Study on the phase structures and toughening mechanism in PP/EPDM/SiO2 ternary composites

In this paper, EPDM rubber and nano-SiO₂ particles were employed to modify PP simultaneously. Our goal was to control the distribution and dispersion of EPDM and nano-SiO₂ particles in PP matrix by using an appropriate processing method and adjusting the wettability of nano-SiO₂ particles toward PP and EPDM, so as to achieve a simultaneous enhancement of toughness and modulus of PP. With regard to this, two kinds of nano-SiO₂ particles (with hydrophilic or hydrophobic) as well as two processing methods (one-step or two-step) were employed to prepare PP/EPDM/SiO₂ ternary composites. A unique structure with the majority of EPDM particles surrounded by SiO₂ particles was first observed by using hydrophilic SiO₂ and two-step processing method, resulting in a dramatically increase of Izod impact strength as the rubber content in the range of brittle-ductile transition (15-20 wt%). The observation that poor adhesion and poor compatibility between particles and PP matrix could result in a significant increase in Izod impact strength was unusual and needed further investigation. This could be tentatively understood as a consequence of the overlap of the ‘stress volume’ between EPDM and SiO₂ particles due to the formation of the unique structure. Our work provided a deep understanding of the toughening mechanism and a new way for the preparation of high performance polymer composites.     

Morphology prediction of ternary polypropylene composites containing elastomer and calcium carbonate nanoparticles filler

In this work, the morphology was studied in ternary composites of polypropylene (PP) with nanosized calcium carbonate (nano‐CaCO₃) fillers and elastomer inclusions and the thermodynamic consideration was used to analyze the formation of phase structure of the composites. The wetting coefficient (ω_a), interfacial tension (γ_AB), and work of adhesion (W_AB) were calculated to predict dispersion state of nano‐CaCO₃ fillers. A comparison of the prediction and SEM analysis was given. The results show that three types of phase structures were formed: an encapsulation of the filler by elastomer, a separate dispersion of the filler and elastomer, and a particular structure of the filler at the PP/elastomer interface. The predictions by ω_a were all successfully supported‐up by SEM analysis and the predictions by W_AB were however trustless. Both γ_AB and W_AB can predict a separate dispersion or an encapsulation phase structure, but they were not available for the particular structure of the filler at the PP/elastomer interface. ω_a was competent and favored for the prediction of all three types of morphology among the three parameters. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 1578–1584, 2007     

Evaluation of PP/EPDM nanocomposites filled with SiO2, TiO2 and ZnO nanofillers as thermoplastic elastomeric insulators

Abstract

Thermoplastic elastomer, which has important characteristics for cable insulation, was developed by melt blending of polypropylene (PP) with ethylene propylene diene monomer (EPDM) at various blend ratios together with SiO₂, TiO₂ and ZnO nanofillers at fixed loading of 2 vol.-%. The influence of EPDM content and the presence of nanofillers in the blend on burning rate, hydrophobicity and dielectric breakdown strength were investigated. Burning rate of PP/EPDM/ZnO was significantly reduced, implying that there was an improvement in fire retardancy with the addition of ZnO nanofillers in the polymer blend. Both SiO₂ and ZnO filled system showed an improvement in hydrophobicity. Furthermore, dielectric breakdown strength showed higher value in EPDM rich blends. In addition, the presence of nanofillers deteriorated the dielectric breakdown strength of PP/EPDM nanocomposites.     

Influence of Elastomer Modification on Impact Strength of PP/Elastomer/CaCO3 Composite

Polypropylene (PP)/elastomer/fine filler particle ternary composite was prepared using polystyrene-block-poly(ethylene-butene)-block-polystyrene triblock copolymer (SEBS) or carboxylated SEBS (C-SEBS) as elastomer and calcium carbonate (CaCO₃) having mean size about 160 nm as filler. First, SEBS (or C-SEBS) and CaCO₃ particles were mixed to form master batch. Second, the prepared master batch and PP matrix were kneaded. In the PP/SEBS/CaCO₃ ternary composite, CaCO₃ particles and SEBS particles were dispersed in the PP matrix separately. In the PP/C-SEBS/CaCO₃ ternary composite, CaCO₃ particles were encapsulated in C-SEBS and formed a core–shell structure at lower CaCO₃ concentration; however, some CaCO₃ particles were dispersed in PP matrix at higher CaCO₃ concentration. In the PP/SEBS/CaCO₃ composite, the impact strength increased with the amount of incorporated CaCO₃ particles. Whereas, in the PP/C-SEBS/CaCO₃ composite, the impact strength increased with the amount of CaCO₃ particles dispersed in PP matrix. The master-batch method was found to be useful for improving the dispersibility of CaCO₃ particles than the commonly used single-batch method.     

Influence of Filler Size on Impact Properties of PP/Elastomer/Filler Ternary Composites

Influence of filler size on impact properties for polypropylene (PP)/elastomer/filler ternary composites was investigated. Calcium carbonate (CaCO₃) particles with a diameter in the range from 120 to 1200 nm were used as a filler and polystyrene-block-poly(ethylene-butene)-block-polystyrene triblock copolymer (SEBS) was used as an elastomer. In the PP/SEBS/CaCO₃ ternary composite, CaCO₃ particles and SEBS particles were dispersed in the PP matrix separately. In the case that SEBS elastomer volume fraction was below 0.12, the impact strength improved gradually with a decrease of CaCO₃ mean diameter from 1200 to 160 nm. In the case that SEBS volume fraction was above 0.17, the impact strength improved significantly by the incorporation of CaCO₃ particles with a mean diameter in the range from 120 to 900 nm. However, the impact strength hardly improved by the incorporation of CaCO₃ particles with a mean diameter of 1200 nm.     

聚甲醛/弹性体/碳酸钙复合材料的研究

用弹性体和CaCO3复合改性POM。采用TPU为增韧剂，CaCO3为增强剂，研究了加工方法、组成比、填料用量、粒径及分散形态等因素对复合材料性能尤其是冲击韧性的影响。结果表明，两步法制备复合材料的冲击韧性大大高于一步法；且纳米级CaCO3填充复合材料的综合性能优于其它粒径大小的填料；适量的弹性体及无机纳米填料的加入利于获得较好的增韧效果，当弹性体用量约为10％，CaCO3用量为3％时，与纯POM相比，冲击强度提高了3倍，弯曲模量与纯POM接近。     

Synergetic toughness and morphology of poly(propylene)/nylon 11/maleated ethylene‐propylene diene copolymer blends

Polypropylene (PP)/nylon 11/maleated ethylene‐propylene‐diene rubber (EPDM‐g‐MAH) ternary polymer blends were prepared via melt blending in a corotating twin‐screw extruder. The effect of nylon 11 and EPDM‐g‐MAH on the phase morphology and mechanical properties was investigated. Scanning electron microscopy observation revealed that there was apparent phase separation for PP/EPDM‐g‐MAH binary blends at the level of 10 wt % maleated elastomer. For the PP/nylon 11/EPDM‐g‐MAH ternary blends, the dispersed phase morphology of the maleated elastomer was hardly affected by the addition of nylon 11, whereas the reduced dispersed phase domains of nylon 11 were observed with the increasing maleated elastomer loading. Furthermore, a core‐shell structure, in which nylon 11 as a rigid core was surrounded by a soft EPDM‐g‐MAH shell, was formed in the case of 10 wt % nylon 11 and higher EPDM‐g‐MAH concentration. In general, the results of mechanical property measurement showed that the ternary blends exhibited inferior tensile strength in comparison with the PP matrix, but superior toughness. Especially low‐temperature impact strength was obtained. The toughening mechanism was discussed with reference to the phase morphology. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Influence of Copolymer Composition and Curing on Toughness of Isotactic Polypropene Blended Together with Metallocene‐EPDM and Ethene/Propene/Vinylcyclohexane Terpolymers

Ethene/propene terpolymers containing either 1‐vinylcylohexene‐4 (VCHen) or vinylcyclohexane (VCHan) as termonomer component were prepared using MAO‐activated rac‐Me₂Si(2‐MeBenz[e]Ind)₂ZrCl₂ (MBI). Propene content was varied between 26 and 72 wt.‐% with less than 1 mol‐% termonomer incorporation. Blends containing 85 vol.‐% isotactic polypropene (i‐PP) and 15 vol.‐% of the two EP terpolymer families were prepared by melt‐compounding in a twin‐screw kneader at 200°C to examine the role of sulfur‐mediated crosslinking of the unsaturated EPDM terpolymer phase in comparison to the corresponding blends containing non‐crosslinked saturated EP/VCHan terpolymers. The observed glass temperature (T_g) depression of the T_g of EP(D)M phases with respect to the T_g of the corresponding bulk EP(D)M was attributed to the presence of thermally induced stresses in both blend systems. Blends of i‐PP with crosslinked EPDM showed smaller T_g depression with respect to those of iPP/EPM blends containing non‐crosslinked EP and EPM dispersed phases. Morphology differences were detected for i‐PP/EPM and dynamically vulcanized i‐PP/EPDM blends by means of atomic force microscopy (AFM). The crosslinked i‐PP/EPDM blends exhibited significantly improved low temperature toughness as compared to the corresponding non‐crosslinked i‐PP/EPM blends. Curing of the EPDM elastomer phase in i‐PP/EPDM (85 vol.‐%/15 vol.‐%) blends afforded significantly improved toughness/stiffness balance and a wider toughness window with respect to the corresponding i‐PP/EPM and i‐PP/EP blends without sulfur‐cured rubber phases.     

Tensile properties and morphology of PP/EPDM/glass bead ternary composites

The tensile properties of three types of injection molded glass bead (GB) filled polypropylene (PP)/ethylene-propylene-diene monomer (EPDM) ternary composites have been determined at room temperature by using an Instron materials testing machine. The effects of the filler surface treatment, the glass bead (GBI) pretreated with a silane coupling agent and the EPDM (EPDM-MA) modified with a maleic anhydride, and the filler content on the tensile mechanical properties of the ternary PP composites have been investigated. The Young's modulus (E_c) increases while the yield stress (σ_yc) and tensile fracture strength (σ_bc) of the composites decrease with increasing the volume fraction of glass beads (ϕ_g) when the volume fraction of EPDM is constant (ϕ_e = 10%). The (E_c) values of PP/EPDM/GBI and ϵ_bc for PP/EPDM-MA/GB2 (no surface pretreated) systems are the highest at the same ϕ_g. The tensile fracture energy (E_bc) and tensile fracture strain (ϵ_bc) of PP/EPDM/GBI and PP/EPDM/GB2 systems appear to peak at ϕ_g = 25%. However, the E_bc and ϵ_bc of PP/EPDM-MA/GB2 system show little changes with increasing ϕ_g. The fracture surfaces of ternary composites have been examined in a scanning electron microscope. The correlation between the tensile properties and morphologies of these materials have been discussed.     

Morphology and properties of PP/EPDM binary blends and PP/EPDM/nano‐CaCO3 ternary blends

In this article, the morphology, crystallization, and rheological behaviors of polypropylene (PP)/ethylene‐propylene‐diene terpolymer (EPDM) binary blend and PP/EPDM/calcium carbonate nanoparticles (nano‐CaCO₃) ternary blend were investigated. Two processing methods, i.e., direct extrusion and two‐step extrusion, were employed to prepare the PP/EPDM/CaCO₃ blend. The influence of EPDM and nano‐CaCO₃ respectively on phase morphology and properties of PP/EPDM blend and PP/EPDM/CaCO₃ blend were characterized by scanning electron microscopy (SEM), differential scanning calorimetry (DSC) and dynamic rheometer. The crystallinity and crystallization temperature of PP/EPDM blend were improved in comparison to pure PP due to addition of EPDM, but kept invariable with the increased EPDM loading. As the EPDM content was increased, the mobility of PP molecular chains was weakened. Compared with direct extruded blend, less and finer nano‐CaCO₃ was dispersed in matrix of two‐step extruded blend. Accordingly, the increased nano‐CaCO₃ in matrix gave rise to a weaker increment in crystallinity and crystallization temperature of two‐step extruded blend, and a later platform of tanδ curve. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

共混工艺及设备对EPDM/PP-TPE力学性能的影响

研究了共混工艺和设备对EPDM/PP-TPE力学性能的影响,结果表明:两阶共混法优于两步共混法,一步共混法最差;比较双辊开炼机和双螺杆挤出机对力学性能的影响,用双螺杆挤出机制备的EPDM/PP-TPE性能较好。     

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     

Reinforcement of polyolefins‐based nanocomposites: combination of compatibilizer with high shear extrusion process

The structure and properties of polypropylene (PP) and ethylene propylene copolymer (EPR) blends filled with nanosilica have been investigated. The nanocomposites were prepared via direct melt mixing using high shear corotating twin screw extruder. The effects of the process as well as adding amaleated‐Polyethylene MAPE compatibilizer were assessed by morphology studies, thermal analysis and mechanical testing. From SEM and TEM investigations, a separate dispersion of filler and rubber in the PP matrix prevails in the PP/EPR/SiO₂ systems. Encapsulation of the filler particles into the elastomer takes place when MAPE is used, promoting filler/polymer interactions and resulting in a simultaneous improvement in stiffness and toughness. Interestingly, the results indicated that high‐shear processing is an effective method to improve the dispersion of the EPR phase and fillers through the matrix. The dispersed phase droplet size was reduced with the increase of the shear rate by varying the screw rotation speed from 300 to 800 rpm, which induces a high shear stress exerted onthe materials. To sum up, what is expected from an efficient compatibilization‐process association is the reduction of the dispersed elastomer domains characteristic size, their stabilization by creation of an interphase and thus, enhanced mechanical properties. POLYM. ENG. SCI., 55:2328–2338, 2015. © 2015 Society of Plastics Engineers     

Effect of the mixing sequence on the morphology and properties of a polypropylene/polydimethylsiloxane/nano‐SiO2 ternary composite

Ternary composites of polypropylene (PP), polydimethylsiloxane (PDMS) elastomer, and nano‐SiO₂, prepared with three different mixing sequences, were studied for dispersion morphology and its effect on the crystallization of PP and the mechanical properties. The mixing sequence produced a significant effect on the dispersion morphology and, thereby, on the mechanical properties of the composites. A two‐step mixing sequence, in which nano‐SiO₂ was added in the second step to the PP/PDMS binary system, produced a significant encapsulation of nano‐SiO₂ by PDMS, and this, in turn, resulted in the poor modulus and impact strength of the composite. A one‐step mixing sequence of all three components produced a separated dispersion of PDMS and nano‐SiO₂ phases in the PP matrix with the occurrence of a fine band of nano‐SiO₂ particles at the boundaries of the PDMS domains and the presence of some nano‐SiO₂ filler particles inside the PDMS domains. This one‐step mixing sequence produced an improvement in the tensile modulus but a decrease in the impact strength with increasing nano‐SiO₂ content. In the third sequence of mixing, which involved a two‐step mixing sequence through the addition of PDMS in the second step to the previously prepared PP/nano‐SiO₂ binary system, the morphology of the dispersion showed separately dispersed PDMS and nano‐SiO₂ phases with a loose network of nano‐SiO₂ particles surrounding the PDMS domains. This latter series of ternary composites had the highest impact strength and exhibited high shear deformation under tensile and impact conditions. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Impact fracture behavior of PP/EPDM/glass bead ternary composites

The effects of glass bead filler content and surface treatment of the glass with a silane coupling agent on the room temperature impact fracture behavior of polypropylene (PP)/ethylene‐propylene‐diene monomer copolymer (EPDM)/glass bead(GB) ternary composites were determined. The volume fraction of EPDM was kept constant at 10%. The impact fracture energy and impact strength of the composites increased with increasing volume fraction of glass beads (?_g). Surface pretreatment of the glass beads had an insignificant effect on the impact behavior. For a fixed filler content, the best impact strength was achieved when untreated glass beads and a maleic anhydride modified EPDM were used. The impact strength exhibited a maximum value at ?_g=15%. Morphology/impact property relationships and an explanation of the toughening mechanisms were developed by comparing the impact properties with scanning electron micrographs of fracture surfaces.     

Phase structure and property relationships in ternary polypropylene/elastomer/filler composites: Effect of elastomer polarity

Ternary composites of polypropylene (PP), elastomer, and calcium carbonate (CaCO₃) filler were prepared to study their structure/property relationships. Two kinds of phase structure were formed, depending on the elastomer present in the composites. Separation of elastomer and filler particles was found when a nonpolar ethylene–octene copolymer was used. Encapsulation of filler by the elastomer was achieved by using a polar ethylene–vinyl acetate elastomer. The mechanical properties of ternary composites were strongly dependent on material composition and their phase structures. In the present study, composites with separate dispersion structure showed higher modulus and impact strength than those of encapsulation type. The deformation mechanisms of both composites were studied using scanning electron microscopy. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 1929–1939, 2000     

Mechanical and rheological properties of multicomponent polypropylene blends

Polypropylene (PP) compositions containing CaCO₃ filler, EPDM (ethylene-propylene-ethylidenenorbornene) elastomer, and a non-reactive surfactant were investigated in the mixing chamber of a plastograph. Rheological properties were determined from the registered torque (M) vs. time and temperature (T) vs. time curves, while tensile characteristics of the blends were measured on compression molded plates. The homogenization process can be followed with the aid of 1 n M vs. 1/T diagrams. In the first few minutes of the mixing, beside homogenization, a significant breaking down of the elastomer takes place, and the size of the particles attains an equilibrium value. Dispersion time increases with increasing amount of EPDM and surface active-agent. Morphological investigations indicate the presence of a continuous PP phase containing dispersed CaCO₃ and elastomer particles. The rheological and tensile characteristics are seemingly determined by the total amount of additives, which imply that the elastomer and the filler has the same effect on the properties of the composite. Separation of the effects proved, however, that the effect of the two components are dissimilar, the filler exerts a larger influence on the investigated properties.     

Glass fiber reinforced polypropylene/EPDM blends. II. Mechanical properties and morphology

Tensile and impact properties of the ternary system polypropylene (PP)/ethylene propylene diene elastomer (EPDM)/glass fiber (GF) and the corresponding binary systems PP/EPDM blend and PP/GF composite are studied. Results are presented and analyzed as functions of compositional variables, viz., (i) matrix PP/EPDM blending ratio at constant GF loadings and (ii) GF loading at constant matrix blending ratios for the ternary system and (iii) EPDM content for PP/EPDM binary system and (iv) GF content for the binary system PP/GF, respectively. The role of individual components EPDM and GF in these mechanical properties is discussed and their combined effects are inspected at certain composition ranges. Theoretical analysis of tensile data is presented which reveals the effect of EPDM on the reinforcing effect of GF. Unlike the conventional role of an elastomer, increase of EPDM content in the presence of GF increases the modulus of the ternary system. Impact strength of the ternary system increases with increasing GF content both in the presence and absence of EPDM, showing a distinct minimum at matrix blending ratio PP/EPDM 90/10. Scanning electron micrographs of impact-fractured surfaces are presented to illustrate the dispersion of the two phases of the polyblend matrix, fiber alignment, and the fiber interface.     

Distribution of oil in olefinic thermoplastic elastomer blends

The distribution of processing oil in two olefinic thermoplastic elastomer (OTPE) blends was determined using dielectric spectroscopy. The OPTE blends are blends of dynamically vulcanised EPDM with polypropylene (PP), TPVs, and blends of PP with SEBS. Both blend types contain paraffinic oil, which is present in both the PP and in the elastomer phase. The determination of the actual oil concentration by measuring the reduction in the glass transition temperatures (T_g) is inaccurate using DSC or DMA, because the glass transition dynamics of the two phases overlap. The blends were made sensible for dielectric spectroscopy by the addition of a probe molecule. The oil distribution was determined by modelling of the dielectric loss of the OPTE blends in the T_g regime from the ones of the binary mixtures. The mean value for the oil distribution coefficient was found to be 0.6 for PP/SEBS blends and 0.63 for TPVs.     

动态硫化EPDM/PP共混型热塑性弹性体的流动性

研究了动态硫化EPDM／PP共混型热塑性弹性体的流动性。结果表明：选择合适的橡胶及塑料品种、橡塑共混比、软化剂用量及改性剂，可使物理力学性能良好的EPDM／PP共混胶获得较好的流动性。