Changes in morphology and properties by grafting reaction in PP/EOR/CaCO3 ternary composites

The phase morphology and mechanical properties of polypropylene (PP) composites containing ethylene–octene elastomer (EOR) and calcium carbonate (CaCO₃) filler were investigated by comparing the toughening effect of unmodified EOR with EOR grafted with maleic anhydride (EOR–MA). EORs of various MA contents were prepared by free‐radical grafting of MA onto the EOR backbone using a reactive extrusion process. The composite morphology was directly explored by scanning electron microscopy technique and indirectly explored by differential scanning calorimetry and dynamic mechanical analysis. Separate dispersion of the elastomer and filler particles was achieved by using unmodified EOR. Modification of EOR by maleic anhydride grafting resulted in encapsulation of the filler particles. The mechanical properties of the composites were found to depend mainly on composite morphology and composition and, to a lesser degree, on maleic anhydride concentration. The results of this study showed that when composites contained an equal or higher amount of elastomer relative to filler, a composite with a separate dispersion structure was preferred. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 3557–3562, 2003     

Characterization and properties of polypropylene‐block‐poly(ethylene‐co‐propylene) synthesized by short‐period polymerization

The morphology and mechanical properties of novel block copolymers consisting of isotactic polypropylene (PP) and ethylene–propylene rubber (EPR) synthesized by a short‐period polymerization method were examined using differential scanning calorimetry, atomic force microscopy, dynamic mechanical analysis, and a rheooptical technique. It was found that the novel block copolymers show a single glass transition and EPR segments are trapped into the amorphous region of PP. Furthermore, the rheooptical analysis demonstrates that a drawing process of the EPR‐rich block copolymer induces orientation of the PP lamellae in the EPR matrix. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 958–964, 1999     

Phase structure and property relationships in ternary polypropylene/elastomer/filler composites: Effect of elastomer polarity

Ternary composites of polypropylene (PP), elastomer, and calcium carbonate (CaCO₃) filler were prepared to study their structure/property relationships. Two kinds of phase structure were formed, depending on the elastomer present in the composites. Separation of elastomer and filler particles was found when a nonpolar ethylene–octene copolymer was used. Encapsulation of filler by the elastomer was achieved by using a polar ethylene–vinyl acetate elastomer. The mechanical properties of ternary composites were strongly dependent on material composition and their phase structures. In the present study, composites with separate dispersion structure showed higher modulus and impact strength than those of encapsulation type. The deformation mechanisms of both composites were studied using scanning electron microscopy. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 1929–1939, 2000     

Dynamically vulcanized blends of polypropylene and ethylene octene copolymer: Influence of various coagents on thermal and rheological characteristics

The present study focuses on the influence of the three structurally different coagents, namely triallyl cyanurate (TAC), trimethylol propane triacrylate (TMPTA) and N,N′‐m‐phenylene dimaleimide (MPDM) on the thermal and rheological properties of thermoplastic vulcanizates (TPVs) based on the polypropylene (PP) and ethylene octene copolymer (EOC). Depending on the structure and reactivity, different coagents show different behaviors. All the TPV compositions were made by melt mixing method in a Haake Rheomix at 180°C. Rheological properties have also been evaluated at the same temperature. Viscoelastic properties of the TPVs were analyzed by a dynamic oscillatory rheometer in the melt state in a Rubber Process Analyzer (RPA 2000). Morphologically, TPVs consist of dense crosslinked rubber domains dispersed in a continuous thermoplastic matrix. The crosslinked rubber particles have a tendency to form agglomerates and build local clusters which undergo disintegration by shearing. A variety of rheological characteristics such as Payne effect, shear rate sensitivity, modulus recovery and dynamics of relaxation were studied by performing strain sweep, frequency sweep and stress relaxation tests. Among the various coagents taken for investigation, MPDM‐based TPVs show improved dynamic functions (complex modulus and complex viscosity) and lower rate of stress relaxation over TAC, TMPTA and the control sample without any coagent. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Dynamically vulcanized blends of polypropylene and ethylene octene copolymer: Influence of various coagents on mechanical and morphological characteristics

Dynamically cured blends of polypropylene (PP) and ethylene octene copolymer (EOC) with coagent‐assisted peroxide curative system were prepared by melt‐mixing method. It was well established that PP exhibits β‐chain scission in the presence of peroxide. Principally, incorporation of a coagent increases the crosslinking efficiency in the EOC phase and decreases the extent of degradation in the PP phase. The present study mainly focused on the influence of three structurally different coagents, namely, triallyl cyanurate (TAC), trimethylol propane triacrylate (TMPTA), and N,N′‐m‐phenylene dimaleimide (MPDM), on the mechanical properties of the PP/EOC thermoplastic vulcanizates (TPVs). The reactivity and efficiency of different coagents were characterized by cure study on EOC gum vulcanizate. TAC showed the highest torque values followed by MPDM and TMPTA. Significant improvements in the physical properties of the TPVs were inferred with the addition of coagents. Among the three coagents used, MPDM showed the best balance of mechanical properties in these TPVs. The results indicated that torque values obtained during mixing and the final mechanical properties can be correlated. Different aspects were explained for the selection of a coagent that forms a product with desired properties. The phase morphologies of the TPVs prepared were studied by scanning electron microscopy. Tensile fracture patterns were also analyzed to study the failure mechanism of the samples. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Morphology and physical properties of closed cell microcellular ethylene–octene copolymer: Effect of precipitated silica filler and blowing agent

The morphology of the microcellular ethylene–octene copolymer (Engage) of both unfilled and precipitated silica‐filled compounds was studied from SEM photomicrographs with variation of blowing agent and silica filler loading. The average cell size, maximum cell size, and cell density varies with variation of blowing agent and filler loading. Physical properties similar to relative density, hardness, tensile strength, elongation at break, modulus, and tear strength decreases with blowing agent concentration. The elastic nature of closed cells reduces the hysteresis loss compared to solid compounds. Set properties improve with blowing agent concentration. It is observed that stress relaxation behavior is independent of blowing agent loading (i.e., density of closed cell microcellular vulcanizates). Theoretically, flaw sizes are found to be about 3.08 times larger than maximum cell sizes observed from SEM photomicrographs. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 357–366, 2002     

Morphology prediction of ternary polypropylene composites containing elastomer and calcium carbonate nanoparticles filler

In this work, the morphology was studied in ternary composites of polypropylene (PP) with nanosized calcium carbonate (nano‐CaCO₃) fillers and elastomer inclusions and the thermodynamic consideration was used to analyze the formation of phase structure of the composites. The wetting coefficient (ω_a), interfacial tension (γ_AB), and work of adhesion (W_AB) were calculated to predict dispersion state of nano‐CaCO₃ fillers. A comparison of the prediction and SEM analysis was given. The results show that three types of phase structures were formed: an encapsulation of the filler by elastomer, a separate dispersion of the filler and elastomer, and a particular structure of the filler at the PP/elastomer interface. The predictions by ω_a were all successfully supported‐up by SEM analysis and the predictions by W_AB were however trustless. Both γ_AB and W_AB can predict a separate dispersion or an encapsulation phase structure, but they were not available for the particular structure of the filler at the PP/elastomer interface. ω_a was competent and favored for the prediction of all three types of morphology among the three parameters. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 1578–1584, 2007     

Effect of strain on the properties of an ethylene–octene elastomer with conductive carbon fillers

Composites that incorporate a conductive filler into an ethylene–octene (EO) elastomer matrix were evaluated for DC electrical and mechanical properties. Comparing three types of fillers (carbon fiber, low structure carbon black, and high structure carbon black), it was found that the composite with high structure carbon black exhibited a combination of properties not generally achievable with this type of filler in an elastomeric matrix. A decrease in resistivity at low strains is unusual and has only been reported previously in a few instances. Reversibility in the resistivity upon cyclic deformation is a particularly unusual feature of EO with high structure carbon black. The mechanical and electrical performance of the high structure carbon black composites at high strains was also impressive. Mechanical reinforcement in accordance with the Guth model attested to good particle–matrix adhesion. The EO matrix also produced composites that retained the inherent high elongation of the unfilled elastomer even with the maximum amount of filler (30% by volume). The EO matrix with other conducting fillers did not exhibit the exceptional properties of EO with high structure carbon black. Composites with carbon fiber and low structure carbon black did not maintain good mechanical properties, generally exhibited an increase in resistivity with strain, and exhibited irreversible changes in both mechanical and electrical properties after extension to even low strains. An explanation of the unusual properties of EO with high structure carbon black required unique features of both filler and the matrix. The proposed model incorporates the multifunctional physical crosslinks of the EO matrix and dynamic filler–matrix bonds. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 894–905, 2000     

Influences of copolymerization conditions on the structure and properties of isotactic polypropylene/ethylene–propylene random copolymer in situ blends

A spherical TiCl₄/MgCl₂‐based catalyst was used in the synthesis of in situ isotactic polypropylene/ethylene–propylene random copolymer blends by propylene bulk polymerization and subsequent gas‐phase copolymerization of ethylene with propylene. Different copolymerization conditions, such as the reaction time, monomer pressure, and composition, were investigated, and their influences on the structure and properties of the products were studied. Raising the monomer pressure was the most effective way of speeding up the copolymerization, but it caused more increases in the random copolymer than the block copolymer fractions. Increasing the ethylene content of the monomer feed also resulted in higher reaction rates and copolymer contents, but the ethylene contents of both the random and block copolymer fractions were also raised. In situ blends that contain more than 50 wt % copolymer were prepared. The mechanical properties of the blends, including the impact strength and flexural modulus, were regulated in a rather broad range with changes in the copolymerization conditions. The properties were highly dependent on the amount, distribution, and chain structure of the copolymer fractions. The impact strength was influenced by both the random copolymer and block copolymer portions in a complicated way, whereas the flexural modulus was mainly determined by the amount of random copolymer. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 445–453, 2002; DOI 10.1002/app.10415     

Effect of silane‐grafted polypropylene on the mechanical properties and crystallization behavior of talc/polypropylene composites

Talc‐filled polypropylene (PP) composites coupled with silane‐grafted polypropylene (PP‐g‐Si) were prepared. Effect of PP‐g‐Si on the mechanical properties, crystallization, and melting behavior of PP composites was investigated. Compared with the uncoupled composites, the mechanical properties of Talc/PP composites coupled with a small amount of PP‐g‐Si were increased to some extent. Meanwhile, PP‐g‐Si can promote crystallization rate and increase crystallization temperature of PP in the composites. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 2974–2977, 2000     

Mechanical properties of injection‐molded isotactic polypropylene/roselle fiber composites

Natural fiber‐thermoplastic composite materials, based on their cost‐effectiveness and environmental friendliness, have attracted much interest both scientifically and technologically in recent years. Other advantages of natural fibers are good specific strength, less abrasion, and less irritation upon inhalation (in comparison with some common inorganic fillers). In the present contribution, roselle (Hibiscus sabdariffa L.) fibers were chosen and used as reinforcing fillers for isotactic polypropylene (iPP) for the first time, due mainly to the cost‐effectiveness and natural abundance on Thai soil. Processibility and mechanical properties of the resulting composites were investigated against the type and the mean size of the fibers. The results showed that the highest mechanical properties were observed when roselle bast fibers were incorporated. When whole‐stalk (WS) fibers (i.e., the weight ratio of bast and core fibers was 40 : 60 w/w) were used, moderate mechanical properties of the resulting composites were realized. The optimal contents of the WS fibers and the maleic anhydride‐grafted iPP compatibilizer that resulted in an improvement in some of the mechanical properties of the resulting composites were 40 and 7 wt %, respectively. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 3291–3300, 2006     

Isotactic polypropylene/ethylene‐co‐propylene blends: Influence of the copolymer microstructure on rheology,morphology, and properties of injection‐molded samples

Meltrheological behavior, phase morphology, and impact properties of isotactic‐polypropylene (iPP)‐based blends containing ethylene–propylene copolymer (EPR) synthesized by means of a titanium‐based catalyst with very high stereospecific activity (EPR_Ti) were compared to those of iPP/EPR blends containing EPR copolymers synthesized by using a traditional vanadium‐based catalyst (EPR_V). The samples of EPR copolymers were synthesized ad hoc. They were characterized by comparable propylene content, average molecular masses, and molecular mass distribution in order to assess the effects of distribution of composition and sequence lengths of the structural units on the structure–properties correlations established in the melt and in the solid state while studying different iPP/EPR pairs.^1–5 Differential scanning calorimetry, (DSC), wide‐angle X‐ray spectroscopy (WAXS), small‐angle X‐ray (SAXS), and scanning electron microscopy (SEM) investigations showed that the EPR_Ti chain is characterized by the presence of long ethylenic sequences with constitutional and configurational regularity required for crystallization of the polyethylene (PE) phase occurring, whereas a microstructure typical of a random ethylene–propylene copolymer was exhibited by the EPR_V copolymer. The different intra‐ and intermolecular homogeneity shown by such EPR phases was found to affect their melt rheological behavior at the temperatures of 200 and 250°C; all the EPR_Ti dynamic–viscoelastic properties resulting were lower than that shown by the EPR_V copolymer. As far as the melt rheological behavior of the iPP/EPR_V and iPP/EPR_Ti blends was concerned, both the iPP/EPR pairs are to be classified as “negative deviation blends” with G′ and G" values higher than that shown by the plain components. The extent of the observed deviation in the viscosity values and of the increase in the amounts of stored and dissipated energy shown by such iPP/EPR pairs was found to be dependent on copolymer microstructure, being larger for the melts containing the EPR_Ti copolymer. The application of the Cross–Bueche equation also confirmed that, in absence of shear, the melt phase viscosity ratio is the main factor in determining the viscosity of iPP/EPR blends and their viscoelastic parameters. The general correlation established between EPR dispersion degree (range of particle size and number‐average particle size), as determined in injection‐molded samples, and melt phase viscosity ratio (μ) was ratified; the type of dependence of EPR size upon μ value was in qualitative agreement with the prediction of the Taylor–Tomotika theory. Contrary to expectation,^1–5 for test temperature close to iPP T_g, EPR_V particles ranging in size between 0.75 and 1.25 μm resulted and were more effective than EPR_Ti particles, ranging in size between 0.25 and 0.75 μm, in promoting multiple craze formation. Also taking into account the SAXS results, revealed that the molecular superstructure (i.e., crystalline lamellar thickness and amorphous interlayer) of the iPP matrix is unaffected by both the presence of EPR_Ti and EPR_V phase. The above finding was related to the ethylenic crystallinity degree shown by the EPR_Ti copolymer. In particular, such a degree of crystallinity was supposed to deteriorate toughening by decreasing the tie molecules density in the EPR_Ti domains, notwithstanding the beneficial effect of the ethylenic lamellar buildup. For test temperature close to room temperature, the ductile behavior exhibited by the iPP/EPR_Ti blends was accounted for by a predominant shear yielding fracture mechanism probably promoted by a high concentration of interlamellar tie molecules among iPP crystallites in agreement with DSC results. Nonisothermal crystallization experiments showed, in fact, that the crystallization peak of the iPP phase from iPP/EPR_Ti melt is shifted to higher temperatures noticeably, thus indicating a material characterized by a comparatively higher number of spherulites per unit value grown at lower apparent undercooling values. Accordingly, WAXS analysis revealed comparatively higher iPP crystal growth in the directions perpendicular to the crystallographic planes (110) and (040) of the iPP. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 72: 701–719, 1999     

Effect of filler content and surface treatment on the tensile properties of glass‐bead‐filled polypropylene composites

The tensile properties of polypropylene (PP) filled with two A‐glass beads with the same size, PP/3000 (glass bead surface pretreated with a silane coupling agent) and PP/3000U (no surface pretreatment), have been measured by using an Instron materials testing machine at room temperature, to identify the effects of the filler surface pretreatment and its content on the tensile properties of these composites. The results show that the Young's modulus E_c of the composites increases non‐linearly with increasing volume fraction of glass beads ϕ_f, while the tensile yield strength σ_yc and tensile stress at break σ_bc of the composites decrease with an increase of ϕ_f, in the ϕ_f range 0–30%. Furthermore, the values of E_c and σ_bc of the PP/3000 system are somewhat higher than those of the PP/3000U system under the same test conditions, but this is in contrast to the tensile strain at break ε_bc and tensile fracture energy E_bc, especially at higher ϕ_f values. Good agreement is shown between the measured tensile strength and the predicted value by using an equation proposed in previous work. In addition, ε_bc and E_bc reach maximum values at ϕ_f = 25% for both systems. This indicates that there is a brittle–ductile transition for the composites in tension. © 2000 Society of Chemical Industry     

Preparation and properties of metallocene ethylene copolymer crosslinked by vinyltrimethoxysilane

Silane‐grafting and water‐crosslinking of ethylene–octene copolymer (EOR) was carried out. The influences of grafting formulation, comonomer content in EOR and time of the crosslinking process on grafting efficiency, degree and rate of crosslinking were investigated. The mechanical properties of various crosslinked samples are reported together with correlations with their gel contents. The results show that the extent of grafting increased with an increase in the amounts of dicumyl peroxide (DCP) and vinyltrimethoxysilane (VTMS) used in the reaction. The degree of crosslinking depended mainly on the extent of grafting, while the rate of the crosslinking process depended on the amount of amorphous phase in the samples. In this study, the variation of gel contents in the samples (0–77 %) had no significant influence on tensile properties. A large number of uncrosslinked regions are believed to exist inhomogeneously within the crosslinked polymers even after the sample has reached maximum gel content. The content of gel did not increase further when the crosslinking time was increased beyond that of reaching maximum gel, but the polymer network became denser, resulting in changes in polymer behaviour. Copyright © 2005 Society of Chemical Industry     

Mechanical properties and morphologies of polypropylene composites synergistically filled by styrene‐butadiene rubber and silica nanoparticles

The mechanical properties and morphologies of PP/SBR/SiO₂ nanocomposites have been studied using mechanical testing, wide‐angle X‐ray diffraction (WAXD), polarizing optical microscopy (POM), scanning electron microscopy (SEM), differential scanning calorimetry (DSC), and thermogravimetric analysis (TGA). The mechanical properties of neat polypropylene can be considerably improved by synergistically filling with SiO₂ and SBR nanoparticles, especially for the notched Izod impact strength. The results from the WAXD, POM, SEM, DSC, and TGA measurements reveal that: (i) the β‐phase crystal structure of PP is formed when SiO₂ and SBR nanoparticles are synergistically filled with polypropylene and its formation plays a role for the enhancement of the impact strength for PP/SBR/SiO₂ nanocomposites; (ii) the dispersion of SiO₂ and SBR nanoparticles in PP/SBR/SiO₂ composites is homogeneous, indicating that synergistic incorporating method decreases the aggregation of nanoparticles and thus increases the sites for dissipation of shock for impact energy in PP/SBR/SiO₂ nanocomposites; (iii) the thermal analysis shows high thermal stability for the PP/SBR/SiO₂ nanocomposites. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

A study on the effects of SEBS‐g‐MAH on the phase morphology and mechanical properties of polypropylene/polycarbonate/SEBS ternary polymer blends

In this work, five ternary blends based on 70% by weight (wt %) of polypropylene (PP) with 30% wt of polycarbonate (PC)/poly(styrene‐b‐(ethylene‐co‐butylene)‐b‐styrene)(SEBS) dispersed phase consists of 15 wt % PC and 15 wt % reactive (maleic anhydride grafted) and nonreactive SEBS mixtures at various ratios were prepared in a co‐rotating twin screw extruder. scanning electron microscopy (SEM) micrographs showed that the blends containing only nonreactive SEBS exhibited a fine dispersion of core‐shell particles. With decreasing the SEBS/SEBS‐g‐Maleic Anhydride (MAH) weight ratio, the morphology changed from the core‐shell particles to a mixed of core‐shell, rod‐like and individual particles. This variation in phase morphology affected the thermal and mechanical properties of the blends. DSC results showed that the blends containing only nonreactive SEBS exhibited a minimum in degree of crystallinity due to the homogeneous nucleation of core‐shell particles. Mechanical testing showed that in the SEBS/SEBS‐g‐MAH weight ratio of 50/50, the modulus and impact strength increased compared with the PP matrix while the yield stress had minimum difference with that of PP matrix. These effects could be attributed to the formation of those especial microstructures revealed by the SEM studies. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Blends of ethylene–methyl acrylate–acrylic acid terpolymers with ethylene–acrylic acid copolymers: Mechanical and thermomechanical properties

The effect of methyl acrylate content in ethylene–methyl acrylate–acrylic acid (E–MA–AA) terpolymers and acrylic acid content in ethylene–acrylic acid (E–AA) copolymers was investigated in blends of these two materials. The E–MA–AA terpolymer with 8 mol % methyl acrylate was not miscible with any E–AA material no matter what the AA content, whereas the terpolymer with only about 2 mol % methyl acrylate was miscible, at least to some extent, with the E–AA copolymer at high acrylic acid contents. Evidence supporting this conclusion derived from gloss, differential scanning calorimetry testing, and dynamic mechanical measurements. For the E–AA polymer material with the highest acid content, there was a synergistic effect for some properties at low added amounts of E–MA–AA copolymer; the tensile strength and hardness were 10% higher than values for the E–AA copolymer, even though the E–AA copolymer was much stiffer. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 2216–2222, 2004     

Steam‐exploded residual softwood‐filled polypropylene composites

Residual softwood sawdust was pretreated by a steam‐explosion technique. It was used as a natural filler in polypropylene (PP)‐based composites. Dynamic mechanical analysis and tensile properties of these materials were studied. The influence of filler loading, steam‐explosion severity, and coating the fiber with a functionalized compatibilizer, such as maleic anhydryde polypropylene (MAPP), on the mechanical behavior of the composite was evaluated. The results were analyzed in relation with scanning electron microscopy observations, and surface energy (dispersive and polar components) and apparent specific area measurements. Experimental data indicate a better compatibility between MAPP‐coated fiber and PP with respect to the untreated one. The coating treatment of the softwood fiber was found to promote interfacial adhesion between both components, and to enhance the tensile properties of the resulting composite. This reinforcing effect was well predicted from theoretical calculations based on a mean field approach (Halpin‐Kardos model). The steam‐explosion pretreatment severity increased the surface energy and apparent specific surface, and resulted in a loss of the fiber entirety. The sorption behavior of these composite materials was also performed. It was found that the composites absorb more water, as the filler content is higher. MAPP coating provided protection from water uptake in the interphase region. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 1962–1977, 1999     

Mechanical and thermal properties of polypropylene/sugarcane Bagasse composites

To determine the possibility of using sugarcane bagasse (SCB) waste as reinforcing filler in the thermoplastic polymer matrix, SCB‐reinforced polypropylene (PP) composites were prepared. The PP and SCB composites were prepared by the extrusion of PP resin with 5, 10, 15, and 20 wt % of SCB filler in a corotating twin screw extruder. The extruded strands were cut into pellets and injection molded to make test specimens. These specimens were tested for physicomechanical properties such as tensile, flexural, Izod, and Charpy impact strengths, density, water absorption, and thermal characteristics, namely, heat deflection temperature (HDT), melt flow index, and thermogravimetric analysis. It was found that the flexural strength increased from 23.66 to 26.84 MPa, Izod impact strength increased from 10.499 to 13.23 Kg cm/cm, Charpy impact strength increased from 10.096 to 13.98 Kg cm/cm, and HDT increased from 45.5 to 66.5°C, with increase in filler loading from 5 to 20% in the PP matrix. However, the tensile strength and elongation decreased from 32.22 to 27.21 MPa and 164.4 to 11.20% respectively. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 3827–3832, 2007