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Shear-thinning Behavior (shear-thinning + behavior)

Distribution by Scientific Domains

Polymers and Materials Science	75%

Selected Abstracts

Thermal and rheological properties of poly(vinyl alcohol) and water-soluble chitosan hydrogels prepared by a combination of ,-ray irradiation and freeze thawing

JOURNAL OF APPLIED POLYMER SCIENCE, Issue 6 2008
Xiaomin Yang
Abstract Poly(vinyl alcohol) (PVA)/water-soluble chitosan (ws-chitosan) hydrogels were prepared by a combination of ,-irradiation and freeze thawing. The thermal and rheological properties of these hydrogels were compared with those of hydrogels prepared by pure irradiation and pure freeze thawing. Irradiation reduced the crystallinity of PVA, whereas freeze thawing increased it. Hydrogels made by freeze thawing followed by irradiation had higher degrees of crystallinity and higher melting temperatures than those made by irradiation followed by freeze thawing. ws-Chitosan disrupted the ordered association of PVA molecules and decreased the thermal stability of both physical blends and hydrogels. All the hydrogels showed shear-thinning behavior in the frequency range of 0.2,100 rad/s. Hydrogels made by freeze thawing dissolved into sol solutions at about 80°C, whereas those made by irradiation showed no temperature dependence up to 100°C. The chemical crosslinking density of the hydrogels made by irradiation followed by freeze thawing was much greater than that of hydrogels made by freeze thawing followed by irradiation. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source]

PHYSICAL, SENSORY AND FLOW PROPERTIES OF WHEAT STARCH,DAIRY BY-PRODUCT SPRAY-DRIED PEKMEZ MIXTURES

JOURNAL OF TEXTURE STUDIES, Issue 2 2008
DURMU
ABSTRACT Pekmez, also known as a concentrated grape juice, was spray dried in a laboratory-type pilot drying unit to obtain pekmez powder (PP). The flow characteristics of PP, wheat starch (WS) and some dairy by-products (whey powder, skim milk powder, calcium caseinate and sodium caseinate) systems as binary and ternary mixtures were studied. The empirical power law model fitted the apparent viscosity,rotational speed data. PP,dairy by-product and WS,dairy by-product mixed solutions exhibited a shear-thinning behavior at 21C with flow behavior index (n) values of 0.86 , n , 0.92 and 0.06 , n , 0.27, respectively. WS,dairy by-product mixed solutions showed high shear-thinning behavior with the highest consistency index (k = 25,425,180,599 mPa·sn). However, PP,WS and PP,WS,dairy by-product mixed solutions at the same temperature exhibited the shear-thickening behavior with flow behavior index (n) values of 1.05 , n , 1.18. PRACTICAL APPLICATIONS Pekmez has become popular as a healthy food product; therefore, its rheologic properties were extensively studied by some researchers. However, pekmez powder (PP) is a new product and has not been produced yet in the food industry. Spray drying of foods has been spread recently in almost all food industry branches because it provides some advantages such as extending the shelf life, storage stability, decreasing the storage costs of the food products, etc. For this reason, production technology is first developed; PP is produced and studied in this study. There is no published data informing the rheologic, physical and sensory properties of pekmez or PP as binary and ternary mixtures with other components such as wheat starch (WS) and any dairy by-product. The purpose of this study was mainly to characterize the rheologic behavior of the PP,WS,dairy by-product mixed solutions and determine their physical and sensory properties. [source]

Rheology and Physical Characteristics of Synthetic Biodegradable Aliphatic Polymer Blends Dispersed with MWNTs

MACROMOLECULAR MATERIALS & ENGINEERING, Issue 4 2010
Seung Woo Ko
Abstract PLA/PBAT blends and PLA/PBAT/MWNT nanocomposite systems were prepared via a melt mixing process to examine their thermal and rheological properties. To compare the polymer blend/MWNT nanocomposite with a pure polymer/MWNT nanocomposite, PLA/MWNT, PBAT/MWNT, and PLA/PBAT/MWNT nanocomposite systems were prepared. TEM and SEM were used to observe that one phase has better affinity with the MWNT, while the MWNT was found to increase both the thermal properties of the PLA/PBAT blends and rheological properties of the PLA/PBAT/MWNT nanocomposite with distinct shear-thinning behavior due to the addition of the MWNT. An increase in the storage (G,) and loss (G,) moduli for the PLA/PBT/MWNT nanocomposite was also observed. [source]

Effect of diatomite/polyethylene glycol binary processing aid on the melt fracture and the rheology of polyethylenes

POLYMER ENGINEERING & SCIENCE, Issue 7 2005
Xiaolong Liu
The influence of polyethylene (PE) glycol (PEG), diatomite, and diatomite/PEG binary processing aid (BPA) on the rheological properties and the sharkskin melt fracture of three PEs was studied using a capillary rheometer. When diatomite or PEG is added to the PE matrix, they have little effect on the viscosity reduction of PEs, while the diatomite/PEG BPA shows a synergetic effect on the viscosity reduction of PEs. The incorporation of small amount of BPA was found to increase the shear-thinning behavior and decrease the melt viscosity significantly. Meanwhile, the critical apparent shear rate for the onset of sharkskin melt fracture of PEs is increased. The mechanism for BPA to improve the rheological properties and the melt flow instability of PEs was discussed. POLYM. ENG. SCI., 45:898,903, 2005. © 2005 Society of Plastics Engineers [source]

Influence of side-chain structures on the viscoelasticity and elongation viscosity of polyethylene melts

POLYMER ENGINEERING & SCIENCE, Issue 11 2002
Gwo-Geng Lin
Metallocene-catalyzed, low-density and linear low-density polyethylenes with similar melt indexes were used to investigate how side-chain structures influence the elongation viscosity and viscoelastic properties. The viscoelastic properties were determined with a rotation rheometer, while the elongation viscosities were acquired by using isothermal fiber spinning. The Phan-Thien-Tanner (PTT) model was also used to understand how the side-chain structure affects the elongation behavior. Experimental results demonstrate that the log G, vs. log G, plot can qualitatively describe the effects of the side chain branch on the rheological properties of polyethylene melts. According to the results determined by the PTT model, low-density polyethylene (LDPE) has low elongation viscosities at high strain rates. This low elongation viscosity can be attributed to the fact that LDPE has high shear thinning behavior. The long-chain branching tends to increase entanglements, thereby enhancing the storage modulus, elongation viscosity and shear-thinning behaviors. Uniform side-chain distribution lowers the entanglements, which results in a low storage modulus, elongation viscosity and shear-thinning behavior. [source]

Synthesis, thermal, and rheological properties of poly(trimethylene terephthalate)/BaSO4 nanocomposites

POLYMERS FOR ADVANCED TECHNOLOGIES, Issue 10 2009
Chenguang Yao
Abstract A novel method was developed for fabricating poly(trimethylene terephthalate) (PTT)/BaSO4 nanocomposites using in situ polymerization. A nano-BaSO4 suspension was prepared by reacting H2SO4 with Ba(OH)2 in 1,3-propanediol (PDO). The mean size of original nano-BaSO4 is 15,23,nm. PTT matrix was synthesized by condensation polymerization of bis(3-hydroxypropyl terephthalate) after the completion of transesterification of dimethyl terephthalate (DMT) with PDO. It was found that the addition of BaSO4 had little influence on the synthesis of PTT. The properties of nanocomposites with a wide range of BaSO4 fraction were systematically studied. The morphologies of the composites were investigated by transmission electron microscopy (TEM), which showed that agglomerate structures did not form until BaSO4 content higher than 8,wt%. The thermal properties of the nanocomposites were investigated by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The DSC results revealed that the triple endothermic melting phenomenon is only observed for the nanocomposites which contained 4,wt% BaSO4, other samples exhibit double endothermic melting. These results indicated that nano-BaSO4 could induce a microcrystal to form more perfect morphology and restrain the formation of much thicker lamellar crystallinity, that is, nano-BaSO4 could induce the formation of more uniform crystallinity. Besides, the crystallization ability of the composites was greatly improved by loading nano-BaSO4. The TGA results suggested that nano-BaSO4 slightly increased the maximum-decomposing-rate temperature 1 (Tmax1), but markedly increased the maximum-decomposing-rate temperature 2 (Tmax2). Furthermore, the steady-state shear behavior of samples was investigated by a parallel-plate rheometer. The storage modulus (G') and loss modulus (G") curves shifted to higher modulus upon addition of 2,16,wt% of nano-BaSO4. All of the samples investigated exhibited the expected shear-thinning behavior. Proper contents of nano-BaSO4 would decrease the shear viscosity of nanocomposites, whereas superfluous amounts would greatly increase the viscosity of nanocomposites and the composites which loaded 8,wt% nano-BaSO4 revealed an equivalent shear viscosity compared to pure PTT. Copyright © 2008 John Wiley & Sons, Ltd. [source]