Jiyun Feng

Double positive temperature coefficient effects of carbon black-filled polymer blends containing two semicrystalline polymers

Abstract Carbon black (CB)-filled polypropylene (PP)/ultra-high molecular weight polyethylene (UHMWPE) composites were prepared by the conventional melt-mixing method. The effects of the PP/UHMWPE weight ratio, CB content and CB particle size on the positive temperature coefficient (PTC) and negative temperature coefficient (NTC) effects, as well as the room temperature resistivity of the composites were elucidated in detail. When the PP/UHMWPE weight ratio is larger than 3/7, the PTC and NTC behaviors of 10xa0wt% CB-filled PP/UHMWPE composites are similar to those of a CB-filled neat PP composite. However, when the weight ratio equals or is smaller than 3/7, the composites exhibit a PTC effect that is similar to that of a CB-filled neat UHMWPE composite. The elimination of the NTC effect in CB-filled polymer blend composites can be achieved by using a very high viscosity polymer as one of its components. The results of an optical microscopic study indicate that the CB particles are selectively localized at the interface between the PP matrix and the UHMWPE particles and in the PP matrix of the composites. This selective localization of the CB particles is attributed to the fact that the viscosity of the UHMWPE particles is so high that the CB particles cannot go inside the UHMWPE particles. In addition, a novel physical phenomenon—double-PTC effect—is observed and quantitatively characterized. The balance between the PTC intensity and the resistivity at room temperature can be achieved by using a mixture of large and small CB particles.

Positive and negative temperature coefficient effects of an alternating copolymer of tetrafluoroethylene-ethylene containing carbon black-filled HDPE particles

Abstract A conductive polymer composite was prepared by melt-mixing of an immiscible semicrystalline polymer blend of an alternating copolymer of tetrafluoroethylene–ethylene (ETFE), high density polyethylene (HDPE), and carbon black (CB). The optical microscopy and time-of-flight secondary mass spectrometry results indicated that the CB particles were selectively localized in the HDPE phase. In addition, it was found that the CB-filled HDPE particles formed a dispersed phase in the ETFE matrix. A double-positive temperature coefficient (PTC) effect was observed in the composite, caused by the large thermal expansion due to the consecutive melting of HDPE and ETFE crystallites. The negative temperature coefficient (NTC) that was observed in this system could not have been caused by the formation of flocculated structures because the size of the CB-filled HDPE particles is significantly large, so that their mobility is extremely limited even at high temperatures. This conclusion was confirmed by observing the morphology of the composite at temperature ranging from 25 to 250°C. These results suggest that new mechanisms need to be uncovered to explain the NTC effect of conductive polymer composites.

Imaging of sub-surface nano particles by tapping-mode atomic force microscopy

Time-of-flight secondary ion mass spectrometry (ToF-SIMS), X-ray photoelectron spectroscopy (XPS), and tapping mode atomic force microscopy (TM-AFM) were used to study the surface of a poly(N-vinyl-2-pyrrolidone) thin film containing nano silica particles. ToF-SIMS results illustrate that the topmost layer of the thin film consists of PVP and a small amount of poly(dimethyl siloxane) (PDMS). Nano silica particles are localized underneath this layer. XPS results suggest that the concentration of the silica particles increases as the sampling depth increases from 5.3 to 7.2 nm. TM-AFM phase imaging is shown to be capable of detecting the presence of these sub-surface nano silica particles.

Influence of chain sequence structure of polymers on ToF-SIMS spectra

Abstract The influence of the chain sequence structure of an alternating ethylene–tetrafluoroethylene (ETFE) copolymer and poly(vinylidene fluoride) (PVDF) on both positive and negative time-of-flight secondary ion mass spectrometry (ToF-SIMS) spectra ( m / z ≤200) was studied. The C 1 , C 2 , C 3 , C 4 and C 5 positive ions were found in the ETFE spectrum, while only the C 1 , C 2 and C 3 positive ions were found in the PVDF spectrum. These results indicate that ETFE can be distinguished from PVDF by the presence of its characteristic C 4 and C 5 positive ions. Even though both ETFE and PVDF produce some of the same C 3 positive ions, these positive ions come from different sequence structures. The negative ToF SIMS spectra of both ETFE and PVDF are totally dominated by F − ( m / z =19) because F − is very stable, due to its largest electronegative value, and fluorine concentration in ETFE and PVDF is relatively high. These results indicate that the chain sequence structure has a significant effect on the positive ToF-SIMS spectra of ETFE and PVDF, especially in the high-mass range. However, the chain sequence structure does not have much effect on the negative spectra of ETFE and PVDF.

Mechanisms for viscosity reduction of polymer blends: Blends of fluoroelastomer and high-density polyethylene

The rheological behavior of fluoroelastomer high-density polyethylene (HDPE) blends was investigated in detail. A capillary rheometer was used to determine the apparent viscosity of the blends as a function of time at various shear rates. The time to attain the steady state and the normalized steady-state apparent viscosity of the blends depend on shear rate and the fluoroelastomer concentration. The reduction in the apparent viscosity is caused by adhesive failure at the interface between the HDPE melt and the fluoroelastomer layer which was formed on the die wall surface during the extrusion of the blends. The presence of the fluoroelastomer layer on the die wall surface was confirmed by x-ray photoelectron spectroscopy and rheological measurements. Based on our previous work and this work, we have discovered that there are at least two different mechanisms—adhesive failure at the interface between the extrudate and the lubricating layer or cohesive failure in the lubricant layer—for viscosity reduction...

Compatibilization of polycarbonate and poly(vinylidene fluoride) blends studied by time-of-flight secondary ion mass spectrometry and scanning electron microscopy

The compatibilization of polycarbonate (PC) and poly(vinylidene fluoride) (PVDF) by poly(methyl methacrylate) (PMMA) was elucidated in detail using time-of-flight secondary ion mass spectrometry (ToF-SIMS) and scanning electron microscopy (SEM). Special PC/(PMMA/PVDF) sandwich-like samples were prepared for ToF-SIMS analysis. The ToF-SIMS results revealed that during the lamination of the PC and PMMA/PVDF sheets at high temperature, PMMA diffused from the PMMA/PVDF blend to the PC side. However, PC did not diffuse from the PC side to the PMMA/PVDF side. These results provided direct evidence to support that the improved interfacial adhesion of the PC/PVDF blend was due to PMMA and also indicated that PMMA may act as a compatibilizer for the PC/PVDF blends. A comparison of ToF-SIMS chemical images obtained from PC/PVDF (70/30) and PC/PMMA/PVDF (70/5/25) blends shows that the addition of PMMA greatly decreases the domain size of the PVDF phase and causes a homogeneous distribution of the PVDF phase. These results further confirmed the compatibilizing effect of PMMA on PC/PVDF blends. The effects of PMMA content and molecular weight on the morphology of PC/PMMA/PVDF blends were also studied and discussed. Copyright

Compatibility and properties of alternating ethylene-tetrafluoroethylene copolymer and poly(methyl methacrylate) blends

Abstract Blends of an alternating ethylene-tetrafluorethylene copolymer (ETFE) and poly(methyl methacrylate) (PMMA) were prepared by melt mixing in a mixer. Compatibility, thermal behaviour and morphology of the blends of various compositions were investigated by using dynamic mechanical analysis (d.m.a.), Fourier transform infra-red spectroscopy (FTi.r.), solid-state nuclear magnetic resonance (n.m.r.) spectroscopy, differential scanning calorimetry (d.s.c.) and wide-angle X-ray diffraction. D.m.a. and d.s.c. results show that the glass transition temperature (Tg) of the ETFE in the blends increases as the PMMA content increases and the Tg of the PMMA moves to low temperatures when the ETFE content increases. In addition, d.s.c. results indicate an additional Tg, which is located between the Tg of PMMA and that of ETFE. The presence of this additional Tg suggests the existence of one semicrystalline phase and two amorphous phases—an ETFE/PMMA phase and a PMMA-rich phase. D.s.c. results also indicate that the melting temperature of ETFE decreases while the crystallinity of ETFE increases slightly as the PMMA content increases. FTi.r. results show that the absorption peak of the carbonyl group of the PMMA in the blends stays almost at the same position as in the pure component. Solid-state n.m.r. results reveal that the changes in chemical shift of the carbonyl group of PMMA in the blends are less than 0.5 ppm. These results confirm that only weak interactions exist between ETFE and PMMA. X-ray diffraction results reveal that no new crystal forms appear in the blends.

Carbon Black Filled Immiscible Blend of Poly(Vinylidene Fluoride) and High Density Polyethylene: Electrical Properties and Morphology

Publisher Summary nThis chapter describes an experiment in which the electrical properties and morphology of a carbon black (CB)-filled immiscible blend of poly(vinylidene fluoride) (PVDF) and high density polyethylene (HDPE) were studied. The electrical conductivity of the composites increased dramatically when the CB content attained the percolation threshold approximately at a 0.035 volume fraction of CB. In addition to the CB content, the PVDF/HDPE volume ratio also affects the electrical conductivity of the composites. The electrical conductivity of the composites increased rapidly after the PVDF/HDPE volume ratio became greater than 0.17. The increase became more gradual when the PVDF/HDPE volume ratio was greater than 0.43. The results suggest that a decrease in HDPE content significantly increases the conductivity of the composites. The positive temperature coefficient (PTC) effect of the composites is caused by the thermal expansion because of the melting of the HDPE phase in the composites.

Blends of phenolphthalein poly(ether ether sulfone) with a thermotropic liquid crystalline copolyester

Abstract Blends of phenolphthalein poly(ether ether sulfone) (PES-C) with a thermotropic liquid crystalline copolyester (LCP) were prepared. Miscibility, morphology, thermal behavior, and mechanical properties of the PES-C/LCP blends with various compositions were studied by using differential scanning calorimetry (DSC), wide-angle x-ray diffraction (WAXD), dynamic mechanical analysis (DMA), tensile tests, and scanning electron microscopy (SEM). Both DSC and DMA studies showed that the blends have two glass transition temperatures (T g) corresponding to those of the PES-C-and LCP-rich phases, respectively. PES-C and LCP are partially miscible, the T gs varying with composition. Youngs modulus increases slightly with increasing LCP content owing to the high modulus of LCP, whereas the tensile strength greatly decreases with increase of LCP content. The interfaces between PES-C and LCP are weakly bonded, with rather poor interaction. SEM observations revealed that the blends have a two-phase structure and...