Controlled degradation and crosslinking of polypropylene induced by gamma radiation and acetylene (original) (raw)
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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.
Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 2007
It is well-known that polypropylene (PP) is difficult to process as a consequence of its linear structure. It is also known that grafting of long-chain branches on PP backbone using ionizing radiation is an effective approach to achieve high melt strength polypropylene (HMS PP). Chain-scission and, in minor extend, crosslinking and grafting are the predominant reaction in order to branch PP backbone. However, if multifunctional monomers are used to promote the grafting reaction, crosslinking can surpass chain scission and grafting, reducing drawability. Therefore, in an effort to enhance the processability and so the drawability, it has been found helpful to add a small amount of polybutene-1. Gamma irradiation technique was used to induce chemical changes in blends of PP and polybutene in acetylene atmosphere (crosslinker promoter) and in HMSPP/polybutene blends. The samples were irradiated with a 60 Co source with doses of 12.5 and 20 kGy in the presence of acetylene. In this work, two different methods of blends processing were compared regarding rheological and mechanical properties. Effects on the strength and elongation at the yield point and at rupture were observed by mechanical tests and showed decrease of tensile strength and increase of elongation at rupture for samples obtained by irradiation of blends. The results from rheology demonstrated an increase in melt strength and drawability of blends.
High-energy radiation forming chain scission and branching in polypropylene
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.
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.
Thermal properties of isotactic polypropylene degraded with gamma irradiation
Polymer Degradation and Stability, 2001
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. #
Radiation Physics and Chemistry, 2007
Controlled rheology polypropylene grades are established commodities in the polymer processing market. However, new types, mainly the so-called high melt strength polypropylene (HMSPP) grades, are being introduced in the last two decades and radiation processing has played an important role. The melt strength properties of a polymer increases with molecular weight and with long-chain branching due to the increase in the entanglement level. As polypropylene (PP) is a linear polymer, the way to improve its elongational viscosity is by the production of a bi-modal polymer. Basell's patents claim the production of long-chain branching on PP by irradiating with electrons under oxygen free atmosphere, followed by two heating steps to allow radical recombination and annihilation reaction. Some other companies have issued patents using electron beam processing, but so far there is no actual production other than the Basell one. As a result of a research joint effort, IPEN, BRASKEM (the biggest Brazilian polymer producer) and EMBRARAD (the major Brazilian radiation processing center) developed a new process to produce HMSPP based on gamma processing. This paper will address some characteristics of each technology and the main industrial opportunities.
In this research, the rheological properties of electron beam irradiated polypropylene homo polymer (PP) containing Polybutene (PB) resin and Trimethylol Propane Trimethacrylate multifunctional monomer is studied. The effect of PB resin in inducing long chain branches on the PP backbone are valuated by various viscoelastic parameters. The zero shear viscosity (g0) of samples containing 5% PB resin considerably decreased to 5500 Pa s, from g0 ¼ 11,500 Pa s, which indicates the plasticizing effect of PB resin on the ease of movement of PP macromolecules. It is found that the presence of PB resin enhanced the branching by facilitating the movement of PP macromolecules in solid state and increasing the recombination efficiency of PP macro radicals. The mobilizing effect of PB resin also reduced chain scission and degradation of PP resin which is traced by shifting the cross over frequency. The PB free radicals formed during the irradiation process can bound to PP free radicals and suppress the degradation process. The evaluation of zero shear viscosity ratios and crossover point ratios of irradiated samples to un-irradiated ones confirmed that using small amount of PB resin increase branching efficiency, which is the evidence of mobilizing effect of PB resin.