| 1. |
- Qu, X., et al.
(författare)
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Effect of lactic/glycolic acid side chains on the thermal degradation kinetics of chitosan derivatives
- 2000
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Ingår i: Polymer. - 0032-3861 .- 1873-2291. ; 41:13, s. 4841-4847
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Tidskriftsartikel (refereegranskat)abstract
- The thermal degradation properties of chitosan and lactic and/or glycolic acid grafted chitosan have been studied by differential scanning calorimetry (DSC) and thermogravimetric analyses (TG) in the range of 25-500 degrees C. Both DSC and dynamic TG results show that the samples are thermal degraded easily after grafting the lactic and/or glycolic acid. From the isothermal TG experiments, the initial activation energy and the activation energy at different stages is obtained. The initial activation energy of all grafted samples is much lower than that of chitosan, especially for the sample GA/CS = 2 and it varies with degree of conversion. The FT-IR spectra of thermally degraded residues give an indication of the chitosan polyscaccharide ring degradation after 30 min in 280 degrees C, while sample GA/CS = 2 will degrade only after 15 min.
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| 2. |
- Qu, X., et al.
(författare)
-
Novel pH-sensitive chitosan hydrogels : swelling behavior and states of water
- 2000
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Ingår i: Polymer. - 0032-3861 .- 1873-2291. ; 41:12, s. 4589-4598
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Tidskriftsartikel (refereegranskat)abstract
- Physically crosslinked chitosan hydrogels were synthesized by grafting D,L-lactic acid (LA) and/or glycolic acid (GA) with different feed ratios. The physical crosslinking was formed due to the hydrophobic side chains aggregation and intermolecular interactions through hydrogen bonds between side and main chains. The crystallinity of original chitosan decreased by grafting LA and GA. The structural change of the hydrogels in different pH buffers was characterized by FT-IR method and the results were interpreted. Differential scanning calorimetry (DSC) was used to probe the states of water in the chitosan hydrogels. Three types of water were found in the samples, i.e. freezing water (namely free water), non-freezing water (namely bound water), and freezing bound water, while there are variations in the amount of bound water for different hydrogels. The effect of hydrophobic side chains on water state and swelling behavior were discussed.
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| 3. |
- Qu, X., et al.
(författare)
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Surface modification of high density polyethylene tubes by coating chitosan, chitosan hydrogel and heparin
- 2001
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Ingår i: Polymer Bulletin. - : Springer Science and Business Media LLC. - 0170-0839 .- 1436-2449. ; 46:03-feb, s. 223-229
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Tidskriftsartikel (refereegranskat)abstract
- Chitosan and chitosan hydrogel were immobilized on both the inside and outside surfaces of high density polyethylene (HDPE) tubes with 2.5x4 mm diameters. First, acrylic acid was grafted on the surfaces of HDPE by electron beam (2.5 Mrad) preirradiation method. Then chitosan/HCl and chitosan/lactic acid solutions were coated on the modified hydrophilic HDPE surfaces, the latter could form a pH-sensitive hydrogel layer on the surfaces. The tube surfaces were further modified with heparin by surface interpenetrating method to improve blood compatibility. ATR-FTIR and ESCA methods were used to characterize the coated surfaces. The morphology changes were monitored by Scanning Electron Microscope (SEM).
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