Controlled molecular reorientation enables strong cellulose fibers regenerated from ionic liquid solutions

Johan Sundberg, Valentina Guccini, Karl M.O. Håkansson, German Salazar-Alvarez, Guillermo Toriz, Paul Gatenholm

Polymer 75 (2015) 119-124.
DOI: 10.1016/j.polymer.2015.08.035

Highlights:
• Strong cellulose fibers spun from ionic liquid solution.
• Extrusion process simulated in silica based upon rheological measurements.
• Increased DO for fibers regenerated with ethanol stretched at high RH.
• Significant improvement of mechanical properties for re-oriented fibers.
• Mechanical properties comparable to commercially available fibers.

Abstract:
Cellulose is difficult to solubilize and undergoes thermal decomposition prior to melting. In recent years ionic liquids have been evaluated as solvents of cellulose. In the regeneration process the non-solvent governs the resulting material's crystallinity. Water adsorbs to amorphous cellulose, acts as plasticizer and lowers the Tg, hence the degree of crystallinity will affect the potential strain induced reorientation. We prepared regenerated cellulose fibers form ionic liquid using different non-solvents. The influence of shear forces upon cellulose chain alignment during extrusion was simulated in silica based upon rheological measurements. The regenerated fibers had different physical, morphological and mechanical properties. Molecular re-orientation in fibers induced by mechanical strain, at humidities above the Tg, resulted in much improved mechanical properties with the Young's modulus reaching 23.4 ± 0.8 GPa and the stress at break 504.6 ± 51.9 MPa, which is comparable to commercially available cellulose fibers.

Thermally insulating and fire-retardant lightweight anisotropic foams based on nanocellulose and graphene oxide

Bernd Wicklein, Andraž Kocjan, German Salazar-Alvarez, Federico Carosio, Giovanni Camino, Markus Antonietti, and Lennart Bergström

Nature Nanotechnology 10 (2015) 277–283
DOI:10.1038/nnano.2014.248

Abstract
High-performance thermally insulating materials from renewable resources are needed to improve the energy efficiency of buildings. Traditional fossil-fuel-derived insulation materials such as expanded polystyrene and polyurethane have thermal conductivities that are too high for retrofitting or for building new, surface-efficient passive houses. Tailored materials such as aerogels and vacuum insulating panels are fragile and susceptible to perforation. Here, we show that freeze-casting suspensions of cellulose nanofibres, graphene oxide and sepiolite nanorods produces super-insulating, fire-retardant and strong anisotropic foams that perform better than traditional polymer-based insulating materials. The foams are ultralight, show excellent combustion resistance and exhibit a thermal conductivity of 15 mW/m·K, which is about half that of expanded polystyrene. At 30 °C and 85% relative humidity, the foams retained more than half of their initial strength. Our results show that nanoscale engineering is a promising strategy for producing foams with excellent properties using cellulose and other renewable nanosized fibrous materials.

[Summer school] Organic–inorganic hybrids and composites: from basic understanding to functional materials

The Chalmers Soft Matter Graduate School is organizing a summer school on “Organic–inorganic hybrids and composites: from basic understanding to functional materials”.  Please find attached the announcement. The summer school will take place between 2-5 of september lunch to lunch and it will be held in Djurönäset in the Stockholm archipelago (www.djuronaset.com).

Scope:
Organic–inorganic hybrids and composites have been playing a major role in research and society in recent years. Traditionally, organic–inorganic hybrids have had a focus on the polymeric matrix filled with relatively passive inorganic components. In parallel, with increased interest in alternatives to fossil fuels, there has been a strong move towards the fabrication of functional materials based on biopolymers that can be extracted from renewable sources. Hybrids and composites based on biopolymers are an ideal component for the fabrication of multifunctional materials in combination with various useful inorganic nanomaterials as they can combine impressive properties with environmentally benign and energy efficient production routes.
This course aims to give the participants an understanding of the properties of the organic and inorganic components, preparation methods, characterisation techniques and also examples of functional hybrid materials.

Topics that will be covered:
• Biopolymers: Properties of biopolymers (cellulose, chitin, DNA, proteins) in solutions and dispersions, JL.
• Bionanomaterials: Types of bionanomaterials, sources and isolation methods, GSA
• Nucleation and assembly: i) Nucleation and growth of inorganic materials, ii)Colloidal processing and assembly of hybrids, LB
• Optical characterisation: Polarised light microscopy, JL
• Morphological characterisation: Electron microscopy and X-ray scattering, GSA
• Surface characterisation: Catechols as model systems, DRM
• Interfacial characterisation: Solid state NMR, DL
• Mechanical characterisation: Tensile, flexural, compression testing and fracture toughness measurements, RL
• Bioinspired composites: High performance composites, RL

Lecturers:

Lennart Bergström (Stockholm University)
Jan Lagerwall (University of Luxembourg)
Danielle Laurencin (Institute Charles Gerhardt of Montpellier, France)
Rafael Libanori (ETH, Zurich, Switzerland)
Daniel Ruiz-Molina (Institut Català de Nanociència i Nanotecnologia, Spain)

German Salazar-Alvarez (Stockholm University)

Registration: 
To apply to the summer school send an email to Christina Schütz (christina.schuetz@mmk.su.se) not later than July 28, 2014. The number of participants is limited to 30 and there is a priority to those students enrolled in the “Soft Matter Graduate School”at Chalmers University (www.chalmers.se/soft/); other students and participants are accepted on a first come, first serve basis. The summer school is free of charge for all students doing their PhD at a Swedish university. For students abroad and other participants, the fee is 6000 SEK (incl. accommodation and all meals; excl. VAT).

Schedule and examination:

time\date	Tuesday 2nd	Wednesday 3rd	Thursday 4th	Friday 5th
9-11.30		Nucleation and assembly	Surface characterisation	Project presentations
11.30-13.00	Arrival and lunch	Lunch	Lunch	Lunch and departure
13.00-15	Biopolymer dispersions and solutions	Optical characterisation	Interfacial characterisation
15-17	Bionanomaterials	Morphological characterisation	Mechanical characterisation
17-18	Free time
18-20	Dinner	School dinner	Dinner
20-21	Project assignments		Bioinspired composites

The students are expected to work actively during the course and the participants will receive material to study in advance. During the course there will be individual assignments and individual presentations. We recommend that students after completing the course will be given 3 ECTS.


Contact:
• German Salazar-Alvarez (course leader) (german@mmk.su.se)
• Christina Schütz (registration and practical issues) (christina.schuetz@mmk.su.se) 

[OPEN ACCESS] Hard and transparent films formed by nanocellulose-TiO2 nanoparticle hybrids

http://dx.doi.org/10.1371/journal.pone.0045828

PLoS ONE 2012, 7, e45828

Christina Schütz, Jordi Sort, Zoltán Bacsik, Vitaliy Oliynyk, Eva Pellicer, Andreas Fall, Lars Wågberg, Lars Berglund, Lennart Bergström, German Salazar-Alvarez

DOI: 10.1371/journal.pone.0045828

Abstract

The formation of hybrids of nanofibrillated cellulose and titania nanoparticles in aqueous media has been studied. Their transparency and mechanical behavior have been assessed by spectrophotometry and nanoindentation. The results show that limiting the titania nanoparticle concentration below 16 vol% yields a homogeneous hybrids with a very high Young’s modulus and hardness, of up to 44 GPa and 3.4 GPa, respectively, and an optical transmittance above 80 %. Electron microscopy shows that higher nanoparticle contents result in agglomeration and an inhomogeneous hybrid nanostructure with a concomitant reduction of hardness and optical transmittance. Infrared spectroscopy suggests that the nanostructure of the hybrids is controlled by electrostatic adsorption of the titania nanoparticles on the negatively charged nanocellulose surfaces.

High strength, flexible and transparent nanocellulose/vermiculite biohybrid films with tunable oxygen and water vapor permeability

http://pubs.rsc.org/en/content/articlelanding/2012/NR/C2NR31726E

Nanoscale, 2012, Accepted Manuscript
DOI: 10.1039/C2NR31726E

Christian Aulin , German Salazar-Alvarez and Tom Lindström

Abstract

A novel, technically benign procedure to combine vermiculite nanoplatelets with nanocellulose fibre dispersions into functional biohybrid films is presented. Nanocellulose fibres of 20 nm diameters and several µm in length are mixed with high aspect ratio exfoliated vermiculite nanoplatelets through high-pressure homogenization. The resulting hybrid films obtained after solvent evaporation are stiff (tensile modulus of 17.3 GPa), strong (strength up to 257 MPa), and transparent. Scanning electron microscopy (SEM) shows that the hybrid films consist of stratified nacre-like layers with a homogenous distribution of nanoplatelets within the nanocellulose matrix. The oxygen barrier properties of the biohybrid films outperform commercial packaging materials and pure nanocellulose films showing an oxygen permeability of 0.07 cm3·μm/m2·day·kPa at 50 % relative humidity. The oxygen permeability of the hybrid films can be tuned by adjusting the composition of the films. Furthermore, the water vapor barrier properties of the biohybrid films were also significantly improved by the addition of nanoclay. The unique combination of excellent oxygen barrier behavior and optical transparency suggest the potential of this biohybrid materials as an alternative in flexible packaging of oxygen sensitive devices like thin-film transistors or organic light-emitting diode displays, gas storage applications and as barrier coatings/laminations in large volume packaging applications.

A transparent hybrid of nanocrystalline cellulose and amorphous calcium carbonate nanoparticles

http://pubs.rsc.org/en/Content/ArticleLanding/2011/NR/c1nr10681c

Nanoscale, 2011, 3, 3563-3566

Denis Gebauer, Vitaliy Oliynyk, Michaela Salajkova, Jordi Sort, Qi Zhou, Lennart Bergström and German Salazar-Alvarez 

DOI: 10.1039/C1NR10681C 

 Abstract:
Nanocellulose hybrids are promising candidates for biodegradable multifunctional materials. Hybrids of nanocrystalline cellulose (NCC) and amorphous calcium carbonate (ACC) nanoparticles were obtained through a facile chemical approach over a wide range of compositions. Controlling the interactions between NCC and ACC results in hard, transparent structures with tunable composition, homogeneity and anisotropy.

Making flexible magnetic aerogels and stiff magnetic nanopaper using cellulose nanofibrils as templates

http://www.nature.com/nnano/journal/v5/n8/abs/nnano.2010.155.html
Nature Nanotechnology 5, 584–588 (2010)
R. T. Olsson, M. A. S. Azizi Samir, G. Salazar-Alvarez, L. Belova, V. Ström, L. A. Berglund, O. Ikkala, J. Nogués & U. W. Gedde

doi:10.1038/nnano.2010.155

Abstract:
Nanostructured biological materials inspire the creation of materials with tunable mechanical properties^{1, 2, 3}. Strong cellulose nanofibrils derived from bacteria⁴ or wood^{5, 6} can form ductile or tough networks^{7, 8} that are suitable as functional materials^{9, 10}. Here, we show that freeze-dried bacterial cellulose nanofibril aerogels can be used as templates for making lightweight porous magnetic aerogels, which can be compacted into a stiff magnetic nanopaper. The 20–70-nm-thick cellulose nanofibrils act as templates for the non-agglomerated growth of ferromagnetic cobalt ferrite nanoparticles¹¹ (diameter, 40–120 nm). Unlike solvent-swollen gels¹² and ferrogels^{13, 14, 15}, our magnetic aerogel is dry, lightweight, porous (98%), flexible, and can be actuated by a small household magnet. Moreover, it can absorb water and release it upon compression. Owing to their flexibility, high porosity and surface area, these aerogels are expected to be useful in microfluidics devices and as electronic actuators.

Cold Consolidation of Metal–Ceramic Nanocomposite Powders with Large Ceramic Fractions

http://onlinelibrary.wiley.com/doi/10.1002/adfm.200800456/abstract

Advanced Functional Materials

Volume 18, Issue 20, pages 3293–3298, October 23, 2008

Enric Menéndez, German Salazar-Alvarez, Alexander P. Zhilyaev, Santiago Suriñach, Maria Dolors Baró, Josep Nogués, Jordi Sort

DOI: 10.1002/adfm.200800456

Abstract

Co/α-Al₂O₃ powder mixtures (5, 10, 20, 30, 40, and 50 mass % of α-Al₂O₃) have been ball-milled and, subsequently, consolidated at room temperature by means of a high pressure torsion procedure in order to produce bulk nanostructured composites. For mixtures up to 20% of α-Al₂O₃, the cold-compaction results in roughly fully dense disks with relatively high microhardness values. However, the compaction for 30, 40, and 50% of α-Al₂O₃ is less effective, resulting in a reduction of the microhardness although a structure in the nanoscale range is still preserved. A detailed structural investigation has been also performed.