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Composite materials based on an ethylene-acrylic acid (EAA) copolymer and 20 wt% cellulose fibers were compounded by two runs in a twin-screw extruder. The composite material with cellulose fibers (CF) and a reference of unfilled EAA were injection molded into plaques using three different temperature profiles with end zone temperatures of 170°C, 200°C, and 230°C. The injection molded samples were then characterized in terms of their mechanical properties, thermal properties, appearance (color and gloss), and surface topography. The higher processing temperatures resulted in a clear discoloration of the composites, but there was no deterioration in the mechanical performance. The addition of cellulose typically gave a tensile modulus three times higher than that of the unfilled EAA, but the strength and strain at rupture were reduced when fibers were added. The processing temperature had no significant influence on the mechanical properties of the composites. Gloss measurements revealed negligible differences between the samples molded at the different melt temperatures but the surface smoothness was somewhat higher when the melt temperature was increased. In general, addition of the cellulose to the EAA reduced the gloss level and the surface smoothness. POLYM. ENG. SCI., 2019. © 2019 Society of Plastics Engineers.

Many polymers, including polyethylene, feature a relatively low melting point and hence must be cross-linked to make them viable for applications that demand a high stiffness and creep resistance at elevated temperatures. The resulting thermoset plastics cannot be recycled, and therefore alternative materials with a reconfigurable internal network structure are in high demand. Here, we establish that such a thermoset-like yet recyclable material can be realized through the addition of a nanocellulose reinforcing agent. A network consisting of cellulose nanocrystals, nano- or microfibrils imparts many of the characteristics that are usually achieved through chemical cross-linking. For instance, the addition of only 7.5 wt % of either nanocellulose material significantly enhances the melt stiffness of an otherwise molten ethylene-acrylate copolymer by at least 1 order of magnitude. At the same time, the nanocellulose network reduces the melt creep elongation to less than 10%, whereas the neat molten matrix would rupture. At high shear rates, however, the molten composites do not display a significantly higher viscosity than the copolymer matrix, and therefore retain the processability of a thermoplastic material. Repeated re-extrusion at 140 °C does not compromise the thermomechanical properties, which indicates a high degree of recyclability. The versatility of dynamic nanocellulose networks is illustrated by 3D printing of a cellulose composite, where the high melt stiffness improves the printability of the resin.

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 °C). Composites containing surface-modified or unmodified CNC (0.1, 1.0 and 10 wt%) 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 wt% 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.

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.

The problem of recovery from neurodegeneration needs new effective solutions. Tissue engineering is viewed as a prospective approach for solving this problem since it can help to develop healthy neural tissue using supportive scaffolds. This study presents effective and sustainable tissue engineering methods for creating biomaterials from cellulose that can be used either as scaffolds for the growth of neural tissue in vitro or as drug screening models. To reach this goal, nanofibrous electrospun cellulose mats were made conductive via two different procedures: carbonization and addition of multi-walled carbon nanotubes. The resulting scaffolds were much more conductive than untreated cellulose material and were used to support growth and differentiation of SH-SY5Y neuroblastoma cells. The cells were evaluated by scanning electron microscopy and confocal microscopy methods over a period of 15 days at different time points. The results showed that the cellulose-derived conductive scaffolds can provide support for good cell attachment, growth and differentiation. The formation of a neural network occurred within 10 days of differentiation, which is a promising length of time for SH-SY5Y neuroblastoma cells.

This study reports the synthesis of conductive polypyrrole (PPy) on electrospun cellulose nanofibers. The cellulose nanofibers were electrospun via cellulose acetate and surface modified using in situ pyrrole polymerization. PPy adhered to the cellulose nanofiber surface as small particles and caused a 105 fold increase in conductivity compared to unmodified cellulose nanofibers. In addition, tests revealed no cytotoxic potential for the PPy coated cellulose nanofiber materials. In vitro culturing using SH-SY5Y human neuroblastoma cells indicated enhanced cell adhesion on the PPy coated cellulose material. SH-SY5Y cell viability was evident up to 15 days of differentiation and cells adhered to the PPy coated cellulose nanofibers and altered their morphology to a more neuron like phenotype.

This study reports the in situ crystal growth of HKUST-1 on electrospun cellulose nanofibers. Two different methods for introducing carboxyl groups on the nanofiber surface were used; HKUST-1 was then synthesized on the cellulose nanofiber surface using a layer-by-layer approach. The distribution of HKUST-1 on the nanofiber surface was highly dependent on the type of anionic pretreatment. The loading of HKUST-1 on the nanofiber surface could be controlled by the layer-by-layer synthesis and the BET surface area could be increased by a factor of 44 to 440 m2 g-1.

Cellulose was electrospun with various concentrations of ionic liquid and cosolvent. Three different cosolvents were used in this study; dimethylacetamide (DMAc), dimethyl formamide (DMF), and dimethyl sulfoxide (DMSO). The cosolvents were added to modify the viscosity, electrical conductivity, and surface tension of the solutions. The solubility of cellulose in ionic liquids is highly affected by changes in solvent properties on the molecular level in the binary solvent systems. The difference in molecular structure of the cosolvents and the interactions between cosolvent and ionic liquid can explain the difference in dissolution power of the cosolvents. Scanning electron microscope (SEM) was used to characterize electrospun cellulose fibers. For the systems tested the importance of having a rather high viscosity and high surface tension, and some degree of shear thinning to produce fibers is shown.