Characterization of the water state of hyaluronic acid and poly(vinyl alcohol) interpenetrating polymer networks

Interpenetrating polymer networks (IPNs) composed of hyaluronic acid and poly(vinyl alcohol) hydrogels were prepared, and the influence of water and the drying kinetics were investigated. The IPN hydrogels were characterized with thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). The glass‐transition temperatures of the IPN hydrogels decreased with increasing water content. The bound water was the sum of the nonfreezing bound water and freezing bound water. From the DSC melting curves, the values of the total water and freezing bound water were evaluated for IPN hydrogels containing large amounts of water. At the same time, the bound water value was estimated with TGA. In the TGA curves, one‐step and two‐step weight losses, corresponding to free water and nonfreezing bound water, were observed. The bound water of the hydrophilic polymers broke the hydrogen bonding between the hydroxyl groups of the polymers. The swollen IPN hydrogels exhibited relatively high bound water contents (43.04–59.17%) by DSC and TGA. The bound water contents of the dry IPN hydrogel films were 10.2–15.29% by TGA. The drying reaction rate constant of the IPN hydrogel increased with increasing temperature. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 1467–1472, 2004     

Oxygen Delignification Chemistry and Its Impact on Pulp Fibers

Abstract

Two southern pine kraft pulps with kappa numbers of 30.0 (SW1-0) and 48.0 (SW2-0) were oxygen delignified by 30–60% by varying the reaction temperature (78–110°C) and charge of sodium hydroxide (1.6–4.4%). O-bleachability was found to be correlated to the incoming kappa number and charge of sodium hydroxide employed. In general, a lower charge of caustic and a higher brownstock kappa number improved pulp bleachability. The residual lignin in the brownstocks and O-delignified kraft pulp samples was isolated and characterized by ¹³C and ³¹P NMR. ¹³C NMR analysis of the residual lignin samples indicated that the post-oxygen delignified pulps were enriched with α-carbonyl groups and carboxylic acid groups. The content of β-O-aryl structures was increased by 23–36% depending on the extent of oxygen delignification. The post-oxygen delignified pulps were also shown to have increased substituted aryl carbons. ³¹P NMR indicated that the relative content of condensed phenolic units increased by 9–20% after the oxygen delignification, depending on the severity of the O-stage. This observation was probably due to the accumulation or formation of 5,5-biphenyl structures in the process. The physical strength properties of brownstock and post-oxygen delignified pulps were assessed in terms of zero-span strength, tensile strength, tear strength, and burst strength. Oxygen delignification led to a slight increase in the curls and kinks of the pulp fibers. The O-stage was shown to cause a 4.8–15.6% decrease in zero-span strength. In contrast, oxygen delignification increased tensile strength. This result could be explained as the improvement of fiber bonding after the oxygen bleaching.     

Water vapor sorption and diffusivity in bark

Physical properties of importance in drying processes have been compiled for bark, including spruce, pine, and birch in Sweden. Water vapor sorption isotherms were determined for the bark of these trees. At 95% relative humidity and 25°C, outer birch bark reached a moisture ratio (kg water/kg dry mass) of 5%, whereas inner birch bark, spruce bark, and pine bark reached moisture ratios of 21, 28, and 25%, respectively. The transverse water vapor diffusivity in samples of spruce bark, pine bark, inner birch bark, and outer birch bark were determined to be 1.1–1.7 · 10^?6, 2.2–9.2 · 10^?7, 1.5–2.6 · 10^?6, and 4.3–13 · 10^?8 m²/s, respectively. The in-plane diffusivity was of the same magnitude as the transverse diffusivity in inner birch bark, whereas in outer birch bark the in-plane diffusivity was several times higher than the transverse diffusivity. These data can be used to model the drying behavior and can thus aid in the design of efficient bark drying processes.     

Online measurement of moisture content,moisture distribution,and state of water in corn kernels during microwave vacuum drying using novel smart NMR/MRI detection system

Moisture content is unevenly distributed and hard to measure when agricultural products are dried using microwave drying. A low-field nuclear magnetic resonance/imaging (NMR/MRI) and microwave vacuum drying (MVD) combination equipment was developed. The residual moisture content, distribution, and state of water (free, immobilized, and bound) in fresh corn kernels during MVD were quickly measured in real time. NMR results indicated that the amplitude of free and immobilized water decreased very rapidly at the early stage of MVD, while the amplitude of bound water experienced a similar rapid decrease at the last stage. MRI results indicated that the moisture content was always distributed unevenly during MVD, especially at the early stage. The moisture distribution tended to become uniform when drying progressed and the bound water became dominant. The residual moisture content of corn kernels and integral (total) amplitude of NMR were found to fit well with a linear model (R²?>?0.991, P?相似文献   

Measurement of bound water content in sludge: The use of differential scanning calorimetry (DSC)

The bound water content of original and frozen activated sludge and an inorganic sludge were measured via differential scanning calorimetry (DSC) and drying tests. Original sludge contained a significant level of bound water which was reduced by about 50% after freeze/thaw treatment. A simple thermodynamic interpretation showed that liquid–solid binding strength played an important role in depression of the freezing point of bound water in a sludge. The choice of a threshold temperature in a DSC test was equivalent to definition of a threshold binding strength dividing bound/non-bound water content. The possible close relationship between the bound water content measured via DSC and the drying test is discussed. The importance for sample uniformity was also examined.     

纸浆纤维的表面电荷分布及测定

分析了漂白马尾松化学浆、漂白芦苇化学浆、马尾松热磨机械浆和废纸浆的长、中、短纤维含量以及它们的总电荷量和表面电荷量。结果表明浆种间纤维组分存在着较大的差别。纸浆纤维的总电荷量远大于表面电荷量,浆种间的电荷分布也大不相同,微细纤维的表面电荷量较高,木浆和废纸浆的表面电荷分布较均匀,芦苇浆的表面电荷量比木浆、机械浆和废纸浆的高,其长纤维组分与短纤维组分的表面电荷量相差较大。     

Effects of soaking and freezing on composites made from wood‐based fillers and biodegradable plastics

Biodegradable plastic composites were subjected to prolonged soaking and freezing treatments to assess the effects on the mechanical performance. Radiata pine flour and thermomechanical pulp fibers were used as fillers at various addition levels in three different commercial polymer matrices. Two were bioderived, one oil‐derived, each with different hydrophobicities. Depending on the nature of the biodegradable polymer matrix, the rates and extents of water uptake were found to be either enhanced or reduced by the wood‐derived fillers. Although the higher aspect ratio of the pulp fibers improved mechanical performance, relative to the wood flour, water uptake was also significantly enhanced in some cases. POLYM. COMPOS. 27:323–328, 2006. © 2006 Society of Plastics Engineers     

Preparation,characterization, and properties of unbleached,bleached, and grafted pulps from JRC‐321 variety jute fiber

Graft copolymerization onto jute pulps opened the door to new concepts in pulp and paper research. Jute pulp from the JRC‐321 variety white jute fiber was prepared by the alkaline sulfite pulping process. The pulp obtained was bleached by the chlorination, extraction, and hypochlorite sequence technique to remove excess lignin for making bright and good quality paper. Special attention was focused on the graft copolymerization of acrylamide monomer onto the unbleached and bleached pulps by the use of a complex initiating system: Cu(II)/glycine/KHSO₅ in aqueous solution. It was found that percentage grafting was high in the case of bleached pulp. The grafted pulps so obtained were characterized by FTIR and their thermal behavior was characterized by TGA. Their mechanical properties such as tensile strength, percentage elongation, and tenacity were measured and compared. The physical properties such as rot‐resistance and water‐retention capacity of the grafted and the ungrafted pulps were determined. The effect of the percentage grafting variation on the above mentioned properties was examined. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 1963–1969, 2002     

Production of Tomato Powder by Refractance Window Drying

The aims of this work were to investigate the drying of tomato pulp by refractance window (RW) and the effects of process conditions on the drying rates and characteristics of the dry powder. Different heating water temperatures (65, 75, 85, and 95°C) and pulp thickness (2 and 3 mm) were studied for drying 4.8–5.2 °Brix pulps. The powder characteristics were assessed from its solubility, dispersion time, water sorption isotherm, and color. Shorter drying time (17 minutes) was observed to the lower pulp thickness and higher drying temperature. The solubility of tomato powders was approximately 80%, and the dispersion time was lower than one minute. The color change (ΔE) of rehydrated powder showed an increase with increasing process temperature. These results indicate that RW is an adequate procedure for the production of tomato powder.     

Thermal properties measurements of renatured gelatin using conventional and temperature modulated differential scanning calorimetry

The thermal properties of amorphous gelatin films and gelatin films with renatured structural order were measured by using conventional and temperature modulated differential scanning calorimetry (DSC). Different amounts of gelatin structural order associated with a melting enthalpic change in the DSC measurement were prepared based on different gelatin drying conditions. Two consecutive heating and cooling DSC measurements on the gelatin films showed that there was no change in the glass‐transition temperature (T_g) for the amorphous gelatin but there was a decrease in the T_g for the structural gelatin on the second DSC scan. This decrease was attributed to the plasticizing effect from the release of originally hydrogen‐bonded water associated with the structural gelatin. In addition, a reversing endotherm observed upon melting of the structural gelatin during a temperature modulated DSC measurement indicated that the transition of bound water to free water occurred as the partial triple‐helix gelatin melted. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 1795–1801, 2006     

Production and Characterization of Cellulose Nanofibrils from Different Chemical and Mechanical Pulps

In this study, mechanical fibrillation for the production of cellulose nanofibrils (CNF) from chemical and mechanical pulps with different chemical compositions was studied. To investigate the effect of nanofibrillation on wood pulps by the grinder, the nanofibrils obtained from grinded pulp were characterized with morphology, particle size distribution, apparent viscosity in aqueous solution, degree of crystallinity, and water retention capacity. The results showed that the low lignin-containing unbleached kraft pulp (UKP) exhibited good performance for fibrillation, resulting in CNF with high viscosity, high water retention value, and small particle size. However, the fibrillation of high lignin-containing chemi-thermomechanical pulp was the most inefficient which resulted in heterogeneous materials with relatively low viscosity, low water retention value, and large particle size compared to chemical pulps. Furthermore, bleached softwood pulp from radiata pine was found to be much faster and for easier fibrillation compared to the bleached hardwood pulp from acacia due to the more rigid structure of hardwood fibers.     

Trocknung als verfahren zur charakterisierung von asymmetrischen ultrafiltrationsmembranen

Drying of membranes is a simple method to get information about their structure and the state of water within them. This process is limited to those membranes, which do not collapse when being dried. From the drying curves of ultrafiltration membranes made from polyamide, polysulfone, and polyethersulfone, resp., the asymmetry can clearly be pointed out. Also the amount of free and bound water can be calculated. These values were confirmed by DSC measurements. Membranes differing in their preparation procedure reveal different drying curves. In addition, the hydrophilicity of membranes made from polyethersulfone varying in the degree of sulfonation can be differentiated by their corresponding drying curves, and the change in the substructure becomes available.     

Thermal and NMR investigation of the change in the states of water caused by volume phase transition of gelatin gel

The occurrence of volume phase transition (VPT) of a polymer gel is often accompanied by the loss of water. In view of the fact that few studies have been made on the change in different states of water during VPT, in this paper, DSC and NMR are used to check the variation in states of water during VPT of glutaraldehyde crosslinked gelatin gel caused by the variation in composition of water–acetone mixture. The results indicate that the volume of gel collapses at 50 % acetone concentration. The contents of free, intermediate and bound water absorbed by gelatin gel decrease with an increase in the amount of acetone. At 50 % and 60 % acetone content, free water disappears; because acetone accounts for 70 % and 85 %, there remains only bound water. Near VPT the relative content of bound water to total water increases sharply. The spin–lattice relaxation times (T₁) determined by NMR show that the T₁ values of intermediate and bound water, respectively, decrease by approximately four and ten times compared with that of free water. Before VPT, most of the water is freezable and highly mobile. After VPT, bound water gradually plays a dominant role in the mobility of water in the gel. The findings are helpful in understanding the dehydration process of protein induced by poor solvent. © 2000 Society of Chemical Industry     

苇浆回用性能的研究

本文研究了漂白硫酸盐苇浆在反复回用过程中物理化学性能的变化规律。试验表明，随着回用次数增加，聚戊糖含量、保水值、纸页紧度、抗张与耐破强度、耐折度逐渐降低，且对原浆打浆有较大的下降趋势；平均聚会度、相对结晶指数与散射系数具有增加的总趋势；纤维平均长度由于细小级分流失有所增加；零距裂断长变化较小。打过浆与未打浆苇浆在回用过程中抗张指数与紧度均成对数直线关系，其斜率分别为2．481和2.09。     

Water in dextran hydrogels

A series of dextran hydrogels were synthesized with potassium chloride as a crosslinker. ¹³C‐NMR and ¹⁷O‐NMR were used to study the crosslinking role of potassium chloride. Differential scanning calorimetry and thermogravimetric analysis were used to study the state and properties of water in the dextran hydrogels. We found there were three kinds of water in the physically crosslinked dextran hydrogels: free water, freezing bound water, and nonfreezing water. The maximum amount of nonfreezing water in the 50% dextran hydrogel was about 8%. Both ¹³C‐NMR and ¹⁷O‐NMR spectra proved that KCl played the crosslinking role and it interacted with dextran via the oxygen atoms linked to C₄ and C₆ and, also, the oxygen atom linked to C₁ on the dextran ring. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

The preparation and properties of acrylic and methacrylic acid grafted cellulose prepared by ceric ion initiation. II. Water retention properties

Bleached sulfite softwood pulp and the corresponding paper have been grafted with acrylic and methacrylic acids and a number of other monomers. A practical, all aqueous, ceric ion method was used as described in Part I of this series. The water and saline retention values of the grafted pulps were determined. Super water sorbency, up to 48 g/g, were obtained after suitable post treatments. A number of variables were studied including the effects of pH, counterion, crosslinking, drying, and beating. It was gratifying that drying did not affect the effeciency of water or saline water retention. Useful linear functional relationships were found between the saline water retention values and the logarithm of the percent sodium chloride in the water. The two “model” parameters of the plots also correlated well with the water retention values and with the degree of grafting expressed as the ion exchange equivalents of the pulps. The osmotic pressure approach to the water sorption as developed by Grignon and Scallan⁵ coupled with the restraining forces of the grafted polymer itself is used to interpret the process.     

Relaxation time,activation energy,and reaction pathway determination of the poly(ethylene glycol dimethacrylate)–dopant (I2) interaction with the nuclear magnetic resonance technique

Conductive polymers were obtained with a new polymerization method in which UV light was used as a photochemical initiator. In a previous work, optimum irradiation times were determined to obtain high conversion percentages. The effect of dopants on the conductivity of the polymer poly(ethylene glycol dimethacrylate) (PEGDM) was studied with LiClO₄ and I₂ as a dopant. The most effective dopant concentration was determined by the measurement of conductivities. Through the tracing of the conductivity change at various temperatures during the reaction of PEGDM with the dopant, the activation energies of the interactions were calculated, and a method was developed to follow the kinetics of the polymerization reaction with a conductometric technique. This work presents a nuclear magnetic resonance (NMR) study of the same polymer prepared under the optimum conditions with the results obtained in a previous study. NMR spectroscopy was used to determine the relaxation time, rate constants, and activation energy of the polymer–dopant interactions. As a preliminary study, pyruvic acid was used, and for acid‐catalyzed pyruvic acid/water reactions, the relaxation time, activation energy, and enthalpy change values (ΔH) were determined. With the same NMR technique, the reaction mechanisms of the polymerization, relaxation times, and rate constants of the polymer–dopant interactions were determined. The polymerization pathway was determined with NMR spectra; the results were confirmed by the calculation of the activation energies and bond‐breaking energies. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100:5087–5101, 2006     

Preliminary Results on an Approach for the Quantification of Lignin-Carbohydrate Complexes (LCC) in Hardwood Pulps

Abstract

The literature on biomass research contains many references to lignin-carbohydrate complexes (LCC) decreasing the rate of delignification in chemical pulp production, decreasing the yield of cellulosic ethanol via fermentation, and decreasing forage digestibility. However, it is difficult to find correlations between rates of the processes above and initial LCC concentration. One of the main reasons for the lack of such correlations is the absence of methods for accurate quantification of LCC. In this investigation, repeatable and reproducible determinations of bound sugars at monomeric concentrations as low as 0.3 wt% on enzymatic lignin (EL) have been achieved. The bound sugars are hydrolyzed by H₂SO₄, most likely as low molecular weight oligomers. In the same H₂SO₄ treatment, the oligomers are hydrolyzed to monomers which are subsequently quantified by ¹H NMR analyses. A significant enrichment of bound arabinan was previously reported when a crude milled wood lignin (MWL) was compared to the starting wood meal. A similar arabinan enrichment was observed for ELs from kraft and soda-AQ (SAQ) pulps in the present study. Also, well-resolved cross-peaks have been obtained in 2D HSQC NMR analyses of ELs. It has so far been confirmed that the EL from a 30.6 kappa number SAQ pulp from sugar maple contained ～30% more benzyl ethers linked to primary-OH groups in sugar units than the corresponding EL from a 33.7 kappa number kraft pulp.     

Effect of crosslinking concentration on mechanical and thermodynamic properties in acrylic acid–co–methyl methacrylate hydrogels

The mechanical and thermodynamic properties of poly(acrylic acid‐co‐methyl methacrylate) hydrogels with varying crosslinker N,N′‐methylenebisacrylamide (NMBA) content are reported. A higher NMBA content generally led to a stronger and harder gel with lower water content. Swelling capacity decreased as the NMBA concentration increased between 0.5% and 2%, remaining constant beyond this range. The temperature changes of the partial molar Gibbs free energy of dilution and enthalpic and entropic contributions were examined. The thermodynamic parameters showed that swelling was an unfavorable and endothermic process. The freezing and nonfreezing water in the hydrogel was determined by differential scanning calorimetry (DSC). Freezing water content decreased with increasing crosslinker (NMBA) content, whereas the ratio of nonfreezing water to total water content increased with NMBA content because of the promoting of hydrophobic interactions in the hydrogels. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 4016–4022, 2006     

Moisture transport and dehydration in heated gypsum, an NMR study

Nuclear magnetic resonance (NMR) is used to non-destructively measure the moisture and dehydration profiles in gypsum during one sided heating to temperatures of 400 °C reflecting the conditions during fire. The temperature and moisture profiles are recorded simultaneously. The gypsum used in the experiments was extensively characterised using TGA, DSC, MIP, and NMR. The influence of the initial moisture content on the drying and dehydration processes was tested by varying the moisture content of the samples: capillary saturated, 50% RH, and 0% RH.By calibrating the NMR signal with moisture content we have shown that it is possible to not only measure free or absorbed water with NMR, but also measure the degree of hydration of the gypsum. Furthermore, by comparing the NMR signal decays it is possible to distinguish between these two water populations. The measured water profiles reveal that during one sided heating of a gypsum sample the dehydration inside is taking place in a two-step reaction. Furthermore, the profiles indicate that the vapour produce by the dehydration reactions condensates and thereby increases the local moisture content. The condensated water forms a so-called moisture peak behind the dehydration front.To our knowledge the measurements described in this article are the first quantitative in-situ evidence for the existence of two dehydration fronts in gypsum during one sided heating. Furthermore, the built up of a moisture peak in gypsum behind the dehydration front has not been reported in the literature to our knowledge. The NMR heating experiments presented in this paper can be used to evaluate and validate hygro-thermal models in the field of fire research on building materials.