Cross sectional nanoidentification as means of adhesion characterisation at the wood-adhesive bond line

Das Ziel dieser Arbeit war es, ”cross sectional nanoindentation”, eine Methode der Adhäsionsmessung, an einer Holz-Klebstoff Grenfläche anzuwenden. In einem ersten Schritt wurden die Proben verschiedenen Oberflächenbehandlungen unterzogen um die Adhäsion zum herabzusetzen. Eine Kontaktwinkelmessung zeigte signifikante Änderungen aufgrund dieser Behandlungen. Gleichzeitig nahm für alle Probentypen die maximale Zugspannung signifikant ab und lag für einen Probentyp sogar bei fast Null. Somit waren gute Vorraussetzungen zur Messung der spezifischen Adhäsion gegeben. Die Nanoindenter-Messungen wurden an der Holz-Leim-Grenzlinie durchgeführt, an Stellen wo ein vollständiger Kontakt des Leims mit der Zellinnenwand gegeben war. Die Ergebnisse eines ersten Versuchs zeigten in Analogie zum Zugschertest eine Abnahme der Adhäsion bei Proben mit höherem Kontaktwinkel. In einem zweiten Versuch wurden verschiedene Beladefunktionen für die Indents verwendet, um deren Einfluss auf das Experiment zu untersuchen. Hierbei zeigte sich ein starker Hysterese-Effekt bei mehrstufigen weggesteuerten Beladefunktionen aufgrund zusätzlicher viskoelastischer Verformung. Das führte zu einer Zunahme der gemessenen spezifischen Indentationsarbeit als auch der spezifischen Adhäsionsarbeit, wobei letztere Werte von 80-170J/m² annahm. Alle Ergebnisse wiesen jedoch die erwartete signifikante Abnahme der Adhäsion auf. Eine Charakterisierung der Materialeigenschaften von Zellwand und Leim zeigte keine ähnlichen Trends, womit die Möglichkeit von Artefakten verworfen werden konnte. Die gefundenen Ergebnisse erlauben den Schluss, dass die Methode der „cross sectional nanoindentation” an Holz-Leim-Grenzflächen eingesetzt werden kann. Sie sollte somit neue Einsichten in die Natur von adhäsiven Verbindungen in holz-basierten Verbunden ermöglichen.The aim of this work was to find a way to apply the method of cross sectional nanoindentation to wood-adhesive interfaces. Samples were subjected to various surface treatments to artificially lower the adhesion strength. Contact angle measurements showed significant changes for all treatments. In the following shear test, one set of samples displayed a shear strength close to zero, giving a good basis for measuring the specific adhesion was given. Nanoindentation experiments were performed directly at the wood-adhesive bond line, where the adhesive was in intimate contact with the inner cell wall of wood cells. Results from a first experiment displayed a clear trend of decreasing adhesion for increasing contact angles, in accordance with the shear test. In a second experiment, indents were performed using varying load functions, to analyse their influence on the experiment. Results showed a strong hysteretic behaviour of the force-displacement curve for displacement controlled multi-load functions due to additional visco-elastic deformation, causing an increase in the measured specific work of indentation as well as the specific work of adhesion, which varied between 80-170J/m². However, all results showed the expected significant decrease in adhesive strength. Material characterisation of the cell wall and the adhesive showed no similar trends for their respective mechanical properties, thus allowing to discard the possibility of artefacts. With these findings, it was concluded that cross sectional nanoindentation can indeed be applied to wood-adhesive interfaces and should provide new insights into the nature of adhesive bonds in wood-based composites

Unmodified multi-wall carbon nanotubes in polylactic acid for electrically conductive injection-moulded composites

Tailoring the properties of natural polymers such as electrical conductivity is vital to widen the range of future applications. In this article, the potential of electrically conducting multi-wall carbon nanotube (MWCNT)/polylactic acid (PLA) composites produced by industrially viable melt mixing is assessed simultaneously to MWCNT influence on the composite’s mechanical strength and polymer crystallinity. Atomic force microscopy observations showed that melt mixing achieved an effective distribution and individualization of unmodified nanotubes within the polymer matrix. However, as a trade-off of the poor tube/matrix adhesion, the tensile strength was lowered. With 10 wt% MWCNT loading, the tensile strength was 26% lower than for neat PLA. Differential scanning calorimetric measurements indicated that polymer crystallization after injection moulding was nearly unaffected by the presence of nanotubes and remained at 15%. The resulting composites became conductive below 5 wt% loading and reached conductivities of 51 S m−1 at 10 wt%, which is comparable with conductivities reported for similar nanocomposites obtained at lab scale. </jats:p

Analysis methods in wood and natural fibre science applying nanoindenter and atomic force microscope

Das Ziel dieser Doktorarbeit war die Entwicklung und Implementierung neuer Methoden zur Mikro- und Nanocharakterisierung im Bereich der Naturfaserforschung. Als Instrumente standen hierbei speziell Nanoindenter und Rasterkraftmikroskop zur Verfügung. In Paper 1 wird eine neue Methode zur Adhäsionsmessung mittels Nanoindenter direkt an der Grenzfläche zwischen Zellwand und Leim präsentiert. Diese Methode wird in Paper 2 angewendet, um Unterschiede im Adhäsionsverhalten zweier Leimtypen an der S2- und S3-Zellwandschicht von Fichtenholz zu untersuchen. Der Zusammenhang zwischen Nanorauheit gemessen mit dem Rasterkraftmikroskop und dem optischen Erscheinen von Lignozelluloseoberflächen wird in Paper 3 undersucht. Paper 4 untersucht zeitabhängige nderungen der Oberflächenchemie der S2- und S3-Schicht der Holzzellwand mittels Kraftscans. In Paper 5 wird die richtungsabhängige Wärmeleitfähigkeit von Holzproben mittels Scanning Thermal Microscopy untersucht. Weitere Arbeiten an dieser Methode mit dem Ziel einer quantitativen Messung werden im Experimentalteil der Arbeit präsentiert.The aim of this doctoral thesis was the development and implementation of new methods for micro- and nano-characterisation in natural fibre science. The main experimental devices for this were nanoindenter and atomic force microscope. A new method for measuring the cell wall-adhesive interaction directly at the interface by means of nanoindentation is presented in Paper 1. This method is applied in Paper 2 to analyse dfferences in the bonding behaviour of two types of adhesives to the S2 and S3 cell wall, respectively, of spruce wood. Measuring nanoscale roughness with the AFM, Paper 3 investigates the influence of roughness on the optical appearance of ligno-cellulosic fibres. Paper 4 examines temporal changes in surface chemistry of the S2- and S3 cell wall layer by applying a mechanical mapping mode. Paper 5 introduces scanning thermal microscopy to evaluate the direction-dependent thermal conductivity of wood samples on the cell wall level. Further work on this method with the aim of obtaining quantitative results for fibrous materials is presented in the experimental section of this thesis.submitted by Michael ObersriebnigAbweichender Titel laut Übersetzung der Verfasserin/des VerfassersZsfassung in dt. SpracheWien, Univ. für Bodenkultur, Diss., 2014OeBB(VLID)193166

A WDR Gene Is a Conserved Member of a Chitin Synthase Gene Cluster and Influences the Cell Wall in Aspergillus nidulans

WD40 repeat (WDR) proteins are pleiotropic molecular hubs. We identify a WDR gene that is a conserved genomic neighbor of a chitin synthase gene in Ascomycetes. The WDR gene is unique to fungi and plants, and was called Fungal Plant WD (FPWD). FPWD is within a cell wall metabolism gene cluster in the Ascomycetes (Pezizomycotina) comprising chsD, a Chs activator and a GH17 glucanase. The FPWD, AN1556.2 locus was deleted in Aspergillus nidulans strain SAA.111 by gene replacement and only heterokaryon transformants were obtained. The re-annotation of Aspergilli genomes shows that AN1556.2 consists of two tightly linked separate genes, i.e., the WDR gene and a putative beta-flanking gene of unknown function. The WDR and the beta-flanking genes are conserved genomic neighbors localized within a recently identified metabolic cell wall gene cluster in genomes of Aspergilli. The heterokaryons displayed increased susceptibility to drugs affecting the cell wall, and their phenotypes, observed by optical, confocal, scanning electron and atomic force microscopy, suggest cell wall alterations. Quantitative real-time PCR shows altered expression of some cell wall-related genes. The possible implications on cell wall biosynthesis are discussed

Hyphal ultrastructural differences triggered by CR and DCB.

<p>(A–B): SEM pictures of (A) CR- and (B) DCB-treated mycelium, showing the presence of small particles accumulating on the hyphal surface. (C–L): AFM images, showing surface topographical gradient (C–F) and adhesion maps (G–L) obtained on samples grown overnight at 37°C in control condition (C and G), with 100 µM CR (D and H), with 1% v/v MetOH (E and I) and 200 µM DCB (F and L). Bars refer to 10 µm (A and B) and 2 µm (C–L).</p

Sensitivity of <i>Aspergillus nidulans</i> to the Cellulose Synthase Inhibitor Dichlobenil: Insights from Wall-Related Genes’ Expression and Ultrastructural Hyphal Morphologies

<div><p>The fungal cell wall constitutes an important target for the development of antifungal drugs, because of its central role in morphogenesis, development and determination of fungal-specific molecular features. Fungal walls are characterized by a network of interconnected glycoproteins and polysaccharides, namely α-, β-glucans and chitin. Cell walls promptly and dynamically respond to environmental stimuli by a signaling mechanism, which triggers, among other responses, modulations in wall biosynthetic genes’ expression. Despite the absence of cellulose in the wall of the model filamentous fungus <i>Aspergillus nidulans</i>, we found in this study that fungal growth, spore germination and morphology are affected by the addition of the cellulose synthase inhibitor dichlobenil. Expression analysis of selected genes putatively involved in cell wall biosynthesis, carried out at different time points of drug exposure (<i>i.e.</i> 0, 1, 3, 6 and 24 h), revealed increased expression for the putative mixed linkage β-1,3;1,4 glucan synthase <i>celA</i> together with the β-1,3-glucan synthase <i>fksA</i> and the Rho-related GTPase <i>rhoA</i>. We also compared these data with the response to Congo Red, a known plant/fungal drug affecting both chitin and cellulose biosynthesis. The two drugs exerted different effects at the cell wall level, as shown by gene expression analysis and the ultrastructural features observed through atomic force microscopy and scanning electron microscopy. Although the concentration of dichlobenil required to affect growth of <i>A. nidulans</i> is approximately 10-fold higher than that required to inhibit plant cellulose biosynthesis, our work for the first time demonstrates that a cellulose biosynthesis inhibitor affects fungal growth, changes fungal morphology and expression of genes connected to fungal cell wall biosynthesis.</p></div