Impact polypropylene copolymers: fractionation and structural characterization (original) (raw)
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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.
Degradation of polypropylene impact-copolymer during processing
Polymer Degradation and Stability, 2008
The effect of processing on molecular structure and properties of polypropylene impact-copolymer (ICPP) was investigated. It was confirmed that multiple extrusions induced changes in molecular weight resulting in increased MFI and decreased long-term thermooxidation stability. In terms of mechanical properties only impact strength well reflected the processing history. Tensile and flexural properties remained almost unchanged. The sizes of rubbery domains observed by SEM exhibited only minimum changes. The results of SSA and TREF techniques provided further data helping to elucidate the phenomena in rubbery phase. Based on indirect indications one could conclude that while typical polypropylene degradation resulting in chain backbone cleavage took place in the PP homopolymer phase, the rubbery phase containing EPR and PE homopolymer underwent a certain extent of crosslinking.
Structure and properties of a β -nucleated polypropylene impact copolymer
Polymer International, 2014
The surface dielectric properties of acid-etched low-density polyethylene (LDPE) were analysed in the frequency range from 20 Hz to 200 kHz. Samples were treated with various acids for a period of one hour, at temperatures ranging from 20 to 70 ∘ C. After the treatment, the samples were analysed with Fourier transform infrared spectroscopy, revealing chemical and crystallinity changes on the surface, as a direct result of the treatment. The sample surfaces were analysed using atomic force microscopy. The micrographs show that the acid treatment increases the roughness of the samples. Compared to untreated LDPE, the etched samples may exhibit significantly different conductance values at low frequencies. It is also observed that an increase in the acid treatment temperature can result in lower values of conductance and susceptance compared to untreated samples. LDPE films with low value of surface AC conductivity after acid treatment are potentially useful substrates for high-speed electro-sensing applications. The presented results indicate that a suitable choice of acid treatment of LDPE can effect surface polarization while preserving low values of surface AC conductivity of the polymer.
Investigation of the crystalline phase morphology of a β-nucleated impact polypropylene copolymer
Journal of Applied Polymer Science, 2014
This study covers the preparation and the characterization of b-nucleated impact polypropylene copolymer (NA-IPC). Calcium stearate (CaSt), as well as pimelic (Pim) and adipic (Adi) acids, were doped into IPC as mono-or bicomponent nucleating agents (NAs) at varying mass ratios. Possible chemical interactions between the NAs and with IPC, as well as the effect of the NAs on the crystallization behavior and nonisothermal crystallization kinetics, were investigated. DSC and XRD results revealed that IPC nucleated with Pim and Pim-CaSt nucleants induced up to 90% b-crystals, whereas Adi and Adi-CaSt formed only about 17% b-crystals. This was associated with the strong nucleation efficiency of Pim. The nonisothermal crystallization kinetics showed that the crystallization of IPC and NA-IPC followed a three-dimensional growth with athermal nucleation mechanism. FTIR showed that none of the NAs chemically reacted with IPC, and the chemical structure of the polymer was thus intact during the treatment. V C 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 39923.
Journal of Applied Polymer Science, 2012
In this article, the equilibrium morphology of a typical polypropylene (PP) impact copolymer (ICP) system is investigated by numerical self-consistent field simulations. The ICP was fractionated using temperature rising elution fractionation (TREF) to obtain the data necessary to define the simulation parameters. The results demonstrated the formation of a stratified droplet structure, in which ethylene content decreases from the center of the droplet toward the PP interface. This structure is shown to be in accordance with observations from transmission electron microscopy, scanning electron microscopy, and atomic force microscopy. The components are confined to a narrow layer whose position is primarily determined by its ethylene content. Leakage into a neigh-boring layer occurs to a degree that is determined by the component molecular weight and the difference in ethylene content between the layers. Simulations for a range of droplet sizes enable calculation of the interfacial tension. A typical drawback of TREF involves the inability to fractionate the amorphous part, leading to a large difference in ethylene content between the matrix and its neighboring layers. Although this effect is shown not to have a significant influence on the stratified structure, it is shown to have a significant influence on the derived interfacial tension.
Journal of Applied Polymer Science, 2012
In this work, composition effects on interfacial tension and morphology of binary polyolefin blends were studied using rheology and electron microscopy. The amount of dispersed phase (5-30 wt %) and its type [ethylene-octene copolymer, linear lowdensity polyethylene (LLDPE), and high-density polyethylene] was varied, and the influence of different matrix materials was also studied by using a polypropylene homopolymer and a ethylene-propylene (EP) random copolymer. The particle size distribution of the blends was determined using micrographs from transmission electron microscopy (TEM). A clear matrix effect on the flow behavior could be found from the viscosity curves of the blends. Analyzing the viscosity of the blends applying the logarithmic mixing rule indicated a partial miscibility of the EP random copolymer with low amounts of the LLDPE in the melt. Micrographs from TEM also showed a clear difference in morphology if the base polymer is changed, with PE lamellae growing out of the inclusions or being present directly embedded in the matrix. To verify these findings, the interfacial tension was determined. The applicability of Palierne's emulsion model was found to be limited for such complex systems, whereas Gramespacher-Meissner analysis led to interfacial tensions comparable with those already reported in the literature. The improved compatibility when changing the matrix polymer from the homopolymer to the random copolymer allows the development of multiphase materials with finer phase structure, which will also result in improved mechanical and optical performance. V
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.