Degradation of polypropylene impact-copolymer during processing (original) (raw)
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Impact polypropylene copolymers: fractionation and structural characterization
Polymer, 1993
Impact polypropylene copolymers may be produced in a two-reactor system to yield a blend of homopolymer with an ethylene-propylene rubber (EPR). The polypropylene homopolymer, which is itself brittle and has low impact strength, is markedly toughened by the presence of the EPR. The rubber-like EPR exists as a phase-segregated discrete particle in a continuous matrix of the hard phase. The molecular structure analysis of the resulting complex mixture is a formidable task. The purpose of this paper is to describe a preparative and an analytical temperature-rising elution fractionation (t.r.e.f.) technique as the primary tools to separate and characterize a commercial impact copolymer. These techniques permit the isolation and subsequent characterization of the components of the impact copolymer by ancillary techniques, primarily 13C nuclear magnetic resonance and differential scanning calorimetry. These techniques were applied to the structural analysis of a commercial impact-grade polypropylene with a melt flow rate of 6. It was found that this impact copolymer was composed of about 75wt% of isotactic polypropylene, about 17wt% of a highly non-crystalline EPR and about 8 wt% of semicrystalline ethylene-propylene copolymers. A major component of the semicrystalline ethylene-propylene copolymers was an ethylene-rich copolymer containing between 0 and 8 wt% of propylene comonomer. The separate characterization of the components of the impact copolymer gives insight into the chemical synthesis process used to produce these copolymers. Further, it permits one to gain a better understanding of the location and function of each of the components in the complex mixture.
Macromolecular Symposia, 2012
Impact polypropylene copolymers (ICPs) have complex microstructures compared to homo-or random copolymers of propylene. Standard analytical techniques are unable to unpack the complex structure of impact copolymers, hence the need to fractionate the material. The investigation of poly(propyleneethylene) block copolymers was conducted in order to understand the copolymer composition and the role of particular components by fractionation. Temperature rising elution fractionation (TREF) was used for fractionation of ICPs which involves breaking up the polymer into small fractions that can be analysed further to give more understanding on the complex microstructures. Two ICP samples (ICP1 and ICP2) with different physical properties were fractionated. The bulk samples as well as the resulting fractions were further analysed using DSC, FTIR and DMA. Below 0 8C, the DMA results of the bulk sample with high ethylene content (ICP1) showed both low storage modulus and stiffness which is in line with expectations. However, it was interesting to note that above 0 8C the trend was reversed, thus ICP2 with low ethylene content had lower storage modulus and stiffness. The DSC and FTIR results of the fractions of the two samples revealed different or inhomogeneous distribution of ethylene content between the samples which explained differences in mechanical properties. The findings emphasize the contributions of phase separation and compatibility between the rubber and the matrix towards physical and mechanical properties.
The present work was done to improve the impact property of isotactic polypropylene (PP), especially at low temperatures, by incorporating ethylene propylene diene monomers (EPDM). This was done by ensuring compatibility between the two polymers with phase modifiers polyethylene grafted with maleic an-hydride (PEg -MA) and initiator dicumyl peroxide (DCP). In addition, attempts were also made to understand the fundamentals of impact toughening as well as fracture toughness, and to correlate the results with that of morphological evidences obtained from scanning electron microscopy (SEM) and X-ray dif-fraction (XRD) methods. Varying the ratios of all blend composition , mechanical properties were studied. It was observed that as the rubber fraction increased, the impact property as well as fracture toughness increased. All these tests also showed promising results when PEg -MA was added, leading to more improvement in all the mechanical properties including increase in crystallite size. It had shown plasticization effect on the compositions , which could be further confirmed by differential scanning calorimetry (DSC) compared to the uncompatibilized ones. But when DCP was added, it behaved like an initiator which directly reacted with the PP matrix, decreasing the molecular weight of the blend with decreasing size of the crystallites.
Macromolecular Symposia, 2017
The role of rubber particle size, À distribution, and the constitutive behaviour of the isotactic Polypropylene matrix has been studied by combining the Lazerri-Dompas energy criterion for cavitation and the Van der Sanden, Meier, Tervoort ligament model, adapted for impact conditions. It is concluded that optimising the morphology offers great potential to achieve ultimate properties with far less rubber and hence achieve a superior Stiffness-Toughness-Processing balance.
Journal of Applied Polymer Science, 2012
Four different grades of commercial, highimpact polypropylene (hiPP) were fractionated by temperature-gradient extraction fractionation, and the chain structure and melting behavior of the fractions were studied by Fourier transform infrared spectroscopy and differential scanning calorimetry. Furthermore, the morphology of the disperse phase in the resins was characterized by scanning electron microscopy of the microtome-cut etched and original samples. The results show that there was a strong relation between the chain structure, content, and distribution of the dispersed phase and the mechanical properties of hiPP. These parameters of the elastomeric phase are really critical in reaching the best rigidity-impact balance in hiPP. V
Effect of Multiple Extrusion on Impact Fracture of Three Poly(propylene) Impact Copolymers
Macromolecular Symposia, 2013
SummaryThe effect of structural changes induced by multiple extrusion on the impact fracture behavior of three reactor poly(propylene) impact‐copolymers (ICPPs) was investigated. The morphogenesis of the complex ICPP structure was controlled by the competition between the intraspherulitic phase separation and crystallization. The rubbery inclusion size was controlled by the rate of spinodal decomposition at the onset of crystallization. The following fast spherulite growth fixed the size and spatial distribution of these inclusions. The Charpy notched impact strength (ak) and critical strain energy release rate (Gc) measured under impact loading decreased significantly with the number of extruder passes. A measurable reduction of the size of the crack tip plastic zone (Rp) with the number of extruder passes was observed using high speed digital camera. While the melt flow index (MFI) dependence of ak exhibited ICPP specific shape, the MFI dependences of Gc fell on a single master cu...
Mechanical and morphological characterization of polypropylene toughened with olefinic elastomer
Materials Research-ibero-american Journal of Materials, 2000
The effect of incorporating (C2-C8) ethylene-octene elastomer on the mechanical properties and morphology of polypropylene copolymers has been investigated employing two types of PP copolymer, with and without nucleating agent. The results were compared to the ones presented by a commercial PP heterophase (reactor impact modified PP/EPR). The addition of the elastomer increases the toughness of the blends but reduces their stiffness. PP blends in the low elastomer content region (< 20%) show low values of the Izod impact strength and both, elastomer content and impact strength, are directly proportional to the area under the β damping peak or its maximum intensity of the elastomer. The morphology is a continuous pattern of segregate elastomeric particles with average particle size in the range of 0.27 µm to 0.39 µm. The average particle size and particle size distribution plotted in log-normal distribution curves, increases slightly with the increase in the elastomer content. The reactor modified PP heterophase has a broader particle size distribution and an average particle size of 0.56 µm, at the lower limit but inside the range for good impact performance, as observed.
Journal of Applied Polymer Science, 2003
A series of isotactic polypropylene/poly(propylene-1-octene) (iPP/PPOc) in-reactor alloys were synthesized by a one-step polymerization process, using Metallocene/ZieglereNatta hybrid catalyst. The alloys were characterized by FT-IR, DSC, optical microscopy and SEM. The results suggested that the spherical morphology was maintained during one-step polymerization process, which provided a potential application for one-step polyolefin in-reactor alloys. A characteristic "shellecore" structure of the nascent alloy particles was observed for the first time. This phenomenon may be due to the difference between the homopolymerization and copolymerization rate at different active centers. It was also found that the majority of the elastomers in the matrix were homogeneously distributed in the alloys. The introduction of the relatively long 1-octene branches could effectively reduce the crystal size and the crystallinity of the obtained iPP/PPOc alloys and made it possible to vary their rigidity and elasticity in a wide range. The crystallization kinetics of the alloys with pure iPP was also investigated. With the increase of elastomer content, an increase of nucleation density (the nuclei number per unit area) and the decrease of crystal perfection could be clearly observed. In comparison with pure PP, the overall crystallization rates and the growth rates of the spherulites of the alloys decreased obviously. These results indicated that the growth rate of the spherulites was the decisive step for the overall crystallization rate in this case, which can be explained on the basis of dilution effect and obstruction effect on the mobility of PP chains in the propyleneeoctene copolymer. Investigation of the mechanical properties indicated that notched Izod impact strength of iPP/PPOc alloys have obviously increased in comparison with that of pure iPP. The improvement of impact strength can be mainly attributed to the increase of random copolymer content. Based on the understanding of microstructure and phase morphology, the correlation between morphological structure and mechanical properties has been established.