Irradiated LDPE Research Articles

Crosslinked networks in electron beam irradiated polyethylenes evaluated by proton low-field NMR spectroscopy

Effect of electron beam (EB) irradiation is analyzed in low and high density polyethylenes (LDPE and HDPE, respectively) at different doses. Parameters as important as degree of crystallinity, melting or crystallization temperatures are dependent on the initial PE molecular architecture, which also controls the gel content developed by action of EB irradiation and the EB dose applied. Thus, this gel amount, ascribed to formation of chain crosslinkings, is raised as irradiation dose increases, being larger in the HDPE than in the LDPE. In both, a plateau value is reached at the highest doses. The molecular changes that take place in both PEs during EB irradiation lead to a hindrance in their crystallization capacity, once macrochains are molten, and, accordingly, to a reduction in crystallinity and to formation of thinner crystallites. Variation with temperature of rigid and soft fractions together with their respective relaxation times is followed in the irradiated LDPE and HDPE specimens by pulse mixed magic-sandwich echo nuclear magnetic resonance (MSE-NMR) measurements. The network structure promoted in these PEs is evaluated by using the multiple-quantum nuclear magnetic resonance (MQ-NMR) approach, showing important differences caused by EB irradiation due to their intrinsic molecular characteristics.

Photodegradation of low‐density polyethylene with prooxidant and photocatalyst

AbstractLow‐density polyethylene (LDPE) composite films with trisilver phosphate (Ag3PO4) and cadmium selenide (CdSe) particles as photocatalysts and manganese stearate as prooxidant were prepared. The film samples were irradiated under UV and visible light and their photodegradation were evaluated using Fourier‐transform infrared spectroscopy, scanning electron microscopy, thermogravimetric analysis, and differential scanning calorimetry. The carbonyl index of the photocatalyst containing samples was very higher than the pure irradiated LDPE and even prooxidant containing film. The morphologies of the irradiated composite films were completely changed and had many cavities and cracks. The thermal stability of the composites was very lower than the pure polyethylene. However the crystallinity of the LDPE films with photocatalysts was enhanced contrarily the LDPE film with manganese stearate. Generally the results showed that the combination of the prooxidant with photocatalyst have synergistic effect on the photodegradation of the LDPE and can be used to accelerate the degradation of the polyethylene films.

Melting and crystallization behaviours of the electrons irradiated LDPE/MWCNTs composites

Electrons are an important constituent part of radiation space of charged particles and could damage microelectronic devices. Therefore, effective radiation protection is very important for the electronic device. So, a radiation protecting material with lightweight, high performance and low cost is urgently needed. Polyethylene (PE) with high hydrogen content/carbon nanotube (CNT) composite as a space shielding material is very promising for spacecraft application in the future. In order to meet the requirement of space applications for PE/CNT composite, it is of important academic value and practical significance to explore melting and crystallization behaviors of LDPE/MWCNT composites. In this paper, melting and crystallization behaviours of the irradiated LDPE/MWCNT composites irradiated by 110 keV electrons are studied by differential scanning calorimetry (DSC), synchrotron radiation X-ray small angle scattering (SAXS) and wide angle diffraction (WAXD). Experimental results show that the irradiation by 110 keV electrons does not affect the thermal characteristics of the LDPE, but can enhance the initial melting temperature and the melting-terminating temperature of LDPE/2% MWCNT composites during melting. Also, the radiation by 110 keV electrons could reduce the initial crystallization temperature and the crystallization-terminating temperature during crystallization. MWCNTs could enhance the initial melting temperature and reduce the melting-terminating temperature of LDPE/2% MWCNT composites during melting. Moreover, MWCNTs could enhance the initial crystallization temperature and crystallinity, and reduce the crystallization-terminating temperature during crystallization. SAXS and WAXD analyses show that with increasing the temperature, long periods of the irradiated/unirradiated LDPE increase during melting. Compared with that of the unirradiated LDPE, at a given temperature, long period of the irradiated LDPE is small. During crystallization, with reducing the temperature, long period of the irradiated/unirradiated LDPE begins to appear and gradually decreases. At the same temperature, long period of the irradiated LDPE is larger than that of the unirradiated one. For LDPE/2% MWCNT composites, long periods of the irradiated/unirradiated samples during melting and crystallization do not exist. The 110 keV electron irradiation mainly influences LDPE matrix of LDPE/2% MWCNT composites during melting and crystallization. The 110 keV electron irradiation can slow down the amorphous region expansion and the initial melting of lamellae of the LDPE matrix during melting. The 110 keV electron irradiation can slow down the amorphous region shrinkage and inhibit crystal from growing up during crystallization. During melting, MWCNTs can hinder the amorphous and crystalline molecular chains of LDPE from moving, which hinders the LDPE matrix from initially melting, but promotes the melting process after the initial melting has begun. During crystallization, MWCNTs could promote the formation of crystal of the LDPE matrix and inhibit the crystal from growing up.

Biodegradation of gamma irradiated low density polyethylene and polypropylene by endophytic fungi

Biodegradation of plastic waste through fungal strains offer a solution to serious issues of pollution as fungi are known to release plastic degrading enzymes. In the present study, the isolated endophytic fungi from two endemic plants, Psychotria flavida and Humboldtia brunonis which produced laccase enzymes and grew profusely over hydrophobic surface of plastic films were tested for biodegrading ability. The fungi were inoculated on the polythene and polypropylene films irradiated with different doses of radiation, (0–1000 kGy for Low Density Polyethylene and 0–100 kGy for Polypropylene) and incubated for 90 days. The extent of biodegradation pattern of endophytic fungi was measured for the highest dose mainly by analyzing changes using FTIR spectroscopy, DSC, SEM, alteration in viscosity and thereby average molecular weight. The decrease in intrinsic viscosity and average molecular weight of gamma irradiated LDPE strips inoculated with Aspergillus sp., Paecilomyces lilacinus from H. brunonis and Lasiodiplodia theobromae from Psychotria flavida indicate fungal efficiency in plastic degradation. Only L. theobromae from P. flavida could degrade irradiated polypropylene film with 0.3 mg on actual weight loss basis. Further work on employing these endophytic fungi in biodegradation of plastics is warranted.

Storing Effects on Electrical Properties of High Energy Electron Beam Irradiated LDPE and HDPE

In this work, the effect of storing time on the variation of surface and volume resistance of the 10 MeV electron beam irradiated LDPE and HDPE samples was investigated. This study was carried out about one month after irradiation. The samples were prepared in sheet form with thickness of 2 ± 0.1 mm and irradiated at the doses of 70 to 370 kGy. All the samples were kept at room temperature. The results show a peak at about 25 days after irradiation in surface resistance for all the samples. The volume resistance measurements did not show any significant variation.

Spectroscopic studies of structural changes in irradiated LDPE and its blends

The low temperature glass transition occurring at low temperature in polyethylene samples was studied using Fourier transform infrared, FT-Raman spec- troscopic techniques, which are known to be sensitive to any structural changes in the investigated samples. Anomalous behavior was obtained in the temperature range (98 K ? 383 K) indicating the existence of phase transition occurring at about 98 K and disappearing at about 323 K while heating for unirradiated virgin low den- sity polyethylene (VPE) sample with or without crosslinking agent (trimethylol pro- pane triacrylate, TMPTA). Addition of TMPTA monomer caused severe changes in the temperature dependence of both unirradiated and irradiated polyethylene sam- ples. The results given indicated the occurrence of abnormal temperature depend- ence, which is thought to be related with low temperature structural change result- ing from local crosslinking in scrapped polyethylene (SPE) sample already suffering from high degree of crosslinking. Differential scanning calorimetry (DSC) thermo- grams confirmed the observed new phase transition observed in both unirradiated and irradiated TMPTA loaded VPE/SPE (50/50 wt %) blend. Irradiation, addition of TMPTA as a crosslinking agent, and blending VPE with SPE were found to affect remarkably the variation of the vibration spectrum of LDPE and consequently the resulting structural changes. The experimental results obtained were discussed and correlated with reorientational disorders of the molecular segments (local crosslinking).

Effects of gamma radiation on commercial food packaging films—study of changes in UV/VIS spectra

The effects of gamma irradiation doses up to 100 kGy on the optical properties of different commercial packaging films were studied in this paper. The packaging films analyzed were: polyethylene “LDPE”, amide 6-amide 6.6 copolymer “PA6-PA6.6” and poly(ethylene terephthalate) “PET”. An investigation on film samples before and after irradiation was performed by UV/VIS spectroscopy. The results showed that, in the absorption spectra of irradiated LDPE and PA6-PA6.6 films, a red-shift in the wavelength of the UV cutoff and a marked reduction in % transmittance (at low wavelengths) occur with increasing radiation dose. With respect to PET samples, no significant changes were observed in either light absorption or transmittance.

Foaming of Electron-Beam Irradiated LDPE Blends Containing Recycled Polyethylene Foam

An experimental study concerning the recycling of slightly crosslinked polyethylene foams produced in the manufacturing process was conducted. The recycled polyethylene (RPE) was blended with virgin low-density polyethylene (PE) and irradiated by electron-beams and expanded by heat to make regenerated foams. Four RPE/PE blends with different RPE contents ranging from 0 to 15 phr were foamed and the amount of blowing agent was varied in order to make foams of various densities. The mean cell size of the RPE/PE blend increased with an increase in the RPE content and the degree of anisotropy was generally higher for foams with larger RPE contents. The homogeneity of cell distribution and the type of cell distribution seem to be independent of the expansion ratio at a low RPE content. Furthermore, RPE/PE blends with 0∼5 phr of RPE were capable of producing good regenerated foams without losses of tensile and tear strength and other properties such as compression set, resiliency, dimensional change on heating, and Asker C hardness.

Characterization of MeV proton irradiated PS and LDPE thin films

Polystyrene PS and commercial low density polyethylene LDPE thin films were irradiated under vacuum with protons of three different energies and fluences. LDPE was more affected by radiation than PS. To correlate the change in structure with properties, the irradiated and unirradiated samples were characterized by FTIR, Raman, UV–Vis, 13C NMR, liquid H–NMR and WAXS spectroscopy as well as by thermal analysis: DSC, TGA and DMA. Obtained changes are strongly dependent on the total deposited energy of the incident ion beam. Radiation induced polycyclic structures were detected by IR, Raman and UV–Vis for PS samples. Hydroxyl (OH) and carbonyl (CO) groups were also recorded by FTIR in both kind of polymers. More drastic changes were observed in LDPE mechanical properties. Based on the results obtained by the analytical techniques used in this study, a free radicals mechanism for PS and LDPE is proposed, with the aim to explain the earlier formation of polycyclic structures, that could be the precursors for clusters or benzene-like ring aggregates. The mechanism suggested for PS presumes crosslinking not only through the main chain but also through the benzenic ring, based on the evidences given by UV–Vis, 1H–NMR as well as properties modification induced by proton irradiation.

Ultraviolet and infrared spectral analysis of irradiated polyethylene films: Correlation and possible application for large-dose radiation dosimetry

A detailed study was performed to develop the dosimetric characteristics of commercial low-density polyethylene film (LDPE), which is, by far, the most commonly used plastic for food and for many other-purpose packaging film, to be used as a film dosimeter for large-dose γ-radiation dosimetry. The useful dose range extends up to 880 kGy. Correlations were established between the absorbed dose of γ-radiation and the radiation-induced changes in LDPE measured using Fourier transform infrared (FTIR) and ultraviolet (UV) spectrophotometry. The results showed a significant dependence of the response on the selected readout tool of measurements whether FTIR (at 1716 cm -1 ) or UV ( at 220 and 270 nm) as well as on the quantity used for calculation. The radiation-chemical yield of the ketonic carbonyl group produced in irradiated LDPE film was found to be 0.7 μmol/J. The assessment of the random uncertainty associated with the measurement of the dose response and the effect of relative humidity during irradiation on the dosimeter performance as well as the postirradiation stability at different storage conditions are discussed.

Chemiluminescence study on the oxidation of several polyolefins: II. Chemiluminescence from γ-irradiated polymers

Chemiluminescence (CL) from isotactic polypropylene (i-PP) and several types of polyethylene, namely low density (LDPE), linear low density (LLDPE) and high density (HDPE), subjected to γ-irradiation in the presence of air, was recorded in both inert (nitrogen) and oxidative (oxygen or air) atmospheres. CL data can be related to the radiation-induced changes observed in the IR spectra of the polymers. The signal recorded in nitrogen may be accompanied by a thermo-luminescence emission, mainly occurring at the melting point of the polymers. The decay of CL emission at 170 °C seems to follow second-order kinetics. It could be related to the presence of two types of luminescent species, perhaps associated with free hydroperoxides. The stability of the polymers subjected to thermal oxidation after irradiation is found to depend on both the polymer type and post-irradiation treatments, such as the thermal decomposition in the inert atmosphere of radiation-induced peroxide products. The shape of the CL curves recorded in air from irradiated LDPE could be related to a competition between oxidation and scission.

Chemiluminescence assessment of the effectiveness of some phenolic antioxidants for heat stabilization of irradiated LDPE

The inhibition of thermal- and irradiation-oxidation of LDPE in the presence of a number of phenols was studied using the Chemiluminescence method. 1-pyrenol and various phenanthrol isomers were compared with a number of commercially available phenolic antioxidants. The following order of efficiency was found: Irganox 1330 ≥ 1-pyrenol > Sumilizer MDP-S > 4-phenanthrol > 1-phenanthrol > 3-phenanthrol > Sumilizer GM-S > 2-phenanthrol > Sumilizer GS > 8-quinolinol > Sumilizer BHT. The antirad effect of the studied antioxidants in LDPE follows, up to 10 Mrad, the same efficiency order as in the thermal oxidation.

Spectroscopic and mechanical changes in irradiated starch-filled LDPE

LDPE containing corn starch (3·9%, 5·8% and 7·9% by weight) without further additives and corn starch in a pro-oxidant formulation (= masterbatch (MB): 10%, 15% and 20% by weight), were analysed by FTIR and drawtesting after irradiation for periods of up to 500 h. The carbonyl index for LDPE-20% MB after 500 h irradiation was 2·5 times the value obtained in pure LDPE and in LDPE-starch. The hydroperoxide index for the same material was three times the value obtained in pure LDPE and in LDPE-starch. During irradiation the tensile strength decreased to almost the same extent for all three materials—a mean value of 70% of the initial value was obtained after irradiation. The elongation at break for pure LDPE decreased during irradiation from 650 to 500%. The addition of starch and MB decreased the initial value from 650 to 500%. After irradiation the decrease was considerable—a mean value of 60% being recorded for the elongation at break of LDPE-MB. A material susceptible to photolysis is thus obtained by the addition of corn starch and a master batch containing LLDPE, styrene-butadiene copolymer (SBS) and manganese stearate. Incorporating only starch into LDPE did not significantly change the susceptibility of the material to photolysis. LDPE-MB is thought to degrade by an initial photo-oxidation (autoxidation) and a subsequent attack by microorganisms (i.e. biodegradation). Further ongoing studies on the biodegradation of pretreated LDPE-MB will be reported elsewhere. The induction time is accelerated by pretreatment. Irradiation or thermal treatment generate free radicals causing autoxidation which should facilitate a later biodegradation.

Thermodynamic elucidation of depression mechanism on sorption of flavor compounds into electron beam irradiated LDPE and EVA films

Thermodynamic elucidation of depression mechanism on sorption of flavor compounds into electron beam irradiated LDPE and EVA films

Enhanced formation of free radicals in irradiated LDPE containing ZnO

The concentration of free radicals formed under γ-irradiation in low-density polyethylene (PE) containing zero, 0.01, 0.02; 0.05; 0.1; 0.2 and 0.4 vol% ZnO was measured by using the technique of ESR spectroscopy. When samples are irradiated in air an increase of the total amount of free radicals compared to that of pure polymer without ZnO was observed. This increase appeared over the whole range of ZnO content, with a maximum at about 0.02 vol% ZnO. The results obtained by ESR are consistent with the data on gel formation reported in a previous paper. (1) A comparison of ESR data obtained on samples in air and in vacuo suggests that the phenomenon is due to the presence of oxygen during irradiation and that it is probably the result of two dominant processes taking part at the interface of ZnO and PE chains: the first one is the preferential formation of free radicals on the chains distorted in the neighbourhood of ZnO particles, whereas the second process is relevant to the interaction between formed radicals and oxygen diffused into the system. Other possible causes of the increased generation of free radicals are also considered.