Radiation effects on polymer materials in radiation sterilization of medical supplies

Radiation degradations of polypropylene were studied by measuring chemiluminescence of the irradiated samples. The chemiluminescence emitted by recombination of peroxy radicals were found to increase with increasing dose, reflecting degree of oxidation of polymers. The degradation of PP may be attributed mainly to the oxidation, since the degradation of PP irradiated in air were markedly larger than that in vacuo. It was found that degree of oxidation of EB-irradiated PP was only one-half that for γ-ray-irradiated one. And also the degree of oxidation was found to be very high at the surface area of the film where oxygen can diffuse during irradiation and decrease sharply with increasing depth from the surface.The degradation during storage after irradiation were estimated by the decay curves of chemiluminescence. The degradation during storage occurred at earlier stage up to three months, while in later stage, it hardly proceeded. The degradation of EB-irradiated samples during storage was much smaller than that found in gamma rays irradiation. Irradiation of 2.5 Mrad with EB caused degradation only during storage. It was suggested that the degradation during storage depends on the degree of radiation oxidation. Both degradations, during irradiation and during storage after irradiation, caused by EB irradiation were also found to be smaller than those by γ-rays. The relationship between radiation degradation and degree of crystallinity of polypropylene was also discussed in this paper.     

Biosensor analysis for the kinetic study of polyphenols deterioration during the forced thermal oxidation of extra-virgin olive oil

The process of artificial rancidification of extra-virgin olive oil due to heating in an oxidizing atmosphere was studied by testing an actual kinetic model of the process and monitoring the thermal oxidative degradation of the polyphenols contained in it. To this end, a series of oxidative degradation experiments were carried out on extra-virgin olive oil samples under isothermal conditions at 98, 120, 140, 160, and 180 °C using a thermostatic silicon oil bath. The experimental procedure used in this study carefully followed the recommendations regarding the study of olive oil rancidification set out in the AOM procedure. The change in polyphenol concentration with time was monitored at selected temperatures using a tyrosinase biosensor operating in an organic phase (n-hexane). The activation energy for the polyphenol degradation process determined using the MacCallum method was found to be practically constant throughout most of the process.

Furthermore, the application of the so-called “model-fitting” method to this process enabled the specific constant rates to be determined at the above-mentioned selected temperatures. In addition, a confirmation of the activation energy value was obtained by the “model-fitting” method and the algorithm of the kinetic model equation best-fitting the experimental curve representing the whole process was checked.

Finally, further very interesting observations were made, for instance, the half-life concentration values of polyphenols at selected temperatures between 98 and 180 °C.     

Surface modification of polymers. IV. UV initiated degradation of polymers with stabilizers grafted onto the surface

Polypropylene (PP), Polyethylene (PE), and polystyrene (PS) films were grafted with glycidylmethacrylate in thin surface layers. To the oxiran groups thus grafted onto the surface three UV stabilizers were attached, 4-amino-2,2,6,6-tetramethylpiperidine (AP), 2,4-dihydroxybenzophenone (DHBP), and phenyl 4-aminosalicylate (PAS). The amount of stabilizer grafted onto the surface varied between 25 and 40 nmol/cm² depending on the polymer substrate. The samples were exposed to UV radiation in air, and the degradation and oxidation of the polymers were studied with IR, UV, and ESCA spectroscopy and by stress–strain measurements. PP grafted with AP exhibited a near 20-fold increase in lifetime compared with the unprotected PP, AP did not stabilize the PE or PS samples. DHBP was an efficient stabilizer of PE, the oxidation rate of the grafted sample being 1/2 to 1/3 of the ungrafted. A similar effect was observed when DHBP was grafted onto PP and PS. PAS underwent a rearrangement reaction when irradiated with UV light, and had only a slight stabilizing effect.     

Comparative investigation of irradiated meat by the methods of electron paramagnetic resonance and gas chromatography

A comparative study of irradiated pork meat containing bone was made by the methods of electron paramagnetic resonance (EPR) and gas chromatography (GC). In this investigation EPR has the advantage to be a very fast and unambiguous method even in the cases of thermal treatment of bones. On the other hand, GC analysis is a time consuming procedure however, it becomes very valuable for meat samples that contain no bones.     

MWD of i-Polypropylene Under Degradation by Selc Using a New Eluting Solvent

Abstract

A new eluting solvent, cyclohexane, for steric exclusion liquid chromatography (SELC) at 70°C of i-polypropylene (PP) has been applied to the study of molecular weight distribution (MWD) of samples of PP under repeated extrusion and under oxidative degradation in the presence of incorporated organic peroxide. Various parameters characterizing the changes in MW and MWD of the samples are listed in TABLE 1. M_z changed pronouncedly with increasing extent of degradation in both degradation processes, while M_n changed very slightly indicating the average number of chain scission per chain had been very small, much less than one. Difference in the mechanism of the mechanical as compared to the oxidative degradation has shown up in the way the low MW end of the MWD curves changed during the progress of the degradation process.     

Thermal oxidative degradation kinetics of flame-retarded polypropylene with intumescent flame-retardant master batches in situ prepared in twin-screw extruder

The thermal oxidative degradation kinetics of pure PP and the flame-retarded (FR) PP materials with intumescent flame-retardant (IFR) master batches in situ prepared in twin-screw extruder were investigated using Kissinger method, Flynn-Wall-Ozawa method and Coats-Redfern method. The results showed that the activation energy order of PP and FR PP samples with different blowing agent/char former ratios obtained by Kissinger method agrees well with that obtained by Coats-Redfern one, which well illustrates the relationship between the composition of IFRs and their flame-retardancy, i.e. FR material with richer carbonization agent has higher activation energy for thermal oxidative degradation, hence leading to a better flame-retardancy. For Flynn-Wall-Ozawa method, due to its adoption of Doyle approximation, the obtained activation energy and its order of samples are very different from those of both Kissinger and Coats-Redfern methods. Criado method was finally used to determine the degradation reaction mechanism of various samples.     

Radiation degradation of blends polypropylene/poly(ethylene-co-vinyl acetate)

Physicochemical and mechanical characteristics of irradiated electron beam polypropylene/ethylene-vinyl acetate (PP/EVA) blends and individual components were investigated. Although oxidation of alkyl radicals in the blends proceeds slower than in PP, the total oxidation effect monitored by content of oxygen-containing groups shows opposite tendency. Blending with EVA does not affect degree of PP crystallinity. The enthalpy of melting and crystallization of the blends reveal phase separation between dispersed copolymer and PP matrix. In all studied blends, degradation prevails over tendency of EVA to cross-linking.     

The effect of adding virgin material or extra stabilizer on the recyclability of polypropylene as studied by multi-cell imaging chemiluminescence and microcalorimetry

The effect of adding virgin material or new stabilizers on the recyclability of polypropylene (PP) was determined. Stabilized PP was subjected to oven ageing at 130 °C for 100, 250 or 500 h before and after upgrading with virgin material (0, 20, 50, 80 or 100%) or additional stabilizer during reprocessing. The effect of upgrading recycled PP with extra stabilizer or virgin material was determined by measuring the elongation at break, yellowness change, oxidation induction time (OIT) or total luminous intensity (TLI) by chemiluminescence (CL) techniques. Selected specimens were analysed by microcalorimetry (MC).It has been shown that upgrading recycled PP with virgin material was not effective. Adding 80% virgin material did not increase the lifetime more than adding 20% virgin material. This indicates that a small amount of recycled material can induce degradation by contamination. Adding extra stabilizers instead of virgin material was much more effective. Of all techniques used the OIT as determined with CL showed a clear difference in residual stability of differently treated materials and seems to be the most valuable analytical method to determine the recyclability of PP. A comparison between CL and MC shows that MC is sensitive enough for measuring the solid-state oxidation of stabilized PP. Slightly lower OITs were detected by MC probably associated with the static atmosphere used during the measurements. The TLI method is not suitable to determine the degradation state of to be recycled material.     

Thermal oxidation of isotactic polypropylene synthesized with a metallocene catalyst

The mechanism and kinetics of thermal oxidation of metallocene PP are investigated. It is shown that the rate of oxidation of the samples synthesized at a high temperature (40–70°C) is higher than that of the samples synthesized at a low temperature (20 and 30°C). The composition of oxidation products of PP samples; the kinetics of the accumulation of these products; and changes in structural, thermal, and thermophysical parameters during oxidation are analyzed in detail. Our data indicate that the oxidation of low-temperature samples and the oxidation of high-temperature samples obey different mechanisms. The oxidation of low-temperature samples corresponds to the radical-chain process, in which the intramolecular transfer of kinetic chains prevails. High-temperature samples are characterized by the intermolecular transfer of oxidation kinetic chains, which leads to the degradation of macromolecules. It is inferred that the rate and mechanism of thermal oxidation are determined by the microstructure of polymer chains.     

Thermal characterization of the oxo-degradation of polypropylene containing a pro-oxidant/pro-degradant additive

The oxo-degradation process of polypropylene (PP) samples containing different concentrations (4% and 10% w/w) of pro-oxidant/pro-degradant additive Envirocare™ AG1000C was investigated under accelerated test conditions. Samples were initially exposed to UV radiation for 300 h. The tendency to biodegradation in soil medium of these UV-aged samples was then indirectly assessed by an indirect method for a period of 6 months. The entire degradation process of these materials was first examined by monitoring changes in their morphological properties (melting temperature, maximum lamellar thickness and crystallinity) with the ageing time, by Differential Scanning Calorimetry (DSC). Then, changes in the thermal properties (onset temperature and maximum decomposition temperature) of these materials with the ageing time were analysed by Thermogravimetric Analysis (TGA). Furthermore, the kinetics of the thermal decomposition of these PP samples with pro-oxidant/pro-degradant was also studied during the oxo-degradation process, by means of the Chang differential method. During exposure to UV radiation, the more significant changes in the morphological and thermal properties that were detected in PP samples containing pro-oxidant/pro-degradant additive compared to pure PP, clearly suggest a higher level of oxidation in these samples, confirming the effectiveness of this pro-oxidant/pro-degradant additive in promoting the abiotic oxidation of polypropylene during UV-irradiation. Moreover, the level of oxidation observed in UV-aged samples seems to be dependent on the additive load.     

Thermal, oxidative and radiation stability of polyimides. Part IV: Polyimides based on N-[4-benzoyl-2-(2,5-dioxo-2,5-dihydro-pyrrol-1-yl)-phenyl]-acetamide and different diamines

Polyimide resins were obtained from the reaction between N-[4-benzoyl-2-(2,5-dioxo-2,5-dihydro-pyrrol-1-yl)-phenyl]-acetamide and the following compounds with terminal amino groups: urea, 4-[(4-aminophenyl)sulfonyl]aniline, thiourea, 2-aminoethylamine, and 4,4′-diaminodiphenylmethane. The thermal and thermooxidative behaviour of the polyimide resins was studied by thermogravimetric measurements (TG) in oxygen and nitrogen. Polyimide resins have been irradiated (500 kGy) and their radiation stability evaluated on the basis of thermal and thermooxidative behaviour of irradiated samples.The thermal and oxidative degradation of the examined polyimides is complex and occurs in two phases. The first step occurs in both nitrogen and oxygen but it is somewhat less pronounced in oxygen due to oxidation and formation of more stable products. All samples showed very good radiation stability and there is almost no change in the first degradation step while the span of the peaks in the second step is narrowed and temperatures are slightly lower.     

Crystallization of oxidized isotactic polypropylene

The effect of processes accompanying thermal oxidation of the polymer on the characteristics of its isothermal crystallization has been revealed. It has been shown that crystallization decelerates with a rise in the degree of PP oxidation. The higher the concentration of functional groups, the stronger the deceleration. The energy of nucleation increases when passing from virgin to oxidized PP samples. The higher the concentration of carbonyl groups accumulated in polymer chains, the more pronounced this effect, although the degradation of the chains must lead to a reduction in this parameter. It has been concluded that the kinetic and thermodynamic parameters of the isothermal crystallization are applicable to investigation of processes accompanying thermal oxidation of the crystallizable polymer.     

Accelerating role of clay in photo-oxidation of polypropylene/clay multifilament yarns

Photo-oxidative degradation of polypropylene/clay multifilament yarns containing different amounts of clay was investigated. These samples and pure polypropylene(PP) multifilametns were exposed to long wavelength radiations(λ 300 nm) under atmospheric condition of constant temperature and relative humidity. The photo-oxidative stability was studied using FTIR spectroscopy, tensile testing and microscopy. The results indicate that the addition of clay particles decreases the stability of PP/clay composites to photo-oxidative degradation according to comparison with pure PP. From FTIR study and tensile properties, it was also found that the multifilaments with higher clay loading reveals a faster loss of mechanical properties, higher photo-oxidative product formation and more reduction in the induction time of photooxidation. Moreover, the crack formation on surface of irradiated filaments corresponds well to the conclusions in tensile properties and FTIR characterization.     

Study of the morphology,thermal and mechanical properties of irradiated isotactic polypropylene films

Thin films of isotactic polypropylene (iPP) are of great economical importance and their production is quite challenging due to the need of very fast uniaxial or biaxial expansion. During the expansion, critical problems usually arise, like structure disruption, shear thinning, causing material, energy and time losses. This work aims to study the surface morphology and compare the thermal, mechanical properties of PP films irradiated by gamma ray in an acetylene atmosphere after uniaxial expansion. PP films were made by compression molding at 190 °C with cooling in water at room temperature and irradiated by gamma ray, at (5, 12.5 and 20 kGy) under acetylene atmosphere. After irradiation the samples were submitted to thermal treatment at 90 °C for 1 h and then stretched out at 170 °C using an Instron machine. The surface of PP films, pristine and modified, (i.e., irradiated), was studied using optical microscopy (OM) and scanning electron microscopy (SEM). The changes in morphology, crystallinity and tensile parameters, like yield stress, rupture stress and elongation strain of the PP with irradiation dose were investigated. The results showed some evidences of gel formation due to crosslinking and/or long chain branching induced by radiation.     

Determination of copper and nickel in vegetable oils by direct sampling graphite furnace atomic absorption spectrometry

The quality of food products has been receiving great attention due to its influence on human nutrition and health. In this sense, the determination of trace metals in foods has turned an important field on food analysis. Concerning vegetable oils, its metal trace composition is an important criterion for the assessment of their quality once it is known that trace metals affect their rate of oxidation, influencing freshness, keeping properties as well as storage. In the present work an analytical method which enables the direct determination of Cu and Ni in vegetable oils by graphite furnace atomic absorption spectrometry (GFAAS), using a “solid” sample strategy is presented: in nature, samples are directly weighed on the graphite platform boat and inserted in the graphite tube. An adequate temperature program permitted the calibration by external aqueous analytical curves. Good concordance between the proposed procedure and EPA procedures was found in the analysis of real samples. Limits of detection of 0.001 and 0.002 μg g⁻¹ were found for Cu and Ni, respectively, in the original samples, and they were comfortably below the concentrations found.     

Facile synthesis of oligo(4‐methoxyphenol) in water and evaluation of its efficiency in stabilization of polypropylene

A hindered polyphenol, oligo(4‐methoxyphenol), has been first successfully synthesized via a mild biocatalytic pathway using horseradish peroxidase as catalyst in water without any additive. Then the efficiency of oligo(4‐methoxyphenol) in stabilization of polypropylene (PP) was evaluated in terms of thermal analysis and accelerated aging test. It was observed that the apparent activation energy for thermal decomposition of PP/oligo(4‐methoxyphenol) calculated by Friedman's method is higher than that of virgin PP. Oligo(4‐methoxyphenol)‐stabilized PP maintains its tensile strength even after aging at 120°C for 800 hours. Oxidation induction time and onset oxidation temperature of PP/oligo(4‐methoxyphenol) are higher than both virgin PP and PP/4‐methoxyphenol, as well as PP stabilized with commercially available 6‐di‐tert‐buty‐4‐methylphenol or 1076. These results indicate that oligo(4‐methoxyphenol) can effectively improve the thermo‐oxidative resistance of PP. Noting that oligo(4‐methoxyphenol) is synthesized via enzymatic polymerization in water under mild condition with a facile procedure, oligo(4‐methoxyphenol) is thus proposed as a new efficiency and readily available antioxidant for PP.     

A look inside the extruder: evolution of chemistry,morphology and rheology along the extruder axis during reactive processing and blending

A simple device was recently developed for fast sampling (within a few seconds) of representative melt samples (about 2 g) on a running extruder. An array of such devices has been mounted on a twin‐screw extruder. The goal of this study was to de‐black‐box reactive processing of polymers by studying some typical examples. ‐ Processing of polyolefins in the presence of peroxides: when the polymer is molten and the melt temperature is sufficiently high branching/cross‐linking of PE and degradation of PP occurs; the conversion follows a convex profile along the screw axis, which profile is similar to the exponential profile calculated for peroxide decomposition. ‐ Free‐radical grafting of maleic anhydride (MA) onto polyolefins: MA grafting onto PE and PP also follows a convex profile with branching/cross‐linking as parallel side reaction for PE and degradation for PP; for PE degradation of the formed grafted/cross‐linked gel is observed at the end of the extruder. ‐ Reactive blending of PA‐6 with EPM‐g‐MA: within a few seconds the in‐situ compatibilization reaction, resulting in PA‐6/EPM graft copolymers, is completed and the degree of rubber dispersion has changed from the mm to the sub‐μm range, regardless of the MA content of EPM‐g‐MA and the EPM‐g‐MA content of the blend; PA degradation occurs along the whole extruder.     

High-performance liquid chromatographic analysis of the unusual pathway of oxidation of L-arginine to citrulline and nitric oxide in mammalian cells

A very unusual pathway of the oxidation of L-arginine to citrulline and nitric oxide has been discovered recently in cytotoxic macrophages. In an attempt to detect molecules generated through this metabolic pathway, a fast radio high-performance liquid chromatographic method was developed to analyse the whole set of radiolabelled L-arginine-derived metabolites produced by mammalian cells after appropriate induction. A new intermediate which might be NG-hydroxy-L-arginine was found.     

X-ray investigation of polypropylene and poly(ethylene-co-vinyl acetate) blends irradiated with fast electronsWAXS investigation of irradiated i-PP/EVA blends

Blends consisting of poly(propylene-ethylene) (PP) and poly(ethylene-co-vinyl acetate) (EVA) copolymers were investigated. Specimens were irradiated with fast electrons at different doses. Some of the samples show thermo-shrinkable properties. The interplanar spacing, paracrystalline factor, degree of crystallinity and crystallite sizes were determined by WAXS measurements. Results have been reported in respect to PP content and irradiation dose. A decrease of the crystallite’s imperfections with the rise of the irradiation dose was observed. An interface built up of partially interpenetrated amorphous molecular chains of incompatible polymers and separate PP and EVA small crystallites is suggested.     

Improved thermal oxidation stability of polypropylene films in the presence of β-nucleating agent

Thermal oxidation behavior of isotactic polypropylene (PP) films with and without nucleating agent was investigated at 100 °C in air. The crystal form of PP was modified with a specific aryl amide derivative as β-nucleating agent (β-NA). Fourier transform infrared spectroscopy (FTIR), polarized optical microscopy (POM), differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA) and tensile tests were performed to determine the extent of chemical degradation and the variations of microstructure of the two kinds of PP films during thermal oxidation. It was found that the mechanism of thermal oxidation of PP films was not changed in the presence of β-NA, but the time to initiation and the rate of oxidation both declined. Moreover, during the thermal oxidation aging, the melting temperature of neat PP significantly decreased while only a slight decrease of the melting temperature occurred for β-PP. Overall, the investigation indicated that the thermal oxidative stability of β-PP was higher than that of neat PP. The underlying mechanism was further analyzed by considering the change in the physical structure, especially the crystalline and the amorphous structure, of PP in the presence of β-NA.