Polypropylene Phase Research Articles

The Effects of Different Processing Methods on the Morphology and Properties of PP/EPDM/Nano-CaCO3 Ternary Blend

The effects of different processing methods (direct extrusion, two-step extrusion or lateral injection extrusion) on the morphology of polypropylene (PP)/ethylene-propylene-diene terpolymer (EPDM)/calcium carbonate nanoparticles (nano-CaCO3) ternary blend were investigated, including the morphology of the EPDM phase and the distribution of nano-CaCO3 particles, by means of scanning electron microscopy (SEM). The results showed that the processing methods had a significant influence on the morphology of the EPDM phase and the distribution of nano-CaCO3 particles. In the lateral injection extruded blends, it was amazingly observed that the EPDM particles encapsulated the PP phase tightly, and the dimension of EPDM particles was remarkably decreased. It was also found that the content of nano-CaCO3 particles in the matrix of the lateral injection extruded blends was less than that of the two-step extruded blend, and that of the direct extruded blend was most. The properties of the ternary blend, including dynamic mechanical properties, rheological properties, and crystallization, were characterized in order to confirm the variety of morphologies caused by the different processing methods. The differences in the crystallization temperature, elastic modulus, and glass transition temperature of the blends prepared by different methods well agreed with the variation of their morphology.

Properties of polypropylene/(natural rubber)/organomontmorillonite nanocomposites prepared by melt blending

AbstractThe aim of this work was to study the effects of an organomontmorillonite or organoclay (OMMT) on the properties of a thermoplastic elastomer blend prepared by melt blending and based on polypropylene (PP) and natural rubber (NR). The results obtained showed a slight improvement of the blend mechanical (strength, modulus, and elongation), thermal, and solvent resistance properties when the amount of the organoclay was 3 phr. Results obtained by XRD analysis showed that at 3 phr of organoclay loading there was a shift toward low angles of the organoclay (001) plane diffraction peak and a disappearance of the PP β–phase peak. This shift signifies an intercalation of the polypropylene/(natural rubber) chains between organoclay platelets. An SEM study revealed that at the 3 phr organoclay concentration the blend became tougher, and the organoclay was located both at the PP/NR interface and inside the NR dispersed phase. A DSC study showed a decrease of the melting temperature of the PP phase at the 3 phr organoclay loading. A rheological study revealed that the addition of organoclay had not increased the melt viscosity of the PP/NR blend, and the stiffness was related to the maximum torque increase as a function of the organoclay loading. J. VINYL ADDIT. TECHNOL., 2011. © 2011 Society of Plastics Engineers

Melt‐mixed polypropylene/acrylonitrile‐butadiene‐styrene blends with multiwall carbon nanotubes: Effect of compatibilizer and modifier on morphology and electrical conductivity

AbstractCocontinuous blends of 45/55 polypropylene (PP)/acrylonitrile‐butadiene‐styrene (ABS) with multiwall carbon nanotubes (MWNT) were prepared by melt‐mixing in a conical twin‐screw microcompounder. PP‐grafted‐maleic anhydride (PP‐g‐MA) and styrene MA were used as compatibilizers for PP/ABS blends. Scanning electron microscopic observations showed phase segregation of PP‐g‐MA in the blends. State of dispersion of MWNT in the presence or absence of the compatibilizers was assessed through AC electrical conductivity measurements and crystallization studies of the blends. An improvement in AC electrical conductivity was observed in blends in presence of either styrene MA or dual compatibilizers. The lowest electrical percolation threshold was achieved at 0.1 wt % of MWNT using sodium salt of 6‐amino hexanoic acid‐modified MWNT. Significant increase in crystallization temperature of PP phase of blends with MWNT was observed in the presence of compatibilizers as compared to blends without compatibilizers. An attempt has been made to address the complex issues of phase segregation, compatibilization, and dispersion of MWNT in cocontinuous blends of PP/ABS. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011

On the metastability of β phase in isotactic polypropylene: experiments and numerical simulation

AbstractPhase transitions in isotactic polypropylene were investigated during isothermal crystallization and heating after isothermal crystallization using various experimental techniques. The results obtained by wide angle x-ray scattering (WAXS), light depolarization technique (LDT), differential scanning calorimetry (DSC) and optical microscopy show that crystallization of isotactic polypropylene can result in simultaneous formation of two crystal modifications, α and β. There is clear experimental evidence that β phase tends to convert into α modification during crystallization as well as during subsequent heating. Experimental results are compared with numerical simulation performed according to the model of nucleation-controlled phase transitions in multiphase systems. The results of simulation show that b phase is not thermodynamically stable in any temperature range. The reason for the appearance of β phase is related to low interfacial tension of melt vs β. It has been also shown that maximum crystallinity reached in experiments does not exceed 40-50% in agreement with the concept of constrained amorphous phase.

Ductile-to-brittle transition in cenosphere-filled polypropylene composites

Cenosphere-filled polypropylene (PP) composites were fabricated and characterized for their structural/morphological and fracture mechanical behaviour. The fracture properties were studied following the essential work of fracture (EWF) approach based on post-yield fracture mechanics (PYFM) concept. The structural attributes and its consequent effects on the dynamic mechanical properties were characterized by wide angle X-ray diffraction (WAXD), hot-stage polarized light optical microscopy (PLOM) and dynamic mechanical analysis (DMA). The WAXD studies have revealed a decrease in crystallinity of the composites with increase in cenosphere content. PLOM studies reveals a threefold reduction in the diameter of the spherulite in case of composite with 10 wt% of cenosphere compared to that of PP followed by an increase of ~50% in the composite with 20 wt% of cenosphere compared to that of the composite with 10 wt% cenosphere. DMA revealed an enhancement in the energy dissipation ability of the composite with 10 wt% of cenosphere and an increase in the storage modulus up to ~30% in the composites relative to the soft PP phase. The non-essential work of fracture (NEWF: βw p) as the resistance to stable crack propagation has shown a maximum at 10 wt% of cenosphere followed by a sharp drop at higher cenosphere content indicating a cenosphere-induced ductile-to-brittle transition (DBT). Fractured surface morphology investigations revealed that the failure mode of the composites undergo a systematic transition from matrix-controlled shear deformation to filler-controlled quasi-brittle modes above a cenosphere loading of 10 wt% in the composites reiterating the possibility of filler-induced semiductile-to-DBT transition.

Study on phase structure and evolution of PP/PEOc blends during heat preservation process under quiescent condition

The phase structure and evolution of polypropylene (PP)/poly(ethylene-1- octene) copolymer (PEOc) blends during heat preservation process under quiescent condition were studied using scanning electron microscopy (SEM). The structure parameters, such as the average area diameter dp, characteristic length L, and average characteristic length Lm, of the dispersed phase in PP/ PEOc blends were calculated by pattern analysis of SEM images. Moreover, the potential fractal behavior of the phase structure and morphology of polymer blends during the process was discussed. The histograms of P(L(t)/Lm) obtained at various time fell on a master curve, demonstrating the self-similar growth of the phase structure of the blends during heat preservation process.

Phase morphology development in a low interfacial tension immiscible polyolefin blend during die extrusion and melt spinning

AbstractWe describe the development of phase morphology in polypropylene (PP)/ethylene–butene copolymer (EBM) blends in both extrusion through dies and in subsequent melt spinning to form filaments. This immiscible blend has a very low interfacial tension around 0.69 dynes/cm. In the die extrusion process, at low extrusion rates, the dispersed PP phase was sheared into fibrils; at higher extrusion rates, the PP fibrils formed an encapsulation layer near the die wall first, then it broke into droplets because of both interfacial tension and long residence time. These droplets agglomerated together to form a network. In melt spinning, the dispersed phase was also drawn down into fibrils, which coalesced into a continuous layer on the outer surface of the filaments at higher drawdown rates. POLYM. ENG. SCI., 50:1969–1977, 2010. © 2010 Society of Plastics Engineers

Non-isothermal crystallization kinetics and thermal stability of the in situ reinforcing composite films based on thermotropic liquid crystalline polymer and polypropylene

The non-isothermal crystallization kinetics and thermal stability of the in situ reinforcing composite thin film, comprising of 10 wt% of thermotropic liquid crystalline polymer (TLCP, Rodrun LC5000) and polypropylene (PP), prepared by a two-step method were investigated using differential scanning calorimetry (DSC) and thermogravimetry (TG), respectively. The DSC results revealed that Mo method was suitable for the crystallization behavior description of both neat PP and 10 wt%TLCP/PP films. The in situ formation of TLCP fibrils in the PP matrix led to reduction in both values of half-time of crystallization (t 1/2) and the kinetic parameter of Mo equation F(T), resulting in a significant increase in the crystallization rate of PP phase. The remarkable lower in crystallization activation energy of the composite films also confirmed that in situ formed TLCP fibrils could influence the molecular chain of PP easier to crystallize, and hence resulted in the faster crystallization rate. The nucleation activity value of composite indicated that TLCP fibrils acted as effective nucleating agents. From TG results and the higher decomposition activation energy, the thermal stability of the composite can be improved by the presence of in situ-formed TLCP fibrils.

Studies on partial compatibility of PP and PS

Blends of polystyrene (PS) and polypropylene (PP) were prepared through melt compounding. With an increase of PS content up to 30 wt%, the tensile strength of PP/PS blends increased from 37.4 MPa to 42.2 MPa, although the blends were widely regarded as immiscible. The DSC results showed that there's slight decrease in melting temperature of PP, showing insufficient evidence for partial compatibility between PP and PS. Almost no variation of distinct characterization peaks were observed in FTIR spectra of PS/PP blends compared with those of neat PP and PS, indicating there is no chemical interactions between PP and PS. Since the morphology investigation showed a droplet structure as PS content was up to 30 wt%, the improvement of tensile strength could be simply considered as due to the reinforcing effect of dispersed rigid PS particles on the PP, combining with partial compatibility between them as evaluated by change of C p at glass transition for both PS and PP. More interestingly, DSC and DMA results showed that the blending of PS and PP could lead to a substantial decrease of the glass transition temperature (T g) of PP, and increase of T g of PS. The annealing experiment was carried out to understand the change of T g in PP/PS blends. It is believed that the compressive stress generated by the contracting PP should be the dominant mechanism for the T g elevation of PS. On the other hand, the T g decrease of PP is likely owing to the creation of a large amount free interface of PP and the dilatation of the PP phase resulting from the corresponding tension exerted by PS during cooling.

Effect of carbon black addition and its phase selective distribution on the stress relaxation behavior of filled thermoplastic vulcanizates

AbstractThe long term mechanical behavior of thermoplastic vulcanizates (TPV) based on polypropylene (PP) and ethylene propylene diene terpolymer (EPDM) and different types and concentrations of carbon black (CB) has been characterized by means of stress relaxation experiments. Evaluation of the relaxation curves was carried out using the two‐component model allowing a division of the initial stress into different stress components which are caused by different networks available in TPV. The discussion focussed on the background of the stress components, which are originated by the CB addition, the non‐relaxing stress components σ, and σ, as well as the relaxing stress components ΔσCB(polymer‐layer) and ΔσCB(network). It was found that the concentration and type of CB as well as the phase specific CB distribution strongly affect the non‐relaxing and relaxing stress components. Up to a CB concentration of 9% in the EPDM phase the composite behaves as a thermo‐rheologically simple material because the impact of CB addition on the α‐relaxation of the crystalline PP phase is still negligible. A master curve was created by the horizontal shift of the relaxing stress curves ΔσComp(t) to a reference curve. At higher local CB loadings the additional relaxation processes induced by CB addition overlap with the α‐relaxation, thus, no master curve could be made in that case. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

Effect of Electron Beam Irradiation and Reactive Compatibilizers on Some Properties of Polypropylene and Epoxidized Natural Rubber Polymer Blends

Effect of reactive compatibilizers on the mechanical, thermal and morphological properties of polymer blends based essentially on polypropylene (PP) and different ratios of epoxidized natural rubber (ENR) was investigated. The same properties were also, studied before and after electron beam irradiation to various doses. The results showed that the mechanical and thermal properties of unirradiated PP/ENR blends were improved after using the reactive compatibilizers: PP graft copolymer with maleic anhydride (PP-g-MAH) or 1,6-hexandiol-diacrylate (HDDA). This improvement was attributed to the formation of interfacial bonding between PP and ENR phases during the melt processing. Further improvement in these properties was observed under effect of electron beam irradiation and the reactive compatibilizer. However, this effect was clear in the case of the monomer HDDA than PP-g-MAH. Scanning electron microscopy (SEM) micrographs indicated that the morphology was improved by the addition of the reactive compatibilizers and electron beam irradiation. The wide angle X-ray diffraction (WAXD) results indicated that the crystallinity of the blend was increased by the addition of the compatiblizing agents due to the plasticizing effect and/or the nucleatating properties of the compatibilizer. However, the crystallinity of the PP/ENR blend was decreased after electron beam irradiation.

Effect of components of a sulfur-containing vulcanizing system on the structure and properties of isotactic polypropylene

With the use of methods of X-ray diffraction analysis and differential scanning calorimetry, the structure and melting and crystallization of isotactic polypropylene are studied in the presence of components of a sulfur-containing vulcanizing system composed of sulfur, zinc oxide, stearic acid, Altax, and thiuram, which is used for synthesis of thermoplastic vulcanizates. It is found that the addition of zinc oxide results in the formation of the β phase of polypropylene, and the content of this product depends on the concentration of a nucleating agent. The heat pretreatment of samples has a strong effect on the formation of β -polypropylene. The addition of residual compounds to polypropylene at the studied concentrations has practically no effect on its structure. With an increase in the content of the β phase, the elastic modulus and elongation at neck formation of polypropylene increase, whereas its tensile strength, elongation at yield, and elongation at break decrease.

Effect of nanosilica on the co-continuous morphology of polypropylene/polyolefin elastomer blends

This paper reports the effect of nanosilica (SiO2) on the morphology of co-continuous immiscible polypropylene (PP)/polyolefin elastomer (POE) blends. The unfilled blends display phase inversion and a co-continuous structure at a ratio of 50/50 PP/POE by weight. Upon addition of SiO2 in the presence of maleated PP compatibilizer a finer structure, consisting of elongated POE particles dispersed within the PP phase is obtained. This transformation is associated to the presence of finely dispersed SiO2 particles that are localized exclusively within the PP matrix. The impact properties, flexural and Young's moduli of the blends increase significantly, pointing to a synergistic effect arising from the presence of the reinforced PP phase, containing high amounts of the finely dispersed elastomeric phase.

In situ microfibrillar blends and composites of polypropylene and poly (ethylene terephthalate): Morphology and thermal properties

Microfibrillar blends were prepared from polypropylene and poly (ethylene terephthalate) by extrusion followed by cold drawing. The draw ratio employed had a prominent effect on the aspect ratio of the microfibrils produced, as revealed by scanning electron microscopy. The subsequent isotropization step between the Tm of the polymers created microfibrillar composites with randomly oriented short microfibrils of poly (ethylene terephthalate). The X ray diffraction patterns of the microfibrillar blends were different from those of corresponding composites although the polypropylene phase in both exhibited predominantly the presence of α crystallites. The crystallization of the polypropylene phase was affected by the orientation and diameter of the poly (ethylene terephthalate) microfibrils. The short microfibrils in the microfibrillar composites were not effectual in hastening the crystallization of polypropylene. The thermal decomposition studies revealed the capability of microfibrillar blends to delay the degradation better than the microfibrillar composites.

Interfacial Interactions in PP/MMT/SEBS Nanocomposites

The intercalation capability of poly(styrene-b-ethylene butylene-b-styrene) (SEBS) in nanocomposites of isotactic polypropylene (PP) with 5 wt % of organically modified montmorillonite (C20A), prepared by melt blending, has been investigated. X-ray diffraction (XRD) and transmission electron microscopy (TEM) studies have shown the presence of intercalated structures in the nanocomposite. In a previous research, we studied the intercalation capability of a commercial compatibilizer.(1) Those results, with the study we present in this work, allow us a better understanding of the mechanism of compatibilization and a deeper characterization of the structure and morphology of the nanocomposite. Scanning transmission X-ray microscopy (STXM) has been used. Because of the excellent chemical sensitivity and the high spatial resolution (∼40 nm) of this technique, we have proved that C20A is not in direct contact with the PP phase because the clay is always located inside the elastomer domains. The elastomer is surr...

The effect of polypropylene/polyamide 66 blending modification on melt strength and rheologic behaviors of polypropylene

Common linear polypropylene (PP) was modified by blending with polyamide 66 (PA66) under the act of compatibilizer in a twin-screw extruder in an attempt to improve the melt strength (MS) of PP. The MS of pure PP and modified PPs were measured by MS testing unit at three temperature of 190, 210, and 230 °C, and the MS improvement of PP was verified. The MS of the modified PPs increased with increasing the content of PA66. The steady- and dynamic-shear rheological behaviors of pure PP and modified PPs were investigated using a capillary rheometer and a parallel-plate rotating rheometer. The steady-shear rheological analysis results revealed that modified PPs had higher melt shear viscosity, stronger non-Newtonian behaviors, and higher zero shear-rate viscosity. The dynamic-shear rheological analysis showed modified PPs had higher melt complex modulus and smaller phase angle, which indicated that the melt viscosity and melt elasticity of PP were also enhanced. The modified PPs was characterized by DSC. DSC results revealed that the PA66 phase and PP phase of the modified PPs were in state of crystallization. The enhancement of MS, melt viscosity, and melt elasticity of modified PPs could be due to undisaggregated PA66 crystallization phase within the melt of PP blends.

Development of isotropic compatible HDPE/PP blends for structural applications

AbstractIn an attempt to provide superior products for the structural applications, this study aimed at preparing isotropic compatible high density polyethylene (HDPE)/ polypropylene (PP) blends without the use of the expensive compatibilization technique. Morphological and structural characterizations of the homopolymers and blends were carried out. In addition, some of the structurally important mechanical and thermal properties were characterized. Such characterizations were performed to investigate whether or not the blends are compatible and therefore acceptable for the structural applications. Scanning electron microscope (SEM) micrographs of the blend samples indicate that the interfacial adhesion between HDPE and PP phases is intimate in the 5/95 HDPE‐PP, good in the 85/15 HDPE‐PP and 95/5 HDPE‐PP, fair in the 30/70 HDPE‐PP and very poor in the 50/50 HDPE‐PP. Similarly, mechanical and thermal responses of the first three blends are remarkable. The 30/70 HDPE‐PP blend displays a fairly good performance. Whereas, the properties of the 50/50 HDPE‐PP blend are very poor. This decides that the first three blends are compatible and, therefore, structurally attractive materials. The fourth is partially compatible and, as a consequence, can be rather acceptable for the structural applications. However, the fifth is incompatible and, of course, is not acceptable for such applications. On the other hand, SEM micrographs and differential scanning calorimetry results indicate that the crystalline structures of individual polymers are appreciably affected by blending. Additionally, the study reveals that the end use performance of blends is strongly dependent on the crystalline structure changes occurring in each component due to blending as well as the compatibility between the blend components. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

Influence of oil contents in dynamically cured natural rubber and polypropylene blends

AbstractMechanical, dynamic, thermal, and morphological properties of dynamically cured 60/40 NR/PP TPVs with various loading levels of paraffinic oil were investigated. It was found that stiffness, hardness, tensile strength, storage shear modulus, complex viscosity, glass transition temperature (Tg) of the vulcanized rubber phase, degree of crystallinity and crystalline melting temperature (Tm) of the polypropylene (PP) phase decreased with increasing loading levels of oil. This is attributed to distribution of oil into the PP and vulcanized rubber domains causing oil‐swollen amorphous phase and vulcanized rubber domains. An increasing trend of elastic response in terms of tension set and damping factor was observed in the TPVs with loading levels of oil in a range of 0–20 phr. It is supposed that a major proportion of oil was first preferably migrated into the PP phase and caused an abrupt decreasing trend of degree of crystallinity and Tm of the PP phase. The dispersed vulcanized rubber domains remained small as particles with a low degree of swelling. Increasing loading levels of oil higher than 20 phr caused a decreasing trend of elongation at break and elastomeric properties. Saturation of oil in the PP phase was expected and the excess oil was transferred to the rubber phase which thereafter caused larger swollen vulcanized rubber domains. The remaining amount of oil was able to separate as submicron pools distributed in the PP matrix. This caused lowering of Tg, Tm, crystallinity of PP phase as well as strength, elastomeric, and dynamic properties of the TPVs. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

Effect of temperature gradient on the development of β phase polypropylene in dynamically vulcanized PP/EPDM blends

Different sample thicknesses were adopted to investigate the effect of temperature gradient on the development of β phase polypropylene (PP) in the compression-molded dynamically vulcanized thermoplastic elastomers (TPVs) based on PP/ethylene-propylene-diene rubber blend. Differential scanning calorimetry and wide-angle X-ray diffraction were employed to study the melting behavior and crystalline structures. The results indicated that the content of β phase increased with the sample thickness of TPV increasing, while the total crystallinity of PP almost kept constant. The simulation of the temperature field showed that there was a temperature gradient along the direction of sample thickness, and the strength of the temperature gradient increased with the thickness of TPV increasing. The reason for the change of β phase content was found to lie in the reduction of the entropy in the temperature gradient field, which was a result from the decrease of the molecular chain conformation.

Effect of spatial confinement on the development of β phase of polypropylene

The focus of this study was the effect of spatial confinement on the development of nucleating agent-induced β phase polypropylene (PP) in the dynamically vulcanized thermoplastic elastomers (TPVs) based on dynamically vulcanized PP/ethylene-propylene-diene rubber (EPDM) blend. The melting behaviors, crystalline structures and the morphologies of the blends were studied by differential scanning calorimetry (DSC), wide-angle X-ray diffraction (WAXD) and scanning electron microscopy (SEM). The results indicate that the EPDM phase undergoes a series of changes from the dispersed phase to a continuous one, and again to the dispersed phase with increased content of curing agent, and the PP component always shows itself in a continuous phase. In this process, with the content of the nucleating agent unchanged, the content of β phase PP in the blends initially increases a little and then decreases with increasing PF (Phenolic resin) content. We believe spatial confinement provides a good explanation for the development of β phase PP.