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Elastic Recovery (elastic + recovery)
Selected AbstractsPolymer Viscoelasticity and Residual Stress Effects on Nanoimprint Lithography,ADVANCED MATERIALS, Issue 10 2007Y. Ding The decay kinetics of polystyrene (PS) gratings are monitored by tracking the intensity of the first-order laser diffraction peak as a function of annealing time. For low-molecular-mass PS (24,kg,mol,1, blue circles), an exponential response suggests that the pattern decay is a surface-tension- driven viscous flow. In high-molecular-mass PS (1007,kg,mol,1, green circles) a complicated response includes a rapid elastic recovery, a power-law creep, and a viscouslike flow (see figure). [source] Modification of cellulose fabrics with reactive polyhedral oligomeric silsesquioxanes to improve their shape-memory performanceJOURNAL OF APPLIED POLYMER SCIENCE, Issue 4 2010Kongliang Xie Abstract Reactive polyhedral oligomeric silsesquioxane (R-POSS) containing multi- N -methylol is a functional and attractive staring monomer for new reinforcement materials. R-POSS has excellent potential as a nanosized core for starburst dendrimers and highly reactive multi- N -methylol. R-POSS can be used for cellulose fabric finishing to improve its shape-memory performance. Factors affecting the crosslinking reaction of the cellulose with R-POSS were investigated. The physical properties and morphological structure of the cellulose fabrics modified with R-POSS are discussed with respect to the crease recovery angle, the whiteness index, micro-Fourier transform infrared spectroscopy, and scanning electron microscopy. The results show that the crease recovery angle of the fabric modified with R-POSS obviously increased. With increasing R-POSS concentration, the crease recovery angle of the modified fabric sharply increased. R-POSS readily crosslinked to cellulose and improved the elastic recovery of the cellulose fabrics. The surfaces of the cellulose fibers modified with R-POSS were smooth and full. The inclusion of R-POSS with dimethylol dihydroxyl ethylene urea to modify the cellulose showed very interesting results. It showed a good combination of an increase of crease recovery angle and a decrease in tensile strength. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010 [source] Crystallization conditions and formation of orthorhombic paracetamol from ethanolic solutionJOURNAL OF PHARMACY AND PHARMACOLOGY: AN INTERNATI ONAL JOURNAL OF PHARMACEUTICAL SCIENCE, Issue 3 2002N. Al-Zoubi Orthorhombic paracetamol exhibits far better tabletability than the monoclinic form and its bulk crystallization from solution attracts much interest. In this study, temperature changes in supersaturated ethanolic solution have been recorded after seeding with orthorhombic crystals under different cooling temperatures (TC) and agitation rates (AR). Average cooling rate (CR), time for maximum temperature deviation (tmax) and area confined between curves of measured and reference temperature plots (AUC) were calculated and correlated with crystal yield (Y). The micromeritic (size and shape) and the compression properties, the density and the orthorhombic content of the crystalline product were evaluated and related to the main crystallization conditions applied (TC and AR). Conditions for optimal crystal yield and orthorhombic content were elucidated. It was found that crystal yield (Y) increased with AR and decreased with TC. The ratio tmax/CR provided good prediction of crystal yield (Y = 58.92 ,1.386 tmax/CR, r2 = 0.964 and P = 0.0001). TC and AR linearly affected crystal size and the size distribution, probably due to alterations in supersaturation, but they did not affect the crystal shape significantly. Density and compression properties (yield pressure and elastic recovery) were determined by the content of the orthorhombic form, which increased linearly with AR (P = 0.009) and with TC (P = 0.039) when agitation was between 300 and 500 rev min,1, while tmax decreased. At 700 rev min,1 orthorhombic content was maximized and became independent to TC. Higher orthorhombic content and crystal yield was expected for lower TC and for lower tmax, which corresponded to higher AR and might have also been affected by alteration of seeding and harvesting procedure. [source] Effect of Mixing Methods on Mechanical Properties of Alginate Impression MaterialsJOURNAL OF PROSTHODONTICS, Issue 4 2005Gary Frey DDS Background: A commercial mechanical mixer is available to make the mixing of alginate more convenient and more consistent for the practitioner; however, there is very little information on the mechanical properties of alginate mixed with this device as compared with hand mixing. Purpose: To compare the mechanical properties of alginate impression materials mixed with a mechanical mixer (Alginator II, Cadco) and hand mixing. Material and Methods: Three alginate impression materials (Identic, Jeltrate, and Kromopan) were tested. Strain in compression, elastic recovery, and compressive strength were measured according to ANSI/ADA specification no. 18-1992; tear energy was measured using a pants tear test. Five specimens were prepared for each group with 12 groups for the mechanical mixer and 12 groups for hand mixing, for a total of 120 specimens. A two-way analysis of variance and Fisher's PLSD test at the 0.05 level of significance were used to analyze the data. Results: There were statistically significant differences in properties among the materials, but mixing technique had no statistically significant effect on strain in compression and tear energy. Conclusion: The mechanical mixer improved elastic recovery and compressive strength of the alginate impression materials tested and had no effect on strain in compression and tear energy. A mechanical mixer facilitates the mixing of alginate impression materials and improves some mechanical properties. [source] Correlating dough elastic recovery during sheeting with flour analyses and rheological propertiesJOURNAL OF THE SCIENCE OF FOOD AND AGRICULTURE, Issue 15 2008DanQiu Ren Abstract The dough rheological behaviors of three flours having different chemical and physical properties were measured, as were changes in thickness and snapback (thickness of the machined dough sheet relative to the roll gap), immediately following sheeting. Dough snapback was determined to be a function of processing parameters, reduction ratio, and dough rest time, as well as different flour properties. The predication equation for dough snapback is based on multiple flour properties and sheeting conditions. Higher protein flours normally have stronger dough properties and larger snapback, compared with low protein flours, but also depend on the protein quality. The snapback will increase either with increased protein content, reduction ratio, or reduced rest time. Dough snapback using flour made by blending two flours 50/50 had intermediate values between the two original flours. Among the variables, Mixograph work, reduction ratio, and dough rest time were the main factors affecting the elastic characteristics of the doughs. Minimum snapback occurred with the weakest flour experiencing the longest rest time and the smallest reduction ratio. A linear 7-factor equation was found to predict the snapback of several flours, by combining reduction ratio, dough rest time, Mixograph work, peak height, and mixing time, Alveograph P/L, and protein content. Only three factor combinations of Mixograph work, reduction ratio, and rest time were needed to develop a second order equation for predicting snapback. Copyright © 2008 Society of Chemical Industry [source] Application of Modified Natural Oils as Reactive Diluents for Epoxy ResinsMACROMOLECULAR SYMPOSIA, Issue 1 2006Piotr Czub Abstract Bisphenol A based low-molecular-weight epoxy resin was modified with epoxidized soybean oil, which exhibit viscosity reducing ability comparable to commercial grade active diluents. The studied compositions showed a non-Newtonian rheological behavior, typical for Bingham liquids. The values of the flow index (n) and the consistency index (k) for the compositions tested in the temperature range 25,65,°C were calculated from the Ostwald-de Waele rheological model and were used to calculate the flow-activation energy (Ea) using the Arhenius equation. Studies of co-crosslinking of mixed oil-resin compositions using isophorone diamine showed essential decrease of the reaction heat and peak maximum temperature. Mechanical properties, thermal stability, water absorption and chemical resistance of the epoxy resin modified with natural oil, were also investigated. Compositions of epoxy resin Ruetapox 0162, modified with the oil diluent, preserved very good mechanical properties of the epoxy resins and demonstrated relatively low water absorption as well as high chemical resistance. The compositions displayed even higher impact strength than pure epoxy resin due to plasticizing effect of the built-in oil. Compositions with the high contents (up to 60 weight %) of the oil were flexible materials with fast elastic recovery. [source] Strain-Controlled Tensile Deformation Behavior and Relaxation Properties of Isotactic Poly(1-butene) and Its Ethylene CopolymersMACROMOLECULAR SYMPOSIA, Issue 1 2004Mahmoud Al-Hussein Abstract The tensile deformation behaviour of poly(1-butene) and two of its ethylene copoloymers was studied at room temperature. This was done by investigating true stress-strain curves at constant strain rates, elastic recovery and stress relaxation properties and in-situ WAXS patterns during the deformation process. As for a series of semicrystalline polymers in previous studies, a strain-controlled deformation behaviour was found. The differential compliance, the recovery properties and the stress relaxation curves changed simultaneously at well-defined points. The strains at which these points occurred along the true stress-strain remained constant for the different samples despite their different percentage crystallinities. The well-defined way in which the different samples respond to external stresses complies with the granular substructure of the crystalline lamellae in a semicrystalline polymer. [source] On surface deformation of melt-intercalated polyethylene,clay nanocomposites during scratchingPOLYMER ENGINEERING & SCIENCE, Issue 11 2006A. Mudaliar Electron microscopy has been used to examine the mechanically-induced surface damage introduced during scratching of polyethylene(PE),clay nanocomposites. The determining role of clay in reducing the susceptibility to surface deformation is predicted from the characteristics of surface morphology and the scratch deformation parameters. The reinforcement of PE with nanoclay reduces the susceptibility to scratch damage and stress whitening. Microcracks and surface deformation features namely wrinkles/ridges are the primary source of light scattering resulting in stress whitening. The scratch deformation behavior is discussed in terms of tensile modulus, percentage crystallinity, elastic recovery, and scratch hardness. Scratch hardness is a relevant parameter that can be appropriately used to determine resistance to scratch deformation. POLYM. ENG. SCI. 46:1625,1634, 2006. © 2006 Society of Plastics Engineers [source] Theoretical and experimental studies of anisotropic shrinkage in injection moldings of semicrystalline polymersPOLYMER ENGINEERING & SCIENCE, Issue 6 2006Keehae Kwon A novel approach to predict anisotropic shrinkage of semicrystalline polymers in injection moldings was proposed using flow-induced crystallization, frozen-in molecular orientation, elastic recovery, and PVT equation of state. The anisotropic thermal expansion and compressibility affected by the frozen-in orientation function and the elastic recovery that was not frozen during moldings were introduced to obtain the in-plane anisotropic shrinkages. The frozen-in orientation function was calculated from amorphous and crystalline contributions. The amorphous contribution was based on the frozen-in and intrinsic amorphous birefringence, whereas the crystalline contribution was based on the crystalline orientation function, which was determined from the elastic recovery and intrinsic crystalline birefringence. To model the elastic recovery and frozen-in stresses related to birefringence during molding process, a nonlinear viscoelastic constitutive equation was used with temperature- and crystallinity-dependent viscosity and relaxation time. Occurrence of the flow-induced crystallization was introduced through the elevation of melting temperature affected by entropy production during flow of the viscoelastic melt. Kinetics of the crystallization was modeled using Nakamura and Hoffman-Lauritzen equations with the rate constant affected by the elevated melting temperature. Numerous injection molding runs on polypropylene of various molecular weights were carried out by varying the packing time, flow rate, melt temperature, and mold temperature. The anisotropic shrinkage of the moldings was measured. Comparison of the experimental and simulated results indicated a good predictive capability of the proposed approach. POLYM. ENG. SCI., 46:712,728, 2006. © 2006 Society of Plastics Engineers [source] Relationship between segment structures and elastic properties of segmented poly(urethane-urea) elastic fibersPOLYMER ENGINEERING & SCIENCE, Issue 11 2003Nori Yoshihara Studies on segmented poly(urethane-urea) (SPUU) elastic fibers having various segment structures were done in terms of elastic recovery and stress-strain relationship (S-S). Three kinds of segment structures were used: 1) the same composition having different sequences of segment units, 2) the same length of soft segments having different molecular weights of polyol, and 3) different segment structures having almost the same stress at 350% elongation. The SPUU elastic fibers having higher sequence numbers of both soft and hard segment units, that is, greater block structures, show better elastic recovery properties, especially delayed elastic recovery. The SPUU elastic fibers showing better elastic recovery take an optimum value for the number-average molecular weight (Mn) of soft segments jointed with urethane bonds. Here the optimum Mn depends on the molecular weight of polytetramethyleneglycol (PTMG) as a starting material. The hysteresis loss in S-S for the pre-elongation decreases with an increase of Mn of PTMG. The SPUU elastic fibers having greater block structures show lower stress with lower 2C1 and 2C1 + 2C2 of Mooney-Rivilin plot constants for elastic fibers having the same composition. This indicates a lower density of crosslinks for finite deformation. An increase of the urea bonds or the molar ratio of urea bond to urethane bond raises the stress. It is found that the polymerization process, as well as composition, is important for design structures of SPUU elastic fibers. [source] | |||||||||||||