Strength and barrier properties of MFC films

Abstract

The preparation of microfibrillar cellulose (MFC) films by filtration on a polyamide filter cloth, in a dynamic sheet former and as a surface layer on base paper is described. Experimental evidence of the high tensile strength, density and elongation of films formed by MFC is given. Typically, a MFC film with basis weight 35 g/m 2 had tensile index 146 ± 18 Nm/g and elongation 8.6 ± 1.6%. The E modulus (17.5 ± 1.0 GPa) of a film composed of randomly oriented fibrils was comparable to values for cellulose fibres with a fibril angle of 50°. The strength of the films formed in the dynamic sheet former was comparable to the strength of the MFC films prepared by filtration. The use of MFC as surface layer (0-8% of total basis weight) on base paper increased the strength of the paper sheets significantly and reduced their air permeability dramatically. FEG-SEM images indicated that the MFC layer reduced sheet porosity, i.e. the dense structure formed by the fibrils resulted in superior barrier properties. Oxygen transmission rates (OTR) as low as 17 ml m -2 day -1 were obtained for films prepared from pure MFC. This result fulfils the requirements for oxygen transmission rate in modified atmosphere packaging.

Direct measurements of non-ionic attraction and nanoscaled lubrication in biomimetic composites from nanofibrillated cellulose and modified carboxymethylated cellulose

“…A low friction coefficient of 0.83 ± 0.20 was obtained when the polymer was adsorbed on both surfaces. Still, the adhesion in this 30 system was of similar magnitude as when only the cellulose sphere was coated with CMC-g-PEG. Nevertheless, the friction coefficient when both surfaces were coated by CMC-g-PEG is slightly higher than in the case where the polymer was only adsorbed on NFC (0.83 ± 0.20 vs. 0.57 ± 0.07), which could be 35 probably due to the entanglement of PEG chains from both surfaces.…”

“…52 It has been reported that the effect of capillary condensation on the adhesion and friction hysteresis between cellulose surfaces is especially pronounced at RH above 60%. 52 In this work force and friction measurements were carried out at 35% RH, well below the 30 indicated threshold of 60% for the formation of capillary condensates. Friction experiments carried out at 8% RH exhibited friction hysteresis similar to the one presented in Fig.…”

“…Since it is challenging to achieve both high Young's modulus and toughness in man-made composites, many groups have turned to nature for inspiration. [1][2][3][4][5] In nature, the hierarchical structure of biological nanocomposites achieves the desired mechanical properties and 30 complex biological functions in a synergistic manner. 6 More specifically these biocomposites have a common design principle of hierarchical self-assembly of a high weight fraction of reinforcing nano-scaled domains promoting stiffness, and a small weight fraction of soft, organic domain enabling energy 35 dissipation and suppressing catastrophic crack propagation.…”

“…However, no experimental evidence exists on the importance of 30 nano-scaled lubrication between the components in dry state, despite the role of lubrication on toughness enhancement.…”

“…CMC-g-PEG was adsorbed either on NFC film, on the cellulose colloidal probe or on both, from 100 mg/L polymer solution at pH 4.5 overnight, followed by rinsing with deionized water and drying under nitrogen flow. Subsequent 30 force and friction measurements were performed at room temperature and at 35% relative humidity (RH). The humidity was controlled with a home-made humidity chamber, inside which a sample of MgCl 2 saturated solution was placed.…”