Plain iPP Research Articles

Morphology and mechanical properties of polypropylene-POSS hybrid nanocomposites obtained by reactive blending

The polypropylene-polyhedral oligomeric silsesquioxane (PP-POSS) organic–inorganic hybrids were obtained and studied. The hybrids were prepared by grafting of POSS on PP chains during a reactive melt-blending of polypropylene (iPP), maleic anhydride functionalized PP (PP-g-MA), and amine-functionalized POSS (aminopropylheptaisobutyl-POSS, ambPOSS, aminopropylheptaisooctyl-POSS, amoPOSS, or aminoethylaminopropylheptaisobutyl-POSS, am2bPOSS), taking advantage of the high efficiency of amino-anhydride reaction in the molten state. The structure, morphology, and physical properties of the obtained hybrids and blends were studied by means of wide- and small-angle X-ray scattering, dynamic scanning calorimetry, scanning electron microscopy, dynamic mechanical thermal analysis, as well as tensile and impact experiments. The influence of POSS chemical structure and grafting degree on the morphological characteristics and mechanical properties was investigated. It was found that grafting of POSS cages on PP chains leads to the POSS dispersion on the molecular level. On contrary, when POSS was mixed with plain iPP any grafting of POSS on iPP chains was impossible, which resulted in phase-separated blend with crystallites of POSS dispersed in iPP matrix. The mechanical tests revealed that modification of polypropylene by grafting with POSS molecules does not affect significantly its mechanical properties, both static and dynamic, except ultimate strain, which is markedly lower in hybrids and their blends than in plain iPP. Also the impact properties of PP were practically not improved by modification with POSS. POLYM. COMPOS., 34:929–941, 2013. © 2013 Society of Plastics Engineers

Influence of CaCO3 nanoparticles shape on thermal and crystallization behavior of isotactic polypropylene based nanocomposites

The influence of calcium carbonate nanoparticles with different shapes (spherical and elongated) on the thermal properties and crystallization behavior of isotactic polypropylene was investigated. CaCO3 nanoparticles were covered by an appropriate coating agent to improve the interfacial adhesion between the filler and the polyolefin matrix. The nanocomposites were prepared by melt mixing and subsequent compression molding. A remarkable effect of CaCO3 on the thermal properties of iPP was observed. Moreover, the analysis of crystallization kinetics showed that CaCO3 nanopowder coated with PP-MA are efficient nucleating agents for iPP, and the overall crystallization rate results higher than plain iPP.

Thermal stability and crystallization kinetics of isotactic polypropylene/organomontmorillonite nanocomposites

AbstractThe thermal stability and crystallization kinetics of isotactic polypropylene (iPP) and iPP/organomontmorillonite (organo‐MMT) nanocomposites were investigated with differential scanning calorimetry and thermogravimetry. The incorporation of organo‐MMT up to a concentration of 4 wt % did not affect the melting temperature of iPP but did increase the peak thermal degradation temperature by 60°C. The isothermal crystallization kinetics showed that the addition of organo‐MMT increased the crystallization rate of iPP but reduced the isothermal Avrami exponent. The crystallization temperature of the nanocomposites measured with nonisothermal crystallization was higher than that of plain iPP, and this indicated an enhanced crystallization rate. The nonisothermal Avrami exponent, like the isothermal exponent, decreased with the addition of organo‐MMT, and this suggested changes in the crystallite growth geometry. Subsequently, the tensile yield strength and the tensile modulus both increased, but the elongation at break and the notched Izod impact strength did not change significantly. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 3404–3415, 2003

Morphology of a melt crystallized iPP/HDPE/hydrogenated hydrocarbon resin blend

The structure, phase structure, morphology, crystallization and melting behavior of isotactic polypropylene (iPP) blended with a master batch (MB), formed by high density polyethylene and hydrogenated hydrocarbon resin (iPP/MB), have been in details investigated by using X-ray diffraction, optical microscopy and differential scanning calorimetry. It was found that the structure and morphology depend on crystallization conditions. A new family of α spherulites of iPP (type I spherulites) can be activated using appropriate crystallization conditions. Nucleation of these spherulites has been explained by using the approach of nucleus migration in polymer blends. Type I spherulites present specific morphological, kinetic and thermal behaviors. In particular it was found that the growth rate of type I spherulites, at a given T c, is higher than the growth rate of spherulites grown from plain iPP.

Nonisothermal crystallization of isotactic polypropylene blended with poly(α‐pinene). I. Bulk crystallization

The influence of a natural terpene resin, poly(α-pinene) (PαP), on the nonisothermal crystallization process of isotactic polypropylene (iPP) was investigated. The solidification process strongly depends on cooling rate, composition, and miscibility of the system. For the blends containing PαP up to 30 wt %, the overall nonisothermal crystallization rate is depressed with respect to plain iPP. This is probably the result of the diluting effect of the polyterpene because the two components are miscible. The 50/50 blend presents, instead, two amorphous phases: an iPP-rich phase and a PαP-rich phase. For this composition, solidification starts at temperatures higher than those for plain iPP and blends with lower PαP content, given that the diluting effect of PαP in the iPP-rich phase is counterweighted by an increased number of nuclei that originate from the polyterpene-rich phase domains. PαP also influences the morphology of iPP spherulites, which are spherical in plain iPP and become more irregular with increasing PαP content. The number and dimension of iPP spherulites depend on blend composition and miscibility of the components. Moreover, the nonisothermal crystallization kinetics of iPP/PαP blends was analyzed with the Ozawa equation. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 358–367, 2001

Nonisothermal crystallization of isotactic polypropylene blended with poly(?-pinene). I. Bulk crystallization

The influence of a natural terpene resin, poly(α-pinene) (PαP), on the nonisothermal crystallization process of isotactic polypropylene (iPP) was investigated. The solidification process strongly depends on cooling rate, composition, and miscibility of the system. For the blends containing PαP up to 30 wt %, the overall nonisothermal crystallization rate is depressed with respect to plain iPP. This is probably the result of the diluting effect of the polyterpene because the two components are miscible. The 50/50 blend presents, instead, two amorphous phases: an iPP-rich phase and a PαP-rich phase. For this composition, solidification starts at temperatures higher than those for plain iPP and blends with lower PαP content, given that the diluting effect of PαP in the iPP-rich phase is counterweighted by an increased number of nuclei that originate from the polyterpene-rich phase domains. PαP also influences the morphology of iPP spherulites, which are spherical in plain iPP and become more irregular with increasing PαP content. The number and dimension of iPP spherulites depend on blend composition and miscibility of the components. Moreover, the nonisothermal crystallization kinetics of iPP/PαP blends was analyzed with the Ozawa equation. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 358–367, 2001

Morphology, crystallization, and thermal behavior of isotactic polypropylene/propylene-g-styrene blends

Optical microscopy, differential scanning calorimetry, and small angle X-ray scattering techniques were used to study the influence of the crystallization conditions on morphology and thermal behavior of samples of binary blends constituted of isotactic polypropylene (iPP) and a novel graft copolymer of unsaturated propylene with styrene (uPP-g-PS) isothermally crystallized from melt, at relatively low undercooling, in a range of crystallization temperatures of the iPP phase. It was shown that, irrespective of composition, no fall in the crystallinity index of the iPP phase was observed. Notwithstanding, spherulitic texture and thermal behavior of the iPP phase in the iPP/uPP-g-PS materials were strongly modified by the presence of copolymer. Surprisingly, iPP spherulites crystallized from the blends showed size and regularity higher than that exhibited by plain iPP spherulites. Moreover, the amount of amorphous material located in the interspherulitic amorphous regions decreased with increasing crystallization temperature, and for a given crystallization temperature, with increasing uPP-g-PS content. Also, relevant thermodynamic parameters, related to the crystallization process of the iPP phase from iPP/uPP-g-PS melts, were found, composition dependent. The equilibrium melting temperature and the surface free energy of folding of the iPP lamellar crystals grown in the presence of uPP-g-PS content up to 5% (wt/wt) were, in fact, respectively slightly lower and higher than that found for the lamellar crystals of plain iPP. By further increase of the copolymer content, both the equilibrium melting temperature and surface free energy of folding values were, on the contrary, depressed dramatically. The obtained results were accounted for by assuming that the iPP crystallization process from iPP/uPP-g-PS melts could occur through molecular fractionation inducing a combination of morphological and thermodynamic effects. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 79: 2286–2298, 2001

Isotactic polypropylene/ethylene-co-propylene blends: effects of composition on rheology, morphology and properties of injection moulded samples

Melt rheology, phase morphology and properties of (30/70) isotactic polypropylene/ethylene-co-propylene (iPP/EPR) blends, containing EPR copolymer synthesised by means of a titanium based catalyst with very high stereospecific activity (EPRTi), were compared to that of (30/70) iPP/EPR blends containing EPR copolymer synthesised by using a traditional vanadium based catalyst (EPRV). It was found that both the melts are to be classified “negative deviation blends” and that, for such a composition ratio, the EPR represents the continuous phase. Scanning electron microscopy (SEM) investigations confirmed that the iPP component segregates in spherical-shaped domains with average size lower than 1.0μm. Such a fine degree of dispersion of the minor component in solid state is found independent of melt phase viscosity ratio and has been correlated with the interfacial tension between iPP and EPR phases. The presence of 70% of EPR copolymer dramatically interfered with the iPP crystallisation process, as strong reduction in iPP crystallinity index (Xc) values is shown by both the iPP/EPR blends. Comparatively lower Xc value is exhibited by iPP phase crystallised in presence of EPRTi copolymer. Differential scanning calorimetry (DSC) experiments revealed, in fact, that the crystallisation process of iPP phase and that of ethylenic sequences along EPRTi chains hinder each other. By small angle X-ray scattering (SAXS) it was shown that the iPP/EPRTi materials are characterised by amorphous inter-lamellar layer (La) considerably higher than that shown by the plain iPP and iPP phase crystallised in presence of EPRV copolymer. This strong La increase was mainly ascribed to entrapping of EPRTi crystalline domains into the iPP amorphous inter-lamellar layer. Wide angle X-ray scattering (WAXS) studies demonstrated that the EPR content determines the ratio between the apparent crystal size of iPP phase grown in a direction perpendicular to the (110) crystallographic plane and the apparent crystal size of iPP phase grown in a direction perpendicular to the (040) crystallographic plane. The higher the EPR content, the higher the thickness of the iPP lamellae in the direction of the radial growth of iPP spherulites, in agreement with increased nucleation density shown by DSC results. The different modulus performance shown by the materials at room temperature was accounted for by distinguishing between effects of phase crystallinity and super-molecular structure.

Nonisothermal Crystallization of Isotactic Polypropylene Blended with Poly(α-pinene). 2. Growth Rates

The influence of the poly(α-pinene), a natural polyterpene, on growth rate of isotactic polypropylene spherulites was investigated using a dynamic solidification method. It was shown that the use of a constant cooling rate allows the obtainment of reliable growth rate data and permits one to enormously enlarge the range of temperature where crystallization data can be measured. The presence of poly(α-pinene) slows the radial growth rate of polypropylene crystals for all blend compositions investigated (0−50% poly(α-pinene)). Analysis of the experimental data with the Hoffman−Lauritzen model showed that a regime II−III transition is present for plain iPP and for the iPP/PαP miscible blends and that the transition temperature decreases with poly(α-pinene) content.

Morphology, crystallization, and thermal behavior of isotactic polypropylene/polystyrene blends: Effects of the addition of a graft copolymer of propylene with styrene

Optical microscopy, differential scanning calorimetry, and small-angle X-ray scattering techniques were used to study the influence of crystallization conditions on the morphology and thermal behavior of samples of ternary blends constituted by isotactic polypropylene (iPP), atactic polystyrene (aPS), and a novel graft copolymer of unsaturated propylene with styrene (uPP-g-PS) with the purpose of assessing the uPP-g-PS capability to act as a compatibilizer for iPP/aPS materials. It was shown that the presence of the uPP-g-PS copolymer affects the interfacial tension between the iPP and aPS phases in the melt state, with the aPS particle size and the particle-size distribution being, in fact, strongly modified. In samples of iPP/aPS/uPP-g-PS blends, isothermally crystallized from the melt at a relatively low undercooling in a range of the crystallization temperature of the iPP phase, the addition of the uPP-g-PS copolymer induced a drastic change both in the aPS mode and the state of dispersion and in the iPP spherulitic texture and inner structure of the spherulite fibrils. In particular, the phase structure developed in the iPP/aPS/uPP-g-PS materials was characterized by a crystalline lamellar thickness of the iPP phase comparable to that shown by the plain iPP. The extent of the induced modifications, that is, the degree of compatibilization achieved, resulted in a combined effect of composition and undercooling. Also, relevant thermodynamic parameters of the iPP phase, such as the equilibrium melting temperature (Tm) and the folding surface free energy (ςe) of the lamellar crystals, were found to be influenced by the presence of the uPP-g-PS copolymer. A linear decrease of the Tm and ςe values with increasing uPP-g-PS content was, in fact, observed. Such results have been accounted for by an increase of the presence of defects along the iPP crystallizable sequences and by the very irregular and perturbed surface of the crystals with increasing copolymer content. The observed decrease in Tm values revealed, moreover, that, in the iPP/aPS/uPP-g-PS blends, the iPP crystal growth occurs under comparatively lower undercooling, in line with higher crystalline lamellar thickness shown by SAXS investigation. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 72: 1429–1442, 1999

Crystallization of isotactic polypropylene/natural terpene resins blends

The influence of two natural terpene resins on the morphology, phase structure and isothermal crystallization process of iPP was investigated by optical (OM) and electron microscopy (SEM) and differential scanning calorimetry (DSC). It was found that in dependence on temperature, composition and chemical nature of the resin, one, two or three phases can be present. The isothermal spherulite growth rate and overall crystallization rate of the blends are depressed compared to plain iPP. This depression was attributed to the increase of the energies relative to the transport of macromolecules in the melt and to the formation of nuclei of critical size, following the addition of resin. The presence of resin seems to lead to the formation of more regular folding surfaces.

Isotactic polypropylene/ethylene-co-propylene blends: effects of the copolymer microstructure and content on rheology, morphology and properties of injection moulded samples

Melt rheology, phase morphology and properties of (60/40) isotactic polypropylene/ethylene-co-propylene (iPP/EPR) blends containing EPR copolymer synthesized by means of a titanium based catalyst with very high stereospecific activity (EPR Ti) were compared to that of (60/40) iPP/EPR blends containing EPR copolymer synthesized by using a traditional vanadium based catalyst (EPR V). It was found that both the melts are to be classified `negative deviation blends' and that for such a composition the copolymer represents the dispersed phase. SEM investigations showed in fact that the EPR phase segregate in to irregular shaped domains localized in the core of the bars, the dispersion coarseness increasing with an increase in the ratio between the EPR viscosity and iPP viscosity. At low temperatures the iPP impact strength was improved, comparatively better properties being shown by the blends containing the EPR V copolymer. The different behaviour of EPR Ti and EPR V phases as impact modifiers was ascribed to their both different dispersion degree and microstructure. For test temperatures higher than EPR T g the ethylenic crystallinity exhibited by the EPR Ti phase was considered to induce toughening deterioration by decreasing tie molecules density in the EPR Ti domains, notwithstanding the beneficial effect of the ethylenic build-up. The reduction in iPP crystallinity index ( X c) value found for iPP/EPR Ti blends indicated a strong interference of the crystallization process of EPR Ti ethylenic sequences with the iPP crystallization process. SAXS investigations revealed in addition that the iPP/EPR Ti materials are characterized by an amorphous interlamellar layer ( L a) higher than that shown by plain iPP and iPP phase crystallized in presence of EPR V copolymer. Taking also into account results obtained studying blends containing lower content of such EPR phases composition effects were investigated. WAXS studies showed that with increasing copolymer content the ratio between the apparent crystal size of iPP phase grown in a direction perpendicular to the (110) crystallographic plane [ D (110)] and that grown in direction perpendicular to the (040) crystallographic plane [ D (040)] increases. Such an effect was related to an increased iPP nucleation density according to DSC results.

Yield and plastic resistance of α-crystals of isotactic polypropylene

Yield behaviour and plastic resistance of the (100)[001] chain slip system in α-crystals of isotactic polypropylene (iPP) were studied in samples of biaxially oriented films of plain iPP and blends of iPP with hydrogenated oligo(cyclopentadiene) (HOCP). Due to the orientation process the films investigated exhibit sharp and nearly one-component texture with the (010) plane parallel to the film surface and the chain direction parallel to the direction of final drawing (transverse direction, TD). The films were studied in tension at various angles with respect to the orientation direction. It was found that the yield stress obeys the Coulomb yield criterion, provided that the angle between the chain orientation axis and tensile axis is within the range of 30–50°. The results suggest that the (100)[001] chain slip is active as a single deformation mechanism in this range of sample orientation. The critical resolved shear stress necessary to activate this slip, τ c, was determined for iPP and iPP/HOCP blend samples. It was also found that the slip process is sensitive to the stress normal to the slip plane, similarly to the slip processes observed in linear polyethylene crystals. The value of τ c determined for plain iPP was 22.6 MPa, while for the 8:2 blend its value increased to 35.5 MPa. The increase is caused most probably by the presence of a small amount of HOCP molecules incorporated within iPP crystals, as well as by the layers of higher concentration of HOCP located at crystal–amorphous interfaces, which both cause immobilization of a part of dislocations and consequently an increase of the yield stress observed in the blend samples. The third probable cause of the increase of yield stress in blends may be an increase of the glass transition temperature of the amorphous phase of iPP in the blend, as compared with plain iPP samples.

Isotactic polypropylene/polymethylmethacrylate blends: Effects of addition of propylene-graft-methylmethacrylate copolymer

A novel graft copolymer of unsaturated propylene with methyl methacrylate (uPP-g-PMMA) was added to binary blends of isotactic polypropylene (iPP) and atactic poly(methyl methacrylate) (aPMMA) with a view to using such a copolymer as a compatibilizer for iPP/aPMMA materials. Optical microscopy (OM), scanning electron microscopy, wide angle X-ray scattering (WAXS), and small angle X-ray scattering (SAXS) techniques showed that, contrary to expectation, the uPP-g-PMMA addition does not provide iPP/aPMMA compatibilized materials, irrespective of composition. As a matter of fact the degree of dispersion of the minor component achieved following the addition of uPP-g-PMMA copolymer remained quite comparable to that exhibited by binary blends of iPP and aPMMA with no relevant evidence of adhesion or interconnection between the phases. On the other hand the crystalline texture was deeply modified by the copolymer presence. With increasing uPP-g-PMMA content (w/w) the iPP spherulites were found to become more open and coarse and the dimensions and number per unit area of the amorphous interspherulitic contact regions were found to increase. According to such OM results the copolymer uncrystallizable sequences were assumed to be mainly located in interfibrillar and interspherulitic amorphous contact regions. SAXS analysis demonstrated that the phase structure developed in the iPP/aPMMA/uPP-g-PMMA blends is characterized by values of the long period increasing linearly with increasing copolymer content (w/w). Assuming a two phase model for the iPP spherulite fibrillae, constituted of alternating parallel crystalline lamellae and amorphous layers, the lamellar structure of the iPP phase in the ternary blends is characterized by crystalline lamellar thickness (Lc) and an interlamellar amorphous layer (La) higher than that shown by plain iPP and Lc and La values both increased with increasing uPP-g-PMMA content (w/w). Such SAXS results have been accounted for by assuming that a cocrystallization phenomenon between propylenic sequences of the uPP-g-PMMA copolymer and iPP occurs. The development of the iPP lamellar structure in the iPP/aPMMA/uPP-g-PMMA blends was thus modeled hypothesizing that during such a cocrystallization process copolymer PMMA chains with comparatively lower molecular mass remain entrapped into the iPP interlamellar amorphous layer forming their own domains. Moreover, evidence of strong correlations between the crystallization process of the uPP-g-PMMA copolymer and the iPP crystallization process was shown also by differential scanning calorimetry and WAXS experiments. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 66: 2377–2393, 1997

Isotactic polypropylene/polystyrene blends: Effects of the addition of a graft copolymer of propylene with styrene

A novel graft copolymer of unsaturated propylene with styrene (uPP-g-PS) was added to binary blends of isotactic polypropylene (iPP) and atactic polystyrene (aPS) with a view to using such a copolymer as compatibilizer for iPP/aPS materials. Differential scanning calorimetry, optical microscopy, scanning electron microscopy (SEM), wide angle X-ray scattering, and small angle X-ray scattering (SAXS) techniques have been carried out to investigate the phase morphology and structure developed in solution-cast samples of iPP/aPS/uPP-g-PS ternary blends. It was found that the uPP-g-PS addition can provide iPP/aPS-compatibilized materials and that the extent of the achieved compatibilization is composition-dependent. Blends of iPP and aPS exhibited a coarse domain morphology that is characteristic of immiscible polymer systems. By adding 2% (wt/wt) of uPP-g-PS copolymer a very broad particle-size distribution was obtained, even though the particles appeared coated by a smooth interfacial layer, as expected according to a core–shell interfacial model. With increasing uPP-g-PS content (5% wt/wt), a finer dispersion degree of particles, together with morphological evidence of interfacial adhesion, was found. With further increase of uPP-g-PS amount (10% wt/wt) the material showed such a homogeneous texture that neither domains of dispersed phase nor holes could be clearly detected by SEM. The type of interface developed in such iPP/aPS/uPP-g-PS blends was accounted for by an interfacial interpenetration model. The iPP crystalline texture, size, neatness, and regularity of iPP spherulites crystallized from iPP/aPS/uPP-g-PS blends were found to decrease when the copolymer content was slightly increased. Assuming, for the iPP spherulite fibrillae, a two-phase model constituted by alternating parallel crystalline lamellae and amorphous layers, it was shown by SAXS that the phase structure generated in iPP/aPS/uPP-g-PS blends is characterized by crystalline lamellar thickness (Lc) and interlamellar amorphous layer thickness (La) higher than that shown by plain iPP; the higher the copolymer content, the higher the Lc and La. It should be remarked that considerably larger increases have been found in La values. Such SAXS results have been accounted for by assuming that a cocrystallization phenomenon between propylenic sequences of the uPP-g-PS copolymer and iPP occurs and that during such a process PS chains grafted into copolymer sequences remain entrapped in iPP interlamellar amorphous layers, where they form their own separate domains. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 65:1539–1553, 1997

Isotactic polypropylene/polystyrene blends: Effects of the addition of a graft copolymer of propylene with styrene

A novel graft copolymer of unsaturated propylene with styrene (uPP-g-PS) was added to binary blends of isotactic polypropylene (iPP) and atactic polystyrene (aPS) with a view to using such a copolymer as compatibilizer for iPP/aPS materials. Differential scanning calorimetry, optical microscopy, scanning electron microscopy (SEM), wide angle X-ray scattering, and small angle X-ray scattering (SAXS) techniques have been carried out to investigate the phase morphology and structure developed in solution-cast samples of iPP/aPS/uPP-g-PS ternary blends. It was found that the uPP-g-PS addition can provide iPP/aPS-compatibilized materials and that the extent of the achieved compatibilization is composition-dependent. Blends of iPP and aPS exhibited a coarse domain morphology that is characteristic of immiscible polymer systems. By adding 2% (wt/wt) of uPP-g-PS copolymer a very broad particle-size distribution was obtained, even though the particles appeared coated by a smooth interfacial layer, as expected according to a core–shell interfacial model. With increasing uPP-g-PS content (5% wt/wt), a finer dispersion degree of particles, together with morphological evidence of interfacial adhesion, was found. With further increase of uPP-g-PS amount (10% wt/wt) the material showed such a homogeneous texture that neither domains of dispersed phase nor holes could be clearly detected by SEM. The type of interface developed in such iPP/aPS/uPP-g-PS blends was accounted for by an interfacial interpenetration model. The iPP crystalline texture, size, neatness, and regularity of iPP spherulites crystallized from iPP/aPS/uPP-g-PS blends were found to decrease when the copolymer content was slightly increased. Assuming, for the iPP spherulite fibrillae, a two-phase model constituted by alternating parallel crystalline lamellae and amorphous layers, it was shown by SAXS that the phase structure generated in iPP/aPS/uPP-g-PS blends is characterized by crystalline lamellar thickness (Lc) and interlamellar amorphous layer thickness (La) higher than that shown by plain iPP; the higher the copolymer content, the higher the Lc and La. It should be remarked that considerably larger increases have been found in La values. Such SAXS results have been accounted for by assuming that a cocrystallization phenomenon between propylenic sequences of the uPP-g-PS copolymer and iPP occurs and that during such a process PS chains grafted into copolymer sequences remain entrapped in iPP interlamellar amorphous layers, where they form their own separate domains. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 65:1539–1553, 1997

Orientation and properties of sequentially drawn films of an isotactic polypropylene/ hydrogenated oligocyclopentadiene blend

Films of isotactic polypropylene (iPP) and a blend of iPP and hydrogenated oligocyclopentadiene (HOCP) oriented by one-way (uniaxial) and two-way (sequential biaxial) drawing were studied. The mechanical and thermal properties of the oriented iPP and iPP/HOCP blends as well as orientation behaviour were investigated by means of mechanical tests, d.s.c. and small- and wide-angle X-ray scattering including the pole figures technique. It was found that drawing of iPP/HOCP blends to a high strain leads to the formation of highly oriented films having mechanical properties greatly improved compared to plain iPP oriented under the same conditions. The studies revealed in one-way drawn samples the multicomponent texture with chain axis, c, oriented in the machine direction, MD, for all texture components. The lamellae are oriented with normals parallel to the c direction. Due to differences in the amorphous phase content the texture in the blend samples is less developed than in deformed plain iPP. The subsequent drawing along the transverse direction, TD, leads to the reorientation of the c axis towards the TD, the sharpening of texture and the destruction of the lamellar structure. It was found that the major deformation mechanisms active in iPP and iPP/HOCP blends are: the crystallographic slips systems of (010)[001], (100)[001], (110)[001] and {110} twinning modes. In addition the interlamellar sliding is active as the main deformation mechanism in the amorphous phase. The (010)[001] system is the easiest of the slip systems active and dominates the other mechanisms.

Small angle scattering study of the structure of isotactic polypropylene-hydrogenated oligo(cyclopentadiene) blends

Blends of isotactic polypropylene ( iPP) and hydrogenated oligo cyclopentadiene (HOCP) have been studied by means of small angle X-ray scattering in the temperature range 70–160°C. The structure of blends containing less than 25% HOCP is very similar to the one of plain iPP, i.e. lamellae whose thickness increases by increasing the temperature. Blends containing more than 25% HOCP are characterized by two kinds of lamellae formed by layers of iPP and amorphous material rich in iPP and in HOCP, respectively. The crystallizable iPP present in both phases crystallizes from the melt, in analogy to what happens in HDPE/HOCP blends and in agreement with the values of the crystallinity referred to the crystallizable polymer, that is almost constant with composition for both blends.

Melt rheology, phase structure and impact properties of injection-moulded samples of isotactic polypropylene/ethylene-propylene copolymer (iPP/EPR) blends: influence of molecular structure of EPR copolymers

Isotactic polypropylene (iPP) based blends containing as second component ethylene-propylene copolymers (EPR) having, for constant propylene (C 3) content (wt/wt), different average molecular masses ( M ̄ w and/or M ̄ n ) and, for constant average molecular mass, different molecular mass distributions ( MMD) were investigated. The study was undertaken to establish the influence of the melt phase viscosity ratio μ in determining the average particle size of the EPR phase in the vicinity of the minimum expected according to the Taylor-Tomotika theory for the average particle size versus log μ function, when μ is about equal to unity (in previous studies we have in fact reached μ values far above 1). Moreoever, we also report the effects of molecular mass and molecular mass distribution of the EPR phase on the melt rheological behaviour of iPP/EPR blends, on the mode and state of dispersion of the EPR phase in the melt, as well as, in the solid state after iPP crystallization in injection moulded samples, on the crystalline lamellar thickness and the thickness of the amorphous interlayer of iPP phase, and finally on the impact properties of blend materials. It should be pointed out that the apparent viscosity of all the iPP/EPR blends investigated is expected to obey the logarithm additivity rule that applies at constant temperature and shear rate. The application of the Cross-Bueche equation revealed that the zero-shear viscosity η o of these iPP/EPR blends deviates positively from the logarithm additivity rule. Assuming that the crystallization of the iPP phase freezes the morphology of the EPR phase, a strict correlation is confirmed to exist between the values of EPR particle size and EPR particle size range, as measured by scanning electron microscopy on samples in the solid state, and μ value. The number average particle diameter ( D ̄ n ) and the particle size range of the EPR phase ( D) are found to increase with increasing μ value as expected according to the Taylor-Tomotika theory. Finally, when the iPP phase crystallizes from its blends with EPR under non-isothermal conditions, the phase structure developed in the blends is characterized by lamellar thickness and interlamellar amorphous layer thickness, respectively, lower and higher than that shown by plain iPP.

Homogeneous nucleation in polypropylene and its blends by small-angle light scattering

The homogeneous primary nucleation of spherulitic crystallization in isotactic polypropylene (iPP) and its blends with atactic polypropylene (aPP) was studied. Bulk samples of iPP and iPP/aPP blends were crystallized isothermally under high undercoolings (∼ 100°C) using a specially designed crystallization cell. In crystallized samples the fifth-order average spherulite radius was determined on the basis of small-angle light scattering measurements. The parameters for homogeneous primary nucleation were obtained from the fitting of curves calculated on the basis of theoretical predictions for regime III to the experimental data. For that purpose the theoretical background for homogeneous nucleation in polymer blends and for small-angle light scattering by an assembly of impinged spherulites was developed. The results obtained for homogeneous nucleation in plain iPP are in very good agreement with theoretical predictions. For iPP/aPP blends it was found that the main reason for depression of nucleation in blends is the additional energy barrier connected with the separation of components of a homogeneous blend during crystallization of one of the components (iPP).