An infrared spectroscopic study of the phase transitions of crystalline aromatic donor-acceptor complexes involving a pseudoplastic state

Variable temperature i.r. spectroscopic studies of weak pi-donor-pi-acceptor complexes in the crystalline state indicate that the complexes undergo order-disorder transitions, the disorder being caused by molecular motion. Thermodynamic data on the phase transitions along with the spectral data suggest that the high-temperature crystalline forms of the complexes are likely to be pseudoplastic.

Laminar forced convection to a pseudoplastic fluid food in circular and annular ducts

In this manuscript we investigated experimentally the steady-state heat transfer to an important pseudoplastic fluid food, the soursop juice, flowing in laminar regime through circular and concentric annular ducts. The mean convection heat transfer coefficients, determined by measuring the bulk temperatures before and after the heating sections with constant temperatures of the tube walls, were used to correlate simple new empiric expressions to estimate the average Nusselt number in the thermal entrance of the considered geometries. In addition, the thermophysical properties of the tested fluid food, as well as the rheological behavior, being essential for the heat transfer analyses, were experimentally determined. (c) 2006 Elsevier Ltd. All rights reserved.

Examination of the flow rheological and textural properties of polymer gels composed of poly(methylvinylether-co-maleic anhydride) and poly(vinylpyrrolidone): rheological and mathematical interpretation of textural parameters.

The purpose of this study was to mathematically characterize the effects of defined experimental parameters (probe speed and the ratio of the probe diameter to the diameter of sample container) on the textural/mechanical properties of model gel systems. In addition, this study examined the applicability of dimensional analysis for the rheological interpretation of textural data in terms of shear stress and rate of shear. Aqueous gels (pH 7) were prepared containing 15% w/w poly(methylvinylether-co-maleic anhydride) and poly(vinylpyrrolidone) (PVP) (0, 3, 6, or 9% w/w). Texture profile analysis (TPA) was performed using a Stable Micro Systems texture analyzer (model TA-XT 2; Surrey, UK) in which an analytical probe was twice compressed into each formulation to a defined depth (15 mm) and at defined rates (1, 3, 5, 8, and 10 mm s-1), allowing a delay period (15 s) between the end of the first and beginning of the second compressions. Flow rheograms were performed using a Carri-Med CSL2-100 rheometer (TA Instruments, Surrey, UK) with parallel plate geometry under controlled shearing stresses at 20.0°?±?0.1°C. All formulations exhibited pseudoplastic flow with no thixotropy. Increasing concentrations of PVP significantly increased formulation hardness, compressibility, adhesiveness, and consistency. Increased hardness, compressibility, and consistency were ascribed to enhanced polymeric entanglements, thereby increasing the resistance to deformation. Increasing probe speed increased formulation hardness in a linear manner, because of the effects of probe speed on probe displacement and surface area. The relationship between formulation hardness and probe displacement was linear and was dependent on probe speed. Furthermore, the proportionality constant (gel strength) increased as a function of PVP concentration. The relationship between formulation hardness and diameter ratio was biphasic and was statistically defined by two linear relationships relating to diameter ratios from 0 to 0.4 and from 0.4 to 0.563. The dramatically increased hardness, associated with diameter ratios in excess of 0.4, was accredited to boundary effects, that is, the effect of the container wall on product flow. Using dimensional analysis, the hardness and probe displacement in TPA were mathematically transformed into corresponding rheological parameters, namely shearing stress and rate of shear, thereby allowing the application of the power law (??=?k?n) to textural data. Importantly, the consistencies (k) of the formulations, calculated using transformed textural data, were statistically similar to those obtained using flow rheometry. In conclusion, this study has, firstly, characterized the relationships between textural data and two key instrumental parameters in TPA and, secondly, described a method by which rheological information may be derived using this technique. This will enable a greater application of TPA for the rheological characterization of pharmaceutical gels and, in addition, will enable efficient interpretation of textural data under different experimental parameters.

Formulation and characterisation of tetracycline-containing bioadhesive polymer networks designed for the treatment of periodontal disease.

This study described the drug release, rheological (dynamic and flow) and textural/mechanical properties of a series of formulations composed of 15% w/w polymethylvinylether-co-maleic anhydride (PMVE-MA), 0-9% w/w polyvinylpyrrolidone (PVP) and containing 1-5% w/w tetracycline hydrochloride, designed for the treatment of periodontal disease. All formulations exhibited pseudoplastic flow with minimal thixotropy. Increasing the concentration of PVP sequentially increased the zero-rate viscosity (derived from the Cross model) and the hardness and compressibility of the formulations (derived from texture profile analysis). These affects may be accredited to increased polymer entanglement and, in light of the observed synergy between the two polymers with respect to their textural and rheological properties, interaction between PVP and PMVE-MA. Increasing the concentration of PVP increased the storage and loss moduli yet decreased the loss tangent of all formulations, indicative of increased elastic behaviour. Synergy between the two polymers with respect to their viscoelastic properties was observed. Increased adhesiveness, associated with increased concentrations of PVP was ascribed to the increasing bioadhesion and tack of the formulations. The effect of increasing drug concentration on the rheological and textural properties was dependent on PVP concentration. At lower concentrations (0, 3% w/w) no effect was observed whereas, in the presence of 9% w/w PVP, increasing drug concentration increased formulation elasticity, zero rate viscosity, hardness and compressibility. These observations were ascribed to the greater mass of suspended drug in formulations containing the highest concentration of PVP. Drug release from formulations containing 6 and 9% PVP (and 5% w/w drug) was prolonged and swelling/diffusion controlled. Based on the drug release, rheological and textural properties, it is suggested that the formulation containing 15% w/w PMVE-MA, 6% w/w PVP and tetracycline hydrochloride (5% w/w) may be useful for the treatment of periodontal disease.

An examination of the rheological and mucoadhesive properties of poly(Acrylic acid) organogels designed as platforms for local drug delivery to the oral cavity

This study examined the rheological/mucoadhesive properties of poly (acrylic acid) PAA organogels as platforms for drug delivery to the oral cavity. Organogels were prepared using PAA (3%, 5%, 10% w/w) dissolved in ethylene glycol (EG), propylene glycol (PG), 1,3-propylene glycol (1,3-PG), 1,5-propanediol (1,5-PD), polyethylene glycol 400 (PEG 400), or glycerol. All organogels exhibited pseudoplastic flow. The increase in storage (G') and loss (G '') moduli of organogels as a function of frequency was minimal, G '' was greater than G '' (at all frequencies), and the loss tangent <1, indicative of gel behavior. Organogels prepared using EG, PG, and 1,3-propanediol (1,3-PD) exhibited similar flow/viscoelastic properties. Enhanced rheological structuring was associated with organogels prepared using glycerol (in particular) and PEG 400 due to their interaction with adjacent carboxylic acid groups on each chain and on adjacent chains. All organogels (with the exception of 1,5-PD) exhibited greater network structure than aqueous PAA gels. Organogel mucoadhesion increased with polymer concentration. Greatest mucoadhesion was associated with glycerol-based formulations, whereas aqueous PAA gels exhibited the lowest mucoadhesion. The enhanced network structure and the excellent mucoadhesive properties of these organogels, both of which may be engineered through choice of polymer concentration/solvent type, may be clinically useful for the delivery of drugs to the oral cavity.

Moisture-Activated Rheological Structuring of Nonaqueous Poloxamine–Poly(Acrylic Acid) Systems Designed as Novel Biomedical Implants

This study reports the formulation/characterisation of novel polymeric platforms designed to behave as low-viscosity systems in the nonaqueous state, however, following uptake of aqueous ?uids, exhibit rheological structuring and mucoadhesion. The rheological/mechanical and mucoadhesive properties of platforms containing poly(acrylic acid) (PAA, 1%, 3%, 5%, w/w) and poloxamines (Tetronic 904, 901, 704, 701, 304), both in the absence and presence of phosphate buffered saline (PBS, pH 7.4) are described. With the exception of Tetronic 904, all formulations exhibited Newtonian ?ow in the nonaqueous state, whereas, all aqueous formulations displayed pseudoplastic ?ow. The consistency and viscoelastic properties were dependent on the concentrations of PAA and PBS and Tetronic grade. PBS signi?cantly increased the consistency, viscoelasticity and mucoadhesion, reaching a maximum at a de?ned concentration of PBS that was dependent on PAA concentration and Tetronic grade. Formulations containing Tetronic 904 exhibited greatest consistency and elasticity both prior to and after dilution with PBS. Increasing PAA concentration enhanced the mucoadhesive properties. Prolonged drug release of metronidazole was observed from formulations containing 10% (w/w) PBS, 3% and, particularly, 5% (w/w) PAA. It is suggested that the physicochemical properties of formulations containing 3% or 5% (w/w) PAA and Tetronic 904, would render them suitable platforms for administration to body cavities.

Rheological destructuring of aqueous gels composed of cellulose ethers following storage in the presence of redox agents

Despite their widespread use, there is a paucity of information concerning the effect of storage on the rheological properties of pharmaceutical gels that contain organic and inorganic additives. Therefore, this study examined the effect of storage (1 month at either 4 or 37 degrees C) on the rheological and mechanical properties of gels composed of either hydroxypropylmethylcellulose (3-5% w/w, HPMC) or hydroxyethylcellulose (3-5% w/w, HEC) and containing or devoid of dispersed organic (tetracycline hydrochloride 2% w/w) or inorganic (iron oxide 0.1% w/w) agents. The mechanical properties were measured using texture profile analysis whereas the rheological properties were analyzed using continuous shear rheometry and modeled using the Power Law model. All formulations exhibited pseudoplastic flow with minimal thixotropy. Increasing polymer concentration (3-5% w/w) significantly increased the consistency, hardness, compressibility, and adhesiveness of the formulations due to increased polymer chain entanglement. Following storage (I month at 4 and 37 degrees C) the consistency and mechanical properties of additive free HPMC gets (but not HEC gels) increased, due to the time-dependent development of polymer chain entanglements. Incorporation of tetracycline hydrochloride significantly decreased and increased the rheological and mechanical properties of HPMC and HEC gels, respectively. Conversely, the incorporation of iron oxide did not affect these properties. Following storage, the rheological and mechanical properties of HPMC and HEC formulations were markedly compromised. This effect was greater following storage at 37 than at 4 degrees C and, additionally, greater in the presence of tetracycline hydrochloride than iron oxide. It is suggested that the loss of rheological/mechanical structure was due to chain depolymerization, facilitated by the redox properties of tetracycline hydrochloride and iron oxide. These observations have direct implications for the design and formulation of gels containing an active pharmaceutical ingredient. (c) 2005 Wiley Periodicals, Inc.

Propriedades intrínsecas e de processamento de termoplásticos elastoméricos incorporando borracha de pneu reciclada

O trabalho apresentado tem por objetivo contribuir para a valorização da borracha proveniente de pneus em fim de vida, assente em princípios de sustentabilidade ambiental. A abordagem adotada para a concretização deste objetivo consiste na incorporação de borracha de pneus em formulações de base termoplástica e elastomérica (TPE), adequadas ao processo de moldação por injeção. São desenvolvidos estudos sobre a morfologia, propriedades mecânicas, térmicas e reológicas das ligas poliméricas à base de granulado de borracha de pneu (GTR). A falta de adesão entre o GTR e a matriz polimérica leva à degradação das propriedades mecânicas dos materiais obtidos. A estratégia explorada passa pela utilização de um elastómero para promover o encapsulamento do GTR e, desta forma, procurar obter ligas com propriedades mecânicas características de um TPE. São analisadas ligas ternárias (TPEGTR) compostas por polipropileno (PP) de elevada fluidez, GTR e elastómero virgem. O efeito da presença de diferentes elastómeros nas ligas é analisado neste trabalho: um elastómero de etilenopropileno- dieno (EPDM), e um novo elastómero de etileno-propileno (EPR) obtido por catálise metalocénica. O estudo da morfologia das ligas obtidas mostra haver interação entre os materiais, sendo possível inferir a viabilidade da estratégia adotada para promover a adesão do GTR. A incorporação de elastómero promove o aumento da resistência ao impacto e da extensão na rotura nas ligas, o que é atribuído, fundamentalmente, ao encapsulamento do GTR e ao aumento da tenacidade da matriz termoplástica. Com o objetivo de avaliar a influência da estrutura cristalina das ligas TPEGTR no seu comportamento mecânico, procede-se à análise do processo de cristalização sob condições isotérmicas e não isotérmicas. Neste estudo, é avaliado o efeito da presença dos materiais que constituem a fase elastomérica na cinética de cristalização. Para cada uma das ligas desenvolvidas, recorre-se ao modelo de Avrami para avaliar o efeito da temperatura no mecanismo de nucleação, na morfologia das estruturas cristalinas e na taxa de cristalização. Recorre-se à reometria capilar para estudar, sob condições estacionárias, o comportamento reológico das ligas TPEGTR. O modelo de Cross-WLF é utilizado para avaliar o comportamento reológico de todos os materiais, obtendo-se resultados similares àqueles obtidos experimentalmente. O comportamento reológico dos polímeros PP, EPR e EPDM é do tipo reofluidificante, tendo o EPR um comportamento reológico similar ao do PP e o EPDM um comportamento reo-fluidificante mais pronunciado. Em todas as ligas analisadas o comportamento reológico revela-se do tipo reo-fluidificante, sendo que a presença de GTR promove o aumento da viscosidade. Os parâmetros obtidos do modelo de Cross-WLF são utilizados para realizar a simulação da etapa de injeção recorrendo a um software comercial. Os resultados obtidos são validados experimentalmente pelo processo de moldação por injeção, evidenciando uma boa adequabilidade da aplicação deste modelo a estas ligas. O trabalho desenvolvido sobre ligas TPEGTR, constitui um contributo para a valorização da borracha proveniente de pneus em fim de vida, assente em princípios de sustentabilidade ambiental.

Préparations de docosanol nanoformulées pour usage topique

La réduction de la taille des particules jusqu’à l’obtention de nanocristaux est l’une des approches utilisées afin d’améliorer la pénétration cutanée des médicaments à usage topique. Nous proposons que la fabrication d’une formulation semi solide (hydrogel) à base de nanosuspension de docosanol, aboutira à une diffusion du principe actif supérieure à celle du produit commercial Abreva®, à travers des membranes synthétiques de polycarbonates. Le broyage humide est la technique proposée pour la production des nanoparticules de docosanol. Nous proposons aussi la préparation d’une formulation semi-solide (hydrogel) à usage topique à partir de la nanosuspension de docosanol. La nanosuspension de docosanol est obtenue par dispersion du docosanol en solution aqueuse en présence du polymère stabilisant hydroxypropylcellulose (HPC) et du surfactant laurylsulfate de sodium (SDS) suivi d’un broyage humide à faible ou à haute énergie. L’hydrogel de docosanol nanoformulé est préparé à l’aide de la nanosuspension de docosanol qui subit une gélification par le carbopol Ultrez 21 sous agitation mécanique suivie d’une neutralisation au triéthanolamine TEA. La taille des particules de la nanosuspension et de l’hydrogel a été déterminée par diffusion dynamique de la lumière (DLS). Une méthode analytique de chromatographie liquide à haute performance (HPLC) munie d’un détecteur évaporatif (ELSD) a été développée et validée pour évaluer la teneur de docosanol dans les préparations liquides, dans les différentes nanosuspensions et dans les hydrogels de docosanol. L’état de cristallinité des nanocristaux dans la nanosuspension et dans l’hydrogel a été étudié par calorimétrie différentielle à balayage. La morphologie de la nanosuspension et de l’hydrogel de docosanol a été examinée par microscopie électronique à balayage (MEB). Les propriétés rhéologiques et de stabilité physique à différentes températures ont été aussi étudiées pour la formulation semi-solide (hydrogel). De même, la libération in vitro du docosanol contenu dans l’hydrogel et dans le produit commercial Abreva® a été étudiée à travers deux membranes de polycarbonates de taille de pores 400 et 800 nm. Dans le cas de nanosuspensions, des cristaux de docosanol de taille nanométrique ont été produits avec succès par broyage humide. Les nanoparticules de tailles variant de 197 nm à 312 nm ont été produites pour des pourcentages différents en docosanol, en polymère HPC et en surfactant SDS. Après lyophilisation, une augmentation de la taille dépendant de la composition de la formulation a été observée tout en restant dans la gamme nanométrique pour la totalité presque des formulations étudiées. Dans le cas des hydrogels examinés, la taille moyenne des particules de docosanol est maintenue dans la gamme nanométrique avant et après lyophilisation. L’analyse thermique des mélanges physiques, des nanosuspensions et des hydrogels de docosanol a révélé la conservation de l’état de cristallinité des nanocristaux de docosanol après broyage et aussi après gélification. L’examen par microscopie électronique à balayage (MEB) a montré que la nanosuspension et l’hydrogel ont tous deux une morphologie régulière et les nanoparticules ont une forme sphérique. De plus les nanoparticules de la nanosuspension ont presque la même taille inférieure à 300 nm en accord avec le résultat obtenu par diffusion dynamique de la lumière (DLS). Les nanoparticules de l’hydrogel ont une légère augmentation de taille par rapport à celle de la nanosuspension, ce qui est en accord avec les mesures de DLS. D’après les mesures rhéologiques, l’hydrogel de docosanol a un comportement pseudoplastique et un faible degré de thixotropie. L’étude de stabilité physique a montré que les formulations d’hydrogel sont stables à basse température (5°C) et à température ambiante (21°C) pendant une période d’incubation de 13 semaines et instable au-delà de 30°C après deux semaines. La méthode HPLC-ELSD a révélé des teneurs en docosanol comprises entre 90% et 110% dans le cas des nanosuspensions et aux alentours de 100% dans le cas de l’hydrogel. L’essai de diffusion in vitro a montré qu’il y a diffusion de docosanol de l’hydrogel à travers les membranes de polycarbonates, qui est plus marquée pour celle de pore 800 nm, tandis que celui du produit commercial Abreva® ne diffuse pas. Le broyage humide est une technique bien adaptée pour la préparation des nanosuspensions docosanol. Ces nanosuspensions peuvent être utilisée comme base pour la préparation de l’hydrogel de docosanol nanoformulé.

Rheological Characteristics of Short Nylon -6 Fiber Reinforced Styrene Butadiene Rubber Containing Epoxy Resin as Bonding Agent

The rheological characteristics of short Nylon-6 fiber-reinforced Styrene Butadiene rubber (SBR) in the presence of epoxy resin-based bonding agent were studied with respect to the effect of shear rate, fiber concentration , and temperature on shear viscosity and die swell using a capillary rheonzeter. All the composites containing bonding agent showed a pseudoplastic nature, which decreased with increasing temperature. Shear viscosity was increased in the presence of fibers. The temperature sensitivity of the SBR matrices was reduced on introduction of fibers. The temperature sensitivity of the melts was found to be lower at higher shear rates. Die swell was reduced in the presence of fibers. Relative viscosity of the composites increased with shear rate. In the presence of epoxy resin bonding agent the temperature sensitivity of the mixes increased. Die swell was larger in the presence of bonding agent.

Rheology of Short Nylon -6 Fiber Reinforced Styrene-Butadiene Rubber

The rheological characteristics of short Nylon-6 fiber reinforced styrene butadiene rubber (SBR) were studied using a capillary rheometer. The study was done with respect to the effect of shear rate, fiber concentration, and temperature on shear viscosity and die swell. All the melts showed pseudoplastic nature, which decreased with increasing temperature. Shear viscosity increased in the presence of fibers. Introduction of fiber reduces the temperature sensitivity of the rubber matrix. A reduction in die swell was found in presence of fibers.

Rheological Properties of Short Polyester Fiber-Polyurethane Elastomer Composite with Different Interfacial Bonding Agents

The rheological behavior of a short-polyester-fiber-filled polyurethane elastomer composite containing different bonding agents has been studied in the temperature range 120-160°C and in the shear rate range 63-608 s-'. The composite with and without bonding agents showed a pseudoplastic behavior which decreased with the increase of temperature. Composites containing bonding agents based on polypropyleneglycol and 4,4'-diphenylmethanediisocyanate showed the lowest viscosity values at a particular shear rate, whereas composites containing a glycerol- (GL) based bonding agent showed the highest viscosity. The viscosity of the composite decreased sharply after a particular temperature (140°C) and the fall was less drastic in the composite containing a GL-based bonding agent.

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.

“Studies on short polyester fiber - polyurethane elastomer composite with different interfacial bonding agents”

The work presented in this thesis is regarding the development and evaluation of new bonding agents for short polyester fiber - polyurethane elastomer composites. The conventional bonding system based on hexamethylenetetramine, resorcinol and hydrated silica was not effective as a bonding agent for the composite, as the water eliminated during the formation of the RF resin hydrolysed the urethane linkages. Four bonding agents based on MDI/'I‘DI and polypropyleneglycol, propyleneglycol and glycerol were prepared and the composite recipe was optimised with respect to the cure characteristics and mechanical properties. The flow properties, stress relaxation pattern and the thermal degradation characteristics of the composites containing different bonding agents were then studied in detail to evaluate the new bonding systems. The optimum loading of resin was 5 phr and the ratio of the -01 to isocyanate was 1:1. The cure characteristics showed that the optimum combination of cure rate and processability was given by the composite with the resin based on polypropyleneglycol/ glycerol/ 4,4’diphenylmethanediisocynate (PPG/GL/MDI). From the rheological studies of the composites with and without bonding agents it was observed that all the composites showed pseudoplastic nature and the activation energy of flow of the composite was not altered by the presence of bonding agents. Mechanical properties such as tensile strength, modulus, tear resistance and abrasion resistance were improved in the presence of bonding agents and the effect was more pronounced in the case of abrasion resistance. The composites based on MDI/GL showed better initial properties while composites with resins based on MDI/PPG showed better aging resistance. Stress relaxation showed a multistage relaxation behaviour for the composite. Within the-strain levels studied, the initial rate of relaxation was higher and the cross over time was lesser for the composite containing bonding agents. The bonding agent based on MDI/PPG/GL was found to be a better choice for improving stress relaxation characteristics with better interfacial bonding. Thennogravimetirc analysis showed that the presence of fiber and bonding agents improved the thennal stability of the polyurethane elastomer marginally and it was maximum in the case of MDI / GL based bonding agents. The kinetics of degradation was not altered by the presence of bonding agents