Reaction mechanism and rheological properties of polypropylene irradiated under various atmospheres (original) (raw)
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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.
Long-Chain Branched Polypropylenes by Electron Beam Irradiation and Their Rheological Properties
Macromolecules, 2004
The aim of this paper is to investigate how the molecular structure of linear polypropylenes can be modified by electron beam irradiation. For this purpose a linear precursor was irradiated with different doses. The samples were analyzed by size-exclusion chromatography coupled with a light scattering detector. With increasing doses, a reduction of molar mass and an increasing number of longchain branches were found. Moreover, conclusions with respect to the topography of the long-chain branches obtained were drawn from the molar mass dependence of the zero shear viscosity of the irradiated samples, which deviates significantly from that of linear polypropylenes. The experimental results can be interpreted in a way that at low doses very few but long branches occur. At higher doses more and shorter branches per molecule exist. The elongational experiments clearly exhibit a change of the strainhardening behavior with irradiation dose, which is in agreement with the structural changes concluded from the shear measurements. The results from rheology and their interpretation demonstrate two features. First, rheological experiments conducted on irradiated polypropylenes are much more sensitive with respect to long-chain branching than the classical characterization methods based on size-exclusion chromatography coupled with light scattering. Second, from a comparison of the rheological behavior of linear and irradiated polypropylenes some conclusions can be drawn regarding the topography of the long-chain branches generated.
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.
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).
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.
Study of the weathering of high melt strength polypropylene (HMS-PP)
One of the reasons for the good acceptance of the commercial PP is the fact that market requires products with features of "engineering plastics" with prices in the range of commodities. High melt strength polypropylene (HMSPP) grades are produced by radiation process and have improved rheology for melt blow processes. The melt strength (MS) properties of a polymer increase with molecular weight and with long chain branching due to the increase in the entanglement level. The main scope of this study was to evaluate the stability of HMS-PP prepared by gamma radiation with doses of 12.5, 20 kGy in comparison with virgin PP. Many variables influence the rate of degradation of polymers by photo-oxidation. The irradiance and permeability to oxygen are the most important factors but other factors such as temperature and moisture have also influenced the degradation rates. Polypropylenes are sensitive to oxidation due to the presence of the tertiary carbon atom. Therefore, effective stabilization against oxidation (thermo and photo oxidation) is required. The samples submitted to the natural aging for a period of six months were characterized by: tensile test, thermogravimetry analysis (TGA), optical microscopy, scanning electronic microscopy (SEM) and infrared spectroscopy (FTIR). SEM analysis showed particular aspects of cracks on the surface. The loss of tensile strength is associated to the presence of fractures. The results showed that pronounced oxidation followed by chain scission occur at the initial periods of weathering exposition of the HMS-PP.
Royal Society Open Science
The influence of electron-beam irradiation on polypropylene (PP) and high-density polyethylene (HDPE) was investigated with a focus on crystallization. A high-temperature (200°C) creep test revealed that the HDPE gradually increased cross-linking density in the range 30–120 kGy, while the PP underwent a chain scission which was quantitatively evaluated by gel permeation chromatography. The mechanical properties were measured in the range -150 to 200°C by a dynamic mechanical analysis. A small presence of C=C and C=O bonds was found in the irradiated PP by a Fourier transform infrared spectroscopy. Crystallization kinetics measured by differential scanning calorimetry and hot-stage optical microscopy results were influenced tremendously by irradiation for HDPE and to a lesser extent for PP. Irradiation caused a decrease in both the number of nucleation centres and the growth rate of individual spherulites. Crystallization was analysed in detail with the help of Hoffman–Lauritzen, Avr...
Polymer Engineering & Science, 2013
The aim of this work is to study the influence of electron beam irradiation on the structure of polypropylene (PP)/polybutene-1 (PB-1) blend in the branching process. The blend with 10 wt% of PB-1 and 0.5 wt% trimethylolpropane trimethacrylate monomer is prepared and irradiated at different doses. The rheological properties of the melts in shear and extensional mode were evaluated, and their thermal behavior, crystalline structure, and morphology are studied by differential scanning calorimetry, wide-angle X-ray diffraction, and scanning electron microscopy. The presence of long chain branched structure is approved by higher zeroshear viscosity (g 0), longer relaxation time and pronounced strain-hardening behavior in the within the range of dose tested. By increasing the irradiation dose and enhancing chain scission in the backbone and long chain branches, the decline in melting temperature, duplication of melting peak, and the decrease in zeroshear viscosity were observed. The morphological study of the blends before and after irradiation revealed no considerable change in PB-1 droplet size and their distribution in the PP matrix. The emulsion theoretical models could predict well the rheological behavior of all samples and no significant change was observed on the interfacial interaction of PP and PB-1. POLYM. ENG.