Long-Chain Branched Polypropylenes by Electron Beam Irradiation and Their Rheological Properties (original) (raw)

Theoretical correlation of linear and non-linear rheological symptoms of long-chain branching in polyethylenes irradiated by electron beam at relatively low doses

Rheologica Acta, 2017

Dynamic and transient shear and elongation flow experiments along with gel permeation chromatography (GPC) and differential scanning calorimetry (DSC) analysis are performed on linear low-density polyethylenes (LLDPEs) irradiated at doses below 25 kGy. GPC data indicate no changes in the molar mass distribution, and there are almost no changes in melt and crystallization temperatures, likewise. Contrary, dynamic shear rheological behavior including thermorheological complexity, type of reduced van Gurp-Palmen curves, and zero shear-rate viscosities all disclose growing levels of long-chain branching with irradiation dose. An inverse tube model is developed for binary blend of linear and star chains and used to extract the fraction of the branched components. Modeling results reveal progressive increase in the length and fraction of star chains, as evidenced by appearance of an anomalous double overshoot in the transient shear viscosities. Detection of strain hardening in extensional stress growth coefficient data, well-quantified by molecular stress function model, is also in agreement with the predictions of tube model.

Rheological Evaluation of Electron Beam Irradiated Polypropylene in the Presence of a Multifunctional Monomer and Polybutene Resin

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.

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.

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.

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.

Rheological and morphological analysis of irradiated high and low density polyethylene samples

Journal of the Serbian Chemical Society, 2022

The influence of intensity of the γ-irradiation on commercial high and low density polyethylene (LDPE and HDPE) granules (Kazanorgsintez PJSC, Kazan, Tatarstan, Russia) on their rheological and morphological properties at irradiation doses of 5 and 10 kGy was studied. Experiments in the oscillation mode revealed an increase in the dynamic moduli values with increasing radiation dose compared to the initial samples. At the same γ-irradiation doses, the HDPE samples compared to the LDPE ones showed the greatest changes in rheological properties, while the zero shear viscosity of HDPE increased by order of magnitude compared to the initial one at the irradiation dose of 10 kGy. Morphology analysis of supramolecular structures revealed an increase in cobweb-type structures for the irradiated sample in comparison with the initial sample, which may indicate the formation of branched structures under γ-irradiation.

Effect of electron beam irradiation dose on the rheology, morphology, and thermal properties of branched polypropylene/polybutene-1 blend

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.

Review on the production process and uses of controlled rheology polypropylene-Gamma radiation versus electron beam processing

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.

Effect of long branches on the rheology of polypropylene

Journal of Rheology, 2004

In order to study the rheology of long chain branched polymers, branches have been added on linear polypropylene precursors in varying amounts using reactive modification with peroxydicarbonates. The branched polypropylene samples show distinct strain hardening, something absent from the linear melt; this considerably improves the melt strength of the modified polymer. The zero shear viscosity and the elasticity measured by the relaxation spectrum also increase with the number of branches per molecule. Two models are applied to describe strain hardening of the viscosity during the course of elongation. The model parameters were found to vary systematically with the degree of branching and, therefore, their values can be used as a measure of this. Consequently, fluidity, elasticity, strain hardening, and melt strength are all related to the degree of long chain branching.