Papers by Author: Debes Bhattacharyya

Abstract: Composites sheets based on short wool fibres and polypropylene were fabricated by extrusion process. A three-factor two-level experimental design using Taguchi method was applied in manufacturing the composites to explore the contribution of each parameter on mechanical properties. Fire retardant behaviour of the composites with different fibre weight ratios was investigated by horizontal burning test and cone calorimetric analysis without the addition of any fire retardant agent. Reduction of burning rate with increase in the wool fibre content was observed and suitable formulation of the composites was selected for evaluation of mechanical properties.

Abstract: The motivation for the need of small-scale devices has made thin films technologically important in the recent years. They have found applications in broad fields, such as microelectronic integrated circuits, magnetic information storage systems, optical coatings and wear resistant coatings. However, the mechanical performance of these materials tends to depend on fabrication and post-processing parameters. With the intent of improving the mechanical properties of the films, a relatively novel concept of sandwich composite films has been tried in this research. Poly-methyl methacrylate (PMMA) and Graphene Oxide (GO) have been used to manufacture the sandwich films, where PMMA films have served as the facings and electrospun PMMA/GO nanofibre mat forms the sandwich core. Dimethylformamide (DMF) and Tetrahydrofuran (THF) solvents are used in suitable proportions to dissolve PMMA, and then GO is added to this solution to obtain a uniform suspension of PMMA/GO for electrospinning. The mechanical and functional properties depend on the fibre quality and their distributions in the mat, which in turn depends on the concentration of the solution. Therefore, design of experiments based on mixture analysis was used to identify the solution concentration for obtaining uniform fibre diameters and their distribution throughout the electrospun core. The analysis suggested 23% PMMA and 2% GO concentrations in the solution would give uniform fibre diameters and dispersion throughout the mat.

Abstract: In the current age of growing environmental awareness, natural fibre composites have gained wide acceptance in various facets of engineering. However, in industries, such as aerospace and mining, their acceptance is primarily dependent on them meeting the stringent fire test requirements. In this paper, symmetric laminates consisting of only glass, glass/flax hybrid and only flax as reinforcements in thermoset matrices were tested for their time to ignition, heat release rate and smoke constituents as per standard ASTM E 1354 in a cone calorimeter. Four fire retardant versions of resin systems, were used in this study. The laminates were manufactured using wet hand-layup technique that was vacuum bagged and cured between hot platens of a hydraulic press. A constant fibre volume fraction of 0.5 for all the laminates was obtained by maintaining a constant laminate thickness of 4mm. The results from the cone calorimeter tests were compared to examine the influence of natural fibres on the fire properties of the laminates. It was observed that the degree of fire retardance in the polyester based composites decreased with the increase in the flax fibre content; however, in the modified urethane composites, flax fibre composites performed better by exhibiting higher ignition time compared to the hybrid and glass fibre composites. Another important observation was that the carbon monoxide emissions during testing decreased with the increase in flax content in the composites, no matter what resin system was used. These preliminary tests suggest that, by judiciously incorporating natural fibres in a synthetic system, a hybrid system could be designed to sustain loads in environments with high fire risks.

Abstract: The concept of introducing self-healing capabilities in polymer materials and systems has been based on mimicking biological self-healing materials and systems, for example, materials like proteins have phenomenal capabilities in self-healing damaged biological structures. This work has been extended to investigate self-healing capabilities of fibre reinforced epoxy composites. Microencapsulated epoxy and mercaptan healing agents were incorporated into a glass fibre reinforced epoxy matrix to produce a polymer composite capable of self-healing. The specimens containing the microencapsulated epoxy and mercaptan healing agents did gain excellent strength and achieved a healing efficiency up to 140%.

Abstract: This paper presents development of tool wear prediction models in end milling of glass fibre reinforced polymer (GFRP) composites. Adaptive network based fuzzy inference system (ANFIS) was employed to accurately predict the amount of tool wear as a function of spindle speed, feed rate and measured machining forces. End milling experiments were performed with K20 tungsten carbide end mill cutter under dry condition in order to gather all experimental data. Results show that ANFIS is capable of estimating tool wear with excellent accuracy in the highly nonlinear region of tool wear and the machining forces relationships. Statistical analyses of the two tool wear-machining force ANFIS models reveal that the tool wear-feed force relationship has better predictive capability compared to that of the tool wear-cutting force relationship.

Abstract: In the present study the amount of xylene remaining in fibrillar scaffolds after their manufacture has been estimated by means of Gas Chromatrography coupled to Mass Spectrometry (GC-MS). For this purpose model scaffolds of poly(ethylene terephthalate) (PET) comprised of microfibrils with diameters of ~1 µm or nanofibrils with diameters of 50-150 nm as well as microfibrillar scaffolds of poly(glycolic acid) (PGA) have been used. An extremely low initial amount of xylene has been found (< 20 ppm). The xylene amount dropped below 2 ppm after drying for 24 h in a vacuum at 80°C. The microfibrillar PGA scaffolds, initially containing more xylene (23.4 ppm), retained only 3.6 ppm after drying for 24 h. After drying for 48 h the amount of xylene in all the scaffolds studied reached the detection limits of the GC-MS apparatus (< 0.5 ppm).

Abstract: The feasibility of manufacturing microfibrillar composites (MFCs) and their novel applications have been studied to a significant extend. In order to achieve commercially viable production rate of MFC materials, consistent fabrication has to be guaranteed. However, it has been shown that continuous production of MFC materials has certain difficulties need to be overcome. This study aims at identifying the production problems and improving the efficiency of manufacturing MFC materials. MFC manufacturing has been reasonably successful by drawing poly(ethylene terephthalate) (PET)/polypropylene (PP) blends. However, when the PP in the polymer blends is replaced by polyethylene (PE) for its ease of subsequent manufacturing, irregular breakage persistently occurs during drawing and this phenomenon also occasionally happens for PP/PET blends. This study involves melt blending of linear low density polyethylene and linear medium density polyethylene with PET in a single screw extruder with 70/30 wt%. Drawing was conducted at temperatures ranging from room temperature to 70°C and with draw ratios of between 1:5 and 1:7. The test results, when comparing MFC with pure PE, show 60% and 80% increase in specific tensile strength and specific tensile stiffness, respectively. It is concluded that by carefully controlling the temperature profile within the drawing chamber and using a moderate draw ratio (1:5), an efficient drawing process can be achieved to produce commercial MFC materials.

Abstract: Starve feed and semi-continuous seed emulsion polymerization were used to control the morphology of core shell latex particles with a vinyl acetate (VAc)/vinyl ester of versatic acid 10(VeoVa10) copolymer core surrounded by a poly(glycidyl methacrylate) (PGMA) shell. Pure core and core-shell structures were confirmed by TEM. The results suggest that core-shell morphology of the two stage emulsion was favoured by higher concentration of emulsifier in the seed latex: the particle size distribution of core-shell latex was broader than that of the core latex, and the average particle size of core-shell latex was larger than that of the core latex. The core-shell structure was not produced using seed emulsion with emulsifier concentration at or below the critical micelle concentration. The core shell emulsion containing epoxy functional group with added ethylene diamine showed an abrupt increase in dynamic shear moduli, G' and G'' and complex viscosity η* (several orders of magnitude) at about 35oC, during temperature ramps, over a wide range of angular frequencies. The time ramps showed that the crosslinking reaction did not occur at 15oC for the core-shell emulsion/amine system. The time for gel formation decreased with increase in temperature.

Abstract: Polymer-reinforced polymer composites have been successfully created from blends of engineering and commodity plastics. These microfibril reinforced composites (MFCs) contain molecularly oriented in-situ fibrils, evenly dispersed throughout a homogeneous matrix. MFCs have several potential applications in a range of areas including food packaging materials and biomedical scaffolds. This paper provides an overview of the characterisation of several MFCs derived from polyethylene/poly(ethylene terephthalate) (PE/PET) blends. It investigates the tensile properties of MFCs with different microfibril orientations as a result of various consolidation techniques. It also describes a study on the oxygen permeability of moulded MFC films and evidence of biological cell growth on microfibrillar polymer structures.

Abstract: Although much research work has been conducted on the production and characterisation of polypropylene/organoclay nanocomposites, the effects of nanoscale fillers with respect to actual morphology through numerical modelling have been rarely addressed. This paper describes a unique development from fabrication and experimental characterisation to the numerical modelling of polypropylene/organoclay nanocomposites based on the real mapping of nano/microstructures. Twin screw extrusion is used with a two-step masterbatch compounding method to prepare such nanocomposites with organoclays (ranging between 1wt% and 10wt%) and maleated polypropylene (1:1 weight ratio). The material characterisation using X-ray diffraction (XRD), scanning electron microscopy (SEM) and dynamic mechanical analysis (DMTA) are conducted and mechanical properties are determined by tensile, flexural and impact tests. Finally, computational models are established by using an innovative object-oriented finite element analysis code (OOF) to predict the overall mechanical properties of nanocomposites.