Microhardness and thermal stability of compatibilized LDPE/PA6 blends

Microhardness tests, water absorption and thermogravimetric measurements have been performed on blends of low density polyethylene (LDPE) with different molar mass and polyamide 6 (PA6) compatibilized with 2 pph poly(ethylene-co-acrylic acid) (Escor 5001 by Exxon). The negative deviation of Vickers microhardness from the additivity has been interpreted by changes in the crystallinity of the blend components. The hardness values of the compatibilized blends that are lower than those of the corresponding uncompatibilized blends have been explained by the decrease of the degree of crystallinity of PA6 phase in the presence of Escor. The molar mass of LDPE almost does not influence on the hardness values. The lower water absorption of the compatibilized blends, caused by the formation of a copolymer between PA6 and the compatibilizer leads to microhardness values of the wet compatibilized blends higher than those of the corresponding uncompatibilized blends. The thermogravimetric measurements demonstrate that the thermal stability of blends increases in the presence of 2 pph Escor 5001. The results confirm the compatibilizing efficiency of Escor 5001 towards LDPE/PA6 blends in a wide composition range.     

Toughening of polycarbonate by core‐shell latex particles: Influence of particle size and spatial distribution on brittle‐ductile transition

The impact toughness of polycarbonate modified with acrylic core‐shell latex particles was investigated. Addition of impact modifiers with size ranging from 115.7 to 231.4 nm can result in maximum impact strength. Equations for spatial distribution of modified particles were proposed to associate the interparticle distance with particle size and modifier volume fraction in terms of two possible morphologies, given by T = d[0.91/(φ)^1/3 ? 1] or T = d[0.88/(φ)^1/3 ? 1]. The influence of particle size on brittle‐ductile transition was also studied. The results indicated that critical interparticle distance was not a definitive value and had a narrow region. Moreover, there existed a linear relationship between critical interparticle distance and modifier size, that is, critical interparticle distance would enlarge with the increasing of core‐shell particle size. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 1970–1977, 2010     

Fractionated crystallization of compatibilized LDPE/PA6 blends

The paper presents differential scanning calorimetry and electron microscopy of the fractionated crystallization and polydispersity of the dispersed PA6 phase in compatibilized LDPE/PA6 75/25 w/w blends. The compatibilizers used were (i) an acrylic acid functionalized polyethylene, Escor 5001 (EAA); (ii) an ethylene-glycidylmethacrylate copolymer, Lotader GMA AX8840 (EGMA); (iii) a polystyrene-poly(ethylene-butylene)-polystyrene triblock copolymer comprising 2 wt.% maleic anhydride grafts, Kraton FG 1901X (SEBS-g-MA). The compatibilizer SEBS-g-MA has the strongest reduction effect upon the size of PA-6 droplets. Its implementation provides the best fractionated crystallization. The fractionated crystallization has not been observed for the blend compatibilized with EGMA. The results show that the degree of compatibilization could be evaluated qualitatively by the progress of the fractionated crystallization. So, the three compatibilizers could be rated according to their effectiveness as follows: SEBS-g-MA > EAA > EGMA. The self-nucleation experiments have demonstrated that the lack of active nuclei in the finely dispersed PA6 droplets is the determining factor for the fractionated crystallization at high supercooling, and not the considered absolute particle size. The measurement of the Vickers microhardness of the compatibilized blends confirms that the compatibilizing activity of SEBS-g-MA and EAA is stronger than that of EGMA.     

Morphologies,interfacial interaction and mechanical performance of super-tough nanostructured PK/PA6 blends

Nanostructured polyketone (PK)/polyamide 6 (PA6) blends can be readily prepared via melt blending technologies and exhibit ultra-high toughness when PA6 is present as the nanoscale phase domains. When PA6 content is 30 vol%, the impact strength of the blends increases from 21.4 kJ/m² of pure PK to 103.2 kJ/m². The impact strength of the PK/PA6 blends with a 5:5 composition ratio reaches as high as 113 kJ/m². The strong intermolecular force between PK and PA6 molecular chains enables the PA6 nanophase to cavitate to dissipate a significant amount of impact energy and effectively prevents the crack propagation or even terminates the cracks. The fracture mechanism of the PK/PA6 blends was further examined by the essential work of fracture method which proves that PK/PA6 blends show improved ability to prevent crack propagation. This work may deepen the understanding of polymer blend systems with strong hydrogen bonding interaction.     

Modeling the effect of compatibilizers in the coarsening of ternary polymer blends with core‐shell morphology

Numerical simulations of the phase separation and coarsening of particulate, ternary polymer blends have been performed using a ternary form of the modified Cahn–Hilliard equation. The third component was chosen to be a compatibilizer, typically being a random copolymer of the major components. The results show that compatibilized blends follow the same Lifshitz–Slyozov coarsening law as binary systems. Slower coarsening rates, indicating system stabilization, were observed for blends containing ∼10% compatibilizer and exhibiting a core‐shell morphology. Larger amounts of compatibilizer resulted in significantly higher coarsening rates. This appears to be a result of the greater affinity of the compatibilizer for the major component and warrants further experimental investigation. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 1301–1306, 2000     

Preparation of gel‐silica/ammonium polyphosphate core‐shell flame retardant and properties of polyurethane composites

A novel intumescent gel‐silica/ammonium polyphosphate core‐shell flame retardant (MCAPP), which contains silicon, phosphorus, and nitrogen, has been prepared by in situ polymerization. The structure of MCAPP was characterized by Fourier transform infrared (FTIR) and X‐ray photoelectron spectroscopy (XPS). The properties of MCAPP were investigated by water solubility, hydrophilicity, and morphological determination. The flame retardancy and thermal stability of polyurethane (PU) composite with MCAPP were evaluated by limiting oxygen index (LOI), UL‐94 test, cone calorimetry, and thermogravimetric analysis (TGA). The results showed that MCAPP could decrease the heat release rate (HRR) and increase the thermal stability of PU materials greatly. Finally, water‐resistant properties of PU/FR composites were also studied. Copyright © 2010 John Wiley & Sons, Ltd.     

Development of morphology and properties of injection‐molded bars of HDPE/PA6 blends along flow direction

The structure and mechanical properties of injection‐molded bars of high‐density polyethylene (HDPE)/PA6 blends were studied in this article. The experimental results showed that the morphologies of injection‐molded bars change gradually along the flow direction, which is tightly related to the melt viscosity and processing conditions. The higher melt viscosity, lower mold temperature, and shorter packing time, restricting the macromolecular relaxation, enhance the difference in morphologies and properties at near and far parts of a mold. An injection‐molded bar (namely H2C5), consisting of 75 wt % of HDPE, 20 wt % of PA6, and 5 wt % of compatibilizer (HDPE‐g‐MAH), showed a greater difference in mechanical properties at near and far parts because of its higher melt viscosity. A clear interface between the skin and core layers of near part in it leads to a much higher impact strength than that of far part. And tensile tests show that its tensile strength of near part is higher than that of far part due to the higher orientation degrees of HDPE matrix and PA6 dispersed phase in near part. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 184–195, 2007     

Reactive compatibilization of polyamide‐6 (PA 6)/polybutylene terephthalate (PBT) blends by a multifunctional epoxy resin

A multifunctional epoxy resin has been demonstrated to be an efficient reactive compatibilizer for the incompatible and immiscible blends of polyamide‐6 (PA 6) and polybutylene terephthalate (PBT). The torque measurements give indirect evidence that the reaction between PA and PBT with epoxy has an opportunity to produce an in situ formed copolymer, which can be as an effective compatibilizer to reduce and suppress the size of the disperse phase, and to greatly enhance mechanical properties of PA/PBT blends. The mechanical property improvement is more pronounced in the PA‐rich blends than that in the PBT‐rich blends. The fracture behavior of the blend with less than 0.3 phr compatibilizer is governed by a particle pullout mechanism, whereas shear yielding is dominant in the fracture behavior of the blend with more than 0.3 phr compatibilizer. As the melt and crystallization temperatures of the base polymers are so close, either PA or PBT can be regarded as a mutual nucleating agent to enhance the crystallization on the other component. The presence of compatibilizer and in situ formed copolymer in the compatibilized blends tends to interfere with the crystallization of the base polymers in various blends. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 23–33, 2000     

The role of interfacial modifier in toughening of nylon 6 with a core‐shell toughener

The effects of nylon 6 matrix viscosity and a multifunctional epoxy interfacial modifier on the notched impact strength of the blends of nylon 6 with a maleic anhydride modified polyethylene‐octene elastomer/semi‐crystalline polyolefin blend (TPEg) were studied by means of morphological observation, and mechanical and rheological tests. Because the viscosity of the TPEg is much higher than that of nylon 6, an increase in the viscosity of nylon 6 reduces the viscosity mismatch between the dispersed phase and the matrix, and increases notched impact strength of the blends. Moreover, addition of 0.3 to 0.9 phr of the interfacial modifier leads to a finer dispersion of the TPEg and greatly improves the notched impact strength of the nylon 6/TPEg blends. This is because the multi‐epoxy interfacial modifier can react with nylon 6 and the maleated TPEg. The reaction with nylon 6 increases the viscosity of the matrix while the coupling reaction at the interface between nylon 6 and the maleated TPEg leads to better compatibilization. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 2664–2672, 1999     

Effect of PBT molecular weight and reactive compatibilization on the dispersed‐phase coalescence of PBT/SAN blends

Poly(butylene terephthalate) (PBT)/styrene‐acrylonitrile copolymer (SAN) blends were investigated with respect to their phase morphology. The SAN component was kept as dispersed phase and PBT as matrix phase and the PBT/SAN viscosity ratio was changed by using different PBT molecular weights. PBT/SAN blends were also compatibilized by adding methyl methacrylate‐co‐glycidyl methacrylate‐co‐ethyl acrylate terpolymer, MGE, which is an in situ reactive compatibilizer for melt blending. In noncompatibilized blends, the dispersed phase particle size increased with SAN concentration due to coalescence effects. Static coalescence experiments showed evidence of greater coalescence in blends with higher viscosity ratios. For noncompatibilized PBT/SAN/MGE blends with high molecular weight PBT as matrix phase, the average particle size of SAN phase does not depend on the SAN concentration in the blends. However noncompatibilized blends with low molecular weight PBT showed a significant increase in SAN particle size with the SAN concentration. The effect of MGE epoxy content and MGE molecular weight on the morphology of the PBT/SAN blend was also investigated. As the MGE epoxy content increased, the average particle size of SAN initially decreased with both high and low molecular weight PBT phase, thereafter leveling off with a critical content of epoxy groups in the blend. This critical content was higher in the blends containing low molecular weight PBT than in those with high molecular weight PBT. At a fixed MGE epoxy content, a decrease in MGE molecular weight yielded PBT/SAN blends with dispersed nanoparticles with an average size of about 40 nm. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2010     

Polyurethane/polyaniline and polyurethane‐poly(methyl methacrylate)/polyaniline conductive core‐shell particles: Preparation,morphology, and conductivity

Polyurethane/polyaniline (PU/PANI) and polyurethane‐poly(methyl methacrylate)/polyaniline (PU‐PMMA/PANI) conductive core‐shell particles were synthesized by a two‐stage polymerization process. The first stage was to produce a core of PU or PU‐PMMA via miniemulsion polymerization using sodium dodecyl sulfate (SDS) as the surfactant. The second stage was to synthesize the shell of polyaniline over the surface of core particles. Hydrogen chloride (HCl) and dodecyl benzenesulfonic acid (DBSA) were used as the dopant agents. Ammonium persulfate (APS) was used as the oxidant for the polymerization of ANI. Different concentrations of HCl, DBSA, and SDS would cause different conformations of PANI chains and thus different morphologies of PANI particles. UV–visible spectra revealed that the polaron band was blue‐shifted because of the more coiled conformation of PANI chains by increasing the concentration of DBSA. Besides, with a high concentration of DBSA, both spherical‐ and rod‐shape PANI particles were observed by transmission electron microscope, and the coverage of PANI particles onto the core surfaces was improved. The key point of formation of rod‐type PANI particles was that DBSA was served with a high concentration accompanied with the existence of HCl or SDS. The better coverage of PANI particles over the core surfaces by charging higher DBSA concentrations resulted in a higher conductivity of hybrid particles. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 3902–3911, 2007     

Preparation and thermal properties of a novel core‐shell structure flame‐retardant copolymer

In order to improve the flame retardancy of polystyrene (PS), a phosphorus and nitrogen comonomer, named AC₂NP₂, was synthesized and then incorporated into various amounts of PS by seeded emulsion polymerization. The modified methacrylate (AC₂NP₂) was used as the core phase, the styrene as the shell phase, then flame‐retardant effect copolymers with core‐shell structure were prepared successfully. The particle size was ranged from 40 to 60 nm, and the structure and properties of the copolymers were characterized in detail. Notably, despite a few amounts of the AC₂NP₂ units in the copolymers, all the copolymers exhibited significantly enhanced thermal stability and reduced flammability as compared with pure PS. Furthermore, from differential scanning calorimetry test, it was observed that the glass transition temperature was tinily influenced with the incorporation of commoner. The incorporation of P‐N comonomer into PS backbone did not lead to negative effect on the glass transition behavior of PS.     

Preparation and properties of novel fluorosilicone thermoplastic vulcanizate with cross‐linking–controlled core‐shell structure

A new fluorosilicone thermoplastic vulcanizate (TPV) composed of poly(vinylidene fluoride) (PVDF), silicone rubber (SR), and fluororubber (FKM) was successfully prepared through dynamic vulcanization. The morphological structure of the TPVs had core‐shell elastomer particles dispersed in a continuous PVDF matrix. Furthermore, the cross‐linking of core‐shell structure was controlled by adopting different curing agent. The effect of cross‐linking–controlled core‐shell structure on the morphology, crystallization behavior, stress relaxation test, solvent‐resistant properties of the obtained TPVs were investigated. It was found that the shell cross‐link had a significant influence on the crystallinity of the PVDF phase. The core‐shell bicross‐linked TPV was found to provide the lowest rate of relaxation. An obvious stress softening phenomenon was observed in the uniaxial loading‐unloading cycles in tension. The bicross‐linked TPV had good solvent resistant properties. The tensile strength of the bicross‐linked TPV was still 12 MPa even after immersed in butyl acetate for 48 hours.     

Thermal behavior of core‐shell rubber/styrene monomer gels

The thermal behavior of core‐shell rubber (CSR)/styrene monomer mixtures was studied using subambient differential scanning calorimetry (DSC). Interaction between the styrene and CSR material was observed as a depression of the freezing and melting points of the styrene monomer and as a shift in the glass transition temperature of the rubbery phase in the CSR materials. The depression of the freezing point of the styrene in the CSR/styrene mixtures was related to the size of the critical nuclei required for crystallization. The heat of crystallization was found to decrease linearly with decreasing styrene content, but calculations showed that not all of the styrene present in the mixtures crystallized upon cooling, confirming that there was an interaction between the CSR material and the styrene monomer. At temperatures below the glass transition temperature of the system, the mixtures contain a pure styrene crystalline phase and an amorphous CSR/styrene phase. The styrene was found to act as a plasticizer, reducing the glass transition temperature of the rubbery core material. The variation of the glass transition temperature of the CSR/styrene systems was determined with respect to the composition of the amorphous phase. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 3136–3150, 2000     

Preparation of magnetic Fe3O4/P (GMA‐DVB)‐PEI/Pd highly efficient catalyst with core‐shell structure

In this paper, a simple route for palladium (Pd) nanoparticles attached to the surface of hollow magnetic Fe₃O₄/P (GMA‐DVB)‐polyethyleneimine (PEI) microspheres was established. Due to the large amount of imidogen groups and tertiary amine groups presenting in the PEI, Pd²⁺ ions could be anchored to the support by complexation with a polyfunctional organic ligand. Thereafter, a magnetic Pd catalyst having a high loading amount and good dispersibility was obtained by reducing Pd²⁺ ions. Afterwards, the prepared catalyst was characterized by TEM, SEM, FTIR, XRD, TGA, VSM, and UV–vis in detail. Ultimately, their catalytic activity was evaluated using the reduction of 4‐nitrophenol (4‐NP). Research showed that the Fe₃O₄/P (GMA‐DVB)‐PEI/Pd catalyst possessed high catalytic performances for the reduction of 4‐NP with a conversion rate of 98.43% within 540 s. Furthermore, the catalyst could be easily recovered and reused at least for nine successive cycles.     

Design of aluminum trihydroxide and P‐N core‐shell structures and their synergistic effects on halogen‐free flame‐retardant polyethylene composites

In order to improve the performance of inorganic/organic composites, aluminum trihydroxide (ATH) core composites with a styrene‐ethylene‐butadiene‐styrene block copolymer grafted with maleic anhydride (MAH‐g‐SEBS) shell phase, and P‐N flame retardant as a synergistic agent, were prepared through an interface design. The effects of polyethylene glycol (PEG) content on the interfacial interaction, flame retardancy, thermal properties, and mechanical properties of high‐density polyethylene (HDPE)/ATH composites were investigated by small angle X‐ray diffraction, rotational rheometer, limiting oxygen index, thermogravimetric analysis (TGA), and tensile testing. The ATH synergistic effects of P‐N flame‐retardant improved the combustion performance of HDPE/ATH/PEG(3%)/MAH‐g‐SEBS/P‐N (abbreviated as HDPE/MH3/M‐g‐S/P‐N) composite by forming more carbon layer, increased the elongation at break from 21% to 558% compared to HDPE/ATH, and increased the interface thickness from 0.447 to 0.891 nm. SEM results support the compatibility of ATH with HDPE increased and the interfacial effect was enhanced. TGA showed the maximum decomposition temperature of the two stages and the yield of the residue at high temperature increased first and then decreased with the increase of PEG content. Rheological behavior showed the storage modulus, complex viscosity, and the relaxation time initially increased and then decreased with the increase of PEG content indicating PEG, M‐g‐S, and ATH powder gradually formed a partial coating, then a full coating, and finally an over‐coated core‐shell structured model.     

Double yielding in PA6/TPV‐MAH blends: Effect of crosslinking degree of the dispersed phase

Thermoplastic vulcanizates (TPVs) based on PP and EPDM (the ratio is 5:5) with different crosslinking degrees were prepared using different contents of phenolic resins, and then blended with polyamide 6 (PA6). The results indicated that with an increase in crosslinking degree, the double yielding phenomenon in PA6/TPV blends became more distinct, the yield stress of the first yield point and the yield stress difference of the two yield points decreased; however, the yield strain of the first yield point did not change with the increasing crosslinking degree of the TPV, but the yield strain of the second yield point increased, resulting in a more broadened yield region. The SEM results showed that with an increase in the crosslinking degree of TPV, the diameter of TPV increased in the core layer, and the orientation degree of TPV in the skin and subskin layer deceased, accompanying with a decrease of the ratio of length to diameter (L/D) of the droplets. The morphology evolution of the PA6/TPV blend during the tensile test was also studied, and the results agreed well with the model we proposed. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 912–922, 2009     

The preparation of amphiphilic core‐shell nanospheres by using water‐soluble macrophotoinitiator

The amphiphilic poly(AM‐co‐SA)‐ITXH macrophotoinitiator was synthesized by precipitation photopolymerization under UV irradiation with isopropylthioxanthone (ITX) as free radical photoinitiator. A novel method has been developed to prepare amphiphilic core‐shell polymer nanospheres via photopolymerization of methyl methacrylate (MMA) in aqueous media, with amphiphilic copolymer macrophotoinitiator poly(AM‐co‐SA)‐ITXH. During polymerization, the amphiphilic macroradicals underwent in situ self‐assembly to form polymeric micelles, which promoted the emulsion polymerization of the monomer. Thus, amphiphilic core‐shell nanospheres ranging from 70 to 140 nm in diameter were produced in the absence of surfactant. The conversion of the monomer, number average molecular weights (M_n), and particle size were found to be highly dependent on the macrophotoinitiator and monomer concentration. The macrophotoinitiator and amphiphilic particles were characterized by FTIR, UV‐vis, ¹H NMR, TEM, DSC, and contact angle measurements. The results showed the particles had well‐defined amphiphilic core‐shell structure. This new method is scientifically and technologically significant because it provides a commercially viable route to a wide variety of novel amphiphilic core‐shell nanospheres. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 936–942, 2010     

Preparation and ferromagnetic properties of Ni0.5Zn0.5Fe2O4/polyaniline core–shell nanocomposites

Magnetic Ni_0.5Zn_0.5Fe₂O₄‐crosslinked polyaniline composites with a core–shell structure were prepared in the presence of Ni_0.5Zn_0.5Fe₂O₄ magnetic powder in a toluene solution containing iron chloride as a surfactant and dopant. Structural characterization by Fourier transform infrared, X‐ray diffraction, scanning electron microscopy, and transmission electron microscopy proved that Ni_0.5Zn_0.5Fe₂O₄ in the composites was responsible for the ferromagnetic behavior of the composites. The effects of the polyaniline and temperature on the magnetic properties of the Ni_0.5Zn_0.5Fe₂O₄/polyaniline composites were studied with electron paramagnetic resonance and superconducting quantum interference device techniques. A clear evolution from ferromagnetic resonance to electron paramagnetic resonance was observed as a function of temperature, which was related to the passage through the Curie point (～420 K). The magnetic properties of the resulting composites showed ferromagnetic behavior, such as high‐saturated magnetization (saturation magnetization = 35–39 emu/g), low coercive force (coercivity = 22–28 G), and low blocking temperatures (～23 K). © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 2657–2664, 2006     

Synthesis of core‐shell structured carboxylated microparticles with a straightforward procedure and their evaluation as a polymer support

Poly(trimethylolpropane trimethacrylate) microspheres with a narrow size distribution were obtained by precipitation polymerization. They were subsequently modified by surface grafting with acrylic acid in a polar ethanol–water reaction medium, without stabilizer, yielding core‐shell particles with diameters in the micrometer range. The resulting polymeric material was characterized by SEM and potentiometric titration, FTIR spectroscopy, and thermal analysis. It was shown that the particle characteristics (size, size distribution, and functionality) obtained by this straightforward procedure can be controlled by modifying the synthesis parameters (monomer concentration, agitation rate, and temperature). The high functionality, the chemical and physico‐mechanical stability, as well as the possibility to control the performances of the resulting polymeric materials by synthesis allow its applications in various areas. Envisaging separation and catalysis domains, Cu(II), Cd(II), and Cr(III) uptake capacity from aqueous solutions was investigated under noncompetitive conditions as a function of synthesized particle functionality, time, and pH range. It was also found that the addition of the carboxylated microparticles to polyethylene stabilized with α‐tocopherol improved the thermo‐oxidative behaviour of the polymeric material. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 5889–5898, 2005