Processing and Characterization of Nano-biocomposites Based on Mater-Bi® with Layered Silicates

The development of new nano-biocomposites has been one of the main research areas of interest in polymer science in recent years, since they can combine the intrinsic biodegradable nature of matrices with the ability to modify their properties by the addition of selected nano-reinforcements. In this work, the addition of mineral nanoclays (montmorillonites and sepiolites) to a commercial starch-based matrix is proposed. A complete study on their processing by melt-intercalation techniques and further evaluation of the main properties of nano-biocomposites has been carried out. The results reported show an important influence of the nano-biocomposites morphology on their final properties. In particular, the rheological and viscoelastic characteristics of these systems are very sensitive to the dispersion level of the nanofiller, but it is possible to assess that the material processing behaviour is not compromised by the presence of these nano-reinforcements. In general, both nanofillers had a positive influence in the materials final properties. Mechanical performance shows improvements in terms of elastic modulus, without important limitations in terms of ductility. Thermal properties are improved in terms of residual mass after degradation and low improvements are also observed in terms of oxygen barrier properties.

Bio-based PLA_PHB plasticized blend films: Processing and structural characterization

Bio-based films formed by poly(lactic acid) (PLA) and poly(3-hydroxybutyrate) (PHB) plasticized with an oligomer of the lactic acid (OLA) were used as supporting matrices for an antibacterial agent (carvacrol). This paper reports the main features of the processing and physico-chemical characterization of these innovative biodegradable material based films, which were extruded and further submitted to filmature process. The effect of the addition of carvacrol and OLA on their microstructure, chemical, thermal and mechanical properties was assessed. The presence of these additives did not affect the thermal stability of PLA_PHB films, but resulted in a decrease in their crystallinity and in the elastic modulus for the active formulations. The obtained results showed the effective presence of additives in the PLA or the PLA_PHB matrix after processing at high temperatures, making them able to be used in active and bio-based formulations with antioxidant/antimicrobial performance.

Spectroscopie Raman de fibres électrofilées : développement de méthodes et application aux fibres individuelles

L’électrofilage est une technique de mise en œuvre efficace et versatile qui permet la production de fibres continues d’un diamètre typique de quelques centaines de nanomètres à partir de l’application d’un haut voltage sur une solution concentrée de polymères enchevêtrés. L’évaporation extrêmement rapide du solvant et les forces d’élongation impliquées dans la formation de ces fibres leur confèrent des propriétés hors du commun et très intéressantes pour plusieurs types d’applications, mais dont on commence seulement à effleurer la surface. À cause de leur petite taille, ces matériaux ont longtemps été étudiés uniquement sous forme d’amas de milliers de fibres avec les techniques conventionnelles telles que la spectroscopie infrarouge ou la diffraction des rayons X. Nos connaissances de leur comportement proviennent donc toujours de la convolution des propriétés de l’amas de fibres et des caractéristiques spécifiques de chacune des fibres qui le compose. Les études récentes à l’échelle de la fibre individuelle ont mis en lumière des comportements inhabituels, particulièrement l’augmentation exponentielle du module avec la réduction du diamètre. L’orientation et, de manière plus générale, la structure moléculaire des fibres sont susceptibles d’être à l'origine de ces propriétés, mais d’une manière encore incomprise. L’établissement de relations structure/propriétés claires et l’identification des paramètres qui les influencent représentent des défis d’importance capitale en vue de tirer profit des caractéristiques très particulières des fibres électrofilées. Pour ce faire, il est nécessaire de développer des méthodes plus accessibles et permettant des analyses structurales rapides et approfondies sur une grande quantité de fibres individuelles présentant une large gamme de diamètre. Dans cette thèse, la spectroscopie Raman confocale est utilisée pour l’étude des caractéristiques structurales, telles que l’orientation moléculaire, la cristallinité et le désenchevêtrement, de fibres électrofilées individuelles. En premier lieu, une nouvelle méthodologie de quantification de l’orientation moléculaire par spectroscopie Raman est développée théoriquement dans le but de réduire la complexité expérimentale de la mesure, d’étendre la gamme de matériaux pour lesquels ces analyses sont possibles et d’éliminer les risques d’erreurs par rapport à la méthode conventionnelle. La validité et la portée de cette nouvelle méthode, appelée MPD, est ensuite démontrée expérimentalement. Par la suite, une méthodologie efficace permettant l’étude de caractéristiques structurales à l’échelle de la fibre individuelle par spectroscopie Raman est présentée en utilisant le poly(éthylène téréphtalate) comme système modèle. Les limites de la technique sont exposées et des stratégies expérimentales pour les contourner sont mises de l’avant. Les résultats révèlent une grande variabilité de l'orientation et de la conformation d'une fibre à l'autre, alors que le taux de cristallinité demeure systématiquement faible, démontrant l'importance et la pertinence des études statistiques de fibres individuelles. La présence de chaînes montrant un degré d’enchevêtrement plus faible dans les fibres électrofilées que dans la masse est ensuite démontrée expérimentalement pour la première fois par spectroscopie infrarouge sur des amas de fibres de polystyrène. Les conditions d'électrofilage favorisant ce phénomène structural, qui est soupçonné d’influencer grandement les propriétés des fibres, sont identifiées. Finalement, l’ensemble des méthodologies développées sont appliquées sur des fibres individuelles de polystyrène pour l’étude approfondie de l’orientation et du désenchevêtrement sur une large gamme de diamètres et pour une grande quantité de fibres. Cette dernière étude permet l’établissement de la première relation structure/propriétés de ces matériaux, à l’échelle individuelle, en montrant clairement le lien entre l’orientation moléculaire, le désenchevêtrement et le module d'élasticité des fibres.

Spectroscopie Raman de fibres électrofilées : développement de méthodes et application aux fibres individuelles

L’électrofilage est une technique de mise en œuvre efficace et versatile qui permet la production de fibres continues d’un diamètre typique de quelques centaines de nanomètres à partir de l’application d’un haut voltage sur une solution concentrée de polymères enchevêtrés. L’évaporation extrêmement rapide du solvant et les forces d’élongation impliquées dans la formation de ces fibres leur confèrent des propriétés hors du commun et très intéressantes pour plusieurs types d’applications, mais dont on commence seulement à effleurer la surface. À cause de leur petite taille, ces matériaux ont longtemps été étudiés uniquement sous forme d’amas de milliers de fibres avec les techniques conventionnelles telles que la spectroscopie infrarouge ou la diffraction des rayons X. Nos connaissances de leur comportement proviennent donc toujours de la convolution des propriétés de l’amas de fibres et des caractéristiques spécifiques de chacune des fibres qui le compose. Les études récentes à l’échelle de la fibre individuelle ont mis en lumière des comportements inhabituels, particulièrement l’augmentation exponentielle du module avec la réduction du diamètre. L’orientation et, de manière plus générale, la structure moléculaire des fibres sont susceptibles d’être à l'origine de ces propriétés, mais d’une manière encore incomprise. L’établissement de relations structure/propriétés claires et l’identification des paramètres qui les influencent représentent des défis d’importance capitale en vue de tirer profit des caractéristiques très particulières des fibres électrofilées. Pour ce faire, il est nécessaire de développer des méthodes plus accessibles et permettant des analyses structurales rapides et approfondies sur une grande quantité de fibres individuelles présentant une large gamme de diamètre. Dans cette thèse, la spectroscopie Raman confocale est utilisée pour l’étude des caractéristiques structurales, telles que l’orientation moléculaire, la cristallinité et le désenchevêtrement, de fibres électrofilées individuelles. En premier lieu, une nouvelle méthodologie de quantification de l’orientation moléculaire par spectroscopie Raman est développée théoriquement dans le but de réduire la complexité expérimentale de la mesure, d’étendre la gamme de matériaux pour lesquels ces analyses sont possibles et d’éliminer les risques d’erreurs par rapport à la méthode conventionnelle. La validité et la portée de cette nouvelle méthode, appelée MPD, est ensuite démontrée expérimentalement. Par la suite, une méthodologie efficace permettant l’étude de caractéristiques structurales à l’échelle de la fibre individuelle par spectroscopie Raman est présentée en utilisant le poly(éthylène téréphtalate) comme système modèle. Les limites de la technique sont exposées et des stratégies expérimentales pour les contourner sont mises de l’avant. Les résultats révèlent une grande variabilité de l'orientation et de la conformation d'une fibre à l'autre, alors que le taux de cristallinité demeure systématiquement faible, démontrant l'importance et la pertinence des études statistiques de fibres individuelles. La présence de chaînes montrant un degré d’enchevêtrement plus faible dans les fibres électrofilées que dans la masse est ensuite démontrée expérimentalement pour la première fois par spectroscopie infrarouge sur des amas de fibres de polystyrène. Les conditions d'électrofilage favorisant ce phénomène structural, qui est soupçonné d’influencer grandement les propriétés des fibres, sont identifiées. Finalement, l’ensemble des méthodologies développées sont appliquées sur des fibres individuelles de polystyrène pour l’étude approfondie de l’orientation et du désenchevêtrement sur une large gamme de diamètres et pour une grande quantité de fibres. Cette dernière étude permet l’établissement de la première relation structure/propriétés de ces matériaux, à l’échelle individuelle, en montrant clairement le lien entre l’orientation moléculaire, le désenchevêtrement et le module d'élasticité des fibres.

Long-term in vivo biostability of poly(dimethylsiloxane) / poly(hexamethylene oxide) mixed macrodiol-based polyurethane elastomers

The long-term biostability of a novel thermoplastic polyurethane elastomer (Elast-Eon(TM) 2 80A) synthesized using poly(hexamethylene oxide) (PHMO) and poly(dimethylsiloxane) (PDMS) macrodiols has been studied using an in vivo ovine model. The material's biostability was compared with that of three commercially available control materials, Pellethane(R) 2363-80A, Pellethane(R) 2363-55D and Bionate(R) 55D, after subcutaneous implantation of strained compression moulded flat sheet dumbbells in sheep for periods ranging from 3 to 24 months. Scanning electron microscopy, attenuated total reflectance-Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy were used to assess changes in the surface chemical structure and morphology of the materials. Gel permeation chromatography, differential scanning calorimetry and tensile testing were used to examine changes in bulk characteristics of the materials. The results showed that the biostability of the soft flexible PDMS-based test polyurethane was significantly better than the control material of similar softness, Pellethane(R) 80A, and as good as or better than both of the harder commercially available negative control polyurethanes. Pellethane(R) 55D and Bionate(R) 55D. Changes observed in the surface of the Pellethane(R) materials were consistent with oxidation of the aliphatic polyether soft segment and hydrolysis of the urethane bonds joining hard to soft segment with degradation in Pellethane(R) 80A significantly more severe than that observed in Pellethane(R) 55D. Very minor changes were seen on the surfaces of the Elast-Eon(TM) 2 80A and Bionate(R) 55D materials. There was a general trend of molecular weight decreasing with time across all polymers and the molecular weights of all materials decreased at a similar relative rate. The polydispersity ratio, M-w/M-n, increased with time for all materials. Tensile tests indicated that UTS increased in Elast-Eon(TM) 2 80A and Bionate(R) 55D following implantation under strained conditions. However, ultimate strain decreased and elastic modulus increased in the explanted specimens of all three materials when compared with their unimplanted unstrained counterparts. The results indicate that a soft, flexible PDMS-based polyurethane synthesized using 20% PHMO and 80% PDMS macrodiols has excellent long-term biostability compared with commercially available polyurethanes. (C) 2004 Elsevier Ltd. All rights reserved.

Effect of deposition conditions on mechanical properties of low-temperature PECVD silicon nitride films

The effect of deposition conditions on characteristic mechanical properties - elastic modulus and hardness - of low-temperature PECVD silicon nitrides is investigated using nanoindentation. lt is found that increase in substrate temperature, increase in plasma power and decrease in chamber gas pressure all result in increases in elastic modulus and hardness. Strong correlations between the mechanical properties and film density are demonstrated. The silicon nitride density in turn is shown to be related to the chemical composition of the films, particularly the silicon/nitrogen ratio. (c) 2006 Elsevier B.V. All rights reserved.

The automation of resonant thermometer probe measurements

An ultrasonic thermometer has been developed for high temperature measurement over a wide temperature range. It is particularly suitable for use in measuring nuclear fuel rod centerline temperatures in advanced liquid metal and high flux nuclear reactors. The thermometer which was designed to determine fuel temperature up to the fuel melting point, utilizes the temperature dependence of the ultrasonic propagation velocity (related to the elastic modulus} in a thin rod sensor as the temperature transducing mechanism. A pulse excitation technique has been used, where the mechanical resonator at the remote end of the acoustic·line is madto vibrate. Its natural frequency is proportional to the ultrasonic velocity in the material. This is measured by the electronic instrumentation and enables a frequency­ temperature or period-temperature calibration to be obtained. A completely digital automatic instrument has been designed, constructed and tested to track the resonance frequency of the temperature sensors. It operates smoothly over a frequency range of about 30%, more than the maximum working range of most probe materials. The control uses the basic property of a resonator that the stored energy decays exponentially at the natural frequency of the resonator.The operation of the electronic system is based on a digital multichannel transmitter that is capable of operating with a predefined number of cycles in the burst. this overcomes a basic defect in the previous deslgn where the analogue time-delayed circuits failed to hold synchronization and hence automatic control could be lost. Development of a particular type of temperature probe, that is small enough to fit into a standard 2 mm reactor tube has made the ultrasonic thermometer a practicable device for measuring fuel temperature. The bulkiness of previous probes has been overcome, the new design consists of a tuning fork, integral with a 1mm line, while maintaining a frequency of no more than 100 kHz. A magnetostrictive rod, acoustically matched to the probe is used to launch and receive the acoustic oscillations. This requires a magnetic bias and the previously used bulky magnets have been replaced by a direct current coil. The probe is supported by terminating the launcher with a short heavy isolating rod which can be secured to the reactor structure. This support, the bias and launching coil and the launcher are made up into a single compact unit. On the material side an extensive study of a wide range of refractory materials identified molybdenum, iridium, rhenium and tungsten as satisfactory for a number of applications but mostly exhibiting to some degree a calibration drift with thermal cycling. When attention was directed to ceramic materials, Sapphire (single crystal alumina) was found to have numerous advantages, particularly in respect of stability of calibration which remained with ±2°C after many cycles to 1800oC. Tungsten and thoriated tungsten (W - 2% Tho2) were also found to be quite satisfactory to 1600oC, the specification for a Euratom application.

Osmotic dehydration in plant tissues

The primary aim of the thesis is to provide a comprehensive investigation of the osmotic dehydration processes in plant tissue. Effort has been concentrated on the modelling for simulating the processes. Two mathematical models for simulating the mass transfer during osmotic dehydration processes in plant tissues are developed and verified using existing experimental data. Both models are based on the mechanism of diffusion and convection of any mobile material that can transport in plant tissues. The mass balance equation for the transport of each constituent is established separately for intracellular and extra-cellular volumes with taking into account the mass transfer across the cell membrane the intracellular and extra-cellular volumes and the shrinkage of the whole tissue. The contribution from turgor pressure is considered in both models. Model two uses Darcy’s law to build the relation between shrinkage velocity and hydrostatic pressure in each volume because the plant tissue can be considered as the porous medium. Moreover, it has been extended to solve the multi-dimensional problems. A lot of efforts have been made to the parameter study and the sensitivity analyses. The parameters investigated including the concentration of the osmotic solution, diffusion coefficient, permeability of the cell membrane, elastic modulus of the cell wall, critical cell volume etc. The models allow us to quantitatively simulate the time evolution of intracellular and extra-cellular volumes as well as the time evolution of concentrations in each cross-section.

The structural permeability of concrete at cryogenic temperatures

The thesis describes a programme of research designed to identify concretes for application at cryogenic temperature, in particular for storage of Liquefield Natural Gas which is maintained at a temperature of -165oC. The programme was undertaken in two stages. Stage 1 involved screening tests on seventeen concrete mixes to investigate the effects of strength grade (and water/cement ratio), air entrainment, aggregate type and cement type. Four mixes were selected on the basis of low temperature strength, residual strength after thermal cycling and permeability at ambient temperature. In Stage 2 the selected mixes were subjected to a comprehensive range of tests to measure those properties which determine the leak tightness of a concrete tank at temperatures down to -165oC. These included gas permeability; tensile strength, strain capacity, thermal expansion coefficient and elastic modulus, which in combination provide a measure of resistance to cracking; and bond to reinforcement, which is one of the determining factors regarding crack size and spacing. The results demonstrated that the properties of concrete were generally enhanced at cryogenic temperature, with reduced permeability, reduced crack proneness and, by virtue of increased bond to reinforcement, better control of cracking should it occur. Of the concretes tested, a lightweight mix containing sintered PFA aggregate exhibited the best performance at ambient and cryogenic temperature, having appreciably lower permeability and higher crack resistance than normal weight concretes of the same strength grade. The lightweight mix was most sensitive to thermal cycling, but there was limited evidence that this behaviour would not be significant if the concrete was prestressed. Relationships between various properties have been identified, the most significant being the reduction in gas permeability with increasing strain capacity. The structural implications of the changing properties of the concrete have also been considered.

Proteoglycan analogues for ophthalmic and orthopaedic applications

The successful development of biomaterials is increasingly influenced by biomimesis essentially the use of biological structures as design templates. This approach has been used here in the design of injectable systems for the nucleus of the intervertebral disc, corneal inlays and intraocular lenses (IOLs). The strategy is based on the use of C-linked sulphonates to mimic the O-linked sulphate groups that are the hydration drivers in proteoglycans. The elastic modulus of the materials can be tailored for specific applications.

Mechanical properties and the evolution of matrix molecules in PTFE upon irradiation with MeV alpha particles

The morphology, chemical composition, and mechanical properties in the surface region of α-irradiated polytetrafluoroethylene (PTFE) have been examined and compared to unirradiated specimens. Samples were irradiated with 5.5 MeV 4He2+ ions from a tandem accelerator to doses between 1 × 106 and 5 × 1010 Rad. Static time-of-flight secondary ion mass spectrometry (ToF-SIMS), using a 20 keV C60+ source, was employed to probe chemical changes as a function of a dose. Chemical images and high resolution spectra were collected and analyzed to reveal the effects of a particle radiation on the chemical structure. Residual gas analysis (RGA) was utilized to monitor the evolution of volatile species during vacuum irradiation of the samples. Scanning electron microscopy (SEM) was used to observe the morphological variation of samples with increasing a particle dose, and nanoindentation was engaged to determine the hardness and elastic modulus as a function of a dose. The data show that PTFE nominally retains its innate chemical structure and morphology at a doses <109 Rad. At α doses ≥109 Rad the polymer matrix experiences increased chemical degradation and morphological roughening which are accompanied by increased hardness and declining elasticity. At  α doses >1010 Rad the polymer matrix suffers severe chemical degradation and material loss. Chemical degradation is observed in ToF-SIMS by detection of ions that are indicative of fragmentation, unsaturation, and functionalization of molecules in the PTFE matrix. The mass spectra also expose the subtle trends of crosslinking within the α-irradiated polymer matrix. ToF-SIMS images support the assertion that chemical degradation is the result of a particle irradiation and show morphological roughening of the sample with increased a dose. High resolution SEM images more clearly illustrate the morphological roughening and the mass loss that accompanies high doses of a particles. RGA confirms the supposition that the outcome of chemical degradation in the PTFE matrix with continuing irradiation is evolution of volatile species resulting in morphological roughening and mass loss. Finally, we reveal and discuss relationships between chemical structure and mechanical properties such as hardness and elastic modulus.

Heavy ion irradiation effects in zirconium nitride

Polycrystalline zirconium nitride (ZrN) samples were irradiated with He +, Kr ++, and Xe ++ ions to high (>1·10 16 ions/cm 2) fluences at ∼100 K. Following ion irradiation, transmission electron microscopy (TEM) and grazing incidence X-ray diffraction (GIXRD) were used to analyze the microstructure and crystal structure of the post-irradiated material. For ion doses equivalent to approximately 200 displacements per atom (dpa), ZrN was found to resist any amorphization transformation, based on TEM observations. At very high displacement damage doses, GIXRD measurements revealed tetragonal splitting of some of the diffraction maxima (maxima which are associated with cubic ZrN prior to irradiation). In addition to TEM and GIXRD, mechanical property changes were characterized using nanoindentation. Nanoindentation revealed no change in elastic modulus of ZrN with increasing ion dose, while the hardness of the irradiated ZrN was found to increase significantly with ion dose. Finally, He + ion implanted ZrN samples were annealed to examine He gas retention properties of ZrN as a function of annealing temperature. He gas release was measured using a residual gas analysis (RGA) spectrometer. RGA measurements were performed on He-implanted ZrN samples and on ZrN samples that had also been irradiated with Xe ++ ions, in order to introduce high levels of displacive radiation damage into the matrix. He evolution studies revealed that ZrN samples with high levels of displacement damage due to Xe implantation, show a lower temperature threshold for He release than do pristine ZrN samples.

High performance liquid level monitoring system based on polymer fiber Bragg gratings embedded in silicone rubber diaphragm

Liquid-level sensing technologies have attracted great prominence, because such measurements are essential to industrial applications, such as fuel storage, flood warning and in the biochemical industry. Traditional liquid level sensors are based on electromechanical techniques; however they suffer from intrinsic safety concerns in explosive environments. In recent years, given that optical fiber sensors have lots of well-established advantages such as high accuracy, costeffectiveness, compact size, and ease of multiplexing, several optical fiber liquid level sensors have been investigated which are based on different operating principles such as side-polishing the cladding and a portion of core, using a spiral side-emitting optical fiber or using silica fiber gratings. The present work proposes a novel and highly sensitive liquid level sensor making use of polymer optical fiber Bragg gratings (POFBGs). The key elements of the system are a set of POFBGs embedded in silicone rubber diaphragms. This is a new development building on the idea of determining liquid level by measuring the pressure at the bottom of a liquid container, however it has a number of critical advantages. The system features several FBG-based pressure sensors as described above placed at different depths. Any sensor above the surface of the liquid will read the same ambient pressure. Sensors below the surface of the liquid will read pressures that increase linearly with depth. The position of the liquid surface can therefore be approximately identified as lying between the first sensor to read an above-ambient pressure and the next higher sensor. This level of precision would not in general be sufficient for most liquid level monitoring applications; however a much more precise determination of liquid level can be made by linear regression to the pressure readings from the sub-surface sensors. There are numerous advantages to this multi-sensor approach. First, the use of linear regression using multiple sensors is inherently more accurate than using a single pressure reading to estimate depth. Second, common mode temperature induced wavelength shifts in the individual sensors are automatically compensated. Thirdly, temperature induced changes in the sensor pressure sensitivity are also compensated. Fourthly, the approach provides the possibility to detect and compensate for malfunctioning sensors. Finally, the system is immune to changes in the density of the monitored fluid and even to changes in the effective force of gravity, as might be obtained in an aerospace application. The performance of an individual sensor was characterized and displays a sensitivity (54 pm/cm), enhanced by more than a factor of 2 when compared to a sensor head configuration based on a silica FBG published in the literature, resulting from the much lower elastic modulus of POF. Furthermore, the temperature/humidity behavior and measurement resolution were also studied in detail. The proposed configuration also displays a highly linear response, high resolution and good repeatability. The results suggest the new configuration can be a useful tool in many different applications, such as aircraft fuel monitoring, and biochemical and environmental sensing, where accuracy and stability are fundamental. © (2015) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.

Grewia gum 1:some mechanical and swelling properties of compact and film

Purpose: To study the mechanical and dynamic swelling properties of grewia gum, evaluate its compression behaviour and determine the effect of drying methods on its properties. Methods: Compacts (500 mg) of both freeze-dried and air-dried grewia gum were separately prepared by compression on a potassium bromide (KBr) press at different pressures and subjected to Heckel analysis. Swelling studies were performed using 200 mg compacts of the gum (freeze-dried or air-dried) compressed on a KBr press. The mechanical properties of the films of the gum prepared by casting 1 % dispersions of the gum were evaluated using Hounsfield tensiometer. The mechanical properties of grewia gum films were compared with films of pullulan and guar gum which were similarly prepared. The effect of temperature on the water uptake of the compacts was studied and the data subjected to Schott's analysis. Results: Drying conditions had no effect on the yield pressure of the gum compacts as both air-dried and freeze-dried fractions had a yield pressure of 322.6 MPa. The plots based on Schott's equation for the grewia gum samples showed that both samples (freeze-dried and air-dried) exhibited long swelling times. Grewia gum film had a tensile strength of 19.22±3.61 MPa which was similar to that of pullulan films (p > 0.05). It had an elastic modulus of 2.13±0.12 N/mm2 which was significantly lower (p < 0.05) than those of pullulan and guar gum with elastic moduli of 3.33±0.00 and 2.86±0.00 N/mm2, respectively. Conclusion: The type of drying method used does not have any effect on the degree of plasticity of grewia gum compacts. Grewia gum obtained by either drying method exhibited extended swelling duration. Matrix tablet formulations of the gum will likely swell slowly and promote sustained release of drug. © Pharmacotherapy Group, Faculty of Pharmacy, University of Benin, Benin City.

Seismic performance of hybrid fiber reinforced polymer-concrete pier frame systems

As an alternative to transverse spiral or hoop steel reinforcement, fiber reinforced polymers (FRPs) were introduced to the construction industry in the 1980’s. The concept of concrete-filled FRP tube (CFFT) has raised great interest amongst researchers in the last decade. FRP tube can act as a pour form, protective jacket, and shear and flexural reinforcement for concrete. However, seismic performance of CFFT bridge substructure has not yet been fully investigated. Experimental work in this study included four two-column bent tests, several component tests and coupon tests. Four 1/6-scale bridge pier frames, consisting of a control reinforced concrete frame (RCF), glass FRP-concrete frame (GFF), carbon FRP-concrete frame (CFF), and hybrid glass/carbon FRP-concrete frame (HFF) were tested under reverse cyclic lateral loading with constant axial loads. Specimen GFF did not show any sign of cracking at a drift ratio as high as 15% with considerable loading capacity, whereas Specimen CFF showed that lowest ductility with similar load capacity as in Specimen GFF. FRP-concrete columns and pier cap beams were then cut from the pier frame specimens, and were tested again in three point flexure under monotonic loading with no axial load. The tests indicated that bonding between FRP and concrete and yielding of steel both affect the flexural strength and ductility of the components. The coupon tests were carried out to establish the tensile strength and elastic modulus of each FRP tube and the FRP mold for the pier cap beam in the two principle directions of loading. A nonlinear analytical model was developed to predict the load-deflection responses of the pier frames. The model was validated against test results. Subsequently, a parametric study was conducted with variables such as frame height to span ratio, steel reinforcement ratio, FRP tube thickness, axial force, and compressive strength of concrete. A typical bridge was also simulated under three different ground acceleration records and damping ratios. Based on the analytical damage index, the RCF bridge was most severely damaged, whereas the GFF bridge only suffered minor repairable damages. Damping ratio was shown to have a pronounced effect on FRP-concrete bridges, just the same as in conventional bridges. This research was part of a multi-university project, which is founded by the National Science Foundation (NSF) - Network for Earthquake Engineering Simulation Research (NEESR) program.