Roles of xyloglucan and pectin on the mechanical properties of bacterial cellulose composite films

Xyloglucan and pectin are major non-cellulosic components of most primary plant cell walls. It is believed that xyloglucan and perhaps pectin are functioning as tethers between cellulose microfibrils in the cell walls. In order to understand the role of xyloglucan and pectin in cell wall mechanical properties, model cell wall composites created using Gluconacetobacter xylinus cellulose or cellulose nanowhiskers (CNWs) derived there from with different amounts of xyloglucan and/or pectin have been prepared and measured under extension conditions. Compared with pure CNW films, CNW composites with lower amounts of xyloglucan or pectin did not show significant differences in mechanical behavior. Only when the additives were as high as 60 %, the films exhibited a slightly lower Young’s modulus. However, when cultured with xyloglucan or pectin, the bacterial cellulose (BC) composites produced by G. xylinus showed much lower modulus compared with that of the pure BC films. Xyloglucan was able to further reduce the modulus and extensibility of the film compared to that of pectin. It is proposed that surface coating or tethering of xyloglucan or pectin of cellulose microfibrils does not alone affect the mechanical properties of cell wall materials. The implication from this work is that xyloglucan or pectin alters the mechanical properties of cellulose networks during rather than after the cellulose biosynthesis process, which impacts the nature of the connection between these compounds.     

Anisotropy of cell wall polymers in branches of hardwood and softwood: a polarized FTIR study

The mechanical and physical properties of wood fibres are dependent on the organisation of their constituent polymers (cellulose, hemicellulose and lignin). Fourier Transform Infrared (FTIR) microscopy was used to examine the anisotropy of the main wood polymers in isolated cell wall fragments from branches of maple and Serbian spruce. Polarised FTIR measurements indicated an anisotropy, i.e. orientation of the cellulose microfibrils that was more or less parallel to the longitudinal axis of the cell wall. The hemicelluloses, glucomannan and xylan appeared to have a close link to the orientation of the cellulose and, thus, an orientation more parallel to the axis of the cell wall. An important result is that, in both maple and spruce samples, lignin was found to be organised in a parallel way in relation to the longitudinal cell wall axis, as well as to the cellulose. The results show that, despite the different lignin precursors and the different types of hemicelluloses in these two kinds of wood, lignin has a similar orientation, when it comes to the longitudinal axis of the cell wall.     

Visualization of the nanoscale pattern of recently-deposited cellulose microfibrils and matrix materials in never-dried primary walls of the onion epidermis

For more than 10 years epidermal cell layers from onion scales have been used as a model system to study the relationship between cellulose orientation, cell growth and tissue mechanics. To bring such analyses to the nanoscale, we have developed a procedure for preparing epidermal peels of onion scales for atomic force microscopy to visualize the inner surface (closest to the plasma membrane) of the outer epidermal wall, with minimal disturbance and under conditions very close to the native state of the cell wall. The oriented, multilayer distribution of cellulose microfibrils, approximately ~3 nm wide, is readily observed over extended lengths, along with other features such as the distribution of matrix substances between and on top of microfibrils. The microfibril orientation and alignment appear more dispersed in younger scales compared with older scales, consistent with reported values for mechanical and growth anisotropy of whole epidermal sheets. These results open the door to future work to relate cell wall structure at the nm scale with larger-scale tissue properties such as growth and mechanical behaviors and the action of cell wall loosening agents to induce creep of primary cell walls.     

A study on the orientation structure and mechanical properties of polyacrylonitrile precursors

The polyacrylonitrile precursors were made through the two‐stage drawing process. The orientation structure was examined through wide‐angle X‐ray diffraction (WAXD). The orientation factors and the modulus were measured through the sound velocity method. The mechanical properties, such as the Young's modulus, the tensile strength and the breaking elongation ratio were obtained by the single fiber tensile test. The results showed that the Young's modulus and the strength of the precursors increased with draw ratio, which is accordant with the enhancement of the micromolecular orientation degree. Therefore the orientation factors obtained from the experiments were compared with the theoretical curves which were predicted through the Crawford and Kolsky's model. The physical meaning of the parameters m and n were analyzed. A good agreement of the orientation factor between the experimental data and the theoretical curve was achieved. Copyright © 2005 John Wiley & Sons, Ltd.     

The spatial orientation and interaction of cell wall polymers in bamboo revealed with a combination of imaging polarized FTIR and directional chemical removal

Cellulose - The mechanical and physical properties of lignocellulosic materials are closely related to the orientation and interaction of the polymers within cell walls. In this work, Imaging...     

Vibrational analysis of 2-nitrophenol. A joint FT-IR,FT-Raman and scaled quantum mechanical study

FT-IR (gas, solution, solid) and FT-Raman (solution, solid) spectra of 2-nitrophenol have been recorded in the range of 4000–30 cm⁻¹. The spectra were interpreted with the aid of normal coordinate analysis based on a scaled Becke3–Lee–Yang–Parr/6-31G^* density functional force field utilising a set of scale factors introduced recently by Rauhut and Pulay (G. Rauhut, P. Pulay, J. Phys. Chem. 99 (1995) 3093). These scale factors, developed on a small training set of organic molecules containing no hydrogen bonding moieties, were found to be well transferable to 2-nitrophenol including the strong intramolecular (O)H⋯O(N) hydrogen bonding moiety as well. The scaled force field reproduced the experimental frequencies of the molecule by a weighted mean deviation of 10.5 cm⁻¹. Based on the calculated results, 38 fundamentals from a total of 39 were identified and assigned, revising the assignments of earlier experimental studies for several fundamentals.     

Influence of mechanical properties of pectin films on charge density and charge density distribution in pectin macromolecule

The hydration and mechanical properties of citrus pectin films were examined in conditions relevant to those in the plant cell wall. The pectins used for this study varied in the degree of esterification (DE) (high or low) and charge distribution on the backbone (random or block). The hydration of the films was controlled in an osmotic pressure experiment using polyethylene glycol solutions (PEG 20000). Hysteresis tests at constant deformation rate (stress vs deformation) were used for investigating the mechanical behaviour of films. Mechanical and hydration properties of pectin films were examined as a function of charge density, charge density distribution and counterion environment—K⁺, Ca²⁺, Mg²⁺. Swelling decreased with increasing counterion concentration. The effect is stronger in the case of Ca²⁺ and Mg²⁺ for low esterified pectins and therefore crosslinks from divalent ions could be assumed. The crosslink effect is confirmed in mechanical experiments where an increase in the film tensile modulus is observed with increasing counterion concentration. It is shown for the first time that in case of highly concentrated pectin solutions Mg²⁺ cations also act as a crosslinker for pectin macromolecules.     

Effects of orientation on the mechanical and dielectric relaxation behavior of cycloaliphatic polyester networks

The mechanical and dielectric relaxation behavior of strained and unstrained networks, prepared from hydroxyl-terminated poly(diethylene glycol-trans-1,4-cyclohexane dicarboxylate) (PDGC), is studied over a wide interval of frequencies and temperatures. The mechanical relaxation spectrum exhibits a glass-rubber absorption, designated β, located in the vicinity of 0°C at 0.1 Hz, followed by a β relaxation which appears to be the result of two overlapping peaks centered at ?80°C (β₁) and ?110°C(β₂). These two peaks coalesce into a single peak in the case of strained networks. The dielectric relaxation spectrum also exhibits an α absorption followed by a subglass β relaxation whose width decreases as the elongation ratio λ increases. The activation energy associated with the mechanical β₁ appears to increase as λ increases. However, the activation energy of the dielectric β process does not show a clear dependence on the elongation ratio. The analysis of the conformational characteristics of PDGC chains indicates that rotational transitions through the C_cy? C* bonds of the acid residue would give rise to high dielectric activity. Conformational changes about the CH₂? CH₂ bonds of the glycol residue would produce significant mechanical activity but, comparatively, low dielectric activity. The glass-rubber absorption is slightly displaced toward the high-temperature side as the elongation ration increases, suggesting that the entropic effects overcome the volume effects. The glass-rubber transition is interpreted in terms of the free volume theory.     

Moisture uptake in native cellulose – the roles of different hydrogen bonds: a dynamic FT-IR study using Deuterium exchange

This paper aims at a better understanding of the interaction between cellulose and moisture. In particular, the role of different hydrogen bonds in moisture uptake is investigated. Dynamic Fourier transform infrared spectroscopy (FT-IR) has been used in combination with deuterium exchange, which permits the labelling of cellulose domains with different accessibilities. The static spectra indicate a marked exchange of deuterium for the O2–H⋯O6 bonds, but only a limited exchange for the O3–H⋯O5 bonds. In the dynamic FT-IR spectra, deuteration gives rise to the growth of a broad band at wavenumbers around 2500 cm⁻¹. The rather unstructured appearance of the band suggests that deuteration is occurring only on the surface of the cellulose crystallites, i.e. in more or less non-load-carrying parts. This is corroborated by the lack of split peaks related to OD bonds in this band. In agreement with these observations, the split peak related to O3–H⋯O5 bonds and assigned to the load carrying cellulose structure increases during both H₂O and D₂O moisture conditioning, indicating a shift of the load transfer towards the backbone of the cellulose structure.     

Effects of orientation and degree of polymerization on tensile properties in the cellulose sheets using hierarchical structure of wood

Cellulose - Structural control is essential for further development of cellulosic materials. Here, we demonstrated the significance of the orientation and degree of polymerization in the integrated...     

Pressurized Hot Water Extraction of anthocyanins from red onion: A study on extraction and degradation rates

Pressurized Hot Water Extraction (PHWE) is a quick, efficient and environmentally friendly technique for extractions. However, when using PHWE to extract thermally unstable analytes, extraction and degradation effects occur at the same time, and thereby compete. At first, the extraction effect dominates, but degradation effects soon take over. In this paper, extraction and degradation rates of anthocyanins from red onion were studied with experiments in a static batch reactor at 110 °C. A total extraction curve was calculated with data from the actual extraction and degradation curves, showing that more anthocyanins, 21-36% depending on the species, could be extracted if no degradation occurred, but then longer extraction times would be required than those needed to reach the peak level in the apparent extraction curves. The results give information about the different kinetic processes competing during an extraction procedure.     

FT-IR and FT-raman spectroscopy study of the cyclic anhydride intermediates for esterification of cellulose: I. Formation of anhydrides without a catalyst

In recent years, extensive efforts have been made to find nonformaldehyde durable press finishes to replace the traditional formaldehyde-based reagents for producing wrinkle-free cotton fabrics. 1,2,3,4-butanetetracarboxylic acid (BTCA) has been the most effective nonformaldehyde crosslinking agent. Our previous research has indicated that a polycarboxylic acid esterifies cellulose in two steps: the formation of a 5-membered cyclic anhydride intermediate by the dehydration of two adjacent carboxyl groups, and the reaction between cellulose and the anhydride intermediate to form an ester linkage. In this research, we used Fourier transform infrared and Fourier transform Raman spectroscopy to study the formation of cyclic anhydride intermediates by BTCA and other polycarboxylic acids without the presence of a catalyst. We found that BTCA and other polycarboxylic acids in a crystalline state start to form 5-membered cyclic carboxylic anhydrides when the temperature reaches the vicinity of their melting points with the exception of bifunctional acids, which form cyclic anhydrides at temperatures much higher than their melting points. Intermolecular hydrogen bonding between carboxylic acid groups prevents the formation of the cyclic anhydride intermediates at lower temperatures. We also found that polycarboxylic acids in an amorphous state form cyclic anhydrides at much lower temperatures.     

Surface architecture of the plant cell: biogenesis of the cell wall, with special emphasis on the role of the plasma membrane in cellulose biosynthesis.

Cell wall structure and biogenesis in the unicellular green alga, Oocystis apiculata, is described. The wall consists of an outer amorphous primary layer and an inner secondary layer of highly organized cellulosic microfibrils. The primary wall is deposited immediately after cytokinesis. Golgi-derived products contribute to this layer. Cortical microtubules underlie the plasma membrane immediately before and during primary wall formation. They function in maintaining the elliptical cell shape. Following primary wall synthesis, Golgi-derived materials accumulate on the cell surface to form the periplasmic layer. This layer functions in the deposition of coating and cross-linking substances which associate with cellulosic microfibrils of the incipient secondary wall. Secondary wall microfibrils are assembled in association with the plasma membrane. Freeze-etch preparations of untreated, living cells reveal linear terminal complexes in association with growing cellulosic microfibrils. These complexes are embedded in the EF fracture face of the plasma membrane. The newly synthesized microfibril lies in a groove of the outer leaflet of the plasma membrane. The groove is decorated on the EF fracture face by perpendicular structures termed "ridges". The ridges interlink with definitive rows of particles associated withe PF fracture face of the innter leaflet of the plasma membrane. These particles are termed "granule bands", and they function in the orientation of the newly synthesized microfibrils. Microfibril development in relation to a coordinated multienzyme complex is discussed. The process of cell wall biogenesis in Oocystis is compared to that in higher plants.     

A comparative FT-IR spectroscopic study of methanethiol and methanol adsorption on sodium X and Y zeolites

Adsorption of CH₃SH and CH₃OH on activated NaX and NaY zeolites has been studied by IR spectroscopy. Only NaX is able to provoke the dissociative adsorption of CH₃SH at room temperature and that of CH₃OH at 623 K. Results are discussed taking into account sodium cations in the S_III position.     

纤维素热解形成左旋葡聚糖机理的理论研究

采用密度泛函理论UB3LYP/6-31G(d)方法,对模型化合物纤维二糖热解反应机理进行了量子化学理论计算研究。设计了三种可能的热解反应途径,对各种反应的反应物、产物、中间体和过渡态的结构进行了能量梯度全优化,计算了不同温度下热解反应的标准热力学和动力学参数。计算结果表明,糖苷键均裂而形成两个自由基中间体IM₁a和IM₁b,吸收热量为321.26kJ/mol,中间体IM₁a经过渡态TS₁a进一步形成左旋葡聚糖P₁,反应势垒为202.72kJ/mol;与分步反应相比,纤维二糖经过渡态TS₂协同反应直接形成左旋葡聚糖P₁和吡喃葡萄糖P₂的反应势垒低于分步反应的总势垒,其反应势垒为377.54kJ/mol;H⁺的加入有利于糖苷键的断裂,断裂形成的中间体IM₃很难进一步反应形成左旋葡聚糖。     

Experimental and molecular simulating study on promoting electrolyte-immersed mechanical properties of cellulose/lignin separator for lithium-ion battery

Lithium-ion batteries have been developing intensively and earn an unprecedented reputation, yet advanced performance and safety issue still require considerable investigation. Separator is vital to comprehensive properties of batteries, where the mechanical properties are key to breaking through of new-type separator. Unfortunately, electrolyte submersion has caused damage to strength of cellulose separator. Whereupon, in this work, cellulose separator is optimized by introducing lignin particles to promote electrolyte-immersed mechanical strength. Experiments are conducted concerning surface morphology, contact angle, porosity, electrolyte uptake, mechanical properties and electrochemical performance. Molecular simulation is implemented to explore the mechanism of tensile behavior of cellulose and lignin subjected to electrolyte solvents. Experimental results confirm positive effect of lignin addition in improving mechanical properties and simultaneously maintaining impressive electrochemical performance of the cellulose/lignin composites separators. Besides, lignin addition amount of 2.5% and 5% is recommended to achieve promising overall properties. Molecular simulation has successfully unveiled that weakening of cellulose separator submerged in electrolyte is resulted by the deformed cellulose amorphous region and the promoting effect of adding lignin is contributed from the new hydrogen bonds generated between cellulose and lignin molecules. Hopefully, this work provides novel insight on preparing remarkable separator and mechanism of materials behavior.     

Solvents effects on the mechanism of cellulose hydrolysis: A QM/MM study

This article reports a combined quantum mechanics/molecular mechanics (QM/MM) investigation on the acid hydrolysis of cellulose in water using two different models, cellobiose and a 40‐unit cellulose chain. The explicitly treated solvent molecules strongly influence the conformations, intramolecular hydrogen bonds, and exoanomeric effects in these models. As these features are largely responsible for the barrier to cellulose hydrolysis, the present QM/MM results for the pathways and reaction intermediates in water are expected to be more realistic than those from a former density functional theory (DFT) study with implicit solvent (CPCM). However, in a qualitative sense, there is reasonable agreement between the DFT/CPCM and QM/MM predictions for the reaction mechanism. Differences arise mainly from specific solute–solvent hydrogen bonds that are only captured by QM/MM and not by DFT/CPCM. © 2015 Wiley Periodicals, Inc.     

Structure of sodium carboxymethyl cellulose aqueous solutions: A SANS and rheology study

We report a small angle neutron scattering (SANS) and rheology study of cellulose derivative polyelectrolyte sodium carboxymethyl cellulose with a degree of substitution of 1.2. Using SANS, we establish that this polymer is molecularly dissolved in water with a locally stiff conformation with a stretching parameter . We determine the cross sectional radius of the chain ( 3.4 Å) and the scaling of the correlation length with concentration (ξ = 296 c^?1∕2Å for c in g/L) is found to remain unchanged from the semidilute to concentrated crossover as identified by rheology. Viscosity measurements are found to be in qualitative agreement with scaling theory predictions for flexible polyelectrolytes exhibiting semidilute unentangled and entangled regimes, followed by what appears to be a crossover to neutral polymer concentration dependence of viscosity at high concentrations. Yet those higher concentrations, in the concentrated regime defined by rheology, still exhibit a peak in the scattering function that indicates a correlation length that continues to scale as . © 2014 The Authors. Journal of Polymer Science Part B: Polymer Physics Published by Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015 , 53, 492–501     

3D printed PCL scaffold reinforced with continuous biodegradable fiber yarn: A study on mechanical and cell viability properties

In this study, poly (ε‐caprolactone) (PCL) scaffolds were printed and reinforced, simultaneously, with biodegradable poly glycolic acid (PGA) suture yarn, as a continuous reinforcing fiber, in the Fused Deposition Modeling (FDM) 3D printing process. Albeit PCL is a suitable material for biomedical applications, its low mechanical properties, and low degradation rate have limited its usage. A biocompatible suture yarn was used as the reinforcing material to enhance the mechanical properties and biodegradation characteristics, via an innovative method of continuous fiber embedding in the FDM process. The reinforced PCL samples were 3D printed with the setting porosity value of 60% and 0°/60°/120° lay-down pattern. The mechanical and biological properties of the scaffolds were tested to prove the effectiveness of the produced scaffolds for bone substitute purposes. Mechanical properties assessments showed that with a 22 vol.% suture yarn content in the 3D printed PCL scaffolds, the tensile strength, and elastic modulus remarkably increased up to 374% and 775%, respectively. The degradation of the reinforced PCL was 20 times higher than that of the non-reinforced PCL samples, after ten weeks, dominated by the fiber degradation phenomenon. After three days of cell culture, the proliferation assay of the built scaffovd the non-toxicity of the reinforced PCL.