PAPER making! g! FROM THE PUBLISHERS OF PAPER TECHNOLOGY INTERNATIONAL ® Volume 9, Number 2, 2023
orientation) and viscous drag during drainage (fiber conformation to the wire topography). Virtual tensile tests performed on thus formed networks reveal that the tensile response is initially softer due to non-affine deformation, and anisotropic due to preferential orientation. Consequently, an orientation dependent power law with a non-unique exponent emerges for the scaling of modulus and strength with the network density. Tensile test simulations reveal the re-alignment of fibers along the loading direction, and strong strain localization resulting in a few fibers (1%) carrying the imposed strain energy. Fiber curl and orientation are observed to govern the degree of non-affine response, stiffness, and strain localization, suggesting that controlling the degree of anisotropy and fiber curl offers the possibility to design networks for specific stiffness and specific strength. TISSUE “The influence of microstructure on the tensile properties of a creped tissue paper: Modeling and experiments”, Shubham Agarwal, Prabhat Srivastava, Sheldon I. Green & A. Srikantha Phani, Mechanics of Materials , Vol.176, January 2023, 104505. Low density tissue papers are soft fiber networks with a folded internal microstructure — deliberately imparted during a widely used manufacturing process, called dry creping. The folded crepe structure enhances a tissue paper’s specific volume, stretchability, and softness. The influence of the micron-scale crepe structure on nonlinear tensile response is studied using experiments and a discrete elasto- plastic model (DEM). First, ‘Crepe Index (CI)’ is defined to quantify the crepe structure. An optical method to obtain high resolution edge images is developed to measure the CI. The relationship between the CI and tensile failure strain and initial elastic stiffness is assessed: the failure strain is observed to be proportional to CI, while the dependence of initial stiffness on CI is unclear – presumably due to the damage induced through the de-densification of fiber layers during the manufacturing. The effect of CI on initial stiffness and failure strain is assessed using DEM by idealizing the creped paper as a segmented triangular wave — each segment governed by a bilinear elastoplastic constitutive law and a strength-based failure criterion. The model reveals that the initial stiffness of a creped sheet depends not only on the CI but also on sheet-thickness to crepe-wavelength ratio, and the stiffness of the uncreped sheet. The failure strain is found to be stretching dominated at low CI, and bending dominated at higher CI. Qualitative agreement is found between the DEM and experiments. The significance of both the material and the geometric non-linearity on the macroscale tensile response of a creped tissue paper emerges from this study. “Creping technology and its factors for tissue paper production: a review”, Tong Qin, Liqin Liu, Haibing Cao, Shuangxi Nie, Bin Lu, Zhengbai Cheng, Hongbin Liu & Xingye An, European Journal of Wood and Wood Products , 2023, online. Tissue products such as facial tissue and paper towels have been playing a crucial role in promoting hygiene and maintaining good health, since they are commonly available and widely used nowadays. The production of low-density tissue paper typically involves a key creping process that contains pressing and adhering the wet web onto a high-speed Yankee cylinder, followed by releasing the creped sheet with a stationary creping blade to form periodic micro-folds within the tissue structure. This paper discusses and reviews the mechanisms of tissue creping technology, as well as the factors that impact the creping process and tissue properties. These factors primarily include the dryness of the tissue web, creping rate, properties of the pulp raw material, Yankee coating, crepe doctor blade, and tissue drying machines. It is indicated that the creping process, as a multifaceted and integrated treatment for tissue production, can be significantly enhanced through the concerted efforts of the aforementioned factors to achieve greater creping efficiency. However, further endeavors are necessary to address the constraints stemming from the
Technical Abstracts
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