Characterization Study of Gamma-Irradiated, High Melt-Strength Polypropylene (original) (raw)
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Controlled degradation and crosslinking of polypropylene induced by gamma radiation and acetylene
Polymer Bulletin, 2009
Isotactic polypropylene (iPP) undergoes crosslinking and extensive main chain scissions when submitted to irradiation. The simultaneous irradiation of PP and acetylene is able to control chain scission and produce grafting. The grafted PP further reacts with PP radicals resulting in branching and crosslinking. In this work, commercial polypropylenes (iPP) of different molecular weights were irradiated with a 60 Co source at dose of 12.5 kGy in the presence of acetylene in order to promote the crosslinking. The mechanical and rheological tests showed a significant increase in melt strength and drawability of the modified samples obtained from resins with high melt flow index. The characterization of the molecular modifications induced by gamma irradiation of isotactic polypropylenes under acetylene atmosphere proved the existence of branching, crosslinking and chain scission in a qualitative way. The G 0 and G 00 indicated the presence of LCB in all samples. Therefore, PP irradiation under acetylene was proved to be an effective approach to achieve high melt strength polypropylene (HMSPP).
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Radiation Physics and Chemistry, 2010
The degradation of high molecular weight isotactic polypropylene (iPP) subjected to gamma rays irradiation up to 100 kGy in inert atmosphere was analyzed. The investigation relied upon complex viscosity, elastic modulus, gel fraction, morphology of the insoluble fraction and deconvoluted molecular weight distribution (MWD) curves. At low irradiation doses, already at 5 kGy, the MWD curve is strongly shifted to the low molecular weight side showing chain scission, which is confirmed using the calculated chain scission distribution function (CSDF). At high dose levels, the appearance of a shoulder in the high molecular weight side of the MWD curve indicates the formation of chain branching. The presence of a considerable insoluble fraction at these high dose levels indicates also the formation of cross-linking, which has different morphology then the insoluble fraction present in the original iPP. The rheological results show changes in the molecular structure of irradiated samples in agreement with the gel content data. The chromatographic and rheological data has shown that gamma irradiation of iPP produces chain scission, branching and cross-linking.
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.
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We discuss some thermal properties, as well as the thermal stability, of irradiated isotactic polypropylene. Sol-gel analysis showed that, despite the fact that irradiation doses were relatively high, no gel was formed. Values for DSC melting temperature, specific enthalpy of melting, crystallization temperature and crystallization enthalpy are different for the first and second scan, but the trend was similar. The melting temperature and specific melting enthalpy decreased with an increase in irradiation dose. TGA results showed that irradiation lowered the thermal stability of PP. #
Production of high melt strength polypropylene by gamma irradiation
Radiation Physics and Chemistry, 2007
High melt strength polypropylene (HMS-PP) has been recently developed and introduced in the market by the major international producers of polypropylene. Therefore, BRASKEM, the leading Brazilian PP producer, together with EMBRARAD, the leading Brazilian gamma irradiator, and the IPEN (Institute of Nuclear Energy and Research) worked to develop a national technology for the production of HMS-PP. One of the effective
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.
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.
Radiation Physics and Chemistry, 2010
Samples of two high-density polyethylenes having different crystallinity levels were gamma irradiated under vacuum at doses ranging from 20 to 300 kGy. Subsequently, the vials containing the irradiated samples were exposed to different post-irradiation treatments. Parts of the specimens were annealed while still under vacuum. The annealing time was 4 h and the annealing temperatures 110 1C or 150 1C. Others were exposed directly to air opening the vials without any thermal treatment. It was verified that in all cases the dosage to produce an incipient gel increases with the crystallinity of the initial sample. The amount of gel produced after exposing specimens of the same polymer to a given dose increases with the annealing temperature. The largest increment in the amount of gel produced at the completion of the post-irradiation treatment was found on the samples with the highest initial crystallinity level. Evidence of oxidation was found in all irradiated samples. The extent of oxidation depends on the initial crystallinity of the sample, the irradiation dose and the type of post-irradiation treatment. The heat of fusion measured in the annealed samples decreases with the gel content while the fusion temperature was slightly affected. Ductile or brittle behaviors were observed after testing specimens under tensile stress. The yield stress increases proportionally to the crystallinity level that, in turn, depends on the total dosage applied to the samples. The extensibility of ductile samples is determined by the amount of gel produced regardless of the degree of initial crystallinity and the type of annealing process applied to each sample.
Effect of Gamma Irradiation on the Structural and Properties of High Density Polyethylene ( HDPE )
2015
This study presents an experimental analysis of the effect of dose parameter during gamma irradiation of commercial highdensity polyethylene (HDPE) samples. The effect of different doses of γ-irradiation on the physical and mechanical properties of HDPE with different thickness (1 mm and 2 mm) was studied. The effect of γ-irradiation on HDPE led to remarkable changes in the physical and mechanical properties of the samples due to chain scission, oxygen effects and crosslinking activities. The experimental results show the mechanical properties reduce as radiation dose increase, also, it was found that HDPE with thickness (1 mm) is more susceptible than HDPE with thickness (2 mm) according to the influence of radiation.