Effect of simple stress on the glass transition of polymers at high pressures

Pae, K. D.; Tang, C.‐L.; Vijayan, Kalyani

doi:10.1007/bf00551509

Cited by 7 publications

(6 citation statements)

References 21 publications

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“…Pae et al used an extension of Gibbs-Dimarzio theory and showed that stress will cause a decrease in the T g of the stressed polymer relative to an unstressed polymer. 57 Strain can also cause the polymer glass transition temperature to increase 58 or decrease. 59 It was proposed that two competing factors contribute to the observed changes in T g with strain: 60 an increase in free volume due to the strain leads to decreasing T g , and a decrease in the polymer conformational entropy leads to an increase in T g .…”

Section: Resultsmentioning

confidence: 99%

Deviations in the Thermal Properties of Ultrathin Polymer Network Films

Lenhart

2002

Macromolecules

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Cross-linked epoxy network films were cast onto silicon wafers with a variety of surface treatments. X-ray reflectivity was used to characterize their electron density and thermal expansion in the rubbery state. A transition from "bulk" to "confined" expansion occurs in the range of 200-400 Å, where thinner films exhibit smaller rubbery expansion coefficients. The thermal expansion behavior of the epoxy films was independent of the substrate surface treatment, which varied in both surface energy and the strength of bonding interactions with the polymer. The thickest epoxy films displayed typical rubbery thermal expansion values for temperatures above the bulk polymer glass transition temperature. The thinnest epoxy films (<120 Å) exhibited typical glassy expansion values even at temperatures 20-40 °C above the bulk polymer glass transition temperature, independent of the surface treatment.

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Section: Resultsmentioning

confidence: 99%

Deviations in the Thermal Properties of Ultrathin Polymer Network Films

Lenhart

2002

Macromolecules

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“…ANOVA showed a significant (p<0.05) drop in polymer T g after HME of the neat polymers, a phenomenon that has been linked to an increase in free volume between the polymer strains due to the shear stress (Pae and Pressure, 1986). This was significant for SOL and EPO, since they have a lower T g and therefore a less rigid structure compared to VA 64.…”

Section: Solid State Characterizationmentioning

confidence: 92%

In-line monitoring of compaction properties on a rotary tablet press during tablet manufacturing of hot-melt extruded amorphous solid dispersions

Grymonpré

Verstraete

Bockstal

et al. 2017

International Journal of Pharmaceutics

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As the number of applications for polymers in pharmaceutical development is increasing, there is need for fundamental understanding on how such compounds behave during tableting. This research is focussed on the tableting behaviour of amorphous polymers, their solid dispersions and the impact of hot-melt extrusion on the compaction properties of these materials. Soluplus, Kollidon VA 64 and Eudragit EPO were selected as amorphous polymers since these are widely studied carriers for solid dispersions, while Celecoxib was chosen as BCS class II model drug. Neat polymers and physical mixtures (up to 35% drug load) were processed by hot-melt extrusion (HME), milled and sieved to obtain powders with comparable particle sizes as the neat polymer. A novel approach was used for in-line analysis of the compaction properties on a rotary tablet press (Modul P, GEA) using complementary sensors and software (CDAAS, GEA). By combining 'in-die' and 'out-of-die' techniques, it was possible to investigate in a comprehensive way the impact of HME on the tableting behaviour of amorphous polymers and their formulations. The formation of stable glassy solutions altered the formulations towards more fragmentary behaviour under compression which was beneficial for the tabletability.Principal component analysis (PCA) was applied to summarize the behaviour during compaction of the formulations, enabling the selection of Soluplus and Kollidon VA 64 as the most favourable polymers for compaction of glassy solutions.

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“…The difference between activation energies for Nafion115 and Nafion NR212 probably can be related to the different processing for these two types of membranes: extrusion is used in processing Nafion 115 while casting for Nafion NR212 membranes. , An extrusion process introduces additional stress to the membrane. It is known that stress tends to reduce the glass transition temperature of an amorphous polymer. , Thus, the annealing temperature used was closer to the glass transition temperature for Nafion 115 than that for Nafion NR 212, which results in a smaller activation energy and a more rapid decay in the ionic conductivity for Nafion 115 membranes.…”

Section: Resultsmentioning

confidence: 99%

“…It is known that stress tends to reduce the glass transition temperature of an amorphous polymer. 53,54 Thus, the annealing temperature used was closer to the glass transition temperature for Nafion 115 than that for Nafion NR 212, which results in a smaller activation energy and a more rapid decay in the ionic conductivity for Nafion 115 membranes. The features revealed in CSAFM images show that the peak current I p , the integrated current I t , and the fwhm of the current distributions of the membranes all change in a synchronized manner, which indicate that conductance of the overall ionic channel network inside the membrane deteriorates upon annealing, but the configuration of the network probably remains about the same.…”

Section: Resultsmentioning

confidence: 99%

Current Sensing Atomic Force Microscopy Study of Thermal Aging of Nafion Membranes

et al. 2017

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We have investigated thermal aging in the ionic conductivity of Nafion membranes being annealed at elevated temperatures using current sensing atomic force microscopy (CSAFM), a unique technique that allows simultaneous imaging surface morphology and surface conductance of the materials. The local current flows on the membranes show an increase after initial annealing, followed by a gradual decrease as the annealing continues. The current distribution extracted from CSAFM images shows that the decrease in the conductance follows approximately an exponential decay which occurs uniformly across the membrane. Least-square fits to the measured conductance versus time t yield time constants at the annealing temperature. Considering aging is a thermally activated process, we used an Arrhenius equation to describe the relationship between the time constant and the annealing temperature, which gives activation energies for the membranes. The activation energy yields following this process are 54 and 83 kJ/mol for Nafion 115 and Nafion NR212, respectively. These results provide guidance for employing the materials for device applications.

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Effect of simple stress on the glass transition of polymers at high pressures

Cited by 7 publications

References 21 publications

Deviations in the Thermal Properties of Ultrathin Polymer Network Films

Deviations in the Thermal Properties of Ultrathin Polymer Network Films

In-line monitoring of compaction properties on a rotary tablet press during tablet manufacturing of hot-melt extruded amorphous solid dispersions

Current Sensing Atomic Force Microscopy Study of Thermal Aging of Nafion Membranes

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