Melt Processing of Ethylene-Acrylic Acid Copolymer Composites Reinforced with Nanocellulose

To investigate the impact of process design factors such as number of passes, screw design and screw type, a poly(ethylene-co-acrylic acid) and a masterbatch containing 40 vol% nanocellulose were compounded using a twin-screw extruder with two different screw configurations. The 20 vol% composite pellets obtained, containing nanocellulose of different morphologies, cellulose nanofibrils and cellulose nanocrystals, were re-extruded several times to study the effect of re-extrusion. The compounded pellets were extruded into films using a single-screw extruder. These films contained aggregates of the nanocellulose material, which was reduced in size upon re-extrusion leading to an improvement in properties of the composites. With the best combination of process factors, the Young\u27s modulus and stress at break of the composites increased by factors of 10 and 1.6, respectively. The presence of a strong network of the cellulosic entities was observed qualitatively using melt rheology upon re-extrusion. Re-extrusion had a negligible effect on the crystallinity of the composites. POLYM. ENG. SCI., 2020. (c) 2020 The Authors. Polymer Engineering & Science published by Wiley Periodicals, Inc. on behalf of Society of Plastics Engineers

Hybrid Metal-Organic Framework-Cellulose Materials Retaining High Porosity: ZIF-8@Cellulose Nanofibrils

Metal-organic frameworks have attracted a great deal of attention for future applications in numerous areas, including gas adsorption. However, in order for them to reach their full potential a substrate to provide an anchor may be needed. Ideally, this substrate should be environmentally friendly and renewable. Cellulose nanofibrils show potential in this area. Here we present a hybrid material created from the self-assembly of zeolitic imidazolate framework (ZIF-8) nanocrystals on cellulose nanofibrils (CNF) in aqueous medium. The CNF/ZIF-8 was freeze dried and formed free standing materials suitable for gas adsorption. A BET area of 1014 m2 g−1 was achieved for the CNF/ZIF-8 hybrid materials ZIF-8@cellulose which is comparable with reported values for free standing ZIF-8 materials, 1600 m2 g−1, considering the dilution with cellulose, and a considerable enhancement compared to CNF on its own, 32 m2 g−1

Cellulose nanofibril-reinforced composites using aqueous dispersed ethylene-acrylic acid copolymer

In order to explore the reinforcing capabilities of cellulose nanofibrils, composites containing high contents of cellulose nanofibrils were prepared through a combination of water-assisted mixing and compression moulding, the components being a cellulose nanofibril suspension and an aqueous dispersion of the polyolefin copolymer poly(ethylene-co-acrylic acid). The composite samples had dry cellulose nanofibril contents from 10 to 70 vol%. Computed tomography revealed well dispersed cellulose fibril/fibres in the polymer matrix. The highest content of 70 vol% cellulose nanofibrils increased the strength and stiffness of the composites by factors of 3.5 and 21, respectively, while maintaining an elongation at break of about 5%. The strength and strain-at-break of cellulose nanofibril composites were superior to the pulp composites at cellulose contents greater than 20 vol%. The stiffness of the composites reinforced with cellulose nanofibrils was not higher than for that of composites reinforced with cellulose pulp fibres. Graphical Abstract: [Figure not available: see fulltext.]

Composites with surface-grafted cellulose nanocrystals (CNC)

Hydroxyazetidinium salts were used to surface-modify cellulose nanocrystals (CNC) by grafting the salts onto the sulphate ester groups on the CNC surfaces. The grafting was confirmed by ζ-potential measurements and by the thermal degradation behaviour of the modified CNC. The thermal stability (onset of degradation) of the CNC was improved by the surface modification (almost 100\ua0\ub0C). Composites containing surface-modified or unmodified CNC (0.1, 1.0 and 10\ua0wt%) with an ethylene-based copolymer as matrix were produced by compression moulding. The thermal stability of the composites was not, however, markedly improved by the surface grafting onto the CNC. It is suggested that this is due to a degrafting mechanism, associated with the alkaline character of the system, taking place at high temperatures. Model experiments indicated, however, that this did not occur at the conditions under which the composites were produced. Furthermore, in the case of a reference based on pH-neutralised polymeric system and modified CNC, an upward shift in the onset of thermal degradation of the composite was observed. The addition of the CNC to the polymer matrix had a strong influence of the mechanical performance. For example, the tensile modulus increased approximately three times for some systems when adding 10\ua0wt% CNC. The surface grafting of the hydroxyazetidinium salts appeared mainly to affect, in a positive sense, the yield behaviour and ductility of the composites. The results of the mechanical testing are discussed in terms of interactions between the grafted units and the matrix material and between the grafted groups

P2X7 receptor: Death or life?

The P2X7 plasma membrane receptor is an intriguing molecule that is endowed with the ability to kill cells, as well as to activate many responses and even stimulate proliferation. Here, the authors give an overview on the multiplicity and complexity of P2X7-mediated responses, discussing recent information on this receptor. Particular attention has been paid to early and late signs of apoptosis and necrosis linked to activation of the receptor and to the emerging field of P2X7 function in carcinogenesis

Chemical Modification of Electrospun Cellulose Nanofibers

The forest industry is a large part of the Swedish economy and the export of pulp, paper and wood products constitutes 11% of the total Swedish export of goods. The main product of a pulp mill is purified cellulose, which has many great properties like biodegradability and non-toxicity. Cellulose pulps are mainly used for paper and board products whereas speciality pulp such as dissolving pulp is used for regenerated cellulose in fiber and cellophane production. Cellulose is difficult to dissolve and process, but some ionic liquids have the ability to dissolve cellulose. Ionic liquids also have low vapor pressure and low flammability which make them suitable for large scale processes.In this thesis sub-micron scale cellulose nanofibers were created by electrospinning of cellulose from ionic liquid. Solution properties were studied and correlated to nanofiber formation. It was found that co-solvents could decrease viscosity and surface tension. As a consequence the rheological properties of the electrospun cellulose solutions could be linked to fiber formation. Successfully electrospun solutions had a high zero shear viscosity were highly shear thinning.Electrospun cellulose nanofibers were thereafter further functionalized towards different applications. They were made conductive by synthesis of a polypyrrole layer on the nanofiber surface. It was shown that polypyrrole adhered to the nanofiber surface and increased the surface roughness of the nanofibers. The non-toxic property of cellulose was retained after polypyrrole synthesis and neural cell culture experiment indicated that polypyrrole enhanced cell adhesion to the nanofibers.Electrospun cellulose nanofibers were chemically modified to give carboxylate rich surfaces. These anionic fibers were used as templates for synthesis of nano-porous structures of metal-organic framework (MOF). Carboxymethylated nanofibers had an even distribution of MOFs over the nanofiber surface. The MOF functionalized cellulose nanofibers had good adsorption properties and the surface area was greatly increased.The concept of synthesizing MOFs on cellulose was transferred to another type of nano structured cellulose, cellulose nanofibrils (CNF), which currently can be produced in larger amounts than electrospun cellulose. A zeolitic imidazolate framework (ZIF) was synthesized on CNF in aqueous medium. Highly porous novel ZIF/CNF hybrid materials were created

Chemical Modification of Electrospun Cellulose Nanofibers

The forest industry is a large part of the Swedish economy and the export of pulp, paper and wood products constitutes 11% of the total Swedish export of goods. The main product of a pulp mill is purified cellulose, which has many great properties like biodegradability and non-toxicity. Cellulose pulps are mainly used for paper and board products whereas speciality pulp such as dissolving pulp is used for regenerated cellulose in fiber and cellophane production. Cellulose is difficult to dissolve and process, but some ionic liquids have the ability to dissolve cellulose. Ionic liquids also have low vapor pressure and low flammability which make them suitable for large scale processes.In this thesis sub-micron scale cellulose nanofibers were created by electrospinning of cellulose from ionic liquid. Solution properties were studied and correlated to nanofiber formation. It was found that co-solvents could decrease viscosity and surface tension. As a consequence the rheological properties of the electrospun cellulose solutions could be linked to fiber formation. Successfully electrospun solutions had a high zero shear viscosity were highly shear thinning.Electrospun cellulose nanofibers were thereafter further functionalized towards different applications. They were made conductive by synthesis of a polypyrrole layer on the nanofiber surface. It was shown that polypyrrole adhered to the nanofiber surface and increased the surface roughness of the nanofibers. The non-toxic property of cellulose was retained after polypyrrole synthesis and neural cell culture experiment indicated that polypyrrole enhanced cell adhesion to the nanofibers.Electrospun cellulose nanofibers were chemically modified to give carboxylate rich surfaces. These anionic fibers were used as templates for synthesis of nano-porous structures of metal-organic framework (MOF). Carboxymethylated nanofibers had an even distribution of MOFs over the nanofiber surface. The MOF functionalized cellulose nanofibers had good adsorption properties and the surface area was greatly increased.The concept of synthesizing MOFs on cellulose was transferred to another type of nano structured cellulose, cellulose nanofibrils (CNF), which currently can be produced in larger amounts than electrospun cellulose. A zeolitic imidazolate framework (ZIF) was synthesized on CNF in aqueous medium. Highly porous novel ZIF/CNF hybrid materials were created