Search results for "isotherm"

Cure monitoring of catalysed cyanate ester resins

2000

The cure behaviour of two bisphenol A-based cyanate ester resins, AroCy B10 and B30, catalysed by copper acetylacetonate and nonylphenol was studied. For this purpose, differential scanning calorimetric (DSC) and rheological measurements were carried out at temperatures between 130 and 170 °C. The cyanate conversion profiles are fitted with a second-order rate law in the kinetically controlled regime where a good time–temperature superposition is attained. However, it is necessary to add an empirical kinetic term to give a good description of the entire range of curing. Simultaneously, times to gelation and vitrification have been determined by dynamic rheological measurements over the same…

Morphology and thermal behavior of dicyanate ester-polyetherimide semi-IPNS cured at different conditions

2000

A high-temperature thermosetting bisphenol-A dicyanate, BADCy was modified with polyetherimide, PEI, at various compositions. Phase separation and rheokinetics through curing were studied by optical microscopy, dynamic and isothermal differential scanning calorimetry, and rheological measurements. The PEI phase separated at the early stages of curing, well before gelation, and did not affect the polycyclotrimerization kinetics. The phase structure and thermal properties of the final network were investigated as a function of the PEI content and cure temperature. For this purpose, dynamic mechanical analysis, scanning electron microscopy studies, and thermogravimetrical analysis were carried…

Polymeric matrix hydrophobicity governs saponin packing-density on nanoparticle surface and the subsequent biological interactions.

2020

Abstract This study investigated the loading behavior of Quillaja saponin as a model surface-active cargo on (NP) nanoparticles prepared with various hydrophobic polymers and using different organic solvents through emulsification/solvent evaporation, and the impact of NP surface hydrophobicity upon the cytotoxic and hemolytic properties of the loaded entity. A superficial monolayered arrangement of saponins on NP was established (R2 > 0.9) for all NP, as the saponin loading values complied with the Langmuir adsorption isotherm over the entire concentration range. Next, based on the measurement of interfacial tension between formulation phases, and the subsequent use of Gibb’s adsorption is…

Thermodynamics of Surfactant, Block Copolymer and Their Mixtures in Water: The Role of the Isothermal Calorimetry

2009

The thermodynamics of conventional surfactants, block copolymers and their mixtures in water was described to the light of the enthalpy function. The two methodologies, i.e. the van't Hoff approach and the isothermal calorimetry, used to determine the enthalpy of micellization of pure surfactants and block copolymers were described. The van't Hoff method was critically discussed. The aqueous copolymer+surfactant mixtures were analyzed by means of the isothermal titration calorimetry and the enthalpy of transfer of the copolymer from the water to the aqueous surfactant solutions. Thermodynamic models were presented to show the procedure to extract straightforward molecular insights from the …

Olive mill wastewaters decontamination based on organo-nano-clay composites

2019

Abstract Green composites for environmental applications were successfully prepared by intercalation of the biosurfactant Quillaja saponin onto montmorillonite mineral clay on varying pH and surfactant/clay ratio. Equilibrium adsorption isotherms were constructed and the system was characterized by performing TGA and XRD analyses. The efficiency of the surfactant-modified clay in the removal of the organic content present in olive mill wastewaters (OMW) was evaluated by means of spectrophotometric measurements. The interest for this cogent issue comes from the consideration that, despite their high pollutant content, OMW can be considered as a potential resource of several organic compounds…

Hygrothermal effect on moisture kinetics and mechanical properties of hemp/polypropylene composite: Experimental and numerical studies

2015

The exposition of thermoplastic composites reinforced with natural fibers to moisture and heat is likely to lower their mechanical properties and restrain their use in the design of parts. The present work is focussed on investigating the effects of hygrothermal aging on the mechanical behaviour of injected polypropylene reinforced with short hemp fibers. Moreover, the kinetic of isothermal moisture absorption has been studied for four immersion temperatures. The experimental results show that the time taken to reach saturation decreases significantly with increase in immersion temperature. These tests also reveal that moisture absorption in this type of materials does not follow Fick's law…

Improved experimental characterization of crystallization kinetics

2005

Polymer solidification occurring in many processes, like for instance injection molding, compression molding and extrusion, is a complex phenomenon, strongly influenced by the thermo-mechanical history experienced by the material during processing. From this point of view, characterization of polymer crystallization in the range of processing con- ditions, i.e. including high cooling rate, is of great technological and academic interest. Quiescent, non-isothermal crys- tallization kinetics of two polypropylene resins were investigated using a new method, based on fast cooling of thin samples with air/water sprays and optical detection of the crystallization phenomenon. The range of cooling …

Polymer Solidification under Pressure and High Cooling Rates

2000

Abstract Polymer solidification under processing conditions is a complex phenomenon in which the kinetics of flow, high thermal gradients and high pressures determine the product morphology. The study of polymer structure formed under pressure has been mainly made using conventional techniques such as dilatometry and differential scanning calorimetry under isothermal conditions or non isothermal conditions but at cooling rates several orders of magnitude lower than those experienced in industrial processes. A new equipment has been recently developed and improved to study the crystallization of polypropylene when subjected to pressure and cooled rapidly. An experimental apparatus essentiall…

1989

Heat of crystallization significantly slows down polymer cooling and thus pressure drop increase during mould filling with thermoplastic crystalline polymers. If a correction of thermal diffusivity can account for such a cooling slow down at least as far as the effect on pressure drop is concerned, the use of nonisothermal crystallization kinetics may be avoided in the simulation of mould filling. A procedure to identify such a correction is outlined in this work. Pressure drop values during cavity filling calculated by using a corrected thermal diffusivity in the model proposed by Lord and Williams favourably compare with literature data taken with polypropylene and polyethylene resins. Be…

Allosteric Models for Multimeric Proteins:  Oxygen-Linked Effector Binding in Hemocyanin

2005

In many crustaceans, changing concentrations of several low molecular weight compounds modulates hemocyanin oxygen binding, resulting in lower or higher oxygen affinities of the pigment. The nonphysiological effector caffeine and the physiological modulator urate, the latter accumulating in the hemolymph of the lobster Homarus vulgaris during hypoxia, increase hemocyanin oxygen affinity and decrease cooperativity of oxygen binding. To derive a model that describes the mechanism of allosteric interaction between hemocyanin and oxygen in the presence of urate or caffeine, studies of oxygen, urate, and caffeine binding to hemocyanin were performed. Exposure of lobster hemocyanin to various pH …