Assessing the long-term performance of polyethylene stabilised with phenolic antioxidants exposed to water containing chlorine dioxide

The addition of chlorine dioxide disinfectant to tap water prevents the spread of infection but has a serious drawback in that it degrades materials used in piping, including pipes made of polyethylene. Efficient methods are required to assess the long-term performance of different combinations of antioxidants and polyethylene grades. We have previously presented a screening method which exposes solutions of phenolic antioxidants in squalane (a liquid, low molar mass analogue of polyethylene) to 70 °C water containing either chlorine dioxide or chlorine. This method assesses the stability of the antioxidants towards these aqueous chlorinated media by determining the oxidation induction time through differential scanning calorimetry. The same experimental set-up with two modifications was used in developing a new method. A 0.3 mm thick polyethylene tape replaced the squalane phase and the supply of fresh water containing chlorine dioxide (10 ppm at pH = 6.8) was continuous; this required minimum attention from the operator over the longer exposure time periods used. Tapes of medium-density polyethylene containing 0.1 wt.% of six different phenolic antioxidants were studied. A linear relationship was established between the times to reach antioxidant depletion in the polyethylene tape samples and the times in the squalane samples (with the same antioxidants at the same concentration). A linear relationship was also found between the initial antioxidant consumption rates in polyethylene and squalane. Infrared spectroscopy and scanning electron microscopy of drawn samples revealed the onset of surface oxidation and surface embrittlement in tape samples exposed beyond the time for antioxidant depletion.     

Kinetics of chlorine-induced polyethylene degradation in water pipes

The presence of chlorine in drinking water supplies in many countries creates the undesirable side effect of causing a relatively under investigated degree of polymer degradation in the polyethylene pipes used for transport. In order to predict pipe lifetimes and ensure safe water supplies, a kinetic model using data for the degradation rates of polyethylenes immersed in chlorine solutions, was developed. In order to replicate phenomena that normally occur very slowly at low concentrations of chlorine, accelerated ageing studies were necessary. These were carried out at high chlorine concentrations under well-defined experimental conditions (70, 400 and 4000 ppm). Results showed that, for the chlorine concentrations studied, a chain scission process associated with carbonyl formation is occurring. It was also shown that the rate of this degradation does not depend on the presence of stabilizer. A kinetic model, taking into account the chlorine concentration, is proposed in order to simulate the molar mass changes occurring. This will facilitate the prediction of the degree of polyethylene embrittlement and ultimately the lifetime.     

Ageing of polyethylene at raised temperature in contact with chlorinated sanitary hot water. Part I - Chemical aspects

In France, hot water quality control inside buildings is occasionally assured by disinfection treatments using sodium hypochlorite (between 0.5 and 1 ppm residual free chlorine). This disinfectant is a strong oxidizer and it could interact with metallic and polymer pipes used in hot water systems. To assess the long-term performance of these pipes, it is then necessary to study the impact of these treatments on the material behaviour, in particular for polymeric materials, even at relatively low disinfectant concentrations as used in potable water treatments. The objective of this work was to study the influence of sodium hypochlorite concentration on PERT/Al/PERT (PolyEthylene Raised Temperature) pipe degradation. Pipe samples were filled with chlorinated water solutions (concentrations ranging between 0 and 100 ppm) and maintained in static conditions during 270 days at 70 °C. The antioxidant depletion profile through a PERT wall was monitored using the oxidation induction time (OIT) method, which is a conventional technique of Differential Scanning Calorimetry. Chemical changes on the aged polymer were checked by Infrared Spectrometry. OIT change showed that the PERT stabilizing system was rapidly chemically consumed by the action of chlorinated water at 25 and 100 ppm concentrations. However, PERT degradation was strictly confined to the immediate inner wall. Only a 0.3 mm thick layer (inner part of the pipe) showed significant antioxidant depletion. An increase of the OH and C-O-C infrared bands was also observed on inner part of any samples during ageing which characterize the oxidation of the PERT on the inner wall.     

Polybutene-1 pipes exposed to pressurized chlorinated water: Lifetime and antioxidant consumption

Pipes of isotactic polybutene-1 were pressure-tested in chlorinated water at a controlled pH (6.5 ± 0.1), and the lifetime was assessed as a function of temperature (95-115 °C) and chlorine content (≤3 ppm). These data were compared with data from pressure testing in hot water (0 ppm chlorine). The lifetime shortening in chlorinated water was significant even at relatively low chlorine contents, 0.5 ppm. A further increase in chlorine content led only to a moderate shortening of the lifetime. The temperature dependence of the lifetime data obeyed the Arrhenius law. The activation energy obtained for failure data in chlorinated water was ∼140 kJ mol⁻¹, which was greater than the value of 108 kJ mol⁻¹ earlier reported for failure data from hot-water pressure testing. A 0.5-mm thick layer of material at the inner wall in the fractured pipes showed depletion of the antioxidant system and the inner wall displayed a large number of surface cracks, confirming that there was a pronounced chemical degradation of the inner wall material. The decrease in the antioxidant concentration was independent of the chlorine concentration in the range 0.5-1.5 ppm. The time to reach depletion of the antioxidant system could be predicted by linear extrapolation in an oxidation induction time (log scale)-exposure time (linear scale) diagram.     

A new method for assessing the efficiency of stabilizers in polyolefins exposed to chlorinated water media

The chlorine used as disinfectant in tap water degrades most materials, including polyethylene. The most adequate (functional) test method, the pressure test, is complicated and expensive because the chlorinated aqueous media (Cl₂ or ClO₂ in water) are unstable and they undergo reactions that are dependent on the pH. A new method which assesses the protection efficiency of phenolic antioxidants in polyolefins was developed. The method uses a liquid hydrocarbon analogue, squalane, in which antioxidants are dissolved. The organic phase was dispersed in the aqueous chlorinated phase (containing 10 ppm of either Cl₂ or ClO₂; pH = 6.8) at 70 °C by intense stirring. The depletion of antioxidant (Irganox 1010) was monitored by standard DSC determination of the oxidation induction time. It was shown that 300 min of exposure was sufficient to obtain useful data.     

Towards a Non Empirical Kinetic Model for the Lifetime Prediction of Polyethylene Pipes Transporting Drinking Water

A kinetic model has been elaborated to predict the lifetime of polyethylene pipes transporting slightly pressurized (3–12 bars) drinking water disinfected by free radical reagents. This model is composed of three levels: i) A system of differential equations, derived from a mechanistic scheme for radical chain oxidation in the presence of free radical reagents, giving access to the spatial distribution (in the pipe wall) of oxidation products and stabilizer concentration; ii) Equations allowing to predict the profiles of average molar masses from the spatial distribution of chain scissions and crosslinking events; iii) An empirical creep equation and a failure criterion derived from regression curves obtained in pure water (without disinfectant). It is assumed that the chemical degradation modifies only the time to transition between ductile and brittle regimes of failure, and that this time is linked to the weight average molar mass according to the classical power law. By superimposing these three levels, it is possible to predict the time to failure under the coupled effects of pressure and chemical degradation. This model is successfully applied to the case of chlorine dioxide.     

Chitosan/PEO nanofibers electrospun on metallized track-etched membranes: fabrication and characterization

The development of next-generation adsorption, separation, and filtration materials is growing with an increased research focus on polymer composites. In this study, a novel blend of chitosan (CS) and polyethylene oxide (PEO) nanofiber mats was electrospun on titanium (Ti)-coated polyethylene terephthalate (PET) track-etched membranes (TMs) with after-treatment by glutaraldehyde in the vapor phase for enhancing the nanofiber stability by crosslinking. The prepared composite, titanium-coated track-etched nanofiber membrane (TTM-CPnf) was characterized by Fourier transform infra-red (FTIR), water contact angle, and scanning electron microscopy (SEM) analyses. Smooth and uniform CS nanofibers with an average fiber diameter of 156.55 nm were produced from a 70/30 CS/PEO blend solution prepared from 92 wt. % acetic acid and electrospun at 15 cm needle to collector distance with 0.5 mL/h flow rate and an applied voltage of 30 kV on the TTM-CPnf. Short (15 min) and long (72 h)-term solubility tests showed that after 3 h, crosslinked nanofibers were stable in acidic (pH = 3), basic (pH = 13), and neutral (pH = 7) solutions. The crosslinked TTM-CPnf material was biocompatible based on the low mortality of freshwater crustaceans Daphnia magna. The composite membranes comprised of electrospun nanofiber and TMs proved to be biocompatible and may thus be suitable for diverse applications such as dual adsorption–filtration systems in water treatment.     

Radiation-induced gas evolution in chlorine- containing polymer. Poly(vinyl chloride), chloroprene rubber,and chlorosulfonated- polyethylene

Gas evolution and oxygen consumption induced by the γ-irradiation of poly(vinyl chloride), chloroprene rubber, and chlorosulfonated-polyethylene were studied. The evolved gases and oxygen consumption were measured by means of gas chromatography. When a chlorine containing polymer is irradiated in vacuum or in oxygen, a large amount of hydrogen chloride (HCl) is evolved. The presence of oxygen is found to increase the HCl evolution in pure poly(vinyl chloride) twofold. The gas evolution and oxygen consumption from chlorine containing polymers are retarded by the presence of plasticezer, vulcanizer and stabilizer. For chlorosulfonated-polyethylene, sulfur dioxide (SO₂ is one of the major products in pure state, but its gas evolution decreases markedly by the addition of vulcanizers and stabilizers.     

Degradation of chlorinated polyethylene. I. Effect of antimony oxide on the rate of dehydrochlorination

The degradation of two chlorinated polyethylene compounds CPE 25 (45% chlorine) and CPE 16 (36% chlorine) was studied by following their rates of dehydrochlorination at two temperatures, 150°C and 180°C in pure nitrogen and pure oxygen atmospheres. Studies on the powdered polymers showed that the dehydrochlorination rate of CPE 25 is about fourteen times faster than that of CPE 16 in nitrogen atmospheres and only three to four times faster in oxygen. The molded polymers gave a lower rate of dehydrochlorination than when in the powdered form. This effect is attributed to diffusion factors. The antimony oxide brought about an induction period in the dehydrochlorination reaction during which only a small amount of HCl is evolved, followed by a very fast rate of dehydrochlorination both in oxygen and nitrogen atmospheres. The duration of the induction period increases with increase in the Sb₂O₃ concentration, but is followed by an accelerated HCl loss which is faster when Sb₂O₃ concentration is higher. This work provides supporting evidence that SbCl₃ was formed and lost during degradation. Mechanisms of dehydrochlorination are suggested for the reaction in the case of pure chlorinated polyethylene and for the polymer containing antimony oxide.     

The effect of polymeric drag reducing agent on pressure drop reduction in circular pipes: Experimental and statistical investigation

The present work deals with investigating the effect of adding Polyacrylonitrile (PAN) as a drag-reducing agent on the water flow’s hydraulic performance within horizontal smooth circular pipes experimentally and statistically. Several experiments were performed under various operating circumstances such as fluid flow rates at the 6,8,10 l/min for preparing turbulent flow regimes, concentrations of 25,100, 300 ppm of PAN, and inner pipe diameters of 1/2,3/4 in, and temperatures of 30, 40, and 50 °C. The maximum percentage of drag reduction (DR%) was 56 at a concentration of 300 ppm, the flow rate of 6 l/min, temperature of 30 °C and the diameter of 3/4 in. Using the Taguchi method, the results were statistically analyzed. The maximum estimated DR% value was 40.187%, and the error between the predicted and experimental values was about 10%. Moreover, the PAN concentration had a contribution of 96.5% in the polymeric solution DR. Finally, there was a new correlation to predict friction coefficient in terms of the Prandtle-Karman relation with the newly set slope as a linear function of polymer concentration. There was an excellent consistency between this correlation and the experimental data.     

Stability of florfenicol in drinking water

Florfenicol, a broad-spectrum antibiotic, is being developed for veterinary application as an oral concentrate intended for dilution with drinking water. When a drug product is dosed via drinking water in a farm setting, a number of variables, including pH, chlorine content, hardness of the water used for dilution, and container material, may affect its stability, leading to a decrease in drug potency. The stability of florfenicol after dilution of Florfenicol Drinking Water Concentrate Oral Solution, 23 mg/mL, with drinking water was studied. A stability-indicating, validated liquid chromatographic method was used to evaluate florfenicol stability at 25 degrees C at 5, 10, and 24 h after dilution. The results indicate that florfenicol is stable under a range of simulated field conditions, including various pipe materials and conditions of hard or soft and chlorinated or nonchlorinated water at low or high pH. Significant degradation (> 10%) was observed only for isolated combinations in galvanized pipes. Analysis indicated that the florfenicol concentration in 8 of the 12 water samples stored in galvanized pipes remained above 90% of the initial concentration (100 mg/L) for 24 h after dilution.     

Aqueous chlorination of sulfamethazine and sulfamethoxypyridazine: Kinetics and transformation products identification

Sulfonamides (SNs) are synthetic antimicrobial agents. These substances are continually introduced into the environment, and they may spread and maintain bacterial resistance in the different compartments. The chlorination of 2 SNs, namely, sulfamethazine (SMT) and sulfamethoxypyridazine (SMP), was investigated to study their reactivity with chlorine at typical concentrations for water treatment conditions. Experiments conducted in purified water show an acceleration of SMT and SMP degradation of a factor 1.5 by comparison to drinking water matrix. This difference is due to pH variation and competitive reactions between SNs and mineral and organic compounds, with chlorine in drinking water. In the presence of an excess of chlorine (6.7 μmol·L⁻¹) in ultrapure water at pH 7.2, second‐order degradation rate constants were equal to 4.5 × 10²M⁻¹·s⁻¹ and 5.2 × 10²M⁻¹·s⁻¹ for SMT and SMP, respectively. The structures of transformation products were investigated by liquid chromatography tandem mass spectrometry analyses with equimolar concentrations between chlorine and SNs. SO₂ elimination, cyclization, and electrophilic substitutions were the main pathways of by‐products formation. Moreover, the toxicity of the proposed structures was predicted by using toxicity estimation software tool program. The results indicated that most by‐products may present developmental toxicity.     

Chlorine contaminants poisoning of solid oxide fuel cells

Investigation has been conducted on the poisoning effect of various contaminants containing chlorine at ppm level (<10 ppm) on the performance of Ni-YSZ anode-supported solid oxide fuel cells. The results indicate that cell performance drops by exposure to 1 ppm Cl₂(g) at 750 °C, whereas the introduction of Cl₂(g) with concentration higher than 5 ppm causes only a slight degradation at 850 °C. The presence of 2–6 ppm CH₃Cl(g) and C₂H₃Cl(g) can also induce measurable cell performance decline at 750 and 850 °C and this deterioration cannot be completely removed after switching to pure fuel at 850 °C. No performance loss is found when the cell is operated in fuel containing 1–8 ppm HCl(g) at 750 and 850 °C. It is thus concluded that chlorine in the form of Cl₂(g) yields the largest poisoning effect at 750 °C, while the degradation rate caused by addition of C₂H₃Cl(g) increases with the increase of operation temperature. Agglomerations at anodic region are observed in the samples after poisoning test by Cl₂(g), CH₃Cl(g), and C₂H₃Cl(g), but the anode microstructure is uniform for the sample exposed to HCl(g) for poisoning test.     

Miscibility of some poly(neopentyl glycol adipate)/chlorinated polymer blends

Poly(neopentyl glycol adipate), PDPA, was found to be miscible with poly(epichlorohydrin-co-ethylene oxide). PDPA also formed miscible blends with chlorinated polyethylene samples containing 48 and 42% by weight of chlorine. Chlorinated polyethylene with a lower chlorine content was not miscible with PDPA.     

Miscible blends of amorphous polymers

Thirty-five polymethacrylate/chlorinated polymer blends were investigated by differential scanning calorimetry. Poly(ethyl), poly(n-propyl), poly(n-butyl), and poly(n-amyl methacrylate)s were found to be miscible with poly(vinyl chloride) (PVC), chlorinated PVC, and Saran, but immiscible with a chlorinated polyethylene containing 48% chlorine. Poly(methyl) (PMMA), poly(n-hexyl) (PHMA), and poly(n-lauryl methacrylate)s were found to be immiscible with the same chlorinated polymers, except the PMMA/PVC, PMMA/Saran, and PHMA/Saran blends, which were miscible. A high chlorine content of the chlorinated polymer and an optimum CH₂/COO ratio of the polymethacrylate are required to obtain miscibility. However, poly(methyl), poly(ethyl), poly(n-butyl), and poly(n-octadecyl acrylate)s were found to be immiscible with the same chlorinated polymers, except with Saran, indicating a much greater miscibility of the polymethacrylates with the chlorinated polymers as compared with the polyacrylates.     

NMR imaging of polyethylene pipes

¹H nuclear magnetic resonance (NMR) imaging techniques have been used to image the extrusion aid (EA) in polyethylene (PE) pipe samples. The resulting two-dimensional images show the distribution of EA within the pipe. EA is found to be uniformly distributed in a normal pipe. Examples of degraded pipes, due to exposure to extreme conditions, show migration of EA to the pipes' wall surfaces. NMR images of a normal pipe and two examples of damaged pipes are presented. The imaging technique and the results are discussed. © 1995 John Wiley & Sons, Inc.     

Visible light photochemical synthesis of ultrasmall palladium/copper bimetallic particles at room temperature and its catalytic application in degradation of p-NP

Pt-based metals are very effective catalysts widely adopted in many fields. But the high cost prevents its further industrial application. One of the effective ways to solve the problem is to replace platinum with relatively cheap palladium and its alloy with copper. However, producing Pd/Cu bimetallic catalysts efficiently and economically with controllable particle size and uniform distribution is still challenging, especially when trying to reduce the consumption of precious metals. In this paper, ultrasmall palladium/copper (Pd/Cu) bimetallic catalysts with even dispersion were prepared on multi-walled carbon nanotubes (MWCNTs) by adding polyethylene glycol 400 (PEG 400) as a reducing agent and stabilizer under visible light irradiation at room temperature. The catalytic performance was studied in the catalysis of p-nitrophenol (p-NP) reduction. Of all the bimetallic catalysts produced in different conditions, the best one was obtained under the reaction condition of pH = 7 and violet light irradiation (wavelength 380–435 nm). The average particle size of 0.85 nm, and the apparent rate constant in the catalysis is 1.47 min^?1. This research probes the role of visible light as a key kinetic controlling method in the formation of ultrasmall particles (UPs). It proves the effectiveness of using visible light irradiation as an effective and more “green chemistry” approach to get precious metal UPs as catalysts beyond the traditional ultraviolet or laser photochemistry methods.     

Flotation/ultrasound‐assisted microextraction followed by HPLC for determination of fat‐soluble vitamins in multivitamin pharmaceutical preparations

Dissolved carbon dioxide flotation–emulsification microextraction technique coupled with high‐performance liquid chromatography was developed for separation and determination of fat‐soluble vitamins (A, D₃, E, and K₃) in multivitamin pharmaceutical preparations. Dissolved carbon dioxide flotation was used to break up the emulsion of extraction solvent in water and to collect the extraction solvent on the surface of aqueous sample in narrowed capillary part of extraction cell. Carbon dioxide bubbles were generated in situ through the addition of 300 μL of concentrated hydrochloric acid into the alkaline sample solution at pH = 11.5 (1% w/v sodium carbonate), which was sonicated to intensify the carbon dioxide bubble generation. Several factors affecting the extraction process were optimized. Under the optimal conditions, the limits of detection were 0.11, 0.47, 0.20 and 0.35 μg/L for A, E, D₃, and K₃ vitamins in water samples, respectively. The inter‐day and intra‐day precision of the proposed method were evaluated in terms of the relative standard deviation and were <10.5%.     

Statistical analysis and optimization of photodegradation efficiency of methyl orange from aqueous solution using cellulose/zinc oxide hybrid aerogel by response surface methodology (RSM)

The photodegradation efficiency of cellulose-X/zinc oxide-Y (CA-X/ZnO-Y) aerogels was studied to degrade methyl orange (MO) as an organic dye pollutant from an aqueous solution under UV light irradiation. In this study, the initial pH of the solution (3, 7, and 11), the photocatalyst dosage (3, 6, and 9 g L^-1), the initial concentration of solution MO (10, 20, and 30 ppm), and the concentration of cellulose in CA-X/ZnO-Y hybrid aerogel (3, 6, and 9 wt%) were selected as four variable parameters, whereas the photoderadation performance was selected as the response. Moreover, the response surface methodology (RSM) analysis was carried out to investigate the influence of four various experimental factors at different times on the degradation of MO. The adequacy result of the proposed models displays that total of the proposed models can predict the photodegradation efficiency of MO by CA-x/ZnO-y aerogel. The optimization results of the process showed that pH = 3 and concentration of MO = 10 ppm, photocatalyst dosage (9 g L^-1), and MCC concentration (9 g) are the optimal level of the studied parameters. Also, the results showed that desirability of 0.96 confirms the acceptance and applicability of the model where the RSM model is a helpful technique for the optimum conditions design.     

Critical considerations for the accelerated ageing of high-density polyethylene potable water materials

Accelerated ageing conditions with chlorinated water were identified that minimize variations in solution chemistry and water sorption, and that also enable the interpretation of HDPE physical and chemical changes during 20 week (3884 h) immersion periods. Of the ten conditions tested, three conditions with an alkalinity concentration of 50 ppm as CaCO₃ at pH 6.5 and at 23 and 37 °C performed best. These three conditions exhibited stable pH, free available chlorine, and alkalinity concentration during 20 weeks of HDPE immersion with 72 h changes of ageing solution. HDPE was periodically characterized using differential scanning calorimetry, thermogravimetric analysis, tensile analysis, a density gradient column, moisture analysis, and optical and infrared spectroscopy. Formation of surface carbonyl bonds and gradual reductions in oxidation induction time were detected, as well as water sorption into HDPE. Ageing solution and water sorption monitoring recommendations from this work should be incorporated into accelerated ageing protocols and considered when characterizing aged PE drinking water pipe.