Polymer stiff

In the case of the Porod-Kratky model, the polymer backbones have a constant curvature c0. Accounting for the polymer stiffness in generating the dense configuration of stream lines, the vector field used must have a homogeneous curvature field with a unique value cq in the entire simulation box T. In order to quantify the success in creating such a vector field, the deviation of the curvature from the ideal Porod-Kratky case, a volume integral has been used by Santos as a penalty function ... 

Starting with a crude model of a polymer melt, consisting of anharmonic springs connecting repulsive beads, with a bending potential to represent the polymer stiffness, the authors show how the time correlation function, C(f), should be expected to behave as a function of the polymer stiffness. 

Elastomer behavior is depicted by the bottom curve in Figure 3.3. Here the modulus (ratio of stress to strain, as of strength to elongation measure of polymer stiffness) is low, but elongations to several hundred percent are possible before failure. 

The addition of smaller molecules such as plasticizers and the entrapment of monomers have an effect similar to that of the absorption of water. In general, the modulus temperature transition (temperature at which polymer stiffness changes abruptly with the polymer being stiffer below the T) and the Tg decrease as the amount of additive is increased. Thus the modulus temperature transition occurs at about 100 °C for PVC itself, 70 °C for PVC containing 10% dioctyl phthalate, and 20 C for PVC containing 30% dioctyl phthalate. 

A key feature of the Hereon dispensing system is the ease of regulating the pheromone emission rate from the dispenser. Thus, the emission rate may be adjusted by varying one or more of a variety of parameters (4) 1) thickness of outer layers of the dispensers, 2) pheromone concentration per unit area of the dispenser, 3) size (area) of the dispenser, 4) amount of flake applied per acre, 5) the polymer used to fabricate the dispenser, and/or 6) polymer stiffness. Duration of effectiveness may also be extended by increasing the thickness of the inner layer of the dispenser, in effect increasing the size of the pheromone reservoir of each flake. 

We have also applied HPTMC to the simulation of phase coexistence for semiflexible polymers. As before, we use a lattice model to represent the polymers. Stiffness is modeled by introducing an energy penalty sb for each kink in a chain. For the particular system studied here, the chain length is n = 100, the energy penalty is b = 5, the simulation box size is L = 50, and eight rephcas are simulated in parallel. 

The atactic polymer is an amorphous somewhat rubbery material of little value, whereas the isotactic polymer stiff, highly crystalline and with... 

The book covers aspects from the morphology to mechanical aspects focused on the elasticity and inelasticity of amorphous to crystalline polyurethane elastomers, in relation to their sensitivity to chemical and physical structure. In such polymers, resilience of the material is an important attribute. In many applications they are in commercial competition with other, relatively soft, elastomeric materials. The choice of material for any given application then hinges on a spectrum of key properties offered by relatively soft polymers—stiffness and strain recovery characterizing their elasticity, but also inelastic effects such as hysteresis and stress relaxation. In these respects the mechanical properties of polyurethane elastomers are similar to those of other elastomers. 

N.T. Tsui, A.J. Paraskos, L. Torun, TM. Swager, E.L. Thomas, Minimization of internal molecular free volume a mechanism for the simultaneous enhancement of polymer stiffness, strength, and ductility. Macromolecules 39 (9) (2006) 3350-3358. 

Chemical resistance of polyCether ester)s varies greatly with copolymer composition. For example, resistance to hydrocarbon solvents depends on the polymer stiffness and stiffer grades exhibited better performance. The chemical resistance of some polyfether ester)s to aliphatic hydrocarbon solvents, oils and greases is very good, even at elevated temperatures, but they are not that resistant to chlorinated solvents. They are also resistant to diluted acids, bases and to polar solvents, such as water and alcohols at room temperature, but not at temperatures above 70 °C. 

The branched low density polyethylenes are preferred as starting materials being less susceptible to crystallization whilst the initial average molecular weights are typically low at about 20 000. Polymer stiffness is at a minimum at about 35% chlorine content above which oil and solvent resistance and high temperature strength increase but this goes hand-in-hand with an undesirable increase in compression set and brittle point. A 35% chlorine content is nowadays used in... 

Hence, the stated above results have shown the modified Kemer equation application correctness for natural nanocomposites elastic response description. Really this fact by itself confirms the possibility of amorphous glassy polymers treatment as nanocomposites. Microcomposite models usage gives the clear notion about factors, influencing polymers stiffness. 

It is actually possible to modulate the tactic ty of the polymer from the medium crystallinity range characteristic of most commercial product (TI > 0.93 to 0.95) to the high crystallinity range (TI above 0.96). This gives access to an exceptional broad range of polymer stiffnesses. 

The extent of degradation upon photolysis of polyurethanes decreases with increasing polymer stiffness and crystallinity [1004]. The extent of photodegradation is accelerated above the glass transition temperature (Tg), indicating the role of chain flexibility and/or oxygen diffusion in the decomposition process [997]. 

Figure 9.15 Experimental data by Tsuji and Ikada for poly(L-lactide) films shows that increasing crystallinity results in an increase in polymer stiffness (a) and strength (b).

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