-MA and SEBS-g-MA. This has resulted in significant enhancement in tensile and impact properties of HNTs filled 80/20 (wt/wt) PP/ABS blends and its composites in presence of PP-g-MA and SEBS-g-MA. Refinement in morphology of dispersed ABS phase results in decrease in crystallinity of HNTs filled 80/20 (wt/wt) PP/ABS blends and its composites in presence of PP-g-MA and SEBS-g-MA. In addition, HNTs act as heterogeneous nucleating agent for the growth of PP crystals, and hence crystallization rate of HNTs filled 80/20 (wt/wt) PP/ABS blends and its composites in presence and absence of PP-g-MA and SEBS-g-MA increases. Thermal stability also increases in case of HNTs filled 80/20 (wt/wt) PP/ABS blends and its composites in presence and absence of PP-g-MA and SEBS-g-MA.

High concentration exfoliation of graphene in ethyl alcohol using block copolymer surfactant and its influence on properties of epoxy nanocomposites

ABSTRACT In this work, high concentration exfoliation (∼0.2 mg/ml) of graphene in ethyl alcohol is achieved in presence of block copolymer of polyethylene oxide–polypropylene oxide–polyethylene oxide (PEO–PPO–PEO) using sonication followed by centrifugation. The obtained graphene solution is used to prepare epoxy nanocomposites. Flexural tests were conducted over epoxy nanocomposites. The 0.018 wt% of PEO–PPO–PEO block copolymer exfoliated graphene in epoxy matrix shows 21.7% and 15.8% enhancement in flexural modulus and flexural strength respectively as compared to pure epoxy. Transmission electron microscopy reveals well dispersion of graphene in epoxy matrix; and fractography of flexural fractured sample shows graphene dispersion restricts the crack propagation. The well-dispersed graphene in epoxy matrix increase the dielectric constant and thermal stability of epoxy nanocomposites. Further, the enhanced graphene dispersion in epoxy nanocomposites reduces the glass transition temperature (Tg). Thus, enhanced mechanical properties achieved by dispersion of block copolymer exfoliated graphene in epoxy nanocomposites make it suitable for several applications.

Influence of surface modification of halloysite nanotubes and its localization in PP phase on mechanical and thermal properties of PP/ABS blends

Abstract Halloysite nanotubes (HNTs) have been successfully modified using polyethyleneimine (PEI). HNTs and PEI-modified HNTs-filled 80/20 (wt/wt) polypropylene (PP)/acrylonitrile butadiene styrene (ABS) blends and its nanocomposites in the presence of dual compatibilizer have been prepared by melt mixing technique. The refinement in matrix–droplet morphology, selective localization of PEI-modified HNTs, increase in crystallinity of PP phase, formation of β-form of PP crystals and improved dispersion of PEI-modified HNTs in PP phase has resulted in a remarkable improvement in tensile modulus, impact strength and thermal stability of PEI-modified HNTs-filled 80/20 (wt/wt) PP/ABS blends in presence of dual compatibilizer. The increase in tensile modulus, tensile strength and impact strength for PEI-modified HNTs-filled 80/20 (wt/wt) PP/ABS blends in presence of dual compatibilizer are 28.8, 26.6 and 38.5%, respectively.

Optimisation of surface finish in abrasive water jet cutting of Kevlar composites using hybrid Taguchi and response surface method

Abrasive water jet cutting (AWJC) is particularly useful for difficult-to-cut materials like composites, super alloys and ceramics. However, the surface finish produced is often poor, necessitating finishing operations like grinding, etc., which lead to delamination in case of polymer composite laminates. Therefore, optimum selection of process parameters is important in AWJC. This paper presents the influence of three process parameters (water jet pressure, abrasive flow rate and quality level) on surface roughness (Ra) in AWJC of Kevlar composites. The optimal parameter setting was determined using a hybrid Taguchi and response surface method (HTRSM). The experimental results and ANOVA analysis indicate that quality level and water jet pressure have more significant effect on Ra. A second order response surface model was developed using the central composite rotatable design (CCRD). Finally, confirmation experiments were conducted to verify the predicted and experimental results at optimal settings, and an excellent agreement was obtained between the two.

Giant permittivity of three phase polymer nanocomposites obtained by modifying hybrid nanofillers with polyvinylpyrrolidone

Abstract In this work, the combination of graphene decorated with graphene quantum dots (G-D-GQDs) and barium titanate (BaTiO3) nanoparticles filled poly (vinyledene fluoride) (PVDF) nanocomposites are prepared using solvent casting method. The modification of G-D-GQDs and BaTiO3 nanoparticles with polyvinyl pyrrolidone (PVP) show finer dispersion in PVDF matrix as compared to unmodified G-D-GQDs and BaTiO3 nanoparticles in PVDF matrix. XRD of PVDF nanocomposites shows the formation of α and β form of PVDF crystals. The incorporation of the combination of PVP modified BaTiO3 nanoparticles and G-D-GQDs in PVDF matrix show a decrease in crystallization temperature (Tc), percent crystallinity (Xc) and increase in thermal stability as compared to unmodified PVDF/BaTiO3/G-D-GQDs nanocomposites, due to interaction of PVP modified nanoparticles with PVDF. Further, the incorporation of the combination of 20 wt.% BaTiO3 nanoparticles and 3 wt.% G-D-GQDs in PVDF matrix show a giant dielectric constant. The giant dielectric constant is achieved due to accumulation of more charges across conductor-insulator interface, more numbers of microcapacitor formed and enhanced interfacial compatibility between BaTiO3/G-D-GQDs with PVDF through PVP. The loss tangent (tan δ) of PVP modified G-D-GQDs and BaTiO3 nanoparticles and its PVDF nanocomposites is low due to lower leakage current, which make the material suitable for various applications. Graphical Abstract