Influence of Magnetic Field Alignment of Cellulose Whiskers on the Mechanics of All-Cellulose Nanocomposites

Abstract

Orientation of cellulose nanowhiskers (CNWs) derived from tunicates, in an all-cellulose nanocomposite, is achieved through the application of a magnetic field. CNWs are incorporated into a dissolved cellulose matrix system and during solvent casting of the nanocomposite a magnetic field is applied to induce their alignment. Unoriented CNW samples, without the presence of a magnetic field, are also produced. The CNWs are found to orient under the action of the magnetic field, leading to enhanced stiffness and strength of the composites, but not to the level that is theoretically predicted for a fully aligned system. Lowering the volume fraction of the CNWs is shown to allow them to orient more readily in the magnetic field, leading to larger relative increases in the mechanical properties. It is shown, using polarized light microscopy, that the all-cellulose composites have a domain structure, with some domains showing pronounced orientation of CNWs and others where no preferred orientation occurs. Raman spectroscopy is used to both follow the position of bands located at ~1095 and ~895 cm(-1) with deformation and also their intensity as a function rotation angle of the specimens. It is shown that these approaches give valuable independent information on the respective molecular deformation and orientation of the CNWs, and the molecules in the matrix phase, in oriented and nonoriented domains of all-cellulose composites. These data are then related to an increase in the level of molecular deformation in the axial direction, as revealed by the Raman technique. Little orientation of the matrix phase is observed under the action of the magnetic field indicating the dominance of the stiff CNWs in governing mechanical properties.

A Review of Natural Fiber Reinforced Poly(Vinyl Alcohol) Based Composites: Application and Opportunity

“…The natural affinity of nanocellulose for self-assembly and structural anisotropy has allowed them to orient under external forces such as magnetic, electric, and shear fields [55,56]. When a magnetic force is applied, the negative diamagnetic susceptibility of nanocellulose can be aligned perpendicular to the magnetic field direction [57].…”

Orientation of cellulose nanocrystals in electrospun polymer fibres

“…Strong matrix-filler interactions leading to efficient stress transfer within composite fibres and oriented CNCs along the fibre axis are expected to enhance anisotropic mechanical properties such as axial stiffness. There have been several studies on directing orientation of different forms of cellulosic materials during processing, via electric fields [13], magnetic fields [14] and conventional wet spinning [15]. However, little work has been published on the orientation of CNCs in fibres produced by electrospinning.…”

“…However, they were not able to investigate the orientation of CNC in fibres with larger diameters. Similarly, Raman spectroscopy has been reported as an essential tool in mapping the orientation of CNCs in polymeric matrices [14]; but to date not electrospun fibres. This approach utilizes the measurement of the intensity of a Raman peak related to the nanofiller as a function of rotation of the specimen with respect to the fixed axis of polarization.…”

Benchmarking Cellulose Nanocrystals: From the Laboratory to Industrial Production

“…23 The literature commonly presents CNCs as reinforcing agents in nanocomposites, rheological modifiers/stabilizers, and as additives in biomedical devices; these and many other applications are described in a number of comprehensive review papers. 9,18,[23][24][25][26][27][28][29] In addition to their high aspect ratio and large surface area, CNCs have unique physical properties, such as their ability to self-assemble into chiral nematic liquid crystalline phases, [30][31][32][33] align in magnetic [34][35][36][37][38][39] and electric fields, [40][41][42] and exhibit piezoelectric reponsivity. 43 Our work on CNCs has primarily focused on developing hybrid nanomaterials such as films, aerogels, and liquid formulated products.…”

“…119 The formation of these structures in all of the CNCs investigated is an advantage for future applications. However, despite the many academic demonstrations and control of CNC selfassembly in magnetic [34][35][36][37][38][39] and electric fields, [40][41][42] exploitation of this behaviour in a commercially relevant and scalable processes remains to be seen. The most significant impact of Soxhlet extraction observed in this work was in the crystal structure of FPL CNCs.…”