The amphiphilic graft copolypeptide, consisting of poly (N-hydroxyethyl L-glutamine) (PHEG) and poly (L-tryptophan (L-Trp)) PTrp (denoted as PHEG-g-PTrp), was synthesized. At the L-Trp composition of 10-25mol%, L-Trp residues aggregated to form the hydrophobic cores in the aqueous solution. The hydrophobic substance could be incorporated in this L-Trp core. This function had not been seen for the random copolypeptide consisting of the same constituent molecules. The aggregation of PHEG-g-PTrp was observed by dynamic light scattering, transmission electron microscopy and small-angle X-ray scattering. The film specimen was prepared from PHEG-g-PTrp by modifying L-Trp residues in trifluoroacetic acid. The hydrophobic substances were incorporated in the high pH region, and the control of the release was achieved by changing pH through the dissociation of the indole rings in the L-Trp residues.
We report control of mechanical properties via morphological control through blending of elastomeric polystyrene-block-polybutadiene-block-polystyrene (SBS) triblock copolymers. For this purpose, we controlled overall composition by blending two SBS triblock copolymers having different compositions and surveyed variation of the mechanical properties with structural change. The microdomain structure was analyzed by the small-angle X-ray scattering (SAXS) technique and the mechanical properties were examined by the tensile stress-strain test. The blending enabled us to change morphology from polystyrene cylinders to alternating lamellae. In between them, a double-gyroid (DG) microdomain structure was also formed. The DG structure is a well-ordered bicontinuous structure, which is formed in a narrow range of composition between cylinder and lamella regions. As a result, the tensile modulus increased tremendously in the narrow range of composition where the DG structure was formed.
About 5wt% of low molecular weight poly (isoprene-block-dimethylsiloxane) was added into a polyisoprene/polydimethylsiloxane 3:7 blend and a polydimethylsiloxane/polyisobutylene 3:7 blend and tested as a surfactant. Samples were sheared at a constant shear rate (16sec-1) by a rheometer using cone-plate geometry. Viscoelastic properties of blends with and without diblock copolymers (bcp) after the pre-shear measured by dynamic measurements were almost the same. After the pre-shear, small amounts of samples were carefully removed from the cone-plate and the variation of domain size was observed by a microscope. After several hours, the domain size of blends without bcp became 4 to 6 times as large as that observed after the cessation of pre-shear, while that of blends with bcp was stable for a long time. Under the successive shear flow with lower shear rate than the pre-shear, it was observed that the dispersed domains of polyisoprene/polydimethylsiloxane/bcp system first coalesced till the size became twice as large as the original size. Then the domains became stable for a long time.
We report the improvement of mechanical and thermal properties of an elastomeric polystyrene-block-poly (ethylene-co-but-1-ene)-block-polystyrene triblock copolymer upon ordering of spherical microdomains on the body-centered cubic (bcc) superlattice. The sample has a minor polystyrene (PS) composition (the volume of PS, φPS =0.084), and therefore forms glassy spherical microdomains being embedded in rubbery poly (ethylene-co-but-1-ene) matrix. The microdomain structures were analyzed by small-angle X-ray scattering technique and transmission electron microscopy. The mechanical properties were examined by dynamic viscoelastic measurements and tensile stress-strain tests. Upon annealing at 130°C for 10h, regularity of the bcc superlattice was improved as compared to a sample annealing at 150°C for 10h. Accordingly, the tensile modulus increased significantly, which can be ascribed to ordering of the glassy PS spheres on the bcc superlattice. Moreover, the thermal resistance was also improved. Namely, a decrease in the tensile modulus above Tg of PS was less remarkable in the film annealed at 130°C for 10h than at 150°C for 10h.
We measured the complex shear modulus, G*=G'+iG", of glassy poly (methyl methacrylate) (PMMA) during its stop-start stretching processes to investigate the relationship between change in mechanical properties due to aging under a finite strain and relaxation of strain-induced nonequilibrium structures. The yield stress as well as the tensile modulus at the beginning of the re-stretching increased with aging time beyond their initial values in the undeformed state, showing the effect of strain aging appeared in these quantities. The storage shear modulus G' also increased with time elapsed in the stress relaxation period. The development of tensile modulus was observed to be much faster than that of the storage shear modulus. As time scales used for the dynamic measurement is much shorter than that for the macroscopic straining, evolution of tensile modulus due to aging under a finite strain is not ascribable only to the relaxation of nonequilibrium glassy structures induced by large deformation.
The effect of the amount of applied deformation on a thermally stimulated deformation recovery for a largely deformed epoxy resin under its glass transition temperature was studied in this paper. Two recovery peaks have been observed in the thermally stimulated deformation recovery curves for both epoxy resin and poly (methyl meth acrylate) (PMMA). The lower temperature recovery peak of the PMMA shifts to a higher temperature with increasing applied strain. However, the lower temperature recovery peak of the epoxy resin was independent of the amount of applied strain. The effect of applied strain on the relaxation curves for the epoxy resin was more significant than for the PMMA. Free deformation recovery curves below the glass transition temperature were simulated using a generalized Maxwell model both with and without the dependence of the recovery curve on the amount of applied strain. The model with strain dependence included reproduced the tendency of the experimental results of the epoxy resin more closely than the model without strain dependence. It seems that the structure of the epoxy resin changed after the lower yielding range to a structure which restricts the relaxation of polymeric structures.
The self-repairing reaction of polymer chains cleaved due to degradation was elucidated through the use of degradation poly phenylene-ether (PPE) related polymer composites. In the case where the cleavage of main chain partially occurred, a spontaneous re-bonding reaction proceeded at the chain ends with copper/amine complex added as a catalyst. The relative value of molecular weight was determined as a criterion of the self-repairing reaction. This reaction was also found to proceed as a redox mechanism for supplying oxygen continuously into the system. Through these processes, the oxidation state of copper was changed from a mono-valent state to a di-valent state that was active for the re-combination reaction between chain ends in polymer. Moreover, blending several kinds of plasticizers with PPE enabled the increase of its molecular weight because of recombination between chain ends that had been cleaved by degradation. During the re-polymerization, water discharge was detected, and the correlation between the ratio of yielded water and increase of molecular weight was clarified. From these results, we concluded that the concept of the self-repairing mechanism could be applied to a wide range of industrial materials and that it had a strong potential to overcome environmental and resource problem in the near future.
Composites consisting of a high-density polyethylene (HDPE) and wastepaper powders were prepared by two different processing methods: the spinning-press method and the roll mixing method. The influence of the processing method on mechanical properties of wastepaper/HDPE composites was studied. The compatibilizing effect of a maleic anhydride-grafted polyethylene (MAHPE) between the wastepaper and HDPE was also investigated. It was found that the flexural properties of spinning-pressed composites were lower than those of roll mixed composites, but spinning-pressed composites showed improved fracture toughness than roll mixed composites. Mechanical measurements and the scanning electron microscopy (SEM) showed that the addition of 5 to 10wt% MAHPE into the HDPE matrix was effective to enhance the mechanical properties of wastepaper/HDPE composites and to improve interfacial adhesion between the wastepaper powders and HDPE matrix.
The building of a sustainable material circulating system is imminent for the threatened waste disposal landfills in Japan. Now, man-aided recycling is active for the purpose of lessening waste. Al-though recycling originally aimed at saving resources and alleviating environmental problems simultaneously, it is nevertheless a current issue that problem of cost and environmental damages have occurred. Also, other problems include the generation of toxic substances due to the mixing of dissimilar materials in the recycling process in each industrial production field, and its progression in the future is feared. This indicates that there is a need to build a purging or purification system in recycling similar to the one originally equipped in the ecosystem. In this report, the category of the poison and the recycling process in the circulating material will be defined and the influence on the material will be examined.
Various constitutive models have been applied to the analyses of localized deformation of solids. However, most of them fall within the framework of the conventional plasticity premising that the interior of yield surface is an elastic domain and obeys the plastic potential theory in which the plastic stretching is independent of the stress rate component tangential to the yield surface. Therefore, they predict a stiff elastic response until the stress reaches the yield state and further a stiff elastoplastic response after yielding. On the other hand, the subloading surface model falling within the unconventional plasticity would be only the model capable of describing pertinently the plastic deformation induced by the rate of stress within the yield surface in general loading process including the unloading, reloading and inverse loading. Further, the numerical calculation by this model is quite efficient disusing the special algorism, e.g. the mean normal method and the radial return method in order to make the stress lie just on the yield surface in the plastic loading process since it contains the controlling function to make the stress approach automatically the yield surface in the plastic loading process. Further, this model is recently extended so as to describe the tangential stress rate effect, i.e. the inelastic deformation induced by the stress rate component tangential to the subloading surface. In this article the post-localized deformation of metal due to the shear band formation is analyzed by the finite element method incorporating the subloading surface model with the tangential stress rate effect. Thus, the influence of the tangential stress rate effect on the shear band formation is discussed exhibiting several examples of the deformation patterns.