Suwabun Chirachanchai

Electrospinning as a new technique to control the crystal morphology and molecular orientation of polyoxymethylene nanofibers

Electrospinning is widely accepted as a simple and versatile technique for producing nanofibers. The present work, however, introduces a new concept of the electrospinning method for controlling the crystal morphology and molecular orientation of the nanofibers through an illustration of a case study of polyoxymethylene (POM) nanofibers. Isotropic and anisotropic electrospun POM nanofibers are successfully prepared by using a stationary collector and a rotating disk collector. By controlling the voltage and the take-up velocity of the disk rotator, the morphology changes between an extended chain crystal (ECC) and a folded chain crystal (FCC) as clarified by a detailed analysis of the X-ray diffraction and polarized infrared spectra of the POM nanofibers. Hermans orientation function and dichroic ratio lead us to a schematic conclusion--that (i) molecular orientation is parallel to the fiber axis in both isotropic and anisotropic POM nanofibers, (ii) a single nanofiber consists of a nanofibril assembly with a size of 60-70 A and tilting at a certain degree, and (iii) the higher the take-up velocity, the smaller the nanofibril under the (9/5) helical structure of the POM chains. It should be emphasized here that the electrospinning method is no longer a single nanofiber producer but that it can be applied as a new instrument to control the morphology and chain orientation characteristics of polymer materials, opening a new research field in polymer science where we can understand the relationship between structure at the molecular level and the properties and performance at the macroscopic level.

Chitosan gallate as a novel potential polysaccharide antioxidant: an EPR study

A novel biopolymer-based antioxidant, chitosan conjugated with gallic acid (chitosan galloylate, chitosan-GA), is proposed. Electron paramagnetic resonance (EPR) demonstrates a wide range of antioxidant activity for chitosan-GA as evidenced from its reactions with oxidizing free radicals, that is, 1,1-diphenyl-2-picryl-hydrazyl (DPPH), horseradish peroxidase (HRP)-H(2)O(2), carbon-centered alkyl radicals, and hydroxyl radicals. The EPR spectrum of the radical formed on chitosan-GA was attributed to the semiquinone radical of the gallate moiety. The stoichiometry and effective concentration (EC(50)) of the DPPH free radical with chitosan-GA show that the radical scavenging capacity is maintained even after thermal treatment at 100 degrees C for an hour. Although the degree of substitution of GA on chitosan was about 15%, its antioxidant capacity, that is, the reaction with carbon-centered and hydroxyl radicals, is comparable to that of GA.

Thermal decomposition processes in polybenzoxazine model dimers investigated by TGA-FTIR and GC-MS

The thermal decomposition processes of a model compound containing Mannich bridge and a series of polybenzoxazine model dimers are investigated using TGA–FTIR and GC–MS. The 2,4-dimethylphenol-based benzoxazine dimers degraded into smaller and highly volatile compounds, leaving no char at the end of degradation. The p-cresol-based benzoxazine dimers degraded into smaller and highly volatile products as well, nevertheless some of which are able to undergo crosslinking and aromatization processes and form char. The major decomposition products for modified p-cresol-based dimers are amines and ester compounds. # 2002 Published by Elsevier Science Ltd.

Optimal γ-Ray Dose and Irradiation Conditions for Producing Low-Molecular-Weight Chitosan that Retains its Chemical Structure

Abstract Yoksan, R., Akashi, M., Miyata, M. and Chirachanchai, S. Optimal γ-Ray Dose and Irradiation Conditions for Producing Low-Molecular-Weight Chitosan that Retains its Chemical Structure. Radiat. Res. 161, 471–480 (2004). This study focuses on the optimal conditions for γ irradiation to reduce the molecular weight of chitosan but still retain its chemical structure. Chitosan was irradiated under various conditions, i.e. flake solid state (condition 1), flake dispersed in water (condition 2), flake dispersed in 0.05, 0.1, 1 and 2% aqueous K2S2O8 solution (conditions 3a, 3b, 3c and 3d, respectively), flake dispersed in 0.5, 1 and 2% aqueous H2O2 solution (conditions 4a, 4b and 4c, respectively), and chitosan acetic acid solution (condition 5). Comparative studies were done using three types of chitosans with molecular weights of the order of 105 Da with degrees of deacetylation of 0.80, 0.85 and 0.90%. For all conditions, after irradiation, there were two regions of molecular weight reduction. A severe degradation occurred in the first region with decreases in the molecular weight of 80% for radiation doses up to 50 kGy for conditions 1, 2 and 3 (3a–3c) and 20 kGy for condition 4. In the second region, a slow degradation occurred, which resembled a plateau stage. The results for conditions 3d and 5 were the most dramatic, since the primary structure of chitosan was changed after the irradiation. The degradation of chitosan by γ rays was found to be most effective for the amorphous structure. The retention of the structure of chitosan after γ irradiation makes it possible to produce a low-molecular-weight chitosan that retains its functionality, as demonstrated by its activity in the coupling reaction with N,N′-carbonyldiimidazole.

Incorporation methods for cholic acid chitosan-g-mPEG self-assembly micellar system containing camptothecin

A water-insoluble anticancer agent, camptothecin (CPT) was incorporated to a polymeric micelle carrier system preparing from cholic acid chitosan-grafted poly (ethylene glycol) methyl ether (CS-mPEG-CA). CS-mPEG-CA formed a core-shell micellar structure with a critical micelle concentration (CMC) of 7.08 microg/ml. Incorporation efficiency was investigated by varying physical incorporation method and initial drug loading. Among three incorporation methods (dialysis, emulsion and evaporation methods), an emulsion method showed the highest CPT incorporation efficiency. Increasing the initial CPT loading from 5 to 40%, the incorporation efficiency decreased. In all examined CPT-loaded CS-mPEG-CA micelles, 5% initial drug loading showed the highest drug incorporation efficiency. Release of CPT from the micelles was sustained when increasing the initial CPT loading. This indicates the importance of incorporation method and the initial drug loading to obtain the optimum particle size with high drug loading and sustained drug release. When compared to the unprotected CPT, CPT-loaded CS-mPEG-CA micelles were able to prevent the hydrolysis of the lactone group of the drug. This novel CS-mPEG-CA polymer presents considerable potential interest in the further development of CPT carrier.

Microwave technique for efficient deacetylation of chitin nanowhiskers to a chitosan nanoscaffold.

A chitosan nanoscaffold in the form of a colloidal solution was obtained from the deacetylation of chitin whiskers under alkaline conditions by using a microwave technique in only 1/7 of the treatment time of the conventional method. Fourier-transform infrared spectroscopy (FTIR) and nuclear magnetic resonance ((1)H NMR) techniques confirm the degree of deacetylation to be above 90% within 3 h. The wide-angle X-ray diffraction (WAXD) pattern clearly shows that the highly crystalline chitin whiskers are changed to amorphous chitosan. SEM micrographs show the aggregation of branched nanofibers, whereas the TEM micrographs reveal the scaffold morphology.

A novel ion extraction material using host-guest properties of oligobenzoxazine local structure and benzoxazine monomer molecular assembly

Bisphenol-A based benzoxazine monomer (BA-m) and its oligomer are applied as an ionophore to study by Pedersens technique, the ion interaction with alkali and alkaline earth ions. Ion extraction efficiencies are significant when the solubility parameter of the organic phase is close to that of BA-m or the x-parameter is 0.34. Ionophore concentration controls the amount of metal ion extraction. Both BA-m and its oligomer show high entrapment efficiency over 70% extraction, for all types of ions.

Water-based oligochitosan and nanowhisker chitosan as potential food preservatives for shelf-life extension of minced pork.

Water-based chitosans in the forms of oligochitosan (OligoCS) and nanowhisker chitosan (CSWK) are proposed as a novel food preservative based on a minced pork model study. The high surface area with a positive charge over the neutral pH range (pH 5-8) of OligoCS and CSWK lead to an inhibition against Gram-positive (Staphylococcus aureus, Listeria monocytogenes, and Bacillus cereus) and Gram-negative microbes (Salmonella enteritidis and Escherichia coli O157:H7). In the minced pork model, OligoCS effectively performs a food preservative for shelf-life extension as clarified from the retardation of microbial growth, biogenic amine formation and lipid oxidation during the storage. OligoCS maintains almost all myosin heavy chain protein degradation as observed in the electrophoresis. The present work points out that water-based chitosan with its unique morphology not only significantly inhibits antimicrobial activity but also maintains the meat quality with an extension of shelf-life, and thus has the potential to be used as a food preservative.

Silane modified starch for compatible reactive blend with poly(lactic acid).

A reactive blend of poly(lactic acid) (PLA) and a surface modified starch by silane coupling agent to achieve compatibility is proposed. A detailed structural analysis by using (1)H-(1)H TOCSY NMR spectrum clarifies, for the first time, that chloropropyl trimethoxysilane (CPMS) forms covalent bonds with starch during starch modification and consequently forms covalent bonds with PLA in the step of blending to produce a reactive blend of PLA and CP-starch. The CP-starch covalently bound with PLA provides the compatibility between PLA and starch and also plays the role as nucleating agent as identified from a significant increase of degree of crystallinity (as high as 10-15 times), as well as induces chain mobility, as identified from a slight decrease in glass transition temperature (∼5-10°C). The PLA/CP-starch film performed as well as neat PLA with slight increases in tensile strength and elongation at break, as compared to other PLA/silane modified starch films.

Metal Ion Guest Responsive Benzoxazine Dimers and Inclusion Phenomena of Cyclic Derivatives

A series of benzoxazine dimers (1–9),esterified benzoxazine dimers (10–18),and benzoxazine dimer based macrocyclic derivatives(19–22) are prepared. The metalion guest responsive properties of the benzoxazine dimersobtained are clarified by using Pedersens technique.The ion extractions of the benzoxazine dimers are controlledby the bulkiness of the functional group at the aza position.The ones with cyclohexyl bulky groups at the aza position,7–9, are two times higher than thosewith methyl groups, 1–3. The extractionsare close to 100% for esterified dimers (10–18).For the macrocyclic derived dimers, the ether cyclic derivatives,21-22, interact with sodium, potassium and cesium ionsat stoichiometric ratios 2:1 and 1:1 depending on themetal species, as evidenced from 1H-NMR.