Abstract
Nanocellulose network in the form of cellulose nanopaper is an important material structure and its time-dependent mechanical response is crucial in many of its potential applications. In this work, we report the influences of grammage and strain rate on the tensile response of bacterial cellulose (BC) nanopaper. BC nanopaper with grammages of 20, 40, 60 and 80 g m−2 were tested in tension at strain rates ranging from 0.1% s−1 to 50% s−1. At strain rates le 2.5% s−1, both the tensile modulus and strength of the BC nanopapers stayed constant at ~ 14 GPa and ~ 120 MPa, respectively. At higher strain rates of 25% s−1 and 50% s−1 however, the tensile properties of the BC nanopapers decreased significantly. This observed anomalous tensile response of BC nanopaper is attributed to inertial effect, in which some of the curled BC nanofibres within the nanopaper structure do not have enough time to uncurl before failure at such high strain rates. Our measurements further showed that BC nanopaper showed little deformation under creep, with a secondary creep rate of only ~ 10–6 s−1. This stems from the highly crystalline nature of BC, as well as the large number of contact or physical crosslinking points between adjacent BC nanofibres, further reducing the mobility of the BC nanofibres in the nanopaper structure.
Highlights
Nanocellulose network in the form of cellulose nanopaper is an important material structure and its time-dependent mechanical response is crucial in many of its potential applications
It can be seen from this figure that bacterial cellulose (BC) nanopaper possessed a web-like structure consisting of a random network of cellulose nanofibres
Our findings suggest that the limited secondary creep deformation, due to the large number of contact or physical crosslinking points between adjacent BC nanofibres combined with the highly crystalline nature of BC, which was measured to be ~ 90% based on our previous s tudies[25], is the main cause for the anomalous tensile response of BC nanopaper at intermediate strain rates
Summary
Nanocellulose network in the form of cellulose nanopaper is an important material structure and its time-dependent mechanical response is crucial in many of its potential applications. Conventional paper possesses a tensile modulus of only ~ 3 GPa and a tensile strength of ~ 40 MPa. The global demand for cellulose nanofibres in 2018 was 10,000 tons and this demand is estimated to increase to more than 70,000 tons by the year 20303, with the highest volume in the paper and packaging sectors, whereby cellulose nanopaper is anticipated to be an important material s tructure[4,5,6,7,8,9,10]. The commercial production of cellulose nanopaper is anticipated to utilise web processing technique, such as roll-to-roll m anufacturing[21] In this context, the time-dependent mechanical response of cellulose nanopaper is important as it is closely connected to the web stress behaviour at different transport velocities[22]. The time-dependent tensile response of BC nanopaper is discussed in terms of its grammage
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