Modifications of polypropylene surface properties by alpha ionizing radiation (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].
Radiation Physics and Chemistry, 2013
Surface modification of polypropylene (PP) sheets was carried out by radiation induced graft polymerization of hydrophilic functional molecules such as N,N-dimethylacrylamide (DMA) and [2-methacryloyloxy)ethyl] trimethylammonium chloride, which is a quaternary ammonium salt (QAS). Polypropylene sheets were activated prior to the grafting reaction by using electron beam radiation. The changes in morphology, crystallinity and tensile parameters like deformation and stress at yield and deformation at break of PP after irradiation were investigated. The results showed that a minor crystalline reorganization takes place during the irradiation of PP at 100 kGy. The grafting has been observed to be strongly dependent on the monomer dilution in the reaction medium. After grafting of QAS (40%) and DMA (20%) it was possible to develop highly hydrophilic surfaces (water contact angle comprised between 30 and 411). The surfaces of virgin, irradiated and grafted PP were studied using polarized optical microscopy (POM) and scanning electron microscopy (SEM). Spherical particles (i.e. polystyrene or silica beads) adhering to the modified samples were studied according to the surface parameters. Adhesion tests confirmed the strong influence of substrate type (mainly hydrophilicity and roughness) and to a lesser extent underlined the role of electrostatic interactions for the design of plastic surfaces for antimicrobial applications.
The alterations in high density polyethylene properties with gamma irradiation
Radiation Physics and Chemistry, 2017
In the present investigation, high density polyethylene (HDPE) polymer has been used to study the alterations in its properties under gamma-irradiation. Physico-chemical properties have been investigated with different spectroscopy techniques, Fourier Transform Infrared spectroscopy (FTIR), X-ray diffraction (XRD), biocompatibility properties, as well as, mechanical properties change. The FT-IR analysis shows the formation of new band at 1716 cm-1 that is attributed to the oxidation of irradiated polymer chains, which is due to the formation of carbonyl groups (C=O). XRD patterns show that a decrease in the crystallite size and increase in the Full Width at Half Maximum (FWHM). This means that the crystallinity of irradiated samples is decreased with increase in gamma dose. The contact angle measurements show an increase in the surface free energy as the gamma irradiation increases. The measurements of mechanical properties of irradiated HDPE samples were discussed.
Study of gel formation by ionizing radiation in polypropylene
Radiation Physics and Chemistry, 2013
The objective of this work is to study the formation of microgel in pristine PP and modified PP. The modified PP in pellets was synthesized by gamma irradiation of pristine PP under a crosslinking atmosphere of acetylene in different doses of 5, 12.5 and 20 kGy, followed by thermal treatment for radical recombination and annihilation of the remaining radicals. The gel content of the modified polypropylenes was determined by extraction in boiling xylene for period of 12 h at 138 1C. The gel formed of pristine PP and modified (i.e., irradiated) was characterized using optical microscopy (OM), scanning electron microscopy (SEM), Fourier transformed infrared spectroscopy (FTIR) and X-ray diffraction (XDR). The PP morphological study indicated the microgel formation with increase of spherulitic concentration with dose.
Reaction mechanism and rheological properties of polypropylene irradiated under various atmospheres
Radiation Physics and Chemistry, 2000
It is well-known that the melt-strength properties of a polymer increases with molecular weight and with long chain branching due to the increase in the entanglement level. This study is a contribution for the understanding of the following points: Ð the role of branching, crosslinking and degradation on melt strength properties; Ð the mechanism and the kinetics of PP irradiation with time of irradiation and the importance of double bond formation.
Rheological study of polypropylene irradiated with polyfunctional monomers
Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 2007
The aim of this paper is to investigate the rheological properties of polypropylene (PP) modified by ionization radiation (gamma rays) in the presence of two different monomers. The samples were mixed in a twin-screw extruder with ethylene glycol dimethacrylate (EGDMA) or trimethylolpropane trimethacrylate (TMPTMA) with concentration in the range of 0.5-5.0 mmol. After that, they were irradiated with 20 kGy dose of gamma radiation. The structural modification of polypropylene was analyzed in the melt state by measuring melt flow rate (MFR), g* (complex viscosity) and G 0 (storage modulus) in the angular frequency range of 10 À1 to 3 • 10 2 rad s À1. From the oscillatory rheology data, one could obtain the values of g 0 (zero shear viscosity) that would be related to the molar mass. All results were discussed with respect to the crosslinking and degradation process that occur in the post-reactor treatment to produce controlled rheology polypropylene. The resulting polymeric materials were submitted the cytotoxicity in vitro test by neutral red uptake methodology with NCTC L 929 cell line from American Type Culture Collection bank. All modified PP samples presented no cytotoxicity.