Ionizing radiation as adjuvant for the abiotic degradation of plastic bags containing pro‐oxidant additives (original) (raw)
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EVALUATION OF ENVIRONMENTAL AGING OF POLYPROPYLENE IRRADIATED VERSUS PRISTINE
Polypropylene (PP) is the most common thermoplastic resin of the plastic market due to its very interesting physical, chemical and processing properties at very low market price, however after its use the resin does not degrade in the environment or it degrades at very low rate. This study has the objective of comparing the environmental exposure of PP irradiated with 20 kGy and pristine PP. Dumbbell samples were manufactured by injection molding and exposed to the environment during 90 days; another one set was subjected to gamma irradiation at 20 kGy total dose and exposed at the same conditions too. The samples were characterized by mechanical testing, visual inspection, infrared spectroscopy (IR), scanning electron microscopy (SEM) and differential scanning calorimetry (DSC). The irradiated samples, after environmental aging, showed oxidation and presence of cracks in samples of the PP 20 kGy. Introduction Polypropylene is a thermoplastic polyolefin obtained by polymerization of propylene monomer. PP is of great importance to the market due to its versatility, easy processing, and good mechanical properties, at very low market price and up to 20% lighter than other polymers [1]. The structural changes, typically chain scission and crosslinking, induced by ionizing radiation cause changes in the physical properties of irradiated polymers. Although the degradation reactions of the type crosslinking or chain scission occur simultaneously during irradiation of the polymer, one of these processes is generally dominant, depending on the chemical structure of the polymer, dose, dose rate, type of radiation and the conditions of the environment (pressure and temperature) in which the material is irradiated. The primary process due to irradiation of the polymer is the generation of excited species and free radicals resulting from the breakage of chemical bonds [2, 3]. Environmental aging is widely used in research and industrial assessment and strictly depends on geographical variables and atmospheric exposure conditions. Reasons for degradation may result from the combination of these variables such as heat, ultraviolet light, moisture, oxygen and pollutants. PP is a sensitive polymer due to the presence of tertiary carbon in their structure and suffers the effects of degradation and alteration of mechanical and aesthetic properties [4-7]. The energy to break the tertiary carbon may also be provided by gamma irradiation, which will modify the chemical structure of the polypropylene by increasing the content of carbonyl and hydroxyl groups suggesting the occurrence of oxidative degradation [8].
Post-irradiation oxidation of different polyethylenes
Polymer Degradation and Stability, 2011
The radiation-induced oxidative degradation of polyethylenes (PEs) with different degrees of crystallinity was characterized after electron-beam irradiation and during storage at room temperature.
Journal of materials science. Materials in medicine, 2001
The aging behavior of ultra-high molecular weight polyethylene (UHMWPE) has been studied following gamma irradiation in air. Accelerated aging procedures used elevated temperature (70 degrees C), pressurized oxygen (5 bar) and applied stress. Shelf and in vivo aged components have also been investigated. The variation in polymer properties with depth into the polymer was determined using density measurements, infra-red spectroscopy and differential scanning calorimetry. Accelerated aging in pressurized oxygen resulted in peaks in polymer density and degree of oxidation up to 500 microm below the polymer surface. Shelf and in vivo aging was also found to result in increased density at or below the component surfaces. Changes in density were mainly due to changes in crystallinity within the UHMWPE and, to a smaller extent, due to oxygen incorporation within the polymer. The application of stress did not appear to influence the accelerated aging of UHMWPE. A method for estimating the r...
The effects of γ-irradiation on compositional changes in plastic packaging films
Packaging Technology and Science, 1999
Sterilization of packaging materials for pharmaceutical or food products with ionizing irradiation can cause chemical and physical changes in polymer materials. The effects of g-irradiation on the formation of solvent extractable radiolysis products of six¯exible packaging materials for foodstuffs and/or pharmaceutical applications were studied after treatment in a 60 Co-irradiation plant. The polymer materials polyethylene, polypropylene, poly(ethylene terephthalate), polyamide, polystyrene and poly(vinyl chloride) were investigated after treating with an irradiation dose of 44 kGy. The compositional changes in solvent extractable radiolysis products of each packaging material were quanti®ed. In most cases the radiolysis products formed could be identi®ed using GC/MS. The polyole®ne materials (PE and PP) showed an increase of low volatile compounds after irradiation due to an oxidative decomposition of the polymer and typical polymer substances like oligomers and additives. Other packaging materials such as PET, PA and PS did not signi®cantly change their amount of solvent extractable compounds after irradiation with 44 kGy. The PVC packaging material used in this study was not resistant to irradiation treatment at all. Because of the release of HCl during irradiation a large amount of volatile substances could be extracted from the PVC sheet. For consumer protection and also to meet general food packaging legislative requirements for irradiated packaging materials, it is necessary to evaluate the compositional changes in the polymers during irradiation, especially for irradiated polyole®nes and PVC. Most attention should be paid to low volatile radiolysis products which are the most likely to migrate into a foodstuff or a pharmaceutical product.
Profile of oxidation in irradiated polyethylene
1998
Following gamma irradiation in air which causes bond scission and yields large concentrations of peroxy radicals, maximum oxidation and an increase in crystallinity occurs on the surface of ultrahigh molecular weight polyethylene. Here, bimolecular reactions of peroxy radicals generate carbonyls, mostly ketones. On the polymer surface, peroxy radicals continue to react over time periods of years to generate carbonyls and chain scission. Peroxy radicals in the interior of the polymer abstract hydrogens and form hydroperoxides, inducing chain reactions and a slow but continue increase of ketone. Within the polymer sample, to a decreasing depth with increasing dose, a reduced concentration of oxygen is available to react with radiolytic radicals, so that more efficient crosslinking and a low level of hydroperoxide chain reaction occur. After long periods of time a surface maximum in carbonyl concentration is produced. Heating polyethylene in high pressures of oxygen accelerates the oxidative process.
Polymers, 2021
The photooxidative degradation process of plastics caused by ultraviolet irradiation leads to bond breaking, crosslinking, the elimination of volatiles, formation of free radicals, and decreases in weight and molecular weight. Photodegradation deteriorates both the mechanical and physical properties of plastics and affects their predicted life use, in particular for applications in harsh environments. Plastics have many benefits, while on the other hand, they have numerous disadvantages, such as photodegradation and photooxidation in harsh environments and the release of toxic substances due to the leaching of some components, which have a negative effect on living organisms. Therefore, attention is paid to the design and use of safe, plastic, ultraviolet stabilizers that do not pose a danger to the environment if released. Plastic ultraviolet photostabilizers act as efficient light screeners (absorbers or pigments), excited-state deactivators (quenchers), hydroperoxide decomposers,...
Applied Sciences, 2022
Poly(lactic acid) (PLA) is a biodegradable polymer used for food packaging. The effects of electron beam radiation on the chemical and physical properties of amorphous PLA were studied. In this study, amorphous, racemic PLA was irradiated at doses of 5, 10, 15, and 20 kGy in the absence of oxygen. Utilizing electron paramagnetic resonance spectrometry, it was found that alkoxyl radicals are initially formed as a result of C-O-C bond scissions on the backbone of the PLA. The dominant radiation mechanism was determined to be H-abstraction by alkoxyl radicals to form C-centered radicals. The C-centered radicals undergo a subsequent peroxidation reaction with oxygen. The gel permeation chromatography (GPC) results indicate reduction in polymer molecular mass. The differential scanning calorimetry and X-ray diffraction results showed a subtle increase in crystallinity of the irradiated PLA. Water vapor transmission rates were unaffected by irradiation. In conclusion, these results suppor...
Kinetics of poly(vinyl chloride) thermal degradation by ionizing radiation
Cadernos UniFOA, 2020
In this study, the relationship between ionizing radiation treatment and thermal degradation kinetics of Poly (vinyl chloride) (PVC) polymer film was investigated. The unirradiated and 25 kGy irradiated samples treated with gamma rays or electron beam radiation were submitted to thermogravimetric analysis (TGA) at different heating rates (10 – 30 K.min-1). The TGA data was used to obtain the apparent activation energy values (Ea) according to Flynn-Wall-Ozawa method. TGA analysis suggested that electron beam radiation promotes a slight increase on maximum temperature for dehydrochlorination reaction on PVC. Gamma-rays irradiation caused a small reduction of maximum temperature of HCl evolution of PVC. Thermal degradation kinetics results showed that 25 kGy irradiated samples presents an apparent activation energy values from 104 - 109 KJ.mol-1. The apparent Ea values suggested that 25 kGy gamma radiation or 25 kGy electron beam radiation convert PVC polymer films more prone to HCl e...
Humid and Thermal Oxidative Ageing of Radiation Cured Polymers—A Brief Overview
Frontiers in Chemistry
This article deals with the long-term behaviour of radiation cured polymers. Among the wide variety of possible ageing modes, the attention is focused on two key processes for users of radio-cured polymers: humid ageing of polymer glasses and thermal oxidative ageing of rubbers. These two processes are illustrated by numerous results coming from literature or our own research works. In both cases, the consequences of the structural modifications on the use properties (in particular, on mechanical properties) are described. It is found that the ageings of radiochemically and thermally cured polymers are not so different. It is thus concluded that a great part of the very abundant literature published on the ageing of thermally cured polymers remains exploitable for radio-cured polymers.