Synthesis of polypropylene‐grafted graphene and its compatibilization effect on polypropylene/polystyrene blends

Polypropylene‐graft‐reduced graphene oxide (PP‐g‐rGO) was synthesized and used as a novel compatibilizer for PP/polystyrene (PP/PS) immiscible polymer blends. SEM observation revealed an obvious reduction of the average diameter for the dispersed PS phase with the addition of PP‐g‐rGO into a PP/PS (70/30, w/w) blend. The compatibilization effect of PP‐g‐rGO will subsequently lead to the enhancement of the tensile strength and elongation at break of the PP/PS blends. The compatibilizing mechanism should be ascribed to the fact that PP‐g‐rGO can not only adsorb PS chains on their basal planes through π‐π stacking but also exhibit intermolecular interactions with PP through the grafted PP chains. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40455.     

In situ compatibilization of polypropylene/polystyrene blend by controlled degradation and reactive extrusion

In situ compatibilization of polypropylene (PP) and polystyrene (PS) was achieved by combinative application of tetraethyl thiuram disulfide (TETD) as degradation inhibitor and di‐tert‐butyl peroxide as degradation initiator in the process of reactive extrusion. The PP/PS blends obtained were systematically investigated by rheological measurement, scanning electron microscopy, and differential scanning calorimetry. The results indicate that peroxide‐induced degradation of PP can be effectively depressed by adding TETD, which may favor the formation of PP‐g‐PS copolymer during melt processing. The PP‐g‐PS copolymer formed may act as an in situ compatibilizer for PP/PS blends, and subsequently decreases the size of dispersed PS phase and changes both rheological and thermal properties of the blends. Based on the present experimental results, the mechanisms for the controlled degradation of PP and in situ formation of PP‐g‐PS copolymer in the PP/PS blends have been proposed. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Phase morphology,thermomechanical, and crystallization behavior of uncompatibilized and PP‐g‐MAH compatibilized polypropylene/polystyrene blends

In this article, we discuss the phase morphology, thermal, mechanical, and crystallization properties of uncompatibilized and compatibilized polypropylene/polystyrene (PP/PS) blends. It is observed that the Young's modulus increases, but other mechanical properties such as tensile strength, flexural strength, elongation at break, and impact strength decrease by blending PS to PP. The tensile strength and Young's modulus of PP/PS blends were compared with various theoretical models. The thermal stability, melting, and crystallization temperatures and percentage crystallinity of semicrystalline PP in the blends were marginally decreased by the addition of amorphous PS. The presence of maleic anhydride‐grafted polypropylene (compatibilizer) increases the phase stability of 90/10 and 80/20 blends by preventing the coalescence. Hence, finer and more uniform droplets of PS dispersed phases are observed. The compatibilizer induced some improvement in impact strength for the blends with PP matrix phase, however fluctuations in modulus, strength and ductility were observed with respect to the uncompatibilized blend. The thermal stability was not much affected by the addition of the compatibilizer for the PP rich blends but shows some decrease in the thermal stability of the blends, where PS forms the matrix. On the other hand, the % crystallinity was increased by the addition of compatibilizer, irrespective of the blend concentration. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42100.     

Relationship between branch length and the compatibilizing effect of polypropylene‐g‐polystyrene graft copolymer on polypropylene/polystyrene blends

Three polypropylene‐g‐polystyrene (PP‐g‐PS) graft copolymers with the same branch density but different branch lengths were evaluated as compatibilizing agents for PP/PS blends. The morphological and rheological results revealed that the addition of PP‐g‐PS graft copolymers significantly reduced the PS particle size and enhanced the interfacial adhesion between PP and PS phases. Furthermore, it is verified that the branch length of PP‐g‐PS graft copolymer had opposite effects on its compatibilizing effect: on one hand, increasing the branch length could improve the compatibilizing effect of graft copolymer on PP/PS blends, demonstrated by the reduction of PS particle size and the enhancement of interfacial adhesion; on the other hand, increasing the branch length would increase the melt viscosity of PP‐g‐PS graft copolymer, which prevented it from migrating effectively to the interface of blend components. Additionally, the crystallization and melting behaviors of PP and PP/PS blends were compared. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40126.     

Effect of styrene–isoprene–styrene,styrene–butadiene–styrene,and styrene–butadiene–rubber on the mechanical,thermal, rheological,and morphological properties of polypropylene/polystyrene blends

The mechanical, thermal, rheological, and morphological properties of polypropylene (PP)/polystyrene (PS) blends compatibilized with styrene–isoprene–styrene (SIS), styrene–butadiene–styrene (SBS), and styrene–butadiene–rubber (SBR) were studied. The incompatible PP and PS phases were effectively dispersed by the addition of SIS, SBS, and SBR as compatibilizers. The PP/PS blends were mechanically evaluated in terms of the impact strength, ductility, and tensile yield stress to determine the influence of the compatibilizers on the performance properties of these materials. SIS‐ and SBS‐compatibilized blends showed significantly improved impact strength and ductility in comparison with SBR‐compatibilized blends over the entire range of compatibilizer concentrations. Differential scanning calorimetry indicated compatibility between the components upon the addition of SIS, SBS, and SBR by the appearance of shifts in the melt peak of PP toward the melting range of PS. The melt viscosity and storage modulus of the blends depended on the composition, type, and amount of compatibilizer. Scanning electron microscopy images confirmed the compatibility between the PP and PS components in the presence of SIS, SBS, and SBR by showing finer phase domains. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 266–277, 2003     

Influences of compatibilization and compounding process on electrical conduction and thermal stabilities of carbon black‐filled immiscible polypropylene/polystyrene blends

The influences of styrene–butadiene–styrene (SBS) copolymer compatibilizer and compounding process on the electrical conduction and thermal stabilities of carbon black (CB)‐filled immiscible polypropylene (PP)/polystyrene (PS) (1/1) blends were investigated. The immiscible CB/PP/PS composite with CB homogeneously located in the PS phase exhibited the highest resistivity and the fastest variation amplitudes of electrical resistivity (ρ) and rheological parameters upon annealing. An optimal content of 5 vol% SBS could significantly lower ρ of the composites by partially trapping CB particles in the PP/PS interfacial region and by reducing the phase size. The compatibilizer markedly slowed down the variation amplitudes of ρ and rheological parameters and the phase coalescence of the composites submitted to thermal annealing. The (SBS/CB)/PP/PS composite with CB located at the PP/PS interface and in the PP phase prepared by blending a (SBS/CB) masterbatch with PP and PS exhibited lower ρ and better thermal stability in comparison with the CB/SBS/PP/PS composite with CB mainly within the PS phase and partially at the PP/PS interface prepared by direct blending. Spreading and wetting coefficients were used to explain the CB distribution and the phase morphology of the composites. © 2012 Society of Chemical Industry     

Kinetics-controlled compatibilization of immiscible polypropylene/polystyrene blends using nano-SiO2 particles

Rigid inorganic filler has been long time used as a reinforcement agent for polymer materials. Recently, more work is focused on the possibility that using filler as a compatibilizer for immiscible polymer blends. In this article, we reported our efforts on the change of phase morphology and properties of immiscible polypropylene(PP)/polystyrene(PS) blends compatibilized with nano-SiO₂ particles. The effects of filler content and mixing time on the phase morphology, crystallization behavior, rheology, and mechanical properties were investigated by SEM, DSC, ARES and mechanical test. A drastic reduction of PS phase size and a very homogeneous size distribution were observed by introducing nano-SiO₂ particles in the blends at short mixing time. However, at longer mixing time an increase of PS size was seen again, indicating a kinetics-controlled compatibilization. This conclusion was further supported by the unchanged glass transition temperature of PS and by increased viscosity in the blends after adding nano-SiO₂ particles. The compatibilization mechanism of nano-SiO₂ particles in PP/PS blends was proposed based on kinetics consideration.     

Rheology,morphology, and mechanical properties of reactive compatibilized polypropylene/polystyrene blends via Friedel–Crafts alkylation reaction in the presence of clay

Attempts were made to study the effect of reactive compatibilization via Friedel–Crafts alkylation reaction, using AlCl₃ as a catalyst, on rheology, morphology, and mechanical properties of polypropylene/polystyrene ( PP/PS) blends in the presence of an organoclay (Cloisite 15A). During the reactive compatibilization process, PS showed much more degradation than that of PP in the presence of AlCl₃. It was found that the effect of generation of PP‐g‐PS copolymer at the interface of the PP/PS blend dominates the effects of degradation of PS and PP phases, which manifested itself by increased toughness as well as uniform dispersion of the dispersed PS particles in the PP matrix. Generation of PP‐g‐PS copolymer was confirmed by using Fourier‐transform infrared analysis. By using rheological and X‐ray diffraction analyses, it was shown that the clay had higher affinity to PS than that of PP. It was also shown that the clay located at the interface of PP and PS phases, leading to increased relaxation time of the deformed PS dispersed particles, exhibited higher dispersion in PP/PS blend, which resulted in higher ductility of the blend. By using the results of rheological studies, it was concluded that during reactive compatibilization of the blend nanocomposite, the clay migrated into the dispersed PS phase, which was confirmed by scanning electron microscopy analysis. It was demonstrated that the rheological studies have a reliable sensitivity to the clay partitioning and phase morphology of the studied blends and blend nanocomposites . J. VINYL ADDIT. TECHNOL., 24:18–26, 2018. © 2015 Society of Plastics Engineers     

Nonisothermal crystallization kinetics of polypropylene/polypropylene‐g‐polystyrene/polystyrene blends

The nonisothermal crystallization kinetics of polypropylene (PP), PP/polystyrene (PS), and PP/PP‐g‐PS/PS blends were investigated with differential scanning calorimetry at different cooling rates. The Jeziorny modified Avrami equation, Ozawa method, and Mo method were used to describe the crystallization kinetics for all of the samples. The kinetics parameters, including the half‐time of crystallization, the peak crystallization temperature, the Avrami exponent, the kinetic crystallization rate constant, the crystallization activation energy, and the F(T) and a parameters were determined. All of the results clearly indicate that the PP‐g‐PS copolymer accelerated the crystallization rate of the PP component in the PP/PP‐g‐PS/PS blends. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

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     

Grafting of polystyrene branches to polyethylene and polypropylene

Polyethylene (PE) and polypropylene (PP) were reacted with benzoyl peroxide (BPO) and 2,2,6,6‐tetramethyl‐1‐piperidinyloxy (TEMPO) to prepare PE‐TEMPO and PP‐TEMPO macroinitiators, respectively. Molecular weight of PP decreased, whereas that of PE increased during the reaction with the BPO/TEMPO system. Polystyrene (PS) branches were grafted to PE and PP backbone chains as a result of bulk polymerization of styrene with the PE‐TEMPO and PP‐TEMPO macroinitiators. A significant amount of PS homopolymer was produced as a byproduct. Weight of the resulting PE‐g‐PS and PP‐g‐PS increased with the polymerization time up to 20 h and then leveled off. Melting point of PE and PP domains in PE‐g‐PS and PP‐g‐PS, respectively, lowered as the content of PS in the copolymers increased. However, glass transition of the copolymers was almost identical with that of PS homopolymer, indicating that the constituents in the copolymers were all phase‐separated from each other. In scanning electron microscopy of the incompatible PE/PS, PP/PS, and PE/PP/PS compounded with PE‐g‐PS and PP‐g‐PS, any clear indication of enhanced adhesion between the phases was not observed. However, phase domains in the blends were, nevertheless, reduced significantly to raise mechanical properties such as maximum stress and elongation at break by 20–75%. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 1103–1111, 2002     

Novel multimonomer‐grafted polypropylene preparation and application in polypropylene/poly(vinyl chloride) blends

A novel grafted polymer was prepared in one step through free‐radical melt grafting in a single‐screw extruder. It was shown that the addition of styrene (St) to the melt‐grafting system as a comonomer could significantly enhance the grafting degree of methyl methacrylate (MMA) onto polypropylene (PP) and reduce the degradation of the PP matrix by means of Fourier transform infrared and melt flow rate testing, respectively. Then, the potential of using multimonomer‐grafted PP, which was designated PP‐g‐(St‐co‐MMA), as the compatibilizer in PP/poly(vinyl chloride) (PVC) blends was also examined. In comparison with PP/PVC blends, the average size of the dispersed phase was greatly reduced in grafted polypropylene (gPP)/PVC blends because of the addition of the PP‐g‐(St‐co‐MMA) graft copolymer. The tensile strength of the gPP/PVC blends increased significantly, and the impact strength was unchanged from that of the pure PP/PVC blends. The results of differential scanning calorimetry and scanning electron microscopy suggested that the compatibility of the PP/PVC blends was improved. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Improved melting strength of polypropylene by reactive compounding with ultrafine full‐vulcanized polybutadiene rubber (UFBR) particles

Ultrafine full‐vulcanized polybutadiene rubber (UFBR) in particle sizes of ca. 50–100 nm has been used for modifying mechanical and processing performances of polypropylene (PP), and PP‐g‐maleic anhydride (PP‐MA) has been used as a compatibilizer for enhancing the interfacial adhesion between the two components. The results show that PP/UFBR possesses rheological behaviors such as highly branched PP when UFBR content in blends reaches 10 wt%, while in contrast, the much low content of UFBR combining small amount of PP‐MA endows the material with rheological characteristics of high melt strength materials like highly branched PP. The mechanism accounting for the rheological behaviors of binary blends and effectiveness of PP‐MA on PP/UFBR blends has been proposed. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers     

Morphological,thermal, rheological,and mechanical properties of PP/EVOH blends compatibilized with PP‐g‐IA

We prepared some blends of polypropylene (PP) and ethylene vinyl alcohol (EVOH) with and without a compatibilizer. As a new compatibilizer, we synthesized polypropylene grafted with itaconic acid (PP‐g‐IA) using Brabender mixing system. We investigated the morphological, thermal, rheological, and mechanical properties of a compatibilized blends (PP/EVOH/PP‐g‐IA) and not compatibilized blends (PP/EVOH). Our experiments showed that carboxylic acid groups in PP‐g‐IA and hydroxyl group in EVOH formed strong in situ hydrogen bond in the compatibilized blends, resulting in better morphological and mechanical properties of the compatibilized blends than those of not compatibilized blends. POLYM. ENG. SCI., 56:1240–1247, 2016. © 2016 Society of Plastics Engineers     

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     

Characterization of carbon black‐filled immiscible polypropylene/polystyrene blends

The electrical and rheological behaviors of carbon black (CB)‐filled immiscible polypropylene (PP)/polystyrene (PS) blends were investigated. The compounding sequence influences the phase morphology of the ternary CB/PP/PS composites and the distribution of CB aggregates. Simultaneous measurements of resistance and dynamic modulus were carried out to monitor the phase coalescence of the ternary composites and CB migration and agglomeration in the PS phase during annealing at temperatures above the melting point of PP. The variation of resistivity is mainly attributed to CB agglomeration in the PS phase and the interfacial region, while the variation of dynamic modulus is regarded as the superimposition of the phase coalescence and CB agglomeration in the PS phase. The ternary composites with the majority of CB particles distributed in the interfacial region show the lowest conductive percolation threshold and the most stable resistivity–temperature performance during heating–cooling cycles. Copyright © 2011 Society of Chemical Industry     

Effect of polypropylene on the rheology of co‐continuous PS/SEBS blends

Polypropylene (PP) was added to a co‐continuous blend of polystyrene (PS) and styrene‐ethylene/butylene‐styrene (SEBS) to investigate the effect of PP on the morphology and rheological behavior of PS/SEBS blends. For this purpose, a reference blend of 50 wt% PS and 50 wt% SEBS was chosen and an isotactic PP was added to it by increments of 10 wt% up to a maximum of 50 wt% of the total weight. Environmental SEM (ESEM) studies on the PS/SEBS/PP blends showed that PP could be added up to 10 wt% without changing the morphology of the co‐continuous PS/SEBS blend, whereas at 20 wt% PP formed a separate discrete phase. The discrete PP phase finally formed a fully developed matrix structure from 40 wt% onwards. Dynamic rheological measurements showed that at low frequencies the storage modulus was largely unaffected by addition of PP in small concentrations (up to 10 wt%), showing a significant effect of the PP/SEBS interface at low deformation rates. Melt strength tests on the PS/SEBS/PP blends showed the existence of a proportional correlation with their corresponding storage moduli, measured at frequencies from 10–100 rad/s. POLYM. ENG. SCI., 45:1432–1444, 2005. © 2005 Society of Plastics Engineers     

Influence of polarity on the preferential intercalation behavior of clay in immiscible polypropylene/polystyrene blend

The immiscible polypropylene (PP)/polystyrene (PS) blend was prepared via melt compounding and the preferential intercalation behavior of clay was investigated by wide angle X‐ray diffraction (XRD) and transmission electron microscope (TEM). It was found that the clay platelets initially located in the PS phase in PP/PS/Clay composites and PS chains intercalated into the clay layers. However, all clay migrated from the PS phase to the modified PP phase after introducing polar maleic anhydride group (MAH) to PP chains. Interestingly, most of clay migrated from the modified PP phase to the modified PS phase again when PS matrix was modified with sulfonic group, and some enriched in the interphase region. The interaction energy density (B) of the blends was determined by combining the melting point variation with the ternary interaction model for heat of mixing. It was found that the value of B decreased with the introduction of polar group (MAH or sulfonic group), indicating that the polarization of PP and PS can enhance interaction between clay platelet and polymer component. Different interaction between clay platelet and polymer component leads to the preferential intercalation behavior. The higher polarity of the polymer generates higher interaction between clay and polymer component as well as results in stronger preferential intercalating ability. Moreover, the results of FTIR spectra after extraction of all samples gave additional explanation of the preferential intercalation behavior of clay in the immiscible PP/PS blends. On the basis of the results of the measurement mentioned above, a possible mechanism was proposed. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Polypropylene/polypropylene‐grafted acrylic acid copolymer/ethylene–Acrylic acid copolymer ternary blends for hydrophilic polypropylene

Ternary blends of polypropylene (PP), a polypropylene‐grafted acrylic acid copolymer (PP‐g‐AA), and an ethylene–acrylic acid copolymer (EAA) were prepared by melt blending. The surfaces of films with different contents of these three components were characterized with contact‐angle measurements. Scanning electron microscopy, Fourier transform infrared spectroscopy, differential scanning calorimetry, and thermogravimetric analysis were used to characterize the microstructure, melting and crystalline behavior, and thermal stability of the blends. The contact angles of the PP/PP‐g‐AA blends decreased monotonically with increasing PP‐g‐AA content. With the incorporation of EAA, the contact angles of the PP/PP‐g‐AA/EAA ternary blends decreased with increasing EAA content. When the concentration of EAA was higher than 15 wt %, the contact angles of the ternary blends began to increase. Scanning electron microscopy observations confirmed that PP‐g‐AA acted as a compatibilizer and improved the compatibility between PP and EAA in the ternary blends. Differential scanning calorimetry analysis suggested that acrylic acid moieties could act as nucleating agents for PP in the polymer blends. Thermogravimetric analysis and differential thermogravimetry confirmed the optimal blend ratio for the PP/PP‐g‐AA/EAA ternary blends was 70/15/15. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 436–442, 2006     

Stress‐relaxation behavior of natural rubber/polystyrene and natural rubber/polystyrene/natural rubber‐graft‐polystyrene blends

We studied the stress‐relaxation behavior of natural rubber (NR)/polystyrene (PS) blends in tension. The effects of strain level, composition, compatibilizer loading, and aging on the stress‐relaxation behavior were investigated in detail. The dispersed/matrix phase morphology always showed a two‐stage mechanism. On the other hand, the cocontinuos morphology showed a single‐stage mechanism. The addition of a compatibilizer (NR‐g‐PS) into 50/50 blends changed the blend morphology to a matrix/dispersed phase structure. As a result, a two‐step relaxation mechanism was found in the compatibilized blends. A three‐stage mechanism was observed at very high loadings of the compatibilizer (above the critical micelle concentration), where the compatibilizer formed micelles in the continuous phase. The aged samples showed a two‐stage relaxation mechanism. The rate of relaxation increased with strain levels. The aging produced interesting effects on the relaxation pattern. The rate of relaxation increased with temperature due to the degradation of the samples. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008