Structural analysis of dextran‐based hydrogels obtained chemoenzymatically

The objectives of this study were to visually examine the surface and interior morphology of a new class of biodegradable hydrogels based on dextran-methacrylate and to quantify the porous structure of these hydrogels in swollen state. Two techniques (scanning electron microscopy and mercury intrusion porosimetry) were used to analyze pore structure of dextran-methacrylate hydrogels as a function of the degree of methacrylate substitution. SEM was used to observe 3-dimensional network structure of cryofixed and fractured swollen dextran-methacrylate hydrogels. Image analysis of the SEM data revealed different pore shapes and sizes, depending on the degree of substitution and the location within the hydrogel. A higher methacrylate-substituted dextran hydrogel showed a compact and rigid pore structure, while a lower substituted hydrogel showed a delicate and fragile pore structure. Mercury intrusion porosimetry analysis of the pore structure of dextran-methacrylate hydrogels provided useful and more reliable quantitative data of pore characteristics, such as total pore area, average pore diameter, their distribution, and bulk density. The total pore area and average pore diameter of swollen dextran-methacrylate hydrogels decreased with an increase in degree of methacrylate substitution, while bulk density increased with an increase in degree of substitution.

Wheat starch carbamate: Production, molecular characterization, and film forming properties

An investigation of the fractal characteristics of the Upper Ordovician Wufeng Formation shale using nitrogen adsorption analysis

Xylan sulphate films

This research investigated the optimized condition (i.e., esterifying agent, reaction time, reaction temperature) to modify lignin for utilization as a precursor in carbon fiber production. The lignin was successfully modified by esterification reaction in dimethylformamide solvent under different reaction temperatures and times using different types of fatty acid chloride including butyryl chloride, octanoyl chloride, and lauroyl chloride as an esterifying agent. The effects of fatty acid chloride chain length and degree of substitution on the chemical structure, functional groups, morphology, crystallinity, thermal properties, and solubility of esterified-lignin were studied. The chemical structure of the obtained product was characterized by FTIR and 1H- and 13C-NMR. The FTIR results showed that modified lignin from all esterifying agents exhibited the evidence of esterification by showing the increasing in the ester bands at 1701 cm-1 (carbonyl C=O stretching of ester) and the significant increasing intensity of the aliphatic carbon peaks at around 2800–2900 cm−1, and the decreasing in the intensity of O-H band at 3400 cm-1. The 1H-NMR spectra showed the peaks of alkyl groups of fatty acid chain between 1.1-1.2 ppm, the decreasing in the intensity of the hydroxyl group at 3.33 ppm. The 13C-NMR spectra of the modified lignin showed the strong increase of the aliphatic carbon signals at around 10-40 ppm along with the peak of ester group at 174 ppm. All modified lignin revealed a packing of small and large particles with a smooth surface depending on the types of esteritying agent. The optimum conditions for the modified lignin that yield low, medium, and high degree of substitution (DS) values with reasonable %weight increase were 2 hr 30 oC (DS 0.27),6 hr 50 oC (DS 0.87), and 4 hr 70 oC (DS 1.28) for lignin butyrate, 2 hr 30 oC (DS 0.62), 2 hr 70 oC (DS 0.96), and 6 hr 70 oC(DS 1.33) for lignin octanoate, and 2 hr 30 oC(DS 1.72), 2 hr 50 oC (DS 2.85), and 4 hr 50 oC (DS 3.68) for lignin laurate, respectively. The thermal stability of all esterified lignins decreased when lignin was modified by fatty acid chloride with different chain lengths. Lignin was insoluble in non-polar solvents (e.g. toluene and xylene); however, after esterification lignin laurate can be dissolved in toluene, chloroform, and xylene. Then, 75%lignin laurate powder (high DS) blended with 25% PLA was fabricated into film by casting method using chloroform as solvent. The results on mechanical properties showed that the tensile strength and elongation at break of PLA-lignin laurate film were 20.66 ± 0.17 MPa and 0.19 ± 0.02 %, respectively. The contact angle value of PLA-lignin laurate films was 71.0 ±1.6◦.

Evolution of multi-scale pore structure of concrete during steam-curing process

Effect of degree of substitution on the structural degradation and butyric acid production of butyrylated starch during in vitro fermentation.

This study investigates the microstructure of lime-treated clayey soils using mercury intrusion porosimetry (MIP) and environmental scanning electron microscopy (ESEM) analyses. Parameters that were varied include lime percent (3, 6, 9%), curing duration (7, 28 days and 1 year), soil pulverization level and mellowing period (1 and 24 h). All samples were compacted at optimum water contents using standard Proctor compaction energy. The 34 MIP and several ESEM analyses conducted on these samples showed that lime content and curing duration had significant impact on the resulting microstructure. MIP results, presented as mercury intrusion curves, total porosity values and pore size distribution histograms revealed that lime stabilization changed the microfabric of clayey soils through a dynamic pore refinement process. Although increases in pore sizes and porosities were observed in the short term (up to 28 days), after a curing period of 1 year, considerable decreases in pore sizes and porosities were noted. A novel “Pore Size Amplification Factor”, (PSAF) was calculated to determine the amplification and/or deamplification of different pore size ranges compared to the untreated soil. ESEM analyses confirmed that while the addition of lime to clayey soils initially increased pore size within the microstructure, over time, as the pores became partially or even completely blocked, the pore sizes reduced. Pores of different sizes and cementation within and on the particles were visible. ESEM findings also showed that pore shapes were not always circular as is assumed in MIP analyses. The results of this study add valuable insight into the time related changes in the microfabric of lime-treated soils.

Full-scale nanopore system and fractal characteristics of clay-rich lacustrine shale combining FE-SEM, nano-CT, gas adsorption and mercury intrusion porosimetry

Cationic polysaccharide polyelectrolytes are important synthetic targets for drug and gene delivery, especially by encapsulation of nucleic acids and proteins through electrostatic interactions. They also have potential as paracellular permeability enhancers that may increase transport across the gastrointestinal (GI) epithelium, especially for therapeutic hydrophilic macromolecules. Semisynthetic chitosan has been more heavily investigated as a cationic polysaccharide polyelectrolyte. This study explores the synthetic conditions needed to produce ammonio and phosphonio cellulose derivatives regioselectively by halogen displacement at C-6 while maximizing the degree of substitution (DS) of cationic substituent. Regioselective substitution was successful, however there were found to be some limitations to the DS and solubility of ammonium derivatives prepared in this way (highest DS 0.43); conversely, water-soluble 6-phosphonio-6-deoxycellulose derivatives were produced with DS > 0.5, with highest DS of 0.73. The repulsion between accumulating positive charges was confirmed as a likely source of DS limitation since high DS (0.9) of 6-triethylamino cellulose was synthesized under comparable conditions. Further reaction of 6-ammonio-co-6-bromo derivatives with a thiol produced 6-ammonio-co-6-thiolated products with improved aqueous solubility. The thiol DS of 0.68 determined by elemental analysis confirmed substitution of residual bromide from low DS (0.30) ammonium products to give essentially complete substitution at C-6.

Aqueous-based particulates were investigated with respect to their use in fabrication of lithium-ion battery cathode as a function of degree of substitution (DS) on carboxymethyl cellulose (CMC). The dispersion properties of particulates were characterized using electroacoustic measurements, rheology, and microstructural observations at two different DS values on CMC. It was found that the suspensions with lower DS had better long-term dispersing efficiency and more compact microstructure than those with higher DS. Furthermore, the electrodes with lower DS exhibited a better electrochemical cycling performance than those with higher DS after the same number of cycles.

Maize starch was reacted with monochloroacetic acid in presence of sodium hydroxide. The reaction involved is known as carboxymethylation. The latter was carried out under a variety of conditions. For every set of conditions carboxymethylation was studied with respect to the extent expressed as degree of substitution (DS) and reaction efficiency (RE). Results indicated that starch:water ratio of 1:2.5 constitutes the optimal material to liquor ratio. Increasing sodium hydroxide concentration up to 8N causes significant enhancement in DS and R. E. while higher concentrations bring about sharp decrement. DS increases as the monochloroacetic acid concentration increases; opposite trend was observed with respect to RE. Increasing duration (0.5–3 h) and temperature (60–70°C) acts in favour of both DS and RE. DS is also governed by the reaction medium. Water and organic solvents were used independently as well as in admixture of solvent/water. It was found that the highest DS is achieved with isopropyl alcohol and the least with water. The DS follows the order: isopropanol > cyclohexane > dimethyl formamide > methanol > acetone > water. Isopropanol: water mixture (80:20) constitutes the most favourable medium for the carboxymethylation reaction under the conditions used.

Shear behavior and microstructural variation in loess from the Yan'an area, China

Preparation and characterization of acetylated maltodextrin and its blend with poly(butylene adipate-co-terephthalate)

Water solubility, thermal characteristics and biodegradability of extruded starch acetate foams