Arto Salminen

Nanofibrillated cellulose/carboxymethyl cellulose composite with improved wet strength

In this paper, nanofibrillated cellulose/carboxymethyl cellulose (CMC) composite films were prepared using tape casting. The obtained transparent films showed shear induced partial alignment of fibrils along the casting direction, resulting in birefringence in cross polarized light. The carboxyl groups of CMC could be further utilized to create ionic crosslinking by treatment with glycidyl trimethyl ammonium chloride (GTMA). The GTMA treated composite films had improved mechanical properties both in wet and dry state. The chemical composition and morphologies of composites were analyzed with X-ray photoelectron spectroscopy, elemental analysis, scanning electron microscopy and wide-angle X-ray scattering.

Crosslinked nanofibrillated cellulose: poly(acrylic acid) nanocomposite films; enhanced mechanical performance in aqueous environments

Nanofibrillated cellulose (NFC) was compounded with poly(acrylic acid) (PAA) via solvent casting. Nanocomposite films were thermally-crosslinked to allow the formation of ester bonds between NFC and PAA, as confirmed by 13CNMR and infrared spectroscopy. The network morphology of the cellulose nanofibrils was left intact by the introduction of PAA and crosslinking. Water absorption and swelling was diminished by the introduction of crosslinking, due to the reduced number of vacant hydroxyl and carboxyl groups available to interact with water molecules. Crosslinking with PAA increased the activation energy required for thermal degradation. PAA effectively reinforced NFC, increasing Young’s modulus, tensile strength and glass transition temperature. Crosslinking imparted restraints on segmental motion of polymer chains, further enhancing the thermomechanical properties and retaining elasticity. Wet-strength properties were enhanced due to the reduced hydrophilicity of crosslinked nanocomposite films.

Effect of interfibrillar PVA bridging on water stability and mechanical properties of TEMPO/NaClO2 oxidized cellulosic nanofibril films

TEMPO/NaClO2 oxidized cellulosic nanofibrils (TCNF) were covalently bonded with poly(vinyl alcohol) (PVA) to render water stable films. Pure TCNF films and TCNF-PVA films in dry state showed similar humidity dependent behavior in the elastic region. However, in wet films PVA had a significant effect on stability and mechanical characteristics of the films. When soaked in water, pure TCNF films exhibited strong swelling behavior and poor wet strength, whereas covalently bridged TCNF-PVA composite films remained intact and could easily be handled even after 24h of soaking. Wet tensile strength of the films was considerably enhanced with only 10 wt% PVA addition. At 25% PVA concentration wet tensile strengths were decreased and films were more yielding. This behavior is attributed to the ability of PVA to reinforce and plasticize TCNF-based films. The developed approach is a simple and straightforward method to produce TCNF films that are stable in wet conditions.

Adsorption of Hydrophobically End-Capped Poly(ethylene glycol) on Cellulose

Adsorption of poly(ethylene glycol), hydrophobically end-capped with octadecenylsuccinic anhydride (OSA-PEG-OSA), on an ultrathin film of cellulose has been studied by quartz crystal microbalance with dissipation monitoring (QCM-D) and atomic force microscopy (AFM). Normally, PEG does not adsorb on cellulosic surfaces, but the use of the telechelic hydrophobic modification was found to promote adsorption. The influence of the conformation of the polymer in solution prior to adsorption and the subsequent properties of the adsorbed layer were investigated. The adsorption experiments were done at concentrations below and above the critical association concentration. The adsorption of OSA-PEG-OSA on cellulose was observed to occur in four distinct stages. Because of the amphiphilic nature of cellulose, further adsorption experiments were performed on hydrophobic (polystyrene) and hydrophilic (silica) model substrates to illuminate the contribution of hydrophobic and hydrophilic factors in the adsorption phenomenon. As expected, the kinetics and the mechanism of adsorption were strongly dependent on the chemical composition of the substrate.

Elastic, crosslinked poly(acrylic acid) filaments: nanocellulose reinforcement and graphene lubrication

Hybrid monofilaments of poly(acrylic acid) (PAA) and 1,6-hexanediol diglycidyl ether (16DGE), compounded with nanofibrillated cellulose (NFC) and graphene, were thermally crosslinked and subsequently spun from aqueous solution. Crosslinking, in the form of ester linkage formation, between PAA and 16DGE was successfully achieved via thermal induction. The monofilaments were elastic and flexible in nature, displaying remarkable elongation and work-to-break values (up to nine times higher than pure PAA–16DGE filaments). This unique behaviour derives from a synergy between the fillers; namely the reinforcing ability of cellulose nanofibrils and the lubricating effect of graphene.