Tensile elongation of high‐fluid polypropylene/ethylene–propylene rubber blends: Dependence on molecular weight of the components and propylene content of the rubber

We studied tensile behavior of low‐molecular‐weight (MW) polypropylene (PP)/ethylene–propylene rubber (EPR; 70/30) blends from the viewpoint of the MWs of PP and EPR and the compatibility between PP and EPR. The value of the melt flow rate of PP varied from 30 to 700 g/10 min at 230°C. We studied the compatibility between PP and EPR by varying the propylene content in EPR (27 and 68 wt %). At the initial elongation stage, crazes were observed in all blends. When blends included EPR with 27 wt % propylene, the elongation at break of the low‐MW PP improved little. The blends with EPR and 68 wt % propylene content were elongated further beyond their yielding points. The elongation to rupture was increased with increasing MW of EPR. Molecular orientation of the low‐MW PP was manifested by IR dichroism measurements and X‐ray diffraction patterns. The blends of low‐MW PP and EPR could be elongated by the partial dissolution of EPR of high‐MW in the PP amorphous phase. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 46–56, 2002     

Isothermal crystallization behavior and properties of polypropylene/EPR blends nucleated with sodium benzoate

The effect of sodium benzoate on the isothermal crystallization behavior of isotactic polypropylene (iPP)/ethylene–propylene rubber(EPR) blends was investigated using differential scanning calorimetry. Dynamic mechanical and physical properties of the iPP/EPR blends nucleated with sodium benzoate were also measured. It was found that the crystallization behavior and physical properties such as heat deflection temperature (HDT), flexural modulus, and impact strength were strongly affected by the competition between the nucleating effect of EPR attributed to its partial compatibility with iPP and the simple addition of the amorphous component, as well as the nucleating effect of sodium benzoate. High impact strength was achieved by addition of EPR and sodium benzoate to iPP. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 201–211, 2002     

Morphology and mechanical properties of polypropylene and poly(ethylene‐co‐methyl acrylate) blends

The morphology and mechanical properties of isotactic polypropylene (iPP) and poly(ethylene‐co‐methyl acrylate) (EMA) blends were investigated. Various EMA copolymers with different methyl acrylate (MA) comonomer content were used. iPP and EMA formed immiscible blends over the composition range studied. The crystallization and melting reflected that of the individual components and the crystallinity was not greatly affected. The size of the iPP crystals was larger in the blends than those of pure iPP, indicating that EMA may have reduced the nucleation density of the iPP; however, the growth rate of the iPP crystals was found to remain constant. The tensile elongation at break was greatly increased by the presence of EMA, although the modulus remained approximately constant until the EMA composition was greater than 20%. EMA with a 9.0% MA content provided the optimum effect on the mechanical properties of the blends. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 175–185, 2003     

Rheological behavior and processability of polypropylene blends with rubber ethylene propylene diene terpolymer

A study of the dynamic complex and steady shear viscosity of isotactic polypropylene (iPP), ethylene–propylene diene terpolymer rubber (EPDM) and three different blends of both polymers are presented over a range of temperatures and frequencies. Moreover, the processability of these materials is studied through torque measurements during blend mixing. The results obtained show that the viscosity gradually increases with rubber content in the blend and decreases with both temperature and frequency. Plots of η″ versus η′ (Cole–Cole plots) show that the blend with the lower rubber content (25%), has a certain rheological compatibility with neat PP. Furthermore, torque curves measured during blend mixing confirm these results, demonstrating that the blend with 25% of elastomer has a similar behavior of iPP during processing. To analyze the morphological structure of the blends, a dynamic mechanical analysis of the solid state is also presented. It is observed that the blends have two distinct values of T_g close to the corresponding values of the pure polymers, confirming that this type of blends based on a semicrystalline polymer and an amorphous elastomer forms a two‐phase system with a limited degree of miscibility between both components. In addition, the polymer present with the higher concentration forms the continuous phase and controls the rheological properties of the blend. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 1–10, 2001     

Deformation and fracture of Mg(OH)2‐filled polyolefin composites under tensile stress

The tensile behavior of high‐density polyethylene (HDPE), polypropylene (PP), and linear low‐density polyethylene composites containing a titanate coupling agent and silicone‐oil‐treated magnesium hydroxide [Mg(OH)₂] was studied. The increase in the extent of the ultimate elongation of the composites was affected by the yield stress and the strain‐hardening tendency of the polymer matrix in the composites. Ethylene–propylene–diene rubber and octane–ethylene copolymer were introduced to adjust the yield stress of PP and HDPE. Although the ultimate elongation of PP/elastomer and HDPE/elastomer blends was higher than that of virgin PP or HDPE, the ultimate elongation of the filled composites dropped at a high content of Mg(OH)₂. Scanning electron microscopy showed that the difference in the uniformity of the interface exfoliation decreased with the yield stress of the matrix. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 3248–3255, 2003     

Partial replacement of EPR by GTR in highly flowable PP/EPR blends: Effects on morphology and mechanical properties

This research analyzes the effect of ground tire rubber (GTR) and a novel metallocene‐based ethylene–propylene copolymer (EPR), with high propylene content, on the morphology and mechanical behavior of ternary polymer blends based on a highly flowable polypropylene homopolymer (PP). The PP/EPR blends morphology, with very small domains of EPR dispersed in the PP matrix, indicates a good compatibility among these materials, which leads to a significant improvement on elongation at break and impact strength. The incorporation of EPR on the rubber phase of thermoplastic elastomeric blends (TPE) based on GTR and PP (TPE^GTR) has a positive effect on their mechanical performance, attributed to the toughness enhancement of the PP matrix and to the establishment of shell‐core morphology between the rubber phases. The mechanical properties of the ternary blends reveal that TPE^GTR blends allow the upcycling of this GTR material by injection molding technologies. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42011.     

Interfacial adhesion evaluation in (low‐density polyethylene)/elastomer blends

Low‐density polyethylene (LDPE) with different elastomers at a ratio of 50/50 wt% blends was prepared by using a co‐rotating twin‐screw extruder. Three kinds of elastomers were used: ground tire rubber (GTR), partially crosslinked butyl rubber (Kalar^®), and styrene‐butadiene‐rubber block copolymer (SBS; Kraton^®). For better characterization of interaction between polyethylene and elastomer, influence of the type of elastomer on the properties of compositions LDPE/elastomer was determined. In the studies, two types of partially crosslinked butyl rubber (differing over filler content and Mooney viscosity) and two types of SBS (differing over structure: linear/branched) were used. The influence of kind and type of elastomer on static mechanical properties (tensile strength, elongation at break, hardness), dynamic mechanical properties, thermal properties, and morphology of obtained compositions were characterized. LDPE/linear SBS copolymer blend had the best mechanical properties, as a result of better compatibility in comparison with other investigated blends. The reason for improved compatibility was an increase of mobility of chain segments in the amorphous phase of polyethylene associated with their partial plasticization by flexible polybutadiene blocks present in SBS copolymer. J. VINYL ADDIT. TECHNOL., 22:492–500, 2016. © 2015 Society of Plastics Engineers     

Morphology,crystalline features,and tensile properties of syndiotactic polypropylene blends

Syndiotactic polypropylene (sPP) was modified with ethylene–octene copolymer (EOC) and ethylene–propylene rubber (EPR), with test samples prepared in a twin‐screw extruder and then injection‐molded. The phase morphology, rheology, and thermal and tensile properties of the modified sPP were investigated. Atomic force microscopy studies showed how the phase morphology of the sPP blends with elastomers depended on the blend compositions, and the results compared with the storage modulus at low frequency. EOC and EPR were dispersed phase in an sPP matrix with spherical shapes when the dispersed content was 20 wt % or lower. The phase cocontinuity started around 40 wt % EOC for the sPP–EOC blends and around 60 wt % EPR for the sPP–EPR. The dispersed phase then formed more complex elongated shapes. The rheological and thermal properties were affected by the sPP–elastomer interphase. EOC promoted the crystallization of sPP; this increased the crystallization temperature and rate. In contrast, EPR had the opposite effect on the crystallization behavior, and the results indicate that sPP and EPR were not completely separated. The tensile properties were studied from ?20 to 100 °C. We found that the tensile properties at low temperature could be improved without a loss in high‐temperature properties. In the particular case of 20 wt % EOC, both the strain at yield and strain at break of the sPP–EOC blend were improved at both ?20 and 100 °C. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134 , 44611.     

Effect of monomethyl itaconate‐grafted HDPE and EPR on the compatibility and properties of HDPE–EPR blends

To improve the compatibility and properties of blends based on high‐density polyethylene (HDPE) and the ethylene–propylene copolymer (EPR), the functionalization of both through grafting with an itaconic acid derivative, monomethyl itaconate (MMI), was investigated. The grafting reaction was performed at 180°C in a Brabender Plasticorder using an initial monomer concentration of 3 phr in the case of HDPE and 5 phr in the case of EPR. 2,5‐Dimethyl‐2,5‐bis(tert‐butylperoxy)hexane was used as a radical initiator for the functionalization of HDPE and dicumyl peroxide was used as a radical initiator for the modification of EPR. The degree of grafting was 1.56% by weight for HDPE and 0.8% by weight for EPR. The effect of grafting on the processability, morphology, and thermal and mechanical properties of the blends are of particular interest. The results show that the grafting reaction increases the toughness and elongation at break of all tested blends and they retained their strength and stiffness. Moreover, the grafted polymers behaved as nucleating agents, accelerating the HDPE crystallization. These results are particularly relevant when both polymeric phases are modified. Morphological studies are in concordance with the mechanical characterization, showing a reduction of the rubber particle size and a better interfacial adhesion when both polymers are functionalized with MMI. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 2239–2248, 2003     

Preparation and characterization of thermoplastic polyurethane elastomer and polyamide 6 blends by in situ anionic ring‐opening polymerization of ϵ‐caprolactam

The blends of thermoplastic polyether‐based urethane elastomer (TPEU) and monomer casting polyamide 6 (MCPA6) were prepared using ε‐caprolactam (CL) as a reactive solvent, and CL sodium as a catalyst at various TPEU contents (2.5–15 phr by weight). In situ anionic ring‐opening polymerization and in situ compatibilization of TPEU/MCPA6 blends were realized in one step. The dissociated TPEU chains acted as macroactivator to initiate MCPA6 chain growth from the TPEU chains. The formed block copolymers (TPEU‐co‐MCPA6), which have been confirmed by Fourier transform infrared spectroscopy and ¹H‐NMR analysis, improved the compatibility between TPEU and MCPA6. In addition, both differential scanning calorimetry and dynamic mechanical analysis studies revealed that the crystallinity temperature, melting temperature, the degree of crystallization, and the glass‐transition temperature of MCPA6 component remarkably shifted to a low temperature with increasing TPEU content. Mechanical properties demonstrated that the impact strength and the elongation‐at‐break of the blends significantly increased with the content of TPEU, whereas a progressive decrease occurred in tensile strength, flexural strength, and flexural modulus. WAXD spectra showed that only α‐form crystal of PA6 component existed in the TPEU/MCPA6 blends. Furthermore, scanning electron microscopes (SEM) of the cryo‐fractured surfaces confirmed a substantially improved compatibility, and reflected a seemly single‐phase morphology. POLYM. ENG. SCI., 46: 1196–1203, 2006. © 2006 Society of Plastics Engineers     

Mechanical properties,morphological structure,and thermal behavior of dynamically photocrosslinked PP/EPDM blends

A dynamically photocrosslinked polypropylene (PP)/ethylene–propylene–diene (EPDM) rubber thermoplastic elastomer was prepared by simultaneously exposing the elastomer to UV light while melt‐mixing in the presence of a photoinitiator as well as a crosslinking agent. The effects of dynamic photocrosslinking and blend composition on the mechanical properties, morphological structure, and thermal behavior of PP/EPDM blends were investigated. The results showed that after photocrosslinking, tensile strength, modulus of elasticity, and elongation at break were improved greatly. Moreover, the notched Izod impact strength was obviously enhanced compared with corresponding uncrosslinked blend. Scanning electron microscopy (SEM) morphological analysis showed that for uncrosslinked PP/EPDM blends, the cavitation of EPDM particles was the main toughening mechanism; whereas for dynamically photocrosslinked blends, shear yielding of matrix became the main energy absorption mechanism. The DSC curves showed that for each dynamically photocrosslinked PP/EPDM blend, there was a new smaller melting peak at about 152°C together with a main melting peak at about 166°C. Dynamic mechanical thermal analysis (DMTA) indicated that the compatibility between EPDM and PP was improved by dynamic photocrosslinking. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 3371–3380, 2004     

Effect of filler partitioning on the mechanical properties of TPO/nanosilica composites

Nanosilica (SiO₂) is used as a reinforcing filler in PP/elastomer thermoplastic polyolefin (TPO) blends containing ethylene‐octene polyolefin elastomer (POE), ethylene‐propylene rubber (EPR), and maleated EPR. The localization and dispersion of the filler are controlled by adding maleated derivatives to the matrix or the dispersed phase. A separated morphology, consisting of SiO₂ residing in the PP matrix, is necessary to achieve improvements in modulus. Filled TPOs containing POE have the best performance and exhibit improved moduli while retaining high values of elongation. J. VINYL ADDIT. TECHNOL., 13:147–150, 2007. © 2007 Society of Plastics Engineers     

Morphology and mechanical properties of binary blends of polypropylene with statistical and block ethylene‐octene copolymers

In the present work, statistical (EOCs) and block (OBCs) ethylene‐octene copolymers, with similar densities and crystallinities, were used as impact modifiers of isotactic polypropylene (iPP), and the toughening effects of these two types of elastomers were compared. The viscosity curves of EOCs were similar to those of OBCs with equivalent melt flow rate (MFR), enabling a comparison of the viscosity ratio and elastomer type as independent variables. No distinct differences on the crystal forms and crystal perfection of iPP matrix in various blends were observed by thermal analysis. Morphological examination showed that OBCs form smaller dispersed domains than EOCs with similar MFRs. The flexural modulus, yield stress, stress and strain at break showed the same variation tendency for all the investigated polypropylene/elastomer blends. However, the room temperature Izod impact toughness of iPP/OBC blend was higher than that of iPP/EOC blend containing elastomer with the similar MFRs. The experimental results indicated that the compatibility of iPP/OBCs was much higher than that of iPP/EOCs. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Preparation and properties of dynamically vulcanised blends of isobutylene–isoprene rubber and isotactic polypropylene

Abstract

Dynamic vulcanisation was employed to prepare blends of isobutylene–isoprene rubber (IIR) and isotactic polypropylene (iPP) with superior properties. The preparation technology, the effects of the presence of IIR on the crystallisation properties of iPP and the mechanical properties of the IIR/iPP thermoplastic vulcanisates (TPVs) were investigated. It was revealed that, under regular shearing at 180°C, dynamic vulcanisation for 10 min produced IIR/iPP TPVs of excellent properties; while degradation occurred when the duration of vulcanisation was extended to 15 min. Incorporation of IIR into iPP dramatically reduced the size of the iPP spherulites, and thus decreased the melting temperature and the degree of crystallinity of the iPP. When the IIR content was 50 wt-%, maximally balanced mechanical properties of IIR/iPP TPVs were obtained with a Charpy impact strength of 53·6 kJ m^?2 and a tensile strength of 31·3 MPa.     

The effect of propylene–ethylene copolymers with different comonomer content on melting and crystallization behavior of polypropylene

The effect of propylene–ethylene copolymers (PEc) with different ethylene‐unit contents on melting and crystallization behaviors of isotactic‐polypropylene (iPP) were investigated by differential scanning calorimetry (DSC) and polarized light microscopy (PLM). The results show that the addition of PEc decreases significantly crystallization temperature (T_c) of iPP, but slightly affects melting temperature (T_m). With increasing the ethylene‐unit content of the propylene–ethylene copolymers, the decrease in crystallization temperature of iPP is smaller. The PLM results show that the spherulite growth rate decreases with increasing crystallization temperature for iPP and iPP/PEc blends. The higher the ethylene‐unit content of the copolymers is, the lower the spherulite growth rate (G) of iPP/PEc blends is. The influence of the PEc on nucleation rate constant (K_g) and fold surface energy (σ_e) of iPP was examined by nucleation theory of Hoffman and Lauritzen. The results show that both K_g and σ_e of iPP/PE20(80/20) and iPP/PE23(80/20) blends are higher than those of iPP, demonstrating that the overall crystallization rate of iPP/PEc blends decreased as compared to that of iPP, resulting from the decrease of the nucleation rate and the spherulite growth rate of iPP. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

A study of dynamic vulcanization for polyamide‐12 and chlorobutyl rubber

Polyamide‐12 and chlorobutyl rubber were blended by dynamic vulcanization in a high shear environment using curing systems based on sulfur, dithiocarbamate/ZnO, and 4,4‐methylenebiscyclohexylamine/MgO. As expected, all blends with curing agents show increased tensile strength and elongation at break in comparison to blends without curing agents. Maximum mechanical properties are obtained at relatively low levels of curing agent in all systems. Hexane extraction of the mixtures and measurement of percentage of insolubles along with the swelling index of the rubber phase confirm that a high level of cure is achieved at low levels of curing agent. Although the curatives are designed for the rubber phase, differential scanning calorimetry results indicate that both phases are affected during the dynamic vulcanization process, with polyamide‐12 showing a reduced melting temperature that is indicative of molecular weight reduction, structure changes, or reaction with the rubber phase. Scanning electron microscopy results indicate that phase size is reduced with increased blending time and level of curing agent. Rheological studies indicate that blends containing curing agents exhibit non‐Newtonian behavior to a greater extent than polyamide or nonvulcanized polyamide/chlorobutyl rubber blends. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 871–880, 2003     

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     

Behavior of ionomers of sulfonated styrene–butadiene–styrene triblock copolymer in polymer blends with crystalline polyolefins and as compatibilizer

The blends of ionomers of sulfonated (styrene–butadiene–styrene) triblock copolymer with two polyolefins as well as the blends of polystyrene (PSt) with two polar, oil‐resistant elastomers, i.e., chlorohydrin rubber (CHR) and chlorosulfonated polyethylene (CSPE), using the ionomer as compatibilizer were studied. The blends of the ionomer with polypropylene or high density polyethylene showed synergistic effects with respect to tensile strength. With increasing PSt content, the blends change their behavior from thermoplastic elastomer to toughened plastics. The synergism is probably because of the thermoplastic interpenetrating polymer networks formed in the blend. The blends exhibited high resistance against diesel oil or toluene. When PSt was blended with CHR or CSPE using the ionomer as compatibilizer, only 2 or 3% ionomer was needed to enhance the mechanical properties of the blends. The effect is due to the ion–polar interaction of the ionomer with the polar polymer. The enhanced compatibility of the blends by the ionomer was demonstrated by DSC and Scanning electron micrograph. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 1887–1894, 2006     

Structure and properties of polyolefin blends

Blends of ethylene–propylene–diene rubber (EPDM) and low density polyethylene (PE_id) or isotactic polypropylene (iPP) crosslinked by dicumyl peroxide (DCP) have been prepared. Their morphology, reactivity of the components and crystallinity have been studied. The blends are microheterogeneous. Both plastomers, but particularly iPP, decrease the crosslinking efficiency of EPDM by DCP. It was found that they also influence the mechanical properties of the blends. The effect of iPP is far more pronounced than that of PE_Id, because of an increase in crystalline phase content. iPP particles play a role as nuclei for propylene monomer units in EPDM, whereas PE_Id particles are solvated by the elastomer matrix.