The study of gamma irradiation effects on poly (glycolic acid) (original) (raw)
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Philosophical Magazine, 2016
The effects of gamma-ray irradiation on the isothermal crystallization of biodegradable poly(ethylene succinate) (PESu) and the growth behavior of PESu spherulites have been studied by differential scanning calorimetry and polarized optical microscopy. The irradiation doses used in the study are 0, 200, 400, and 600 kGy. The kinetic parameters for the isothermal crystallization have been determined, using the Avrami relationship. The nucleation constants and activation energy for the growth of the PESu spherulites have been analyzed, using the Lauritzen-Hoffman growth theory. Triple melting points have been observed for all the irradiated PESu. The gamma irradiation has no observable effect on the Avrami exponent, and the composite rate constant increases first with the increase of the crystallization temperature, reaches maximum at the crystallization temperature of ~35 °C, and then decreases with the increase of the crystallization temperature for both the non-irradiated and irradiated PESu. There exists a transition of the growth of the PESu spherulites from regime II to regime III. Both the nucleation constants and activation energy increase with increasing the irradiation dose. The gamma irradiation increases the energy barrier for the migration of polymer chains.
Structural Modifications of Gamma Irradiated Polymers: An FT-IR Study
A comprehensive study of structural modifications of gamma irradiated polymers in the dose range of 10 1 Gy to 10 6 Gy, was conducted using FT-IR technique. The results were varied in nature, proving that all polymers do not undergo similar type of destruction under similar irradiation conditions. The IR spectrum of polypropylene polymer confirmed the total destruction of isotactic arrangements of the polymer. The destruction of the polypropylene polymer lead to the formation of alcoholic and ketonic groups. For polyacetate polymer, elimination of carbon dioxide took place due to destruction of the ester group. Interestingly, for polycarbonate polymer also, it was observed that at the dose of 10 6 Gy, phenolic group formed due to cleavage of ester bonds. For polyvinyl chloride, there was a clear spectral indication regarding the formation of C=C bond and simultaneous decrease in concentration of C-Cl bond which took place upon gamma irradiation.
Bulletin of the Institute for Chemical Research, Kyoto University, 1962
Dilute aqueous solutions of poly(acrylic acid) in acid form and in sodium-salt form have been irradiated with gamma-rays from a Co-60 source both in the presence and in the absence of air. Changes in gelation dose and viscosity have been measured. On irradiation in the absence of air, gel-formation was observed, and both the gelation dose and the critical concentration for gel-formation increased as the degree of neutralization of polymers increased. The critical concentrations were 0.25, 0.30, 0.56 and 1.0 wt. %, for polymers with degrees of neutralization of 0, 5, 10 and 20%, respectively. When NaC1 was added to the solution for irradiation so as to diminish the ionization of carboxyl groups, gelation occurred more readily with increasing NaC1 concentration, if the NaC1 concentration was relatively low. However, as the concentration of NaC1 became higher than O.O1N, gel-formation was increasingly suppressed with increasing NaC1 concentration. This fact demonstrates that there is an optimum expansion of polyion for crosslinking in aqueous solution. On irradiation in the presence of air, the polymer appeared to degrade exclusively. The higher the degree of neutralization, the higher the degree of degradation. If, however, NaCl was present sufficiently in the solution for irradiation, degradation did not occur practically.
Materials Research, 2012
B r a z i l i a n p o l y (3-h y d r o x y b u t y r a t e) , P (3-H B) , a n d i t s c o p o l y m e r, p o l y (3-hydroxybutyrate-co-3-hydroxyvalerate), P(3-HB-co-3-HV) were irradiated with gamma radiation (60 Co) at room temperature and in the presence of oxygen. The viscosity-average molar mass (Mv) was analyzed by viscometry using an Ostwald-type capillary viscometer. Both polymers showed a decrease in molar mass with the increase in dose, reflecting that random main chain scissions occurred. The value G (scissions/100 eV of energy transferred to the system) and the parameter α (scissions per original molecule) were also determined. Mechanical properties decrease with the increase in dose, revealing that P(3-HB) underwent significant changes, especially at doses higher than 50 kGy. Tensile at break and impact resistance properties were the most affected by radiation, while the elastic modulus remained virtually unaltered up to 100 kGy dose.
Influence of γ‐irradiation on poly(methyl methacrylate)
Journal of Applied Polymer Science, 2002
Poly(methyl methacrylate) (PMMA) was γ‐irradiated (5–20 kGy) by a 137Cs source at room temperature in air. The changes in the molecular structure attributed to γ‐irradiation were studied by mechanical testing (flexure and hardness), size‐exclusion chromatography, differential scanning calorimetry, thermal gravimetric analysis, and both Fourier transform infrared and solution 13C‐NMR spectroscopy. Scanning electron microscopy was used to investigate the influence of the dose of γ rays on the fracture behavior of PMMA. The experimental results confirm that the PMMA degradation process involves chain scission. It was also observed that PMMA presents a brittle fracture mechanism and modifications in the color, becoming yellowish. The mechanical property curves show a similar pattern when the γ‐radiation dose increases. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 886–895, 2002
Radiation degradation of poly(α-hydroxyisobutyric acid) and poly(glycollic ester)
Journal of Polymer Science: Polymer Chemistry Edition, 1978
As part of a search for improved polymeric electron-beam resists, we have been interested in the propensity of polymers to undergo chain scission on exposure to ionizing radiation.' One prerequisite for a good e-beam resist is that it exhibit a reasonably high glass-transition temperature. Thus we have been searching for readily degradable polymers with high T, values. Both poly(glycol1ic acid), Sci., to be published.
Macromolecular Symposia, 2008
Their biodegradable properties make polyhydroxyalkanoates (PHAs) ideal candidates for innovative applications. Many studies have been primarily oriented to poly(3-hydroxybutyrate) (PHB) and poly(3-hydroxybutyrate-co-3-valerate) (PHBV) and afterwards to blends of PHAs with synthetic biodegradable polymers, such as poly(e-caprolactone) (PCL). Medical and pharmaceutical devices require sterilization and g irradiation could provide a proper alternative since it assures storage stability and microbiological safety. This contribution presents the effect of g irradiation on the mechanical and thermal properties and on the biodegradation of PHB, PHBV and a commercial PHB/PCL blend. Samples, prepared by compression moulding, were irradiated in air at a constant dose rate of 10 kGy/h, from 10 to 179 kGy. Polymer chain scission was assessed by changes in the molecular weight, thermal properties and tensile behaviour. The correlation between absorbed dose and changes in the mechanical properties and biodegradation is discussed in detail. The optimum dose to guarantee microbiological sterilization without damage of the structure or meaningful loss of the mechanical properties is also reported.
Radiation induced crystallinity damage in poly(L-lactic acid)
Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 2002
The radiation-induced crystallinity damage in poly(L L -lactic acid) (PLLA) in the presence of air and in vacuum, is studied. From the heat of fusion enthalpy values of gamma irradiated samples, some changes on the thermal properties were determined. To identify these changes, first the glass transition temperature (T g ) of L L -lactic acid polymers irradiated to various doses in air and vacuum have been investigated and it is found that it is independent of irradiation atmosphere and dose. The fraction of damaged units of PLLA per unit of absorbed energy has been measured. For this purpose, SAXS and differential scanning calorimetry methods were used, and the radiation yield of number of damaged units ðGðÀuÞÞ is found to be 0.74 and 0.58 for PLLA samples irradiated in vacuum and air, respectively.
Bulletin of the Institute For Chemical Research Kyoto University, 1963
When polyvinyl acetate (PVAc) was subjected to gamma radiation in various organic solvents at a concentration of 10 weight %, the polymer resulted in crosslinking in methanol and benzene, but in many other organic solvents degradation occurred predominantly. As the solvents became poorer, crosslinking was promoted at low concentrations but retarded at high concentrations of the polymer. The most optimum concentration for crosslinking of the polymer in methanol solution was about 20%, where it was found that degradation hardly ever occurred. When PVAc was irradiated in methanol-organic solvent mixtures, the rate of crosslinking was retarded as the solubility of the polymer in solution was raised. However, in methanol-water mixtures, no correlation was observed between the radiation-induced changes and the solubility, but the rate of crosslinking increased monotonically with increasing water content in the mixtures, which may indicate that water is a very effective solvent for crosslinking. The radiation-induced changes were very slight during irradiation at-50°C but relatively large at 70°C. The minimum doses needed for gelation in the 10% benzene solutions were inversely proportional to the degree of polymerization of the initial polymer. It was directly confirmed that the density of crosslinked units was proportional to the radiation dose, and that crosslinks were formed not only from the main chain radicals (not end radicals), but also from the side chain radicals.
Advances in Applied Science Research, 2013
When polymeric materials like Polyallyl diglycol carbonate (PADC), Polycarbonate (PC), Polyvinyl Chloride (PVC), Polypropylene (PP) etc. are exposed to gamma radiation, they show pronounced changes in their physical and chemical properties. Interestingly, the changes due to irradiation are varied in nature, proving that all polymers do not undergo similar type of modifications under similar irradiation conditions. Thus, while polymers like PADC and PVC do not reveal any change in the IR spectral pattern, the IR spectrum of polypropylene polymer confirms the total destruction of isotactic arrangements of the polymer leading to the formation of alcoholic and ketonic groups. The etch-rates are drastically enhanced due to irradiation at the highest dose for all types of PADC detectors which is not the case for polycarbonates. For polyacetate polymer, elimination of carbon dioxide takes place due to destruction of the ester group. Interestingly, in polycarbonate polymer it was observed t...