Sri Bandyopadhyay

Short jute fiber reinforced polypropylene composites: effect of compatibiliser, impact modifier and fiber loading

Abstract The jute–PP granules were made in a K-mixer and molded using Injection Molding Machine to produce ASTM test pieces. In general it was found that increase in toughness was always with decreasing tensile/flexural properties. However, the extent of increase/decrease depends on the type of modifier, its dose and its compatibility with the jute–PP system. Variation of notched / un-notched Izod impact strength, flexural strength/modulus and tensile strength/modulus with different impact modifiers at 0,4,9 and 14 wt.% are shown graphically. Effect of impact modifier on% compatibiliser was also analyzed and found that both impact and tensile properties showed increasing trend with the compatibiliser but reverse was true for the flexural properties. Effect of impact modifier on fiber loading, however, showed different results. There was increase in impact strength with rise in fiber loading. Tensile and flexural properties were found to optimize at 40% fiber loading. Interface studies were carried out by field emission scanning electron microscope (FESEM) to investigate the fiber surface morphology, fiber pull out and fiber polymer interface.

The effect of weave pattern on the mode-I interlaminar fracture energy of E-glass/vinyl ester composites

In this work, the effect of weave structure on the mode-I interlaminar fracture energy (GIc) of glass/toughened vinyl ester laminates has been investigated. The matrix material used was commercially available rubber-modified vinyl ester resin, DERAKANE 8084. The glass fibres used were E-glass plain weave, twill weave, quadran 4-harness satin weave, and 8-harness satin weave with weave index of 2, 3, 4 and 8 respectively. The specimens were prepared by a vacuum bagging technique. The mode-I delamination tests have been done at a constant displacement rate of 2 mm/min in an Instron testing machine, using specimens machined in accordance with ASTM D5528-94a. By using a HITACHI S-4500 scanning electron microscope, microscopic details of crack growth in the interply region were examined after fracture testing. The twill-weave laminate with weave index ng=3 yielded the highest value of fracture energy for critical crack propagation (GIc). Whilst the 8-harness satin-weave laminate gave the highest value of initial fracture energy (GIi). Partial debonding of transversely oriented yarns results in the delamination resistance for twillweave, quadran 4-harness satin-weave, and 8-harness satin-weave laminates. Fracture of debonded fibres ascribed to as ‘fibre bridging’ was observed in the twill-weave, quadran 4-harness satin-weave and 8-harnes satin-weave laminates. No indications of fibre bridging were observed in the plain-weave laminate. # 2002 Elsevier Science Ltd. All rights reserved.

Electrical properties of natural rubber nanocomposites: effect of 1-octadecanol functionalization of carbon nanotubes

This article reports the results of studies on the effect of 1-octadecanol (abbreviated as C18) functionalization of carbon nanotubes (CNT) on electrical properties of natural rubber (NR) composites. Dispersion of CNT in NR matrix was studied by transmission electron microscopy (TEM) and electrical resistivity measurements. Fourier transform infra red spectrometry (FTIR) indicates characteristic peaks for ether and hydrocarbon in the case of C18 functionalized CNT. Dielectric constant increases with respect to the filler loading for both unmodified and functionalized CNTs, the effect being less pronounced in the case of functionalized CNT due to its better dispersion in the matrix. Stress–strain plots suggest that the mechanical integrity of the NR/CNT composites, measured in terms of tensile strength, increases on C18 functionalization of the nanofiller. TEM reveals that the functionalization causes improvement in dispersion of CNT in NR matrix, which is corroborated by the increase in electrical resistivity in the case of the functionalized CNT/NR composites.

Effect of –COOH Functionalized Carbon Nanotubes on Mechanical, Dynamic Mechanical and Thermal Properties of Polypropylene Nanocomposites

Multi-walled carbon nanotubes (CNTs) were functionalized on treatment with nitric acid and the surface-modified CNT was characterized using Fourier transform infrared spectroscopy (FTIR). Isotactic polypropylene (iPP)/CNT composites at different CNT loadings (i.e., 0.1, 0.25, 1.00, and 5.00 wt%) were prepared by melt blending in a mini blender. The differential scanning calorimetric (DSC) studies showed the nucleating effect of CNTs on the crystallization behavior of iPP. Results of X-ray diffraction studies are in conformity with the results of DSC studies. Results of stress–strain measurements reveal that Youngs modulus increases, while elongation at break decreases with increase in CNT loading and the ductility of the composites is adversely affected at high loading of CNTs (>1.0 wt%). Functionalization of CNTs causes an improvement in Youngs modulus, at all loadings studied, but elongation at break increases only up to 0.25%. At higher loading, the elongation at break drops down. Storage modulus increases with increase in CNT loading and the effect is greater in the case of functionalized CNTs. Tan δ shows a decrease with increase in CNT loading, but the effect is less pronounced at high CNT loading (>0.1 wt%).

Atomic force microscopy studies of short melamine fiber reinforced EPDM rubber

Atomic Force Microscopy (AFM) was used to investigate the morphology and interfacial properties of unaged and aged Ethylene Propylene Diene (EPDM) rubber-melamine fiber composites. Interfacial adhesion between the fiber and the matrix was weak in the absence of a dry bonding system consisting of hexamethylene tetramine, resorcinol and hydrated silica (HRH). AFM images revealed the formation of an interface between the fiber and the matrix with the addition of the bonding agents. Ageing of the composites improved the adhesion between the fiber and the matrix, which was evident from the topographic images of the aged composites. It was found that two-dimensional and three-dimensional topographic images from AFM could be used to determine fiber geometry, fiber diameter and fiber-matrix adhesion in short fiber-rubber composites.

Influence of Cl-, Br-, NO 3 - and SO 4 2- ions on the corrosion behaviour of 6061 Al alloy

The effects of anions like Cl-, Br-, NO3- and SO42- on the anodic dissolution of the monolithic Al 6061 alloy have been investigated at neutral pH through immersion testing and electrochemical techniques like potentiodynamic polarization and a.c. impedance spectroscopy. Scanning electron microscopy was employed to characterize the corroded surface and to observe the extent of pitting in different media. From the evaluated corrosion parameters it was found that the dissolution of the matrix was extensively reduced in presence of aqueous solutions containing Br-, NO3- and SO42- ions while Cl- ions aggravated corrosion by penetrating into the barrier oxide film on the surface of the material. Pronounced effect of pitting was observed in presence of Cl- and the level of pitting in NO3- and Br- were mild. In presence of SO42- ions passivity was extended over a wide potential range and breakdown of passivity occurs when the material was polarized beyond pitting potential. The departure of capacitive behaviour towards resistive behaviour was clearly observed through impedance measurements when investigations were conducted in Cl- media and in presence of the other electrolytes. Corrosion rates were, however, controlled during prolonged exposure in the electrolytic media, specially in case of chloride media, due to the predominance of film repair kinetics.

The reinforcement of an age-hardenable Al-Cr matrix alloy in situ and by SiC/Al2O3 particles : tailoring of the interface

Abstract Al–Cr alloys containing less than 0.75% Cr give rise to an age-hardening effect and the alloys also exhibited a good combination of strength and ductility properties. The achievable high toughness of these alloys led to an attempt to produce in situ composites with an Al–Cr solid solution as the matrix phase and excess insoluble intermetallics of chromium aluminides as the reinforcing constituent. The development of composites based on the Al–Cr matrix alloy with SiC and/or Al2O3 as the reinforcing phase was also attempted by a casting route. It was observed that the increase in strength was quite considerable even with a relatively good ductility. The precipitation behaviour and its kinetics in this newly developed composite were also studied by differential scanning calorimetry (DSC) and transmission electron microscopy (TEM).

Development of Hybrid Nanocomposites for Electronic Applications

Hybrid inorganic–organic nanocomposite materials with their widely varying electrical and mechanical properties offer promising applications in many areas of the electronic industry and have been traditionally employed as insulators and dielectrics. The development of new materials has broadened their utilization into areas where their semi-conducting and conducting properties have encouraged use in many novel applications. In this chapter we have reviewed on the material aspects of nanocomposites used in the following electronic applications: integrated circuits, embedded capacitors, transistors, lithium ion batteries, light emitting diodes, information storage, and briefly about liquid crystal, flat panel displays and ultra large scale integrated (ULSI) devices.

Microstructural evolution of a cold-deformed 6061Al reinforced with SiC particles during subsequent annealing

The microstructural development during annealing of a cold-deformed 6061Al metal matrix composite (MMC) reinforced with either 3 or 20 μm diameter SiC particles has been investigated. The composites were compressed to low (< 10%) levels of strain and then annealed at either 350 or 450°C for different times. Microstructure examination was carried out by transmission electron microscopy and optical microscopy. The results reveal that prior grain boundaries and constituent particles are the dominant sites for recrystallization in both composites, although some nucleation was observed adjacent to the larger SiC particles. The concurrent presence of Mg2Si precipitates affected the progress of recrystallization.

Magnetodielectric effect in Ni0∙5Zn0∙5Fe2O4–BaTiO3 nanocomposites

Composites comprising of nanoparticles of Ni0∙5Zn0∙5Fe2O4 (NZF) and BaTiO3 (BT), respectively were synthesized by a chemical method. The particles had diameters in the range of 15–31 nm. NZF was prepared by a coprecipitation technique. This was soaked in a sol containing BT. Compositions synthesized were xNZF-(1 – x) BT, where x = 0∙7, 0∙5 and 0∙3, respectively. The composites showed ferromagnetic hysteresis loops due to NZF phase. The analysis of coercivity variation as a function of temperature gave blocking temperatures in the range of 306–384 K depending on the diameter of the ferrite nanoparticles. This implied that superparamagnetic interactions are above these temperatures. The nanocomposites also exhibited ferroelectric behaviour arising due to the presence of BT. The remanent polarization of the samples was small. This was adduced to the nanosize of BT. The specimens showed magneto-dielectric (MD) effect in the magnetic field range 0–0∙7 Tesla. The MD parameter measured at the maximum magnetic field was around 2%. This was one order of magnitude higher than that reported so far in similar composite systems. This was explained on the basis of a two-phase inhomogeneous medium model with an interface between them, the phases possessing drastically different electrical conductivities.