Dynamic mechanical properties, linear

Dynamic Mechanical Properties. The dynamic mechanical properties of branched and linear polyethylene have been studied in detail and molecular interpretation for various transitions have already been given, although not necessarily agreed upon in terras of molecular origin.(52-56) Transitions for conventional LDPE (prepared by free radical methods) when measured at low frequencies, are located around +70°C, -20°C and -120°C and are assigned to o, 5, and y transitions respectively. (53) Recently Tanaka et al. have reported the dynamic mechanical properties for a sample of HB which was also prepared by anionic polymerization, but contrary to our system the hydrogenation of the polybutadiene was carried out by a coordinate type catalyst.(12) The transitions reported for such a polymer at 35 Hz are very similar to those of LDPE.(12)... 

Figure 10. Dynamic mechanical properties of a model latex with a linear power feed process ethyl acrylate varied 0- 1 and styrene varied 1- 0.

Recently, the dynamic mechanical properties of the resins cured with a series of linear poly anhydrides having the structures shown in Table 5 were studied by Ramon41 . The dynamic mechanical properties are very similar to those of the resins cured with diamine hardeners as shown in Fig. 10. The relationships between the number of CH2 groups n and Tg Eire shown in Fig. 8. Tg drops rapidly below that of an alkyldiamine-cured resin as n increases. This is considered reasonable because, compared with the hardener.unit in an amine-cured resin, the acid anhydride segment existing in the main chain of the anhydride-cured resin is twice as long. 

When a sinusoidal strain is imposed on a linear viscoelastic material, e.g., unfilled rubbers, a sinusoidal stress response will result and the dynamic mechanical properties depend only upon temperature and frequency, independent of the type of deformation (constant strain, constant stress, or constant energy). However, the situation changes in the case of filled rubbers. In the following, we mainly discuss carbon black filled rubbers because carbon black is the most widespread filler in rubber products, as for example, automotive tires and vibration mounts. The presence of carbon black filler introduces, in addition, a dependence of the dynamic mechanical properties upon dynamic strain amplitude. This is the reason why carbon black filled rubbers are considered as nonlinear viscoelastic materials. The term non-linear viscoelasticity will be discussed later in more detail. 

A linear relationship exists between the toughness (integrated stress-strain curve) and the dynamic mechanical dissipation factor. The types of materials that fit this relationship include glassy polymers, elastomers, and an impregnated fabric. The existence of this relationship indicates that toughness arises from the molecular motions which give rise to the dynamic mechanical properties. 

Dynamic mechanical properties of all pure components and blends were measured as a function of percent strain and indicated a linear viscoelastic region up to approximately 30-35 percent. Therefore, all rheological experiments were conducted at a strain rate of 20 percent. In cases where thermal degradation occurred (as seen in time sweep), the heating chamber was continuously purged with liquid nitrogen. Frequency sweeps, and in some cases frequency-temperature sweeps, were performed on all pure components and blends. 

A polyurethane (PU)/poly(n-butyl methacrylate) (PBMA) system has been selected for an investigation of the process of phase separation in immiscible polymer mixtures. Within this system, studies are made of the XX, lx, xl, and the 11 forms. In recognition of the incompatibility of PBMA with even the oligomeric soft segment precursor of the PU, no attempt was made to equalize the rates of formation of the component linear and network polymers. Rather, a slow PU formation process is conducted at room temperature in the presence of the PBMA precursors. At suitable times, a relatively rapid photopolymerization of the PBMA precursors is carried out in the medium of the slowly polymerizing PU. The expected result is a series of polymer mixtures essentially identical in component composition and differing experimentally only in the time between the onset of PU formation and the photoinitiation of the acrylic. This report focuses on the dynamic mechanical properties cf these materials and the morphologies seen by electron microscopy. 

Figure 1. Dynamic mechanical properties of linear polyurethane encapsulants at 11 Hz. Formulation nomenclature the first number refers to the weight ratio of polyether (ET) in the soft segment and the remainder is assumed to be the polyester the second number designates the overall weight percent of the diisocyanate.

We have reported previously the sulfonation of a polypentenamer (PP) under reaction conditions that preclude the formation of covalent cross-links (J). The sulfonated materials are isolated in the form of sodium salts to give ion-containing elastomers. The thermal and dynamic mechanical properties of the sulfonated PP s indicate the existence of phase-separated ionic clusters above a sulfonate concentration of roughly 10 mol % (2). It has been shown (J) that the unsaturation in the sulfonated PP s can be removed by a diimide hydrogenation reaction to yield a material that is essentially linear polyethylene with pendant sulfonate groups. In this manner the effect of backbone crystallinity on... 

Plastics - Thermomechanical analysis (TMA) - Determination of linear thermal expansion coefficient and glass transition temperature Plastics - Thermomechanical analysis (TMA) - Determination of softening temperature Plastics - Determination of dynamic mechanical properties -General principles Plastics - Dynamic mechanical analysis - Determination of glass transition temperature Plastics - Dynamic mechanical analysis - Calibration... 

H. Shi, S.H. Chen, M.E. De Rosa, T.J. Running, W.W. Adams, Dynamic mechanical properties of cyclohexane-based glass-forming liquid crystals and a linear side-chain polymer analogue. Liq. Cryst. 20, 277-282 (1996)... 

Alpha Technologies manufactures an instrument that measures linear viscoelastic dynamic mechanical properties. 

S. Shinoj, R. Visvanathan, S. Panigrahi, and N. Varadharaju, Dynamic mechanical properties of oil palm fibre (OPF)-linear low density polyethylene (LLDPE) biocomposites and study of fibre-matrix interactions. Biosyst. Eng. 109,99-107 (2011). 

Dynamic mechanical methods (typically oscillatory parallel plate rheometry) are commonly used to measure the dynamic mechanical properties from the liquid state to the solid state. By using small-amplitude oscillatory deformations (linear viscoelastic regime), the dynamic storage and loss moduli can be obtained. From these quantities, the viscosity and modulus can be calculated (71) (see Dynamic Mechanical Analysis). 

The dynamic mechanical properties were measured in the linear regime with a Bohlin CS apparatus equipped with coaxial cylinders (d = 25 mm). The polymer solution, preheated at 80 C (or 130X), was rapidly added between the coaxial cylinders thermostated at the requested temperature. Solutions were cooled from 80 C or 130X down to the requested temperature within ca. 1 minute (as measured with a thermocouple) and the measurements were then immediately started. 

In a very extensive study of both stress relaxation and dynamic mechanical properties in simple extension, on single crystal mats of fractions of linear polyethylene, Takayanagi and collaborators were able to combine data at different temperatures by reduced variables over most of the range from 16°C up to the temperature of crystallization and also to show that the dynamic and transient data corresponded fairly closely, provided the latter were corrected for nonlinear behavior by an extrapolation procedure to zero strain. It is characteristic of crystalline polymers that departures from linear viscoelastic behavior appear at very small strains, and are sometimes significant in stress relaxation even at a tensile strain of = 0.001. In dynamic measurements, the strains are usually small enough to fall within the linear range. 

Chapter 4 investigates the rheological and the dynamic mechanical properties of rubber nanocomposites filled with spherical nanoparticles, like POSS, titanium dioxide, and nanosilica. Here also the crucial parameter of interfacial interaction in nanocomposite systems under dynamic-mechanical conditions is discussed. After discussing about filled mono-matrix medium in the first three chapters, the next chapter gives information about the nonlinear viscoelastic behavior of rubber-rubber blend composites and nanocomposites with fillers of different particle size. Here in Chap. 5 we can observe a wide discussion about the influence of filler geometry, distribution, size, and filler loading on the dynamic viscoelastic behavior. These specific surface area and the surface structural features of the fillers influence the Payne effect as well. The authors explain the addition of spherical or near-spherical filler particles always increase the level of both the linear and the nonlinear viscoelastic properties whereas the addition of high-aspect-ratio, fiberlike fillers increase the elasticity as well as the viscosity. 

Nitta, K.-H., and Tanaka, A. Dynamic mechanical properties of metallocene catalyzed linear polyethylenes, 42 (2001),1219-1226. 

Gouinlock EV, Porter RS (1977) Linear dynamic mechanical properties of an SBS block copolymer. Polym Eng Sci 17 535-543... 

Bates FS (1984) Block copolymers near the microphase-separation transition. 2. Linear dynamic mechanical properties. Macromolecules 17 2607-2613... 

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