Mechanisms of Fracture of Cellulose Products—From Network Structure to Strength

Paper is a network material composed of cellulose fibers. The relationship between the structure of the fiber network and the properties of various types of paper has been studied extensively. Despite this interest, the mechanism of failure and the relation between structure, strength, and toughness are not entirely understood. In this work, we aim to establish the functional dependence of the strength and toughness of a quasi-two-dimensional network of fibers on the architecture and parameters of the fiber assembly. We investigate two failure mechanisms – controlled by bond failure and controlled by fiber failure, respectively and determine the parametric regime in which one mechanism dominates over the other. Further, we explore and observe strong effects of structural parameters such as density, fiber length, and volume fraction on the mesoscale failure mechanism exhibited as a transition from brittle to ductile failure of the material under tension. This, in turn, affects the effective strength and toughness of the material. We summarize these observations as a phase diagram that relates the structural parameters and material properties of interest. Our findings not only contribute to the fundamental understanding of failure mechanisms in fibrous network materials but also provide practical insights for the development of advanced paper products with tailored mechanical performance.