Swati Neogi

Development of Manufacturing Technology for Cab Front Using Resin Transfer Molding Process

The development of a new composite product through resin transfer molding (RTM) process requires the identification of an effective injection strategy and optimization of the process variables and raw material parameters of the manufacturing process. This article presents an effective manufacturing technology for a cab front model using RTM isothermal mold-filling simulation technique. The simulations performed were based on the finite element method for which a commercial RTM simulation package was utilized. A number of isothermal mold-filling simulations using different injection strategies and process variables were carried out. Injection strategy using constant flow or pressure was executed to find optimum locations for injection ports and air vents requiring minimum mold -fill time. The effect of process variables, such as injection pressure, and raw material parameters, such as resin viscosity and mat permeability, on the mold-filling time was also studied. The simulation results show that the injection strategy of four injection points on the front face and four vents at the corners of the cab front with constant pressure of 5 atm delivers an optimum mold-fill time of 32 min without dry spots.

Enhancement of Microwave Absorption Properties of Epoxy by Sol–Gel-Synthesised ZnO Nanoparticles

Abstract The microwave absorption property of epoxy resins is generally poor, which can be improved by introducing fillers such as carbon nanotubes and metal oxide nanoparticles (NPs) having good microwave absorption characteristics. In this paper, the microwave absorption properties of epoxy-ZnO nanocomposites have been studied. The ZnO NPs were synthesised using the sol–gel technique and characterised for size, shape and composition. It was observed that the NPs had a polycrystalline structure and an average particle size of 27.5 nm. The synthesised NPs were incorporated into the epoxy resin at 1% and 2% loading using a closed mould technique. The flexural strength of the composites was examined using Universal Testing Machine and the glass transition temperature was measured using differential scanning calorimetry. It was seen that the flexural modulus increased by around 6% and 11% for 1% and 2% ZnO loading. The microwave absorbance of pure and ZnO-filled epoxy was tested using a Network Analyzer and it was found that the microwave absorbance is dependent on the frequency and nanoparticle loading and it increased with the increase in ZnO loading.

Chemical treatments of rice husk filler and jute fiber for the use in green composites

The development of green composites using different natural fiber reinforcements is an area of active research to reduce the environmental footprint. These composites have serious limitations with high water absorption and reduced mechanical strength. The objective of this work is to develop polymeric green composite form natural reinforcements — jute and rice husk, with improved water resistance and flexural characteristics. Rice husk and jute mat were chemically treated with acrylic acid and sodium hydroxide. The effective treatment conditions such as treatment temperature, time and concentration of the chemical to minimize water absorption, were determined. The effective acrylic acid concentration, temperature and time for acrylic treatment process were 10 volume percent, 60 °C and 4 hours for rice husk and 10 volume percent, 90 °C and 6 hours for jute mat respectively. The flexural properties were also reported for the composites. The surface chemistry, surface morphology and composition (hydroxyl, cellulose and hemicelluloses content) of the treated and untreated natural reinforcements were also analysed. It was observed that the acrylic treatment reduced the water absorption of the composites significantly with marginal reduction on mechanical property. Alkali treatment (using sodium hydroxide) improved the flexural strength of the rice husk reinforced composite, however it exhibits an adverse effect on water resistance properties.

Long term performance study of glass reinforced composites with different resins under marine environment

For marine structural applications which poses significant challenges to the choice of materials due to presence of corrosive seawater, polymer matrix based fiber reinforced composites are increasingly becoming the material of choice. However the performance properties of composites are greatly influenced by the moisture absorbed by the composite. In the current study, the long term performance is assessed by determining the amount of moisture absorbed and the reduction of mechanical properties over 12 months in a simulated sea-water environment at different temperatures. Three commonly used thermoset resins with different chemistry such as unsaturated polyester (USP), epoxy resin (EP) and vinylester (VE) are chosen. The effect of fiber reinforcement on the long term performance is investigated. A suitable method for manufacturing glass reinforced composite with good interfacial bonding and high volume fraction is also developed in current study. It is observed that vinylester plaques and composites absorb lesser moisture compared to USP and Epoxy systems resulting in lesser reduction in flexural strength and making the best performing among polymers studied. It is also found that sea-water diffusion into the composite follows non-Fickian behaviour and diffusion relaxation model fits well with the experimental data and corresponding model parameters are evaluated.

UV resistance and fire retardant property enhancement of unsaturated polyester composite

Polymer matrix composites are increasingly being used due to their low cost and simple fabrication methods. Polyester resins are amongst the most cost effective and efficient types of resins. But certain drawbacks limit the performance of these resins to be used as structural materials. These limitations include poor fire retardant properties, degradation on exposure to UV radiations and moisture diffusivity. To overcome these drawbacks, certain additives have been used such as aluminium trihydroxide (ATH) and carbon black. ATH serves the purpose of improving the fire retardant properties and carbon black provides UV resistance to the composite. In the present work, the effect of ATH and carbon black, to improve fire resistant properties and UV resistance of unsaturated polyester resin, has been investigated. An estimation of the limited oxygen index, smoke density rating and thermogravimetric analysis of ATH-filled resins has been carried out. Results indicate that the mechanical properties such as tensile strength and tensile modulus can be used to estimate the extent of degradation of carbon-filled resin on exposure to UV radiations. It has been found that even after UV exposure, the mechanical properties of carbon-filled samples do not decrease significantly. These tests have been performed at different loadings of the filler materials. Apart from the extent of loading, the amount of dispersion of the filler in the matrix is also found to influence the final properties of the polymer composite. The appropriate method of dispersion has been developed based on the observations made from the scanning electron microscope images.

Lifetime estimation of glass reinforced epoxy pipes in acidic and alkaline environment using accelerated test methodology

Accelerated ageing test methodology is valid and widely accepted procedure for estimating the lifetime of isotropic homogeneous polymeric materials. However for non-isotropic and heterogeneous polymeric compounds such as glass reinforced epoxy (GRE) pipes, accelerated ageing test methodology has not been much investigated. Various standards such as ASTM D 3681, ASTM D 5365 are being used to estimate the lifetime of GRE pipes using regression analysis which is time consuming, and requires large number of test specimens and fixtures specific to pipe dimensions. Accelerated ageing test methodology can be a viable method for estimating the lifetime. The research on accelerated test methodology as a vital tool to determine the lifetime of GRE pipes has been limited. The major concern for using accelerated ageing test methodology is primarily due to the degradation kinetics of the anisotropic composite materials which may not be governed by the Arrhenius principle. The present study on the estimation of lifetime of GRE pipes in extreme acidic and alkaline medium reveals that degradation of the composite pipe follows the Arrhenius principle and the degradation mechanism can be described by first order reaction kinetics. The degradation rate, the temperature dependence of the degradation rate and lifetime of the glass reinforced epoxy pipes in extreme acidic and alkaline medium as found in the current study are presented here, along with the morphological study of aged and un-aged GRE pipes.

Optimization of Plasma Treatment for Enhanced Filler Matrix Adhesion in Manufacturing Green Composites with Rice Husk

Abstract The objective of the current work is to study the effect of plasma treatment of rice husk (RH) to reduce the water absorption of natural filler (RH) reinforced unsaturated polyester matrix composite. RH was treated by low-pressure radio frequency plasma in a capacitively coupled plasma reactor at room temperature using nitrogen gas. It was observed that the composites manufactured from plasma-treated RH had lower water absorption as compared with non-treated ones. An experimental matrix for nitrogen plasma treatment of RH with the key process variables such as RF power, treatment time and reactor pressure was determined and experiments were performed according to the experimental matrix to optimize the process parameters by response surface methodology of a central composite design. A quadratic model was developed to predict the percentage reduction of water absorption owing to change in plasma process variables. The process variables were optimized using the predicted model and the optimum conditions were verified by experimental data.

Study of the effect of silica nanofillers on the sea-water diffusion barrier property of unsaturated polyester composites

With successful applications in every other field, composites have been used in making boats, offshore structures and various marine structural applications for past few decades, owing to their superior strength-to-weight ratio and performance-to-cost ratio. Usually, marine environment poses serious challenges to the choice of materials due to the presence of corrosive seawater which significantly decreases their life-time. Slowly, nanocomposites are increasingly becoming popular because of nanoscale effects, large interface area and strong interfacial interactions between nanoparticles and polymer. In the present study, Silicon dioxide nanofillers were used as additive in order to enhance the barrier property of composites against water diffusion and hence to prevent it from mechanical degradation. Being one of the most commonly used resin for making composites, unsaturated polyester was chosen for study. Resistance to sea-water diffusion and water absorption rate was studied while varying parameters like ambient temperature and salinity of water. It was observed that the presence of nanoparticles significantly decreases the maximum water uptake and moisture diffusivity in the composite. It was also found that as the salinity of sea-water increases and temperature decreases, degradation due to water absorption decreases.

Influence of curing agents on gelation and exotherm behaviour of an unsaturated polyester resin

A judicious choice of curing agents such as initiator and promoter and their ratio to the resin can avoid reduced gel-time and shortened exothermic reactions in applications such as liquid composite moulding processes. In this study, effects of different ratio of initiator and promoter to the unsaturated polyester resin on curing of the resin were investigated by measuring gel-time and peak exotherm using ASTM D2471 standards. Methyl ethyl ketone peroxide (MEKP) was used as an initiator and a cobalt salt was employed as an accelerator for the free radical polymerization of curing resin at ambient temperatures. It was observed that the resin gelation starts closely with the initial rise in exotherm temperature and time of gelation decreases with the increase in initiator or accelerator volume proportions. It was also found that the exotherm-peak and rate of temperature rise indicating that the curing rate increases with the initiator or accelerator proportions also increased. A nonlinear regression analysis of all gel-time and cure data were performed to quantify the dependence of curing parameters on the volume proportions of accelerator and initiator. Thus, for this polymerization initiation system, the gel-time and cure parameters can be predicted for any initiator and cobalt levels within the ranges studied.

Indian composites industry makes progress

Indias biggest composites event, the International Conference and Exhibition on Reinforced Plastics (ICERP), was held in Mumbai, India, in February. The fourth in the series, this event demonstrated a big step up for the countrys composites industry. Amanda Jacob reports.