Dynamic crack initiation and growth in cellulose nanopaper

Abstract

Cellulose nanopaper (CNP) made of cellulose nanofibrils (CNF) has gained extensive attention in recent years for its lightweight and superior mechanical properties alongside sustainable and green attributes. The mechanical characterization studies on CNP at the moment have generally been limited to tension tests. In fact, thus far there has not been any report on crack initiation and growth behavior, especially under dynamic loading conditions. In this work, crack initiation and growth in self-assembled CNP, made from filtration of CNF suspension, are studied using a full-field optical method. Dynamic crack initiation and growth behaviors and time-resolved fracture parameters are quantified using Digital Image Correlation (DIC) technique. The challenge associated with dynamic loading of a thin strip of CNP has been overcome by an acrylic holder with a wide pre-cut slot bridged by edge-cracked CNP. The ultrahigh-speed digital photography is implemented to map in-plane deformations during pre-and post-crack initiation regimes including dynamic crack growth. Under stress wave loading conditions, macroscale crack growth occurs at surprisingly high-speed (600-700 m/s) in this microscopically fibrous material. The measured displacement fields from dynamic loading conditions are analyzed to extract stress intensity factors (SIF) and energy release rate (G) histories. The results show that the SIF at crack initiation is in the range of 6-7 MPa(m) 1/2 , far superior to many engineering plastics. Furthermore, the measured values increase during crack propagation under both low-and high-strain rates, demonstrating superior fracture resistance of CNP valuable for many structural applications.

In Situ Lignin Modification Enabling Enhanced Interfibrillar Interactions in Lignocellulosic Nanomaterials toward Structural Applications

“…It is reported that lignin could act as ball-bearing, lubricating, and stress-transferring agents in the lignocellulose nanofibril matrix, thus facilitating energy dissipation under applied tension to achieve favorable ductility and toughness of nanopaper. ,, This is assumed to be a main reason for the superior toughness of OLNP to conventional CNP. Furthermore, the stress-transferring effect of lignin can be also verified by the fracture morphology of nanopaper samples . As shown in Figure c, LNP and OLNP revealed rough fracture surfaces accompanied by a remarkable fibril pull-out case, implying significant fibril slippage under applied tension.…”

“…Furthermore, the stress-transferring effect of lignin can be also verified by the fracture morphology of nanopaper samples. 65 As shown in Figure 3c, LNP and OLNP revealed rough fracture surfaces accompanied by a remarkable fibril pull-out case, implying significant fibril slippage under applied tension. On the contrary, the fracture surface of CNP was flatter without distinct fibril pull-out, suggesting a typical brittle fracture mechanism.…”

Cellulose Nanopaper: Fabrication, Functionalization, and Applications

“…The pulping and bleaching technology of modern pulp and paper mills could be amenably upgraded for nanocellulose production, which also provides a new development strategy for traditional pulp and paper enterprises and open up a valuable path for the high-value utilization of various biomass resources [ 29 – 31 ]. Cellulose nanopaper (CNP), a kind of film material mainly constructed from nanocellulose, has superior physical–chemical properties, such as tunable optical transmittance, high thermal stability, low thermal expansion coefficient (< 8.5 × 10 –6 K −1 ), and good mechanical properties (high modulus of 7.1–14 GPa) [ 32 – 34 ]. Moreover, combining nanocellulose with other functional nanomaterials would endow the CNP with diverse new functionalities, leading to the expansion of the applications from traditional areas to high-tech fields such as electronic devices, clean energy, biomedicine, and water treatment [ 35 – 39 ].…”

Nacre‐Inspired Bacterial Cellulose/Mica Nanopaper with Excellent Mechanical and Electrical Insulating Properties by Biosynthesis

“…[17][18] In recent years, cellulose nanopaper (CNP), a kind of macroscopic film material mainly composed of CNFs, has perfectly inherited the unique physical properties of CNFs mentioned above, making it one of the most promising candidates for materials that can be used in extreme environments. [19][20][21][22] Nevertheless, the practical application puts forward higher requirements on CNPs. Therefore, it is essential to impart more functionalities to CNPs without sacrificing their mechanical properties.…”