Influence of the molecular weight of ethylene vinyl acetate copolymers on the flow and mechanical properties of uncompatibilized polystyrene/ethylene–vinyl acetate copolymer blends

Rubber‐toughened polystyrene (PS) has been extensively studied and is a well‐established material. However, the use of thermoplastic elastomers to toughen PS is new and not well understood. In this study, three types of ethylene vinyl acetate (EVA) copolymers with the same vinyl acetate (VA) content (27.2–28.8 wt %) but with different melt flow indexes (MFI; g (10 min)⁻¹) of 365–440 (Elvax 210), 38.0–48.0 (Elvax 240) and 2.6–3.4 (Elvax 265) were used as impact modifiers for PS. The uncompatibilized blend systems at different compositions were prepared using a twin‐screw extruder and injection moulding to produce the required test pieces. The viscosity of the dispersed phase (EVA) has a significant effect on the mechanical properties of the blends. Rheological studies show that uncompatibilized PS/EVA265 blends exhibit some degree of compatibility when the amount of EVA265 added is below 30 wt %. These results indicate that EVA265 with the lowest melt flow index or highest molecular weight is the most effective impact modifier for PS. The mechanism for such behaviour is still unclear. © 2001 Society of Chemical Industry     

Influence of the polarity of ethylene–vinyl acetate copolymers on the morphology and mechanical properties of their uncompatibilised blends with polystyrene

Rubber‐toughened polystyrene has been extensively studied and is a well‐established technology. However, the use of thermoplastic elastomers to toughen polystyrene (PS) is new and has the potential for further investigations. In the present study, three EVAs (ethylene–vinyl acetate copolymers) with identical melt flow indices (MFIs), of ～2.5 dgmin^?1, but different vinyl acetate (VA) contents, of 9.3 wt% (EVA760), 18.0 wt% (EVA460) and 28.0 wt% (EVA265), were melt blended with PS at 180 °C, and various ASTM test pieces were injection moulded at 200 °C. The polarity of the dispersed phase (ie EVA), has a significant effect on the mechanical properties of the blends. Both mechanical and rheological studies reveal that the uncompatibilised PS/EVA265 blends exhibit some degree of compatibility when the amount of EVA265 is lower than 30 wt%. These results indicate that EVA265 with the highest VA content is the most effective impact modifier for PS. The results clearly show that increasing the VA content in EVA increases the polarity of the dispersed phase, approaching that of the matrix (ie PS) and subsequently improving the compatibility between the two phases in terms of interfacial adhesion. © 2002 Society of Chemical Industry     

Polystyrene and polyether polyurethane elastomer blends compatibilized by SMA: Morphology and mechanical properties

Blends of polystyrene (PS) and the polyether polyurethane elastomer (PU‐et) were prepared by melt mixing using poly(styrene‐co‐maleic anhydride) (SMA) containing 7 wt % of maleic anhydride as a compatibilizer. The polyurethane in the blends was crosslinked using dicumyl peroxide or sulfur. The content of maleic anhydride was varied in the blends through the addition of different SMA amounts. The morphology of the blends was analyzed by SEM and a drastic reduction of both the domain size and its distribution was observed with increase of the anhydride content in the blends. The morphology of the PU‐et blends also showed dependence on the crosslinker agent used for the elastomer, and larger domains were obtained for the elastomer phase crosslinked with dicumyl peroxide. The mechanical properties of the blends were evaluated by flexural and impact strength tests. The blend containing 0.5 wt % of maleic anhydride and 20 wt % of PU‐et crosslinked with sulfur showed the highest strength impact, which was three times superior to the PS strength impact, and the blends containing 20 wt % of PU‐et crosslinked with dicumyl peroxide showed the highest deflection at break independent of the anhydride content. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 830–837, 2002     

An investigation on recycled PET/PP and recycled PET/PP‐EP compatibilized blends: Rheological,morphological, and mechanical properties

The effectiveness of P(E‐co‐MA‐co‐GMA) as a compatibilizer for recycled PET/PP and recycled PET/PP‐EP (polypropylene (ethylene‐propylene) heterophase copolymer) blends was investigated by means of morphological (scanning electron microscopy), rheological (small amplitude oscillatory shear), mechanical (tensile, flexural and impact tests), and thermal (differential scanning calorimetry) properties. Compatibilizer concentration ranged from 1 to 5 wt % with respect to the whole blend. All blends were obtained in a 90/10 composition using a twin screw extruder. Compatibilization effects for PETr/PP‐EP were more pronounced due to ethylene segments present in both PP‐EP and P(E‐co‐EA‐co‐GMA). PETr/PP‐EP has shown greater dispersed phase size reduction, a more solid‐like complex viscosity behavior and larger storage modulus at low frequencies in relation to PETr/PP blend. For both investigated blends, mechanical properties indicated an improvement in both elongation at break and impact strength with increasing compatibilizer content. PETr/PP‐EP blends showed improved performance for the same level of compatibilizer content. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41892.     

Miscibility,phase behavior,and mechanical properties of ternary blends of poly(vinyl chloride)/polystyrene/chlorinated polyethylene-graft-polystyrene

The effectiveness of chlorinated polyethylene-graft-polystyrene (CPE-g-PS) as a polymeric compatibilizer for immiscible poly(vinyl chloride)/polystyrene (PVC/PS) blends was investigated. The miscibility, phase behavior, and mechanical properties were studied using differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), Izod impact tests, tensile tests, and scanning electron microscopy (SEM). DSC and DMA studies showed that PVC is immiscible with chlorinated polyethylene (CPE) in CPE-g-PS, whereas the PS homopolymer is miscible with PS in CPE-g-PS. The PVC/PS/CPE-g-PS ternary blends exhibit a three-phase structure: PVC phase, CPE phase, and PS phase that consisted of a PS homopolymer and PS in CPE-g-PS. The mechanical properties showed that CPE-g-PS interacts well with both PVC and PS and can be used as a polymeric compatibilizer for PVC/PS blends. CPE-g-PS can also be used as an impact modifier for both PVC and PS. SEM observations confirmed, after the addition of CPE-g-PS, improvement of the interfacial adhesion between the phases of the PVC/PS blends. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 69: 995–1003, 1998     

Compatibilization effects of styrenic/rubber block copolymers in polypropylene/polystyrene blends

Compatibilizing effects of styrene/rubber block copolymers poly(styrene‐b‐butadiene‐b‐styrene) (SBS), poly(styrene‐b‐ethylene‐co‐propylene) (SEP), and two types of poly(styrene‐b‐ethylene‐co‐butylene‐b‐styrene) (SEBS), which differ in their molecular weights on morphology and selected mechanical properties of immiscible polypropylene/polystyrene (PP/PS) 70/30 blend were investigated. Three different concentrations of styrene/rubber block copolymers were used (2.5, 5, and 10 wt %). Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used to examine the phase morphology of blends. The SEM analysis revealed that the size of the dispersed particles decreases as the content of the compatibilizer increases. Reduction of the dispersed particles sizes of blends compatibilized with SEP, SBS, and low‐molecular weight SEBS agrees well with the theoretical predictions based on interaction energy densities determined by the binary interaction model of Paul and Barlow. The SEM analysis confirmed improved interfacial adhesion between matrix and dispersed phase. The TEM micrographs showed that SBS, SEP, and low‐molecular weight SEBS enveloped and joined pure PS particles into complex dispersed aggregates. Bimodal particle size distribution was observed in the case of SEP and low‐molecular weight SEBS addition. Notched impact strength (a_k), elongation at yield (ε_y), and Young's modulus (E) were measured as a function of weight percent of different types of styrene/rubber block copolymers. The a_k and ε_y were improved whereas E gradually decreased with increasing amount of the compatibilizer. The a_k was improved significantly by the addition of SEP. It was found that the compatibilizing efficiency of block copolymer used is strongly dependent on the chemical structure of rubber block, molecular weight of block copolymer molecule, and its concentration. The SEP diblock copolymer proved to be a superior compatibilizer over SBS and SEBS triblock copolymers. Low‐molecular weight SEBS appeared to be a more efficient compatibilizer in PP/PS blend than high‐molecular weight SEBS. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 72: 291–307, 1999     

Morphology and mechanical properties of reactive compatibilized polystyrene/ethylene‐vinyl acetate‐vinyl alcohol blends

A reactive compatibilizer, styrene‐maleic anhydride (SMA) was used to compatibilize the blends of polystyrene (PS) and ethylene‐vinyl acetate‐vinyl alcohol (EVAOH), which was synthesized from ethylene‐vinyl acetate (EVA) using transesterification reaction. The compatibilized blends with different compositions were prepared using a twin‐screw extruder and injection molded into the required test specimens. Morphology of Charpy impact‐fractured surfaces, tensile, and impact properties of the blends were investigated. Fourier‐transform infrared spectroscopy (FTIR) was also applied for specific samples to elucidate the presence of the functional groups reaction necessary for reactive compatibilization. The results of the ternary PS/EVAOH/SMA blends illustrate that the addition of SMA as a compatibilizer slightly reduce the elongation at break. From the impact‐fractured surfaces of the blends, it is evident that the morphology developed sizable pores when SMA was added into the blends. This might be attributed to the residual octanol‐1, produced from the synthesis of EVAOH, as there is a possibility of a reaction between hydroxyl groups in the octanol‐1 and the anhydride groups in the SMA. This disrupted the stability of the morphology and resulted in the decrease in the elongation, and hence, the tensile toughness. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 209–217, 2002     

Mechanical behaviors of ethylene/styrene interpolymer compatibilized polystyrene/polyethylene blends

In this study, ethylene/styrene interpolymer was used as a compatibilizer for the blends of polystyrene (PS) and high‐density polyethylene (HDPE). The mechanical properties including tensile and impact properties and morphology of the blends were investigated by means of uniaxial tension, instrumented falling‐weight impact measurements, and scanning electron microscopy. Tensile tests showed that the yield strength of the PS/HDPE/ESI blends decreases considerably with increasing HDPE content. However, the elongation at break of the blends tended to increase significantly with increasing HDPE content. The excellent tensile ductility of the HDPE‐rich blends resulted from shield yielding of the matrix. Izod and Charpy impact measurements indicated that the impact strength of the blends increases slowly with HDPE content up to 40 wt %; thereafter, it increases sharply with increasing HDPE content. The impact energy of the HDPE‐rich blends exceeded that of pure HDPE, implying that the HDPE polymer can be further toughened by the incorporation of brittle PS minor phase in the presence of ESI compatibilizer. The correlation between the impact property and morphology of the blends is discussed. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 4001–4007, 2007     

The effect of mercapto‐modified EVA on rheological and dynamic mechanical properties of NBR/EVA blends

The effect of mercapto‐modified ethylene vinyl acetate copolymer (EVALSH) on the rheological and dynamic mechanical properties of acrylonitrile butadiene rubber (NBR) and ethylene vinyl acetate copolymer (EVA) blends was evaluated at different blend compositions. The addition of 5 phr of EVALSH in the blends resulted in an increase of the melt viscosity and a substantial decrease of the extrudate swell ratio. These results can be attributed to the interactions occurring between the double bond of the NBR phase and the mercapto groups along the EVALSH backbone. The power–law index also presents a slight increase in the presence of EVALSH, indicating a decrease in the pseudoplastic nature of the compatibilized blends. The reactive compatibilization of NBR/EVA blends with EVALSH was also confirmed by the decrease of damping values and an increase of glass transition temperature, in dynamic mechanical analysis. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 2335–2344, 2002     

Effect of vinyl acetate content on the mechanical and thermal properties of ethylene vinyl acetate/MgAl layered double hydroxide nanocomposites

Ethylene vinyl acetate (EVA)/Mg‐Al layered double hydroxide (LDH) nanocomposites using EVA of different vinyl acetate contents (EVA‐18 and EVA‐45) have been prepared by solution blending method. X‐ray diffraction and transmission electron microscopic studies of nanocomposites clearly indicate the formation of exfoliated/intercalated structure for EVA‐18 and completely delaminated structure for EVA‐45. Though EVA‐18 nanocomposites do not show significant improvement in mechanical properties, EVA‐45 nanocomposites with 5 wt % DS‐LDH content results in tensile strength and elongation at break to be 25% and 7.5% higher compared to neat EVA‐45. The data from thermogravimetric analysis show that the nanocomposites of EVA‐18 and EVA‐45 have ≈10°C higher thermal decomposition temperature compared to neat EVA. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Cure characteristics,morphology, mechanical properties,and aging characteristics of silicone rubber/ethylene vinyl acetate blends

Silicone rubber/ethylene vinyl acetate (SR/EVA) rubber mixes with different ratios were prepared by using dicumyl peroxide (DCP) and benzoyl peroxide (BP) as curing agents. The vulcanization characteristics such as cure kinetics, activation energy, and cure rate of the blends were analyzed. The effects of blend ratio and curing agents on the mechanical properties such as stress–strain behavior, tensile strength, elongation at break, tear strength, relative volume loss, hardness, flex crack resistance, and density of the cured blends have been investigated. Almost all the mechanical properties have been found to be increased with increase in EVA content in the blends particularly in DCP‐cured systems. The increment in mechanical properties of the blends with higher EVA content has been explained in terms of the morphology of the blends, attested by scanning electron micrographs. Attempts have been made to compare the experimental results, from the evaluation of mechanical properties, with relevant theoretical models. The aging characteristics of the cured blends were also investigated and found that both the DCP‐ and BP‐cured blends have excellent water and thermal resistance. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 1069–1082, 2006     

Cocontinuous morphologies in polystyrene/ethylene–vinyl acetate blends: The influence of the processing temperature

The influence of the compression‐molding temperature on the range of cocontinuity in polystyrene (PS)/ethylene–vinyl acetate (EVA) copolymer blends was studied. The blends presented a broad range of cocontinuity when compression‐molded at 160°C, and they became narrower when compression‐molded at higher temperatures. A coarsening effect was observed in PS/EVA (60:40 vol %) blends upon compression molding at higher temperature with an increase in the phase size of the cocontinuous structure. Concerning PS/EVA (40:60 vol %) blends, an increase in the mixing and molding temperatures resulted in a change from a cocontinuous morphology to a droplet–matrix morphology. This effect was observed by selective extraction experiments and scanning electron microscopy. The changes in the morphology with the molding conditions affected the storage modulus. An increase in the storage modulus in blends compression‐molded at 160°C was observed as a result of dual‐phase continuity. An EVA copolymer with a higher vinyl acetate content (28 wt %) and a higher melt‐flow index resulted in blends with a broader range of cocontinuity. This effect was more pronounced in blends with lower amounts of PS, that is, when EVA formed the matrix. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 386–398, 2003     

Polystyrene/EVA melt blends compatibilized with EVA-graft-polystyrene

The influence of poly[(ethylene-co-vinyl acetate)-g-polystyrene] (EVA-g-PS) on the mechanical and morphological properties of polystyrene and the blends with EVA copolymers has been investigated. The melt blends have been performed in a twin-screw extruder. The addition of the graft copolymer enhances the mechanical properties and impact resistance of the PS matrix and PS/EVA (90 : 10 wt %) blends. Better results on impact strength and elongation at break have been achieved by using a EVA-g-PS graft copolymer with a higher EVA proportion by weight. This graft copolymer also contains a lower molecular weight of the PS-grafted segments than the PS matrix. Morphological studies by scanning electron microscopy revealed some interfacial adhesion between the components in the compatibilized polymer blends. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 65: 2141–2149, 1997     

Melt rheology of compatibilized polystyrene/low density polyethylene blends

Investigations have been made on the melt rheological behaviors of compatibilized blends composed of polystyrene, low density polyethylene and hydrogenated (styrene‐butadiene‐styrene) triblock copolymer used as a compatibilizer. The experiments were carried out on a capillary rheometer. The effects of shear stress, temperature and blending ratio on the activation energy for viscous flow and melt viscosity of the blends are described. The study shows that the viscosity of the blends exhibits a maximum or minimum value at a certain blending ratio. The activation energy for viscous flow decreases with increasing LDPE content. Furthermore, the concept of equal‐viscosity temperature is presented and its role in the processing of the blend is discussed. In addition, the morphology of the extrudate sample of the blends was observed by scanning electron microscopy and the correlation between the morphology and the rheological properties is explored. © 1999 Society of Chemical Industry     

Mechanical properties of ethylene–vinyl acetate/polystyrene blends studied by in situ polymerization

This study examined ethylene–vinyl acetate (EVA)‐toughened polystyrene (PS). EVA is well‐known to be incompatible with PS; thus, the PS graft to the EVA backbone (EVA‐g‐PS) was used as a compatibilizer and provided good adhesion at the interface of PS and EVA. In addition, the mechanical properties and impact resistance of the PS matrix were obviously improved by EVA‐g‐PS and by EVA itself. Meanwhile, differential scanning calorimetry results showed that the grafted PS chain influenced the crystallization of EVA; for example, the melting temperature, the crystallization temperature, and the percentage crystallinity related to EVA were reduced. Moreover, the addition of 10% EVA increased the impact strength by a factor of five but reduced the modulus by the same factor. Additionally, a lower number‐average molecular weight EVA delayed phase inversion and resulted in poor mechanical properties. A fracture surface photograph revealed that the major mechanism of EVA‐toughened PS was craze and local matrix deformation. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 699–705, 2003     

Correlation between the morphology and dynamic mechanical properties of ethylene vinyl acetate/linear low‐density polyethylene blends: Effects of the blend ratio and compatibilization

The effects of the blend composition and compatibilization on the morphology of linear low‐density polyethylene (LLDPE)/ethylene vinyl acetate (EVA) blends were studied. The blends showed dispersed/matrix and cocontinuous phase morphologies that depended on the composition. The blends had a cocontinuous morphology at an EVA concentration of 40–60%. The addition of the compatibilizer first decreased the domain size of the dispersed phase, which then leveled off. Two types of compatibilizers were added to the polymer/polymer interface: linear low‐density polyethylene‐g‐maleic anhydride and LLDPE‐g phenolic resin. Noolandi's theory was in agreement with the experimental data. The conformation of the compatibilizer at the blend interface could be predicted by the calculation of the area occupied by the compatibilizer molecule at the interface. The effects of the blend ratio and compatibilization on the dynamic mechanical properties of the blends were analyzed from ?60°C to +35°C. The experiments were performed over a series of frequencies. The area under the curve of the loss modulus versus the temperature was higher than the values obtained by group contribution analysis. The loss tangent curve showed a peak corresponding to the glass transition of EVA, indicating the incompatibility of the blend system. The damping characteristics of the blends increased with increasing EVA content because of the decrease in the crystalline volume of the system. Attempts were made to correlate the observed viscoelastic properties of the blends with the morphology. Various composite models were used to model the dynamic mechanical data. Compatibilization increased the storage modulus of the system because of the fine dispersion of EVA domains in the LLDPE matrix, which provided increased interfacial interaction. Better compatibilization was effected at a 0.5–1% loading of the compatibilizer. This was in full agreement with the dynamic mechanical spectroscopy data. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 4526–4538, 2006     

Improvement of mechanical properties for PP/PS blends by in situ compatibilization

The effect of the in situ compatibilization on the mechanical properties of PP/PS blends was investigated. The application of Friedel-Crafts alkylation reaction to the PP/PS-blend compatibilization was assessed. Styrene/AlCl₃ was used as catalyst system. The graft copolymer (PP-g-PS) formed at the interphase showed relatively high emulsifying strength. Scission reactions, occurring in parallel with grafting, were verified for PP and PS at high catalyst concentration, but no crosslinking reactions were detected. Tensile tests were performed on dog-bone specimens of the blends. Both elongation at break and toughness increased with catalyst concentration. At 0.7% AlCl₃, a maximum was reached, which amounted to five times the value of the property for the uncompatibilized blend. At higher catalyst concentrations these properties decreased along with the PP molecular weight due to chain-scission reactions. On the other hand, the tensile strength did not change with the catalyst concentration. The in situ compatibilized blends showed considerable improvement in mechanical properties, but were adversely affected by chain scissions at high catalyst contents.     

Compatibilization of poly(vinyl chloride)/polystyrene blends with epoxidized styrene-butadiene-styrene block copolymers

The effectiveness of epoxidized styrene-butadiene-styrene (ESBS) block copolymer as a polymeric compatibilizer for the incompatible polystyrene/poly(vinyl chloride) (PS/PVC) blend was investigated. ESBS at two epoxidation levels (34 and 49 mol% oxirane units) was used and the study covered mainly compositions with up to 30 wt% PS content in the ternary blends. The results support the view that ESBS can serve as a compatibilizer at these levels of epoxidation and when added in amounts in excess of 5 wt%. Ternary blends may also have good elongation properties due to the thermoplastic elastomer character of ESBS.     

Morphology and mechanical properties of PET/PE blends compatibilized by nanoclays: Effect of thermal stability of nanofiller organic modifier

Poly(ethylene terephtalate)/poly(ethylene) (PET/PE) blends (80/20 wt %) were prepared by melt‐extrusion and compatibilized by addition of nanoclays. Two commercially available organically modified montmorillonites (Cloisite© 10A and 30B) were chosen as reference and a third one was specially organomodified at lab scale with a thermally stable phosphonium surfactant using conventional cationic exchange reaction. The size of the dispersed polymer phase (PE droplets) and the ductility of the blends depend more on the thermal stability of the surfactant of the organomodified clay than on the enthalpic interactions between the blend components and the surfactants used for the modification of the clays. The highest mechanical properties (yield stress and elongation at break) and the better compatibilization efficiency (smallest dispersed PE droplets) were observed in the presence of phosphonium organomodified montmorillonite compared to other less thermally stable commercial organoclays. The analysis of the thermal stability, morphology, and mechanical properties of PET/PE blends containing the surfactants alone in the absence of clay made it possible to evidence separately the effects of the surfactant and of the nanofiller. The role of the surfactant as compatibilization agent was demonstrated. In the absence of nanofiller, the finest morphological and highest ductility were again obtained with the phosphonium surfactant which is the most thermally stable. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Compatibilization of polypropylene/polystyrene blends with poly(styrene-b-butadiene-b-styrene) block copolymer

The compatibilizing effect of the triblock copolymer poly(styrene-b-butadiene-b-styrene) (SBS) on the morphology and mechanical properties of immiscible polypropylene/polystyrene (PP/PS) blends were studied. Blends with three different weight ratios of PP and PS were prepared and three different concentrations of SBS were used for investigations of its compatibilizing effects. Scanning electron microscopy (SEM) showed that SBS reduced the diameter of the PS-dispersed particles as well as improved the adhesion between the matrix and the dispersed phase. Transmission electron microscopy (TEM) revealed that in the PP matrix dispersed particles were complex “honeycomblike” aggregates of PS particles enveloped and joined together with the SBS compatibilizer. Wide-angle X-ray diffraction (WAXD) analysis showed that the degree of crystallinity of PP/PS/SBS slightly exceeded the values given by the addition rule. At the same time, addition of SBS to pure PP and to PP/PS blends changed the orientation parameters A₁₁₀ and C significantly, indicating an obvious SBS influence on the crystallization process in the PP matrix. SBS interactions with PP and PS influenced the mechanical properties of the compatibilized PP/PS/SBS blends. Addition of SBS decreased the yield stress and the Young's modulus and improved the elongation at yield as well as the notched impact strength in comparison to the binary PP/PS blends. Some theoretical models for the determination of the Young's modulus of binary PP/PS blends were used for comparison with the experimental results. The experimental line was closest to the series model line. © 1998 John Wiley & Sons, Inc. J. Appl. Polym. Sci. 69: 2625–2639, 1998