How the nature of an observation affects single-trajectory entropies

Projection of a Markov process with constant rates of transition to a small number of observable aggregated states can result in complex kinetics with memory. Here, we define the entropy production along a single sequence of aggregated states and show that it obeys detailed and integral fluctuation theorems. More importantly, we prove that projection shifts the distribution of entropy production over the ensemble of paths for a nonequilibrium process toward one characteristic of a system at equilibrium. This statement represents an analog of the second law of thermodynamics for path-dependent entropies and thus a new form of constraint of irreversible systems. Numeric examples are presented to illustrate these ideas.     

Physical and chemical modifications of cellulose fibers for food packaging applications

Cellulose - Cellulose fibers have gained considerable interest for use as gas barriers and reinforcing fillers in food packaging materials because of their interesting properties, including...     

An ESCA study of chemical reactions on the surfaces of cellulose fibers

Cellulose fibers in the form of paper sheets were chemically modified with different functional groups using trichloro-s-triazine as coupling moiety. The treatments made the paper surfaces hydrophobic, as was indicated by an increase in contact angle against water. ESCA was used for the chemical characterization of the paper surfaces. The shape of the carbon 1s peak depended on the chemical functionality of the triazine derivatives. As a reference, ESCA spectra were also recorded for the triazine derivatives precipitated on aluminum plates. The chemical composition of modified cellulose surfaces could then be determined using a computer program for the peak separation and peak area measurement.     

Influence of pretreatment and mechanical nanofibrillation energy on properties of nanofibers from Aspen cellulose

Cellulose - The characteristics of cellulose nanofibers (CNFs) depend on many factors such as the raw material, type and intensity of the pre-treatment, and type and severity of the mechanical...     

How electrolyte and polyelectrolyte affect the adsorption of the anionic surfactant SDS onto the surface of a cellulose thin film and the structure of the cellulose film. 1. Hydrophobic cellulose

The nature of hydrophobic thin cellulose films, formed by Langmuir-Blodgett (LB) deposition on silica, has been studied using neutron reflectivity (NR). The impact of electrolyte and a polyelectrolyte, poly(dimethyldiallylammonium chloride) (polydmdaac), on the adsorption of the anionic surfactant sodium dodecyl sulfate (SDS) onto the surface of the hydrophobic cellulose film and upon the structure of the cellulose film has been investigated. The results show how a combination of polyelectrolytes and electrolyte can be used to manipulate surfactant adsorption onto hydrophobic cellulose surfaces and modify the structure of the cellulose film by swelling and penetration. The results illustrate how polyelectrolytes can be used to reverse adsorption and swelling of cellulose films which are not reversible simply by dilution in solvent.     

Key role of the hemicellulose content and the cell morphology on the nanofibrillation effectiveness of cellulose pulps

The effect of the hemicellulose content and that of the fibre morphology on the nanofibrillation behaviour of delignified cellulose pulps were studied. For this purpose, pulps from two non-woody plants, alfa (Stipa tenacissima) and sunflower (Helianthus annuus), were delignified using NaClO₂/acetic acid and the NaOH pulping processes to obtain fibres with different hemicellulose contents. The ensuing fibres were characterized by chemical analysis, SEM, FTIRS and X-ray diffraction. The fibres were then disintegrated into nanofibrillated cellulose (NFC) using either a high pressure homogenizer or a domestic blender. The degree of fibrillation and the morphology of the nanofibrillated fractions were evaluated by centrifugation and Field-emission scanning electron microscopy. Pulps containing the highest hemicellulose content showed higher yields of the nanofibrillated fraction and a better aptitude for the individualization of the microfibrils. Furthermore, it was shown that fibres from sunflowers exhibiting a thinner cell wall were easier to fibrillate and could be disintegrated into NFC by just using a simple domestic-blender once deliginification process was carried out using the NaClO₂/acetic acid method. Eucalyptus fibres were also used to further confirm the key role of hemicelluloses in the nanofibrillation process of woody plants.     

The mechanism of chemical modification of artificial fibers based on cellulose derivatives

A fabric based on cellulose derivatives has been hydrophobized via coating with oligochloromethylethoxysiloxane and then treated with butyl alcohol, benzyl alcohol, and higher fatty alcohols. With the use of X-ray photoelectron spectroscopy, it has been shown that the reaction of alcohols with the siloxane coating proceeds through the exchange of ethoxysilane groups for higher alkoxy groups, whereas the expected reaction of chloromethyl groups with alcohols (the Williamson reaction) does not occur under the chosen conditions.     

Indirect evidence of supramolecular changes within cellulose microfibrils of chemical pulp fibers upon drying

Dried and never-dried chemical pulps were subjected to strong sulfuric acid hydrolysis and the dimensions of the resulting cellulose nanocrystals (CNCs) were characterized by AFM image analysis. Although the average length of CNCs was fairly similar in all samples (55–65 nm), the length distribution histograms revealed that a higher number of longer crystals and a lower number of shorter crystals were present in the CNC suspensions prepared from never-dried pulps. The distinction was hypothetically ascribed to tensions building in individual cellulose microfibrils upon drying, resulting in irreversible supramolecular changes in the amorphous regions. The amorphous regions shaped by tensions were deemed as more susceptible to acid hydrolysis.     

Energy requirements for the disintegration of cellulose fibers into cellulose nanofibers

Cellulose nanofibers have a bright future ahead as components of nano-engineered materials, as they are an abundant, renewable and sustainable resource with outstanding mechanical properties. However, before considering real-world applications, an efficient and energetically friendly production process needs to be developed that overcomes the extensive energy consumption of shear-based existing processes. This paper analyses how the charge content influences the mechanical energy that is needed to disintegrate a cellulose fiber. The introduction of charge groups (carboxylate) is achieved through periodate oxidation followed by chlorite oxidation reactions, carried out to different extents. Modified samples are then subjected to different levels of controlled mechanical energy and the yields of three different fractions, separated by size, are obtained. The process produces highly functionalized cellulose nanofibers based almost exclusively on chemical reactions, thus avoiding the use of intensive mechanical energy in the process and consequently reducing drastically the energy consumption.     

Crosslinking and structural changes of cellulose fibers

The supermolecular structure of various cellulose fibers modified with crosslinking reagents has been investigated by electron microscopy methods. The density, degree of crystallinity (DC), and length changes in alkaline solutions were measured for the modified celluloses. The samples treated with monofunctional analogs of the crosslinking reagents as well as the fiber preparations containing linear and network polymer were also investigated. Three main problems are suggested for the discussion: (1) the general regularities of the structural changes in cellulose in the process of crosslinking; (2) the specific features of the structural changes, as observed in different cellulose samples; (3) the relation between the degree of modification, the type of modifying reagent, and the structure of the crosslinked cellulose. The characteristic structural changes, i.e., the increase in the thickness of fragments, the specific cogged edges, the increase in the lateral dimensions of structural elements all seem to be most representative in native cellulose fibers and are perfectly well distinguished. Similar changes are found in viscose fibers but are less clearly defined. Crosslinking proceeds rather uniformly through the whole of the fiber cross section. It appeared to be most evident when the cross sections are treated with solvents, or when etched in gaseous discharge. Only in cases when the modification is performed in nonaqueous solutions does the reaction proceed mainly in the peripherial regions of the fiber. In fibers subjected to strong swelling, crosslinking results in a real increase in the lateral dimensions of the microfibrils, with the layer thicknesses remaining the same. As a rule, the modification does not imply significant changes in the fiber surface. The crystallite size decreases in the process of crosslinking. This appears to be peculiar to viscose fibers, especially to those subjected to crosslinking in the swollen state. The degree of crystallinity and density of the fibers decrease sharply, which seems to be especially evident in epichlorohydrin-modified samples. Cellulose structure remains unchanged when linear or network polymer forms in the fiber or when the samples are treated with monofunctional reagents. Changes in properties and structure of cellulose caused by crosslinking are most apparent if elongation of the fibers in alkaline solution before and after the modification is compared.     

Hydrodynamically induced formation of cellulose fibers. I. Observations on the formation of cellulose fibers from stirred solutions

Like synthetic polymers, a natural polymer such as cellulose may crystallize in fibrous form from stirred solutions. In the present work, it is demonstrated that cellulose fibers can be formed by precipitation from dimethyl sulfoxide/paraformaldehyde solutions by two methods that involve different mechanisms of fiber formation, viz., (A) precipitation of cellulose by addition of nonsolvent to the stirred cellulose solution, and (B) precipitation of cellulose by coagulation of droplets of cellulose solution in a stirred precipitant. Both processes yield fibers with properties depending on the stirring speed and the coagulant strength. The molecular orientation and tensile strength of the fibers produced by method A was low, but increased with the stirring speed, while some fibers formed by method B reached extremely high orientation, depending on the thickness of the fibers. The two mechanisms of fiber formation are discussed on the basis of the experimental observations.     

Hydrophobization and characterization of internally crosslink-reinforced cellulose fibers

Transforming hydrophilic cellulose fibers into hydrophobic, non-hygroscopic fibers could potentially lead to a variety of new products, such as flexible packaging, self-cleaning films and strength-enhancing agents in polymer composites. To achieve this, softwood cellulose pulp was chemically modified with successive chemical treatments. First the C2 and C3 hydroxyl groups of the glucose units were selectively oxidized by periodate oxidation to reactive dialdehyde units on the cellulose chain, followed by a Schiff base reaction with 1,12-diaminododecane to crosslink the microfibrils within the fiber wall. This was done, because introducing high levels of alkylation resulted in fiber disintegration, which could be prevented by crosslinking. After internal crosslinking a second Schiff base reaction was performed with butylamine. This procedure yielded highly hydrophobic and low-hygroscopic cellulosic materials. The modified cellulose fibers were investigated by a variety of techniques, including Fourier transform infrared spectroscopy, nuclear magnetic resonance, field-emission scanning electron microscopy, thermogravimetric analysis, X-ray diffraction, moisture sorption and water contact angle measurements. The water uptake of the fibers after being modified reduced from 4 to around 1 %. Various reaction conditions were studied for optimum performance.     

Physical nature of the chemical bond

The effect of such variables as size of basis set, number of S and P type functions in the basis set, size of initial exponent in the basis set, size of multiplicative factor in the geometrical progression of exponents, and interatomic distance has been examined by a self-consistent-field calculation with Gaussian orbitals on HeH⁺. A quasi-optimized wave function has been obtained by allowing only the initial exponent and multiplicative factor to vary in the optimization process.     

Electrospinning of ultrafine cellulose acetate fibers: Studies of a new solvent system and deacetylation of ultrafine cellulose acetate fibers

Electrospinning of cellulose acetate (CA) in a new solvent system and the deacetylation of the resulting ultrafine CA fibers were investigated. Ultrafine CA fibers (∼2.3 μm) were successfully prepared via electrospinning of CA in a mixed solvent of acetone/water at water contents of 10–15 wt %, and more ultrafine CA fibers (0.46 μm) were produced under basic pH conditions. Ultrafine cellulose fibers were regenerated from the homogeneous deacetylation of ultrafine CA fibers in KOH/ethanol. It was very rapid and completed within 20 min. The crystal structure, thermal properties, and morphology of ultrafine CA fibers were changed according to the degree of deacetylation, finally to those of pure cellulose, but the nonwoven fibrous mat structure was maintained. The activation energy for the deacetylation of ultrafine CA fibers was 10.3 kcal/mol. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 5–11, 2004     

Model films of cellulose ID – improved preparation method and characterization of the cellulose film

An optimization study of the preparation of spin-coated cellulose model films from the NMMO/DMSO system on silicon wafers has been made. The study shows that the cellulose concentration ID the solution determines the cellulose film thickness and that the temperature of the solution affects the surface roughness. A lower solution temperature results ID a lower surface roughness at cellulose concentrations below 0.8%. Using the described method, ID ID possible to prepare films with thicknesses of 30–90 nm with a constant surface roughness by changing the cellulose concentration, i.e. by dilution with DMSO. On these films, water has a contact angle less than 20° and about 50% of the material can, according to CP/MAS ¹³C-NMR spectroscopy on corresponding fibrous material, be considered to consist of crystalline cellulose ID type material. ID has further been shown that AFM can be used to determine the thickness of cellulose films, ID both dry and wet states. ID this method, the difference ID height between the top surface and the underlying wafer has been measured at an incision made into the cellulose film. The cellulose films have also been spin-coated with the same technique as on the silicon oxide wafer onto the crystal ID a quartz crystal microbalance (QCM). These model films were found to be suitable for swelling measurements with the QCM. The films were very stable during this type of measurement and films with different amounts of charges gave different swelling responses depending on their charges. As expected, films with a higher charge showed a higher swelling.     

On the thermal degradation of cellulose in cotton fibers

Thermal decomposition of cellulose has been widely studied for the past several years. It has been reported that the source of cellulose and its composition greatly affect its pyrolysis. One of the most widely used analytical tools for the study of cellulose pyrolysis is thermogravimetric (TG) analysis. Several model-fitting methods have been employed to study cellulose pyrolysis kinetics. An alternative to the model-fitting approach is the so-called model-free method developed by Vyazovkin. This isoconversional technique calculates the activation energy as a function of the degree of the conversion. In this article, the pyrolysis of cellulose in cotton fibers compared to microcrystalline cellulose (Avicel, PH 105) was investigated. TG curves were acquired as a function of the heating rates (4, 5, 8, 10, and 16 °C min^?1) and the model-free method was used to analyze the data. Activation energies of cotton fibers and Avicel were obtained, and compared to the data reported in the literature. In addition, models for isothermal decomposition were calculated and compared with experimental data at the same temperature.     

Thermal characterization and electrical properties of Fe-modified cellulose long fibers and micro crystalline cellulose

Thermal properties of polylactic acid (PLA) filled with Fe-modified cellulose long fibers (CLF) and microcrystalline cellulose (MCC) were studied using thermo gravimetric analysis (TG), differential scanning calorimetry, and dynamic mechanical analysis (DMA). The Fe-modified CLFs and MCCs were compared with unmodified samples to study the effect of modification with Fe on electrical conductivity. Results from TG showed that the degradation temperature was higher for all composites when compared to the pure PLA and that the PLA composites filled with unmodified celluloses resulted in the best thermal stability. No comparable difference was found in glass transition temperature (T _g) and melting temperature (T _m) between pure PLA and Fe-modified and unmodified CLF- and MCC-based PLA biocomposites. DMA results showed that the storage modulus in glassy state was increased for the biocomposites when compared to pure PLA. The results obtained from a femtostat showed that electrical conductivity of Fe-modified CLF and MCC samples were higher than that of unmodified samples, thus indicating that the prepared biocomposites have potential uses where conductive biopolymers are needed. These modified fibers can also be tailored for fiber orientation in a matrix when subjected to a magnetic field.     

Characterization and evaluation of the hydrolytic stability of trifluoroacetylated cellulose fibers

The controlled heterogeneous modification of cellulose fibers with trifluoroacetic anhydride was investigated. The characterization of the ensuing materials was performed by elemental analysis, FTIR spectroscopy, X-ray diffraction (XRD), thermogravimetry, and surface analysis (XPS, ToF-SIMS, and contact angles measurements). The trifluoroacetylation enhanced significantly the hydrophobic and lipophobic character of the fibers, whereas their thermal stability and cristallinity were only modestly affected by this treatment, except under the most severe conditions for the latter. Their hydrolytic stability to water vapour was also assessed as a function of the air humidity and shown to be lower than that of still liquid water in the case of a saturated atmosphere.