Optimized mechanical and impact performance of high strength tempo oxidized cellulose nanofibril (TOCNF)—epoxy laminates

Endrina S Forti,Jeffrey P Youngblood,Daniela B Jimenez,Gregory T Schueneman,Robert J Moon

doi:10.1007/s10570-021-04229-3

Endrina S Forti, Jeffrey P Youngblood + Show 3 more

Open Access

https://doi.org/10.1007/s10570-021-04229-3

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Abstract

In this work, TEMPO cellulose nanofibril (TOCNF) laminates were fabricated using a layup method. Two different TOCNF layers were tested, a neat TOCNF and a TOCNF with polyvinyl alcohol (PVA) strengthening aid with four different epoxy formulations as interlayers for the laminates. Flexural testing showed a correlation between the presence of stronger layers (TOCNFs + PVA) in the laminate with a higher flexural strength, bending modulus, and work of failure. Different modes of fracture within the laminates occurred based on epoxy type. A stiffer epoxy generated a reduced mechanical response and substantial intralayer damage. On the other hand, a more ductile epoxy increased the WOF of the laminates, inducing a higher delamination at the interface. The addition of a silane coupling agent (APTES) resulted in a higher compatibility between the TOCNFs and epoxy, generating an increased ultimate tensile strength (UTS) and a decreased energy to rupture associated with the reduction of crack digression mechanisms in the system. In general, laminates with stronger TOCNF layers (TOCNF + PVA) and increased adhesion (APTES), showed a flexural strength increase of 61%, a bending modulus increase of 80% and the same work of failure when compared with the original laminates. Finally, impact testing of TOCNF materials was performed for the first time in literature, the specific energy to rupture of laminates was comparable to those achieved by acrylic and borosilicate glass, while maintaining a higher or similar specific strength to glass. Laminates showed good transparency and low haziness.Graphic abstract

Highlights

TEMPO (2,2,6,6-tetramethylpiperidine-1-oxyl)-oxidized cellulose nanofibrils (TOCNF) are polysaccharide nanomaterials that are extracted mainly from wood, plants and other biomass sources (Isogai et al 2011; Moon et al 2011; Clarkson et al 2020)
All the laminates tested were comprised of 10 layers of neat TEMPO cellulose nanofibril (TOCNF) or TOCNF + polyvinyl alcohol (PVA) composite films and different epoxy interlayers
Information about the different epoxy formulations can be found on Table 1

Summary

Introduction

TEMPO (2,2,6,6-tetramethylpiperidine-1-oxyl)-oxidized cellulose nanofibrils (TOCNF) are polysaccharide nanomaterials that are extracted mainly from wood, plants and other biomass sources (Isogai et al 2011; Moon et al 2011; Clarkson et al 2020). These materials have attracted attention due to their sustainable and bio-renewable nature and are usually produced by chemically aided methods, where the catalyst TEMPO is used in conjunction with a primary oxidizer (usually hypochlorite or chlorite) to covert the primary hydroxyl groups on the surface of the fibrils to carboxylic acids. Even when films show high strength and stiffness, their brittleness and the high residual stresses generated within the films during drying, makes the production of thick materials difficult and reduce the potential for industrial applications (Forti et al 2020)

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