PTCR characteristics of poly(styrene‐co‐acrylonitrile) copolymer/stainless steel powder composites

Positive temperature coefficient of resistivity (PTCR) characteristics of poly(styrene‐co‐acrylonitrile) copolymer (SAN)/stainless steel (SS) powder (80 wt %) composites prepared by melt‐mixing method has been investigated with reference to SAN/carbon black (CB) composites. The SAN/CB (10 wt %) composites showed a sudden rise in resistivity (PTC trip) at 125°C, above the glass transition temperature (T_g) of SAN (T_g ≈ 107°C). However, the PTC trip temperature of SAN/SS (80 wt %) composites appeared at 94°C, well below the T_g of SAN. Addition of 1 phr of nanoclay increased the PTC trip temperature of SAN/CB (10 wt %) composites to 130°C, while SAN/SS (80 wt %)/clay (1 phr) nanocomposites showed the PTC trip at 101°C. We proposed that the mismatch in coefficient of thermal expansion (CTE) between SAN and SS played a key role that led to a disruption in continuous network structure of SS even at a temperature below the T_g of SAN. The dielectric properties study of SAN/SS (80 wt %) composites indicated possible use of the PTC composites as dielectric material. DMA results showed higher storage modulus of SAN/SS composites than the SAN/CB composites. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Effect of nanoclay on positive temperature coefficient to resistivity characteristics of high density polyethylene/silver‐coated glass bead composites

Positive temperature coefficient to resistivity characteristics of high density polyethylene (HDPE)/silver (Ag)‐coated glass bead (45 wt%) composites, without and with nanoclay, has been investigated with reference to HDPE/carbon black (CB) (10 wt%) composites. Plot of resistivity versus temperature of HDPE/CB (10 wt%) composites showed a sudden rise in resistivity (PTC trip) at ≈128°C, close to the melting temperature (T_m) of HDPE. However, for HDPE/Ag coated glass bead (45 wt%) composites, the PTC trip temperature (≈88°C) appeared well below the T_m of HDPE. Addition of 1 phr clay in the composites resulted in an increase in PTC trip temperature of HDPE/Ag‐coated glass bead (45 wt%) composites, whereas no significant effect of clay on PTC trip temperature was evident in HDPE/CB/clay composites. We proposed that the PTC trip temperature in HDPE/Ag‐coated glass bead composites was governed by the difference in coefficient of thermal expansion of HDPE and Ag‐coated glass beads. The room temperature resistivity and PTC trip temperature of HDPE/Ag‐coated glass bead (45 wt%) composites were found to be very stable on thermal cycling. Dynamic mechanical analyzer results showed higher storage modulus of HDPE/Ag‐coated glass bead (45 wt%) composites compared with the HDPE/CB (10 wt%) composites. Thermal stability of HDPE/Ag‐coated glass bead (45 wt%) composites was also improved compared with that of HDPE/CB (10 wt%) composites. POLYM. COMPOS., 2012. © 2012 Society of Plastics Engineers     

PTCR characteristics of polycarbonate/nickel‐coated graphite‐based conducting polymeric composites in presence of poly(caprolactone)

The effect of poly(caprolactone) (PCL) on the positive temperature coefficient of resistivity characteristics of polycarbonate (PC)/nickel (Ni)‐coated graphite (40 wt%) composites was investigated. The PTC trip temperature of PC/Ni‐coated graphite composites appeared at 155°C. On addition of PCL to PC/Ni‐coated graphite composites, the PTC trip temperature reduced to 125°C, well below the T_g of the PC (∼147°C), as well as the PC/PCL (∼136°C) blend. It is noteworthy that the observed PTC effect for PC/PCL (8 wt%)/Ni‐coated graphite (40 wt%) composites is highly reproducible during many heating cycles. The coefficient of thermal expansion (CTE) of PC was increased in presence of PCL. Thus, the mismatch in CTE of the PC and Ni‐coated graphite at a temperature well below the T_g of PC was enough to disrupt the continuous network structure that increased the resistivity of the composites. Storage modulus of PC/PCL/Ni‐coated graphite composites was higher than PC/Ni‐coated graphite composites. POLYM. COMPOS., 2011. © 2011 Society of Plastics Engineers     

Highly reversible and repeatable PTCR characteristics of PMMA/Ag‐coated glass bead composites based on CTE mismatch phenomena

Positive temperature coefficient of resistivity (PTCR) behavior of poly(methyl methacrylate) PMMA/silver (Ag)‐coated glass bead composites has been investigated with reference to the conventional PMMA/carbon black (CB) composites. The PMMA/CB composites showed a sudden rise in resistivity (PTC trip) at 115°C, close to the glass transition temperature (T _g, 113°C) of the PMMA. However, the PTC trip temperature (92°C) of PMMA/Ag‐coated glass bead composites was appeared well below the T _g of PMMA. The room temperature resistivity and PTC trip temperature of the composites were also very much stable upon thermal cycling. Addition of 1 phr of nanoclay increased the PTC trip temperature of PMMA/CB composites to 120°C, close to the T _g (118°C) of PMMA/clay nanocomposites, while PMMA/clay/Ag‐coated glass bead nanocomposites showed the PTC trip at 98°C. We proposed that the mismatch in coefficient of thermal expansion (CTE) between PMMA and glass beads played a key role that led to a disruption in continuous network structure of Ag‐coated glass beads even at a temperature well below the T _g of PMMA. The decrease in dielectric permittivity of PMMA/Ag‐coated glass bead composites on increasing frequency indicated possible use of the PTC composites as dielectric material. POLYM. ENG. SCI., 2011. © 2011 Society of Plastics Engineers     

Morphology,Resistivity, and PTC behavior of EVOH/CB composites prepared by solvent‐casting saponification and precipitation saponification

Poly(ethylene‐co‐vinyl alcohol)/carbon black (EVOH/CB) composites were prepared by a solvent‐casting saponification (‐D) and precipitation saponification (‐P) methods with a poly(ethylene‐co‐vinyl acetate)/CB (EVA/CB) toluene suspension. The effects of the CB content and saponification time on the morphology, electrical resistivity, thermal, and mechanical properties of EVA/CB composites were examined. The volume resistivity (ρ _v) of the EVA/CB‐D and EVA/CB‐P samples decreased significantly with increasing CB content and the percolation threshold of such composites was determined about 10 wt%. At 10 wt% of CB content, the ρ _v of EVA/CB‐D composite decreased significantly with the saponification time, whereas ρ _v of EVA/CB‐P composites did not change. As the saponification time increased, EVA/CB25wt% composites form cavity structure which CB is usually located in oval cavities larger than the particles themselves. This oval cavity structure almost resembles extruded high‐density polyethylene (HDPE)/CB composites. The morphology and PTC behavior of prepared composites were compared with those of HDPE/CB and the mechanism of PTC and NTC effects was discussed. POLYM. COMPOS., 38:1462–1473, 2017. © 2015 Society of Plastics Engineers     

Influence of morphology on positive temperature coefficient effect for conductive polymer composites with carbon black dispersed at interface

Selective localization of carbon black (CB) at the interface of polymer blends was achieved by the method that EBA‐g‐MAH was first reacted with CB, and then blended with poly(ethylene‐co‐butyl acrylate)/nylon6 (EBA/PA6). In CB‐filled EBA/PA6 blends, EBA and PA6 phases formed cocontinuous morphology and CB was localized in PA6 phase. The percolation threshold was 5 wt%. A single PTC (positive temperature coefficient) effect was observed in this composite. The appearance of PTC effect was originated from the thermal expansion of EBA phase. In the EBA‐g‐MAH filled EBA/PA6 blends, TEM results showed that CB particles were induced by EBA‐g‐MAH to localize at the interface, resulting that the percolation threshold was much lower than that of EBA/PA6/CB. Influence of morphology on PTC effect of EBA/PA6/EBA‐g‐MAH/CB composites was studied. In the composites with sea‐island morphology, the conductive network was fabricated by dispersed phase and CB at the interface. Thermal expansion of matrix interrupted the contact of dispersed phases and conductive network formed by CB particles at the interface, resulting in the double PTC effect. The composites with co‐continuous morphology exhibited single PTC effect due to the fact that conductive network was only fabricated by CB localized at the interface. POLYM. ENG. SCI., 53:2640–2649, 2013. © 2013 Society of Plastics Engineers     

Effect of coefficient of thermal expansion on positive temperature coefficient of resistivity behavior of HDPE–Cu composites

Positive temperature coefficient of resistivity (PTCR) characteristics of (high density polyethylene) HDPE–Cu composites has been investigated with reference to the conventional HDPE–CB (carbon black) composites. Plot of resistivity against temperature of HDPE–CB composites showed a sudden rise in resistivity (PTC trip) at 127°C, close to the melting temperature of HDPE. However, the PTC trip temperature (98°C) for HDPE–Cu composites was appeared well below the melting temperature of HDPE. Addition of 1 phr nanoclay in the composites resulted in an increase in PTC trip temperature of HDPE–Cu composites, whereas no significant effect of nanoclay on PTC trip temperature was evident in case of HDPE–CB–clay composites. We proposed that the PTC trip temperature in HDPE–Cu composites was governed by the difference in coefficient of thermal expansion (CTE) of HDPE and Cu. The room temperature resistivity and PTC trip temperature of HDPE–Cu composites were very much stable upon thermal cycling. DMA results showed higher storage modulus of HDPE–Cu composites than the HDPE–CB composites. Thermal stability of HDPE–Cu composites was also improved compared to that of HDPE–CB composites. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Resistivity‐temperature behavior and morphology of low density polyethylene/graphite powder/graphene composites

In this work, the positive‐temperature‐coefficient (PTC) effect of resistivity of low density polyethylene/graphite powder (45%) composites (LDPE/GP) in the presence of graphene before and after crosslinked was comparatively investigated by differential scanning calorimetry (DSC), X‐ray diffraction (XRD), scanning electron microscopy, Raman spectrum, and resistivity‐temperature test. The composites showed the repeatability of the PTC effect with heating cycles and a certain improvement in the room temperature resistivity. After crosslinked, the composites presented a higher PTC trip temperature at about 140°C than pure LDPE (T_m = 112°C), and stronger PTC intensity than room temperature resistivity (over 5 orders of magnitude). The results from DSC, XRD, and Raman spectrum indicated that the addition of graphene resulted in the gradual enhancement in the crystallization of LDPE matrix, which was the origin of the improvement of the PTC behavior of the composites. As a result, we could conclude that the additional conducting filler could improve the PTC effect of the conducting composite system. POLYM. COMPOS., 35:1453–1459, 2014. © 2013 Society of Plastics Engineers     

Adaptation of polystyrene/multi‐wall carbon nanotube composite properties in respect of its thermal stability

Polystyrene (PS)/multi‐wall carbon nanotube (MWCNT) nanocomposites were prepared by melt mixing and by coagulation of PS/MWCNT sonicated dispersion. Before mixing and coagulation particles of MWCNT were covered with PS nanospheres by microemulsion polymerization to increase their dispersibility and compatibility with the matrix. Microemulsion polymerization was carried out under sonication in the presence of surfactants and a cross‐linking agent. The structure of modified MWCNT filler was revealed by SEM and TEM microscopy analyses. They show that PS is well grafted onto surface of MWCNT in form of ca 30 nm nanospheres or as ca 3–8 nm PS film layer. Significant changes in properties were recorded mainly for the coagulated sample. Although no shift of T_g was recorded for the melt mixed composite, the coagulated sample shows an increase by 9°C. Also the reinforcing effect of MWCNT was more pronounced for the same method of preparation (further supported by the filler modification). The creep response of this material shifts to longer times not only in the T_g area, but also as low as 70°C below it, which is perceived as an improvement of temperature stability (the same properties kept for a longer time). This was also proved by the increase of creep modulus, and consequently by the prolonged time needed to reach the same tensile creep compliance after aging. POLYM. COMPOS., 2010. © 2009 Society of Plastics Engineers     

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     

Noncovalent compatibilization of polypropylene/MWCNT composites using an amino‐pyridine grafted polypropylene matrix

Polypropylene (PP)/multiwalled carbon nanotube (MWCNT) composites are prepared by implementing noncovalent compatibilization. The compatibilization method involves PP matrix functionalization with pyridine (Py) aromatic moieties, which are capable of π–π interaction with MWCNT sidewalls. Imaging revealed that the addition of 25 wt% of PP‐g‐Py to neat PP is capable of drastically reducing nanotube aggregate size and amount, compared to a matrix containing the equivalent amount of a maleated PP (PP‐g‐MA). Raman spectroscopy confirms improved polymer/nanotube interaction with the PP‐g‐Py matrix. The electrical percolation threshold appears at a MWCNT loading of approximately 1.2 wt%, and the maximum value of the electrical conductivity achieved is 10⁻² S/m, irrespective of the functionalization procedure. The modulus of the composites is improved with the addition of MWCNTs. Furthermore, composites functionalized with Py display significant improvements in composite ductility compared with their maleated counterparts because of the improved filler dispersion. POLYM. COMPOS., 37:2794–2802, 2016. © 2015 Society of Plastics Engineers     

Styrene butadiene rubber/epoxidized natural rubber/carbon filler nanocomposites: microstructural development and cure characterization

Microstructural development of elastomeric nanocomposites based on (50/50 wt%) styrene butadiene rubber (SBR) and epoxidized natural rubber (50 mol% epoxidation, ENR50) as the rubber matrix including two types of carbon fillers, carbon black (CB) and functionalized multiwall carbon nanotube (NH₂-MWCNT), which were prepared through melt mixing, was studied. The results from FTIR analysis show that there is interaction between functional groups on MWCNT surface and the rubber chains. The AFM analysis also indicates good dispersion of filler particles in the rubber phases. FESEM images from cryo-fractured surface of samples have revealed that nanotubes were rarely pulled out of matrix and their diameter increased, resulting from good interaction between MWCNTs and rubber chains. The DMA results confirm good interfacial interaction between them. Furthermore, the reduced difference between the two T_gs of phases (ΔT_g) shows that the incorporation of 3 phr MWCNT into the blend leads to increment in rubber phase compatibility but at higher MWCNT content (5 phr) due to lower Mooney viscosity of SBR phase, MWCNTs tend to remain in this phase. The bound rubber was adopted to characterize the polymer–filler interaction, showing that bound rubber content has an increasing trend with increasing in fillers content. The cure rheometric studies reveal that MWCNTs accelerate the cure process due to the presence of amine groups on the nanotube surface. In addition, the mechanical properties of samples show an increasing trend by increasing nano-filler content.

     

Sulfonated poly(sulfone‐pyridine‐amide)/sulfonated polystyrene/multiwalled carbon nanotube‐based fuel cell membranes

In this study, aromatic sulfonated poly(sulfone‐pyridine‐amide) (S‐PSPA) has been prepared via polycondensation of sulfonated monomer 1‐(4‐thiocarbamoylaminophenyl‐sulfonylphenyl)thiourea and 2,6‐pyridinedicarboxylic acid at high temperature. Mechanically robust and thermally stable hybrid membranes were prepared using non‐functional and functional multiwalled carbon nanotube (MWCNT) i.e., S‐PS/S‐PSPA/MWCNT‐NF and S‐PS/S‐PSPA/MWCNT via solution blending. Field emission scanning electron microscopy exhibited porous membrane structure for 0.1–0.5 wt% nanotube loading, whereas well‐aligned functional MWCNT were observed in 1 wt% loaded sample. Increasing the functional nanotube content from 0.1 to 1 wt% increased tensile strength of functional S‐PS/S‐PSPA/MWCNT hybrids from 62.19 to 65.29 MPa compared with non‐functional hybrid (53.34 MPa) and neat S‐PS/S‐PSPA. 10% decomposition temperature of S‐PS/S‐PSPA/MWCNT 0.1–1 was in the range 491–502°C, while S‐PS/S‐PSPA/MWCNT‐NF showed relatively lower thermal stability (T₁₀ 489°C). Glass transition temperature of functional S‐PS/S‐PSPA/MWCNT was also higher (201–243°C) relative to S‐PS/S‐PSPA/MWCNT‐NF (194°C). Furthermore, functional MWCNT‐based membranes had higher ion exchange capacity (IEC) 3.2–3.6 mmol/g and lower activation energies (95–36 kJ/mol). Novel functional membranes also revealed high proton conductivity 1.68–2.55 S/cm in a wide range of humidity at 80°C higher than that of perfluorinated Nafion® membrane (1.1 ×10^?1 S/cm) at 80°C (94% RH). POLYM. ENG. SCI., 55:1776–1786, 2015. © 2014 Society of Plastics Engineers     

Morphological effect of fillers on graphite reinforced polydicyclopentadiene based composites

Graphite reinforced polydicyclopentadiene (polyDCPD) composites were synthesized via the in situ ring‐opening metathesis polymerization (ROMP) of DCPD with vapor‐grown carbon fiber (VGCF), acidified multiwall carbon nanotube (a‐MWCNT), and mildly oxidized graphene oxide (MOGO) as distinctive reinforcing fillers, respectively. We studied the morphological effect of the fillers on the mechanical and thermal properties of graphite/polyDCPD composites. Mechanical property tests showed that the addition of VGCF greatly strengthened the tensile strength, the introduction of a‐MWCNT dramatically extended the elongation at break, whereas the incorporation of MOGO enhanced both performances of the resulting composites. Impact tests showed that the maximum mechanical performances of a‐MWCNT/polyDCPD and MOGO/polyDCPD composites both were got with 0.4 wt% of fillers (a‐MWCNT and MOGO) loading. Meanwhile, all of the reinforced composites exhibited increased thermal stabilities compared with the unfilled polyDCPD, confirmed by increased T_gs and thermal decomposition temperatures at 5 wt% weight loss. POLYM. COMPOS., 35:1918–1925, 2014. © 2014 Society of Plastics Engineers     

The experimental results and simulation of temperature dependence of brittle‐ductile transition in PVC/CPE blends and PVC/CPE/nano‐CaCO3 composites

The effect of chlorinated polyethylene (CPE) content and test temperature on the notched Izod impact strength and brittle‐ductile transition behaviors for polyvinylchloride (PVC)/CPE blends and PVC/CPE/nano‐CaCO₃ ternary composites is studied. The CPE content and the test temperature regions are from 0–50 phr and 243–363 K, respectively. It is found that the optimum nano‐CaCO₃ content is 15 phr for PVC/CPE/nano‐CaCO₃ ternary composites. For both PVC/CPE blends and PVC/CPE/nano‐CaCO₃ ternary composites, the impact strength is improved remarkably when the CPE content or test temperature is higher than the critical value, that is, brittle‐ductile transition content (C_BD) or brittle‐ductile transition temperature (T_BD). The T_BD is closely related to the CPE content, the higher the CPE content, the lower the T_BD. The temperature dependence of impact strength for PVC/CPE blends and PVC/CPE/nano‐CaCO₃ ternary composites can be well simulated with a logistic fitting model, and the simulation results can be illustrated with the percolation model proposed by Wu and Jiang. DMA results reveal that both PVC and CPE can affect the T_BD of PVC/CPE blends and PVC/CPE/nano‐CaCO₃ composites. When the CPE content is enough (20 phr), the CPE is more important than PVC for determining the T_BD of PVC/CPE blends and PVC/CPE/nano‐CaCO₃ composites. Scanning electron microscopy (SEM) observations reveal that the impact fractured mechanism can change from brittle to ductile with increasing test temperature for these PVC systems. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Fine dispersion of carbon black in fluorene‐based resin

The dispersion ability of fluorene‐based epoxy resin (FBE), bisphenol A based epoxy resin (PBE), fluorene‐based polyester (FBP), and polycarbonate (PC) in carbon black (CB) was evaluated. CB/FBE composite had a lower L value (reflectance, blackness) than that of CB/PBE composite, for the same CB content. Aggregations of CB in CB/FBE composites were much smaller than those in CB/PBE composites. The strong interaction between fluorene with cardo structure and CB resulted in a fine dispersion of CB in FBE. FBP had much higher dispersion ability of CB than PC. CB (50 wt%) was dispersed into FBP compared with the 10 wt% of CB dispersed in PC by melt blending. The effect of CB on the mechanical properties of FBP was much higher than that on PC due to fine dispersion of CB in FBP. The effect of CB addition on the T_g of FBP was also higher than that of CB on the T_g of PC. Computational simulation indicates that most stable energy between fluorene with a cardo structure and graphite structure was smaller than the energy between bisphenol A and graphite. It was also shown that the minimum energy appeared when the fluorene structure was almost parallel to the graphite plane. POLYM. COMPOS., 2008. © 2008 Society of Plastics Engineers     

Polymer/carbon nanotube composite film formation: A fluorescence study

In this study, the effect of multi‐walled Carbon nanotube (MWNT) on film formation behavior of Polystrene (PS) latex film was investigated by using steady state fluorescence technique. Films were prepared by mixing of pyrene (P)‐labeled PS latex with different amounts of MWNTs varying in the range between 0 and 20 wt%. After drying, MWNT containing films were separately annealed above glass transition temperature (T_g) of PS ranging from 100 to 270°C for 10 min. In order to monitor film formation behavior of PS/MWNT composites, Scattered light (I_s) and fluorescence intensities (I_P) from P were measured after each annealing step to monitor the stages of film formation. At 0–20 wt% range of MWNT content films, minimum film formation (T_o), void closure (T_v), and healing, (T_h) temperatures were determined. Void closure and interdiffusion stages were modeled and related activation energies were determined. It was observed that while void closure activation energies increased, backbone activation energies decreased as the percent of MWNT is increased in the composite films. POLYM. COMPOS., 35:817–826, 2014. © 2013 Society of Plastics Engineers     

Phase diagrams of thermally stable,polymer‐dispersed liquid crystals: Exploring the impact of chain length and chemical structure

Polymer‐dispersed liquid crystals (PDLCs) have garnered significant interest and motivated the investigation of the phase behavior of thermally stable smectic liquid crystals (LCs) via thermally induced phase separation (TIPS). In this study, we examined a series of two, biphenyl‐based smectic LCs suitable for high temperature polymer blend processing. Phase diagrams for LC/polystyrene (PS) blends at various compositions (0–60 wt%) were constructed. Less than 15 wt% of 8B8 (1,1′‐biphenyl‐4,4′‐diyl dioctanoate) LC in PS led to good polymer miscibility, while phase separation was induced at concentrations higher than 15 wt%. The LC concentration at saturation decreased with increasing aliphatic chain length. We also investigated the chain length (C6‐C16) effect on the PS glass transition temperature (T_g) at the LC saturation point. The T_g increased with increasing chain length due to reduced plasticization. We further examined the role of chemical structure (relatively less polar ether vs. more polar ester) on the phase diagram regions and the T_g of the nonpolar PS matrix, respectively. It is anticipated that these LC/PS phase diagrams will benefit elevated temperature processing for TIPS by highlighting the role of LC chemical structure and chain length on blend morphology. POLYM. ENG. SCI., 56:388–393, 2016. © 2016 Society of Plastics Engineers     

Preparation and thermal,electrical, and morphological properties of multiwalled carbon nanotubeand epoxy composites

Multiwalled carbon nanotube (MWCNT)/epoxy composites are prepared, and the characteristics and morphological properties are studied. Scanning electron microscopy microphotographs show that MWCNTs are dispersed on the nanoscale in the epoxy resin. The glass‐transition temperature (T_g) of MWCNT/epoxy composites is dramatically increased with the addition of 0.5 wt % MWCNT. The T_g increases from 167°C for neat epoxy to 189°C for 0.5 wt % CNT/epoxy. The surface resistivity and bulk resistivity are decreased when MWCNT is added to the epoxy resins. The surface resistivity of CNT/epoxy composites decreases from 4.92 × 10¹² Ω for neat epoxy to 3.03 × 10⁹ Ω for 1 wt % MWCNT/epoxy. The bulk resistivity decreases from 8.21 × 10¹⁶ Ω cm for neat epoxy to 6.72 × 10⁸ Ω cm for 1 wt % MWCNT/epoxy. The dielectric constant increases from 3.5 for neat epoxy to 5.5 for 1 wt % MWCNT/epoxy. However, the coefficient of thermal expansion is not affected when the MWCNT content is less than 0.5 wt %. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 1272–1278, 2007     

Polystyrene/CaCO3 composites with different CaCO3 radius and different nano‐CaCO3 content—structure and properties

The Archimedes' principle and physical theory are attempted to analysis the densification and structure of the polystyrene (PS) composites by melt compounding with CaCO₃ having different particle size. The difference between the measured specific volume (ν) andthe theoretically calculated specific volume (ν_mix), Δν = ν−ν_mix, can reflect the densification of the composites. It is clearly demonstrated that the PS composites become more condensed with the reduction of the CaCO₃ particle size. Especially, when the content for nano‐CaCO₃ achieves 2 wt%, the Δν value of the composites reaches the least, which shows the best densification. Meanwhile, the glass transition temperature (T_g) reaches the maximum value of about 100°C by differential scanning calorimetry (DSC) and thermal mechanical analysis (TMA), which indirectly reveals the composites microstructure more condensed. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) reveal that 2 wt% nano‐CaCO₃ uniformly disperses in PS composites. The CaCO₃ selected in this experiment has certain toughening effect on PS. The impact and tensile strength increase with addition of nano‐CaCO₃, but the elongation at break decreases. When nano‐CaCO₃ content achieved 2 wt%, the impact and tensile strength present the maximum value of 1.63 KJ/m² and 44.5 MPa, which is higher than the pure PS and the composites filled with the same content of micro‐CaCO₃. POLYM. COMPOS., 31:1258–1264, 2010. © 2009 Society of Plastics Engineers