Xiao-Feng Sun

Hemicellulose-based pH-sensitive and biodegradable hydrogel for controlled drug delivery.

Hydrogels based on hemicellulose of wheat straw were prepared as a novel carrier for controlled drug delivery. The chemical structure and morphology of the hydrogels were characterised using FT-IR and SEM, respectively. The swelling ratios of the hydrogels were determined, and the results showed that the hydrogels were pH-responsive. The swelling kinetics of the hydrogels followed a Fickian diffusion process in media with a pH of 1.5, and water uptake was controlled collaboratively by hydrogel relaxation and water diffusion in media with pH values of 7.4 and 10.0. The degradation test of the hydrogels was conducted under simulated physiological conditions, and both hemicellulose content and the crosslinking density of the hydrogels were major factors that affected the biodegradability of the hemicellulose-based hydrogels. A comparison of the in vitro release of acetylsalicylic acid and theophylline indicated that the drug release was controlled both by the hydrogel and by the intrinsic character of the drug. According to the results presented here, hemicellulose-based hydrogels can be used in biomedical fields, especially for controlled drug release.

Preparation and adsorption property of xylan/poly(acrylic acid) magnetic nanocomposite hydrogel adsorbent

Adsorbents based on natural polysaccharides have attracted increasing interest because of their low-cost and biodegradability, particularly, polysaccharide-based nanocomposite adsorbents. In this study the xylan/poly(acrylic acid) magnetic nanocomposite hydrogel adsorbent was prepared from wheat straw xylan and Fe3O4 nanoparticles, and its adsorption property was studied on methylene blue removal. The prepared hydrogel adsorbent had a semi-interpenetrating network structure and exhibited a macro-porous structure with interconnected porous channels. Super-paramagnetic characteristic behavior was observed from magnetic analysis using a vibrating sample magnetometer. The optimum condition for methylene blue adsorption on the adsorbent was found at pH 8 with an adsorbent dosage of 3g/L and an initial concentration of 400mg/L, and the removal percentage reached above 90%. The adsorption isotherm of methylene blue on the prepared hydrogel adsorbent was fitted to the Langmuir model, and the pseudo-second-order kinetic model could describe the adsorption process. All obtained results indicated that the prepared hydrogel adsorbent is promising for water treatment applications.

Extraction and characterisation of hemicelluloses from maize stem

INTRODUCTION Extraction and characterisation of hemicelluloses are very important for converting them into functional materials and chemicals. OBJECTIVE To develop a method for isolation of hemicelluloses from all cell walls. METHODOLOGY Sequential steps using 90% dioxane, 80% acidic dioxane, 100% dimethyl sulphoxide and 8% NaOH were used for extraction of the hemicellulosic preparations (H(1), H(2), H(3) and H(4)) from maize stem. Advanced NMR techniques were used for the analysis of native hemicelluloses. RESULTS Hemicelluloses with high yieldd were isolated from all cell walls, and contained arabinoxylan as the major polysaccharide. H(3) was substituted by α-L-arabinofuranose, α-D-xylopyranose, and acetyl groups (degree of saturation = 0.12/0.09) at O-3/O-2 of xylan. H(4) had a long continuous side chain of arabinose residues, and associated closely with non-cellulosic glucose. The hemicelluloses formed more linkages with guaiacyl lignins, and some p-coumaric acids built a bridge between hemicelluloses and lignin in maize stem. CONCLUSION This modified method is successful for the isolation of hemicelluloses with high yields from all cell walls of maize stem.

Properties and Microstructure Study of Polyimide Foam Plastic

Five kinds of polyimide (PI) foams were prepared from dianhydride and diamine by esterification process. The microstructure of foam was characterized by SEM and visualization methods, and many properties of material were measured, including heat resistance, fire resistance, compressive strength, heat insulation and acoustic absorption. It was shown that the cell size of foam was from 1 to 1.5 mm. The cell edge of PIBM and PIBO foam was obscure, and the cell wall was thinner than the PIBD, PIOD and PIBO-DM foam with thicker cell edge and poor cell size homogeneity. Five types of PI foams presented the trait of flexible foam plastics. All of them possess high decompose temperature, and their limiting oxygen index surpassed 40 percent, and thermal diffusion coefficients were less than 0.030 W/m·°C. In addition, PIBO, PIOD, and PIBO-DM foam had excellent acoustic absorption.

Visualization Study of Solid Poly (Ester-Amine Salt) Precursor Foaming Process

In this research, solid poly (ester-amine salt) precursor was used to prepare polyimide foams. The foaming process was observed by microscope, and effects of particle size on bubble growth were highlighted. The results showed that the powder particles with a size between 25 and 150 μm favor to grow into single bubble mesostructure, and the ones which grow into a multi-bubble mesostructure beyond this size. On the contrary, the bubble growth terminated when the particle size below 25 μm. Sieving was an effective method to narrow size distribution and uniform the particle size, which is of benefit to the formation of polyimide foams. After filtrated with 100 mesh sieve, the retreated particles were situated in optimal band to produce polyimide foams with single bubble mesostructure.