Electron beam irradiated polyamide-6,6 films—II: mechanical and dynamic mechanical properties and water absorption behavior

Electron beam irradiation of poly(iminohexamethylene-iminoadipoyl) (Polyamide-6,6) films was carried out over a range of irradiation doses (20–500 kGy) in air. The mechanical properties were studied and the optimum radiation dose was 200 kGy, where the ultimate tensile stress (UTS), 10% modulus, elongation at break (EB) and toughness showed significant improvement over the unirradiated film. At a dose of 200 kGy, the UTS was improved by 19%, the 10% modulus by 9% and the EB by 200% over the control. The dynamic mechanical properties of the films were studied in the temperature region 303–473 K to observe the changes in the glass transition temperature (T_g) and loss tangent (tan δ) with radiation dose. The storage modulus of the film receiving a radiation dose of 200 kGy was higher than the unirradiated film. The water uptake characteristics of the Polyamide-6,6 films were investigated. The water uptake was less for the films that received a radiation dose of 200 and 500 kGy than the unirradiated film. The role of crystallinity, crosslinking and chain scission in affecting the tensile, dynamic mechanical and water absorption properties was discussed.     

Synthesis of colloidal SnSe quantum dots by electron beam irradiation

Water-soluble orthorhombic colloidal SnSe quantum dots with an average diameter of 4 nm were successfully prepared by a novel irradiation route using an electronic accelerator as a radiation source and hexadecyl trimethyl ammonium bromide (CTAB) as a surfactant. The quantum dots exhibit a large direct bandgap of 3.89 eV, greatly blue shifted compared with that of bulk SnSe (1.0 eV) due to the quantum confinement effect. The quantum dots show blue photoluminescence at ∼420 nm. The influence of CTAB on the growth of the quantum dots was investigated and a possible reaction/growth mechanism was proposed.     

Modelling molecular weight changes induced in polydimethylsiloxane by gamma and electron beam irradiation

A commercial linear polydimethylsiloxane (PDMS) was subject to gamma irradiation under vacuum and in air, as well as to accelerated electron beam radiolysis (EB). All irradiation treatments were done at room temperature. The molecular weight changes induced by the radiation processes have been investigated using size exclusion chromatography (SEC) with refraction index (RI) and multi angle laser light scattering (MALLS) detectors to obtain the number and weight average molecular weights of the irradiated samples.

The analysis of the data indicates that crosslinking reactions predominated over scission reactions in all cases. Gamma irradiation under vacuum was the most efficient process within the analyzed dose range, reaching the gel point earlier. Irradiation in the presence of oxygen induces oxidative effects, both in gamma and EB irradiations. A previously developed mathematical model of the irradiation process that accounts for simultaneous scission and crosslinking and allows for both H and Y crosslinks fitted well the measured molecular weight data.     

Effects of electron beam irradiation on cork volatile compounds by gas chromatography-mass spectrometry

Summary The effects of electron beam irradiation on cork volatile compounds was studied at different doses (25, 100, 1000 kGy). Volatiles were isolated from cork using the dynamic headspace-sampling technique, then identified by gas chromatography-mass spectrometry (GC-MS). Similar gas chromatographic profiles were obtained for non-irradiated and irradiated corks. Quantitative differences induced by the three doses were evaluated by calculating peak areas for each compound identified. The quantitative differences between non-irradiated corks and those irradiated at 25 kGy were significant for only a few substances, whereas significant quantitative differences were found in samples irradiated at 100 and 1000 kGy. For these doses, the content of volatile compounds generally increased, especially that of aliphatic hydrocarbons and carbonyl compounds. The behaviour of radiolytic hydrocarbons indicates that the mechanisms proposed for their formation in irradiated foods could take place even in cork.     

Degradation of epoxy resins under high energy electron beam irradiation: Radio-oxidation

The degradation of two epoxy systems exposed to electron beam irradiation in oxygen atmosphere has been studied and compared to our previous results obtained under helium atmosphere. A multi-scale approach to the degradation has been carried out using a variety of analytical methods including solid state NMR spectroscopy, 2D-WISE experiments, SEC measurements and infrared spectroscopy associated with chemical derivatisation treatments. It is shown that the degradation of both polymers is governed by radiolytic processes which involve chain scissions. The formation of oxidation products, mainly carboxylic acid chain ends, was shown at the surface of the irradiated film. Oxidative degradation is limited to the first 20 μm of the film due to the low oxygen diffusion coefficient in epoxy polymers combined with the high dose rates of irradiation.     

Degradation and stability of polyaniline on exposure to electron beam irradiation (structure-property relationship)

Polyaniline (PAni) was prepared by electrochemical polymerization and subjected to different doses of electron beam (EB) irradiation. The effect of EB irradiation causes both chain scission and cross-linking process in PAni, which depends on irradiation dose. The degree of chain scission and cross-linking in PAni by EB irradiation is characterized through XRD, TGA, DSC, solubility, EPR and electrical properties measurement. The results reveal that with increase in EB irradiation dose from 0 to 150 kGy DC and AC conductivity and dielectric constant are found to increase mainly due to the chain scission or further doping in PAni. Due to irradiation there is change in the structure of PAni, such as decrease in the d-spacing, inter-chain separation, thermal stability and T_g but increase in the percent crystallinity and solubility. With further increase in the EB irradiation dose from 150 kGy onwards the DC and AC conductivity and dielectric constant are decreased due to the cross-link formation or dedoping in PAni, which causes the decrease in percentage of crystallinity and solubility and increase in d-spacing, inter-chain separation, thermal stability and T_g of PAni.     

Tacticity, molecular weight, and molecular-weight-distribution relationships in stereoregular polyacrylonitrile prepared by electron beam irradiation canal polymerization

The preparation and characterization of stereoregular isotactic polyacrylonitrile (PAN) by electron beam (EB) irradiation on a urea canal complex are described. The EB method has several advantages over the ordinary γ-ray irradiation method: a very short polymerization time is needed (within a few seconds) and EB irradiation is carried out intermittently, and so all the polymer properties can be studied as a function of the EB irradiation dose. The structure–properties relationships of PAN, such as intrinsic viscosity versus the number-average molecular weight and the viscosity versus the isotacticity range were clarified. Significant information for the optimization of the tacticity of PAN was extracted. Received: 23 August 1999 Accepted : 10 January 2000     

Influence of electron beam irradiation on physicochemical properties of poly(trimethylene carbonate)

Electron beam (EB) irradiation of poly(trimethylene carbonate) (PTMC), an amorphous, biodegradable polymer used in the field of biomaterials, results in predominant cross-linking and finally in the formation of gel fraction, thus enabling modification of physicochemical properties of this material without significant changes in its chemical structure. PTMC films (M_w: 167-553 kg mol⁻¹) were irradiated with different doses using an electron accelerator. Irradiation with a standard sterilization dose of 25 kGy caused neither significant changes in the chemical composition of the polymer nor significant deterioration of its mechanical properties. Changes in viscosity-, number-, weight-, and z-average molecular weights of PTMC for doses lower than the gelation dose (D_g) as well as gel-sol analysis and swelling tests for doses above D_g indicate domination of cross-linking over degradation. EB irradiation can be considered as an effective tool for increasing the average molecular weight of PTMC and sterilization of PTMC-based biomaterials.     

Crosslinking of recycled polyethylene by gamma and electron beam irradiation

Recycling of polymeric materials is usually accompanied by degradation and deleterious properties. Irradiation crosslinking of recycling low density polyethylene by electron beam and gamma rays could be the solution to improve their properties. This paper presents a comparison on the effects of gamma and electron irradiation on virgin and recycled polyethylene. Their mechanical, thermal and chemical properties were analyzed. VPE samples shown higher crosslinking percentages than RPE samples in all range of doses studied, unirradiated RPE samples had higher values on their tensile properties than VPE. Percentage crystallinity was similar in all range of doses studied.     

Influence of silica fillers during the electron irradiation of DGEBA/TETA epoxy resins, part III: Solid-state NMR investigations

The influence of silica fillers on chemical modifications of diglycidyl ether of bisphenol A/triethylene tetramine (DGEBA/TETA) epoxy resins induced by electron beam irradiation has been studied by ¹³C CP-MAS (Cross Polarisation and Magic Angle Spinning) NMR. Four kinds of silica filler were investigated: a pure micrometric silica, a treated micrometric silica, a pure nanometric silica and a treated nanometric silica. On the unirradiated epoxy resins, the magnetization transfer curves reveal structural differences due to the kind of silica fillers. A decrease of the epoxy network rigidity in the presence of nanometric silica fillers is shown. During irradiation, the formation of phenolic ends and enamine functions is confirmed. The slowing of the magnetization transfer of the pure and treated micrometric silica filled epoxy resin reveals an important decrease of the rigidity of these resins. On the pure and treated nanometric silica filled epoxy resins, reactions of the reactive species created by the irradiation in the epoxy resin and the silica particles surface are shown.     

Investigation of electron beam irradiation effects on anti-nutritional factors, chemical composition and digestion kinetics of whole cottonseed, soybean and canola seeds

This study was completed to determine effects of electron beam (EB) irradiation at doses of 15, 30 and 45 kGy on anti-nutritional factors, ruminal degradation and in vitro crude protein (CP) digestibility of whole cottonseed (WCS), soybean (SB) and canola seeds (CS). EB-irradiation eliminated completely (P<0.001) phytic acid of WCS, SB and CS at a dose of 30 kGy. EB-irradiation decreased linearly (P<0.001) the total glucosinolate content of CS. Trypsin inhibitor activity of 15, 30 and 45 kGy EB-irradiated SB was decreased by 19, 73 and 88%, respectively. Free gossypol content of WCS was reduced linearly (P<0.001) by irradiation. EB-irradiation increased linearly (P<0.001) CP digestibility of feeds. In conclusion, EB-irradiation was an effective processing method for improving the nutritive value of WCS, SB and CS.     

Electron beam irradiation effects on poly(ethylene terephthalate)

Changes in poly(ethylene terephthalate) subjected to electron beam irradiation at doses up to 15 MGy and dose rate of 1.65 MGy/h, were investigated by differential scanning calorimetry, molecular weight measurement, X-ray photoelectron spectroscopy, and scanning electron microscopy. Irradiated samples showed a decrease of molecular weight with a minimum at 5 MGy, which is attributed to chain scission of the macromolecules and then an increase at further doses due to branching and some degradation effect. Irradiation in air is not an important factor because the high dose rate of irradiation inhibits oxygen diffusion in the samples.     

Structural and physico-chemical studies on modification of polypropylene and its polyphenolic antioxidant by electron beam irradiation

As polypropylene (PP) is widely used in medical and pharmaceutical fields, the effect of sterilization on both the polymer and its additives must be taken into account. In this study, PP and its antioxidants Irganox 1010 and 1076 were electron beam irradiated in order to evaluate by Fourier transform infrared spectroscopy, differential scanning calorimetry and size exclusion chromatography, their structural and physico-chemical modifications. A good correlation between those analytical techniques has indicated the formation of oxidation products, chain scissions as well as crosslinking. The effect of the absorbed dose is underlined.     

Effect of electron irradiation on nitrofurans and their metabolites

Research on the degradation of aqueous furazolidone, nitrofurantoine and semicarbazide (SC) solutions, and 3-amino-2-oxazolidinone (AOZ) residues in tissues of chicken and crucian under electron beam irradiation have been carried out. Results showed that about 75% furazolidone and 70% nitrofurantoine degraded at 6 kGy dose, and SC with the initial concentration of 667 μg/L degraded by 94% at 12 kGy dose. While AOZ in the crucian and chicken degraded by 22.5% and 20.7%, respectively, after being irradiated at 12 kGy. The degradation conditions were investigated to provide a reference to improve irradiation techniques.     

Variation of mechanical and thermal properties of the thermoplastics reinforced with natural fibers by electron beam processing

With restrictions for environmental protection being strengthened, the thermoplastics reinforced with natural fibers (NFs) such as jute, kenaf, flax, etc., appeared as an automobile interior material instead of the chemical plastics. Regardless of many advantages, one shortcoming is the deformation after being formed in high temperature of about 200 °C, caused by the poor adhesion between the natural fibers and thermoplastics. Also, the energy saving in connection with car air-conditioning becomes very important. In this study, the thermal conductivity, tensile strength, and deformation of several kinds of thermoplastic composites composing of 50% polypropylene (PP) and 50% natural fiber irradiated by the electron beam (energy: 0.5 MeV, dose: 0–20 kGy) were measured. The length and thickness of PP and NF are 80±10 mm and 40–120 μm, respectively. The results show that the thermal conductivity and the tensile strength changed and became minimum when the dose of electron beam is 10 kGy, and the deformation after the thermal cycle were reduced by the electron beam.     

Effect of electron beam irradiation on morphology and sieving characteristics of nylon-66 membranes

Nylon-66 is a typical semicrystalline polymer that can be crosslinked through electron beam (EB) irradiation. Crosslinking can dramatically change polymer properties. The objective of this research was to observe how EB irradiation affects morphology and sieving characteristics of nylon-66 membranes. EB irradiation was carried out in air at 60, 70 and 80 kGy doses. Scanning electron microscopy (SEM), swelling and gel content studies evidenced the morphological changes and crosslinking of nylon-66 membranes. Sieving characteristics were also measured using pure water permeation, and rejection of raffinose, vitamin B12, and mono- and divalent salts. These results show that nylon-66 membrane surface and permeation characteristics changed with different irradiation doses. The nylon-66 surface became denser and the gel content increased with increasing irradiation dose. Furthermore, pure water permeation decreased and small molecules were increasingly rejected with greater irradiation doses. The amount of rejection was between 33% and 88.4% for vitamin B12 and between 16% and 83% for raffinose. The highest vitamin B12 and raffinose rejection was seen with a N-80 membrane, and no rejection was measured with N-0 or N-60 membranes. Salt rejection, however, was very low, especially for NaCl, with only 10.51-46% rejected. Based on flux, permeability and uncharged solute (vitamin B12 and raffinose) rejection data, nylon-66 type N-70 and N-80 membranes were estimated to be in the nanofiltration (NF) range.     

Effect of vinyl acetate content and electron beam irradiation on the flame retardancy, mechanical and thermal properties of intumescent flame retardant ethylene-vinyl acetate copolymer

Ethylene vinyl acetate copolymer (EVA) flame retarded by ammonium polyphosphate (APP) and pentaerythritol (PER) was cross-linked by electron beam irradiation. The effects of vinyl acetate content and electron beam irradiation on the flame retardancy, mechanical and thermal properties of EVA composites were investigated. The volatilized products of EVA/APP/PER composites were characterized by thermogravimetric analysis/infrared spectrometry. As VA content increased, the volatilized products increased in the second decomposition step, but decreased in the third decomposition step. For all samples, the increase of irradiation dose could improve both the gel content and the Limit Oxygen Index (LOI, the minimum oxygen concentration by volume for maintaining the burning of a material) values of irradiated composites. The mechanical and thermal properties of the irradiated EVA composites were also evidently improved at appropriate irradiation dose as compared with those of unirradiated EVA composites, whereas these properties decrease at higher irradiation dose because of the electron beam irradiation-induced oxidative degradation or chain scission.     

Gamma polymorph and branching formation as inductors of resistance to electron beam irradiation in metallocene isotactic polypropylene

The influence of a wide dose range of electron beam (EB) irradiation is analyzed on films obtained from metallocene isotactic polypropylene (iPP) under two different thermal processing conditions. A greater irradiation resistance is observed in those films with content in γ crystallites higher than in α monoclinic entities in terms of melting temperature variation with irradiation. This change is on the order of 0.5 °C per 100 kGy in slowly crystallized films while a value of 1.5 °C per 100 kGy is found in quenched specimens. On the other hand, dual studies on films and pellets have proved that branching takes place in this metallocene iPP. The scission processes that occur during irradiation cannot account by themselves for the observed changes in molecular weight distribution as demonstrated by simulation. The observed changes in the rheological behaviour of the irradiated iPP corroborate that increasing degrees of branching are generated by the irradiation process.     

The effect of high-energy electron beam irradiation and content of ATH upon mechanical and thermal properties of EVA copolymer

Mechanical and thermal properties of ethylene vinyl acetate (EVA) mixed with various amounts of alumina trihydrate (ATH), irradiated with 5 MeV electron beam at dose range varied from 38 to 190 kGy, have been studied. A small amount (1%) of triallyl cyanurate has been used as a radiation sensitizer. It has been found that (i) EVA samples with various contents of ATH are crosslinked, (ii) crosslinking increases with irradiation dose, (iii) the mechanical properties of samples improve by irradiation and (iv) decomposition of samples takes place at two stages and due to irradiation, decomposition temperatures shift to higher values. These studies were carried out in order to obtain a suitable compound for wire and cable insulation.     

Optical and microstructural studies on electron irradiated PMMA: A positron annihilation study

The effect of electron irradiation on the free volume related microstructural and optical properties of Poly(methyl methacrylate) have been studied using Positron Annihilation and other techniques. The FTIR spectral study on the irradiated films suggests the existence of CC group and is understood by invoking the carbonaceous clusters as a consequence of chain scission in PMMA. Using UV-Visible absorption spectra the optical parameters like optical energy bandgap and activation energy were determined and the variation of these parameters suggests the existence of defects within the irradiated sample. Following Robertson’s theory, the carbonaceous cluster size is estimated and it increases with increase in electron dose. The XRD study indicates the enhancement of amorphous nature of the film due to chain scission by irradiation. The Positron annihilation result shows that electron irradiation affects the free volume related microstructure and the carbonaceous clusters may act as positron scattering centers.