Gamma-irradiated Polypropylene Research Articles

Surface Properties of Gamma-Irradiated Polypropylene

Surface Properties of Gamma-Irradiated Polypropylene

Surface Properties of Gamma-Irradiated Polypropylene

polypropylene (PP) has been studied as a function of the absorbed dose. It has been established that γ-irradiation leads to an increase in the free surface energy of the polymer, its acid–base component, and the surface polarity. An analysis of the IR spectra of γ-irradiated PP samples indicated the formation of oxygen-containing groups in the composition of PP macromolecules, which was confirmed by the values of the surface acidity parameter. An increase in the dose led to an increase in the concentration of products of radiation-induced conversion. A significant increase in the melt flow index (MFI) of polypropylene up to an absorbed dose of 150 kGy also evidenced the occurrence of oxidation and destruction processes. The MFI decreased at radiation doses above 150 kGy, and this fact indicates that such doses of ionizing radiation lead to the predominance of the processes of polymer structuring or crosslinking.

Accelerated environmental degradation of gamma irradiated polypropylene and thermal analysis

Polypropylene (PP) is one of the most important plastic commodities in the world. It can be used in many applications since it has outstanding properties at low cost. However, PP has very low environmental degradation rate; therefore, the discarded PP can accumulate in the environment. The aim of this study is the degradation control of PP using gamma radiation. Dumbbell samples were manufactured by injection molding followed by irradiation using gamma radiation at different doses: 5, 12.5 and 20 kGy. The irradiated samples were exposed to environmental aging during 90 days and characterized by scanning electron microscopy, thermogravimetric analysis, differential scanning calorimetry and X-ray diffraction. The irradiated dumbbell samples PP 5, 12.5 and 20 kGy, exposed to environmental aging, showed intense oxidation with the presence of surface cracks compared with the PP non-irradiated.

Fabrication of polypropylene/silver nanocomposites for biocidal applications

This paper presents a study on biocidal effect of polymer nanocomposite films of gamma irradiated polypropylene (PP) and silver nanoparticles. The modified polypropylene was obtained from isotactic polypropylene (iPP) in pellets form by irradiation with gamma rays in the presence of acetylene. A new morphology with long chain branching of PP and distinct rheology is obtained by this process. The blend of 50/50wt% neat PP and PP modified by gamma radiation were further mixed using a twin screw extruder. The AgNPs were infused into this polymer blend at different concentrations of: 0.1%; 0.25%; 0.5%; 1.0%; 1.0% (PVP), 2.0% and 4.0% by wt%. These polymer nanocomposites were characterized by Raman spectroscopy, scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), thermogravimetric analysis (TG), differential scanning calorimetry (DSC), X-ray diffraction (XRD), transmission electron microscopy (TEM), cytotoxicity test and Kirby-Bauer disk diffusion techniques. The bactericidal effect of Pseudomonas aeruginosa (P. aeruginosa) and Staphylococcus aureus (S. aureus) were assessed in detail.

Stress–strain and thermo-gravimetric analysis of Co-60 gamma-irradiated polypropylene and polyimide

By irradiating two macromolecules, namely polypropylene and polyimide having notably different physicochemical properties, with the same radiation under identical conditions, it is inferred that the mechanical and thermal degradation or the stability of the macromolecule exposed to high-energy radiation strongly correlates with its physicochemical structure. This is well supported by two distinct characterizations, namely stress–strain analysis and thermogravimetric analysis.

Comparison of Molecular Structure and Rheological Properties of Electron-Beam- and Gamma-Irradiated Polypropylene

Polypropylene (PP) irradiated with electrons or electromagnetic waves (gamma-rays) undergoes chain scission, and the macroradicals generated form branched molecules as shown by size-exclusion chromatography coupled with laser scattering. Information on the irradiation modification of the molecular structure of PP is still limited in the literature, especially with respect to the controlled generation of long-chain branches (LCB). This paper examines the branching structure of an electron-beam- and gamma-irradiated polypropylene. In general, appropriate irradiation conditions lead to the formation of LCB, which were analyzed in detail by rheological means. At smaller doses, the zero shear-rate viscosities η0 of the electron-beam-irradiated PP lie above the values for the unmodified PP with the same Mw but are distinctly lower than the linear reference at higher doses. This result can be interpreted by the change from a starlike to a treelike branching topography. The gamma-irradiation leads to η0 values smaller than those of the linear reference, giving rise to the assumption of the generation of treelike molecules. The measurements of the elongational viscosities support this molecular picture. An explanation of these findings is given along the line that the electron irradiation conducted at dose rates higher than the gamma-irradiation creates a larger concentration of short-living radicals, which will partially annihilate each other, but favor the growth of some long branches, which get branched themselves at higher doses. The structure of the gamma-irradiated samples is postulated to consist of a blend of linear and treelike molecules.

Insights into oxidation mechanisms in gamma-irradiated polypropylene, utilizing selective isotopic labeling with analysis by GC/MS, NMR and FTIR

In an effort to shed additional light on the chemical mechanisms underlying the radiation–oxidation of polypropylene (PP), we are using samples having selective 13C isotopic labeling at the three unique sites within the macromolecular structure. After radiation exposure, we applied GC/MS, solid-state 13C NMR, and FTIR to evaluate the applicability of each technique in identifying the molecular labeling of the oxidation products, with the goal of determining the site of origin of the products with respect to the macromolecule. Using GC/MS, we have identified the position of origin of CO 2 and CO from the polymer. Most of the CO 2 (60%) and CO (>90%) come from the C(1) (methylene) position of PP, with (30%) of the CO 2 originating from the C(3) (methyl) position, and 10% coming from the C(2) (tertiary) position. By GC/MS we have also identified the labeling patterns in four volatile oxidation products (acetone, methylisobutylketone, isobutane, and methyl acetate), and have used this information to map each compound onto the macromolecular framework. Using NMR we have quantified the time-dependent formation of solid-phase degradation products occurring from post-irradiation aging of PP samples held for 28 months at room temperature in air. Most of the solid oxidation products occur at the C(2) (tertiary) site; the predominant species, C(2) peroxides, increase linearly during the first 2 years, after which they plateau at a relatively high concentration.

Transitions and relaxations in gamma-irradiated polypropylene studied by positron annihilation lifetime spectroscopy

The changes in the relaxation and transition temperatures in PP due to gamma irradiation in a vacuum were measured by means of positron annihilation lifetime spectroscopy. It was shown that the gamma and beta relaxation temperatures, as well as the melting point follow the changes in the crystallinity with the irradiation dose. For the glass transition temperatures and premelting point, after irradiation dose of 88 kGy, an inverse of the changes was observed.

Kinetics of non-isothermal melting and crystallization of gamma-irradiated isotactic polypropylene

Abstract The non-isothermal kinetics of melting and crystallization of gamma-irradiated isotactic polypropylene were investigated by differential scanning calorimetry. At constant temperature the melting rate increased with the dose. During the melting, the average lamellar thickness, the free surface energy and the transport energy through the phase boundary reduced with increasing the dose. The crystallization rate decreased with increasing dose at constant temperature. Mixed α-γ spherulites were grown during crystallization. The non-isothermal crystallization rate expressed, in fact, the rate of secondary nucleation of the lamellae in the spherulites and their growth. Raising the irradiation doses led to a decrease of the crystallization temperature. A critical dose of irradiation of about 200 kGy was found, where the dependences of the calculated kinetic parameters underwent an important change. This change could be successfully connected with the effect of radiation annealing and melting.

Spectroscopic and thermal studies of gamma irradiated polypropylene polymer

Thin films of polypropylene have been irradiated with different doses of gamma radiation from a 60Co source. IR, UV-VIS spectra of this polymer before and after irradiation have been recorded and from the spectral data some modifications in the properties have been investigated. The spectra indicated that polypropylene film was oxidised at the dose of 106 Gy. Due to the removal of additives, total destruction of the polymer takes place at this dose. Isotactic arrangement of the polymer is no longer present after irradiation. Growth of carbon cluster takes place above a gamma dose of 102 Gy. Thermal stability of the polymer changes due to irradiation and the polymer seems to decompose in four different steps at the highest dose of 106 Gy.

Electric field effect on positronium formation in gamma-irradiated polypropylene and polyethylene

The effect of an external electric field (up to 48 kV cm −1) on positronium (Ps) formation in γ-irradiated polypropylene and polyethylene has been studied by means of positron lifetime spectroscopy. The application of an electric field to unirradiated polypropylene and polyethylene considerably decreased the Ps formation. For example, the intensity of the longest-lived component ( I 3) for one of the polypropylene samples was reduced from 26% to 18% by a field of 48 kV cm −1. It was found that the electric field effect for the irradiated samples becomes weaker when increasing the irradiation dose. This result is discussed on the basis of the spur reaction model of Ps formation.

The post-irradiation oxidation of polypropylene. II: Influence on the mechanical properties

The drop of the elongation at break of gamma irradiated polypropylene samples has been studied as a function of dose and of time after irradiation. A simple relation is proposed that takes into account two chain scission mechanisms, one occurring during irradiation and the other operative after irradiation. The relation includes two parameters measuring the relative importance of those two mechanisms. It allows the prediction of the life-time of radio-sterilised samples.

Post irradiation degradation of polypropylene radiation durability of polypropylene stabilized with phenolic stabilizer (II)

Post irradiation degradation of 60Co gamma irradiated polypropylene stabilized with a phenolic type stabilizer has been followed up to two years after being irradiated. The effectiveness of the stabilizer at various concentrations on the polypropylene samples irradiated up to 150 kGy has been studied and the buildup of carbonyl group in the irradiated samples measured. The obtained results indicated that the oxidative reactions are retarded by addition of stabilizer. The variation of bend strength of the irradiated samples with and without stabilizer was also followed. This property was found to be greatly improved for the stabilized samples irradiated at low doses. However at high doses the effectiveness of the stabilizer declined. In order to correlate these results with the change in the molecular weight of polymer, trends of the change in rheological behaviour such as melt viscosity (μ a) and flow behavior parameters ( K, n) of both stabilized and unstabilized samples have been investigated. Results showed that at low doses, addition of the stabilizer greatly reduces the extent of chain scission, and therefore, the mechanical properties of the irradiated polymer are retained.

Radiation Resistant Polypropylene- New Developments

For health care packaging applications, polypropylene (PP) has the advantages of being nontoxic and inert to liquids and drugs. Its low cost and the ease with which it can be extruded or shaped are also important. For medical purposes, it is necessary to sterilize these materials using gamma radiation to ensure total and reliable sterility. However, gamma-irradiated polypropylene is subject to degradation or embrittlement over time. Radiation causes degradation of the polymer by direct energy transfer and subsequent ox idation. The need for radiation sterilizable plastics which are resistant to this type of degradation is important because of the increased use of gamma irra diation as a preferred sterilization method. To retard degradation in polypro pylene, it is important to control these reaction kinetics. Methods to improve polypropylene's resistance to such degradation are focused on the relationships of morphology and radiation effects. New developments in this area are dis cussed regarding methods to make PP film radiation resistant.

Thermal expansion of irradiated polypropylene from 10?340 K

The coefficient of thermal expansion of gamma-irradiated polypropylene (PP) has been measured from 10-340 K by using the three-terminal capacitance technique. The samples were irradiated to 500 Mrad in air at room temperature with gamma rays from a $^{60}Co$ source at a dose rate of 0.26 Mrad $h ^{-1}$. The crystallinity of the sample was measured by X-ray diffraction technique. The crystallinity was found to decrease with radiation dose from 55% at 0 Mrad to 44.7% at 500 Mrad. The thermal expansion coefficient was found to be almost constant with radiation dose from 10-125 K and decreases with radiation dose from 125-34O K.

Grafting of 2‐(dimethlamino) ethyl methacrylate onto gamma irradiated polypropylene fabric

AbstractPolypropylene fabric was gamma pre‐irradiated at doses of 1,2 and 3 Mrads. The irradiated fabric was grafted with an aqueous solution of 2‐(dimethylamino) ethyl methacrylate. The graft yield was studied as a function of the different variable conditions such as storage time, monomer concentration (10–40%), reaction time, and temperature (50, 70, 100°C). The grafted polypropylene was further quaternized with dimethyl sulphate or monochloroacetic acid. The grafted and quarternized fabrics were dyed with an acid dye. The fixation properties of the dyed samples were determined by DMF extraction. The moisture regain and mechanical properties were also measured.

Morphology of gamma-irradiated polypropylene gels crystallised from xylene solution—1. Optical microscopy and sals

A γ-irradiated in bulk PP was investigated. It was swollen and partially dissolved in boiling xylene. After this it was crystallised by evaporation of the solvent. The supermolecular structure was characterised by means of microscopy and SALS. It was suggested that the crystallisation proceeds from viscous melts. The melts contained soluble and insoluble parts. The insoluble part consisted of micro- and macrogel of crosslinked PP with low and irregular crosslinking density. The spherulites and crystallites had a high defect density. They were built up of α-γ dendrite twins. It is shown that the rate of primary nucleation increases sharply at about 0.1 MGy, remaining further constant. The rates of the secondary nucleation and lamellar growth decrease sharply with dose. It has been suggested that the rates of primary and secondary nucleation depend not only on the number of radiation defects, but also on the direction of the spreading of the energy released by the interaction of γ quants with the crystal lattice of the polymer.

Morphology of gamma-irradiated polypropylene gels crystallised from xylene solution—2. Kinetics of melting and crystallisation

The kinetics of melting and the non-isothermal crystallisation of PP gels obtained through irradiation in bulk, boiling in xylene and subsequent drying was investigated by means of DSC. When the irradiation dose increases the melting temperatures decrease, the enthalpies are low and do not depend on the dose applied. At constant temperature the melting rate increases with the dose. The viscosity of the superheated crystals and the activation energy for transport through the phase boundary crystal-melt decrease with the dose. The temperatures of non-isothermal crystallisation decrease when the irradiation dose increases. The crystallisation rate decreases with dose at constant temperature. The viscosity of the supercooled melts increases sharply with dose. The dependences described confirm the suggestion that the primary nucleation during the gel formation and their subsequent recrystallisation does not depend on the dose. The general crystallisation rate includes both the secondary nucleation rate and the growth rate of the lamellae, which depends on the diffusion of crystallisable molecules in the viscous melt. The data obtained prove the validity of the previously defined rate of non-isothermal processes and further the possibility for application of the equations of kinetics of melting and non-iosthermal crystallisation.

Mixed spherulites of alpha and gamma phases in gamma-irradiated and thermal-treated isotactic polypropylene

Samples of commercial bulk gamma irradiated i-PP are recrystallized at various temperatures. Optical microscopy, (SALS), and (DSC) are used. All common types of PP spherulites are observed. Investigation shows that number of dendritic spherulites and their positive birefringences increase with doses. It is supposed that spherulites observed consist of twins built up of triclinic and monoclinic crystallites of i-PP. A mechanism of their growth is proposed.