Recoverable creep compliance JR(t) was analytically calculated for polymer chains relaxing through the Rouse and reptation mechanisms at short and long time scales, respectively. The ratio of the longest relaxation times of these mechanisms, rτ = τRouse/τrep, was varied from 0.056 to 0.0033. The calculation indicated that the effect of the fast Rouse mechanism on the distribution of slow modes of JR(t) decreases with decreasing rτ but a considerable effect remains even for rτ as small as 0.0033, i.e., even for the case of reptation-dominance in the terminal relaxation behavior. This result demonstrates an important difference between the creep and relaxation processes, the former being associated with a correlation (or interplay) of eigenmodes of chain motion due to the constant stress requirement.
We investigated concentration profile of end segment at the surface and the inside of thin polymer films by the mean field theory module of OCTA system (SUSHI) in various cases. In all cases, the end segments were placed near the surface and the tendency was notable with being thinner film. When the solvents existed in the system, it was clear that not only poor solvent but also good solvent bled out from the surface. And in the case of bimodal polymer blend, the surface layer consisted mainly by the low molecular weight component, but there also existed some high molecular weight component. We found that the ratio of the end segment of the high molecular weight component in the surface layer in this case was not low. Moreover, the concentration profile of low and high molecular weight component was vibrating many times to the center of the film.
A new method of manufacturing phosphor screens for flat CRT displays is developed by a combination of screen printing and thermal transfer processes. The main issues for high resolution displays are the printability and firing properties of phosphor pastes, and packing density of particles deposited on panels. The most important components which are closely connected with these requirements are the polymeric binders. The polymeric binders which lead to weak flocculation of phosphor particles provide the good rheological properties for reproduction of precise micropatterns. Because of weak adsorption affinity for the particle surfaces, the pastes prepared with such binders are thoroughly fired without ashes on heating at the temperature where the complete decomposition of binder polymers takes place. The glass panels are incorporated with electron gun and the CRT panels are built as model displays. The brightness of newly developed displays will be acceptable for practice applications.
Carbon black (CB)-filled composites of polyethylene (PE), polypropylene (PP), and PP/PE blend with weight composition of 40/60 have been prepared by twin screw extruder, and their electrical resistivities have been investigated. In order to improve the surface properties of CB, γ-aminopropyl trimethoxysilane (APS) was used for the surface treatment of CB. The surface treatment of CB by APS was found to effectively decrease percolation threshold, φc, i.e., the electrical resistivity showed drastic decrease when the CB content was larger than φ c. Temperature dependence of APS-treated CB/PP/PE composites exhibited almost constant electrical resistivity (~106 Ωcm) in the range of 25-130°C, and it was increased drastically to ~1012Ωcm above the melting temperature of PE, resulting high positive temperature coefficient (PTC) intensity (ca. 106). This high resistivity was maintained even at the higher temperature than 150°C, and only weak negative temperature coefficient (NTC) behavior was observed. The surface treatment of CB by APS is effective to obtain CB/PP/PE composites having excellent thermal electrical property as a switching material.
Poly(ethylene terephthalate) (PET) / poly(ethylene naphthalate) (PEN) blends with 50/50 composition have been prepared by melt-mixing at the temperatures above 280°C and subsequent heating at 280°C before hot-press molding. Progress of transesterification reaction and formation of PET-PEN random copolymers during these melt-blending processes have been confirmed by 1H-NMR measurement. Dynamic viscoelasticity, DSC thermograms, and SEM images for the PET/PEN blends with shorter heating time at 280°C suggested that the blend sample was in an immiscible state when the transesterification level (T) was less than 5%. With the increase of the heating time, the sample changed to miscible state with T > 5 % and exhibited transparency. The phase-separated morphology was fine and the size of the phase-separated domain was several hundred nanometer when T ≈ 5%. Flexural test for the blend samples revealed that the PET/PEN blends exhibited the maximum flexural strength when T ≈ 5 %. Increase in the melt-mixing temperature was found to accelerate the transesterification reaction, and to shorten the processing time to obtain the miscible PET/PEN blend.
We propose a simple numerical method to calculate the relaxation time distribution, which is not based on the regularization method. This method is as precise as the nonlinear regularization method developed by Honerkamp and Weese4), and is simpler in mathematical aspects. Our method is an iterative nonlinear mapping that maps any initial distribution to the set of distribution functions whose element H(n)(τ) generates moduli very close to those generated by the exact distribution, and is smooth whenever the initial distribution is smooth. By the mapping, the initial distribution becomes close to the exact distribution within less than 10 iterations. This implies that the iterative nonlinear mapping itself contains the role as the regularization term used in the existing regularization methods, while the mapping is not formulated by constructing a counterpart of the regularization term. In other words, this method is free from parameters such as regularization parameter used in the previous regularization methods. Furthermore, our method needs no constraint to keep the distribution non-negative.
For evaluation of thermal endurance in foamed plastics, temperature and time characteristics of compression dynamic modulus of four hard polyurethane foams were investigated by the dynamic viscoelastic measurements. Compression dynamic modulus of each polyurethane foams lessened gradually with time, probably due to a decrease of inner pressure of closed-cell, which influenced stiffness of foam skeletons. Logarithm of time t, at which the compression dynamic modulus came to be 50% of its initial value at the beginning of the dynamic measurement has been found to be a linear function of reciprocal of the absolute temperature T−1. Thermal endurance characteristics can be evaluated from the linear relations between log t and T −1.