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Gel Time (gel + time)

Distribution by Scientific Domains

Polymers and Materials Science	100%

Selected Abstracts

Properties of phenol,formaldehyde resin modified with organic acid esters

JOURNAL OF APPLIED POLYMER SCIENCE, Issue 5 2008
Rados, aw Mirski
Abstract Properties of liquid and cured phenol,formaldehyde (PF) resin modified with esters were analyzed in this study. Esters with different carbon chain lengths, both in the acid and alcohol groups, were applied in the experiments. It was found that the modification of phenolic resin with applied esters does not deteriorate its pot life at the temperature of 20°C. It results in an increase of its reactivity at higher temperatures, manifested in the shortening of gel time at 130°C and a decrease of activation energy. Results of FTIR tests of polycondensed modified PF resin showed that products of alkali hydrolysis of esters not only catalyze the curing reaction of resin, but also become embedded in its structure. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source]

Properties of epoxy systems with clay nanoparticles

MACROMOLECULAR SYMPOSIA, Issue 1 2003
Markéta Zelenková Mysková
Abstract Low molecular epoxy resin was mixed with different concentrations of montmorillonite clay with alkylamine-modified surface. The presence of the clay nanoparticles influences the gel time of the amine cured resin as well as the mechanical properties. Toughness and modulus, both in the glass and the rubberlike region, increase with clay concentration. An increasing amount of lower mobility phase with increased clay concentration was observed. [source]

Preparation and properties of polyurethane/montmorillonite nanocomposites cured under room temperature

POLYMER COMPOSITES, Issue 5 2006
Hangbin Jiang
The polyurethane/C16C18 -MMT (the montmorillonite modified with cetyloctadecyldimethyl ammonium bromide) nanocomposites were synthesized by intercalative polymerization and cured under room temperature. The d -spacing and the dispersion of the C16C18 -MMT in the nanocomposites were measured by X-ray Diffraction (XRD) and Transmission Electron Microscope (TEM). The mechanical and thermal properties of the nanocomposites were measured by Universal Testing System, Electric Anti-fold Instrument, Thermogravimetric Analysis (TGA), and Differential Scanning Calorimetry (DSC). It was found out that introducing C16C18 -montmorillonite (MMT) in the polyurethane (PU) displayed good mechanical properties and thermal stability. Rheology behavior in liquid state showed that the addition of the C16C18 -MMT to PU resulted in low gel time and high viscosity. POLYM. COMPOS. 27:470,474, 2006. © 2006 Society of Plastics Engineers. [source]

Processability studies of silica-thermoset polymer matrix nanocomposites

POLYMER ENGINEERING & SCIENCE, Issue 2 2008
C. Lekakou
The aim of this study is to investigate the processability of silica-thermoset polymer matrix nanocomposites in terms of dispersion of silica nanoparticles and their effect on curing. Two thermosetting resins were considered, an epoxy and a polyester resin, with 5% silica, although 1% silica was also used in preliminary studies in the polyester system. Various combinations of mechanical mixing and sonication were investigated for the dispersion of silica nanoparticles under different processing conditions and times in solvent-free and solvent-containing systems. It was found that the best dispersion route involved a solvent-aided dispersion technique. Consequently, different procedures for the solvent removal were investigated. Optical microscopy and SEM were used to characterize the resulting nanocomposites. DSC and rheological DMTA tests demonstrated that the silica nanoparticles shorten the gel time and promote curing in these thermosetting systems. POLYM. ENG. SCI., 2008. © 2007 Society of Plastics Engineers [source]

Gel point prediction of metal-filled castor oil-based polyurethanes system,

POLYMERS FOR ADVANCED TECHNOLOGIES, Issue 10-12 2002
Anil Srivastava
Abstract Prediction of gel point conversion and network formation is of great importance in polycondensation during synthesis as well as processing. It enables one to estimate the safe conversions for reactor operation without gelation and the cycle time during processing, and plays an important role in controlling the molding parameters used for reinforced reaction injection molding (RRIM), reaction injection molding (RIM) and compression molding. Theories of gelation have been extensively published in the literature and supported by experimental data for various polycondensation systems. However, most such studies relate to unfilled systems. In this work, metal-filled polyurethanes have been synthesized in bulk by reacting toluene di-isocyanate with castor oil and its polyols possessing different hydroxyl values. Metallic aluminum powder (10,40% by weight) was dispersed thoroughly in castor oil and its polyols before reacting at different temperatures (30,60,°C) in a moisture-free, inert environment. The gel point conversions were measured experimentally and an empirical model from the experimental data has been developed to predict the gelation behavior. The proposed model could be of immense importance in the paints, adhesives and lacquers industries, which use castor oil in bulk. From these experiments it was concluded that: (i) fine metal powder gives a rise in viscosity; (ii) metal fillers not only restrict the molecular motion due to the increase in viscosity, but also lower the conversion; (iii) the vegetable oil and its polyols have a number of bulky groups, which also impart the delay tendency in gel time; (iv) there is a change in gelation dynamics at 50,°C , this is due to the change in reactivity of di-isocyanates; (v) the presence of metal filler does not initiate the intermolecular condensation; (vi) there is a gap between theoretical and experimental gel point owing to the unequal reactivity of the secondary alcohol position; (vii) there is an inverse relationship of gel time with the reaction temperature and hydroxyl value of polyols. An empirical model based on process parameters, i.e., hydroxyl value, temperature, shape factor and filler concentration, has been derived and found to be adequate for the metal-filled system. The correlation coefficient on the data is on the lower side in some cases because the following were not taken into account: (i) the first-order kinetics followed by the reaction in the second half while it is tending towards gelation; (ii) the error in observing the gel point viscosity; (iii) errors in assuming the spherical shape of aluminum metal powder; (iv) errors due to failure to maintain the constant speed in agitation. Copyright © 2003 John Wiley & Sons, Ltd. [source]