Propylene-based Elastomer Research Articles

Structure, mechanical, and dielectric properties of polypropylene blended with ethylene and propylene‐based elastomers

AbstractPolypropylene (PP) has been widely researched in power cable insulation due to its excellent resistance against high temperatures and high voltages. Since PP is too stiff for power cable extrusion, elastomers have been blended with PP to improve its stiffness. Although effects of elastomers on electro‐mechanical properties of PP have been widely studied, fundamental issues governing changes in dielectric properties of PP/elastomer blends have yet to be fully understood. This paper therefore reports on the properties of PP blended with ethylene‐based elastomer (EBE) and propylene‐based elastomer (PBE) by correlating their structural, mechanical, and dielectric investigations with respect to elastomer types and contents. The results show that blending increasing amounts of EBE and PBE improves mechanical flexibility of PP, with Young's modulus reduces by 53% at 40 wt% of elastomer content. Morphology‐wise, PBE demonstrates better compatibility with PP and less disrupted crystallinity compared to EBE. Furthermore, PP/PBE has better breakdown performance over PP/EBE, albeit that their breakdown strengths reduce with increasing elastomer contents. Specifically, direct current breakdown strength of PP/PBE reduces by only 21% at 40 wt% of PBE loading compared to 31% at equivalent EBE loading. Potential mechanisms governing breakdown changes are discussed with structural, mechanical, and dielectric interpretations.

Study on thermal cycling ageing resistance of performances of polypropylene/elastomer/boron nitride nanocomposites for high voltage direct current cable insulation

AbstractThe influences of thermal cycling ageing on structures and insulation performances of polypropylene (PP)/elastomer/boron nitride (BN) nanocomposites are investigated. The Melt blending method was used to prepare the nanocomposites, in which propylene‐based elastomer (PBE) or ethylene‐octene copolymer elastomer (EOC) was contained for comparison. Then, the samples were treated using a thermal cycling process with a temperature range from −30 to 150°C, and the number of thermal cycles was set from 0 to 15. Scanning electron microscope (SEM), Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry and X‐ray diffraction measurements were taken to facilitate the comprehension of structural changes. Additionally, measurements were taken to assess the trap distribution and direct current (DC) breakdown strength of the samples. The obtained results revealed that following thermal cycling ageing, the morphology and crystallinity of PP/PBE/BN remained almost unchanged. In contrast, PP/EOC/BN exhibited substantial microstructural damage accompanied by a significant reduction in crystallinity. As the number of thermal cycles increased, the trap level and DC breakdown strength of PP/PBE/BN were maintained at high levels, while those of PP/EOC/BN initially remained stable but then experienced a sharp decline. It is suggested that the addition of BN nanoparticles enhances the thermal cycling ageing resistance of the PP/PBE blend, whereas it weakens this resistance of the PP/EOC blend.

Experimental and density functional theory study of the effect of polar groups on interaction at the polyolefin-aluminum laminated film interface

Good adhesive strength and joint durability are necessary for aluminum (Al)/polymer laminated film for lithium-ion battery packages. A modified propylene-based elastomer (mPBE) was prepared as the inner adhesive in this study. The polar group was grafted onto the PBE molecular chain via melt grafting with the assistance of styrene. The adhesive performance of PBE modified with glycidyl methacrylate is significantly higher than that of commercially available inner adhesives, Mitsui A and Dupont 739. Moreover, environmentally friendly trivalent chromium [Cr(III)] chemical conversion was used to treat Al foil and improve the adhesive joint. The wettability behavior of adhesive melt on the surface of Al foil was studied using high-temperature contact angle testing. The results indicate that wettability is not the sole factor impacting interfacial strength, surface energy of the adhesive melt also plays a role. To further study the effect of polar groups on the mPBE adhesion, a solvent casting-evaporation method was developed to prepare an ultra-thin mPBE coating on the Al foil surface. The morphology of mPBE-coated Al foils and the thickness of the coating were studied by atomic force microscope. The bonding mechanism at the interface was studied through time-of-flight secondary ion mass spectroscopy, and it was shown that the Cr(III) conversion coating could react with polar groups via acid-base interaction. Moreover, quantum chemical calculations based on density functional theory were used to reveal the bonding mechanism at the molecular level, and it is found that the adhesive strength is related to the electron-donor abilities and reactivity of the adhesive molecules.

Effect of pretreatment on the interfacial bonding strength between modified polyolefin and aluminum foil treated with trivalent chromium chemical conversion: Experimental, quantum chemical calculations and molecular dynamics simulation

Good adhesive strength and joint durability are necessary for aluminum (Al)/polymer laminated film for lithium-ion battery packages. A pretreatment method involving alkaline degreasing followed by acid pickling was employed to treat the Al foil surface to facilitate the deposition of trivalent chromium [Cr(III)] conversion coating on the surface. The adhesive strength between propylene-based elastomer grafted glycidyl methacrylate (GMA-g-PBE) and Cr(III)-converted Al foil pretreated with 0.5 M HF pickling was 51% higher than Cr(III)-converted Al foil without pretreatment. Moreover, the effect of different pretreatments on the interfacial bond strength of GMA-g-PBE/Cr(III)-converted Al foil was studied from macroscopic to microscopic perspectives. The results indicate that the pretreatment of 0.5 M HF pickling results in complete coverage of the Cr(III) compounds and the formation of a thicker Cr(III) conversion coating on the Al foil compared to other pretreatments. A higher content of Cr(III) compounds results in an increased surface free energy of Cr(III)-converted Al foil, improving the wettability of adhesive melt on the substrate and enhancing the adhesion strength. Moreover, quantum chemical calculations and molecular dynamics simulations were used to investigate the interface bonding mechanism, and the results indicate that GMA in the adhesive exhibits a higher binding energy with Cr(III) oxides and hydroxides compared to Al oxides and hydroxides.

Thermal Cycling Induced Aging on Polypropylene/Elastomer Blends for DC Cable Insulation

This paper reports on the ageing phenomenon of the polypropylene (PP) /elastomer blends that are used as DC cable insulation. The elastomers employed are propylene-based elastomer (PBE) and ethylene-octene copolymer elastomer (EOC), which are blended into the PP to form the test samples. The samples go through thermal cycling treatment with temperatures from -30 to 150 °C, after which the trap distribution and the DC breakdown strength are measured. Structural changes in the samples are estimated through Fourier transform infrared spectroscopy (FTIR), scanning electron microscope (SEM) and differential scanning calorimetry (DSC) measurements. The test results indicate that, with the growth of the thermal cycling number, the trap center decreases whereas the trap density increases, and the DC breakdown strength tends to be reduced. The appearance of oxidation product, loose structure and decreased crystallinity with the thermal cycling ageing should be responsible for the encouragement in charge transport and the reduction in the breakdown strength. The degradation of PP/EOC is more obvious than that of PP/PBE due to its worse compatibility, the PP/PBE exhibits better resistance to the thermal cycling ageing.

Improvement of partial discharge resistance of polypropylene under AC voltage by blending elastomer

This paper reports on the partial discharge (PD) erosion characteristics of polypropylene (PP)/elastomer blends where ethylene-octene copolymer elastomer (EOC) and propylene-based elastomer are involved. The PD erosion is performed through a pair of needle-to-plane electrodes by applying 5 kV AC voltage for 2 h. A high-frequency current transformer, optical recorder, and ozone sensor are used to capture the information released during the PD erosion process. In addition, a 3D optical profilometer is employed to record the erosion profile, from which the erosion depth and the surface roughness can be extracted. Carrier trap distribution is derived from the isothermal surface potential decay measurement. The influences of elastomer type and content on the PD resistance are analyzed. The results show that the resistance is improved with the addition of elastomer, and the blend containing EOC of 20 wt% has the best PD resistance among all samples, which is 61.9% higher than that of the pure PP. It is proposed that the carrier trap characteristics, the property of elastomer, and the free volume in the material play important roles in the improvement of the PD resistance. This work provides a potential method to enhance the PD resistance of PP by blending elastomer with proper type and content.

Large-Scale Preparation of Micro-Nanofibrous and Fluffy Propylene-Based Elastomer/Polyurethane@Graphene Nanoplatelet Membranes with Breathable and Flexible Characteristics for Wearable Stretchy Heaters.

Effective personal thermal management is crucial for protecting human health during cold weather. Therefore, wearable heaters based on electric-heating membranes are one of the most promising devices to become essential appliances in our daily lives. The main challenge toward this goal is the development of electric-heating membranes with adequate breathable, flexible, and stretchable characteristics. In the work presented here, micro-nanofibrous fluffy electric-heating membranes were prepared by coating polyurethane/graphene nanoplatelet (PU@GNP) films onto melt-blown propylene-based elastomer (PBE) micro-nanofibrous membranes via a facile, cheap, and large-scale method consisting of a coating-compressing cyclic process. Investigation of the resulting PBE/PU@GNP membranes showed that the PU@GNP films were uniformly deposited onto the PBE micro-nanofiber surfaces, forming fluffy interconnected conducting channels. By applying a voltage of 36 V to the prepared PBE/PU@GNP membranes, the temperature increased to 69.7 °C, confirming excellent electric-heating features. Moreover, the porosity of the fabricated membrane could be tailored readily by adjusting the coating-compressing cycles. Benefiting from the conducting channels, the PBE/PU@GNP membranes exhibited efficiently regulated air permeability ranging from 212 to 60.2 mm/s, a prominent softness score of 53.8, and an excellent elastic recovery rate of 85.5%. These findings demonstrate that PBE/PU@GNP micro-nanofibrous fluffy membranes may well be suitable for application in electric-heating clothing. The cyclic coating-compressing preparation process may be attractive in industrial manufacturing.

Fundamental influences of propylene‐based elastomer on the foaming properties of high melt strength polypropylene based on extrusion foaming

AbstractHigh melt strength polypropylene (HMS‐PP)/propylene‐based elastomer (PBE) microcellular foams were prepared by the extrusion foam method. The fundamental mechanism of PBE improving the foaming properties of HMS‐PP was investigated. PBE 6102, with a low melt flow rate and high ethylene content, enables HMS‐PP/PBE blends to form a microphase‐separated structure and maintain good melt strength and pronounced strain hardening, which would promote cell nucleation and hold cell structure at relatively high temperatures. Furthermore, PBE 6102 postpones HMS‐PP crystallization and decreases the optimum foaming temperature, which helps balance melt elasticity and viscosity near the foaming window to avoid cell rupturing and merging. The introduction of PBE 6102 does not reduce the crystallization rate of HMS‐PP nor the crystallinity of the foamed samples, fixing the cell structure to prevent collapse during the cell solidification stage. Microcellular HMS‐PP/PBE 6102 foams with a high expansion ratio, small cell size, and large cell count were successfully fabricated.

Melt Spinning of Flexible and Conductive Immiscible Thermoplastic/Elastomer Monofilament for Water Detection.

In many textile fields, such as industrial structures or clothes, one way to detect a specific liquid leak is the electrical conductivity variation of a yarn. This yarn can be developed using melt spun of Conductive Polymer Composites (CPCs), which blend insulating polymer and electrically conductive fillers. This study examines the influence of the proportions of an immiscible thermoplastic/elastomer blend for its implementation and its water detection. The thermoplastic polymer used for the detection property is the polyamide 6.6 (PA6.6) filled with enough carbon nanotubes (CNT) to exceed the percolation threshold. However, the addition of fillers decreases the polymer fluidity, resulting in the difficulty to implement the CPC. Using an immiscible polymers blend with an elastomer, which is a propylene-based elastomer (PBE) permits to increase this fluidity and to create a flexible conductive monofilament. After characterizations (morphology, rheological and mechanical) of this blend (PA6.6CNT/PBE) in different proportions, two principles of water detection are established and carried out with the monofilaments: the principle of absorption and the short circuit. It is found that the morphology of the immiscible polymer blend had a significant role in the water detection.

Structural evolution in propylene-based elastomer with γ form during stress relaxation

The stress relaxation and the structural evolution of a random propylene-ethylene copolymer of about 12 mol% of ethylene co-units with pure γ form (iPPcoE12-γ), which was pre-stretched to various strains at 30 °C, were investigated by means of in situ wide angle X-ray diffraction techniques. The two-dimensional X-ray diffraction patterns were decomposed into oriented and unoriented parts. It turned out that the unoriented fraction of the iPPcoE12-γ sample became oriented in the process of the relaxation. Due to the unique “cross-β” arrangement in the γ form, the fraction of elastic stress of iPPcoE12-γ was higher than that of iPPcoE12-α with pure α form at a small pre-stretched strain (εH = 0.27) and the increased fraction of oriented parts was much less than that of iPPcoE12-α at medium strains (εH = 0.71 and 1.27). A comparative analysis of the relaxation behavior of iPPcoE12-γ and iPPcoE12-α revealed that the elasticity and stability of iPPcoE12-γ were more attractive at smaller strains (smaller than critical strain C—the strain of the starting of the fragmentation of crystalline blocks), while at larger strains (larger than 1.27) iPPcoE12-α had its advantages in elasticity. In addition, it was found that the γ to α transition occurred during the relaxation, and the unoriented crystallites with γ form were more difficult to transform than the oriented one.

Development of Flexible and Conductive Immiscible Thermoplastic/Elastomer Monofilament for Smart Textiles Applications Using 3D Printing.

3D printing utilized as a direct deposition of conductive polymeric materials onto textiles reveals to be an attractive technique in the development of functional textiles. However, the conductive fillers—filled thermoplastic polymers commonly used in the development of functional textiles through 3D printing technology and most specifically through Fused Deposition Modeling (FDM) process—are not appropriate for textile applications as they are excessively brittle and fragile at room temperature. Indeed, a large amount of fillers is incorporated into the polymers to attain the percolation threshold increasing their viscosity and stiffness. For this reason, this study focuses on enhancing the flexibility, stress and strain at rupture and electrical conductivity of 3D-printed conductive polymer onto textiles by developing various immiscible polymer blends. A phase is composed of a conductive polymer composite (CPC) made of a carbon nanotubes (CNT) and highly structured carbon black (KB)- filled low-density polyethylene (LDPE) and another one of propylene-based elastomer (PBE) blends. Two requirements are essential to create flexible and highly conductive monofilaments for 3D-printed polymers onto textile materials applications. First, the co-continuity of both the thermoplastic and the elastomer phases and the location of the conductive fillers in the thermoplastic phase or at the interface of the two immiscible polymers are necessary to preserve the flexibility of the elastomer while decreasing the global amount of charges in the blends. In the present work based on theoretical models, when using a two-step melt process, the KB and CNT particles are found to be both preferentially located at the LDPE/PBE interface. Moreover, in the case of the two-step extrusion, SEM characterization showed that the KB particles were located in the LDPE while the CNT were mainly at the LDPE/PBE interface and TEM analysis demonstrated that KB and CNT nanoparticles were in LDPE and at the interface. For one-step extrusion, it was found that both KB and CNT are in the PBE and LDPE phases. These selective locations play a key role in extending the co-continuity of the LDPE and PBE phases over a much larger composition range. Therefore, the melt flow index and the electrical conductivity of monofilament, the deformation under compression, the strain and stress and the electrical conductivity of the 3D-printed conducting polymer composite onto textiles were significantly improved with KB and CNT-filled LDPE/PBE blends compared to KB and CNT-filled LDPE separately. The two-step extrusion processed blends presented the best properties and almost similar to the ones of the textile materials and henceforth, could be a better material for functional textile development through 3D printing onto textiles.

Compatibility dependent space charge accumulation behavior of polypropylene/elastomer blend for HVDC cable insulation

Polypropylene (PP)/elastomer blend is a promising candidate for high voltage direct current (HVDC) cable insulation. Space charge accumulation in HVDC cable is an important factor for safe and stable operation of HVDC transmission system. In this paper, propylene based elastomer (PBE) and ethylene-octene copolymer elastomer (EOC) were added into PP to prepare the blend sample. Space charge accumulation behavior was estimated by the pulsed electro-acoustic (PEA) method, and the influence of compatibility between the PP and the elastomer on the charge accumulation behavior was investigated. Polarized optical microscope (POM), differential scanning calorimetry (DSC), X-ray diffraction (XRD) and dynamic mechanical analysis (DMA) measurements were performed to assist the understanding of the compatibility dependent space charge accumulation behavior. The obtained results showed that the amount of space charge in the PP/PBE blend was lower than that in the PP/EOC blend. As compared with the PP/EOC blend, higher crystallinity with integrated crystal morphology and β-crystal form were observed in the PP/PBE blend for better compatibility between PP and PBE. It is suggested that deeper trap centers are formed in the PP/PBE blend than in the PP/EOC blend due to the compatibility, by which the charge injection is restricted.

Strain dependent evolution of structure and stress in propylene-based elastomer during stress relaxation

The stress relaxation behaviors of propylene-based elastomer with pure α form were investigated at 30 °C at various pre-stretched strains by means of in situ wide angle X-ray diffraction techniques. The stress decreased rapidly at the beginning of relaxation process and then showed a slow decay independent of pre-stretched strains. This decrease in stress during relaxation was accompanied by an obvious increase in the orientational degree and the crystallinity. However, the processes of increasing the crystallinity depended strongly on the imposed strain. At small strain (εH 0.17), besides the transition of some oriented amorphous phase into oriented crystals, a fraction of unoriented amorphous phase transformed into unoriented crystals. At medium strains (εH 0.76 and 1.28), a fraction of unoriented amorphous and unoriented crystals transformed to oriented crystals. A very small fraction of unoriented amorphous phase transformed into unoriented mesomorphic phase. At large strains (εH 1.63 and 1.85), a fraction of oriented amorphous phase transformed to oriented crystals. The different network with varied fraction of amorphous and crystalline phases accounted for the distinct transformation processes at different pre-stretched strains. Especially at medium strains, the “appropriately stretched” high elastic network was formed so that higher portion of stress remained after the relaxation. Furthermore, it was found that crystallization during stress relaxation provides an alternative route for lowering the macroscopic stress by reducing the effective number of network chain segments in unit volume.

Binary structured polypropylene-/propylene-based elastomer fibrous membranes with enhanced flexibility

Polypropylene (PP) fibrous membranes are widely used in medical and healthcare due to its sustainability. However, pristine PP fibrous membranes show poor flexibility, which limits their advanced functional application in medical and healthcare. Therefore, to improve the flexibility of PP fibrous membranes, propylene-based elastomer (PBE), a copolymer compatible with PP, was introduced by using the melt blowing technique in this study. The SEM images show that the PP/PBE fibrous membrane samples expressed a binary structured network morphology consisting of fibers with a diameter distribution ranging from 0.4 to 15 µm. With an increase in PBE mass ratio from 15 to 80 wt%, the frequency of fibers with a diameter <3 µm increased from 48.6 to 61.2%, thus making the elastic recovery rate in the machine direction (MD) increase from 62.9 to 80.3% and softness values increase from 15.88 to 54.31. Meanwhile, air permeability increased from 856 to 2257 m3/m2 · h as the mass per unit area of the samples decreased from 129.9 to 40.1 g/m2. This work provides an alternate method for producing flexible fibrous membranes that have potential for application in items such as surgical gown cuffs, bandages, and face mask ear loops.

Controllably coated graphene oxide particles with enhanced compatibility with poly(ethylene-co-propylene) thermoplastic elastomer for excellent photo-mechanical actuation capability

This paper reports the utilization of the controllable coating via SI-ATRP technique as a promising approach for controlling stimuli-responsive capabilities of graphene oxide (GO) based nanocomposites. Various polymer brushes with controlled molar mass and narrow dispersity were grown from the surface of GO particles. Modification of GO with poly(methyl methacrylate) and poly(n-butyl methacrylate) was proved by transmission electron microscopy, thermogravimetric analysis with online FTIR recording and finally by X-ray photoelectron spectroscopy (XPS). Densities of GO-based materials were investigated and conductivity measurements showed the increase values. XPS and Raman shift was used to confirm the GO particles reduction. A compatibility of the filler with propylene-based elastomer was elucidated by melt rheology. The light-induced actuation capability was investigated on composite samples to show, that polymer hybrid particles based on GO have better compatibility with the polymer matrix and thus their proper dispersibility was significantly improved. In addition the plasticizing effect of the short polymer grafts present on the GO filler surface has the crucial impact on the matrix stiffness and thus the ability of composite material to reversibly respond to the external light stimulation.

Toughened High-Flow Polypropylene with Polyolefin-based Elastomers.

Polyolefin is the most widely used and versatile commodity polymer. In this work, three types of polyolefin-based elastomers (PBEs) were adopted to toughen a high-flow polypropylene to improve its overall performance. The chain microstructures of these PBEs, including ethylene/1-octene (E/O) random copolymer from Dow Chemical′s polyolefin elastomer (POE), olefin block copolymers (OBCs) of E/O from Dow, and ethylene/propylene random copolymer from ExxonMobil’s propylene-based elastomer, were elucidated by GPC, 13C NMR, TREF, and DSC techniques. The mechanical, thermal and optical properties, and morphology analysis of the PP/PBE blends were also studied to investigate the toughening mechanism of these PBEs. The results showed that all three types of PBEs can effectively improve the Izod impact strength of the PP/PBE blends by the addition of the rubber compositions, at the cost of the stiffness. PBE-1 and PBE-2 were found to have a great stiffness–toughness balance with about 1700 MPa of flexural modulus, about 110 °C of HDT and 3.6 kJ/m2 of impact strength on the prepared PP/PBE blends by forming separated rubber phase and refined spherulite crystals. As a result, the OBC with alternating hard and soft segments could achieve a similar toughening effect as the E/P random copolymer. Surprisingly, no obvious rubber phase separation was observed in the PP/PBE-4 blend, which might be due to the good compatibility of the E/P random chains with the isotactic PP; therefore, the PP/PBE blend obtains great toughness performance and optical transparency with the highest Izod impact strength of 4.2 kJ/m2 and excellent transparency.

Temperature and trap distribution dependence of electrical tree growth characteristics in polypropylene/elastomer blends for recyclable cable insulation

Polypropylene (PP)/elastomer blends as a promising cable insulation material have to face the challenge of electrical treeing which possibly leads to unexpected insulation failure. In this work, two types of elastomers, i.e. polyolefin elastomer and propylene-based elastomer, have been blended into isotactic PP. Effects of the elastomer content and type on electrical treeing behaviours have been investigated under different ambient temperatures. Isothermal surface potential decay measurement has been performed to explore the influence of trap distribution on the treeing behaviour, scanning electron microscope and differential scanning calorimetry measurements were performed to characterise the structure of blends. It was found that with the increase of elastomer content, the trap energy level was reduced and the shallow trap density was increased, which resulted in the enhancement of the tree growth rate and the decrease in the breakdown time. With the temperature changing from 20 to 100°C, the growth rate tended to be increased except that an anomalous reduction in the rate occurred at 80°C. It is suggested that the compatibility between PP matrix and elastomer plays an important role in determining the morphology of blends, which in turn influences the trap distribution and the temperature dependent treeing behaviours.

Synthesis and Effect of Hierarchically Structured Ag-ZnO Hybrid on the Surface Antibacterial Activity of a Propylene-Based Elastomer Blends.

In this study, a hybrid Ag-ZnO nanostructured micro-filler was synthesized by the drop technique for used in plastic and medical industry. Furthermore, new antibacterial polymer nanocomposites comprising particles of Ag-ZnO up to 5 wt % and a blend of a thermoplastic polyolefin elastomer (TPO) with polypropylene were prepared using twin screw micro-compounder. The morphology and crystalline-phase structure of the hybrid Ag-ZnO nanostructured microparticles obtained was characterized by scanning electron microscopy and powder X-ray diffractometry. The specific surface area of this filler was investigated by means of nitrogen sorption via the Brunauer-Emmet-Teller method. A scanning electron microscope was used to conduct a morphological study of the polymer nanocomposites. Mechanical and electrical testing showed no adverse effects on the function of the polymer nanocomposites either due to the filler utilized or the given processing conditions, in comparison with the neat polymer matrix. The surface antibacterial activity of the compounded polymer nanocomposites was assessed against Escherichia coli ATCC 8739 and Staphylococcus aureus ATCC 6538P, according to ISO 22196:2007 (E). All the materials at virtually every filler-loading level were seen to be efficient against both species of bacteria.

Trap Distribution and Dielectric Breakdown of Isotactic Polypropylene/Propylene Based Elastomer With Improved Flexibility for DC Cable Insulation

In this paper, we report on electrical and mechanical properties of isotactic polypropylene (PP) blended with polyolefin elastomer (POE) and propylene-based elastomer (PBE). Carrier trap distribution of the samples was estimated by isothermal surface potential decay measurement, while dc breakdown strength was measured through a pair of semicircle electrodes. Elongation at break and tensile strength were obtained to examine the variation in mechanical property of PP caused by the addition of elastomers. Furthermore, scanning electron microscope (SEM), differential scanning calorimetry (DSC), and dynamic mechanical analysis (DMA) have been employed to assist the understanding of morphology of the blends, thermal properties, and mechanical properties. Obtained results have indicated that with the increase of the elastomer content from 0 to 30 wt%, the trap depth appeared to be shallower and the dc breakdown strength tended to be reduced for both PP/PBE and PP/POE samples. Compared with PP/POE blend, PP/PBE blend had deeper trap depth, which should be responsible for its higher dc breakdown strength. In addition, PP/PBE blend has presented a better performance in elongation at break and tensile strength measurement. With the growth of the elastomer content, the crystallinity of the blends appeared to decrease, whereas the melting and the crystallization temperatures did not change remarkably. The SEM inspections and DMA results revealed better compatibility between PP and PBE compared with that between PP and POE, which should be the reason for the better electrical and mechanical properties of PP/PBE blend. The blend of PBE with low content could result in remarkably improved flexibility of PP with acceptable electrical strength for dc cable insulation.

Analysis of Diffuse SAXS Intensity in the Vicinity of Zero Scattering Angle Reveals the Location of the Flexibilizer in Homopolypropylene Compounds

Vistamaxx performance polymer which is one type of propylene-based elastomer acting as the flexibilizer for toughening the homopolypropylene (HPP) was studied using X-ray scattering at wide, small, and ultrasmall angle regimes and dynamic mechanical analysis techniques. The well-overlapped scattering curves at wide angle and ultrasmall angle indicate the unaffected structure on the atomic scale and hundreds of nanometer scale for all the compounds. The different scattering intensity at the moderate scattering vector indicates the existence of heterogeneities induced by the flexibilizer on the nanometer scale from 20 to 100 nm. The flexibilizer exfoliated the lamellae from the periodic stacks in HPP. The heterogeneities could be ascribed to the phase-separated flexibilizer and the exfoliated lamellae. The phase-separated flexibilizer domains block the formation of the complete crystalline skeleton that lowers the storage modulus of the compounds compared with the pure HPP.