TEMPO-mediated oxidation of MCC at high temperature: Synthesis and characterization of high-hydrophilic polymer

Microcrystalline cellulose was reacted with catalytic amounts of 2, 2, 6, 6-tetramethyl-1-piperidine oxoammonium salt (TEMPO), sodium hypochlorite and sodium bromide in Na₂CO₃/NaHCO₃ buffer solution at different temperatures (30 °C, 40 °C, 50 °C). The oxidation procedures included first oxidation and second oxidation. The yield of cellouronic acid produced in the second oxidation was higher than the yield of cellouronic acid produced in the first oxidation at the same oxidation temperature. Moreover, an interesting “high-hydrophilic” phenomenon appeared at higher temperature during microcrystalline cellulose second oxidation (30 °C, 40 °C, 50 °C). Properties associated with the chemical characteristics are discussed by XRD, FTIR, ¹³C-NMR and Laser Particle Analyzer in view of its interesting high-hydrophilic effects.     

Preparation of regenerated cellulose fiber via carbonation. I. Carbonation and dissolution in an aqueous NaOH solution

Cellulose carbonate was prepared by the reaction of cellulose pulp and CO₂ with treatment reagents, such as aqueous ZnCl₂ (20–40 wt%) solution, acetone or ethyl acetate, at −5–0°C and 30–40 bar (CO₂) for 2 hr. Among the treatment reagents, ethyl acetate was the most effective. Cellulose carbonate was dissolved in 10% sodium hydroxide solution containing zinc oxide up to 3 wt% at −5–0°C. Intrinsic viscosities of raw cellulose and cellulose carbonate were measured with an Ubbelohde viscometer using 0.5 M cupriethylenediamine hydroxide (cuen) as a solvent at 20°C according to ASTM D1795 method. The molecular weight of cellulose was rarely changed by carbonation. Solubility of cellulose carbonate was tested by optical microscopic observation, UV absorbance and viscosity measurement. Phase diagram of cellulose carbonate was obtained by combining the results of solubility evaluation. Maximum concentration of cellulose carbonate for soluble zone was increased with increasing zinc oxide content. Cellulose carbonate solution in good soluble zone was transparent and showed the lowest absorbance and the highest viscosity. The cellulose carbonate and its solution were stable in refrigerator (−5°C and atmospheric pressure).     

Preparation and properties of fibers produced from a cellulose/complex PA solvent system precipitating in diverse coagulants

Ethanol, as the first coagulation bath, and several common organic solvents, as well as aqueous solutions of NH₄Cl, NaHCO₃ and NaOH were explored and demonstrated to be adopted as the second coagulation bath for cellulose/phosphoric acid/tetraphosphoric acid (cellulose/complex PA solvent) solution to produce novel cellulose fibers by two-stage dry-wet spinning in a laboratory scale, and effect of coagulants, cellulose concentration, solvent concentration (P₂O₅ concentration) and coagulation temperature on crystal structure and properties of corresponding fibers were investigated. Surface morphology of regenerated fibers as-spun from different coagulants was observed by scanning electronic microscope (SEM), indicating that methanol and 8 wt% NaOH aqueous solution all rendered cellulose fibers relatively dense and smooth surface. X-ray diffraction (XRD) analysis showed that cellulose fiber precipitated from 8 wt% NaOH aqueous solution had pronounced characteristic peak of cellulose II than those of fibers precipitated from other coagulants, and highest crystallinity and orientation. Meanwhile, those two coagulants referred above also gave cellulose fibers relatively higher tensile strength under the same prerequisite. TGA curves exhibited that fibers were thermally stable produced from two salt aqueous solutions (8 wt% NH₄Cl and NaHCO₃) since they had the relatively higher onset decomposition temperatures. By evaluating the effect of cellulose concentration, P₂O₅ concentration and coagulation temperature on the structure and properties of asprepared fibers, it was preferable to produce cellulose fiber from a solution at 20 wt% cellulose concentration, 73 % P₂O₅ concentration, and coagulating in methanol at coagulation temperature of 60 °C at the second-stage.     

Influence of cultivar and prewarming on texture retention of thermally processed potatoes

Summary Potato cubes (2.5 cm) of six cultivars were soaked in CaCl₂ solution (0.004% calcium) at 4°C for 21 h, prewarmed at 75°C for 30 min, and boiled (20 min) or microwaved (2 min, 15 sec). Prewarming treatment significantly retained fracturability (g force at first break point) of boiled samples over non-treated controls. Thirty min prewarming at 75°C gave maximum fracturability retention for boiled samples; prewarming time had no effect on texture of microwaved samples. Cultivar differences in fracturability correlated with inherent tuber calcium content.     

Isolation and characterization of nanocrystalline cellulose from different precursor materials

Nanocrytalline cellulose (NCC) was isolated using cellulose extracted from two different precursor materials: Eucalyptus globulus and rice straw. The two ground precursor materials were autoclaved with a 10 % NaOH solution at 120 °C for 3 h. The alkali-treated precursor materials were bleached using sodium chlorite/acetic acid and sodium hypochlorite. The bleached precursor materials were acid-hydrolyzed in 65 % (w/w) sulfuric acid at 45 °C for 30-120 min. The changes in the chemical composition of the two precursor materials were studied before and after bleaching by Fourier transform infrared spectroscopy according to the NREL report and TAPPI standards. Hydrolyzates were characterized by X-ray diffractometry, thermogravimetric analysis, Zeta-potential analysis, and transmission electron microscopy. The results revealed that the physical properties of NCC were strongly dependent on the acid-hydrolysis time.     

Preparation,functional characterization and hemostatic mechanism discussion for oxidized microcrystalline cellulose and its composites

Effective and affordable hemostatic materials are of great interests in the development of biomaterials. Lignocellulose, which is a raw material for microcrystalline cellulose, is one of the most economical and readily available polymers in the nature. The oxidized microcrystalline cellulose particles prepared in NO₂/CCl₄ oxidation system may be a type of affordable, effective and nontoxic hemostatic biomaterial. The FT-IR and ¹³C solid state NMR results showed that the hydroxyl groups on C6 of cellulose were highly selectively oxidized. The increase of carboxyl content and Zeta potential of OMCC were highly dependent on the oxidation time at the first 64 h. XRD spectra indicated that the crystallinity changed from 70.01 % (MCC) to 60.63 % (OMCC-96 h), and the particle size decreased to 80 µm (OMCC-96 h). To composite with oxidized regenerated cellulose gauze, the OMCC-64 h was optimal, based on the dramatically reduced DP value after 64 h oxidization. The results showed this novel composite with negative charge exhibited good hemostatic property and antibacterial activity. The composite was possessed of both the good biocompatibility for mouse endothelial cells in vitro and the superior biodegradation for rabbits in vivo. Moreover, the data of enzyme-linked immunosorbent assay and blood coagulation tests in vitro suggested that the composite could adsorb and activate the platelets, and then the platelet glycoprotein (GPIIb/IIIa) receptor became competent to bind soluble fibrinogen. The composite also greatly accelerated the activation of the blood coagulation factor XII, and promoted the generation of thrombin, so that the extrinsic route of blood coagulation was initiated.     

Novel fibers prepared from cellulose in NaOH/thiourea/urea aqueous solution

The regenerated cellulose fibers were prepared by wet-spinning from NaOH/thiourea/urea aqueous solvent system for the first time. The effects of coagulation and stretch conditions on the structure, morphology, and mechanical properties of the prepared fibers were investigated by wide-angle X-ray diffraction (WAXD), scanning electron microscope (SEM), and tensile tester, respectively. When the cellulose spinning dope was coagulated in 10% H₂SO₄/12.5% Na₂SO₄ aqueous solution at 15 °C, the prepared fibers had a typical crystalline structure of cellulose II and circular cross-sectional shapes with smooth surface and slightly high tensile properties to viscose fibers.     

Optimization of Cellulose Extraction from Jute Fiber by Box-behnken Design

Cellulose was isolated from plant material for the first time in 1839 by the French chemist Anselme Payen. In recent years, due to the need in reduce the world’s environmental problems, there has been an increase in studies related to the physical and chemical factors of cellulose. It is important to emphasize that experiments and studies with a cellulose occur individually, because of the variation in the amount of cellulose and the extraction method that differs from plant to plant. In the present study, we determined the optimal conditions for cellulose extraction of jute fiber, using the response surface method. The Box-Behnken Design (BBD) was used statistically evaluate the ratio effects of sodium hydroxide (NaOH) and sodium hypochlorite (NaClO), temperature and extraction time in the process used. The analysis of the results showed a significant variable in the linear and quadratic terms of the temperature and also a significant level of interaction in the effect between the variables of temperature and time. Besides this, the BBD used for the analysis of the extraction yield, resulted in a polynomial regression of second order, in complete agreement with experimental results, with R²=0.9627 (p<0.05). The optimal condition was obtained in a ratio of 1.3 at 45 °C for 2 h. Under the best possible conditions, the obtained experimental value is in accordance with the value predicted by the model, thus indicating a model combination and success to optimize the extraction conditions of the jute fiber pulp in the response surface methodology.     

Thermal and oxidation protection of carbon fiber by continuous liquid phase pre-ceramic coatings for high temperature application

Thermal and oxidation resistant coating is necessary for carbon fiber (CF) in CF reinforced concrete (CFRC) composite application in order to fulfil a high level of safety standard in case of fire. Pre-ceramic coatings such as Polysilazane, Polysiloxane, and Methyl silicone resin have been deposited on CF filament yarn by means of wet chemical continuous dip coating method. The surface analyses e.g. scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and infrared spectroscopy (IR) results showed the changes of surface morphology by the coatings. Thermo gravimetric analysis (TGA) revealed that the high temperature (up to 800 °C) oxidation stability of CF was significantly improved with coatings. Thermo-mechanical properties also significantly enhanced up to 600 °C. CF yarn retains its original strength and elasticity modulus/stiffness at 700 °C due to thermal and oxidation resistant coatings.     

Synthesis of high performance phosphorine antioxidants and their application to mCOC

Cyclic olefin copolymers, mCOC, produced using a metallocene catalyst, have been developed since 1990. Besides their high cost and difficulty of processing, oxidation and degradation are one of the critical problems in commercializing high-T_g mCOC products. In this work, a series of mCOCs whose T_g values were 132 °C, 194 °C and 260 °C were synthesized successfully. Additionally, high-performance phosphorine antioxidants, 1,4-di[6-oxo-dibenz[c,e][1,2] oxaphosphorine] benzene (HPB) and 2,5-di-tert-butyl-1,4-di[6-oxo-dibenz[c,e][1,2] oxaphosphorine]benzene(HTPB) were synthesized. The oxidation induction time (OIT), the carbonyl index (CI) and the yellowness index (YI) were determined by DSC, FTIR and spectrophotometry, respectively. The results indicate that blending phosphorine antioxidants with hindered phenolic antioxidant, increases the OIT from 31.8 to 44.1 mins and causes the synergy to exceed 180 %. The CI variation showed that the embrittlement time could be increased from 100 hrs to over 450 hrs by thermal aging at 140 °C. Finally, the YI dropped from 29.3 to 9.2. Briefly, HTPB and HPB, successfully synthesized herein, exhibit a synergy with hindered phenolic agents in antioxidant performance for mCOC polymer.     

Oxidation of regenerated cellulose with nitrogen dioxide/carbon tetrachloride

This paper explores the influence of oxidation time on selective oxidation of regenerated cellulose with NO₂/CCl₄ as oxidation system. FTIR and other testing methods are used to characterize the structure of oxidized regenerated cellulose (ORC), showing that the regenerated cellulose is oxidized at C6 by the NO₂/CCl₄ system with extremely high selectivity. With the extension of oxidation duration, the carboxyl content in ORC increases gradually from 12.11 to 21.29 % while the degree of polymerization (DP) decreases from 92.86 to 53.40 and the strength of monofilament decreases gradually. In case of the reaction duration of 24 h, the performance of oxidation product can satisfy the requirement of absorbing hemostatic materials, i.e., with good hemostatic performance, while it is also provided with excellent antibacterial activity, which the reduction in colony forming units (CFU) is more than 99.9 %.     

Synthesis and characterization of boron doped alumina stabilized zirconia fibers

Boron doped PVA/Zr-Al acetate nanofibers were prepared by electrospinning using PVA as a precursor. The effect of calcination temperature on morphology and crystal structure was investigated at 250, 500, and 800 °C. The study also establishes the effect of boron doping on the morphology of PVA/Zr-Al acetate nanofibers at various calcination temperatures. The measurements showed that the conductivity, pH, viscosity and the surface tension of the hybrid polymer solutions have increased with boron doping. In addition, the fibers were characterized by FTIR, DSC, XPS, XRD and SEM techniques. The addition of boron did not only increase the thermal stability of the fibers, but also increased the average fiber diameters, which gave stronger fibers. The DSC results indicated that the melting temperature (Tm) of the fibers was increased from 256 to 270 °C with the addition of boron. XRD peak patterns showed that after further heat treatment at 800 °C, zirconia exists in two phases of tetragonal and monoclinic modifications. Moreover, alumina does not transform into the γ-Al₂O₃ and θ-Al₂O₃ phase at 800 °C. The SEM appearance of the fibers showed that the addition of boron resulted in the formation of crosslinked bright surfaced fibers.     

Carbon dioxide enrichment and temperature effects on cotton canopy photosynthesis,transpiration, and water-use efficiency

The objectives of this study were to evaluate effects of ambient and double ambient [CO₂] at a range of growing temperatures on photosynthesis, respiration, transpiration, water-use efficiency and dry matter accumulation of cotton plants (Gossypium hirsutum L., cv. DPL 50). In Experiment I, plants were grown outdoors until first bloom, then transferred into naturally lit growth chambers and grown for 22 days at 30/18°C with five CO₂ concentrations varying from 350 to 900 μl l⁻¹. In Experiment II, air temperatures were maintained at 20/12, 25/17, 30/22, and 35/27°C day/night during a 70-day experimental period with [CO₂] of 350 and 700 μl l⁻¹ at each temperature. Photosynthesis increased with [CO₂] from 350 to 700 μl l⁻¹ and with temperature. Plants grown at 35/27°C produced fewer bolls due to abscission compared with plants grown at optimum temperatures (30/20°C). At higher [CO₂], water-use efficiency increased at all temperatures due mainly to increased canopy photosynthesis but also to more limited extent to reduced canopy transpiration. Increased photosynthesis at higher [CO₂] resulted in greater dry matter accumulation at all temperatures except at 20/12°C. Respiration increased as dry matter and temperature increased. Plants grown at higher [CO₂] had less respiration per unit dry matter but more per unit area. These results indicate that future increases in [CO₂] are likely to benefit cotton production by increasing carbon assimilation under temperatures favorable for cotton growth. Reduced fruit weights at higher temperatures indicate potential negative effects on production if air temperatures increase as projected in a high-CO₂ world.     

Investigation on degradation and stability of oxidized regenerated cellulose

The selective oxidation of nitrogen dioxide in CCl₄ for regenerated cellulose to C6 oxidized regenerated cellulose (ORC) was proved using FTIR and NMR, and the ORC were dried under three different conditions, including vacuum-dried at high temperature, air-dried at room temperature and frozen-dried at low temperature. The degrees of polymerization (DP) of ORC gradually decreased with the increase of the oxidation time, which was probably due to the decarboxylation reaction. The DP of ORC further decreased and the color became deep as the increase of drying temperature, which was probably due to the ??-elimination reaction from C2 or C3-carbonyl group, and the yellow color of ORC was due to chromophoric enol structure. The final DP was determined by two kinds of degradation process based on the oxidation of C6 and little C2 or C3, respectively.     

Reinforcement of wet milled jute nano/micro particles in polyvinyl alcohol films

Textile industry generate significant amount of waste fibres in form of short lengths during mechanical processing. However these short fibres possess excellent properties suitable for many other applications. The objective of this work was to use them for the preparation of nanoparticles/nanofibres as fillers in biodegradable composite applications such as food packaging, agriculture mulch films, automotive plastics, etc. The present paper concerns with jute fibres as a source of nanocellulose for reinforcement of PVA mulch films. Jute fibres were first refined to micro/nanoscale particles in form of nanofibrillar cellulose (NFC) by high energy planetary ball milling process in dry and wet condition. Wet milling was observed more efficient than dry milling in terms of unimodality of size distribution with reduction in size below 500 nm after milling for 3 hours. Later the obtained particles were used as fillers in Poly vinyl alcohol (PVA) films and their reinforcement evaluated based on thermal properties. It was observed that glass transition temperature (T_g) of PVA films improved from 84.36 °C to 95.22 °C after addition of 5 % jute particles without affecting % crystallinity and melting temperature (T _m) of PVA. Dynamic mechanical analysis of composite films with 5 % jute particles showed higher value of 14×10⁸ Pa for storage modulus in comparison to 9×10⁸ Pa of neat composite film. The percolation effect was observed more above glass transition temperature which consequently resulted in improved transfer of stiffness from jute particles to PVA matrix above 50 °C. The percolation phenomena also explained the improvement in thermal stability by 10 °C for every increased loading of jute particles due to formation of hydrogen bonds with PVA matrix.     

Effect of aging at different temperatures on LAOS properties and secondary protein structure of hard wheat flour dough

The effects of aging from t = 0–108 h at two different temperatures (4 and 25 °C) on the non-linear viscoelastic rheological properties and secondary protein structure of hard wheat flour dough (HWD) were investigated using large amplitude oscillatory shear tests (LAOS) coupled with Fourier transform infrared spectroscopy (FTIR) and SDS-PAGE. Storage (G') and loss (G'') moduli rapidly decreased during aging at 25 °C. Subjecting HWD to progressively longer aging times at 25 °C caused dramatic changes in the non-linear viscoelastic properties demonstrated by strain softening (negative values of e₃/e₁) and shear thinning (negative values of v₃/v₁) behavior. Elastic Lissajous curves of the unaged control dough showed clockwise turn and wider elliptical trajectories as dough aging proceeds especially at higher temperatures. Other non-linear LAOS parameters (G'_M-G''_L, η'_M-η'_L, S and T) supported that aging process at higher temperature caused a progressive change in dough structure from strain stiffening to strain softening behavior while dough samples aged at 4 °C showed fairly close behavior with the control dough sample. FTIR spectra indicated that the relative content of β-sheet and β-turn structures decreased while the content of α-helix structure increased for all dough samples as a result of dough aging. SDS-PAGE results supported the breakdown of high molecular weight (HMW) and low molecular weight (LMW) glutenin subfractions. Aging at the higher temperature of 25 °C decreased the HMW/LMW ratio from 0.77 to 0.59, while the ratio was 0.73 for the dough aged at 4 °C which is fairly close to the control sample. Our results show that the degradation rate of gluten/starch network was triggered by aging at higher temperature, longer aging time, and natural fermentation which resulted in increasing acidity and increase in endogenous proteolytic and amylolytic activity, and also increasing gluten solubility and break down of intermolecular disulfide bonds at acid pH.     

High performance fibers production process using Taguchi experimental design

In this research, results of an experimental interaction effect of operating parameters on tensile strength carbon fibers from a commercial PAN-based precursor are investigated. Ten parameters at two and four levels (L₃₂=2¹×4⁹) were investigated: stabilization temperature at first stage (STFIS), stabilization duration time at first stage (SDTFIS), stabilization temperature at second stage (STSS), stabilization duration time at second stage (SDTSS), stabilization temperature at third stage (STTS), stabilization duration time at third stage (SDTTS), stabilization temperature at fourth stage (STFOS), stabilization duration time at fourth stage (SDTFOS), carbonization temperature (CT), and carbonization duration time (CDT). In this study, Taguchi method was used initially to plan a minimum number of experiments. Statistical analysis, analysis of variance (ANOVA), was also employed to determine the relationship between experimental conditions and yield levels. ANOVA was applied to calculate sum of square, variance, ratio of factor variance to error variance and contribution percentage of each factor on response. The results show that increasing all of parameters improves tensile strength performance. The optimum levels of influential factors, determined for tensile strength are STFIS 200 °C, SDTFIS 120 min, STSS 225 °C, SDTSS 120 min, STTS 240 °C, SDTTS 120 min, STFOS 260 °C, SDTFOS 60 min, CT 1400 °C and CDT 10 min. The results showed that CT and ODTFIS are the most and the less effective factors on response, respectively.     

Thermal stability and pyrolysis kinetics of organosolv lignins obtained from Eucalyptus globulus

In the present work, thermogravimetric analysis of 17 organosolv lignin samples was carried out to determine their thermal stability and calculate the kinetic parameters of their pyrolysis. The thermal stability has been estimated by the measurement of the degradation temperature (T_d), calculated according to the maximum reaction rate. In addition, degradation temperature at 10% of conversion (T_10%) has been obtained in order to compare the initial stability of the samples with T_d for all samples. The values of T_d are comprised between 262 and 389 °C and the average value is 340 °C. The range for T_10% is 251–320 °C and the average value is 270 °C. The ashes content of the samples has been analyzed and all the residues presented values lower than 4 wt%. Kinetic parameters of lignin pyrolysis were calculated by Borchardt–Daniels’ method assuming nth order reaction. The activation energy values obtained are comprised between 17.9 and 42.5 kJ/mol and the average value is 28.1 kJ/mol. These results are in agreement with the bibliography.     

The volatility of components of grass silage on oven drying and the inter-relationship between dry-matter content estimated by different analytical methods

This study reviews the volatility coefficients used to convert the oven dry‐matter (DM) content of grass silage to an accepted true DM base, volatile‐corrected oven dry matter (VCODM). The revised coefficients quoted for DM determination at 60°C, 85°C and 100°C are based on 18 grass silages with DM contents in the range 153–365 g kg^–1. The volatility coefficients for drying at 60°C, 85°C and 100°C were 0·090, 0·224 and 0·375 for lactic acid and 0·554, 0·716 and 0·892 for total volatile fatty acids respectively. The volatilities of ammonia and total alcohols remained unchanged from previous work and showed no temperature dependences in the range 60°C to 100°C. These revised coefficients were validated using 36 grass silages from three harvests in 1996 and 1997, and no significant differences were found among absolute dry matter (GCDM), alcohol‐corrected toluene dry matter (ATDM) and VCODM contents based on the three drying temperatures (VCODM₁₀₀, VCODM₈₅ and VCODM₆₀). A series of regression equations relating absolute DM content to oven DM content determined at different temperatures gave coefficients of 1·024, 1·013 and 1·000 and constants of 12·67, 11·43 and 11·16 for oven drying at 60°C, 85°C and 100°C respectively. Mathematical manipulation of these equations enables interconversion of DM contents at the three drying temperatures. A new method is described for the analysis of volatile fatty acid, lactic acid and alcohol concentrations in grass silage by gas–liquid chromatography using a single injection in an automated procedure that makes the routine estimation of VCODM a practical proposition to satisfy routine high‐volume requirements. Finally, in a separate study over 4 years using 2381 grass silages from research and commercial farms throughout Ireland, a simple regression is described, which, for advisory purposes, allows true silage DM content to be estimated from oven dry matter content (ODM) for silages in which ODM is >200 g kg^–1.     

Temperature,cyanide, and oxygen effects on the respiration,chip color,sugars, and organic acids of stored tubers

The possibility that sugar accumulation of potatoes stored at low temperatures may be linked to activation of cyanide-resistant respiration (CRR) was investigated. After a lag period of several days, continuous HCN treatment stimulated CO₂ production of tubers stored in 20% O₂. At 1°C in 20% O₂, HCN treatment increased respiration over that effected by low temperature treatment. After several weeks of treatment, cyanide-stimulated CO₂ production was greater at 1°C than at 10°C. Sucrose and malate levels of HCN treated tubers were sometimes higher than those of the 10°C control tubers, but they were always lower than those of the 1°C control tubers. This indicated that CRR alone could not account for the sugar increases at 1°C. Storage in 2% O₂ blocked the increase in CO₂ production and changes in constituents associated with HCN treatments in 20% O₂. HCN treatment had no significant effect on chip color. The level of CRR was measured in freshly cut slices from Monona, Norchip, and Kennebec tubers previously stored at 10°, 5°, or 1°C for several months. Slices from tubers previously stored at 1°C had increased CRR, but there was no difference in CRR between the 5°C and 10°C treatments. Sugars accumulated at 5°C, again indicating that sugar accumulation in potatoes stored at low temperatures was at least partially independent of the activation of CRR.