Influence of carboxyl‐terminated (butadiene‐co‐acrylonitrile) loading on the mechanical and thermal properties of cured epoxy blends

A mixture of epoxy with liquid nitrile rubber, carboxyl‐terminated (butadiene‐co‐acrylonitrile) (CTBN) was cured under various temperatures. The cured resin was a two‐phase system, where spherical rubber domains were dispersed in the matrix of epoxy. The morphology development during cure was investigated by scanning electron microscope (SEM). There was slight reduction in the glass transition temperature of the epoxy matrix (T_g) on the addition of CTBN. It was observed that, for a particular CTBN content, T_g was found to be unaffected by the cure temperature. Bimodal distribution of particles was noted by SEM analysis. The increase in the size of rubber domains with CTBN content is due probably to the coalescence of the rubber particles. The mechanical properties of the cured resin were thoroughly investigated. Although there was a slight reduction in tensile strength and young's modulus, appreciable improvements in impact strength, fracture energy, and fracture toughness were observed. Addition of nitrile rubber above 20 parts per hundred parts of resin (phr) made the epoxy network more flexible. The volume fraction of dispersed rubbery phase and interfacial area were increased with the addition of more CTBN. A two‐phase morphology was further established by dynamic mechanical analysis (DMA). © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 2531–2544, 2004     

Simultaneous enhancement of electrical conductivity and impact strength via formation of carbon black‐filler network in PP/EPDM Blends

The electrical conductivity and impact strength of polypropylene(PP)/EPDM/carbon black ternary composites were investigated in this paper. Two processing methods were employed to prepare these ternary composites. One was called one‐step processing method, in which the elastomer and the filler directly melt blended with PP matrix. Another one was called two‐step processing method, in which the elastomer and the filler were mixed first, and then melt blended with pure PP. To get an optimal phase morphology that favors the electrical conductivity and impact strength, controlling the distribution of CB in PP/EPDM blend was a crucial factor. Thus the interfacial tension and the work of adhesion were first calculated based on the measurement of contact angle, and the results showed that CB tended to be accumulated around EPDM phases to form filler‐network structure. Expectably, the filler‐network structure was observed in PP/EPDM/CB(80/20/3) composite prepared by two‐step processing method. The formation of this filler‐network structure decreased the percolation threshold of CB particles in polymer matrix, and the electrical conductivity as well as Izod impact strength of the composite increased dramatically. This work provided a new way to prepare polymer composites with both improved conductivity and impact strength. Copyright © 2009 John Wiley & Sons, Ltd.     

Impact‐specific essential work of fracture of maleic anhydride‐compatibilized polypropylene/elastomer blends and their composites

Charpy drop‐weight‐impact and essential work of fracture (EWF) characteristics of maleic anhydride (MA)‐compatibilized styrene–ethylene butylene–styrene (SEBS)/polypropylene (PP) blends and their composites reinforced with short glass fibers (SGFs) were investigated. MA was grafted to either SEBS copolymer (SEBS‐g‐MA) or PP (PP‐g‐MA). The mPP blend was prepared by the compounding of 95% PP and 5% PP‐g‐MA. Drop‐weight‐impact results revealed that the mPP specimen had an extremely low impact strength. The incorporation of SEBS or SEBS‐g‐MA elastomers into mPP improved its impact strength dramatically. Similarly, the addition of SEBS was beneficial for enhancing the impact strength of the SGF/SEBS/mPP and SGF/SEBS‐g‐MA/mPP hybrids. A scanning electron microscopy examination of the fractured surfaces of impact specimens revealed that the glass‐fiber surfaces of the SGF/SEBS/mPP and SGF/SEBS‐g‐MA/mPP hybrids were sheathed completely with deformed matrix material. This was due to strong interfacial bonding between the phase components of the hybrids associated with the MA addition. Impact EWF tests were carried out on single‐edge‐notched‐bending specimens at 3 m s^?1. The results showed that pure PP, mPP, and the composites only exhibited specific essential work. The nonessential work was absent in these specimens under a high‐impact‐rate loading condition. The addition of SEBS or SEBS‐g‐MA elastomer to mPP increased both the specific essential and nonessential work of fracture. This implied that elastomer particles contributed to the dissipation of energy at the fracture surface and in the outer plastic zone at a high impact speed of 3 m s^?1. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 1881–1892, 2002     

Influence of interfacial interactions on the mechanical behavior of hybrid composites of polypropylene / short glass fibers / hollow glass beads

Ternary composites of Polypropylene (PP)/Short Glass fibers (GF)/Hollow Glass Beads (HGB), with varying total and relative GF/HGB contents and using untreated and aminosilane-treated HGB compatibilized with maleated-PP, were prepared by direct injection molding of pre-extrusion compounded GF and HGB concentrates. The mechanical strength properties (tensile, flexural and Izod impact) were correlated with theoretical model predictions for hybrid composites, which identified synergistic gains over the rule of hybrid mixtures, depending upon the degree of interfacial interactions between the components of the hybrid composite. SEM analysis of cryofractured composites surfaces revealed that the presence of untreated HGB particles induces fiber-polymer interfacial decoupling under mechanical loading of the hybrid composites at much lower stress levels than in the presence of treated HGB particles. Higher storage modulus (E′) and lower mechanical damping (tan δ) from DMTA established the importance of strong polymer-hybrid reinforcement interfacial interactions in the development of lightweight/high strength PP syntactic foams.     

A positron annihilation study on the microstructure of cyanate ester resin toughened by carboxyl‐terminated butadiene‐acrylonitrile rubber system

The toughness of cyanate ester (CE) resin matrix improves significantly with the addition of carboxyl‐terminated butadiene‐acrylonitrile rubber (CTBN). The curing behavior of the system was studied by differential scanning calorimetry (DSC) and Fourier transform infrared (FTIR) spectroscopy. The results show that carboxyl groups on the CTBN chain have a slight activation effect on the CE curing reaction at the beginning of the curing process. Phase separation was found to be the main toughening mechanism for CE/CTBN composites. The existence of macro‐size pores induced by the decomposition of a small amount of the low weight molecular part of CTBN might be another toughening mechanism. It is confirmed that positron annihilation lifetime spectroscopy (PALS) is still valid in such a system where macropores filled with gas molecules exist. When a high weight percentage of CTBN (>8%) was added to CE, free‐positron annihilation was found to be the dominant annihilation process in the macropores. For CTBN weight percentage higher than 8%, the contribution of ortho‐positronium (o‐Ps) annihilation in the macropores to τ₃ and I₃ was found to be insignificant. It is effective to use PALS as a probe of free‐volume properties in such systems by determining the changes in the τ₃ and I₃ of the composite. The compatibility and interfacial adhesion of the composites can be estimated from the changes in the free‐volume properties of the composites. Copyright © 2008 John Wiley & Sons, Ltd.     

Surface modification of boron nitride via poly (dopamine) coating and preparation of acrylonitrile‐butadiene‐styrene copolymer/boron nitride composites with enhanced thermal conductivity

A biology‐inspired approach was utilized to functionalize hexagonal boron nitride (h‐BN), to enhance the interfacial interactions in acrylonitrile‐butadiene‐styrene copolymer/boron nitride (ABS/BN) composites. The poly (dopamine), poly (DOPA) layer, was formed on the surface of BN platelets via spontaneously oxidative self‐polymerization of DOPA in aqueous solution. The modified BN (named as mBN) coated with poly (DOPA) was mixed with ABS resin by melting. The strong interfacial interactions via π‐π stacking plus Van der Waals, both derived from by poly (DOPA), significantly promoted not only the homogeneous dispersion of h‐BN in the matrix, but also the effective interfacial stress transfer, leading to improve the impact strength of ABS/mBN even at slight mBN loadings. A high thermal conductivity of 0.501 W/(m·K) was obtained at 20 wt% mBN content, reaching 2.63 times of the value for pure ABS (0.176 W/(m·K)). Meanwhile, the ABS/mBN composites also exhibited an excellent electrical insulation property, which can be expected to be applied in the fields of thermal management and electrical enclosure.     

Morphology and performance of styrene butadiene rubber filled with modified graphite nanoplatelet and carbon black

In our work, effects of 2‐mercapto‐1‐methylimidazole modified graphite nanoplatelet (MMI–GN) and carbon black (CB) on static and dynamic mechanical properties of styrene butadiene rubber (SBR) composites were studied. MMI–GN is synthesized by ball‐mill process, and the result reveals that π–π interactions existed between MMI and GN. The results demonstrate that the static and dynamic mechanical performances of SBR/CB/MMI–GN composites are significantly improved over these of SBR/CB and SBR/CB/GN composites. Compared with SBR/CB, the tensile strength, tear strength, and modulus at 300% elongation of SBR/CB/MMI–GN–3 are greatly improved by 45%, 27%, and 4%, respectively. And the rolling resistance of SBR/CB/MMI–GN–3 is reduced by 3.7% with remaining almost unchanged in the wet grip property. The superiority of MMI–GN in the enhancement for the overall performance of SBR/CB composites is attributed to the well dispersion of GN throughout the SBR matrix and the enhanced interfacial interactions between GN and the SBR matrix. This work might expedite synthesis of the graphite‐based materials for enhancing rubber composites, and enlarge the potential applications of modified graphite to fabricate the high‐performance rubber composites. Copyright © 2016 John Wiley & Sons, Ltd.     

Synergistically toughening high‐density polyethylene with calcium carbonate and elastomer

The microstructure, impact strength, and rheological properties of blends consisting of high‐density polyethylene (HDPE) and maleated poly (ethylene‐octene) (POEg) and/or calcium carbonate (CaCO₃) were investigated. The improvement of impact strength of HDPE/POEg was limited due to the high miscibility between them. The introduction of CaCO₃ had a negative impact on the toughness of the matrix because of the poor interfacial adhesion. In ternary blends of HDPE/POEg/CaCO₃, an elastomer layer was formed around CaCO₃ particles due to the strong interaction between POEg and CaCO₃, which improves the HDPE‐CaCO₃ interfacial strength and the toughness of the blends. A significant enhancement of dynamic viscosity, storage modulus, and the low‐shear viscosity were observed as the results of the high miscibility of HDPE with POEg and strong interaction between POEg and CaCO₃. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 3213–3221, 2005     

Synthesis and Characterization of Aramid Fiber‐Reinforced Polyimide/Carbon Black Composites and Their Use in a Supercapacitor

The aramid fabric (AF )‐reinforced polyimide (PI ) composites filled with carbon black (CB ) were fabricated by means of a thermal imidization and their mechanical, thermal and electrochemical behaviors were comparatively investigated. Experimental results showed that the tensile strength of composite increased with an increase of the CB , meanwhile, the addition of 5 wt% CB and AF increased the tensile modulus to 5682.0 MPa . The superior mechanical properties of the composites were attributed to the good dispersion and effective stress transfer between the polymer and CB , as evidenced by the results from X‐ray diffraction (XRD ) and morphological studies. Besides, the thermal‐nonoxidative stability of PI was significantly improved by the incorporation of CB and AF . Furthermore, the CB /AF /PI composite was employed as the supercapacitor electrode in the 6 mol/L KOH aqueous electrolyte solution, which exhibited a specific capacitance of 510 F•g⁻¹ at 10 mV •s⁻¹. It also exhibited excellent long‐term stability, and the energy density was stable with the increase in the power density. The super performance of the composite electrode is attributed to the synergistic effects of CB particles and organic polymer.     

Effect of compounding procedure on morphology and crystallization behavior of isotactic polypropylene/high‐density polyethylene/carbon black ternary composites

The effect of compounding procedure on morphology and crystallization behavior of isotactic polypropylene/high‐density polyethylene/carbon black (iPP/HDPE/CB) composite was investigated. iPP/HDPE/CB composites were prepared by four compounding procedures (A: iPP + HDPE + CB; B: iPP/HDPE + CB; C: HDPE/CB + iPP; D: iPP/CB + HDPE). Scanning electron microscopy observation showed that CB particles are mainly distributed in HDPE in all composites, and the phase morphology of composites was obviously affected by a compounding procedure. The size of the HDPE/CB domains in the composites prepared by procedures A and D decreased with the increase in CB content, whereas that of HDPE/CB in the composites prepared by procedures B and C rarely changed with the increase in CB content. The crystallization behaviors of the composites were significantly affected by their phase morphology, which resulted from the variation of compounding procedure. The isothermal crystallization rate of iPP in the composites prepared by procedures A and D was obviously increased, which may originate from the small HDPE/CB droplets dispersed in the iPP phase. The non‐isothermal crystallization curves of composites prepared by procedure D represented two peaks because the iPP component in these composites had the fastest crystallization rate, whereas the curves of composites prepared by other compounding sequences only exhibited one peak. Moreover, the crystallinity of HDPE almost increased by one time with the incorporation of only 1 phr CB because the CB particles selectively located in the HDPE phase, and the crystallinity of HDPE decreased with the further increase of CB content because of the strong restriction of CB on the HDPE chains. Copyright © 2011 John Wiley & Sons, Ltd.     

The effect of surface coating of CNTs on the mechanical properties of CF‐filled HDPE composites

Mechanical properties of carbon fiber (CF) and carbon nanotube (CNT)‐filled thermoplastic high‐density polyethylene (HDPE) composites were studied with particular interest on the effects of filler content and fiber surface treatment by coupling agent. Surface‐treated CF‐filled HDPE composites increased their tensile strength and impact strength, which is further increased with the addition of CNT. SEM showed that CNT‐coating‐treated CF‐HDPE composites show better dispersion of the filler into the matrix, which results in better interfacial adhesion between the filler and the matrix. Copyright © 2014 John Wiley & Sons, Ltd.     

The addition of clay on the mechanical properties of surface‐treated CF‐filled PA66 composites

Polyamide 66 (PA66) composites filled with clay and carbon fiber (CF) were prepared by twin‐screw extruder in order to study the influence of nanoparticle reinforcing effect on the mechanical behavior of the PA66 composites (CF/PA66). The mechanical property tests of the composites with and without clay were performed, and the fracture surface morphology was analyzed. The results show that the fracture surface area of the clay‐filled CF/PA66 composite was far smoother than that of the CF/PA66 composite, and there formed a tense interface on the CF surface after the addition of clay. The tensile and flexural strength of CF/PA66 composites with clay was improved. The impact strength decreased because of the high interfacial adhesion. In conclusion, the addition of clay favored the improvement of the higher interface strength and so had good effect on improving the tensile and flexural properties of the composites. Copyright © 2017 John Wiley & Sons, Ltd.     

Positive‐temperature‐coefficient/negative‐temperature‐coefficient effect of low‐density polyethylene filled with a mixture of carbon black and carbon fiber

Low‐density polyethylene (LDPE) filled with carbon black (CB) and carbon fiber (CF) composites were prepared by a conventional melt‐mixing method. The effects of a mixture of CB and CF on the positive‐temperature‐coefficient (PTC) effect and the negative‐temperature‐coefficient (NTC) effect, as well as the percolation threshold, were examined in detail. A synergy effect between CB and CF occurred, in that continuous conductive pathways formed within the CB/CF‐filled composite. The percolation threshold was moved to a reduced filler content with the addition of CF to an LDPE/CB composite. A model was proposed to explain the difference in the PTC behavior of composites containing CB and CF and composites containing only CB or CF. In addition, the NTC effect was weakened with a mixture of CB and CF, and a relatively small radiation dose was required to eliminate the NTC phenomenon in LDPE/CB/CF composites. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 3094–3101, 2003     

Preparation of Sheet‐like Polymer‐Encapsulated Composite Particles by Seeded Polymerization from Sub‐micrometer Sheets

Seeded polymerization has been widely used to fabricate polymer‐encapsulated inorganic particles (IPs). The most frequently used seeds are spherical, whereas nonspherical particles are not well documented. Recently, sheet‐like IPs have attracted much attention in the context of polymer composites. This article is therefore dedicated to understanding seeded polymerization from submicron sheets and focuses on the control of the overall morphology of the composite particles obtained. However, it was found that the composite particles only maintained the sheet‐like morphology of the seeds at a low polymer content, whereas they became hamburger‐like at a high polymer content owing to minimization of the interfacial energy. Interestingly, when cross‐linked, the sheet‐like morphology could be well preserved, even at a rather high polymer content. With the encapsulating polymer layer, the obtained sheet‐like composite particles showed improved compatibility with the polymer matrix and could be well dispersed in polymer matrix when simply blended.     

Structural and mechanical behavior of polypropylene/ maleated styrene‐(ethylene‐co‐butylene)‐styrene/sisal fiber composites prepared by injection molding

Hybrid composites consisting of isotactic poly(propylene) (PP), sisal fiber (SF), and maleic anhydride grafted styrene‐(ethylene‐co‐butylene)‐styrene copolymer (MA‐SEBS) were prepared by melt compounding, followed by injection molding. The melt‐compounding torque behavior, thermal properties, morphology, crystal structure, and mechanical behavior of the PP/MA‐SEBS/SF composites were systematically investigated. The torque test, thermogravimetric analysis, differential scanning calorimetric, and scanning electron microscopic results all indicated that MA‐SEBS was an effective compatibilizer for the PP/SF composites, and there was a synergism between MA‐SEBS and PP/SF in the thermal stability of the PP/MA‐SEBS/SF composites. Wide‐angle X‐ray diffraction analysis indicated that the α form and β form of the PP crystals coexisted in the PP/MA‐SEBS/SF composites. With the incorporation of MA‐SEBS, the relative amount of β‐form PP crystals decreased significantly. Mechanical tests showed that the tensile strength and impact toughness of the PP/SF composites were generally improved by the incorporation of MA‐SEBS. The instrumented drop‐weight dart‐impact test was also used to examine the impact‐fracture behavior of these composites. The results revealed that the maximum impact force (F_max), impact‐fracture energy (E_T), total impact duration (t_r), crack‐initiation time (t_init), and crack‐propagation time (t_prop) of the composites all tended to increase with an increasing MA‐SEBS content. From these results, the incorporation of MA‐SEBS into PP/SF composites can retard both the crack initiation and propagation phases of the impact‐fracture process. These prolonged the crack initiation and propagation time and increased the energy consumption during impact fracture, thereby leading to toughening of PP/MA‐SEBS/SF composites. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 1214–1222, 2002     

Enhancement of composite‐metal interfacial adhesion strength by dendrimer

The interface between carbon fiber reinforced polymer composites and metal plays a critical role in determining the strength of epoxy/metal laminated composites. We propose to introduce one dendrimer layer into the epoxy/metal interface, aiming to enhance the interfacial adhesion strength so that the interface could more effectively transfer the load from epoxy to metal. In this paper, the preparation and adsorption of dendrimer layer onto the alumina surface were systematically investigated. The results show that a highly stable and nanopatterned dendrimers layer was dip‐coated onto alumina substrates by adsorbing poly (amidoamine) dendrimers. It was confirmed that the dendrimers were adsorbed onto the alumina via acid‐base chemical interactions. The adsorption depends on the reaction time. The adhesion property between dendrimers and alumina was examined by sonication method. Copyright © 2010 John Wiley & Sons, Ltd.     

STUDY ON NYLON 6/SUPERFINE RUBBER PARTICLES COMPOSITES VIA IN SITU POLYMERIZATION

Two highly cross-linked superfine styrene-butadiene rubber particles, one with 1 wt% of carboxyl groups and theother without such groups having particle sizes of 130-150 nm and 80-100 nm respectively, were used to prepare nylon6/rubber composites via in situ polymerization. It was found that carboxylic styrene-butadiene dispersed uniformly in nylonmatrix and there was strong interfacial interaction because of the graft polymer formed by the reaction of nylon with carboxylgroup of the rubber, resulting in considerably improved impact strength with almost unchanged tensile strength. However,the addition of styrene-butadiene without carboxyl groups showed intensive agglomeration of the rubber particles and weakinterfacial interactions, and the toughness of the materials was improved slightly. The crystallization and rheological behavior of the composites were also discussed.     

Interfacial studies on the ozone and air‐oxidation‐modified carbon fiber reinforced PEEK composites

In this work, ozone modification method and air‐oxidationwere used for the surface treatment of polyacrylonitrile(PAN)‐based carbon fiber. The surface characteristics of carbon fibers were characterized by XPS. The interfacial properties of carbon fiber‐reinforced (polyetheretherketone) PEEK (CF/PEEK) composites were investigated by means of the single fiber pull‐out tests. As a result, it was found that IFSS (interfacial shear strength) values of the composites with ozone‐treated carbon fiber are increased by 60% compared to that without treatment. XPS results show that ozone treatment increases the amount of carboxyl groups on carbon fiber surface, thus the interfacial adhesion between carbon fiber and PEEK matrix is effectively promoted. The effect of surface treatment of carbon fibers on the tribological properties of CF/PEEKcomposites was comparativelyinvestigated. Experimental results revealed that surface treatment can effectively improve the interfacial adhesion between carbon fiber and PEEK matrix. Thus the wear resistance was significantly improved. Copyright © 2009 John Wiley & Sons, Ltd.     

Effect of silane coupling agent on mechanical interfacial properties of glass fiber‐reinforced unsaturated polyester composites

A silane coupling agent, γ‐methacryloxypropyltrimethoxysilane, for the surface modification of glass fibers was varied between 0.1 and 0.8 wt %. To understand the role of interfacial adhesion of glass fiber/unsaturated polyester composites, contact angles of the silane‐treated glass fibers were measured by the wicking method on the basis of the modified Washburn equation with deionized water, diiodomethane, and ethylene glycol as testing liquids. As a result, silane‐treated glass fibers led to increased surface free energy, mainly because of their increased specific or polar component. The mechanical interfacial behaviors based on the interlaminar shear strength (ILSS) of the composites determined by short‐beam tests and the critical stress‐intensity factor (K_IC) were also improved in the case of silane‐treated composites. The surface free energy and the mechanical interfacial properties especially showed the maximum value in the presence of 0.4 wt % silane coupling agent. It revealed that the increase of a specific component of the surface free energy or hydrogen bonding between the glass fibers and the coupling agents plays an important role in improving the degree of adhesion at interfaces in a composite system. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 55–62, 2003     

Preparation and enhanced properties of poly(propylene)/ silica‐grafted‐hyperbranched polyester nanocomposites

A series of poly(propylene) silica‐grafted‐hyperbranched polyester nanocomposites by grafting the modified hyperbranched polyester (Boltorn? H20), possessing theoretically 50% end carboxylic groups and 50% end hydroxyl groups, which endcapped with octadecyl isocyanate (C19), onto the surface of SiO₂ particles (30 nm) through 3‐glycidoxy‐propyltrimethoxysilane (GPTS) was prepared. The effect of silica‐grafted‐modified Boltorn? H20 on the mechanical properties of polypropylene (PP) was investigated by tensile and impact tests. The morphological structure of impact fracture surface and thermal behavior of the composites were determined by scanning electron microscopy (SEM) and differential scanning calorimetry (DSC), respectively. The melt viscosity of composites was investigated by melt flow index (MFI). The obtained results showed that: (1) the modified Boltorn? H20 was successfully grafted onto the SiO₂ surface confirmed by FT‐IR and X‐ray photoelectron spectroscopy (XPS) analysis; (2) the incorporation of silica‐grafted‐modified Boltorn? H20 (3–5 wt% SiO₂) greatly enhanced the notched impact strength as well the tensile strength of the composites; (3) the incorporation of silica‐grafted‐modified Boltorn? H20 had no influence on the melting temperature and crystallinity of PP phase; (4) the MFI of PP composites increased when the silica‐grafted‐modified Boltorn? H20 particles were added compared with PP/SiO₂ or PP/SiO₂‐GPTS composites. Copyright © 2004 John Wiley & Sons, Ltd.