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Degradation of paper and the consequent loss of its chemical and mechanical properties has been studied for many decades. For conservators an understanding of the loss of mechanical properties of paper during degradation is highly relevant from a practical point of view. Considering the fibrous microstructure of paper, the mechanical properties of single cellulose fibers and their change in time has been of interest in paper degradation studies. With current advances in experimental micromechanics, the characterization of cellulose fibers is achievable at small scales and with very high accuracy. Such detailed analyses on naturally aged paper in combination with accelerated aging experiments lead to valuable insight in the degradation of paper. The current study represents a novel methodology for the accurate mechanical characterization of micro-scale fibers, such as cellulose fibers. To this end, in-situ mechanical tests are performed using high resolution optical profilometry (white light interferometry) in combination with Digital Image Correlation (DIC) to attain detailed strain measurements. Given the curly geometry of cellulose fibers, there is considerable out-of-plane deformation during a micro-tensile test, making is necessary to use profilometric images. An in-house built setup is used for application of micro-scale speckle pattern needed for DIC. Reliable evaluation of the cross-sectional area of fibers is attained by acquiring profilometric images of both the front and back sides of each fiber, using a mirror in a novel self-calibrating setup. Detailed analyses of the results from different samples show the accuracy and reliability of the measurements and the methodology. By these means, an accurate evaluation of the stiffness and strength of cellulose fibers is attained. Performing such measurements on cellulose fibers from aged papers is expected to result in better understanding of the effect of cellulose degradation on the mechanical properties of paper.
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