The Influence of the Multi-level Structure Under High Drawing on the Preparation of High Strength Lyocell Fiber

In order to research the multi-level structure of Lyocell fiber at different draw ratios and to reveal the limiting factors for preparing the high strength Lyocell fiber, the paper reports on the effect of draw ratio including low drawing (1–5), high drawing (6–11) and excessive drawing (12–20) on the multi-level structure and the mechanical properties of Lyocell fiber. The structure was determined by wide-angle X-ray diffraction, small-angle X-ray scattering and fibrillation test, and the result showed that, at low draw ratio stage, the breaking strength, yield strength and modulus of the fiber increased with the draw ratio owing to crystallinity as well as orientation increased while the micropore decreased, and there are almost no microfibrils on the fiber surface. At high draw ratio stage, the orientation of amorphous region increasing was the principal reason for the increase of fiber mechanical properties, and the micropores continued to decrease and a few short and thick microfibril was formed. At excessive draw ratio stage, the breaking strength remained constant mainly due to the basically unchanged crystallinity and orientation of the fibers, the yield strength and modulus decreased due to the slip of the highly crystallized and oriented elementary fibril. Meanwhile, the micropores still decreased and became much slenderer, the number of microfibrils increased and the microfibrils showed tenuous structure. It could be summarized that Lyocell fiber had the characteristics of multi-level structure, and the fundamental reason limiting the improvement of mechanical properties with draw ratio increase was the slip of elementary fibril.

Multiscale fibril structure of hollow windmill palm fibers

Windmill palm fiber is a kind of multicellular lignocellulose fiber material. Multiscale structure is an essential factor in mechanical properties and applications. The multiscale fibrils under sulfuric acid treatment had been prepared to improve the understanding of the macro-, micro-, and nanoscale structure of the windmill palm fiber. Scanning electron microscopy, atomic force microscopy, wide-angle X-ray scattering, and X-ray diffraction were used to analyze these samples’ structure. Furthermore, the result showed that the elementary fibril diameter was 4–10 nm, whereas that of the microfibrils was 20–70 nm. The diameters of macrofibril and macrofibril bundles were 0.4–1.0 µm and 1.2–5.5 µm, respectively. The elementary fibril assembled into spiral microfibril with an angle of 46°. The crystallinity of nanofibril extracted from windmill palm fiber was about 62%.

DNA-Guided Assembly for Fibril Proteins

Current advances in computational modelling and simulation have led to the inclusion of computer scientists as partners in the process of engineering of new nanomaterials and nanodevices. This trend is now, more than ever, visible in the field of deoxyribonucleic acid (DNA)-based nanotechnology, as DNA’s intrinsic principle of self-assembly has been proven to be highly algorithmic and programmable. As a raw material, DNA is a rather unremarkable fabric. However, as a way to achieve patterns, dynamic behavior, or nano-shape reconstruction, DNA has been proven to be one of the most functional nanomaterials. It would thus be of great potential to pair up DNA’s highly functional assembly characteristics with the mechanic properties of other well-known bio-nanomaterials, such as graphene, cellulos, or fibroin. In the current study, we perform projections regarding the structural properties of a fibril mesh (or filter) for which assembly would be guided by the controlled aggregation of DNA scaffold subunits. The formation of such a 2D fibril mesh structure is ensured by the mechanistic assembly properties borrowed from the DNA assembly apparatus. For generating inexpensive pre-experimental assessments regarding the efficiency of various assembly strategies, we introduced in this study a computational model for the simulation of fibril mesh assembly dynamical systems. Our approach was based on providing solutions towards two main circumstances. First, we created a functional computational model that is restrictive enough to be able to numerically simulate the controlled aggregation of up to 1000s of elementary fibril elements yet rich enough to provide actionable insides on the structural characteristics for the generated assembly. Second, we used the provided numerical model in order to generate projections regarding effective ways of manipulating one of the the key structural properties of such generated filters, namely the average size of the openings (gaps) within these meshes, also known as the filter’s aperture. This work is a continuation of Amarioarei et al., 2018, where a preliminary version of this research was discussed.

Wood Moisture-Induced Swelling at the Cellular Scale—Ab Intra

Wood, a complex hierarchical material, continues to be widely used as a resource to meet humankind’s material needs, in addition to providing inspiration for the development of new biomimetic materials. However, for wood to meet its full potential, researchers must overcome the challenge of understanding its fundamental moisture-related properties across its many levels of hierarchy spanning from the molecular scale up to the bulk wood level. In this perspective, a review of recent research on wood moisture-induced swelling and shrinking is presented from the molecular level to the cellular scale. Numerous aspects of swelling and shrinking in wood remain poorly understood, sub-cellular phenomena in particular, because it can be difficult to study them experimentally. Here, we discuss recent research endeavors at each of the relevant length scales, including the molecular, cellulose elementary fibril, secondary cell wall layer nanostructure, cell wall, cell, and cellular levels. At each length scale, we provide a discussion on the current knowledge and suggestions for future research. The potential impacts of moisture-induced swelling pressures on experimental observations of swelling and shrinking in wood at different length scales are also recognized and discussed.

Ultrastructure of the elementary fibril in extended and condensed chromatin and in metaphase chromosomes

The chromatin Ultrastructure of nuclei in ultrathin sections of root meristem in <i>Cucurbita pepo</i> - the species poor in DNA, and in <i>Haemanthus katharinae</i> - rich in DNA was compared. Four combinations of fixation and embedding were used: 1) OsO₄ (pH 7.2), methacrylates; 2) OsO₄ (pH 7.2), Epon; 3) OsO₄ (pH 6.8), Epon; 4) glutaraldehyde (pH 7.2-7.4) with OsO4 postfixation, Epon embedding. Most suitable was OsO₄ fixation (pH 7.2) and embedding in Epon because of the smallest dispersion of dimensions of chromatin fibrils and good visibility of their substructure. Fibrils of condensed chromatin, components of chromocenters (heterochromatin) in <i>Cucurbita pepo</i>, bands of chromonemata visible in the light microscope and metaphase chromosomes in <i>Haemanthus katharinae</i> showed a diameter of about 11.5 nm after OsO₄ fixation, or 14-19 nm after glutaraldehyde. Fibrils of extended chromatin (euchromatin) in <i>Cucurbita pepo</i> are thinner, their diameter is about 10 nm after OsO₄ fixation and Epon embedding, and about 14.5 nm after glutaraldehyde. There are no visible differences in the width of elementary fibrils after OsO₄ fixation and embedding in methacrylates. In both species the fibrils of extended chromatin are built up of one coiled deoxyribonucleohistone (DNH) thread about 2.3 nm in diameter, while the fibrils of condensed chromatin consist of two DNH threads, each about 3 nm in diameter. The diameter of DNH threads is determined neither by the fixative nor by the way of embedding; they are less visible in the material embedded in methacrylates. The results obtained show that the structure of chromatin fibrils depends on the kind of chromatin, but not on DNA content. In <i>Haemanthus katharinae</i>, the species rich in DNA, the greater amount of chromatin appears in condensed form.

Near-Infrared Spectroscopic Monitoring of the Diffusion Process of Deuterium-Labeled Molecules in Wood. Part II: Hardwood

Fourier transform near-infrared (FT-NIR) transmission spectroscopy was applied to monitor the diffusion process of deuterium-labeled molecules in hardwood (Beech). The results are compared with previous data obtained on softwood (Sitka spruce) in order to consistently understand the state of order in cellulose of wood. The saturation accessibility and diffusion rate varied characteristically with the OH groups in different states of order in the wood substance, the diffusants, and the wood species, respectively. The variation of saturation accessibility should be associated with the fundamental difference of the fine structure such as the microfibrils in the wood substance. The effect of the anatomical cellular structure on the accessibility was reflected in the variation of the diffusion rate with the wood species. The size effect of the diffusants also played an important role for the diffusion process in wood. Since the volumetric percentage of wood fibers and wood rays is relatively similar, the dichroic effects due to the anisotropy of the cellulose chains were apparently diminished. Finally, we proposed a new interpretation of the fine structure of the microfibrils in the cell wall by comparing a series of results from hardwood and softwood. Each elementary fibril in the hardwood has a more homogeneous arrangement in the microfibrils compared to that in the softwood.

The Effect of Deesterification on the Molecular Organization of Pectin

Negatively stained preparations of high molecular weight pectic acids contain long elementary fibrils about 30A in diameter. Analogous preparations of high ester pectins contain much shorter elementary fibrils of the same diameter.To investigate the relationship between esterification and elementary fibril length, a 0.1% solution of 86% ester pectin was enzymatically deesterified. The extent of deesterification was monitored during the reaction by titration with NaOH. Samples were removed during deesterification, mixed with an equal volume of 2% PTA (pH 7), and the mixture was applied to film covered grids. Length measurements were made from electron micrographs using an optical micrometer.