Morphology,resistivity, and thermal behavior of EVOH/carbon black and EVOH/graphite composites prepared by simple saponification method

Poly(ethylene‐co‐vinyl alcohol) (EVOH)/carbon black (CB) and EVOH/graphite (GP) electro‐conductive composites were prepared by saponification of poly(ethylene‐co‐vinyl acetate) (EVA)/CB and EVA/GP composites in ethanol/KOH solution. The electrical resistivity change and positive temperature coefficient (PTC) behavior of these composites were investigated. The volume resistivity of EVA/CB and EVA/GP composites was decreased with saponification time. It can be observed that EVA/CB10 and EVA/GP05 composites showed a significant reduction in resistivity after saponification for 1 h. With the increase in saponification time, PTC peak temperature of both composites was shifted at a higher temperature. Tensile properties, morphology, and thermal behavior of the prepared composites have been also evaluated using universal test machine, scanning electron microscopy, and differential scanning calorimetry, respectively. POLYM. COMPOS., 2011. © 2011 Society of Plastics Engineers     

PVDF/CB composites prepared by novel solvent casting method for low voltage PTC temperature regulation applications

A novel solvent casting preparation technique utilizing three variants of poly(vinylidene fluoride) (PVDF) to achieve a thermal cut off and a self regulation effect at a low applied voltage is reported in this study. The positive temperature coefficient (PTC) composites were prepared by dissolving PVDF in 1‐methyl‐2‐pyrrolidone (NMP) solvent, blending with Vulcan® XC72 carbon black (CB) filler, crosslinking with vinyl trimethoxysilane (VTMOS) and quenching in water. All composites displayed a highly macrovoidal structure that promoted a PTC effect when subjected to a thermal expansion effect via an electrical current. Subsequently the current was cut off and self regulation behavior was exhibited. Kynar® 761A PVDF resulted in the strongest PTC effect, and displayed temperature regulation at around 100°C which may be attributed to the highly semi crystalline nature and the larger molecular weight of this polymer in comparison with the other PVDF composites studied. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Resistivity and PTC behaviour of electro-conductive PVOH/MWNT and EVOH/MWNT nanocomposites

Electro-conductive poly(vinyl alcohol)/multi-walled carbon nanotube (PVOH/MWNT) and poly(ethylene-co-vinyl alcohol) (EVOH)/MWNT nanocomposites were prepared by precipitation saponification method. The MWNT was functionalised by electron beam irradiation in air at 1200?kGy doses. The electrical resistivity, thermal and mechanical properties, and positive temperature coefficient (PTC) behaviour of these nanocomposites were investigated. The melting and crystallisation peak temperatures of both nanocomposite systems were shifted at a higher temperature with the increase in saponification time. Their crystallinity and mechanical strength also increased with saponification time, indicating an increase in intermolecular hydrogen bond between vinyl alcohol groups. With the saponification time, PTC peak temperature of EVA28/MWNT and EVA40/MWNT nanocomposites was shifted at a higher temperature and followed by a negative temperature coefficient (NTC) of resistivity. However, the saponified PVAc/MWNT nanocomposites showed only NTC behaviour over a temperature range of 30–140°C.     

Morphology of CuFe2O4/CNT composites prepared by precipitation

Abstract

In this study, the effect of carbon nanotube (CNT) supports on the morphology and structural of copper ferrite nanoparticles has been investigated. The synthesis of CuFe₂O₄ nanoparticles has been done through direct precipitation in aqueous solution with CNT content. The morphology of the synthesised samples has been studied by the use of scanning electron microscopy; structural properties have been investigated through X-ray diffraction spectrometer. Fourier transform infrared spectroscopy apparatus was used to identify the functional groups on the surface of CNTs. The findings showed that the presence of CNT support in nanocomposite powder, the size of CuFe₂O₄ significantly decreased and the powder morphology changed from agglomerate state to nanorodes.     

PVDF‐PZT‐5H composites prepared by hot press and tape casting techniques

Piezoelectric polymer–ceramic composites are promising materials for transducer applications, and they are widely used in underwater hydrophones, biomedical imaging with ultrasound, and nondestructive testing applications. The critical factor in the 0–3 composite is to ensure homogeneous distribution of the filler in the matrix. To ensure this objective, PVDF‐PZT composite was prepared by two different routes: hot press and tape casting techniques. Loss on ignition and scanning electron microscopy studies were conducted to find out the uniformity of the composites prepared. It is found that hot press technique gives better uniformity compared to tape casting technique. PZT concentration was varied from 20 to 60 vol %. Physical and dielectric properties were studied. FT‐IR, DSC, and XRD characterization studies of PVDF were also recorded. Density of the composites was 2.74 to 5.13 g/cm³ as PZT concentration increased from 20 to 60 volume fractions. The dielectric constant of composites at 1 MHz varied from 16.74 to 98.48 as PZT concentration increased from 20 to 60 volume fractions. Hot press technique that combines solution and melt processing was found to be the better method for the preparation of 0–3 composites. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Studies on nylon‐6/EVOH/clay ternary composites

Nylon‐6 (Ny‐6)/EVOH blends are interesting host multiphase systems for incorporation of low clay contents. The Ny‐6/EVOH blend is a unique system, which tends to chemically react during melt‐mixing, affecting thermal, morphological and mechanical properties of the ternary systems containing clay. The addition of clay seems to interrupt the chemical reaction between the host polymers at certain compositions, leading to lower blending torque levels when clay is added. A competition between Ny‐6 and EVOH regarding the intercalation process takes place. Ny‐6 seems to lead to exfoliated structure, whereas EVOH forms intercalated structure, as revealed from XRD and TEM analyses, owing to thermodynamic considerations and preferential localization of the clay in Ny‐6. Hence, the ternary systems have combined intercalated and delaminated morphology or complete exfoliated morphology depending on blend composition and clay content. Selective extraction experiments (gel content) indicate the formation of chemical reaction between the Ny‐6 and EVOH, and give an indirect indication of the polymer content residing in the galleries. The thermal properties of the polymers were found to be affected by the occurrence of chemical reaction, the level of intercalation and exfoliation and plasticizing effect of the low molecular weight onium ions treating the clay. Of special interest is the increased storage modulus attained upon the addition of only 1.5 wt% clay. POLYM. COMPOS. 27:15–23, 2006. © 2005 Society of Plastics Engineers     

Viscoelastic behavior and constitutive modeling of PP/HNT composites prepared by water‐assisted extrusion

Poly(propylene) (PP) nanocomposites containing 5, 10, and 15 wt% unmodified halloysite nanotubes (HNTs) were prepared using extrusion with and without water injection. Scanning electron microscopy micrographs show that HNT aggregates prepared by water injection are smaller than those prepared by conventional melt extrusion (without water injection). The nanocomposites prepared by water injection exhibit higher storage modulus (G′) and complex viscosity (η*) values than those by conventional melt extrusion. Stress relaxation results indicate that the interaction between HNTs and PP matrix at low concentration (5 wt%) is stronger than its non‐water injection counterpart. Subsequently, for 5 wt% HNT sample, the transient viscosity is simulated numerically using the Kaye–Bernstein–Kearsley–Zapas (K‐BKZ) integral constitutive equation along with experimentally determined damping functions. It is found that the samples prepared by water injection exhibit a more obvious overshoot behavior than conventional samples and the Papanastasiou‐Scriven‐Macosko (PSM) model can predict the transient viscosity of the samples more accurately than Wagner model. Further, the relationship between the dispersion of HNTs and the damping factors in the constitutive models is discussed. The results of this investigation would improve the theoretical understanding of possible polymer–filler interaction during shear flow. POLYM. ENG. SCI., 59:1585–1592 2019. © 2019 Society of Plastics Engineers     

Influences of crystallization histories on PTC/NTC effects of PVDF/CB composites

Two switching phenomena of poly (vinylidene fluoride) (PVDF) containing carbon black (CB) with different crystallization histories are studied. Both the percolation threshold (Φpc) and the critical concentration of the positive temperature coefficient (PTC) materials (Φc) increase as the crystallization temperature declines. PTC and the negative temperature coefficient (NTC) effect become obvious when the cooling speed is reduced. The morphologies of PVDF crystals play an important role in modifying the shape of the resistivity-temperature (ρ-T) curves. The PTC and NTC intensities of these systems, whose CB contents lie between Φpc and Φc, increase with increasing crystallinity, which are realized by altering the crystallization histories of the matrices. © 1996 John Wiley & Sons, Inc.     

Morphology,thermal, and rheological behavior of nylon 11/multi‐walled carbon nanotube nanocomposites prepared by melt compounding

Nylon 11 (PA11) nanocomposites with different loadings of multi‐walled carbon nanotubes (MWNTs) were prepared by melt compounding. Scanning electron microscopy images on the fracture surfaces of the composites showed a uniform dispersion of MWNTs throughout the matrix. The presence of the MWNTs significantly improved the thermal stability and enhanced the storage modulus (G′) of the polymer matrix. Melt rheology studies showed that, compared with neat PA11, the incorporation of MWNT into the matrix resulted in higher complex viscosities (|η*|), storage modulus (G′), loss modulus (G″), and lower loss factor (tanδ). PA11 and its nanocomposites containing less than 1 wt% MWNTs showed similar frequency dependencies and reached a Newtonian plateau at low frequencies. For the nanocomposite with 2 wt% MWNTs, the regional network was destroyed and the orientation of the MWNTs during shearing exhibited a very strong shear thinning effect. The complex viscosities (|η*|) of the nanocomposites are larger than that of neat PA11 and decreased with increasing the temperature. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers     

Morphology and properties of Nafion membranes prepared by solution casting

In this study, dilute Nafion solutions consisting of solvents with various dielectric constants ? and solubility parameters δ, i.e. N,N′-dimethyl acetamide, N,N′-dimethyl formamide, N-methyl formamide, methanol-water mixture (4/1 g/g), ethanol-water mixture (4/1 g/g), and isopropanol-water mixture (4/1 g/g), were freeze dried and the conformations of Nafion molecules in dilute solutions were observed using transmission electron microscope. The membranes were prepared by solution casting from these solutions and evaporating the solvents at temperatures below T_G of Nafion, then annealing the membranes at 150 °C which was ∼50 °C above T_G of Nafion. We show Nafion molecular conformations in dilute solutions are strongly influenced by δ and ? of solvents. And, thus the morphology, water uptake, proton conductivity, and methanol permeability of membranes prepared by solution casting are also influenced by δ and ? of solvents.     

A high‐barrier PP/EVOH membrane prepared through the multistage biaxial‐stretching extrusion

The polypropylene (PP)/ethylene vinyl alcohol copolymer (EVOH) membranes were prepared by a novel extrusion die with an assembly of laminating‐multiplying elements (LMEs). A biaxial‐stretching occurred when polymer melts flowing through a LME. The morphology development of PP/EVOH blends and its effect on gas‐barrier property, solvent‐absorption property and mechanical properties were characterized by scanning electron microscope (SEM), polarized optical microscope (POM), gas‐permeability test, immersion experiment, differential scanning calorimetry (DSC), and tensile test. With the introduction of LME and the increasing of its number, morphology of EVOH phase in PP matrix gradually changed from zero‐dimension spherical particles to one‐dimension fibers, and then to two‐dimension sheets. As a result, the nitrogen permeability coefficient decreased nearly by two orders of magnitude and the permeability coefficient of toluene‐PP/EVOH system declined by almost four times. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45016.     

Resistivity relaxation behavior of carbon black filled high‐density polyethylene conductive composites

The variation of resistivity for high‐density polyethylene (HDPE) conductive composites filled with carbon black (CB) with time was investigated under the excitation of different temperature field. The movement of CB particles in the HDPE matrix was not a momentary equilibrium process, but a relaxation process. The relaxation of resistivity of the composites was monotonic, and it could be described by an exponential form above melting temperature. However, the relaxation of resistivity was nonmonotonic below melting temperature, herein a parameter t₀ which was the beginning time of the resistivity attenuation could be introduced into the exponential equation. The attenuation of resistivity at constant temperature was limited for the composites with certain content of CB. The resistivity of the composites would incline to a constant value with the prolongation of time no matter what the heat treatment temperature was. Heating rate had influence on the relaxation of resistivity of the composites, and the lower heating velocity resulted in less time to approach to the equilibrium resistivity. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Mechanical and crystalline properties of monomer casting Nylon‐6/Sio2 composites prepared via in situ polymerization

A series of monomer casting (MC) nylon‐6/SiO₂ composites were prepared via in situ polymerization. It was found that the tensile strength, storage modulus, and notched charpy impact strength of the composites were improved and reached maximum at 3–5 wt% loading of SiO₂. The α relaxation peak corresponding to the glass transition temperature (T_g) shifted to high temperature with increasing SiO₂ content. Addition of SiO₂ led to an increase of the melting and crystallization temperatures, and crystallinity. It also reduced the induction time of crystallization, advance the crystallization process of MC nylon‐6, and improve the crystal growth rate. The self‐nucleation crystallization analysis indicated that SiO₂ particles played the role of facilitating the crystallization of the matrix mainly via accelerating the generation of crystal nucleus. By addition of SiO₂ particles, the fracture surface of MC nylon‐6 changed to distant striations with many yield folds accompanied by a large number of stress whitening, displaying much obvious character of tough fracture. SiO₂ particles can be pulled‐out under stress by being covered with MC nylon‐6 resin due to strong interfacial interaction and presented a skin–core structure. © 2012 Society of Plastics Engineers.     

Morphology and thermal stability of BR/clay composites prepared by a new method

A new potential preparation method named in situ organic modification was used to prepare intercalated polybutadiene rubber (BR)/clay/dimethyl dihydrogenated tallow ammonium chloride (DDAC) composites. That is, BR, pristine clay, and intercalatant DDAC were directly mixed in a Haake rheometer without pretreating the pristine clay with the intercalatant. The morphology of the BR/clay composites was investigated by means of X‐ray diffraction and scanning electron microscopy. The thermal stability of the BR/clay composites was analyzed by thermogravimetric analysis (TGA). The dispersion of clay particles in the BR/clay/DDAC composites is much better than that in the BR/pristine clay and similar to that in the BR/organoclay DK4 (modified with DDAC) composites. BR/clay/DDAC composites have much higher thermal stability than the gum BR, BR/pristine clay, and BR/DK4 composites. The clay/intercalatant ratio has little influence on the thermal stability of the BR/clay/DDAC composites, while clay content has a significant effect on their thermal stability. The enhanced thermal stability of the BR/clay/DDAC composites is related to the dispersion state of clay particles in BR. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 905–913, 2006     

Morphology of carbon/TiC composite films prepared by carbonization of polyimide/titania composites

Polyimide/titania (PI/TiO₂) composite was synthesized by in situ sol–gel polymerization, and carbon/titanium carbide (TiC) composite films were prepared by carbothermal reduction of the PI/TiO₂ composite at 1,600 °C under flowing argon. The structure and properties of the composites were studied by wide angle X-ray diffraction (WAXD), Fourier transform infrared spectrometer (FTIR), scanning electron microscopy, and energy dispersive X-ray spectroscopy. The carbon/TiC composite films exhibited metallic luster on the surface and compact structure in cross section with well dispersed TiC particles. WAXD intensity distribution revealed that TiC particles formed by tightly bonding between elemental carbon and titanium formed crystallites which as a filler provided tough films. The results indicated that heat treatment of PI/TiO₂ under argon is a promising method for preparing tough carbon composite films.     

Morphology and thermal behavior of MCPA6/SAN blends prepared by anionic ring‐opening polymerization of ϵ‐caprolactam

In this article, a series of blends of monomer casting polyamide 6 and styrene‐co‐acrylonitrile (MCPA6/SAN) were prepared by in situ anionic ring‐opening polymerization of ?‐caprolactam. Their morphology and thermal behaviors were investigated by means of scanning electron microscope, differential scanning calorimeter, and wide‐angle X‐ray diffraction (WAXD), respectively. The SAN phase had much finer domain in MCPA6/SAN than that in the PA6/SAN blends prepared by melt blending of PA6 and SAN. All the melting and crystallization parameters of MCPA6/SAN blends decreased gradually with the increase of SAN content, while the melting temperature was almost unchanged. These results were due to the hydrolysis reaction of SAN that occurred during the anionic polymerization of ?‐caprolactam. In addition, WAXD results showed that only α crystal forms existed in the MCPA6/SAN blends. In addition, the mechanical property of MCPA6 was improved obviously by incorporating a certain amount of SAN. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 1357–1363, 2006     

Morphology and properties of PBT/nylon 6/EVA‐g‐MAH ternary blends prepared by reactive extrusion

Morphology and properties of poly(butylene terephthalate) (PBT)/nylon 6 (PA6)/EVA‐g‐MAH ternary blends were investigated. The blends were prepared in a corotating, intermeshing, twin‐screw extruder. The incorporation of maleic anhyride (MAH) grafted onto ethylene‐vinyl acetate copolymer (EVA) (EVA‐g‐MAH) in the PBT/PA6 binary blends decreased the tensile and flexural strength but increased the impact strength, while the mechanical properties of the PBT/PA6 blends were decreased with increasing PA6 content regardless of the presence or absence of the EVA‐g‐MAH. The morphology studies of the ternary blends showed gross phase separation. The rheological properties of the ternary blends suggested that excessively high reactivity between amine end groups of PA6 and MAH grafted onto EVA makes the compatibility between PBT and PA6 worse, although EVA‐g‐MAH was expected to work as a compatibilizer for PBT/PA6 blends. The degree of reactivity between functional groups in PBT, PA6, and EVA‐g‐MAH was also examined by investigating the effect of blending sequence on the properties of the ternary blends.     

Morphology,crystallization, and thermal behavior of isotactic polypropylene/propylene‐g‐styrene blends

Optical microscopy, differential scanning calorimetry, and small angle X‐ray scattering techniques were used to study the influence of the crystallization conditions on morphology and thermal behavior of samples of binary blends constituted of isotactic polypropylene (iPP) and a novel graft copolymer of unsaturated propylene with styrene (uPP‐g‐PS) isothermally crystallized from melt, at relatively low undercooling, in a range of crystallization temperatures of the iPP phase. It was shown that, irrespective of composition, no fall in the crystallinity index of the iPP phase was observed. Notwithstanding, spherulitic texture and thermal behavior of the iPP phase in the iPP/uPP‐g‐PS materials were strongly modified by the presence of copolymer. Surprisingly, iPP spherulites crystallized from the blends showed size and regularity higher than that exhibited by plain iPP spherulites. Moreover, the amount of amorphous material located in the interspherulitic amorphous regions decreased with increasing crystallization temperature, and for a given crystallization temperature, with increasing uPP‐g‐PS content. Also, relevant thermodynamic parameters, related to the crystallization process of the iPP phase from iPP/uPP‐g‐PS melts, were found, composition dependent. The equilibrium melting temperature and the surface free energy of folding of the iPP lamellar crystals grown in the presence of uPP‐g‐PS content up to 5% (wt/wt) were, in fact, respectively slightly lower and higher than that found for the lamellar crystals of plain iPP. By further increase of the copolymer content, both the equilibrium melting temperature and surface free energy of folding values were, on the contrary, depressed dramatically. The obtained results were accounted for by assuming that the iPP crystallization process from iPP/uPP‐g‐PS melts could occur through molecular fractionation inducing a combination of morphological and thermodynamic effects. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 79: 2286–2298, 2001     

Ecofriendly behavior of host matrix in composites prepared from agro‐waste and polypropylene

Composites were prepared by two methods: (1) graft copolymerization (GFC) of isotactic polypropylene (PP) with coupling agent maleic anhydride (MAH), followed by esterification with coir fiber; (2) by direct reactive mixing (DFC) of PP, MAH, and peroxide with coir fiber in a minimax molder. These composites, after molding in films (5 × 5 cm, ～100 μm thickness) were examined for susceptibility to biological attack by measuring the percentage weight loss in compost up to 6 months, periodically, and fungal colonization on surface of the samples, when kept as sole carbon source for the growth of Aspergillus niger in culture medium up to 40 days. Photodegradation was evaluated by monitoring the variations in a Fourier transform infrared spectrum and crack formation after successive treatment with ultraviolet (UV) light (≥290 nm) for 0, 20, 50, and 100 h at 60°C in the presence of air. Specimens of virgin PP were taken as a reference during all periods of photo‐ and biodegradations. Significant consequences of the manner of composite preparation on photo/biodegradation were observed during the whole study. DFC samples degraded faster than GFC during the composting whereas, in culture, GFC was covered by fungi in a highly well‐uniform way. It is shown that photo‐oxidative aging directly enhanced the biodegradability of composites, as an increase in fungal growth rate and decrease in weight during composting was found. It was concluded that extent of compatibilization has a profound effect on photo/biodegradation of composite material; consequently, ester bonds were the main units during fungal consumption. Surface erosion was maximum in the case of 100 h UV‐treated GFC and minimum for unirradiated PP after culture exposure, as shown by scanning electron microscopy, which is due to the use of composite films as energy source by microbes. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 1009–1017, 2003     

炭黑/碳纳米管/环氧树脂复合材料的导电渗流行为研究

采用超声分散溶液混合法制备炭黑/碳纳米管/环氧树脂(CB/CNTs/EP)复合材料,研究了不同几何结构的炭系填料的导电作用,并且通过体积电阻率测试和扫描电镜等手段分别对其电性能和微观形貌进行了表征与分析。结果表明,在CB/CNTs/EP复合材料中,CB和CNTs按质量比4:1填充复合体系的渗流阈值为3.8%,介于两种填料单独使用时的两个渗流阈值之间。不同结构纳米材料(CB和CNTs)的混用会在环氧树脂体系中形成更稳定的导电网络,提高了复合材料的导电性。