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Imane Belyamani, Joshua U. Otaigbe, Dana Nelson, Brian Strom, James Roberds
Rheological properties of southern pine oleoresins
Appl. Rheol. 25:5 (2015) 53708 (12 pages) ►

Despite the economic and ecologic importance of pine oleoresins, their rheology remains little explored. In this report we describe rheological properties of oleoresins produced by mature trees of four southern pines native to North America (loblolly, slash, longleaf, shortleaf). Results indicate that these oleoresins are structured fluids that exhibit viscoelastic behavior, but differ in flow behavior. Slash pine oleoresin exhibited Newtonian flow behavior while the oleoresin from the longleaf and shortleaf pines showed pseudoplastic behavior and the loblolly pine oleoresin showed Bingham fluid behavior with a yield stress of about 1.980 Pa. Temperature-dependent viscosities for the oleoresin samples studied were well described by the Arrhenius model, yielding flow activation energies ranging from 153.5 to 219.7 kJ/mol. The viscosity of the slash pine oleoresin sample was found to be less sensitive to temperature than that of the shortleaf or longleaf pine samples. The time-temperature superposition principle was successfully applied to pine oleoresins to show behavior over the temperature range of 25 - 65°C typical for a thermorheologically simple system. Such behavior is consistent with the temperature dependent viscoelastic properties found for these complex fluids, and supports the effective use of rheological evaluations for describing physical properties of pine oleoresins.

► Cite this publication as follows:
Belyamani I, Otaigbe JU, Nelson D, Strom B, Roberds J: Rheological properties of southern pine oleoresins, Appl. Rheol. 25 (2015) 53708.

Yan Meng, Joshua Otaigbe
Mechanism of unexpected viscosity decrease of polymer melts by low-Tg inorganic phosphate glass during processing
Appl. Rheol. 21:4 (2011) 42654 (11 pages) ►

We report unprecedented non-Einstein-like viscosity decrease of polymer melts by special low glass transition, Tg, inorganic tin fluorophosphate glass (Pglass) that is remarkably counter to widely accepted dispersions, suspensions, and composites theories. The well dispersed low-Tg Pglass dramatically decrease the polymer melt viscosity while increasing its Young's modulus in the solid state at low loading (<2%) however decreasing with high loading (>2%), making the hybrid Pglass/polymer solid material stronger yet easier to process in the liquid state. Disruption of the Nylon 6 melt dynamics, strong physicochemical interactions, and submicrometer nanophase separation (proved by rheometry, FTIR, DSC, SEM, NMR and XRD) are thought to be responsible for this experimental fact. This finding should beneficially impact our ability to prepare lower viscosity, very highly filled Nylon 6 melts from already existing materials and polymer processing methods such as injection molding and extrusion, making the simple strategy potentially widely applicable in a number of applications such as thinner barrier resistant thin films, composites, and membranes for heterogeneous catalysis.

► Cite this publication as follows:
Meng Y, Otaigbe J: Mechanism of unexpected viscosity decrease of polymer melts by low-Tg inorganic phosphate glass during processing, Appl. Rheol. 21 (2011) 42654.

Sunil B. Adalja, Joshua U. Otaigbe
Melt rheology of tin phosphate glasses
Appl. Rheol. 11:1 (2001) 10-18 ►

The melt rheology of a low Tg tin phosphate glass [Pglass] has been studied with oscillatory shear flow experiments to accelerate efforts to melt process the glass with different organic polymers. The w dependence of the complex viscosity h* of the Pglass is easily predicted by a modified Rouse model with two relaxation times. The complex viscosity of the glass at different temperatures and frequencies can be superposed and described by the Arrhenius equation. At higher temperatures, the melt viscosity of the Pglass increased monotonically with time. This viscosity rise is thought to be due to sample crystallization. The Pglass was melt-mixed with two different thermoplastic polymers (low-density polyethylene and polystyrene) to produce unique hybrid materials with interesting microstructures.

► Cite this publication as follows:
Adalja SB, Otaigbe JU: Melt rheology of tin phosphate glasses, Appl. Rheol. 11 (2001) 10.

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