DYNAMIC VISCOELASTIC

Fig. 21. Dynamic viscoelastic properties of a low density polyethylene (LDPE) at 150°C complex dynamic viscosity Tj, storage modulus G and loss modulus G" vs angular velocity, CO. To convert Pa-s to P, multiply by 10 to convert Pa to dyn/cm, multiply by 10.

PMMA-b-PBA shows improved izod impact strength compared to PMMA homopolymer (41). Polyisobutylene (PIB) or its hydrogenated one (PIB-H) also acts as an impact modifier [31]. PSt-b-PIB, PSt-b-PIB-H, and PMMA-b-PIB-H derived from MAI have high- and wide-range molecuiar weight and show high flexibiiity and flow property [42]. The improved flexibiiity of PMMA-b-PEG synthesized as an elastomer, was confirmed by dynamic viscoelastic measurement [43]. 

It seems that results rather close in their meaning should be obtained, provided that monodisperse polymers are taken as dispersion media. Investigations into dynamic (viscoelastic) properties of such liquids with highly active filler have shown that [6],... 

Thermal and thermomechanical analyses44 are very important for determining die upper and lower usage temperature of polymeric materials as well as showing how they behave between diose temperature extremes. An especially useful thermal technique for polyurethanes is dynamic mechanical analysis (DMA).45 Uiis is used to study dynamic viscoelastic properties and measures die ability to... 

The specimen was prepared by the following method. After mixing HAF carbon black (50 phr) with natural rubber (NR) in a laboratory mixer, carbon gel was extracted from unvulcanized mixture as an insoluble material for toluene for 48 h at room temperamre and dried in a vacuum oven for 24 h at 70°C. We made the specimen as a thin sheet of the carbon gel (including carbon black) by pressing the extracted carbon gel at 90°C. The cured specimen was given by adding sulfur (1.5 phr) to the unvulcanized mixture and vulcanized for 30 min at 145°C. The dynamic viscoelastic measurement was performed with Rheometer under the condition of 0.1% strain and 15 Hz over temperatures. 

The dynamic viscoelasticity of particulate gels of silicone gel and lightly doped poly-p-phenylene (PPP) particles has been studied under ac excitation [55]. The influence of the dielectric constant of the PPP particles has been investigated in detail. It is well known that the dielectric constant varies with the frequency of the applied field, the content of doping, or the measured temperature. In Fig. 11 is displayed the relationship between an increase in shear modulus induced by ac excitation of 0.4kV/mm and the dielectric constant of PPP particles, which was varied by changing the frequency of the applied field. AG increases with s2 and then reaches a constant value. Although the composite gel of PPP particles has dc conductivity, the viscoelastic behavior of the gel in an electric field is qualitatively explained by the model in Sect. 4.2.1, in which the effect of dc conductivity is neglected. 

Fig. 4 Dynamic viscoelasticity measurements after equal mixing of 5 wt%...

The dynamic viscoelastic properties of acetylated wood have been determined and compared with other wood treatments in a number of studies. Both the specific dynamic Young s modulus (E /j) and tan S are lower in acetylated wood compared with unmodified wood (Akitsu etal., 1991, 1992, 1993a,b Korai and Suzuki, 1995 Chang etal., 2000). Acetylation also reduces mechanosorptive creep deformation of the modified wood (Norimoto etal., 1992 Yano etal, 1993). In a study of the dynamic mechanical properties of acetylated wood under conditions of varying humidity, it was concluded that the rate of diffusion of moisture into the wood samples was not affected by acetylation (Ebrahimzadeh, 1998). 

Korai, H. and Suzuki, M. (1995). Dimensional stability and dynamic viscoelasticity of double-chemically treated wood. Mokuzai Gakkaishi, 41(1), 51-62. 

Sugiyama, M. and Norimoto, M. (1996). Temperature dependence of dynamic viscoelasticities of chemically treated woods. Mokuzai Gakkaishi, 42(11), 1049-1056. 

Suzuki, M., Araki, M. and Goto, T. (1963a). Water sorption and dynamic viscoelastic properties of untreated, HCl-treated and HCHO-treated wood. Mokuzai Gakkaishi, 9(1), 11-17. 

The static modulus and dynamic storage modulus were investigated for some open-celled PE foams by static compression tests and dynamic viscoelastic measurements in compression mode. Experimental data were compared with theoretical predictions. 8 refs. 

The dynamic storage modulus of closed-cell PE foams was investigated by dynamic viscoelastic measurement in the compression mode. It was found that dynamic modulus correlated with compression hardness and that the resistance against pressure inside the cells had no effect upon static modulus or dynamic storage modulus. 8 refs. 

Massa,D,J., Schrag,J.L., Ferry,J.D. Dynamic viscoelastic properties of polystyrene in high-viscosity solvents. Extrapolation to infinite dilution and high-frequency behavior. Macromolecules 4,210-214 (1971). 

Tanaka,H., Sakanishi,A., Kaneko,M., Furiuchi,J. Dynamic viscoelastic properties of dilute polymer solutions. J. Polymer Sci. Pt. C15,317-330 (1966). 

I. Dynamic viscoelasticity of narrow-distribution polystyrenes. Macromolecules 3, 109-116(1970). 

Onogi,S., Masuda,T., Kitagawa,K. Rheological properties of anionic polystyrenes. I. Dynamic viscoelasticity of narrow-distribution polystyrenes. Macromolecules 3, 109-116 (1970). 

Dynamic viscoelastic and stress-optical measurements are reported for blends of crosslinked random copolymers of butadiene and styrene prepared by anionic polymerization. Binary blends in which the components differ in composition by at least 20 percentage units give 2 resolvable loss maxima, indicative of a two-phase domain structure. Multiple transitions are also observed in multicomponent blends. AU blends display an elevation of the stress-optical coefficient relative to simple copolymers of equivalent over-all composition. This elevation is shown to be consistent with a multiphase structure in which the domains have different elastic moduli. The different moduli arise from increased reactivity of the peroxide crosslinking agent used toward components of higher butadiene content. 

It is important to quantify the dynamic viscoelastic properties of the materials. Normally the analysis of these systems is performed using the frequency as the variable, and the relationship between the dynamic parameters and the parameters for step-function suppose the application of an oscillatory shear strain with angular frequency w expressed as ... 

Fatkullin NF, Kimmich R, Kroutieva M (2000) The twice-renormalised Rouse formalism of polymer dynamics Segment diffusion, terminal relaxation, and nuclear spin-lattice relaxation. J Exp Theor Phys 91(1) 150-166 Ferry JD (1980) Viscoelastic properties of polymers, 3rd edn. Wiley, London Ferry JD (1990) Some reflections on the early development of polymer dynamics Viscoelasticity, dielectric dispersion, and self-diffusion. Macromolecules 24 5237-5245 Ferry JD, Landel RF, Williams ML (1955) Extensions of the Rouse theory of viscoelastic properties to undilute linear polymers. J Appl Phys 26 359-362 Fikhman VD, Radushkevich BV, Vinogradov GV (1970) Reological properties of polymers under extension at constant deformation rate and at constant extension rate. In Vinogradov GV (ed) Uspekhi reologii polimerov (Advances in polymer rheology, in Russian). Khimija, Moscow, pp 9-23... 

Kohyama, K., Iida, H., and Nishinari, K. (1993). A mixed system composed of different molecular weights konjac glucomannan and kappa carrageenan large deformation and dynamic viscoelastic study. Food Hydrocoll. 7 213—226. 

The dynamic viscoelasticity and the thermal behaviour of films of Thermoelastic 125 cast from solutions in four solvents - toluene (T), carbon tetrachloride (C), ethyl acetate (E), and methyl ethyl ketone (M) — have been studied by Miyamato133 The mechanical loss tangent (tan 8) and the storage modulus E dependences exhibit two transitions at —70 °C and 100 °C which have been attributed to onset of motion of polybutadiene and polystyrene segments, respectively. The heights of the polybutadiene peaks on tan 6 curves decrease in the order C > T > E > M, while for polystyrene the order is reversed C < T < E < M. These phenomena have been related to the magnitude of phase separation of the polystyrene and polybutadiene blocks. 

Finally it may be remarked that the dynamic viscoelastic properties of plasticized cellulose derivatives seem to give no evidence of any unusual temperature dependence of the chain conformations. Thus, Landel and Ferry (162, 163, 164) successfully applied the method of reduced variables [see, for example, Ferry (6)] to various concentrated solutions of cellulosic polymers, and found that the temperature reduction factors were quite similar to those for other flexible polymers such as poly(isobutylene). 

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