An overview is presented on the materials for the membranes of the ionophore-based ion-selective electrodes (ISEs). The basics of these membranes are briefly discussed. Bearing in mind that polyvinylchloride (PVC) is so far predominating as the ionophore-based ISE membrane matrix, and the limited life-time of these electrodes is due to an insufficient lipophilicity of the membrane components, the plasticizers in the first place, a discussion is presented on polymers alternative to PVC and ionophores immobilized on the polymer backbone. Data are presented on ISEs with membranes based on perfluorocompounds, which are especially important for the medical and biological applications. Studies are briefly described where instead of the replacement of PVC with self-plasticized polymers, the low-molecular plasticizers are replaced with polymeric analogs, retaining PVC as the polymeric matrix. Use of ionic liquids as the ISE membrane components is discussed, together with the interpretation of the literature data on the regularities in the functioning of such electrodes. Issues, studied mostly from the material science view are discussed throughout the review in their relation to electrochemistry.

Materials for the ionophore-based membranes for ion-selective electrodes: Problems and achievements (review paper)

Complicity of degradable polymers in health-care applications

HDPE chemical recycling promoted by phenol solvent

Degradation of waste polystyrene is carried out in presence of hydrogen using several metal oxide catalysts at elevated temperature and pressure for recycling. Benzene is used as a solvent for degradation. Initial hydrogen pressure in the autoclave is kept at 7.0 kg/cm2 (g) and polystyrene degradation is carried out at 240 °C. After degradation, degraded polystyrene residue is separated and analyzed by Fourier transform infra red (FTIR) spectroscopy whereas filtrate is analyzed by gas chromatography (GC) for finding the degradation mechanism of polystyrene. Degradation rate is enhanced in presence of hydrogen and time dependent weight average molecular weight of degraded polystyrene is determined using viscosity method. Degradation rate constants for the different catalysts are calculated based on the proposed degradation mechanism. Alkali metal oxide catalyst shows higher reactivity towards polystyrene degradation as compare to the transition metal oxide catalyst i.e., degradation rate constant decreases with the increase in electro negativity of metal element of the catalyst. Though manganese (IV) oxide is a transition metal catalyst, but shows higher reactivity due to its reduction towards stable manganese (II) oxide under degradation environment. Finally, degradation rate constant of polystyrene is correlated with the catalyst activity i.e., electro negativity of metal element in the catalyst.

Effect of Metal Oxide Catalysts on Degradation of Waste Polystyrene in Hydrogen at Elevated Temperature and Pressure in Benzene Solution

Three active cellulose-based papers coated in chitosan (P-CH), chitosan-TiO2 (P-CH-TiO2) and chitosan-Ag/TiO2 (P-CH-Ag/TiO2), respectively were real-time aged for 6 months at 4°C, 55% relative humidity, 15 h light/9 h dark cycle and characterized in relation to plain paper (P). The reduction in the chitosan cristallinity, N-deacetylation of chitosan, degradation of cellulosic fibers and loss in the active agents (proven by SEM, FTIR, EDX techniques and physical-chemical-microbial measurements) occurred during storage explains the deterioration of the barrier and antimicrobial properties of the active papers and subsequently the decrease in their preservation efficiency. Experimental results indicate that after storage for 6 months of the clarified butter the most effective package was P-CH-Ag/TiO2 for which the lowest levels of PV (2.72 mEq O2/kg), yeasts and molds (5.8 CFU/g) and E. coli (6.12 CFU/g) counts were measured. By mathematical modeling of the evolution of the PV, E. coli, yeasts and molds experimental profiles the shelf-life of the clarified butter packed in P, P-CH, P-CH-TiO2 and P-CH-Ag/TiO2 was assessed in respect to their admitted limits to 1.6, 2, 4 and 9.3 months, respectively. At the end of storage the appearance of P-CH-Ag/TiO2 package was clean, without greasy spots, as opposed to that of P, P-CH and P-CH-TiO2, which proves its self-cleaning property.

Active packaging based on cellulose-chitosan-Ag/TiO2 nanocomposite for storage of clarified butter

The fluorescence quenching of poly (4-methylstyrene), poly (4-methoxystyrene), poly (α-methylstyrene) and poly (4-tert-butylstyrene) by dimethyl terephthalate, diethyl terephthalate, dibutyl phthalate and dioctyl terephthalate has been investigated in solvent of different polarities. Fluorescence spectra of these derivatives reveal the presence of both monomeric and excimeric emissions in all used solvents and were affected by the type of substituent and the polarity of the solvents. Monomeric and excimeric emissions were quenched by the addition of plasticizer as electron donors and quenching efficiency was affected by the polarity of solvents as well as the molar mass of the added plasticizer. As a result of the quenching processes no exciplex emission was observed in all used solvents. Quenching parameters such as quenching rate constants and quenching cross-sections for these quenching processes were calculated in all used solvents.

Substituent effect on the fluorescence quenching of polystyrene derivatives by polymeric plasticizers

Photodegradation kinetics of poly(para-substituted styrene) in solution

The influence of dibutyl phthalate, dioctyl phthalate, dimethyl terephthalate, diethyl terephthalate, and dioctyl terephthalate-plasticizers on poly (para-methoxy styrene) photodegradation was investigated by UV–vis, fluorescence, and FT-IR spectroscopic methods. The increase in irradiation time caused an increase in the absorption band of the polymer and an increase in the absorption of new band at longer wavelength, thus indicating a possibility of photodegradation of polymer films. The study on poly (para-methoxy styrene) photodegradation was also compared to varying phthalate and terephthalate plasticizers in order to provide an understanding of its photodegradation vis the presence of phthalates and terephthalates plasticizers. The decrease in the excimer fluorescence upon the increase in the time of exposure to UV-radiation provides an evidence for the degradation of polymeric chains through a chin scission processes. The increase in the photodegradation of the polymer increased with the increase in the bulkiness of added plasticizer molecule. IR-spectra of irradiated pure and blended polymer films indicated that the photodegradation of the polymer occurred, by the formation of new absorption bands, and the increase in the intensity of other bands.

Effect of plasticization on the photodegradation of poly (para-methoxystyrene) films

The photodegradation of thin films of poly(para-tert-butylstyrene) with 265 nm radiation in the presence of oxygen, and as a function of irradiation time, has been studied using fluorescence, Fourier transform-infrared spectroscopy, and ultraviolet-visible spectroscopy. The influence of phthalate and terephthalate plasticizers on photo-oxidative degradation was also investigated. Blending with phthalate plasticizers was found to cause a higher efficiency of degradation than that obtained for doping with terephthalate plasticizers. The intensity of absorption was also found to increase with time of irradiation and in the intensity of a new absorption band at longer wavelength, thus indicating a possibility of photodegradation of polymer films. The analysis of the Fourier transform-infrared spectra of the irradiated and non-irradiated samples showed an increase in the intensities of the carbonyl and hydroxyl regions of the Fourier transform-infrared spectra providing evidence for the photodegradation as well as the photo-oxidation of polymeric chains. The increase in the analyzed ranges is attributed to the formation of alcohols, aliphatic ketones and to the increase in the number of polyene structures that resulted from hydrogen abstraction during photodegradation reactions.

Khalid E. Al Ani

Papers

Substituent effect on the fluorescence quenching of polystyrene derivatives by polymeric plasticizers

Photodegradation kinetics of poly(para-substituted styrene) in solution

Effect of plasticization on the photodegradation of poly (para-methoxystyrene) films

Study of the influence of UV-irradiation on the photodegradation of plasticized poly(para-tert-butylstyrene) films

Solvent effect on thermal degradation of plasticized para-substituted polystyrenes