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Bidiville A.,Q - Cells SE | Bidiville A.,Ecole Polytechnique Federale de Lausanne | Neulist I.,Q - Cells SE | Wasmer K.,Empa Swiss Federal Laboratories for Material Testing and Research | Ballif C.,Ecole Polytechnique Federale de Lausanne
Solar Energy Materials and Solar Cells | Year: 2011

The wafers used by the photovoltaic industry are mostly produced by multi-wire slurry sawing. One of the key factors determining the wafer quality (presence of saw marks and chips, increased roughness, wafer thickness variations and wafer strength) is the abrasive slurry. For cost reduction, the slurry is regularly exchanged and the debris it contains is removed in a recycling operation. To optimise the slurry usage, it is of utmost importance to understand the effects of the silicon debris concentration in the slurry. This was studied by sawing several bricks one after the other with the same slurry. It was found that when the amount of debris is too high (more than 4% of the slurry volume), saw marks appear on the wafers and they become more fragile. Finally, a first qualitative model explaining the apparition of the saw marks and the reduction of wafer strength is proposed. © 2011 Elsevier B.V.


Ermeydan M.A.,Max Planck Institute of Colloids and Interfaces | Cabane E.,ETH Zurich | Cabane E.,Empa Swiss Federal Laboratories for Material Testing and Research | Gierlinger N.,ETH Zurich | And 4 more authors.
RSC Advances | Year: 2014

As an engineering material derived from renewable resources, wood possesses excellent mechanical properties in view of its light weight but also has some disadvantages such as low dimensional stability upon moisture changes and low durability against biological attack. Polymerization of hydrophobic monomers in the cell wall is one of the potential approaches to improve the dimensional stability of wood. A major challenge is to insert hydrophobic monomers into the hydrophilic environment of the cell walls, without increasing the bulk density of the material due to lumen filling. Here, we report on an innovative and simple method to insert styrene monomers into tosylated cell walls (i.e. -OH groups from natural wood polymers are reacted with tosyl chloride) and carry out free radical polymerization under relatively mild conditions, generating low wood weight gains. In-depth SEM and confocal Raman microscopy analysis are applied to reveal the distribution of the polystyrene in the cell walls and the lumen. The embedding of polystyrene in wood results in reduced water uptake by the wood cell walls, a significant increase in dimensional stability, as well as slightly improved mechanical properties measured by nanoindentation. This journal is © the Partner Organisations 2014.


Ermeydan M.A.,ETH Zurich | Ermeydan M.A.,Empa Swiss Federal Laboratories for Material Testing and Research | Ermeydan M.A.,Max Planck Institute of Colloids and Interfaces | Cabane E.,ETH Zurich | And 6 more authors.
Green Chemistry | Year: 2014

Materials derived from renewable resources are highly desirable in view of more sustainable manufacturing. Among the available natural materials, wood is one of the key candidates, because of its excellent mechanical properties. However, wood and wood-based materials in engineering applications suffer from various restraints, such as dimensional instability upon humidity changes. Several wood modification treatments increase water repellence, but the insertion of hydrophobic polymers can result in a composite material which cannot be considered as renewable anymore. In this study, we report on the grafting of the fully biodegradable poly(ε-caprolactone) (PCL) inside the wood cell walls by Sn(Oct)2 catalysed ring-opening polymerization (ROP). The presence of polyester chains within the wood cell wall structure is monitored by confocal Raman imaging and spectroscopy as well as scanning electron microscopy. Physical tests reveal that the modified wood is more hydrophobic due to the bulking of the cell wall structure with the polyester chains, which results in a novel fully biodegradable wood material with improved dimensional stability. This journal is © the Partner Organisations 2014.


Civardi C.,Empa Swiss Federal Laboratories for Material Testing and Research | Civardi C.,ETH Zurich | Schwarze F.W.M.R.,Empa Swiss Federal Laboratories for Material Testing and Research | Wick P.,Empa Swiss Federal Laboratories for Material Testing and Research
Environmental Pollution | Year: 2015

Copper (Cu) is an essential biocide for wood protection, but fails to protect wood against Cu-tolerant wood-destroying fungi. Recently Cu particles (size range: 1 nm-25 μm) were introduced to the wood preservation market. The new generation of preservatives with Cu-based nanoparticles (Cu-based NPs) is reputedly more efficient against wood-destroying fungi than conventional formulations. Therefore, it has the potential to become one of the largest end uses for wood products worldwide. However, during decomposition of treated wood Cu-based NPs and/or their derivate may accumulate in the mycelium of Cu-tolerant fungi and end up in their spores that are dispersed into the environment. Inhaled Cu-loaded spores can cause harm and could become a potential risk for human health. We collected evidence and discuss the implications of the release of Cu-based NPs by wood-destroying fungi and highlight the exposure pathways and subsequent magnitude of health impact. © 2015 Elsevier Ltd. All rights reserved.


Thygesen L.G.,Copenhagen University | Gierlinger N.,ETH Zurich | Gierlinger N.,Empa Swiss Federal Laboratories for Material Testing and Research | Gierlinger N.,Johannes Kepler University
Journal of Structural Biology | Year: 2013

Polarised Raman micrsospectroscopy was employed to study the molecular structure within dislocations (slip planes) in the cell walls of Hemp fibre cells (Cannabis sativa (L.)). It was found that the cellulose microfibrils within dislocations have a different orientation than in the surrounding cell wall, and that the cellulose in the transition zones between a large dislocation and the surrounding wall may have yet another orientation. Furthermore, cellulose orientation seemed to be less uniform within dislocations than in the surrounding cell wall. © 2013 Elsevier Inc.


Kuttner C.,University of Bayreuth | Hanisch A.,University of Bayreuth | Schmalz H.,University of Bayreuth | Eder M.,Max Planck Institute of Colloids and Interfaces | And 5 more authors.
ACS Applied Materials and Interfaces | Year: 2013

In fiber-reinforced composites, the interphase nanostructure (i.e., the extended region between two phases in contact) has a pronounced influence on their interfacial adhesion. This work aims at establishing a link between the interphase design of PS-based polymeric fiber coatings and their influence on the micromechanical performance of epoxy-based composite materials. Thiol-ene photochemistry was utilized to introduce a polymeric gradient on silica-like surfaces following a two-step approach without additional photoinitiator. Two complementary grafting-techniques were adapted to modify glass fibers: "Grafting-onto" deposition of PB-b-PS diblock copolymers for thin-film coatings (thickness <20 nm) at low grafting density (<0.1 chains/nm 2) - and "grafting-from" polymerization for brush-like PS homopolymer coatings of higher thickness (up to 225 nm) and higher density. Polymer-coated glass fibers were characterized for polymer content using thermogravimetric analysis (TGA) and their nanostructural morphologies by scanning electron microscopy (SEM). Model substrates of flat glass and silicon were studied by atomic force microscopy (AFM) and spectroscopic ellipsometry (SE). The change in interfacial shear strength (IFSS) due to fiber modification was determined by a single fiber pull-out experiment. Thick coatings (>40 nm) resulted in a 50% decrease in IFSS. Higher shear strength occurred for thinner coatings of homopolymer and for lower grafting densities of copolymer. Increased IFSS (10%) was found upon dilution of the surface chain density by mixing copolymers. We show that the interfacial shear strength can be increased by tailoring of the interphase design, even for systems with inherently poor adhesion. Perspectives of polymeric fiber coatings for tailored matrix-fiber compatibility and interfacial adhesion are discussed. © 2013 American Chemical Society.


Keplinger T.,ETH Zurich | Keplinger T.,Empa Swiss Federal Laboratories for Material Testing and Research | Cabane E.,ETH Zurich | Cabane E.,Empa Swiss Federal Laboratories for Material Testing and Research | And 10 more authors.
Acta Biomaterialia | Year: 2015

The hierarchical structure of wood is composed of a cellulose skeleton of high structural order at various length scales. At the nanoscale and microscale the specific structural features of the cells and cell walls result in a lightweight structure with an anisotropic material profile of excellent mechanical performance. By being able to specifically functionalize wood at the level of cell and cell walls one can insert new properties and inevitably upscale them along the intrinsic hierarchical structure, to a level of large-scale engineering materials applications. For this purpose, however, precise control of the spatial distribution of the modifying substances in the complex wood structure is needed. Here we demonstrate a method to insert methacryl groups into wood cell walls using two different chemistry routes. By using these methacryl groups as the anchor points for grafting, various polymers can be inserted into the wood structure. Strikingly, depending on the methacryl precursor, the spatial distribution of the polymer differs strongly. As a proof of concept we grafted polystyrene as a model compound in the second modification step. In the case of methacryloyl chloride the polymer was located mainly at the interface between the cell lumina and the cell wall covering the inner surface of the cells and being traceable up to 2-3 μm in the cell wall, whereas in the case of methacrylic anhydride the polymer was located inside the whole cell wall. Scanning electron microscopy, Fourier transform infrared spectroscopy and especially Raman spectroscopy were used for an in-depth analysis of the modified wood at the cell wall level. © 2014 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.


PubMed | ETH Zurich and Empa Swiss Federal Laboratories for Material Testing and Research
Type: | Journal: Environmental pollution (Barking, Essex : 1987) | Year: 2015

Copper (Cu) is an essential biocide for wood protection, but fails to protect wood against Cu-tolerant wood-destroying fungi. Recently Cu particles (size range: 1 nm-25 m) were introduced to the wood preservation market. The new generation of preservatives with Cu-based nanoparticles (Cu-based NPs) is reputedly more efficient against wood-destroying fungi than conventional formulations. Therefore, it has the potential to become one of the largest end uses for wood products worldwide. However, during decomposition of treated wood Cu-based NPs and/or their derivate may accumulate in the mycelium of Cu-tolerant fungi and end up in their spores that are dispersed into the environment. Inhaled Cu-loaded spores can cause harm and could become a potential risk for human health. We collected evidence and discuss the implications of the release of Cu-based NPs by wood-destroying fungi and highlight the exposure pathways and subsequent magnitude of health impact.

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