iPP/HDPE blends. II. Modification with EPDM and EVA

Past work has shown that addition of high-density polyethylene (HDPE) to polypropylene (PP) resulted in a significant reduction in the elongation at break and in the gate-region impact strength of injection molded articles. In this study, we report on the compatibilization of these blends with ethylene/propylene/diene monomer (EPDM) or ethylene/vinyl acetate (EVA) copolymers. EPDM is effective at improving the impact strength and gate puncture resistance of a 90/10 PP/HDPE blend. EVA, on the other hand, is effective at improving the impact strength and the elongation at break of this material. It was also found that EVA is a better impact modifier for PP than is EPDM. DSC analysis indicated that EPDM, when blended with PP, caused a significant reduction in the degree of crystallinity of the PP. This was not observed in the case of EVA/PP blends. Further, our results indicate that care must be taken in designating a particular material as a better compatibilizer than some other material. It is crucial that conditions be attached to the label compatibilizer, indicating in particular the desired mechanical properties of the blend. © 1996 John Wiley & Sons, Inc.     

Effect of the elastomer type on the microstructure and mechanical properties of polypropylene

In this study, the effects of the elastomer type—ethylene–propylene–diene monomer (EPDM), three kinds of ethylene vinyl acetate (EVA 9, EVA 18, and EVA 28, where the number is the vinyl acetate concentration), and styrene–butadiene–styrene—and content on the microstructure and mechanical and thermal properties of isotactic polypropylene (i‐PP) blends were investigated. Five different elastomer concentrations (3, 6, 9, 12, and 15 wt %) were added to i‐PP to produce polypropylene/elastomer blends. The yield and tensile strengths, elastic modulus, impact strength, hardness, melt flow index (MFI), and structural properties of the blends were investigated. The tensile and yield strengths, elastic modulus, and hardness decreased gradually, whereas the impact strength and MFI increased as the elastomer content increased. As a result, with respect to the impact strength, the most effective elastomers were EPDM with 15 wt % and EVA 28 with 15 wt % for higher impact strength values. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 1445–1450, 2005     

Rheological properties and crystalline structure of the dynamically cured EPDM and PP/HDPE ternary blends

The rheological properties and crystalline structure of the polyolefin ternary blends of EPDM/polypropylene/high density polyethylene were studied. Blends were prepared in a laboratory internal mixer by two different methods. In blend–cure process, blending and curing were performed simultaneously and EPDM was cured by dicumyl peroxide (DCP) in the presence of PP/HDPE under shear. The cure–blend was to cure EPDM alone first under shear (dynamic curing) and then mix the cured EPDM with PP and HDPE. The effect of DCP concentration, intensity of the shear mixing, and the rubber/plastic composition were studied using capillary rheometer and X-ray diffractometer. The PP-rich ternary blends showed the effect of the mechanooxidative degradation of PP by shear and peroxide. The melt viscosity increased with increasing DCP concentration in blends of EPDM-rich compositions. X-ray diffraction studies revealed that the inclusion of 25 wt % of linear EPDM in the PP/HDPE mixture for the PP-rich ternary blends changed the crystal structure of polypropylene component in the ternary blends. However, the dynamic curing did not alter the crystal structure of PP or HDPE in the blends.     

Viscoelastic,thermal, and morphological analysis of HDPE/EVA/CaCO<Subscript>3</Subscript> ternary blends

High density polyethylene (HDPE), calcium carbonate (CaCO₃), and ethylene vinyl acetate (EVA) ternary reinforced blends were prepared by melt blend technique using a twin screw extruder. The thermal properties of these prepared ternary blends were investigated by differential scanning calorimetry. The effect of EVA loading on the melting temperature (T _m) and the crystallization temperature (T _C) was evaluated. It was found that the expected heterogeneous nucleating effect of CaCO₃ was hindered due to the presence of EVA. The melt viscosities of the ternary reinforced blends were affected by the % loading of CaCO₃, EVA, and vinyl acetate content. Viscoelastic analysis showed that there is a reduction of the storage modulus (G′) with increasing of EVA loading as compared to neat HDPE resin or to HDPE/CACO₃ blends only. The morphology of the composites was characterized by scanning electron microscopy (SEM). The dispersion and interfacial interaction between CaCO₃ with EVA and HDPE matrix were also investigated by SEM. We observed two main types of phase structures; encapsulation of the CaCO₃ by EVA and separate dispersion of the phases. Other properties of ternary HDPE/CaCO₃/EVA reinforced blends were investigated as well using thermal, rheological, and viscoelastic techniques.     

Effect of ethylene-propylene copolymer with residual PE crystallinity on mechanical properties and morphology of PP/HDPE blends

Morphology and mechanical properties of polypropylene (PP)/high density polyethylene (HDPE) blends modified by ethylene-propylene copolymers (EPC) with residual PE crystallinity were investigated. The EPC showed different interfacial behavior in PP/HDPE blends of different compositions. A 25/75 blend of PP/HDPE (weight ratio) showed improved tensile strength and elongation at break at low EPC content (5 wt %). For the PP/HDPE = 50/50 blend, the presence of the EPC component tended to make the PP dispresed phase structure transform into a cocontinuous one, probably caused by improved viscosity matching of the two components. Both tensile strength and elongation at break were improved at EPC content of 5 wt %. For PP/HDPE 75/25 blends, the much smaller dispersed HDPE phase and significantly improved elongation at break resulted from compatibilization by EPC copolymers. © 1995 John Wiley & Sons, Inc.     

Influence of coalescence and interfacial tension on the morphology of PP/HDPE compatibilized blends

In this paper, the compatibilization of polypropylene (PP)/high-density polyethylene (HDPE) blend was studied through morphological and interfacial tension analysis. Three types of compatibilizers were tested: ethylene-propylene-diene copolymer (EPDM), ethylene-vinylacetate copolymer (EVA) and styrene-ethylene/butylene-styrene triblock copolymer (SEBS). The morphology of the blends was studied by scanning electron microscopy. The interfacial tension between the components of the blends was evaluated using small amplitude oscillatory shear analysis. Emulsion curves relating the average radius of the dispersed phase and the interfacial tension to the compatibilizer concentration added to the blend were obtained. It was shown that EPDM was more efficient as an emulsifier for PP/HDPE blend than EVA or SEBS. The relative role of interfacial tension reduction and coalescence reduction to particle size reduction was also addressed. It was observed that the role of coalescence reduction is small, mainly for PP/HDPE (90/10) blends compatibilized by EPDM, EVA or SEBS. The results indicated that the role of coalescence reduction to particle size reduction is lower for blends for which interfacial tension between its components is low at compatibilizer saturation.     

Modification of Ethylene Propylene Diene Terpolymer Rubber by Some Thermoplastic Polymers

Abstract

Blends of ethylene propylene diene terpolymer (EPDM) rubber with thermoplastic polyolefins such as low‐density polyethylene (LDPE), high‐density polyethylene (HDPE), high molecular weight polypropylene (PP), and polypropylene random copolymer grade (PP‐R) were prepared by melt mixing. The physico‐mechanical properties, equilibrium swelling in benzene, and aging properties of the binary blends were investigated, analyzing the effect of the rubber/thermoplastics ratio and the type of the thermoplastic material on these properties. The data obtained indicate that EPDM/PP‐R blend in 20/80 w/w% shows the highest physico‐mechanical properties with improved retained tensile strength at 90°C for 7 days. This blend ratio also gives excellent retained equilibrium swelling in benzene at room temperature for 7 days, although EPDM/LDPE blend in 80/20 w/w% imparts the highest retained elongation at break at 90°C for 7 days.     

Effect of core‐shell morphology evolution on the rheology,crystallization, and mechanical properties of PA6/EPDM‐g‐MA/HDPE ternary blend

In this article, polyamide 6 (PA6), maleic anhydride grafted ethylene‐propylene‐diene monomer (EPDM‐g‐MA), high‐density polyethylene (HDPE) were simultaneously added into an internal mixer to melt‐mixing for different periods. The relationship between morphology and rheological behaviors, crystallization, mechanical properties of PA6/EPDM‐g‐MA/HDPE blends were studied. The phase morphology observation revealed that PA6/EPDM‐g‐MA/HDPE (70/15/15 wt %) blend is constituted from PA6 matrix in which is dispersed core‐shell droplets of HDPE core encapsulated by EPDM‐g‐MA phase and indicated that the mixing time played a crucial role on the evolution of the core‐shell morphology. Rheological measurement manifested that the complex viscosity and storage modulus of ternary blends were notable higher than the pure polymer blends and binary blends which ascribed different phase morphology. Moreover, the maximum notched impact strength of PA6/EPDM‐g‐MA/HDPE blend was 80.7 KJ/m² and this value was 10–11 times higher than that of pure PA6. Particularly, differential scanning calorimetry results indicated that the bulk crystallization temperature of HDPE (114.6°C) was partly weakened and a new crystallization peak appeared at a lower temperature of around 102.2°C as a result of co‐crystal of HDPE and EPDM‐g‐MA. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Time‐temperature superposition principle applicability for blends formed of immiscible polymers

In this work, the linear viscoelastic behavior of PP/PS and PP/HDPE blends modified with SEBS and EPDM, respectively, was studied. Small amplitude oscillatory shear measurements were carried out at different temperatures, ranging from 190°C to 240°C. The storage (G') and loss (G") moduli curves obtained were horizontally shifted and curves of angle delta (δ) (δ = atan (G"/G')) as a function of complex shear modulus (G*), known as van Gurp plots, were obtained at several temperatures, to test the applicability of time‐temperature superposition principle (TTS) to these blends. The results showed that successful application of TTS depends on the flow energy of activation and horizontal shift factors of the individual components of the blend, on the interfacial properties of the blend and on the concentration of compatibilizer added to the blend. TTS application failed for PP/PS blend, but held for PP/HDPE blend. Addition of SEBS to PP/PS blends promoted successful TTS application at specific concentrations that corresponded to interfacial saturation of the dispersed phase. Addition of EPDM did not imply sensitive change on TTS application for the PP/HDPE blends.     

Structure and properties of dynamically cured EPDM/PP blends

The structure and properties of polyolefin blends of ethylene–propylene–diene terpolymer (EPDM) and polypropylene were studied. Blends were prepared in a laboratory internal mixer where EPDM was cured with PP under shear with dicumyl peroxide (DCP) at different shear conditions (blend–cure). Blends were also prepared for comparison from EPDM which were dynamically cured in the absence of PP and blended later (cure–blend). The effect of DCP concentration, intensity of the shear mixing, and rubber/plastic composition were studied. In blend–cure, the melt viscosity increased with increasing DCP concentration in blends of 75% EPDM and 25% PP, but it decreased with increasing DCP concentration in blends of 75% PP and 25% EPDM. In cure–blend, however, the melt viscosity increased with increasing DCP concentration for all compositions. The melt viscosity decreased with increasing intensity of the shear mixing presumably due to the formation of the smaller segregated microdomain of the crosslinked EPDM gels in both blend–cure and cure–blend materials. The crystallization rate was higher in EPDM/PP blends than in PP homopolymer. The crystallization rates for various blending conditions were also compared.     

Studies on binary and ternary blends of polypropylene with SEBS,PS, and HDPE. II. Tensile and impact properties

Studies are reported on tensile and impact properties of several binary and ternary blends of polypropylene (PP), styrene-b-ethylene-co-butylene-b-styrene triblock copolymer (SEBS), high-density polyethylene (HDPE), and polystyrene (PS). The blend compositions of the binary blends PP/X were 10 wt % X and 90 wt % PP, while those of the ternary blends PP/X/Y were 10 wt % of X and 90 wt % of PP/Y, or 10 wt % Y and 90 wt % PP/X (PP/Y and PP/X were of identical composition 90:10); X, Y being SEBS, HDPE, or PS. The results are interpreted for the effect of each individual component by comparing the binary blends with the reference system PP, and the ternary blends with the respective binary blends as the reference systems. The ternary blend PP/SEBS/HDPE showed properties distinctly superior to those of PP/SEBS/PS or the binary blends PP/SEBS and PP/HDPE. Differences in the tensile yield behavior of the different samples and their correlation with impact strength suggested shear yielding as the possible mechanism of enhancement of impact strength. Scanning electron microscopic study of the impact fractured surfaces also supports the shear yielding mechanism of impact toughening of these blends.     

Studies on binary and ternary blends of polypropylene with SEBS,PS, and HDPE. I. Melt rheological behavior

Studies are reported on melt rheological behavior of some binary and ternary blends of polypropylene (PP) with one or two of the following polymers: styrene–b-ethylene butylene–b-styrene triblock copolymer (SEBS), polystyrene (PS), and high-density polyethylene (HDPE). Blend composition of the binary blends PP/X or ternary blends PP/X/Y were so chosen that the former represent addition of 10 wt % X to PP while the latter represent 10 wt % addition of X or Y to the PP/Y or PP/X blend of constant composition 90:10 by weight, X/Y being SEBS, PS, or HDPE. Measurements were made on a capillary rheometer using both temperature elevation and constant temperature methods to study the behaviors prior to flow and in the flow region. Flow behavior, measured at a constant temperature (200°C) and varying shear stress (from 1.0 to 5.0 × 10⁶ dyn/cm²) to evaluate melt viscosity and melt elasticity parameters, is discussed for its dependence on the nature of the blend. Extrudate distortion, studied as a function of shear stress to evaluate the critical shear stress for the onset of extrudate distortion, showed differences in the tendency for extrudate distortion or melt fracture of these different blends. Also discussed is the effect of melt viscosity and melt elasticity on extrudate distortion behavior at the critical condition, which showed a unique critical value of the ratio (melt elasticity parameter)^1/2 (melt viscosity) for all these blends. Blend morphologies before and after the flow through the capillary are investigated through scanning electron microscopy, and their correlations with rheological parameters of the melt are discussed.     

PET/PC blends: Effect of chain extender and impact strength modifier on their structure and properties

Methylene diphenyl diisocyanate (MDI) affects the morphology, rheological, mechanical, and relaxation properties, as well as tendency to crystallize of PET in PET/PC/(PP/EPDM) ternary blends produced by the reactive extrusion. Irrespective of the blend phase structure, the introduction of MDI increases the melt viscosity (MFI dropped), resulting from an increase in the molecular weight of the polymer chains; the PET crystallinity was also reduced. MDI favors compatibility of PET with PC in PET/PC/(PP/EPDM) blends. This is explained by intensified interphase interactions on the level of segments of macromolecules as well as monomer units. The presence of MDI causes a substantial rise in the dynamic shear modulus within the high‐elastic region of PET (for temperature range between T_g,PET and that of PET cold crystallization); the processes of PET cold crystallization and melt crystallization become retarded; the glass‐transition temperatures for PET and PC become closer to each other. MDI affects insignificantly the blend morphology or the character of interactions between the disperse PP/EPDM blend and PET/PC as a matrix. PP/EPDM reduces the intensity of interphase interactions in a PET/PC/(PP/EPDM), but a rise in the degree of material heterogeneity. MDI does not change the mechanism of impact break‐down in the ternary blends mentioned above. Increased impact strength of MDI‐modified materials can be explained by higher cohesive strength and resistance to shear flow at impact loading. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Tensile properties and morphology of the dynamically cured EPDM and PP/HDPE ternary blends

The tensile properties and morphology of the polyolefin ternary blends of ethylenepropylene–diene terpolymer (EPDM), polypropylene and high density polyethylene were studied. Blends were prepared in a laboratory internal mixer where EPDM was cured in the presence of PP and HDPE under shear with dicumyl peroxide (DCP). For comparison, blends were also prepared from EPDM which was dynamically cured alone and blended with PP and HDPE later (cure–blend). The effect of DCP concentration, intensity of the shear mixing, and rubber/plastics composition was studied. The tensile strength and modulus increased with increasing DCP concentration in the blends of EPDM-rich compositions but decreased with increasing DCP concentration in blends of PP-rich compositions. In the morphological analysis by scanning electron microscopy (SEM), the small amount of EPDM acted as a compatibilizer to HDPE and PP. It was also revealed that the dynamic curing process could reduce the domain size of the crosslinked EPDM phase. When the EPDM forms the matrix, the phase separation effect becomes dominant between the EPDM matrix and PP or HDPE domain due to the crosslinking in the matrix.     

Polymer Blends of PBT and PP Compatibilized by Epoxidized Ethylene Propylene Diene Rubber

Summary In this paper, ethylene-propylene-diene-rubber (EPDM) was epoxidized with an in situ formed performic acid to prepare epoxided EPDM(eEPDM). The eEPDM were used to compatibilize poly(butylenes terephthalate)(PBT) and polypropylene(PP) blends in a haake mixer. FTIR results showed that the EPDM had been epoxidized. FTIR and torque test showed the epoxy functional groups in the eEPDM can react with the carboxylic acid or hydroxyl terminal groups in PBT at the interface to form PBT-g-EPDM copolymers. SEM observation showed that these in situ formed grafted copolymers tent to concentrate along the interface to reduce the interfacial tension at the melt and suppress coalescence by steric hindrance. higher quantity of eEPDM compatibilizer in the blend results in a better compatibilized blend in terms of finer phase domains. Notched Izod impact tests showed that both the adding of rubber and the formation of PBT-g-EPDM copolymer improved the toughness of PBT/PP blends.     

Phase morphology and melt rheological behavior of uncrosslinked and dynamically crosslinked polyolefin blends: role of macromolecular structure

Thermoplastic vulcanizates (TPVs) based on polypropylene (PP) with ethylene–octene copolymer (EOC) and ethylene propylene diene rubber (EPDM) have been prepared by co-agent-assisted peroxide crosslinking system. The study was pursued to explore the influence of two dissimilar polyolefin polymers having different molecular architecture on the state and mode of dispersion of the blend components and their influence on melt rheological properties. The effects of dynamic crosslinking of the PP/EOC and PP/EPDM have been compared with special reference to the concentration of crosslinking agent and ratio of blend components. Morphological analyses show that, irrespective of blend ratio, dynamic vulcanization exhibits a dispersed phase morphology with crosslinked EOC or EPDM particles in the continuous PP matrix. It was found that viscosity ratio plays a crucial role in determining the state and mode of dispersion of blend components in the uncrosslinked system. The lower viscosity and torque values of uncrosslinked and dynamically crosslinked blends of PP/EOC in the melt state indicates that they exhibit better processing characteristics when compared to corresponding PP/EPDM blends.     

高韧性和高流动性PP／EPDM共混材料的研制

研究了乙丙橡胶的门尼粘度和结晶性对聚丙烯增韧效果的影响，结果表明，高门尼粘度，部分结晶性橡胶在获得较好韧性的同时不保持较高的刚性，但流动性较差，通过加入ＨＤＰＥ能在复合增韧的同时提高共混物的流动性，添加少量油酸酰胺和硬脂酰胺敢能适当提高共混物的流动性，采用过氧化物降解聚丙烯可以显著提高共混物的流动性，但韧性明显下降，采用可控降解和动态硫化相结合的技术是在得到高韧性，高流动性共混ＰＰ的有效途径。     

Melt rheology of HDPE/EVA blends: The effects of blend ratio,compatibilization, and dynamic vulcanization

The melt rheological behavior of high‐density polyethylene (HDPE)/ethylene vinyl acetate (EVA) blends has been examined with reference to the effect of blend ratio, shear stress, and temperature. The HDPE/EVA blends exhibit pseudoplastic behavior, and the observed rheological behavior of the blends was correlated with the extrudate morphology. The experimental values of the viscosity were compared with the theoretical models. The effect of maleic‐ and phenolic‐modified PE compatibilizers on the viscosity of H₇₀ blend was analyzed and found that compatibilization did not significantly increase the viscosity. The effect of dynamic vulcanization and temperature on the viscosity was also analyzed. The activation energy of the system decreased with increase in EVA content in the system. The phase continuity and phase inversion points of the blends were theoretically predicted and compared with the experimental values. The melt flow index (MFI) values of the blends were also determined and found that the MFI values decreased with increase in EVA content in the system. POLYM. ENG. SCI., 2010. © 2009 Society of Plastics Engineers     

Reactive mixing of PET and PET/PP blends with glycidyl methacrylate–modified styrene‐b‐(ethylene‐co‐olefin) block copolymers

Styrene‐b‐(ethylene‐co‐butylene)‐b‐styrene (SEBS) and styrene‐b‐(ethylene‐co‐propylene) (SEP, SEPSEP) block copolymers with different styrene contents and different numbers of blocks in the copolymer chain were functionalized by melt radical grafting with glycidyl methacrylate (GMA) and employed as compatibilizers for PET‐based blends. Binary blends of PET with both functionalized (SEBS‐g‐GMA, SEP‐g‐GMA, SEPSEP‐g‐GMA) and neat (SEBS, SEP, SEPSEP) copolymers (75 : 25 w/w) and ternary blends of PET and PP (75 : 25 w/w) with various amounts (2.5–10 phr) of both modified and unmodified copolymers were prepared in an internal mixer, and their properties were evaluated by SEM, DSC, melt viscosimetry, and tensile and impact tests. The roles of the chemical structure, grafting degree, and concentration of the various copolymers on blend compatibilization was investigated. The blends with the grafted copolymers showed a neat improvement of phase dispersion and interfacial adhesion compared to the blends with nonfunctionalized copolymers. The addition of grafted copolymers resulted in a marked increase in melt viscosity, which was accounted for by the occurrence of chemical reactions between the epoxide groups of GMA and the carboxyl/hydroxyl end groups of PET during melt mixing. Blends with SEPSEP‐g‐GMA and SEBS‐g‐GMA, at concentrations of 5–10 phr, showed a higher compatibilizing effect with enhanced elongation at break and impact resistance. The effectiveness of GMA‐functionalized SEBS was then compared to that of maleic anhydride–grafted SEBS. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 2201–2211, 2005     

Ethylene vinyl acetate/ethylene propylene diene terpolymer‐blend‐layered double hydroxide nanocomposites

Ethylene vinyl acetate (EVA‐45)/ethylene propylene diene terpolymer (EPDM) blend‐layered double hydroxide (LDH) nanocomposites have been prepared by solution blending of 1:1 weight ratio of EVA and EPDM with varying amounts of organo LDH (DS‐LDH). X‐ray diffraction and transmission electron microscopy analysis suggest the formation of partially exfoliated EVA/EPDM/DS‐LDH nanocomposites. Measurement of mechanical properties of the nanocomposites (3 wt% DS‐LDH content) show that the improvement in tensile strength and elongation at break are 35 and 12% higher than neat EVA/EPDM blends. Dynamic mechanical thermal analysis also shows that the storage modulus of the nanocomposites at glass transition temperature is higher compared to the pure blend. Such improvements in mechanical properties have been correlated in terms of fracture behavior of the nanocomposites using scanning electron microscopy analysis. Thermal stability of the prepared nanocomposites is substantially higher compared to neat EVA/EPDM blend, confirming the formation of high‐performance polymer nanocomposites. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers