Tamikazu Kume

Radiation-induced degradation of sodium alginate

Abstract Alginates were irradiated as solids or in aqueous solution with Co 60 gamma rays in the dose range of 20 to 500 kGy to investigate the effect of radiation on alginates. Degradation was observed both in the solid state and solution. The degradation in solution was remarkably greater than that in the solid. For example, the molecular weight of alginate in 1% (w/v) solution decreased from 6×10 −5 for 0 kGy to 8×10 −3 for 20 kGy irradiation while the equivalent degradation by solid irradiation required 500 kGy. Degradation G-values were 1.9 for solid and 55 for solution, respectively. The free radicals from irradiated water must be responsible for the degradation in solution. The degradation was also accompanied by a color change to deep brown for highly degraded alginate. Little color change was observed on irradiation in the presence of oxygen. UV spectra showed a distinct absorption peak at 265 nm for colored alginates, increasing with dose. The fact that discoloration of colored alginate was caused on exposure to ozone suggests a formation of double bond in the pyranose-ring.

Hydrogel of biodegradable cellulose derivatives. I. Radiation-induced crosslinking of CMC

Radiation crosslinking of carboxymethylcellulose (CMC) with a degree of substitution (DS) from 0.7 to 2.2 was the subject of the current investigation. CMC was irradiated in solid-state and aqueous solutions at various irradiation doses. The DS and the concentration of the aqueous solution had a remarkable affect on the crosslinking of CMC. Irradiation of CMC, even with a high DS, 2.2 in solid state, and a low DS, 0.7 in 10% aqueous solution, resulted in degradation. However, it was found that irradiation of CMC with a relatively high DS, 1.32, led to crosslinking in a 5% aqueous solution, and 20% CMC gave the highest gel fraction. CMC with a DS of 2.2 induced higher crosslinking than that with a DS of 1.32 at lower doses with the same concentration. Hence, it was apparent that a high DS and a high concentration in an aqueous solution were favorable for high crosslinking of CMC. It is assumed that; high radiation crosslinking of CMC was induced by the increased mobility of its molecules in water and by the formation of CMC radicals from the abstraction of H atoms from macromolecules in the intermediate products of water radiolysis. A preliminary biodegradation study confirmed that crosslinked CMC hydrogel can be digested by a cellulase enzyme

Syntheses of PVA/starch grafted hydrogels by irradiation

A series of excellent polyvinyl alcohol (PVA)/starch blend hydrogels were prepared by gamma and electron beam radiation at room temperature. The influence of dose, the content of starch in blend systems on the properties of the prepared hydrogels was investigated. The gel strength was improved obviously after adding starch into PVA hydrogels, but the swelling properties decreased slightly due to poor hydrophilicity of starch. In order to elucidate the effect of component of starch on the properties of PVA/starch hydrogels as well as the formation mechanism of PVA/starch blend hydrogels under irradiation, the two components of starch, amylose and amylopectin, were chosen to blend with PVA to prepare the hydrogels, respectively. The results indicated that the amylose of starch was a key component that influenced the properties of PVA/starch blend hydrogels. The further analyses of FTIR, DSC and TGA spectra of the prepared gels after extracting sol manifested that there was a grafting reaction between PVA and starch molecules besides the crosslinking of PVA molecules under irradiation, and the amylose of starch was a key reactive component.

Synthesis of antibacterial PVA/CM-chitosan blend hydrogels with electron beam irradiation

A series of excellent hydrogels were prepared from poly(vinyl alcohol) (PVA) and carboxymethylated chitosan (CM-chitosan) with electron beam irradiation (EB) at room temperature. Electron spectroscopy analysis of the blend hydrogels revealed that good miscibility was sustained between CM-chitosan and PVA. The properties of the prepared hydrogels, such as the mechanical properties, gel fraction and swelling behavior were investigated. The mechanical properties and equilibrium degree of swelling improved obviously after adding CM-chitosan into PVA hydrogels. The gel fraction determined gravimetrically showed that a part of CM-chitosan was immobilized onto PVA hydrogel. The further analyses of FTIR and DSC spectra of the prepared gels after extracting sol manifested that there was a grafting interaction between PVA and CM-chitosan molecules under irradiation. The antibacterial activity of the hydrogels against Escherichia coli was also measured via optical density method. The blend hydrogels exhibited satisfying antibacterial activity against E. coli, even when the CM-chitosan concentration was only 3 wt%.

Degradation of poly(l-lactic acid) by γ-irradiation

Abstract Poly( l -lactic acid) (PLA), was irradiated with γ-rays in air and in vacuum at 25°C. Melting point T m , glass transition temperature T g and number-average molecular weight M n decreased with increasing irradiation dose. At low doses, T m , T g and M n decreased sharply and then the rate became slower. Up to 200 kGy, PLA was predominantly degraded by random chain-scission. Above 200 kGy, recombination reactions or partial crosslinking may occur in addition to chain-scission. The degree of chain-scission G s of irradiated PLA was calculated to be 1.97 in air and 0.83 in vacuum. The decrease in M n , T m and T g of the sample in air was faster than in vacuum because of oxidative chain-scission. Biodegradation of PLA was retarded with increasing dose due to the introduction of crosslinking during irradiation. ESR spectroscopy showed five kinds of radicals assigned to three kinds of ESR spectra.

Radiation modification of starch-based plastic sheets

Transparent starch-based plastic sheets were prepared by irradiation of compression-molded starch-based mixture in physical gel state with electron beam (EB) at room temperature. The influence of radiation, plasticizers, water and poly vinyl alcohol (PVA) on the properties of the sheets was investigated. After irradiation, the ductility and tensile strength of the sheets was improved due to the chemical reactions, which was demonstrated by determination of gel fraction and DSC profiles, between starch macromolecules under the action of ionizing radiation. Glycerol, ethylene glycol (EG), poly ethylene glycol (PEG, 600, 1000) was selected as plasticizer to add into starch sheets. The results showed that glycerol was an excellent plasticizer of starch so that the ductility of starch sheets was improved obviously (elongation at break increased). The presence of water was necessary for the preparation of the sheets in this work. With the increasing of the content of starch in starch-based mixture, the tensile strength of the sheets decreased due to the decrease of the degree of the crosslinking of starch. Furthermore, PVA, a biodegradable and flexible-chain polymer, was incorporated into starch-based sheets, the properties of the sheets such as the flexibility (elongation at break) and wet strength was improved obviously.

Hydrogels of polysaccharide derivatives crosslinked with irradiation at paste-like condition

Abstract Polysaccharides such as cellulose, starch, chitin/chitosan and their water-soluble derivatives have been known as degradable type polymers under action of ionizing radiation. Recently, we found that water-soluble polysaccharides derivatives such as carboxymethylcellulose (CMC), carboxymethylstarch (CMS) and carboxymethylchitin (CMCT), carboxymethylchitosan (CMCTS) lead to radiation crosslinking at high concentrated aqueous solution (more than 10%, paste-like state). It was proved that the crosslinking was remarkably affected by their concentration. It was assumed that radiation formation of hydrogels of these polysaccharides derivatives were mainly due to the mobility of side chains. Side-chains radicals were formed mostly via indirect effects, by the abstraction of H atoms by the intermediate products of water radiolysis. Some important characteristics of these novel hydrogels were also investigated. These hydrogels exhibited good swelling in water and possess satisfying biodegradability. In addition, the antibacterial activity against E.coli was also found in CMCTS hydrogel.

Growth-promotion of plants with depolymerized alginates by irradiation

Abstract Alginate has been degraded by gamma-ray irradiation from a Co-60 source in liquid state (aqueous solution) and in solid state (powder form). The irradiated alginate with a molecular weight less than 10 4 shows a strong effect on the growth-promotion of rice and peanut. Low concentration of degraded alginate from 4% solution irradiated at 100 kGy is effective for the growth-promotion of plants and the suitable concentrations are ca 50 ppm for rice and ca 100 ppm for peanut.

Utilization of carbohydrates by radiation processing

Abstract Upgrading and utilization of carbohydrates such as chitosan, sodium alginate, carrageenan, cellulose, pectin have been investigated for recycling these bio-resources and reducing the environmental pollution. These carbohydrates were easily degraded by irradiation and various kinds of biological activities such as anti-microbial activity, promotion of plant growth, suppression of heavy metal stress, phytoalexins induction, etc. were induced. On the other hand, some carbohydrate derivatives, carboxymethylcellulose and carboxymethylstarch, could be crosslinked under certain radiation condition and produce the biodegradable hydrogel for medical and agricultural use.

Changes in structural and antigenic properties of proteins by radiation

Abstract Radiation effect on structural and antigenic properties of proteins (0.2% in 0.01 M phosphate buffer, pH 7.4) were investigated using ovalbumin (OVA) and bovine serum albumin (BSA). Aggregation of OVA and BSA was induced by radiation and the molecular mass increased significantly in N 2 . Significant changes in surface hydrophobicity and [ θ ] 222 nm of CD were also observed by radiation showing the destruction of secondary structure of proteins. Antigenicity of irradiated OVA measured by the method of immunodiffusion was decreased by radiation, and the reactivity to anti-OVA antibody was almost diminished at 8 kGy in N 2 and 4 kGy in O 2 , respectively. The reactivity of BSA was diminished at 4 kGy both in N 2 and O 2 . Changes in hydrophobicity of OVA did not correspond to the decrease in antigenicity, whereas the changes in [ θ ] 222 nm relatively well corresponded to the antigenicity. The SDS-PAGE and immunoblotting analysis showed that radiation at higher doses induced the production of protein aggregates and degraded fragments with reactivity to the specific antibodies. These results suggest that the main part of conformation-dependent antigenic structure (conformational epitope) is easily lost by radiation, but some antigenicity, which is mostly due to the amino acid sequence-dependent antigenic structures (sequential epitopes), remains even at higher dose.