K. E. George

Studies on Recyclable Nylon-reinforced PP Composites: Effect of Fiber Diameter

A commercial grade of polypropylene (PP) is reinforced with nylon-6 fibers of three diameters at levels up to 30wt% PP. The addition of the fibers improve the mechanical properties such as tensile strength and flexural strength. The least diameter fibers give the maximum improvement in mechanical properties. Attempts are made to improve the interfacial adhesion between the fibers and the matrix by grafting the matrix with maleic anhydride in presence of styrene. The mechanical properties show significant improvements as a result of these modifications. The recyclability of these composites are also studied, the PP/ nylon composites/blends obtained by recycling the composites also have better tensile properties.

Silane Grafting of Polyethylenes

ABSTRACT Reactive extrusion is an attractive means of polymer processing since the shaping and reaction take place in a single operation. In this paper we report the silane grafting of polyethylenes in a single screw extruder. The optimum conditions for silane grafting, viz. temperature, shear rate, silane and DCP concentrations, were determined on a torque rheometer and then actual extrusion was performed using these conditions. The study shows that an optimum low level of grafting/crosslinking can be introduced into polyethylene during its extrusion for better mechanical behavior and/or thermal stability without affecting the processability.

Short Nylon Fiber-reinforced HDPE: Melt Rheology

Short fiber-reinforced thermoplastics have generated much interest these days since fibrous materials tend to increase both mechanical and thermal properties, such as tensile strength, flexural strength, flexural modulus, heat deflection temperature, and creep resistance, and some times impact strength of thermoplastics. If the matrix and reinforcement are both based on polymers the composite are recyclable. The rheological behavior of recyclable composites based on nylon fiber-reinforced high density polyethylene (HDPE) is reported in this paper. The rheological behavior is evaluated both using a capillary rheometer and a torque rheometer. The study shows that the composite becomes pseudoplastic with fiber content and hence fiber addition does not affect processing adversely at higher shear rates. The torque rheometer data resemble that obtained from the capillary rheometer. The energy of mixing and activation energy of mixing also do not show much variation from that of HDPE alone.

Short Nylon Fibre Reinforced PP: Melt Rheology

Short fiber reinforced thermoplastics have generated much interest these days since fibrous materials tend to increase both mechanical and thermal properties, such as tensile strength, flexural strength, flexural modulus, heat deflection temperature, creep resistance, and some times impact strength of thermoplastics. If the matrix and reinforcement are both based on polymers the composite are recyclable. The rheological behavior of recyclable composites based on nylon fiber reinforced polypropylene (PP) is reported in this paper. The rheological behavior was evaluated both using a capillary rheometer and a torque rheometer. The study showed that the composite became pseudoplastic with fiber content and hence fiber addition did not affect processing adversely at higher shear rates. The torque rheometer data resembled that obtained from the capillary rheometer. The energy of mixing and activation energy of mixing also did not show much variation from that of PP alone.

Polymer-Solvent Interaction Parameter for NR/SBR and NR/BR Blends

Abstract Polymer-solvent interaction parameters for the blends of natural rubber (NR) with styrene-butadiene rubber (SBR) and polybutadiene rubber (BR) are calculated using the Flory-Rehner equation by equating the network density of the vulcanizates in two solvents.

Kinetics of Peroxide Vulcanization of Natural Rubber

This study was undertaken to optimize the vulcanization conditions and explore the effect of residual peroxide in the peroxide vulcanization of natural rubber. The study was followed through the kinetics of the vulcanization reaction at various temperatures viz. 150,155,160 and 165°C. Dicumyl peroxide (DCP) was used as the crosslinking agent. The Monsanto Rheometer was used to investigate the different crosslinking stages and vulcanization kinetics. The thermal decomposition of peroxide followed a first order free radical decomposition reaction. Half-lives at various temperatures were determined. The percentage of residual peroxide was calculated from the cure kinetic data. The effect of residual peroxide on mechanical properties was studied at various peroxide levels and also by extending the cure time (from t90 to t95 and then to t100). Mechanical properties such as tensile strength, elongation at break, modulus and compression set (70 and 100°C) were measured. Excess peroxide was found to cause a high compression set at elevated temperature and the cure time was selected to achieve minimum residual peroxide in the product. Results indicate that peroxide concentration is the dominant factor controlling the crosslink density and hence the properties of the vulcanizates.

Recyclable PP/polyamide composite

A commercial grade of polypropylene matrix reinforced with waste polyamide (nylon 6) fibres of two diameters at levels up to 40wt% (100 polypropylene + 40 polyamide) was studied. Smaller diameter fibres showed better mechanical properties than larger diameter ones. Attempts were made to improve the interfacial adhesion between the fibres and the matrix by grafting with maleic anhydride and with also styrene maleic anhydride. The mechanical properties showed significant improvements as a result of these modifications. Thermal stability was also marginally improved. These composites could be easily recycled by processing them above the melting point of the reinforcing fibres.

Studies on Maleated Natural Rubber/Organoclay Nanocomposites

Maleic-anhydride-grafted natural rubber prepared by gamma radiation was used for preparing natural-rubber-based nanocomposites. Modified clay (up to 7 wt.%) was used for the reinforcement. Maximum improvement in mechanical properties was observed at a filler content of 5 wt.%. The maleic anhydride concentration was varied from 1 to 5% and was found to have a significant effect on the properties of the nanocomposites. The XRD pattern shows that there is a considerable improvement in the d spacing of nanoclay with the incorporation of rubber. Exfoliated layers can be seen from TEM micrographs.

Rheological Behaviour of Layered Silicate–Natural Rubber Latex Nanocomposites

The rheological behaviour of prevulcanised natural rubber (NR) latex nanocomposites based on layered silicates such as sodium bentonite and sodium fluorohectorite was studied. A typical commercial clay (non-layered version) was chosen as the reference. The effect of layered silicates on flow properties was analysed by investigating latex viscosity as a function of shear rate, temperature, and filler loading. In the presence of layered silicates, latex compounds show enhanced viscosity, probably owing to a network formation of silicate layers in the latex phase. The shear thinning behaviour exhibited by the nanocomposites at high temperature may be due to the network breakdown of silicate layers. Latex–layered silicate systems show pseudoplastic behaviour and increased zero shear viscosity and yield stress.

Thermal Behaviour of Recyclable Short Nylon Fibre Reinforced PP Composite

The thermal and crystallisation behaviour of short nylon fibre reinforced PP composites was studied by thermogravimetry (TG) and differential scanning calorimetry (DSC). Dynamic paramteres such as storage modulus, loss modulus and loss factor or damping efficiency (tan δ) were determined in a resonant frequency mode over a wide range of temperatures using dynamic mechanical analysis (DMA). Attempts were made to improve the interfacial adhesion using styrene maleic anhydride–grafted PP. The thermal properties of the composites were analysed by TG analysis. It was found that modified matrix composites show superior properties compared to the unmodified system. DSC measurements exhibited an increase in the crystallisation temperature and crystallinity, upon the addition of fibres to the PP matrix. This is attributed to the nucleating effects of the fibre surfaces. DMA of the composite shows higher dynamic stress than the neat matrix material with increase in storage modulus and decrease in loss factor.