Radiation-induced Degradation Of Poly Research Articles

Optimization of Radiolytic Degradation of Poly(vinyl alcohol)

Ionizing radiation-induced degradation of poly(vinyl alcohol) (PVA) in aqueous solutions was investigated. Experimental results demonstrate that PVA degradation was initiated by attack of •OH and H•, followed by random chain scission and formation of ketones, enols, aldehydes, acids, etc. Complete mineralization of PVA could be achieved providing that a sufficient radiation dose was supplied. The collaborative effects of initial PVA concentration, pH of the solution, and H2O2 dosage with irradiation dose rate on PVA degradation efficiency were evaluated by using a response surface methodology. Lower initial PVA concentrations, higher dose rates, and acidic or alkaline conditions were found to be favorable for PVA degradation. At a certain dose rate, there was an optimal H2O2 dosage to facilitate the PVA degradation. In addition, the presence of O2 was beneficial for PVA degradation. Tentative interpretation and theoretical analysis on these effects are presented.

Initial Process in the Radiation-induced Degradation of Poly(ethylene terephthalate) Detected by Fluorescence Measurements.

Initial Process in the Radiation-induced Degradation of Poly(ethylene terephthalate) Detected by Fluorescence Measurements.

UV Radiation-Induced Degradation of Poly(n-Propylmethylsilane-Co-Isopropylmethylsilane) in Solution

The photodegradation of poly(n-propylmethylsilane-co-isopropylmethylsilane) (NPIPSC) in solution was investigated. The results obtained indicate that a low-pressure Hg lamp photoinduces degradation. Therefore, this light source can be used as an acceptable radiation source for the photobleaching of NPIPSC. Gel permeation chromatography/light scattering (GPC/LS) measurements indicate that two photodegradation stages exist in this process. The first occurs at less than 6 s of exposure, where scission is very rapid. The second occurs between 6 and 12 s of exposure. The latter does not result in a significant loss of molecular weight. A change of slope in the plot of molecular weight as a function of elution volume is observed in the degradation process. This result indicates the presence of at least two species with different conformations. The ratio of scissions to cross-linking related to photodegradation was calculated and revealed that the scission process predominates over cross-linking. The presence of isopropylmethylsilane (IPMS) units in the copolymer appears to induce a decrease in the NPIPSC degradation efficiency. The linear plot of degradation degree as a function of exposure time suggests that there are no weak links in the copolymer. This result can be correlated with the chemical composition of the copolymer, which was nearly the same between 0 and 10 s of UV exposure. After 12 s of exposure, the IPMS was removed from the NPIPSC.

Radiation-induced degradation of poly(styrene-co-methylmethacrylate) and blends of polystyrene and polymethylmethacrylate

The γ-ray-induced degradation of poly(styrene-co-methyl-methacrylate) [poly(St-co-MMA)] and blends of polystyrene (PSt) and polymethylmethacrylate (PMMA) was investigated by ultraviolet (UV), Fourier transform infrared (FTIR) spectroscopy and viscosity measurements. The optical density around 250 nm decreases linearly with the electron fraction of PSt in the blends, but this does not hold in case of the degradation of poly(St-co-MMA). Similar trends are seen for the decrease in the amount of ester groups, oxidation product formation and the number of chain scission (Cs). A protective effect due to the St component was observed in case of the degradation of poly(St-co-MMA), but it was not observed for the blends. The spatial extent of protection affected by St unit was deduced by assuming a random distribution of MMA and St throughout the copolymer molecule.

Radiation-induced degradation of poly(3-hydroxybutyrate) and the copolymer poly(3-hydroxybutyrate- co-3-hydroxyvalerate)

Poly(3-hydroxybutyrate) {P(3HB)} and the copolymer poly(3-hydroxybutyrate- co-3-hydroxyvalerate) {P(3HB- co-3HV)} were irradiated with γ-rays at 25°C in air and in vacuum. Melting points ( T m) and glass-transition temperatures ( T g) were measured by differential scanning calorimetry. Number-average molecular weights ( M n ) were analyzed by gel permeation chromatography. No significant differences were observed between T m values of P(3HB) and P(3HB- co-3HV) irradiated in air and in vacuum, which decreased almost linearly with increasing irradiation dose. The M n values of both samples decreased sharply with increasing dose, reflecting typical random chain scission. The decrease in M n of the sample irradiated in vacuum was smaller than that irradiated in air with the same dose, implying the occurrence of crosslinking. The T g values for both polymers irradiated in vacuum remained almost unchanged over a wide dose range, while those irradiated in air decreased as the irradiation dose increased. Both the T m and T g of samples irradiated in air were inversely proportional to M n . Biodegradability was clearly promoted with decreasing molecular weight.

Elementary processes in the radiation-induced degradation of poly(ethylene terephthalate)—A note

Elementary processes of γ-irradiated poly(ethylene terephthalate) (PET) have been investigated by electron spin resonance (esr) and optical absorption measurements. On irradiating PET films with γ-rays at −196°C and in the dark, they develop a reddish purple color and show esr spectra which are assigned to ionic species of PET. The optical absorption spectra of γ-irradiated PET films at −196°C and those of a model compound (diethylterephthalate(DET))-2-methyltetrahydrofuran system also confirm these assignments. A possible mechanism for the elementary processes of γ-ray-induced degradation of PET is proposed.

Photo- and radiation-induced degradation of vinyl polymers in solution. Part 4. Radiation-induced degradation of poly(α-methylstyrene) in solution

Etude dans le benzene. Influence de l'addition de composes contenant du chlore sur la scission de chaine

Photo- and radiation-induced degradation of poly(styrene-co-methyl methacrylate)

The photo- and radiation-induced degradation of poly(styrene-co-methyl methacrylate) (poly(St-co-MMA)) has been investigated by both electron spin resonance (ESR) and viscosity measurements. On ultraviolet irradiation of poly(St-co-MMA) film at 30°C in vacuum, the scission type radical from poly(methyl methacrylate) is produced in the initial stages of the photo-irradiation. The polystyryl radical from polystyrene gradually increases with irradiation time. The resulting ESR spectrum is composed of those of both radicals. The ratio of the radicals produced in poly(St-co-MMA) by photo-irradiation was estimated by comparison with simulated ESR spectra. The viscosity average molecular weight, Mv of photo-irradiated poly(St-co-MMA) decreases at short irradiation times and gradually increases at longer irradiation times. This phenomenon reflects the fact that the photo-degradation of the copolymer begins from the MMA component in poly(St-co-MMA). The γ-ray-induced degradation of poly(St-co-MMA) has also been examined by the same methods as those used in the photo-degradation and confirms that the degradation begins from the MMA component in the copolymer. The protective effect of polystyrene was also found for the radiation-induced degradation of the polymethyl methacrylate units in poly(St-co-MMA).