Effect of dynamic shear on the microcellular foaming of polypropylene/high‐density polyethylene blends

Dynamic shear in the axial direction of a rotor was vertically superposed on the melt flow direction, and its effects on the shear rate and melt strength were investigated theoretically. Polypropylene/high‐density polyethylene blends were microcellularly foamed with different vibration parameters. The experimental results were compared with those of a theoretical analysis, and the effects of dynamic shear on the foamability and ultimate cell structure were analyzed in detail. The theoretical results showed that the shear rate and melt strength increased with an increase in the vibration amplitude and frequency. The enhanced melt strength could effectively restrict cell growth, prevent cell rupture, and improve foamability. The experimental results showed that the cell orientation decreased and the cell structure was improved when axial dynamic shear induced by rotor vibrations was superposed on the melt flow direction. Furthermore, the cell diameter decreased and the cell density increased with increases in the vibration amplitude and frequency. The experimental results were very consistent with the theoretical analysis. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Effect of the high‐density polyethylene melt index on the microcellular foaming of high‐density polyethylene/polypropylene blends

The effect of high‐density polyethylene (HDPE)/polypropylene (PP) blending on the crystallinity as a function of the HDPE melt index was studied. The melting temperature and total amount of crystallinity in the HDPE/PP blends were lower than those of the pure polymers, regardless of the blend composition and melt index. The effects of the melt index, blending, and foaming conditions (foaming temperature and foaming time) on the void fractions of HDPEs of various melt indices and HDPE/PP blends were also investigated. The void fraction was strongly dependent on the foaming time, foaming temperature, and blend composition as well as the melt index of HDPE. The void fraction of the foamed 30:70 HDPE/PP blend was always higher than that of the foamed 50:50 HDPE/PP blend, regardless of the melt index. The microcellular structure could be greatly improved with a suitable ratio of HDPE to PP and with foaming above the melting temperature for long enough; however, using high‐melt‐index HDPE in the HDPE/PP blends had a deleterious effect on both the void fraction and cell morphology of the blends. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 364–371, 2004     

Improving polypropylene microcellular foaming through blending and the addition of nano‐calcium carbonate

This article reports an attempt to improve polypropylene (PP) microcellular foaming through the blending of PP with high‐density polyethylene (HDPE) as a minor component and the incorporation of nano‐calcium carbonate (nano‐CaCO₃) into PP and its blends with HDPE. Three HDPEs were selected to form three blends with a viscosity ratio less than, close to, or greater than unity. Two concentrations of nano‐CaCO₃, 5 and 20 wt %, were used. The blends and nanocomposites were prepared with a twin‐screw extruder. The foaming was carried out by a batch process with supercritical carbon dioxide as a blowing agent. The online shear viscosity during compounding and the dynamic rheological properties of some samples used for foaming were measured. The cell structure of the foams was examined with scanning electron microscopy (SEM), and the morphological parameters of some foams were calculated from SEM micrographs. The rheological properties of samples were used to explain the resulting cell structure. The results showed that the blend with a viscosity ratio close to unity produced a microcellular foam with the minimum mean cell diameter (0.7 μm) and maximum cell density (1.17 × 10¹¹ cells/cm³) among the three blends. A foamed PP/nano‐CaCO₃ composite with 5 wt % nano‐CaCO₃ exhibited the largest cell density (8.4 × 10¹¹ cells/cm³). © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Effect of die geometry on foaming behaviors of high‐melt‐strength polypropylene with CO2

This article reports on a systematic study that was conducted to investigate the effects of die geometry (i.e., pressure and pressure drop rate) on the cell nucleation and growth behaviors of noncrosslinked high‐melt‐strength (HMS) polypropylene (PP) foams blown with supercritical CO₂. The experimental results showed that the cellular morphologies of PP foams were sensitive to the die geometry. Furthermore, the initial expansion behavior of the foam extrudate at the die exit was recorded using a high‐speed CCD camera. This enabled us to achieve a more thorough understanding of the effect of die geometry on both the initial expansion behavior and the final cellular morphology of HMS PP foams. The effect of die temperature on cell morphology was also studied. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci 2008     

Mechanical properties of Mg(OH)2/polypropylene composites modified by functionalized polypropylene

Modified Mg(OH)₂/polypropylene (PP) composites were prepared by the addition of functionalized polypropylene (FPP); and acrylic acid (AA) and by the formation of in situ FPP. The effects of the addition of FPP and AA and the formation of in situ FPP on the mechanical properties of Mg(OH)₂/PP composites were investigated. Experimental results indicated that the addition of Mg(OH)₂ markedly reduced the mechanical properties of PP. The extent of reduction in notch impact strength of PP was higher than that in flexural strength and tensile strength. However, tensile modulus and flexural modulus increased with increased Mg(OH)₂ content. The addition of FPP facilitated the improvement in the flexural strength and tensile strength of Mg(OH)₂/PP composites. The higher the Mg(OH)₂ content was, the more significant the effect of FPP was. The incorporation of AA resulted in further increased mechanical properties, in particular the flexural strength, tensile strength, and notch impact strength of Mg(OH)₂/PP composites containing high levels of Mg(OH)₂. It not only improved mechanical properties but also increased the flame retardance of Mg(OH)₂/PP composites. Although the mechanical properties of composites modified by the formation of in situ FPP were lower than those of composites modified by only the addition of AA in the absence of diamylperoxide, the mechanical properties did not decline with increased Mg(OH)₂ content. Moreover, the mechanical properties increased with increasing AA content. The addition of an oxidation resistant did not influence the mechanical properties of the modified Mg(OH)₂/PP composites. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 2139–2147, 2003     

Fracture morphology of Mg(OH)2/polypropylene composites modified by functionalized polypropylene

The morphologies of the fracture surface under impact and flexural testing of Mg(OH)₂/Polypropylene (PP) composites and their modified composites were investigated by scanning electron microscopy. Experimental results indicated that addition of functionalized polypropylene (FPP) and acrylic acid (AA) and the formation of in situ FPP changed the fracture morphologies of Mg(OH)₂/PP composites. We believe that addition of these modifiers improved the interfacial interaction and enhanced the interface adhesion between the particle and the matrix in Mg(OH)₂/PP composites. The degree of improvement was more significant in Mg(OH)₂/PP composites modified by the formation of in situ FPP. At low Mg(OH)₂ content, 2 phr AA exhibited a marked effect, but at high Mg(OH)₂ content, 4 phr AA afforded good effect. Due to the improved interface adhesion by interface interactions the fracture mechanism transformed from interface debonded fracture into a matrix fracture. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 2148–2159, 2003     

Fundamental foaming mechanisms governing the volume expansion of extruded polypropylene foams

This article describes the fundamental foaming mechanisms that governed the volume expansion behavior of extruded polypropylene (PP) foams. A careful analysis of extended experimental results indicated that the final volume expansion ratio of the extruded PP foams blown with butane was governed by either the loss of the blowing agent or the crystallization of the polymer matrix. A charge coupling device (CCD) camera was installed at the die exit to carefully monitor the shape of the extruded PP foams. The CCD images were analyzed to illustrate both mechanisms, gas loss and crystallization, during foaming at various temperatures, and the maximum expansion ratio was achieved when the governing mechanism was changed from one to the other. In general, the gas loss mode was dominant at high temperatures and the crystallization mode was dominant at low temperatures. When the gas loss mode was dominant, the volume expansion ratio increased with decreasing temperature because of the reduced amount of gas lost. By contrast, when the crystallization mode was dominant, the expansion ratio increased with increasing temperature because of the delayed solidification of the polymer. The processing window variation with the butane concentration, the change in the temperature ranges for the two governing modes, and the sensitivity of melt temperature variations to the volume expansion ratio are discussed in detail on the basis of the obtained experimental results for both branched and linear PP materials. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 2661–2668, 2004     

A study on the onset surface melt fracture of polypropylene materials with foaming additives

The melt fracture behaviors of linear and branched polypropylene resins with foaming additives were investigated. The effects of branching, processing temperature, additives, and blowing agent on the surface melt fracture of polypropylene materials were thoroughly studied. A CCD camera was installed at the die exit to precisely observe the onset of surface melt fracture of extruded foams. The critical wall shear stress was determined for various linear and branched polypropylene resins using a capillary die. It was found that the branching required to foam polypropylene resins also promotes melt fracture: the critical shear stress was decreased by 0.0175 MPa with an increase of 0.1 n/1000c in long‐chain branching. It was also observed that the dissolved blowing agent (butane) significantly suppressed the melt fracture of both linear and branched polypropylene resins. On the other hand, a noticeable increase in the critical shear stress of branched polypropylene materials was observed with the nucleating agent (talc) and the aging modifier (glycerol mono stearate), whereas almost negligible effect of the additives on the critical shear stress was observed for linear polypropylene materials. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Different factors in the supercritical CO2‐assisted grafting of poly(acrylic acid) to polypropylene

The grafting of poly(acrylic acid) to polypropylene was realized with supercritical CO₂ as a substrate swelling agent and a monomer/initiator carrier. The effects of different supercritical CO₂‐assisted impregnation conditions on the substrate mass increment and grafting efficiency were studied. The original isotactic polypropylene and the grafting product were characterized through IR spectroscopy, differential scanning calorimetry, and scanning electron microscopy. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 4280–4285, 2006     

Effect of the polymer microstructure on the behavior of syndiotactic polypropylene/organophilic layered silicate composites

Syndiotactic polypropylenes (sPPs) with several microstructures (i.e., syndiotacticities and molecular weights) and synthesized by means of two metallocenic catalysts were melt‐blended with 1 and 3 wt % organophilic layered silicates in the presence of a compatibilizer. X‐ray diffraction and transmission electron microscopy analysis showed that the clay was well dispersed in the composites, although the filler morphology depended on the polymer microstructure. Polypropylenes with low syndiotacticities and molecular weights presented the best clay dispersion. Nonisothermal differential scanning calorimetry analysis showed that the polymer microstructure and the clay content modified the thermal behavior of the composites. The compatibilizer and the clay acted as nucleant agents to increase the crystallization temperature of the matrix. Moreover, the double endothermic peak observed during heating scan and associated with the melt/recrystallization/remelt processes of the pure polymer matrix was reduced in the composites. With regard to the mechanical properties under tensile conditions, a synergic effect of the compatibilizer and the clay was observed. In particular, the addition of the compatibilizer alone was able to increase by about 20% the elastic modulus relative to the neat samples, whereas increases between 35 and 50% were measured when the clay was also added, depending on the polymer microstructure. Our results show that the microstructure of sPPs had strong effects on the behavior of its composites with clay in the presence of a compatibilizer. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Rheological behavior of polypropylene/novolac blends

The rheological behavior of polypropylene/novolac blends was investigated with special reference to the effects of the blend ratio, compatibilization, and dynamic cure. The polypropylene and all the polypropylene/novolac blends presented evidence of shear‐thinning behavior. The novolac, compatibilizer, and dynamic cure had dramatic effects on the rheological behavior of the polypropylene. Various rheological plots, including plots of the viscosity, storage modulus, loss modulus, and loss angle, Han plots, and Cole–Cole plots, were used to analyze the polypropylene/novolac blends. The results showed that the compatibilization together with the dynamic cure could increase the viscosity and modulus because of the formation of a grafting polymer between the maleic anhydride grafted polypropylene and the curing novolac resin. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

Effect of the introduction of polydimethylsiloxane on the foaming behavior of block‐copolymerized polypropylene

We investigated the effect of polydimethylsiloxane (PDMS) on the foaming properties of block‐copolymerized polypropylene (B‐PP) by blending different contents of PDMS with B‐PP in the extrusion process using supercritical CO₂ as the blowing agent. The experimental results indicate that the addition of PDMS greatly increased the expansion ratio of the foamed samples. At the same time, the cell population density of foams obtained from the blends also increased to a certain degree and provided a new perspective on improving B‐PP's foaming performance. The addition of PDMS also decreased the die pressure because of the reduced viscosity of the B‐PP/PDMS blends compared with that of the B‐PP matrix. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Dynamically cured polypropylene/epoxy blends

The dynamic vulcanization process, usually used for the preparation of thermoplastic elastomers, was used to prepare polypropylene (PP)/epoxy blends. The blends had crosslinked epoxy resin particles finely dispersed in the PP matrix, and they were called dynamically cured PP/epoxy blends. Maleic anhydride grafted polypropylene (MAH‐g‐PP) was used as a compatibilizer. The effects of the reactive compatibilization and dynamic cure were studied with rheometry, capillary rheometry, and scanning electron microscopy (SEM). The crystallization behavior and mechanical properties of PP/epoxy, PP/MAH‐g‐PP/epoxy, and dynamically cured PP/epoxy blends were also investigated. The increase in the torque at equilibrium for the PP/MAH‐g‐PP/epoxy blends indicated the reaction between maleic anhydride groups of MAH‐g‐PP and the epoxy resin. The torque at equilibrium of the dynamically cured PP/epoxy blends increased with increasing epoxy resin content. Capillary rheological measurements also showed that the addition of MAH‐g‐PP or an increasing epoxy resin content increased the viscosity of PP/epoxy blends. SEM micrographs indicated that the PP/epoxy blends compatibilized with PP/MAH‐g‐PP had finer domains and more obscure boundaries than the PP/epoxy blends. A shift of the crystallization peak to a higher temperature for all the PP/epoxy blends indicated that uncured and cured epoxy resin particles in the blends could act as effective nucleating agents. The spherulites of pure PP were larger than those of PP in the PP/epoxy, PP/MAH‐g‐PP/epoxy, and dynamically cured PP/epoxy blends, as measured by polarized optical microscopy. The dynamically cured PP/epoxy blends had better mechanical properties than the PP/epoxy and PP/MAH‐g‐PP/epoxy blends. With increasing epoxy resin content, the flexural modulus of all the blends increased significantly, and the impact strength and tensile strength increased slightly, whereas the elongation at break decreased dramatically. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 1437–1448, 2004     

Compatibilization of polypropylene/nylon 6 blends with a polypropylene solid‐phase graft

The compatibilization of polypropylene (PP)/nylon 6 (PA6) blends with a new PP solid‐phase graft copolymer (gPP) was systematically studied. gPP improved the compatibility of PP/PA6 blends efficiently. Because of the reaction between the reactive groups of gPP and the NH₂ end groups of PA6, a PP‐g‐PA6 copolymer was formed as a compatibilizer in the vicinity of the interfaces during the melting extrusion of gPP and PA6. The tensile strength and impact strength of the compatibilized PP/PA6 blends obviously increased in comparison with those of the PP/PA6 mechanical blends, and the amount of gPP and the content of the third monomer during the preparation of gPP affected the mechanical properties of the compatibilized blends. Scanning electron microscopy and transmission electron microscopy indicated that the particle sizes of the dispersed phases of the compatibilized PP/PA6 blends became smaller and that the interfaces became more indistinct in comparison with the mechanical blends. The microcrystal size of PA6 and the crystallinity of the two components of the PP/PA6 blends decreased after compatibilization with gPP. The compatibilized PP/PA6 blends possessed higher pseudoplasticity, melt viscosity, and flow activation energy. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 420–427, 2004     

Study on thermoplastic polyurethane/polypropylene (TPU/PP) blend as a blood bag material

Blends with different ratios of thermoplastic polyurethane/polypropylene (TPU/PP) were prepared by melt mixing using an internal Haake mixer. Properties of the blends were investigated using SEM micrographs of cryofractures and measurement of the mechanical strength, water absorption, cell culture, and platelet adhesion in vitro tests, which were compared with those of PVC blood bags. The effect of the addition of the ethylene–vinyl acetate (EVA) copolymer on the TPU/PP blend properties was investigated. The results indicated that a TPU/PP/EVA = 80/20/5 blend can be used as a new blood bag material. It was observed that the blend is homogeneous with higher mechanical strength than that of the commercial PVC blood bag. This blend also showed a compatible cell response in contact with L929 fibroblast cells and fewer tendencies to interaction with platelets compared to the PVC blood bag. Although the blends were immissible and no chemical reaction at the interface could be found, the blood compatibility of the blends were improved. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 2496–2501, 2003     

Influence of the preparation on the mechanical,thermal, and gas permeation properties of polypropylene/oligopinene thin films

The mechanical, thermal, and gas permeation properties of polypropylene (PP)/oligopinene systems in the form of compression thin films 10 μm thick, which were prepared by quenching (with liquid nitrogen) and slow‐cooling (15°C/min) techniques, were examined. The addition of oligopinene to PP changed the stress–strain curve of the polyolefin. Both for quenching and slow‐cooling films, with a higher oligomer content, no more yielding was observed, and the elongation at break abruptly decreased with greater than 10% oligomer. The elastic modulus and stress at break changed according to the thermal conditions of the film preparation. Thermal analysis revealed that the blend system had two glass‐transition temperatures for both types of films. The values of permeation to CO₂ were independent of the film preparation and were practically unchangeable with the oligomer content in the blends, indicating that the overall decrease in the crystallinity was counterbalanced by the rigidity of the two amorphous phases. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 2253–2260, 2003     

Barrier properties of polypropylene/organoclay nanocomposites

Polypropylene/clay nanocomposites are attractive candidates for applications requiring good barrier properties because of the inherent features of the polymer matrix. To assess their potential, systematic research relating the barrier performance to the structural characteristics of polypropylene/montmorillonite samples has been conducted. The nanocomposites have been tested in the presence of helium, water vapor, toluene, and methanol, and the unmodified matrix has been found to exhibit better properties than its mixtures with the compatibilizer and/or clay. The method for the interpretation of the results proposed in this study considers the composition of the samples, the morphology of the semicrystalline polymer matrix, and the state of dispersion/exfoliation of the clay layers, along with the specific interactions between the solvent molecules and the system components. In this way, several points have been identified for understanding and improving the performance of the nanocomposites. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 618–625, 2007     

Characteristic properties of polypropylene cationic fabrics and their derivatives

Polypropylene fabrics were modified with 2N‐morpholino ethyl methacrylate by electron beams and grafting. Then, the modified fabrics were quaternized with different alkylating agents, such as benzyl chloride, monochloroacetic acid, chlorosulfonic acid, and chloroethanol. The reaction completion was calculated from the increase in the fabric weight. The modified polypropylene fabrics were characterized by microanalysis and IR spectroscopy. The moisture regain was measured at 20°C and 65% relative humidity. The modified fabrics were sufficiently hydrophilic to adsorb the metal ion Cu²⁺ from a CuSO₄ solution. Their antimicrobial properties were evaluated. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 2917–2922, 2003     

Electron‐beam‐radiation‐induced grafting of acrylonitrile onto polypropylene fibers: Influence of the synthesis conditions

Electron‐beam‐radiation‐induced grafting of acrylonitrile onto polypropylene fibers was investigated with a pre‐irradiation method. Grafting conditions such as the solvents, additives, monomer concentration, radiation dose, and temperature were varied, and the effects on the degree of grafting were studied. The nature of the reaction medium and additives had a considerable influence on the degree of grafting. The dilution of acrylonitrile with N,N‐dimethylformamide significantly enhanced the degree of grafting in comparison with other solvents. The addition of sulfuric acid to the reaction mixture led to an increase in the degree of grafting and an acceleration of the rate of grafting. The order of dependence of the rate of grafting on the pre‐irradiation dose and monomer concentration was found to be 1.31 and 1.21, respectively, in the presence of sulfuric acid. The activation energy for grafting was calculated to be 21.9 kJ/mol. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Electrochemical properties of polypropylene membranes modified by the plasma polymerization coating of SO2/acetylene

Polypropylene membranes were modified by the plasma etching of SO₂, SO₂? O₂, or SO₂? H₂O, followed by the plasma polymerization coating of SO₂/acetylene. The conditions for SO₂ plasma etching were optimized by the measurement of the ion‐exchange capacity (IEC) as a function of the plasma‐etching power (10–30 W), gas pressure (40–60 mTorr), and treatment time (15–120 s). For the plasma etching of SO₂? O₂ and SO₂? H₂O, only the pressure ratio (SO₂/O₂ and SO₂/H₂O) was optimized under the optimized conditions determined from SO₂ plasma etching. Plasma etching was then combined with the plasma polymerization coating of SO₂/acetylene, for which the conditions were again optimized by the measurement of the IEC as a function of the plasma power (10–40 W), chamber pressure (50–200 mTorr), SO₂/acetylene ratio (15/135–60/90), and treatment time (0–10 min). Next, the electrical resistance and water uptake were evaluated. The modified membranes were also analyzed with scanning electron microscopy, whereas plasma polymer coatings were characterized with Fourier transform infrared/attenuated total reflection. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 99: 3692–3699, 2006