Dispersed Polypropylene Research Articles

The influence of carbon nanotube functionalization route on the efficiency of dispersion in polypropylene by twin-screw extrusion

The joint effect of chemical functionalization and polymer melt blending conditions on carbon nanotube dispersion in polypropylene, as well as its influence on the electrical and mechanical properties of the resulting composites were investigated. Melt blending was performed using a prototype twin screw extruder enabling sampling along the barrel. The carbon nanotube dispersion was assessed by optical and scanning electron microscopy. The functionalization reaction was tailored for compatibility with the polymer, and characterized by X-ray photoelectron spectroscopy. In particular, nanotubes covalently bonded to polypropylene showed distinctive dispersion ability, while the carbon nanotube dispersion remained stable even after re-melting. However, the polypropylene-functionalized nanotubes produced composites with higher electrical resistivity, possibly due to the insulating effect of the polymer bonded to the nanotubes surface.

Crystallization behavior of polypropylene/ethylene butene copolymer blends

AbstractOne polypropylene (PP) was mixed with two ethylene butene copolymers (EBM). EBM1 had 12.5 mol % of butene and was immiscible with the PP. EBM2 had 51.6 mol % of butene and was miscible with the PP. The dispersed PP in EBM1 showed fractionalized crystallization behavior with a crystallization temperature at around 45°C and a much slower isothermal crystallization rate comparing to the neat PP. The PP did not exhibit fractionalized crystallization behavior in EBM2. EBM1 did not decrease both the crystallization and melting temperatures of the continuous PP. However, EBM2 could decrease both the two temperatures. It was found that EBM2 could largely suppress the epitaxial lamellar branching of the PP. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

Effects of calcium carbonate and compounding sequence on the phase morphology and properties of maleic anhydride‐grafted polypropylene compatibilized polyamide 6/polypropylene blend

AbstractEffects of calcium carbonate (CaCO3) and compounding sequence on the phase morphology of maleic anhydride‐grafted polypropylene (MAPP) compatibilized polyamide 6 (PA6)/polypropylene (PP) blend were investigated. The morphology in the subskin and core regions of injection molded specimen was observed using scanning electron microscopy, which shows great changes due to the incorporation of CaCO3. With the addition of CaCO3 (25 phr), oriented “ginger‐like” network (directly mixing) or loose elongated network (mixing PA6, PP, and MAPP with premixed PA6/CaCO3 masterbatch) of PP phase is formed in the core region, instead of spherical dispersed PP domains for unfilled blend. The distribution of CaCO3 in PA6 and PP phases was determined by selectively dissolving PA6 phase and thermogravimetric analysis of PP phase. A possible mechanism is proposed based on the morphology evolution process to interpret the morphological differences. The mechanical properties and heat distortion temperature of the materials were tested and correlated with the morphology formed. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

Thermostimulative shape memory effect of linear low‐density polyethylene/polypropylene (LLDPE/PP) blends compatibilized by crosslinked LLDPE/PP blend (LLDPE–PP)

AbstractA novel linear low‐density polyethylene (LLDPE)/polypropylene (PP) thermostimulative shape memory blends were prepared by melt blending with moderate crosslinked LLDPE/PP blend (LLDPE–PP) as compatibilizer. In this shape memory polymer (SMP) blends, dispersed PP acted as fixed phase whereas continuous LLDPE phase acted as reversible or switch phase. LLDPE–PP improved the compatibility of LLDPE/PP blends as shown in scanning electron microscopic photos. Dynamic mechanical analysis test showed that the melt strengths of the blends were enhanced with increasing LLDPE–PP content. A shape memory mechanism for this type of SMP system was then concluded. It was found that when the blend ratio of LLDPE/PP/LLDPE–PP was 87/13/6, the blend exhibited the best shape memory effect at stretch ratio of 80%, stretch rate of 25 mm/min, and recovery temperature of 135°C. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011.

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

Polypropylene‐dispersed domain as potential nucleating agent in PS and PMMA solid‐state foaming

AbstractThe potential of using dispersive domains in a polymer blend as a bubble nucleating agent was investigated by exploiting its high dispersibility in a matrix polymer in the molten state and its immiscibility in the solid state. In this experiments, polypropylene (PP) was used as the nucleating agent in polystyrene (PS) and poly(methyl methacrylate) (PMMA) foams at the weight fraction of 10, 20, and 30 wt %. PP creates highly dispersed domains in PS and PMMA matrices during the extrusion processing. The high diffusivity of the physical foaming agent, i.e., CO2 in PP, and the high interfacial tension of PP with PS and PMMA could be beneficial for providing preferential bubble nucleation sites. The experimental results of the pressure quench solid‐state foaming of PS/PP and PMMA/PP blends verified that the dispersed PP could successfully increase the cell density over 106 cells/cm3 for PS/PP and 107 cells/cm3 for PMMA/PP blend and reduce the cell size to 24 μm for PS/PP and 9 μm for PMMA/PP blends foams. The higher interfacial tension between PP and the matrix polymer created a unique cell morphology where dispersed PP particles were trapped inside cells in the foam. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011

Effect of surface treatment on the properties of polypropylene/nanoboehmite composites

AbstractBoehmite nanoparticles are surface modified with alkyl phosphorous acid to improve their dispersion in polypropylene. Effective grafting is evidenced by NMR, elemental analysis and by the fact that the dispersion ability (or disagglomeration) of grafted boehmite particle in nonpolar solvent is significantly altered. High dispersibility level in PP is obtained with long alkyl chain surface modifiers. The improvement of the nanocomposites thermal stability is correlated with the nanoparticles dispersion level. However, composite with well dispersed nanoparticle did not demonstrate enhanced mechanical properties because of weak polymer/filler interactions with the PP matrix. Better reinforcement is noticed for polypropylene composite loaded with untreated boehmite or treated with shorter alkyl chain. For these composites, the nanoparticles acted as nucleating agents. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

New polypropylene blends toughened by polypropylene/poly(ethylene-co-propylene) in-reactor alloy: Compositional and morphological influence on mechanical properties

Abstract A new toughening agent, polypropylene/poly(ethylene-co-propylene) in-reactor alloy (EP-P), has been adopted to modify isotactic polypropylene (PP) in present study. Systematic investigation has been performed on the inter-compositional interaction, crystalline structure, and phase morphology of a series of PP/EP-P blends. It has been found that the PP component from EP-P is thoroughly miscible with neat PP and they together serve as the matrix of the PP/EP-P blends, while the ethylene–propylene random copolymers (EPR) act as the dispersed phase. The ethylene–propylene segmented copolymers (EPS), behaving as the compatibilizer between the EPR dispersed phase and PP matrix, strengthen mutual incorporation and effective diffusion of the amorphous PP segments and the EPR molecules. Based on the in-depth understanding of the crystalline structure and phase morphology, the correlation between morphological structure and mechanical properties has been established. The excellent impact toughness of PP/EP-P blends with higher EP-P content is mainly attributed to the small PP crystallites scattered in the blends and the well dispersed EP copolymer domains in PP matrix.

Enhanced Clay Dispersion in Polypropylene by the Modification of Clay with Poly(Oxypropylene) Diamine

Polypropylene (PP) is a highly non-polar polymer. Where as the clay is a polar material. Hence generally we get poor dispersion out of it. In this work, effort has been taken to improve the dispersion of clay in to polypropylene matrix. Clay was modified with Poly (oxypropylene) ammonium chloride. Composites were prepared by melt blending method in a twin screw extruder. Three different ratios namely 1.5, 3.0, and 4.5 weight % loadings of clay were adopted to prepare these composites by this technique. Their structures were characterized by FTIR, x-ray diffraction (XRD). Notable change in the crystallization and melting temperatures were observed by differential scanning calorimetry (DSC). The distribution of clay in the matrix was also studied through optical microscope (OM) and scanning electron microscope (SEM). The effect of clay modification on the performance of the composites was studied.

Organophilic Boehmite Nanoparticles by ATRP Methacrylates Polymerization: Synthesis, Characterization and Dispersion in Polypropylene

Boehmite nanoparticles covered with a polymer shell enhancing the organophilicity of the surface were prepared by physical adsorption of a polyelectrolyte atom transfer radical polymerization (ATRP) macroinitiator followed by graft-polymerization of methyl methacrylate or 2-hydroxyethyl methacrylate. The presence of polymer chains adsorbed/grafted on the Boehmite was confirmed by attenuated total reflection infrared (ATR-IR) spectroscopy and by thermo-gravimetric analysis (TGA), which showed a significant amount of polymer covering the particles. The methodology of polymerization and the kinetics suggested the possibility to modulate the amount, type and thickness of grafted polymer shell. These organic-inorganic hybrid materials were melt compounded in a Brabender mixer with isotactic polypropylene in the presence of functionalized polypropylene. The dispersion degree of Boehmite nanoparticles in the polypropylene matrix as well as their reinforcing effect were studied by morphology characterization [scanning electron microscopy (SEM) and X-ray diffraction (XRD)], whereas thermal and thermo-mechanical properties were assessed by differential scanning calorimetry (DSC) and dynamic mechanical thermal analysis (DMTA).

Evaluation of nanoparticle dispersion in polypropylene by small‐angle X‐ray scattering

AbstractA small‐angle X‐ray scattering method has been developed for the quantitative evaluation of the effectiveness of nanoparticle dispersion in polymer matrices; it is termed the nanoscale dispersion index. This method was applied to dispersions of nanosized TiO2 fillers in polypropylene. Master batches prepared with lower filler contents showed better dispersion as evaluated by the nanoscale dispersion index. The addition of 1,3:2,4‐di(3,4‐dimethylbenzylidene) sorbitol to the compounds did not affect the degree of nanoscale dispersion as estimated by the nanoscale dispersion index. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

The dynamics of montmorillonite clay dispersion and morphology development in immiscible ethylene–propylene rubber/polypropylene blends

The evolution of morphology during the melt compounding of polypropylene (PP), maleated ethylene–propylene rubber (EPR-g-MAn) and onium-ion exchanged montmorillonite clay (NR4+-MM) is described. Irrespective of the ratio of components, clay partitions into the EPR-g-MAn phase exclusively, with significant amounts of mineral exfoliation occurring in the very early stages of compounding. These changes in filler distribution and dispersion are accompanied by reductions in the size of the dispersed PP phase, as the rate of droplet coalescence falls in response to an elevated EPR-g-MAn matrix viscosity. However, when NR4+-MM is localized in a dispersed EPR-g-MAn phase, coalescence increases as a result of hindered particle break-up.

Morphological studies of polypropylene–nanoclay composites

AbstractPolypropylene–clay nanocomposites were prepared by a solution technique and a subsequent melt‐mixing process. A titanate coupling agent was used to improve the compatibility of the nanoclay particles with the polypropylene. The dispersion of the nanoclay particles in polypropylene was studied with X‐ray diffraction (XRD) and transmission electron microscopy (TEM). An increased d‐spacing value of the clay particles in the nanocomposites was observed, and it was compared with the values of as‐mined (pristine) and as‐received (organophilic) clay particles. The number of intercalated layers in a single clay crystallite was determined to be 4, and the number was confirmed with XRD data and TEM images. On the basis of the Daumas–Herold model (which is widely used for graphite intercalation compounds), the stage 2 and stage 3 structures of montmorillonite particles in polypropylene were recommended. A study on the stage structure suggested a way of determining the presence of polymer molecules in the clay galleries. The results confirmed the existence of single‐layered platelets with improved dispersion in polypropylene. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 218–226, 2005

Investigation of the regularities of phase transitions in multicomponent polymer blends

The influence of the compatibilizers of an ethylene-vinyl acetate copolymer and sodium oleate on the processes of melting and crystallization and the supermolecular structure of polypropylene/copolyamide blends of composition 20/80, 40/60, and 50/50 wt.% has been investigated. It has been shown that a specific fiberization is clearly realized in the compatibilized blends even for compositions corresponding to the region of phase change. Two to three peaks of crystallization of polypropylene in the blends containing an ethylene-vinyl acetate copolymer or sodium oleate have been revealed, which is attributed to the increase in the degree of dispersion of polypropylene as a result of the improvement in the specific fiberization and to the growth in the fraction of polypropylene in the interphase transition layer.

Effects of vibration blending on the subsequent crystallization behavior of polycarbonate/polypropylene blends

The effects of blending in a novel vibration internal mixer on the subsequent multiple crystallization of 70/30 w/w polycarbonate (PC)/polypropylene (PP) were investigated by differential scanning calorimetry, wide-angle X-ray diffractogram, and microscopy. The vibration internal mixer was reformed from a conventional internal mixer through parallel superposition of an oscillatory shear on a steady shear. For this polypropylene-minor phase blend, three possible crystallization peaks were observed. The crystallization behavior was sensitive to the sizes and the size distribution of the dispersed polypropylene droplets. Larger amplitude and/or higher-frequency vibration produced more small droplets (<2 μm) and increased the number of medium droplets (2–8 μm) as a result of the spatially wider and temporally quicker variation of shear rate. The resulting subsequent low-temperature crystallization peak became larger and shifted to lower temperature, and the intermediate-temperature peak became obvious. On the contrary, the coalescence of small droplets, resulting from the heating treatment, weakened the low-temperature peak but strengthened the intermediate-temperature peak and rendered the high-temperature peak to be wider. Mixing at the too high amplitude produced the unstable, partially cocontinuous phase morphology restricting the medium droplets and enlarging the surface area, such that the intermediate-temperature crystallization peak did not appear. Multiple crystallization was related to phase morphology and the nucleation density as well as surface effects. Double-fusion endotherms of the PP component were also observed, corresponding to the melting of different forms of polypropylene crystals. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 92–103, 2002

Novel milling route for controlling structure and properties in SBS elastomer blends containing dispersed PA6 and PP particles

A novel technique to optimise the morphology and thus to enhance the mechanical properties of styrene/butadiene/styrene (SBS) triblock copolymer blends containing dispersed polyamide 6 (PA6)/polypropylene (PP) is reported. The SBS-PA6-PP composite was prepared by blending SBS with PA6-PP ultrafine powder, which was obtained by pulverising PA6 and PP in a pan mill at ambient temperature. The mechanical properties of the composite were determined and the variations of the phase structure of the composites prepared at different processing temperatures were studied by TEM. The thermooxidative stabilities of the composites were tested by thermogrivimetry (TG). The results indicate that preparing a PA6-PP ultrafine powder by the solid state mechanochemical process can improve the compatibility of PA6 with PP and SBS and accelerate the dispersion of PP and PA6 as well as their combination with SBS at the phase interface. The tensile strength of the composite can be increased greatly with an ultrafine powder content of 4-8%, while the elongation at break remains approximately constant. The variation of processing temperature causes a change in the phase structure of the plastics, which has a great effect on the properties of the composite. When the processing is carried out at the melting temperature of the PP, the PP particles combine to form a fibrillar structure that can increase the tensile strength of the matrix from 12·7 to 25 0 MPa. The temperature at which a 10% weight loss occurs in the composite increases from 396·0 to 412·7°C and the temperature of maximum weight loss increases from 454·3 to 479·3°C with an ultrafine powder content of 4%. PRC/1747

Morphology of nylon 6/polypropylene blends compatibilized with maleated polypropylene

AbstractTransmission electron microscopy (TEM) was used to examine the morphology of blends of nylon 6 and polypropylene (PP) containing various maleated polypropylenes (PP‐g‐MA). The size of the dispersed polypropylene particles decreases as the content of maleic anhydride in the PP‐g‐MA increases for binary blends of nylon 6 and the maleated polypropylenes. Ternary blends of nylon 6, PP, and PP‐g‐MA show morphologies that depend on the content of maleic anhydride of the PP‐g‐MA and on the miscibility of PP and PP‐g‐MA. Blends where PP and PP‐g‐MA are immiscible show a bimodal distribution of particle sizes. Miscibility of the PP and PP‐g‐MA was determined by TEM using a special staining technique. Experimental observations of miscibility were further corroborated by thermodynamic calculations. The morphology of the ternary blends was also found to be dependent on the ratio of PP/PP‐g‐MA. By changing this ratio it was possible to induce drastic changes of morphology, going from a continuous nylon 6 phase to a continuous PP phase at a fixed composition. The mechanical properties of these blends were found to be dependent on their morphology. ©1995 John Wiley &amp; Sons, Inc.

Effects of molecular weights and compatibilizing agents on the morphology and properties of blends containing polypropylene and nylon‐6

AbstractPolymer blends containing nylon‐6 of different molecular weights (MW) and polypropylene (PP) were prepared by using a twin screw extruder in order to examine the effects of molecular weights of nylon and the influences of different types of compatibilizing agents on the phase morphology and the properties. The morphology of the resulting blends was characterized by using both scanning electron microscope (SEM) and optical microscope and the properties measured included Izod impact strength, melt flow index (MI), flexural modulus, and heat distortion temperature (HDT). It was found that the molecular weights of the nylon matrix had a significant effect on the phase morphology. The fracture surface of the low MW nylon blend demonstrated a uniformed phase morphology with the dispersed PP particles of dimensions in the range of 1 μm in diameter embedded in the nylon matrix, suggesting an improved compatibility as compared with the high MW nylon system, even though these two constituents were incompatible in nature. Three different types of compatibilizers, including maleic anhydride modified PP (MA‐g‐PP), acrylic acid modified PP (AA‐g‐PP), and ethylene glycidyl methacrylate copolymer (EGMA), were used to examine their effects. It seemed that blends compatibilized with MA‐g‐PP exhibited the most homogeneous phase morphology and superior mechanical properties among the three. In the blends containing low MW nylon as the matrix phase, the Izod impact strength was shown to have increased by about 40% as compared with the noncompatibilized blend, while a 20% increase of the impact strength was measured in the high MW nylon system. The effects of nylon's molecular weights and the compatibilizers were also studied in systems of PP/nylon blends reinforced with silane‐treated glass fibers. It was shown that the properties of the composites relied on the phase morphology which, in turn, was affected by both the molecular weight of nylon and the compatibilizing agents. © 1995 John Wiley &amp; Sons, Inc.

Structure-property relationships in annealed blends of linear low density polyethylene with isotactic polypropylene

Blends of isotactic polypropylene (PP) and linear low density polyethylene (LLDPE) have been analysed by thermal analysis and wide-angle X-ray scattering to determine the effect of thermal history on morphology and mechanical behaviour. The blends were quenched directly from the melt, slow cooled and annealed at 130°C. In all cases it was observed that the two components were insoluble and the crystallization behaviour was determined by the blend morphology, particularly in dispersed PP domains in which heterogeneous nucleation was the rate determining step. Slow cooled speciments with the higher degree of crystallinity had the highest yield stresses, and the lowest elongation to break was achieved in the vicinity of 50% blends, characteristic of the effect of blend morphology on properties.

Rubber phase dispersion in polypropylene

Impact properties of rubber-modified blends are significantly dependent on particle size and size distribution (dispersion). Past work has shown strong variations in these particle parameters with different processing conditions and these variations reflect, in part, different shear fields developed during melt extrusion and moulding. A major problem ensues involving property variability because of process variability. It is neither practical nor economical to place stringent controls on process variability in a plant. Instead, our current research has indicated that lightly crosslinking the rubber reduced drastically the sensitivity of dispersion to processing conditions, and, with the correct rheology between the rubber and the resin, the same dispersion could be maintained through both the extrusion and moulding stages resulting in finished parts with increased chance of dispersion and property consistency. Four rubbers of different degrees of crosslinking and three polypropylenes of different melt flow and structure were blended at six rubber levels. Mixing was carried out with two twin-screw configurations and the blends were cast or injection moulded using a ram or a screw moulder representing six different processing shear histories. Dispersion was quantitatively characterized by scanning electron microscopy (SEM). Spherical rubber particles revealed on the fracture surface were counted and measured to determine particle size and size distribution for the individual blends. Correlation of the results indicated how particle size and size distribution was influenced by crosslinking and the rubber/resin rheology. This provided some understanding of the mechanics of soft-phase dispersion in these blends.