Studies on the Effect of an External Flaw on the Tensile Strength of Short Kevlar Fiber-Thermoplastic Polyurethane Composites

The effect of an external flaw on the tensile strength of short kevlar fiber-thermoplastic composites has been studied with respect to fiber content, fiber orientation, location of the external flaw, and the temperature of test. The composites showed a three-step reduction in tensile strength with increasing flaw size. The critical flaw-length region was shifted to higher flaw-size levels with increasing fiber content. With increasing temperature, the critical flaw length was increased in the case of unfilled TPU, whereas it remained more or less constant in the case of short kevlar fiber-filled-TPU composite.

Studies on the Flammability of Short Kevlar Fiber-Thermoplastic Polyurethane Composite

The flammability of short Kevlar aramide fiber-thermoplastic polyurethane (TPU) has been investigated with respect to fiber loading and various flame retardant additives such as halogen containing polymers, antimony oxide/chlorine donor combination, zinc borate, and aluminum hydroxide. Smoke generation was reduced drastically, while the oxygen index was reduced marginally in the presence of short fibers. The best improvement in the oxygen index was obtained with antimony oxide/chlorinated paraffin wax combination, in the weight ratio 1:6. A 70 phr loading of aluminum hydroxide improved LOI and reduced smoke generation.

Thermal degradation of short kevlar fibre thermoplastic polyurethane composite

The thermal degradation of short kevlar fibre-thermoplastic polyurethane (TPU) composites has been studied by Thermogravimetric Analysis (TGA) and Differential Scanning Calorimetry (DSC). TGA showed that the thermal degradation of TPU takes place in two steps with peak maxima (T1max and T2ma,) at 383°C and 448°C, respectively. In the presence of 10-40 phr of short kevlar fibres, T1_ and T2max were shifted to lower temperatures. The temperature of onset of degradation was increased from 245 to 255°C at 40 parts per hundred rubber (phr) fibre loading. Kinetic studies showed that the degradation of TPU and kevlar-TPU composite follows first-order reaction kinetics. The DSC study showed that there is an improvement in thermal stability of TPU in the presence of 20 phr of short kevlar fibres.

Synthesis and Characterisation of Thermoplastic Ionomers based on Natural Rubber

Chemically modified novel thermo-reversible zinc sulphonated ionomers based on natural rubber (NR), radiation induced styrene grafted natural rubber (RI-SGNR), and chemically induced styrene grafted natural rubber (CI-SGNR) were synthesized using acetyl sulphate/zinc acetate reagent system. Evidence for the attachment of sulphonate groups has been furnished by FTIR spectra. which was supplanted by FTNMR results. Estimation of the zinc sulphonate group was done using spectroscopic techniques such as XRFS and ICPAES. The TGA results prove improvement in the therrno-oxidative stability of the modified natural rubber. Both DSC and DMTA studies show that the incorporation of the ionic groups affect the thermal transition of the base polymer. Retention of the improved physical properties of the novel ionomers even after three repeated cycles of mastication and molding at 120 degree C may be considered as the evidence for the reprocessabiJity of the ionomer. Effect of both particulate (carbon black. silica & zinc stearate) and fibrous fillers (nylon & glass) on the properties of the radiation induced styrene grafted natural rubber ionomer has been evaluated. Incorporation of HAF carbon black results in maximum improvement in physical properties. Silica reinforces the backbone chain and weakens the ionic associations. Zinc stearate plays the dual role of reinforcement and ptasticization. The nylon and glass filled lonorner compounds show good improvement in the physical properties in comparison with the neat ionomer. Dispersion and adhesion of the fillers in the ionomer matrix has been amply supported by their SEM micrographs. Microwave probing of the electrical behavior of the 26.5 ZnSRISGNR ionomer reveals that the maximum relative complex conductivity and the complex permittivity appear at the frequency of 2.6 GHz. The complex conductivity of the base polymer increases from 1.8x 10.12 S/cm to 3.3xlO·4 S/cm. Influence of fillers on the dielectric constant and conductivity of the new ionic thermoplastic elastomer has been studied. The ionomer I nylon compound shows the highest microwave conductivity. Use of the 26.5 ZnS-RISGNR ionomer as a compatibilizer for obtaining the technologically compatible blends from the immiscible SBR/NBR system has been verified. The heat fugitive ionic cross-linked natural rubber may be, therefore, useful as an alternative to vulcanized rubber and thermoplastic elastomer

Studies on Thermoplastic Elastomers Based on Polyethylene/Elastomer Blends

Department of Polymer Science and Rubber Technology, Cochin University of Science and Technology.

Modification of Polyethylenes by Reactive Extrusion

The main aim of the study was to optimise the reactive extrusion conditions in the conventional modification processes of polyethylenes in a single screw extruder.The optimum conditions for peroxide crosslinking of low density polyethylene (LDPE), linear low density polyethylene (LLDPE) and their blend were determined in a torque rheometer. The actual reactive extrusion was performed in a laboratory single screw extruder using the optimum parameters. The influence of the coagent, triaUyl cyanurate (TAC), on the cross linking of low density polyethylene in the presence of peroxide was also investigated. The peroxide crosslinking was found to improve the mechanical properties and the thermal stability of the polyethylenes. The efficiency of crosslinking was found to be improved by the addition of coagent such as TAC.The optimum conditions for silane grafting viz temperature, shear rate, silane and DCP concentrations were determined on a torque rheometer in the case of LDPE, LLDPE and their blend. Silane grafting of LDPE in the presence of peroxide was performed with and without addition of water. Compounding of such mixtures in the melt at high temperatures caused decomposition of the peroxide and grafting of alkoxy silyl groups to the polyethylene chains.The optimum parameters for maleic anhydride modification of LDPE, LLDPE and their blend were determined. The grafting reaction was confinned by FTIR spectroscopy. Modification of polyethylenes with maleic anhydride in the presence of dicumyl peroxide was found to be useful in improving mechanical properties. The improvement was found to be mainly due to the grafting of carboxyl group and formation of crosslinks between the chains. The cross linking initiated improvements indicate extended property profiles and new application fields for polyethylenes.On the whole the study shows that the optimum conditions for modifying polyethylenes can be determined on a torque rheometer and actual modification can be performed in a single screw extruder by employing the optimum parameters for improved mechanical! thermal behaviour without seriously affecting their processing behaviour.

Development of thermoplastic conducting polymer composites based on polyaniline and polythiophenes for microwave and electrical applications

The microwave and electrical applications of some important conducting polymers are analyzed in this investigation.One of the major drawbacks of conducting polymers is their poor processability,and a solution to overcome this is sought in this investigation.Conducting polymer thermoplastic composites were prepared by the insitu polymerization method to improve the extent of miscibility probably to a semi IPN level.The attractive features of the conducting composite developed are excellent processability,good microwave and electrical conductivity,good microwave absorption,load sensitivity and satisfactory mechanical properties.The composite shows typical frequency selective microwave absorption and refelection behaviors.

Studies On Thermoplastic Elastomers With Special Reference To Triblock Copolymers And Nbr/Pvc Blends

Thermoplastic elastomers are a relatively new class of materials which compete with thermoset rubbers in some areas and thermoplastic materials in other areas. The main thrust of the present investigation is a comparative study’ on commercially .available triblock. styrene thermoplastic elastomers and those derived from blends of acrylonitrile-butadiene rubber and poly(vinyl chloride). The styrene—based thermoplastic elastomers are gaining acceptance as a replacement for both natural and synthetic rubber‘ in many‘ applications. TPEs based on blends of elastomers and plastics ix: the fastest growing segment of the broad class of thermoplastic elastomers. Broad applicability and simple technology of production are the attractive features of this class of TPES. NBR/PVC thermoplastic elastomers were selected for this investigation due to the versatility of PVC, its number one position, low cost. ability to Ina compounded into various flexible and rigid form with good physical and chemical and weathering properties etc., which will be passed over to PVC blends especially NBR/PVC blends which are known to form miscible systems

High Styrene–Rubber Ionomers, an Alternative to Thermoplastic Elastomers

High styrene rubber ionomers were prepared by sulfonating styrene–butadiene rubber of high styrene content (high styrene rubber) in 1,2-dichloroethane using acetyl sulfate reagent, followed by neutralization of the precursor acids using methanolic zinc acetate. The ionomers were characterized using X-ray fluorescence spectroscopy, Fourier transform infrared spectroscopy (FTIR), nuclear magnetic resonance spectroscopy (NMR), dynamic mechanical analysis (DMA), and also by the evaluation of mechanical properties. The FTIR studies of the ionomer reveal that the sulfonate groups are attached to the benzene ring. The NMR spectra give credence to this observation. Results of DMA show an ionic transition (Ti) in addition to glass–rubber transition (Tg). Incorporation of ionic groups results in improved mechanical properties as well as retention of properties after three cycles of processing

Growth of the lava dome and extrusion rates at Soufrière Hills Volcano, Montserrat, West Indies: 2005–2008

The third episode of lava dome growth at Soufrière Hills Volcano began 1 August 2005 and ended 20 April 2007. Volumes of the dome and talus produced were measured using a photo-based method with a calibrated camera for increased accuracy. The total dense rock equivalent (DRE) volume of extruded andesite magma (306 ± 51 Mm3) was similar within error to that produced in the earlier episodes but the average extrusion rate was 5.6 ± 0.9 m3s−1 (DRE), higher than the previous episodes. Extrusion rates varied in a pulsatory manner from <0.5 m3s−1 to ∼20 m3s−1. On 18 May 2006, the lava dome had reached a volume of 85 Mm3 DRE and it was removed in its entirety during a massive dome collapse on 20 May 2006. Extrusion began again almost immediately and built a dome of 170 Mm3 DRE with a summit height 1047 m above sea level by 4 April 2007. There were few moderate-sized dome collapses (1–10 Mm3) during this extrusive episode in contrast to the first episode of dome growth in 1995–8 when they were numerous. The first and third episodes of dome growth showed a similar pattern of low (<0.5 m3s−1) but increasing magma flux during the early stages, with steady high flux after extrusion of ∼25 Mm3

Impact damage characterisation of thermoplastic matrix composites using transmission transient thermography

In this work, IR thermography is used as a non-destructive tool for impact damage characterisation on thermoplastic E-glass/polypropylene composites for automotive applications. The aim of this experimentation was to compare impact resistance and to characterise damage patterns of different laminates, in order to provide indications for their use in components. Two E-glass/polypropylene composites, commingled ®Twintex (with three different weave structures: directional, balanced and 3-D) and random reinforced GMT, were in particular characterised. Directional and balanced Twintex were also coupled in a number of hybrid configurations with GMT to evaluate the possible use of GMT/Twintex hybrids in high-energy absorption components. The laminates were impacted using a falling weight tower, with impact energies ranging from 15 J to penetration. Using IR thermography during cooling down following a long pulse (3 s), impact damaged areas were characterised and the influence of weave structure on damage patterns was studied. IR thermography offered good accuracy for laminates with thickness not exceeding 3.5 mm: this appears to be a limit for the direct use of this method on components, where more refined signal treatment would probably be needed for impact damage characterisation.

Sensory and instrumental analyses of volatiles generated during the extrusion cooking of oat flours

Three batches of oats were extruded under four combinations of process temperature (150 or 180 °C) and process moisture (14.5 and 18%). Two of the extrudates were evaluated by a sensory panel, and three were analyzed by GC-MS. Maillard reaction products, such as pyrazines, pyrroles, furans, and sulfur-containing compounds, were found in the most severely processed extrudates (high-temperature, low-moisture). These extrudates were also described by the assessors as having toasted cereal attributes. Lipid degradation products, such as alkanals, 2-alkenals, and 2,4-alkadienals, were found at much higher levels in the extrudates of the oat flour that had been debranned. It contained lower protein and fiber levels than the others and showed increased lipase activity. Extrudates from these samples also had significantly lower levels of Maillard reaction products that correlated, in the sensory analysis, with terms such as stale oil and oatmeal. Linoleic acid was added to a fourth oat flour to simulate the result of increased lipase activity, and GC-MS analysis showed both an increase in lipid degradation products and a decrease in Maillard reaction products.

Cyclic extrusion of a lava dome based on a stick-slip mechanism

Lava dome eruptions are sometimes characterised by large periodic fluctuations in extrusion rate over periods of hours that may be accompanied by Vulcanian explosions and pyroclastic flows. We consider a simple system of nonlinear equations describing a 1D flow of lava extrusion through a deep elastic dyke feeding a shallower cylindrical conduit in order to simulate this short-period cyclicity. Stick-slip conditions depending on a critical shear stress are assumed at the wall boundary of the cylindrical conduit. By analogy with the behaviour of industrial polymers in a plastic extruder, the elastic dyke acts like a barrel and the shallower cylindrical portion of the conduit as a die for the flow of magma acting as a polymer. When we applied the model to the Soufrière Hills Volcano, Montserrat, for which the key parameters have been evaluated from previous studies, cyclic extrusions with periods from 3 to 30 h were readily simulated, matching observations. The model also reproduces the reduced period of cycles observed when a major unloading event occurs due to lava dome collapse.

Measuring large topographic change with InSAR: lava thicknesses, extrusion rate and subsidence rate at Santiaguito volcano, Guatemala

Lava flows can produce changes in topography on the order of 10s-100s of metres. A knowledge of the resulting volume change provides evidence about the dynamics of an eruption. We present a method to measure topographic changes from the differential InSAR phase delays caused by the height differences between the current topography and a Digital Elevation Model (DEM). This does not require a pre-event SAR image, so it does not rely on interferometric phase remaining coherent during eruption and emplacement. Synthetic tests predicts that we can estimate lava thickness of as little as �9 m, given a minimum of 5 interferograms with suitably large orbital baseine separations. In the case of continuous motion, such as lava flow subsidence, we invert interferometric phase simultaneously for topographic change and displacement. We demonstrate the method using data from Santiaguito volcano, Guatemala, and measure increases in lava thickness of up to 140 m between 2000 and 2009, largely associated with activity between 2000 and 2005. We find a mean extrusion rate of 0.43 +/- 0.06 m3/s, which lies within the error bounds of the longer term extrusion rate between 1922-2000. The thickest and youngest parts of the flow deposit were shown to be subsiding at an average rate of �-6 cm/yr. This is the first time that flow thickness and subsidence have been measured simultaneously. We expect this method to be suitable for measurment of landslides and other mass flow deposits as well as lava flows.

Enteric coated spheres produced by extrusion/spheronization provide effective gastric protection and efficient release of live therapeutic bacteria

We present a novel but simple enteric coated sphere formulation containing probiotic bacteria (Lactobacillus casei). Oral delivery of live bacterial cells (LBC) requires live cells to survive firstly manufacturing processes and secondly GI microbicidal defenses including gastric acid. We incorporated live L. casei directly in the granulation liquid, followed by granulation, extrusion, spheronization, drying and spray coating to produce dried live probiotic spheres. A blend of MCC, calcium-crosslinked alginate, and lactose was developed that gave improved live cell survival during manufacturing, and gave excellent protection from gastric acid plus rapid release in intestinal conditions. No significant loss of viability was observed in all steps except drying, which resulted in approximately 1 log loss of viable cells. Eudragit coating was used to protect dried live cells from acid, and microcrystalline cellulose (MCC) was combined with sodium alginate to achieve efficient sphere disintegration leading to rapid and complete bacterial cell release in intestinal conditions. Viability and release of L. casei was evaluated in vitro in simulated GI conditions. Uncoated spheres gave partial acid protection, but enteric coated spheres effectively protected dried probiotic LBC from acid for 2 h, and subsequently released all viable cells within 1h of transfer into simulated intestinal fluid.