Bending strength of a 2D-C/C composite was studied by experimental and theoretical approaches, and the prediction method on the basis of stress-related fracture mode was proposed. In the experiment, three-point bending test and observation of fracture surface were carried out to clarify the stress-related fracture modes. From the fracture surface observation, three kinds of fracture modes were identified: the compressive, tensile and the shear fracture modes. In the theoretical approach, the Weibull strength theory and the proposed method were applied to estimate the bending strength prediction. As a result of this study, it was found that the proposed method is applicable to the bending strength prediction of the 2-C/C composite, whereas the Weibull strength theory is not applicable.
The existing freezing and thawing test method leaves much room for improvement concerning the dimension and shape of specimen, and the exposure condition from the viewpoint of the materials science research; that is, the concrete specimen is too large and heavy and the testing time is so long that the testing itself is not intended for practical use in order to evaluate the durability. Thus, the authors have already reported that the standard cylindrical specimen (∅10×20cm) for the quality control of concrete is the best type and that the development of the accelerative test method by virtue of the exposure temperature of ±5°C. In addition, the phenomenal fact that the freezing and thawing action makes the neutralization accelerate has been discovered by the authors in recent year. Such a phenomenal fact is especially remarkable to the marine RC structures under the severe meteorological action. This paper mainly deals with the fundamental deterioration mechanism of durability at the early stage due to the freezing and thawing action, thereby being able well to explain the reason of neutralizing acceleration, by assuming the existence of the semipermeable membrane on the interface of air void shell.
Novel lignin-based polymers, lignophenols, have been derived from native lignins through the phase-separation system composed of phenol derivatives and conce ntrated acid. The molecular weight of lignophenol was controlled from ca. 7400 to ca. 520, using the intramolecular switching function under the alkaline condition. By the blending of the biopolyester [poly (3-hydroxybutyrate)] with butylhydroxyanisole (BHA), triacetin and lignophenol 2nd derivative, the elongation ratios of the resulting films became 5, 5 and 20 times higher, respectively, compared with the control film without additives. For the composite films with BHA and triacetin, the shrinkages and the weight losses were observed with increasing temperature, due to the evaporation of additives. On the other hand, for the composite film with lignophenol 2nd derivative, no shrinkage was observed, and the thermogravimetric profiles were almost compatible with that of the control film. The DSC analysis indicated that the crystallization enthalpies of biopolyester-lignophenols films decreased with increasing contents of lignophenols.
Through the phase-separation system composed of phenol derivatives and concentrated acid, lignocellulosics were separated to highly hydrolyzed carbohydrates and lignin-based material (lignophenols) quantitatively. Lignophenols mainly composed of 1, 1-bis(aryl) propane type units had unique properties such as high phenolic property, obvious phase transition point and switching function (nucleophilic attack of Cα-phenoxide to adjacent Cβ followed by the cleavage of aryl ether linkages). Controlling the hydrolysis of carbohydrates in the system, lignophenol-carbohydrate (LC) composites containing lignophenols and carbohydrates which left no fibrous structures were prepared in the yield of 80-90% from the wood meals. LC composites had significant thermal plasticity at around 170°C. The softening point of the acetylated LC composites was much lower than that of the original ones due to blocked hydrogen bonds of lignophenol and carbohydrates. On the other hand, the hydroxymethylated LC composites (grafted phenol derivative in lignophenol; p-cresol) had no softening point because of linked structures formed in lignophenol. The hydroxymethylated LC composites (phenol derivative: 2, 4-dimethylphenol), however, softened at 170°C because lignophenols in the composites were hydroxymethylated at terminal phenolic nuclei to give linear type polymer. The molds from the acetylated LC composites had the highest density and excellent water resistance. The hydroxymethylated LC molds with p-cresol type lignophenol showed high dimensional stability having slight water absorption and volumetric swelling, because of porous structures and the network of lignophenol. LC composites and molds could be separated into lignophenol and carbohydrate moieties efficiently by simple solvent extraction or using switching function of lignophenol.