Mechanical Properties and Morphology of Ternary PP/EPDM/PE Blends

The ternary blends of high‐density polyethylene (PE), EPDM terpolymer and polypropylene (PP) have been used as a model low interfacial tension system to study encapsulation dynamics in ternary blends and their relation to the blends' mechanical properties. It was found that the modulus, tensile strength and impact resistance can be improved by PE addition if the PE is localized within the EPDM phase. A range of blend morphology was found depending on the PE viscosity and polymer incorporation sequence in the twin‐screw extruder. In the most favorable sequence, PE and EPDM were mixed together prior to their dispersion in the PP matrix. This practice resulted in a 50% increase in impact resistance when compared to mixing the three components in a single‐step.     

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 addition of polyethylene on properties of polypropylene/ethylene–propylene rubber blends

Toughening of polypropylene was carried out by adding two types of ethylene-propylene rubber (EPR) having different ethylene content, and three commercial types of EPR containing high density polyethylene (PE). The concentration of EPR was varied from 0–30%. Globular morphology of the dispersed phase was observed at all concentrations. Average particle size of the dispersed phase (EPR) was about 2–4 μm with about 10% within the 0.5–1 μm range. Although most of the properties were not affected by the presence of polyethylene, high notched Izod impact strength was achieved only with samples containing PE. Melt flow rate, yield strength and modulus were found to decrease almost linearly with increasing elastomer concentration in the blend. Elongation at break was enhanced by the addition of EPR, particularly those containing PE. The contribution of PE to the properties was explained by the specific EPR/PE particle morphology (core-shell or interpenetrating) but the exact mechanism of toughening of PP with EPR in the presence of PE is not clear. © 1996 John Wiley & Sons, Inc.     

PP/HDPE/EPDM复合体系微孔发泡实验

聚丙烯(PP)是结晶性聚合物,熔体强度低,发泡性能差.为了提高PP的微孔发泡性能,首先将PP和聚乙烯(PE)共混,然后在PP/PE共混体系中加入少量EPDM,研究EPDM的质量含量对PP/PE共混体系熔体强度和最终泡孔结构的影响.分析机理,寻找能够提高PP熔体强度和改善发泡性能的材料.     

Surface segregation of polyethylene in low‐density polyethylene/ethylene–propylene–diene rubber blends: Aspects of component structure

Aspects of the molecular weight and its distribution, the branching of low‐density polyethylene (LDPE), and the molecular composition of the ethylene–propylene–diene rubber (EPDM) matrix are presented in this article in terms of their influence on the surface segregation of polyethylene (PE) in elastomer/plastomer blends. All of the PEs studied, despite different weight‐average molecular weights and degrees of branching, segregated to the surface of the LDPE/EPDM blends. Atomic force microscopy pictures demonstrated defective crystalline structures on the surface of the blends, which together with a decrease in the degrees of their bulk crystallinity and a simultaneous increase in their melting temperatures, pointed to a low molecular weight and a defective fraction of PE taking part in the surface segregation. The extent of segregation depended on the molecular structure of the EPDM matrix, which determined the miscibility of the components on a segmental level. The higher the ethylene monomer content in EPDM was, the lower was the PE content in the surface layer of the blends. The composition and structure of the surface layer was responsible for its lower hardness in comparison with the bulk of the blends studied. The surface gradient of the mechanical properties depended on the physicochemical characteristics of the components and the blend composition, which created the possibility of tailoring the LDPE/EPDM blends to dedicated applications. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 625–633, 2006     

Linear low-density polyethylene addition to polypropylene/elastomer blends: Phase structure and impact properties

Morphology features and effects of particle size and composition of the disperse phase on the impact properties have been studied for the blends of isotactic polypropylene (PP)/ethylene-propylene-diene terpolymer and (EPDM)/linear low-density polyethylene (LLDPE). The blend components were mixed in a twin-screw extruder, press molded, and analyzed by scanning electron microscopy, SEM (fractured and toluene etched samples), and by transmission electron microscopy, TEM (RuO₄ stained samples). TEM was most effective for the identification of component distribution and particle size measurement. An increasing degree of LLDPE and EPDM interpenetration was observed with the PE content. Not one case of a neat component separation was detected. LLDPE addition improves the EPDM dispersability, affecting mainly the larger particles. The impact properties at room temperature were especially dependent on the rubber content, whereas at low temperature the particle diameter appears to be the controlling parameter. The affect of LLDPE on blend toughness is more evident in the latter case.     

Enhancing the mechanical,morphological, and rheological behavior of polyethylene/polypropylene blends with maleic anhydride-grafted polyethylene

This is the first study to showcase the use of maleic anhydride-grafted polyethylene (MAPE) to compatibilize polyethylene (PE)-rich blends, where polypropylene (PP) represents the minor phase. By first mixing PP with MAPE, and then adding PE, MAPE was assumed to be localized at the PE/PP interface. Microscopy analysis confirmed that MAPE led to a remarkably fine PE/PP/MAPE morphology, with PP being uniformly dispersed into PE and having an average diameter 267% smaller than that in the PE/PP blend. According to mechanical and rheological tests, this translated into a 14%, 20%, and 14% enhancement of tensile strength, tensile modulus, and tensile toughness, respectively, as well as a 10% and 20% drop in PE/PP viscosity mismatch and interfacial tension, respectively. Finally, PE/PP/MAPE tensile toughness and elongation at break were greater than those of virgin PP, while PE/PP/MAPE strength and stiffness were similar to the ones of neat PP. Therefore, this study provides industries with the possibility to utilize products rich in PE instead of those made of more expensive PP, while still keeping the level of performance high; hence, creating a paradigm shift in the development of advanced lightweight polyolefin materials with tuned functionalities.     

Annealing of polypropylene/poly(ethylene-co-propylene) blend. II. Influence of the structure and properties of poly(ethylene-co-propylene) and blended polyethylene on impact strength

The effect of annealing on the impact strength of PP/poly(ethylene-co-propylene) (PEP) and PP/PEP/PE blends was studied with regard to the structure of PEP and the polyethylene crystallinity. The tensile impact strength of annealed blends was remarkably affected by the PEP structure such as molecular weight and comonomer composition and the annealing temperature, while the brittle temperature was scarcely affected. For the PP/PEP/PE blends, annealing at temperatures above the melting point of PE lowers the tensile impact strength in a similar manner as the PP/crystalline PEP blend. These phenomena were explained on the basis of the deformation mechanism presented in the previous article, that is, a thicker interfacial layer of PP and PEP forms by means of annealing to increase the energy needed to deform the interface. By using a scanning electron microscope, the transition layer was observed at the interface between amorphous PEP and PE in the PP/amorphous PEP/PE blend after etching with nitric acid. The formation of a thicker transition layer between amorphous PEP and PE and a sizeable increase in PE particle size by annealing was observed. The phenomena should be correlated with the impact sensitivity, especially tensile impact strength, in the PP/crystalline PEP and PP/amorphous PEP/PE blends. A reasonable explanation of the microstructure in PP/PEP blends has been developed in terms of comonomer composition and melting property of PEP.     

Morphologies of polyethylene–ethylene/propylene/diene monomer particles in polypropylene‐rich polyolefin blends: Flake structure

Morphologies of polyethylene–ethylene/propylene/diene monomer (PE/EPDM) particles in 93/7 polypropylene (PP)/PE blends were investigated. SEM micrographs of KMnO₄‐etched cut surfaces and fracture surfaces of the blends revealed the existence of the “flake” structure. In the particles, crystalline PE formations with flake shape, which remain after etching, are called flakes. In addition to the PE‐crystalline flakes, amorphous PE, located between PE crystalline lamellae and EPDM rubber, complement the flake structure. The flakes are usually linked with the PP matrix, as seen in the heptane‐treated cut surfaces. These links, although observed with compatibilized samples, originate from the crystalline nature of PE particles, if no compatibilizer is added. Separately, the morphology of Royalene (consisting of high‐density PE and EPDM rubber, used as a PP/PE compatibilizer) was investigated by low‐voltage scanning TEM. The interaction of the components in the PE/EPDM blends can explain the formation of the flakes and toughening of the PP/PE blends. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 3087–3092, 2003     

Polymer compounds based on the three-component blend PP-EPDM-oil: effect of their structure on physical properties

The variation of structure and properties of a triple blend of polypropylene (PP), ethylene-propylene-diene monomer rubber (EPDM), and oil with mixing conditions was studied. The structure and physical properties of this blend are mainly determined by the intermolecular interaction of EPDM and PP components. The interaction depends on the EPDM/PP ratio at the molecular level and on the mixing regime. The optimal mixing conditions that determined the better physical properties of these blends were defined.     

Study on morphology of ternary polymer blends. II. Effect of composition

The composition effect on morphology of polypropylene/ethylene–propylene–diene terpolymer/polyethylene (PP/EPDM/PE) and polypropylene/ethylene–propylene–diene terpolymer/polystyrene (PP/EPDM/PS) ternary blends has been investigated. In all of the blends, polypropylene as the major phase was blended with two minor phases, that is, EPDM and PE or PS. From morphological studies using the SEM technique a core–shell morphology for PP/EPDM/PE and separated dispersed morphology for PP/EPDM/PS were observed. These results were found to be in agreement with the theoretical predictions. The composition of components affected only the size of dispersed phases and had no appreciable effect on the type of morphology. The size of each dispersed phase, whether it forms core or shell or disperses separately in matrix, can be related directly to its composition in the blend. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 1138–1146, 2001     

Polypropylene composites. II: Structure-property relationships in two- and three-component polypropylene composites

Two- and three-component polypropylene (PP) blends and composites were prepared to study their structure/property relationships. Butadiene-styrene (BDS) copolymers of low compatibility formed large particles of poor adhesion in PP resulting in inferior mechanical properties. Better miscibility of ethylene-propylene-diene (EPDM) elastomer results in more finely dispersed particles and the experimental results indicate a transition to an interpenetrating network (IPN)– like structure with increasing elastomer content. Effective impact modification can be achieved only with EPDM elastomers of sufficient miscibility. Mutual wettability and adhesion of the components determine the structure and properties in PP/elastomer/filler systems. Modification of PP by acrylic acid grafting promotes PP/filler adhesion which, in turn, results in the separate dispersion of the components. In an unmodified PP matrix, a significant amount of the filler is encapsulated by the elastomer. At low filler content, better low temperature impact strength is achieved in the case of separately dispersed components, while encapsulation is more advantageous at high filling grades.     

聚烯烃改性PET的研究

通过PET与PP、HDPE、EPDM挤出共混，注射模塑制得试样。经DTA、SEM和力学性能测试，表征了共混体系的热行为、结构形态和力学性能。结果表明，在PET/PP(EPDM、HDPE)共混体系中，加入少量的PP-g-MI(EPDM-g-MAH、PE-g-MI)，可较好地改善PEt与PP(EPDM、HDPE)之间的相容性，使分散相在PET基体连续相中分散均匀，分散相尺寸减小，增加了两相间界面的粘结力；同时对PET的结晶有较强的促进作用，使其冷结晶温度降低，改善了PET的加工性能；并且能大幅度提高共混物的冲击强度。     

Mechanical,thermal, and morphological characteristics of compatibilized and dynamically vulcanized polyoxymethylene/ethylene propylene diene terpolymer blends

Dynamically vulcanized blends of polyoxymethylene (POM) and ethylene propylene diene terpolymer (EPDM) with and without compatibilizer were prepared by melt mixing in a twin screw extruder. Maleic anhydride (MAH) grafted EPDM (EPDM‐g‐MAH) has been used as a compatibilizer. Dicumyl peroxide was used for vulcanizing the elastomer phase in the blends. Mechanical, dynamical mechanical, thermal, and morphological properties of the blend systems have been investigated as a function of blend composition and compatibilizer content. The impact strength of both dynamically vulcanized blends and compatibilized/dynamically vulcanized blends increases with increase in elastomer content with decrease in tensile strength. Dynamic mechanical analysis shows decrease in tanδ values as the elastomer and compatibilizer content increased. Thermograms obtained from differential scanning calorimetric studies reveal that compatibilized blends have lower T_m values compared to dynamically vulcanized blends, which confirms strong interaction between the plastic and elastomer phase. Scanning electron microscopic observations on impact fractured surface indicate reduction in particle size of elastomer phase and its high level of dispersion in the POM matrix. In the case of compatibilized blends high degree of interaction between the component polymers has been observed. POLYM. ENG. SCI., 47:934–942, 2007. © 2007 Society of Plastics Engineers     

Largely improved toughness of PP/EPDM blends by adding nano-SiO2 particles

As a part of long-term project aimed at super polyolefin blends, in this work, we report the toughness and phase morphology of polypropylene (PP)/EPDM/SiO₂ ternary composites. Two processing methods were employed to prepare PP/elastomer/filler ternary composites. One was called one-step processing method, in which the elastomer and the filler directly melt blended with PP matrix. Another one was called two-step processing method, in which the elastomer and the filler were mixed first, and then melt blended with pure PP. Two kinds of PP (grafted without or with maleic anhydride (PP-g-MA)) and SiO₂ (treated with or without coupling agent) were used to control the interfacial interaction among the components. The dependence of the phase morphology on interfacial interaction and processing method was investigated. It was found that the formation of filler-network structure could be a key for a simultaneous enhancement of toughness and modulus of PP and its formation seemed to be dependent on the work of adhesion (W_AB) and processing method. As the W_AB of PP/EPDM interface was much lower than that of PP/SiO₂ and EPDM/SiO₂, and the two-step processing method was used, the formation of filler-network structure was favorable. In this case, a super toughened PP ternary composite with the Izod impact strength 2-3 times higher than PP/EPDM binary blend and 15-20 times higher than pure PP could be achieved.     

The Use of Ethylene/Propylene Copolymers as Compatibilizers for Recycled Polyolefin Blends

Compatibilizing effects of ethylene/propylene (EPR) diblock copolymers on the morphology and mechanical properties of immiscible blends produced from recycled low‐density polyethylene (PE‐LD) and high‐density polyethylene (PE‐HD) with 20 wt.‐% of recycled poly(propylene) (PP) were investigated. Two different EPR block copolymers which differ in ethylene monomer unit content were applied to act as interfacial agents. The morphology of the studied blends was observed by scanning‐ (SEM) and transmission electron microscopy (TEM). It was found that both EPR copolymers were efficient in reducing the size of the dispersed phase and improving adhesion between PE and PP phases. Addition of 10 wt.‐% of EPR caused the formation of the interfacial layer surrounding dispersed PP particles with the occurrence of PE‐LD lamellae interpenetration into the layer. Tensile properties (elongation at yield, yield stress, elongation at break, Young's modulus) and notched impact strength were measured as a function of blend composition and chemical structure of EPR. It was found that the EPR with a higher content of ethylene monomer units was a more efficient compatibilizer, especially for the modification of PE‐LD/PP 80/20 blend. Notched impact strength and ductility were greatly improved due to the morphological changes and increased interfacial adhesion as a result of the EPR localization between the phases. No significant improvements of mechanical properties for recycled PE‐HD/PP 80/20 blend were observed by the addition of selected block copolymers.     

PP／EPDM／云母共混复合材料的研究

冲击强度和弯曲模量是聚丙烯共混材料中存在的一个矛盾，通过ＰＰ／ＥＰＤＭ／云母三元共混得一以具有高冲击强度和高弯曲模量的硬而韧的复合材料，并将其用于汽车塑料件中。本文研究了ＰＰ／ＥＰＤＭ／云母的共混物配方、共混体系中ＥＰＤＭ和云母含量与冲击强度和弯曲模量间的关系，分析了云母的表面处理及ＰＰ／ＥＰＤＭ／云母材料断面ＳＥＭ照片，提出了该材料的结构形态模型。     

The effect of conditions of mixing of polypropylene/ethylene-propylene elastomer blends on their morphological structure and impact strength

The dependence of morphological structure and notch impact strength of polypropylene/ethylene-propylene elastomer blends on conditions of mixing was investigated. Two types of polypropylene and two types of ethylene-propylene elastomer having different viscosities were used. At low rates and short times of mixing the samples contain both regions showing fine dispersion and regions showing large elastomeric inclusions surrounded with pure polypropylene. With increasing rate and time of mixing the large inclusions gradually disappear. The conditions of mixing which are necessary for reaching a homogeneous structure of the blends depend on viscosities of the components. The independence of particle size of the rate of mixing in homogeneous samples is discussed on the basis of a dynamic equilibrium between the break up and coalescence of droplets. The notch impact strength of the individual samples of the same blend is determined by the size and number of inhomogeneities (large inclusions) in the given sample.     

Effect of ultrasound on extrusion of polypropylene/ethylene–propylene–diene terpolymer blend: Processing and mechanical properties

The effects of ultrasonic irradiation on extrusion processing and mechanical properties of polypropylene (PP)/ethylene–propylene–diene terpolymer (EPDM) blends are examined. Results show that appropriate irradiation intensity can prominently decrease die pressure and apparent viscosity of the melt, increase output, as well as increase toughness of PP/EPDM blends without harming rigidity. In case the blends are extruded with ultrasonic irradiation twice, the impact strength of the blend rises sharply at 50–100 W ultrasonic intensity, and amounts to more than 900 J/m, 1.5 times as high as that of blend without ultrasonic irradiation. Scanning electron microscopy observation shows that with ultrasonic irradiation, morphology of uniform dispersed EPDM phase and good adhesion between EPDM and PP matrix was formed in PP/EPDM blend. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 3519–3525, 2003     

不同弹性体增韧聚丙烯的研究

通过双螺杆挤出机制备了三种不同的弹性体EPR、EPDM、POE与PP的共混物,测试了共混物的力学性能, 比较了三种弹性体的增韧效率。结果表明:三种弹性体都是PP有效的增韧剂,其中POE的增韧效率最高,其冲击强度是纯PP的25倍。通过扫描电镜观察了弹性体在PP中的分散,发现POE在基体中相区尺寸最小,其冲击强度最大;EPDM相区尺寸最大,其冲击强度最小,这意味着共混物的相形态与性能有很好的相关性,三种弹性体在PP中分散尺寸不同的主要原因是由于弹性体与PP的黏度比不同引起的。DMA分析表明低模量的弹性体有利于提高共混物的韧性。