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Abstract Explanations of the deviations of polymer crystallisation isotherms from Avrami equations are considered in the light of the assumptions inherent in the derivation of the equations and analysis of the crystallisation isotherms;... more
Abstract Explanations of the deviations of polymer crystallisation isotherms from Avrami equations are considered in the light of the assumptions inherent in the derivation of the equations and analysis of the crystallisation isotherms; these explanations are rejected. ...
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An account is given of the construction of a simple thermistor-bridge thermostat unit suitable for a hot-stage microscope and capable of giving a temperature control within ±0.02 degC. Such a control is necessary for measuring... more
An account is given of the construction of a simple thermistor-bridge thermostat unit suitable for a hot-stage microscope and capable of giving a temperature control within ±0.02 degC. Such a control is necessary for measuring crystallization kinetics of stereoregular polymers.
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The kinetics of enthalpic relaxation in compatible blends of polyether ehter ketone, PEEK and polyetherimide, PEI have been measured by DSC, and interpreted in terms of a broad spectrum of relaxation processes, in that the overall... more
The kinetics of enthalpic relaxation in compatible blends of polyether ehter ketone, PEEK and polyetherimide, PEI have been measured by DSC, and interpreted in terms of a broad spectrum of relaxation processes, in that the overall fractional extent of conversion φ(t) at time t obeys the relationship, 1−φ(t)=exp(−t/τ)β, where τ is the relaxation time and β is a measure of the reciprocal breadth of the relaxation spectrum. Similar analysis has been carried on the dynamic and dielectric response of the blends, but there is little similarity in the β values so determined. Although the 50:50 blend exhibits a single glass transition temperature, the observed value of β, 0.2 for the dielectric relaxation spectra is consistent with some heterogeneity developing at the molecular level.
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Page 1. Polymer International Polym Int 55:611 (2006) DOI: 10.1002/pi.1903 Isothermal crystallization and spherulite nucleation in blends of polypropylene with metallocene-prepared polyethylene Mohammad Razavi-Nouri1 ...
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ABSTRACT The evidence for a radical elimination of hydrogen chloride during the thermal degradation of homopolymers and copolymers of vinylidene chloride is summarized and confirmed by an ESR spectroscopic study of the degradation... more
ABSTRACT The evidence for a radical elimination of hydrogen chloride during the thermal degradation of homopolymers and copolymers of vinylidene chloride is summarized and confirmed by an ESR spectroscopic study of the degradation residues. However, sufficient differences in the degradation characteristics exist between these polymers and those of vinyl chloride to suggest that a radical process alone is not sufficient. No evidence of a radical process can be obtained from an ESR spectroscopic analysis of the elimination. The paramagnetic character of the degraded polymer is attributed to the polyene structure produced on dehydrochlorination.
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ABSTRACT A liquid crystal, BL038, which was observed not to crystallize, has a glass transition at 215 K and a nematic to isotropic transition at 380 K. Samples aged below the glass transition at various temperatures T a, exhibited an... more
ABSTRACT A liquid crystal, BL038, which was observed not to crystallize, has a glass transition at 215 K and a nematic to isotropic transition at 380 K. Samples aged below the glass transition at various temperatures T a, exhibited an endotherm at the transition which developed with extent of ageing time, t a. We attribute this endotherm to the relaxation of the glass towards the equilibrium liquid. The progress of the relaxation process was measured using differential scanning calorimetry. On subsequent reheating, the aged glass showed an apparent shift in the glass transition to higher temperatures. The endotherm was used to define the extent of enthalpic relaxation and the maximum value observed was found to increase initially then decrease, with the extent of undercooling from the glass transition temperature, Δ T, passing through a maximum for a Δ T = 15 K. From the temperature dependence of the relaxation times, an apparent activation enthalpy for the relaxation process of 85 ± 10 kJ mol-1 was determined. The small value of the activation enthalpy compared with that found in the ageing of polymers reflects differences in the molecular species involved in relaxation processes.
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ABSTRACT The molecular weight distribution of fractionated and unfractionated polystyrene samples has been determined by temperature drop turbidimetry, in which polymer is precipitated from dilute solutions in cyclohexanol by... more
ABSTRACT The molecular weight distribution of fractionated and unfractionated polystyrene samples has been determined by temperature drop turbidimetry, in which polymer is precipitated from dilute solutions in cyclohexanol by progressively cooling from 388 to 310 K. Estimates of the molecular weight averages and the polydispersities, obtained by calibration of the temperature of initial onset of precipitation, Ti, and the weight-average molecular weight were low, but could be substantially improved by correcting for concentration changes during precipitation. An empirical procedure correlating the breadth of turbidity-temperature curves to the logarithm of the polydispersity, as measured by gel permeation chromatography, appeared to be a simpler method of characterizing the polymer samples and as accurate as the computational methods above.
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ABSTRACT A kinetic model simulating the glass transition and enthalpic relaxation in poly(3-hydroxybutyrate) is introduced. The model is based on the concept that enthalpic relaxation or physical ageing is a continuation of the glass... more
ABSTRACT A kinetic model simulating the glass transition and enthalpic relaxation in poly(3-hydroxybutyrate) is introduced. The model is based on the concept that enthalpic relaxation or physical ageing is a continuation of the glass forming process and uses the KWW function to describe the glass formation process and the subsequent ageing of the glass. Non-linearity is introduced by incorporating a dependence of the relaxation time on the fictive temperature. The effects of non-linearity on the distribution of relaxation times and the physical ageing process are investigated together with the development of the endothermic ageing peak at the glass transition with increasing extents of ageing.
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ABSTRACT The relationships between the molecular weight and several thermal properties of 2,2-bis(4-hydroxy-phenyl)propane polycarbonate are reported. It is shown that the amount of thermal degradation, measured thermogravimetrically,... more
ABSTRACT The relationships between the molecular weight and several thermal properties of 2,2-bis(4-hydroxy-phenyl)propane polycarbonate are reported. It is shown that the amount of thermal degradation, measured thermogravimetrically, increases with decrease in molecular weight and is affected by the nature of the end groups present. The heat of fusion at the crystalline melting point has been measured by differential scanning calorimetry and correlated with density and X-ray diffraction estimates of total crystallinity. The heats of melting obtained were 30.4 cal/g and 32.9 cal/g respectively. The effect of molecular weight on specific heat, annealing peaks and glass transition temperature are also reported.
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Page 1. Crystallization Characteristics of Polymer Blends. I. Polyethylene and Polystyrene AHMAD AREF-AZAR, JAMES N. HAY,* BRIAN J. MARSDEN, and NEIL WALKER, The Centre for Materials Science and The Department ...
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ABSTRACT Crosslinking of amorphous poly (ether ether ketone) films was carried out by means of thermal annealing at 400°C as well as by irradiation with 11.0 MeV proton beam at different dose rate ranging from 1.75 to 15.5 kW g−1. The... more
ABSTRACT Crosslinking of amorphous poly (ether ether ketone) films was carried out by means of thermal annealing at 400°C as well as by irradiation with 11.0 MeV proton beam at different dose rate ranging from 1.75 to 15.5 kW g−1. The materials properties of the resulting films were investigated by mean of light microscopy, sol-gel analysis, two-dimensional infra-red correlation spectroscopy, 2DCOS-IR, and differential scanning calorimetry (DSC). It was found that both chain scission and crosslinking yields were decreased by an increase of dose rate and the ratio of crosslinks to chain scission was increased from 0.9 to 1.4. The 2DCOS-IR analysis in the region 1400–1800 cm−1 showed progressive development of new bands at 1470 and 1740 cm−1, which have been used to support the presence of crosslinking and chain scission reactions. The glass transition temperature also increased in line with increasing crosslinking density, but the results showed a limiting plateau value for the glass transition , which depended only on the absorbed dose. This suggests that crosslinking was limited and did not increase after a specific value of the dose rate. Crosslinking by irradiation has many advantages over thermal annealing; in particular it is a one step rapid process producing a variety of homogeneously crosslinked, good quality films available for chemical modification. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 41999.
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ABSTRACT A liquid crystal, BL038, which was observed not to crystallize, has a glass transition at 215 K and a nematic to isotropic transition at 380 K. Samples aged below the glass transition at various temperatures T a, exhibited an... more
ABSTRACT A liquid crystal, BL038, which was observed not to crystallize, has a glass transition at 215 K and a nematic to isotropic transition at 380 K. Samples aged below the glass transition at various temperatures T a, exhibited an endotherm at the transition which developed with extent of ageing time, t a. We attribute this endotherm to the relaxation of the glass towards the equilibrium liquid. The progress of the relaxation process was measured using differential scanning calorimetry. On subsequent reheating, the aged glass showed an apparent shift in the glass transition to higher temperatures. The endotherm was used to define the extent of enthalpic relaxation and the maximum value observed was found to increase initially then decrease, with the extent of undercooling from the glass transition temperature, Δ T, passing through a maximum for a Δ T = 15 K. From the temperature dependence of the relaxation times, an apparent activation enthalpy for the relaxation process of 85 ± 10 kJ mol-1 was determined. The small value of the activation enthalpy compared with that found in the ageing of polymers reflects differences in the molecular species involved in relaxation processes.
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... 7 Lakshmi, VV; Choudhary, V.; Varma, IK Macromolecules Symp 2004, 210, 21–29. Direct Link: ... 8 Muthu, LRTS; Choudhary, V.; Varma, IK J Mater Sci 2005, 40, 629–636. ... 9 Yen, SPS; Narayanan, SR; Halpert, G.; Graham, E.; Yavrouian,... more
... 7 Lakshmi, VV; Choudhary, V.; Varma, IK Macromolecules Symp 2004, 210, 21–29. Direct Link: ... 8 Muthu, LRTS; Choudhary, V.; Varma, IK J Mater Sci 2005, 40, 629–636. ... 9 Yen, SPS; Narayanan, SR; Halpert, G.; Graham, E.; Yavrouian, A. US Patent 5,795,496, 1998. ...
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The effects of irradiation with ions, EB, and γ rays on poly(ether-ether-ketone) (PEEK) have been extensively studied,210 and it has been shown that the predominant process that accounts for the change in properties of amorphous PEEK is... more
The effects of irradiation with ions, EB, and γ rays on poly(ether-ether-ketone) (PEEK) have been extensively studied,210 and it has been shown that the predominant process that accounts for the change in properties of amorphous PEEK is crosslinking. However, to our ...
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The strain fields around diamond-shaped cavities in cold-drawn rigid PVC have been determined by the application of fine grids to the specimen surface. An element of material adjacent to the diamond tip deforms predominantly in simple... more
The strain fields around diamond-shaped cavities in cold-drawn rigid PVC have been determined by the application of fine grids to the specimen surface. An element of material adjacent to the diamond tip deforms predominantly in simple shear with a direction of strain parallel to the draw direction. Each element attains a maximum shear strain before the next element begins to shear. This process, possibly analogous to neck propagation in tensile tests, produces the characteristic diamond shape. Simple extension and simple shear tests on cold-drawn PVC confirm that under the stress system around a cavity, simple shear in the draw direction is a favourable mode of deformation.