24 research outputs found
Nano-mechanical characterization of the wood cell wall by AFM studies: comparison between AC- and QIâą mode
Abstract Background Understanding the arrangement and mechanical properties of wood polymers within the plant cell wall is the basis for unravelling its underlying structureâproperty relationships. As state of the art Atomic Force Microscopy (AFM) has been used to visualize cell wall layers in contact resonance- and amplitude controlled mode (AC) on embedded samples. Most of the studies have focused on the structural arrangement of the S2 layer and its lamellar structure. Results In this work, a protocol for AFM is proposed to characterize the entire cell wall mechanically by quantitative imaging (QIâą) at the nanometer level, without embedding the samples. It is shown that the applied protocol allows for distinguishing between the cell wall layers of the compound middle lamella, S1, and S2 of spruce wood based on their Youngâs Moduli. In the transition zone, S12, a stiffness gradient is measured. Conclusions The QIâą mode pushes the limit of resolution for mechanical characterization of the plant cell wall to the nanometer range. Comparing QIâą- against AC images reveals that the mode of operation strongly influences the visualization of the cell wall
A close-up view of the wood cell wall ultrastructure and its mechanics at different cutting angles by atomic force microscopy
Main conclusion AFM measurements on spruce sample cross-sections reveal that the structural appearance of the Sâ layer changes from a network structure to a concentric lamellar texture depending on the cutting angle. The structural assembly of wood constituents within the secondary cell wall has been subject of numerous studies over the last decades, which has resulted in contradicting models on the spatial arrangement and orientation of the wood macromolecules. Here, we use multichannel atomic force microscopy by means of quantitative imaging, to gain new insights into the macromolecular assembly. Cross-sections of spruce wood, which had been cut at different angles ranging from 0° to 30° were investigated. Strikingly, depending on the cutting angle, the structural appearance of the Sâ layer changed from a network-like structure to a distinct concentric lamellar texture. This makes us conclude that the often visualized lamellar organization of the secondary cell wall is not the consequence of a continuous inherent ring pattern, but rather a result of the specific surface cross-section appearance of cellulose aggregates at larger cutting angles. By analyzing the recorded force distance curves in every pixel, a nano-mechanical characterization of the secondary cell wall was conducted. Substantially lower indentation modulus values were obtained compared to nanoindentation values reported in the literature. This is potentially due to a smaller interaction volume of the probe with a by far less deep indentation.ISSN:0032-0935ISSN:1432-204
Stadtentwicklungsplanung Osnabrueck 6. mittelfristiges Stadtentwicklungsprogramm 1983-1988
SIGLETIB: L rau 905/AC 1695 (6) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman
Delignified and Densified Cellulose Bulk Materials with Excellent Tensile Properties for Sustainable Engineering
Todayâs materials research
aims at excellent mechanical performance in combination with advanced
functionality. In this regard, great progress has been made in tailoring
the materials by assembly processes in bottom-up approaches. In the
field of wood-derived materials, nanocellulose research has gained
increasing attention, and materials with advanced properties were
developed. However, there are still unresolved issues concerning upscaling
for large-scale applications. Alternatively, the sophisticated hierarchical
scaffold of wood can be utilized in a top-down approach to upscale
functionalization, and one can profit at the same time from its renewable
nature, CO<sub>2</sub> storing capacity, light weight, and good mechanical
performance. Nevertheless, for bulk wood materials, a wider multipurpose
industrial use is so far impeded by concerns regarding durability,
natural heterogeneity as well as limitations in terms of functionalization,
processing, and shaping. Here, we present a novel cellulose bulk material
concept based on delignification and densification of wood resulting
in a high-performance material. A delignification process using hydrogen
peroxide and acetic acid was optimized to delignify the entire bulk
wooden blocks and to retain the highly beneficial structural directionality
of wood. In a subsequent step, these cellulosic blocks were densified
in a process combining compression and lateral shear to gain a very
compact cellulosic material with entangled fibers while retaining
unidirectional fiber orientation. The cellulose bulk materials obtained
by different densification protocols were structurally, chemically,
and mechanically characterized revealing superior tensile properties
compared to native wood. Furthermore, after delignification, the cellulose
bulk material can be easily formed into different shapes, and the
delignification facilitates functionalization of the bioscaffold