A Stiffnesstester of paper, the principle of which is based on the measuring of the bending monent of a piece of Sheet-paper by the aid of a pendulum, the moment of which was, previously, calculated, has been devised by authors.
The measuring conditions by this tester were settled and the errors caused on measuring it were discussed.
From the data of stiffness obtained, the static Young's modulus were calculated and compared with the dynamic Young's modulus obtained by the vibration method, which consists of giving vibration to a piece of sheetpaper.
The static Young's modulus do not almost coincide with the dynamic Young's modulus ; and as a general tendency, the former is smaller than the latter and the softer the paper is, the larger the difference becomes.
Such a difference will be, on the one hand, caused by the defect of the stiffnesstester, and on the other hand, by the visco-elastic structure of paper itself.
But as a routine work, this stiffnesstester will be able to provide a numerical data of stiffness of paper, which are provably affected by the paper making conditions : such as freeness of fibre, type of beating of stock, additives, sorts of pulps, bonded area of fibre etc ; and the relationships among them were investigated on the data obtained by this test. As a factor affecting to the stiffness, the bonded area of fiber has been recognized to be prominent.
From the above experiments, it will be considered that there is a closs relation between the stiffness and the micro-structure of paper. To investigate the stiffness of paper will, therefore, be able to contribute toward the study on the micro-structure of paper.
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