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 (L_c) and interlamellar amorphous layer thickness (L_a) higher than that shown by plain iPP; the higher the copolymer content, the higher the L_c and L_a. It should be remarked that considerably larger increases have been found in L_a 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/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 (L_c) and an interlamellar amorphous layer (L_a) higher than that shown by plain iPP and L_c and L_a 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     

Optimizing the balance between impact strength and stiffness in polypropylene/elastomer blends by incorporation of a nucleating agent

Isotactic polypropylene (iPP) blends were prepared with two different thermoplastic elastomers, a triblock copolymer styrene–ethylene butylene–styrene (SEBS) and a metallocenic ethylene‐octene copolymer (EO). The mechanical properties and morphology of blends with 0–50 wt% elastomer were studied to determine the influence of the presence of the elastomer on the improvement of toughness. The addition of a nucleating agent as a third component exerted a significant effect on the overall properties. Dynamic mechanical properties, flexural modulus, and impact strength as well as morphology were studied for nucleated and nonnucleated iPP/SEBS and iPP/EO blends. The improvement of impact properties found in binary blends was accompanied by a decrease in stiffness. However, the addition of the nucleating agent provided a good balance between impact strength and stiffness. From the results, SEBS was determined to be a better impact modifier for iPP than EO. The nucleated iPP/SEBS blends demonstrated improved mechanical properties compared with both the nucleated iPP/EO blends and the nonnucleated blends. POLYM. ENG. SCI., 48:80–87, 2008. © 2007 Society of Plastics Engineers     

Microstructural characteristics of glass bead‐ and wollastonite‐filled isotactic‐polypropylene composites modified with thermoplastic elastomers

Microstructural characteristics of isotactic‐polypropylene/glass bead (iPP/GB) and iPP/wollastonite (iPP/W) composites modified with thermoplastic elastomers, poly(styrene‐b‐ethylene‐co‐butylene‐b‐styrene) copolymer (SEBS) and corresponding block copolymer grafted with maleic anhydride (SEBS‐g‐MA), were investigated. Scanning electron microscopy (SEM), differential scanning calorimetry (DSC), and dynamic mechanical analyses (DMA) showed that the iPP/SEBS and iPP/SEBS‐g‐MA blends were partially compatible two‐phase systems. Well‐dispersed spherical GB and acicular W particles without evidence of interfacial adhesion were observed in the iPP/GB and iPP/W binary composites respectively. Contrary to the blends, melt flow rates of the iPP/GB and PP/W composites decreased more with SEBS‐g‐MA than with SEBS because of enhanced interfacial adhesion with SEBS‐g‐MA elastomer. The SEM analyses showed that the ternary composites containing SEBS exhibited separate dispersion of the rigid filler and elastomer particles (i.e., separate microstructure). However, SEBS‐g‐MA elastomer not only encapsulated the spherical GB and acicular W particles completely with strong interfacial adhesion (i.e., core‐shell microstructure) but also dispersed separately throughout iPP matrix. In accordance with the SEM observations, the DSC and DMA revealed quantitatively that the rigid filler and SEBS particles in iPP matrix acted individually, whereas the rigid filler particles in the ternary composites containing SEBS‐g‐MA acted like elastomer particles because of the thick elastomer interlayer around the filler particles. The Fourier transform infrared analyses revealed an esterification reaction inducing the strong interfacial adhesion between the SEBS‐g‐MA phase and the filler particles. POLYM. COMPOS., 31:1265–1284, 2010. © 2009 Society of Plastics Engineers     

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     

Influence of phase modifiers on morphology and properties of thermoplastic elastomers prepared from ethylene propylene diene rubber and isotactic polypropylene

A series of thermoplastic elastomers (TPEs) were prepared from a binary blend of ethylene propylene diene rubber (EPDM) and isotactic polypropylene (iPP) using different types of phase modifiers. The influence of sulphonated EPDM, maleated EPDM, styrene‐ethylene‐co‐butylene‐styrene block copolymer, maleated PP, and acrylated PP as phase modifiers showed improved physico‐mechanical properties (like maximum stress, elongation at break, moduli, and tension set). Scanning electron and atomic force microscopy studies revealed better morphologies obtained with these phase modified EPDM‐iPP blends. The dependence of the phase modifier type and concentration was optimized with respect to the improvement in physical properties and morphology of the blends. Physical properties, dynamic mechanical properties, and morphology of these blends were explained with the help of interaction parameter, melt viscosity, and crystallinity of the blends. Theoretical modeling showed that Kerner, Ishai‐Cohen, and Paul models predicted the right morphology–property correlation for the prepared TPEs. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers.     

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 (T_m) and the folding surface free energy (ς_e) of the lamellar crystals, were found to be influenced by the presence of the uPP‐g‐PS copolymer. A linear decrease of the T_m and ς_e 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 T_m 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     

Blends of propylene-ethylene and propylene-1-butene random copolymers: I. Morphology and structure

Samples of propylene-ethylene (EP) and propylene-(1-butene) (BP) random copolymers with various comonomer content (2-3.1 wt% ethylene, 9.9 wt% 1-butene), were melt-mixed in Brabender internal mixer at various compositions (25/75, 50/50, 75/25). Films of copolymers and blends, as well as of a homopolymer sample (iPP), obtained by compression moulding and with different thermal history were characterized by optical and scanning electron microscopy (OM, SEM), small-angle light scattering (SALS), small- and wide angle X-ray scattering (SAXS, WAXS) and differential scanning calorimetry (DSC). It was found that all copolymers and blends studied crystallized exclusively in monoclinic α-modification forming spherulitic structure in a very broad undercooling range. The average size of spherulites is smaller in the copolymer containing 1-butene as compared to those containing ethylene or to iPP homopolymer, due to enhanced heterogeneous nucleation in BP copolymer. SEM microscopic observations demonstrated that EP and BP copolymers were miscible at all examined compositions and form homogeneous blends. Structural and morphological analysis indicated that the comonomer units are incorporated into growing crystallites in both EP and BP copolymers, while the non-crystallizing material is rejected out of the crystallites. For small concentrations of comonomer some of non-crystallizing species are pushed ahead of the front of growing spherulite into interspherulitic regions. For higher comonomer concentration these species are mostly trapped in intraspherulitic regions. Melting behavior of copolymers reflects the incorporation of comonomer into crystalline phase: melting temperature and crystallinity degree decrease in copolymers and blends as compared to plain iPP.     

Isotactic polypropylene toughened with poly(acrylonitrile–butadiene–styrene): Compatibilizing role of maleic anhydride grafted polypropylene

The β‐nucleating activity and toughening effect of acrylonitrile–butadiene–styrene (ABS) graft copolymer on isotactic polypropylene (iPP) and the compatibilizing role of maleic anhydride grafted polypropylene (PP‐g‐MAH) on the iPP/ABS blends were investigated. The results show that ABS can induce the formation of β‐crystal in iPP, and its β‐nucleating efficiency depends on its concentration and dispersibility. The relative content of β‐crystal form is up to 36.19% with the addition of 2% ABS. The tensile and impact properties of the iPP were dramatically enhanced by introducing ABS. The incorporation of PP‐g‐MAH into the iPP/ABS blends inhibits the formation of β‐crystal. The crystallization peaks of the blends shift toward higher temperature, due to the heterogeneous nucleation effect of PP‐g‐MAH on iPP. The toughness of iPP/ABS blends improved due to favorable interfacial interaction resulting from the compatibilization of PP‐g‐MAH is significantly better than the β‐crystal toughening effect induced by ABS. POLYM. ENG. SCI., 59:E317–E326, 2019. © 2019 Society of Plastics Engineers     

Influence of a nucleating agent on the crystallization behaviour of isotactic polypropylene and elastomer blends

The influence of a nucleating agent on the crystallization behaviour of isotactic polypropylene (iPP), in their blends with poly(styrene-b-ethylene butylene-b-styrene) (SEBS), and a metallocenic ethylene-octene copolymer (EO) was investigated by DSC, optical microscopy and real-time small and wide angle X-ray scattering (SAXS and WAXS) experiments using synchrotron radiation. In non-nucleated iPP/SEBS blends, the crystallization of the iPP matrix occurred in the presence of the styrenic domains which induced a nucleating effect on the process, as observed in the synchrotron experiments. The metallocenic elastomer did not affect the crystallization behaviour of iPP in the iPP/EO blends in non-isothermal experiments, however, the development of crystallinity in the elastomer was restricted. In the nucleated isotactic polypropylene/elastomer blends a significant increase in the crystallinity and the crystallization rate of the iPP matrix was observed due to the presence of the nucleating agent. However, the nucleating efficiency of the additive was strongly affected by the nature and content of the elastomeric component. The nucleating agent efficiency was higher in the presence of the ethylene-octene component than the styrenic elastomer.     

Interfacial crystallization and its mechanism in in-situ dynamically vulcanized iPP/POE blends

The effect of in-situ crosslinking of poly (ethylene-co-octene) (POE) rubber phase on the interfacial crystallization of isotactic polypropylene (iPP) in dynamically vulcanized iPP/POE blends was studied. The results showed that in situ crosslinking of POE obviously increased the interfacial crystallization of iPP in the dynamically vulcanized blends, comparing with that of pure iPP and the unvulcanized blend. The interfacial crystallization of iPP was further increased with the increase in crosslink degree. After annealing, the obvious interfacial crystallization was still obtained in the blend with high crosslink degree. Based on the fluctuation assisted nucleation mechanism in solution blended iPP/polyolefin block copolymer (OBC) blends, we proposed for the first time the interfacial crystallization mechanism in dynamically vulcanized blends: the oriented chains of iPP formed by concentration fluctuation at the interface during phase separation or shearing stress during melt mixing can be maintained because of the in situ crosslinking of POE phase, resulting in the enhancement of nucleation density at the iPP/POE interface. Our study proposes a new interfacial crystallization mechanism, and provides guidance for the preparation of high performance thermoplastic vulcanizates (TPVs) product by tailoring the interfacial crystallization of TPVs.     

Structure and properties of new reversibly crosslinked iPP/LDPE blends

Reversibly crosslinked blends of isotactic polypropylene and low density polyethylene (iPP/LDPE) were prepared in the presence of crosslinking agents using reactive extrusion. The structure and properties of the modified blends were investigated by means of wide-angle X-ray scattering (WAXS), differential scanning calorimetry (DSC), and macro- and micro-mechanical measurements. The crystallinity of the modified samples (LDPE, iPP, and their blends) does not seem to be so much affected by the crosslinking process. Results show that the microhardness of the iPP/LDPE blends notably increases with the iPP content. The micromechanical properties of the modified blends only improve slightly as a consequence of the crosslinking process. In the iPP samples, and also in the iPP/LDPE blends, this process gives rise to the appearance of new, crystalline ethylenic chains, as evidenced by the calorimetric measurements. Furthermore, the impact strength of the modified materials is improved as compared with that of the original ones, while some of the crosslinked blends show a ductile fracture behavior. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

The supermolecular structure of isotactic polypropylene/atactic polystyrene blends

The supermolecular structure of binary isotactic polypropylene/atactic polystyrene (iPP/PS) injection‐molded blends were studied by wide‐angle X‐ray diffraction, differential scanning calorimetry, and optical microscopy. The combination of different methods gives a possibility of analysis of relation between the phase transformation in polypropylene and crystallization parameters. Effect of compatibilization of poly(styrene‐b‐ethylene‐co‐butylene‐b‐styrene) grafted with maleic anhydride (SEBS‐g‐MA) block copolymers in the iPP/PS blends on the structure, nucleation, crystal growth, solidification, and the phase morphology was analyzed. We found that the β‐crystallization tendency of polypropylene matrix can be enhanced by adding atactic polystyrene. However, the incorporation of SEBS‐g‐MA into iPP/PS blends resulted in an important decrease in β‐content of iPP. It is evident that the presence of compatibilizing agent caused a very significant reduction of the α‐spherulite growth rates and the crystal conversion as well as increases of half‐time crystallization in comparison with the iPP/PS systems. The relation between kinetic parameters of crystallization process and polymorphic structure of iPP in blend systems has been satisfactorily explained. Moreover, a strong effect of processing parameters on the β‐phase formation was observed. The results clearly show that at a higher temperature of mold and lower injection speed, the amount of β‐phase of iPP matrix slightly decreases. POLYM. ENG. SCI., 2011. © 2011 Society of Plastics Engineers     

Effects of SBS on phase morphology of iPP/aPS blends

The supermolecular structure of binary isotactic polypropylene/poly(styrene‐b‐butadiene‐h‐styrene) (iPP/SBS) and isotactic polypropylene/atactic polystyrene (iPP/aPS) compression molded blends and that of ternary iPP/aPS/SBS blends were studied by optical microscopy, scanning and transmission electron microscopy, wide‐angle X‐ray diffraction and differential scanning calorimetry. Nucleation, crystal growth, solidification and blend phase morphology are affected by the addition of amorphous components (SBS and aPS). As a compatiblizer in immiscible iPP/aPS blends, SBS formed interfacial layer between dispersed honeycomb‐like aPS/SBS particles and the iPP matrix, thus influencing the crystallization process in iPP. The amount of SBS and aPS, and compatibilizing efficiency of SBS, determine the size of dispersed aPS, SBS, and aPS/SBS particles and, consequently, the final blend phase morphologies: well‐developed spherulitic morphology, cross‐hatched structure with blocks of sandwich lamellae and co‐continuous morphology. The analysis of the relationship between the size of spherulites and dispersed particles gave the criterion relation, which showed that, in the case of a well‐developed spherulitization, the spherulites should be about fourteen times larger than the incorporated dispersed particles; i.e. to be large enough to engulf dispersed inclusions without considerable disturbing of the spherulitic structure.     

Morphology and thermal properties in the binary blends of poly(propylene-co-ethylene) copolymer and isotactic polypropylene with polyethylene

The morphology and thermal properties of isothermal crystallized binary blends of poly(propylene-co-ethylene) copolymer (PP-co-PE) and isotactic polypropylene (iPP) with low molecular weight polyethylene (PE) were studied with differential scanning calorimeter (DSC), dynamic mechanical analysis (DMA), polarized optical microscopy (POM) and wide-angle X-ray diffraction (WAXD). In PP-co-PE/PE binary blends, however, the connected PE acted as a phase separating agent to promote phase separation for PP-co-PE/PE binary blends during crystallization. Therefore, the thermal properties of PP-co-PE/PE presented double melting peaks of PE and a single melting temperature of PP during melting trace; on the other hand, at cooling trace, the connected PE promoted crystallization rate because of enhanced segmental mobility of PP-co-PE during crystallization. At isothermal crystallization temperature between the melting points of iPP and PE, the binary blend was a crystalline/amorphous system resulting in persistent remarkable molten PE separated domains in the broken iPP spherulite. And then, when temperature was quenched to room temperature, the melted PE separated domains were crystallized that presented a crystalline/crystalline system and formed the intra-spherulite segregation morphology: these PE separated domains/droplet crystals contained mixed diluent PE with connected PE components. On the other hand, in the iPP/PE binary blends, the thermal properties showed only single melting peaks for both PE and iPP. Moreover, the glass transition temperature of iPP shifted to lower temperature with increasing PE content, implying that the diluent PE molecules were miscible with iPP to form two interfibrillar segregation morphologies: iPP-rich and PE-rich spherulites. In this work, therefore, we considered that the connected PE in PP-co-PE functioned as an effective phase separating agent for PP and diluent PE may be due to the miscibility between connected PE and diluent PE larger than that between PP and dispersed PE.     

Isotactic polypropylene/ethylene‐co‐propylene blends: Influence of the copolymer microstructure on rheology,morphology, and properties of injection‐molded samples

Meltrheological behavior, phase morphology, and impact properties of isotactic‐polypropylene (iPP)‐based blends containing ethylene–propylene copolymer (EPR) synthesized by means of a titanium‐based catalyst with very high stereospecific activity (EPR_Ti) were compared to those of iPP/EPR blends containing EPR copolymers synthesized by using a traditional vanadium‐based catalyst (EPR_V). The samples of EPR copolymers were synthesized ad hoc. They were characterized by comparable propylene content, average molecular masses, and molecular mass distribution in order to assess the effects of distribution of composition and sequence lengths of the structural units on the structure–properties correlations established in the melt and in the solid state while studying different iPP/EPR pairs.^1–5 Differential scanning calorimetry, (DSC), wide‐angle X‐ray spectroscopy (WAXS), small‐angle X‐ray (SAXS), and scanning electron microscopy (SEM) investigations showed that the EPR_Ti chain is characterized by the presence of long ethylenic sequences with constitutional and configurational regularity required for crystallization of the polyethylene (PE) phase occurring, whereas a microstructure typical of a random ethylene–propylene copolymer was exhibited by the EPR_V copolymer. The different intra‐ and intermolecular homogeneity shown by such EPR phases was found to affect their melt rheological behavior at the temperatures of 200 and 250°C; all the EPR_Ti dynamic–viscoelastic properties resulting were lower than that shown by the EPR_V copolymer. As far as the melt rheological behavior of the iPP/EPR_V and iPP/EPR_Ti blends was concerned, both the iPP/EPR pairs are to be classified as “negative deviation blends” with G′ and G" values higher than that shown by the plain components. The extent of the observed deviation in the viscosity values and of the increase in the amounts of stored and dissipated energy shown by such iPP/EPR pairs was found to be dependent on copolymer microstructure, being larger for the melts containing the EPR_Ti copolymer. The application of the Cross–Bueche equation also confirmed that, in absence of shear, the melt phase viscosity ratio is the main factor in determining the viscosity of iPP/EPR blends and their viscoelastic parameters. The general correlation established between EPR dispersion degree (range of particle size and number‐average particle size), as determined in injection‐molded samples, and melt phase viscosity ratio (μ) was ratified; the type of dependence of EPR size upon μ value was in qualitative agreement with the prediction of the Taylor–Tomotika theory. Contrary to expectation,^1–5 for test temperature close to iPP T_g, EPR_V particles ranging in size between 0.75 and 1.25 μm resulted and were more effective than EPR_Ti particles, ranging in size between 0.25 and 0.75 μm, in promoting multiple craze formation. Also taking into account the SAXS results, revealed that the molecular superstructure (i.e., crystalline lamellar thickness and amorphous interlayer) of the iPP matrix is unaffected by both the presence of EPR_Ti and EPR_V phase. The above finding was related to the ethylenic crystallinity degree shown by the EPR_Ti copolymer. In particular, such a degree of crystallinity was supposed to deteriorate toughening by decreasing the tie molecules density in the EPR_Ti domains, notwithstanding the beneficial effect of the ethylenic lamellar buildup. For test temperature close to room temperature, the ductile behavior exhibited by the iPP/EPR_Ti blends was accounted for by a predominant shear yielding fracture mechanism probably promoted by a high concentration of interlamellar tie molecules among iPP crystallites in agreement with DSC results. Nonisothermal crystallization experiments showed, in fact, that the crystallization peak of the iPP phase from iPP/EPR_Ti melt is shifted to higher temperatures noticeably, thus indicating a material characterized by a comparatively higher number of spherulites per unit value grown at lower apparent undercooling values. Accordingly, WAXS analysis revealed comparatively higher iPP crystal growth in the directions perpendicular to the crystallographic planes (110) and (040) of the iPP. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 72: 701–719, 1999     

Structure and properties of polyamides‐epoxidized elastomers blends

Blends of aliphatic polyamides (PA6, PA66, and PA12), containing 0–15 wt % nonepoxidized or epoxidized elastomers (statistical copolymer butadiene–styrene BS/EBS or linear block copolymer styrene–butadiene–styrene SBS/ESBS) were investigated. For PA6‐elastomer blends, taken as an example, it was shown that with increasing blending time, mechanical properties of blends increase, especially, if ESBS copolymer is used. It can be treated as an indirect sign of reactions between components. It was also found that in blends considerable changes of glass temperatures of components occur. Polyamides in blends with elastomers have smaller heats of fusion in comparison with virgin polyamides. It testifies to hindering of PA crystallization by elastomers. In some cases, significant shifts of melting points are also observed. Measurements of water contact angle show that all blends have very similar values of contact angles, which are lower than those of virgin polyamides. Elastomer content does not also affect the blend water uptake. However, it depends on the polyamide and elastomer type contrary to contact angle. Highest water uptake changes are observed in blends of PA66, especially for epoxidized elastomers. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 1872–1879, 2006     

Tensile properties in the oriented blends of high-density polyethylene and isotactic polypropylene obtained by dynamic packing injection molding

In this article, tensile properties have been discussed in terms of phase morphology, crystallinity and molecular orientation in the HDPE/iPP blends, prepared via dynamic packing injection molding, with aid of scanning electron microscopy (SEM), differential scanning calorimetry (DSC) as well as two dimensional X-ray scattering (2D WAXS). For the un-oriented blends, the tensile properties (tensile strength and modulus) are mainly dominated by the phase morphology and interfacial adhesion related to the influenced crystallization between HDPE and iPP component. A maximum in tensile strength and modulus is found at iPP content in the range of 70-80 v/v%. As for the oriented blends, however, the presence of dispersed phase in the blends, independent of phase morphology and crystallinity, always makes tensile properties to be deteriorated through reducing molecular orientation of matrix. It is molecular orientation of matrix that determines the tensile properties of oriented blends. In the blends with HDPE as matrix, steep decreasing of tensile properties is related to the rapid reducing of molecular orientation of HDPE, whereas in the blends with iPP as a major component, slight decreasing of molecular orientation of iPP results in slight reducing of tensile properties. Other factors, such as interfacial properties and phase morphology, seem to be little contribution to the modulus and tensile strength.     

The study of polystyrene blends: The relationship of phases and structure in blends of polystyrene with ethylene–propylene diene monomer rubber and its grafted copolymer

Pressed films of blends of polystyrene (PS) with ethylene–propylene diene monomer rubber (EPDM) or grafted copolymer of styrene (St) onto EPDM (EPDM-g-St) rubber were examined by small-angle X-ray scattering (SAXS), and scanning electron microscope (SEM). Small-angle X-ray scattering from the relation of phase was analyzed using Porod's Law and led to value of interface layer on blends. The thickness of interface layer (σ_b) had a maximum value at 50/50 (PS–EPDM-g-St) on blends. The radius of gyration of dispersed phase (domain) and correlation distances a_c in blends of PS–EPDM-g-St were calculated using the data of SAXS. The morphology and structure of blends were investigated by SEM. © 1998 John Wiley & Sons, Inc. J. Appl. Polym. Sci. 70: 805–810, 1998     

Greatly improved toughness of isotactic polypropylene blends with traces of carbon nanotubes

In this work, the β‐nucleated isotactic polypropylene (iPP)/ ethylene‐octene copolymer (POE) blends demonstrated greatly enhanced impact toughness by adding traces of carbon nanotubes (CNTs) (only 0.05 wt%). When the POE content was 30 wt%, the impact strength of β‐nucleated iPP/POE blends with CNTs was as high as 51.7 kJ/m², about 5.6 kJ/m² higher than β‐nucleated iPP/POE blends, 15.2 kJ/m² higher than CNTs‐filled iPP/POE blends, and almost 19 times of pure iPP sample. This significantly improved impact toughness was considered to be attributed to the shear yielding and multiple‐crazing, originating from the presence of abundant β‐crystals in the iPP matrix, the enhanced mobility of the molecular chains in the confined amorphous region of iPP lamellae and the homogenous distribution of POE dispersed phase with a small size, indicating the synergistic effect of CNTs, β‐nucleating agent and POE on the toughness of iPP. POLYM. ENG. SCI., 59:757–764, 2019. © 2018 Society of Plastics Engineers