Influence of biological origin on the tensile properties of cellulose nanopapers

Katri S Kontturi,Eero Kontturi,Koon-Yang Lee,Mitchell P Jones,Alexander Bismarck,William W Sampson

doi:10.1007/s10570-021-03935-2

Abstract

Cellulose nanopapers provide diverse, strong and lightweight templates prepared entirely from sustainable raw materials, cellulose nanofibers (CNFs). Yet the strength of CNFs has not been fully capitalized in the resulting nanopapers and the relative influence of CNF strength, their bonding, and biological origin to nanopaper strength are unknown. Here, we show that basic principles from paper physics can be applied to CNF nanopapers to illuminate those relationships. Importantly, it appeared that ~ 200 MPa was the theoretical maximum for nanopapers with random fibril orientation. Furthermore, we demonstrate the contrast in tensile strength for nanopapers prepared from bacterial cellulose (BC) and wood-based nanofibrillated cellulose (NFC). Endemic amorphous polysaccharides (hemicelluloses) in NFC act as matrix in NFC nanopapers, strengthening the bonding between CNFs just like it improves the bonding between CNFs in the primary cell wall of plants. The conclusions apply to all composites containing non-woven fiber mats as reinforcement.Graphic abstract

Highlights

It is obvious that the cellulose nanofibers (CNFs) and their bundles are more conspicuous on the bacterial cellulose (BC) nanopaper because amorphous hemicelluloses
For these and all subsequent tensile data reported, we overcome the systematic overestimate of thickness identified in our discussion of Fig. 2b by first calculating the specific strength by dividing the failure load per unit width by the grammage. We multiply this value by the intrinsic density (1.49 g cm-3) to give the strength in MPa. This weight-dependence phenomenon has been observed for conventional paper and ascribed to the more dominant influence of the surface in thinner papers: the fibers on the surface are bonded from one side only and their contribution to the network is relatively high with lower grammages, such that the tensile strength is correspondingly lower.(I’Anson et al 2008) More unexpected is the difference between the two raw materials as BC nanopapers exhibit systematically lower tensile strength values than the nanofibrillated cellulose (NFC) nanopapers – despite the obvious similarity in intrinsic density (Fig. 2b and c)
When assessing how each factor contributes to the network strength, an important observation in Fig. 3b is that the zero-span strength appears to be independent of the biological origin of the CNF, which is sensible since the constituent fibers in the network consist of similar semi-crystalline cellulose fibrils

Summary

Introduction

For these and all subsequent tensile data reported, we overcome the systematic overestimate of thickness identified in our discussion of Fig. 2b by first calculating the specific strength (referred to as ‘tensile index’ in paper physics) by dividing the failure load per unit width by the grammage.

Results

Conclusion