聚丙烯/石墨导电纳米复合材料的制备与性能

用溶液插层及其与熔体混合相结合的母料熔体混合 (MMM)方法制备了聚丙烯 (PP) 马来酸酐接枝聚丙烯 (gPP) 膨胀石墨 (EG) (gPP EG =3 2wt)导电纳米复合材料 ,其室温逾渗阀值 (c)分别为 6wt%和 8wt % ,明显低于直接熔体混合制得复合材料和PP EG对照材料的c=11wt%和 12wt% .增加gPP含量 (Cg)能提高复合材料的电导率 (σ) ,例如对于MMM法制备的复合材料 ,固定PP gPP =1 1wt时 ,c 降为 7wt% ;保持EG含量 =9wt%时 ,σ在Cg>30wt %后跃升 7个数量级以上 .通过TEM、SEM和OM观察 ,从制备方法、EG和gPP含量影响复合材料形态和微结构的角度 ,分析说明了出现上述差异和现象的原因 .     

Rheological,morphological and mechanical properties of flax fiber polypropylene composites: influence of compatibilizers

In this work, the rheological, mechanical and morphological properties of flax fiber polypropylene composites were investigated. The effect of incorporating a polypropylene grafted acrylic acid or a polypropylene grafted maleic anhydride on these properties has been studied as well. According to scanning electron microscopic observations and tensile tests, the addition of a compatibilizer improved the interfacial adhesion between the flax fibers and the polymer matrix. The tensile modulus of composite containing 30 wt% flax fibers was improved by 200 % and the tensile strength improved by 60 % in comparison with the neat PP. Plasticizing effect of the compatibilizers as a result of their lower melt flow index was also shown to decrease the rheological properties of the composites, even though the effect was not pronounced on the mechanical properties.     

多壁碳纳米管对聚甲醛性能的影响

将多壁碳纳米管(MWCNTs)和聚甲醛(POM)在转矩流变仪中熔融混合得到POM/MWCNT复合材料.研究了复合材料的形态,导热性能,导电性能,流变性能和结晶性能.结果表明,MWCNTs在没有经过处理的情况下能够均匀地分散在POM基体中;当向POM中添加1.0 wt%含量MWCNTs时,复合材料的导热系数上升到0.5289 W/(K m),比纯POM的导热系数0.198 W/(K m)提高1.5倍,通过有效介质方法(EMA)验证了体系导热系数提高幅度不大的原因是MWCNTs与POM之间形成了很高的界面热阻;当MWCNTs的含量为1.0 wt%时,体系产生了导电逾渗效应,逾渗值在0.5 wt%~1.0 wt%之间;MWCNTs对POM有显著的成核作用,当向POM中添加0.5 wt%含量的MWCNTs时,POM的结晶温度提高6℃左右,但当MWCNTs的添加量进一步增加时,结晶温度几乎不再变化,成核效果呈现"饱和"状态.另外,材料的复数黏度,储能模量和损耗模量随MWCNTs含量的增加而增加.     

Rheological Behavior of Spinning Dope of Multiwalled Carbon Nanotube/Polyacrylonitrile Composites

The spinning dope of Multiwalled carbon nanotube/polyacrylonitrile composites was prepared by in-situ polymerization in 50wt% NaSCN solution. The rheological behavior of the dope containing carbon nanotubes from 0.19wt% to 1.9wt% was investigated using rotational rheometry at 60°C.The nanotubes have diameters between 30-50nm and lengths ranging from 6 to 10 μm. The apparent viscosity decreases with the addition of carbon nanotubes; this can be explained by the inhibition of carbon nanotubes during polymerization progress. The spinning dope containing various contents of carbon nanotubes exhibits a shear thickening effect. However, the dynamic rheological test shows there is a peak of complex viscosity with the increasing in frequency.     

Stability of electrical and mechanical properties of polyethylene/carbon black composites

The stability of electrical and mechanical properties of two kinds of polymer composites ‐ polyethylene/carbon black and polyethylene/carbon black modified by polypyrrole ‐ was investigated during slow cycle heating and cooling. Conductivity in composites was measured in heating/cooling cycles in the temperature range from 16°C to 125°C. It was found that the thermal treatment resulted in the conductivity changes and the mechanical properties of treated composites have also been influenced. The effect was explained by increased crystallinity in the polymer matrix of thermally treated composites.     

Complementary effects of multiwalled carbon nanotubes and conductive carbon black on polyamide 6

This article introduces a newly innovative idea for preparation of superconductive ternary polymeric composites of polyamide 6 (PA6), conductive carbon black (CCB), and multiwalled carbon nanotubes (MWCNTs) with different weight ratios by a melt‐mixing technique. The complementary effects of CCB and MWCNTs at different compositions on rheological, physical, morphological, thermal, and dynamic mechanical and electrical properties of the ternary composites have been examined systematically. We have used a novel formulation to produce high‐weight fraction ternary polymer composites that show extremely higher conductivity when compared with their corresponding binary polymer composites at the same carbon loading. For example, with an addition of 10 wt % MWCNTs into the CCB/PA6 composite preloaded with 10 wt % CCB, the electrical conductivity of these ternary composites was about 5 S/m, which was 10 times that of the CCB/PA6 binary composite (0.5 S/m) and 125 times that of the MWCNT/PA6 binary composite (0.04 S/m) at 20 wt % carbon loading. The incorporation of the MWCNTs effectively enhanced the thermal stability and crystallization of the PA6 matrix in the CCB/PA6 composites through heterogeneous nucleation. The MWCNTs appeared to significantly affect the mechanical and rheological properties of the PA6 in the CCB/PA6 composites, a way notably dependent on the MWCNT contents. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 1203–1212, 2010     

Mechanical and rheological properties of poly(ethylene-co-ethyl acrylate) as a function of carbon black content

Carbon black (CB) filled poly(ethylene-co-ethyl acrylate) (EEA-CB) is used as conductive phase in conductive polymer composites (CPC). Electrical conductivity of CPC obtained from blends of immiscible polymers results from CB particles localization within the material, which depends on composition and processing conditions. It is particularly important to control viscosity of such systems as this parameter determines both the phase morphology and conductive pathway structure. The small scale, at which CB particle aggregation/dispersion phenomena occur within CPC, makes direct observations difficult. But the effect of carbon black particles/polymers interactions is clearly visible by means of rheological measurements. A strong reinforcing effect of CB on CPC in both solid and liquid states has been noticed. This phenomenon has been analyzed using classical models as a function of temperature and CB content. The results confirm the necessity of CPC rheology control especially during the process to achieve good reproducibility of electrical properties.     

Thermal Analysis of Micro- and Nano-Lignocellulosic Reinforced Styrene Maleic Anhydride Composite Foams

The aim of this study was to measure the thermal properties of foamed nano/macro filler–reinforced styrene maleic anhydride (SMA) composites. SMA (66%) as a polymer matrix (10% maleic anhydride content) and various fillers including wood flour, starch, α-cellulose, microcrystalline cellulose and cellulose nanofibrils as reinforcing agents (30%) and lubricant (4%) were used to manufacture the composites in a twin-screw extruder. According to the thermogravimetric analysis (TGA) results, thermal degradation of all the foamed composites was found to be lower than that of SMA composites. The storage modulus values were negatively affected with a second time foaming (reprocessing [recycling] the initially processed composites a second time), as were loss modulus and T_g. As a result, second-time-foamed composite modulus values were lower than those of the foamed composites. According to the melt flow index (MFI) results, viscosity of the SMA was found to increase with the addition of fillers.     

Rheological and single screw extrusion processability studies of isotactic polypropylene composites filled with basalt powder

The development of novel composite materials with beneficial mechanical, thermal and electrical properties often focus only on the final properties of the products. However, in many cases their significant application potential may be suppressed by limitations resulting from their rheological and processing properties. The isotactic polypropylene (iPP) composites filled with basalt powder (BP) are known for their good thermomechanical stability and stiffness. The paper presents the complex results of off-line rheological measurements (oscillatory, capillary and torque rheometry) related to processing behavior obtained in a laboratory conditions with the use of a processing machine (single screw extruder), which allow understanding the different manner of the processing behavior occurring during the melt processing of iPP-BP composites. It was found that the addition of BP may cause unusual, beneficial effect of lowered viscosity of the melt. While the addition of up to 5 wt% of BP results in a profitable reduction of the pressure in the barrel during extrusion without influence on the throughput, a higher amount of the filler may lead to significant processing limitations due to strong wall slip.     

Shear‐induced clay dispersion in HDPE/PEgMA/organoclay composites as studied via real‐time rheological method

In current study, a real‐time rheological method was used to investigate the intercalation and exfoliation process of clay in high‐density polyethylene/organoclay (HDPE/OMMT) nanocomposites using maleic anhydride grafted polyethylene (PEgMA) as compatibilizer. To do this, a steady shear was applied to the original nonintercalated or slightly intercalated composites prepared via simple mixing. The moduli of the composites were recorded as a function of time. The effect of matrix molecular weight and the content of compatibilizer on the modulus were studied. The role of the compatibilizer is to enhance the interaction between OMMT and polymer matrix, which facilitates the dispersion, intercalation, and exfoliation of OMMT. The matrix molecular weight determines the melt viscosity and affects the shear stress applied to OMMT platelets. Based on the experimental results, different exfoliation processes of OMMT in composites with different matrix molecular weight were demonstrated. The slippage of OMMT layers is suggested in low‐molecular weight matrix, whereas a gradual intercalation process under shear is suggested in high‐molecular weight matrix. Current study demonstrates that real‐time rheological measurement is an effective way to investigate the dispersion, intercalation, and exfoliation of OMMT as well as the structural change of the matrix. Moreover, it also provides a deep understanding for the role of polymer matrix and compatibilizer in the clay intercalation process. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 302–312, 2010     

Effect of Silane Coupling Agent and Compatibilizer on Properties of Short Rossells Fiber/Poly(propylene) Composites

Rossells fiber reinforced polypropylene composites were prepared by melt mixing. The fiber content was 20 wt%. Octadecyltrimethoxysilane (OTMS) and maleic anhydride grafted polypropylene (MAPP) were used to improve the adhesion between poly(propylene) (PP) and the fiber. The mechanical, rheological, and morphological properties, and heat distortion temperature (HDT) of the composites were investigated. Tensile strength, impact strength, flexural strength and HDT of MAPP modified PP composites increased with an increase in MAPP content. However, no remarkable effect of MAPP content on the Young's modulus of the composites was found. OTMS resulted in small decreases of tensile strength and Young's modulus, and increase in impact strength. Scanning electron micrographs revealed that MAPP enhanced surface adhesion between the fiber surface and PP matrix.     

LDPE／CPE／炭黑三相复合导电体系的亚微形态和导电性能

对ＬＤＰＥ／ＣＰＥ／炭黑三相复合导电体系的亚微形态和导电性能进行了研究。实验发现,该体系的亚微形态在共混比ＬＤＰＥ／ＣＰＥ大于和小于５０／５０时为典型的“海－岛”结构,在５０／５０时,为两相连续交错“互锁”结构;在共混比大于５０／５０时,ＬＤＰＥ／ＣＰＥ炭黑复合体系的导电性能较单一的ＬＰＤＰＥ树脂与炭黑复合体系的高２－５个数量级。     

Influence of thermal and UV treatment on the polypropylene/graphite composite

Electrically conductive polypropylene/graphite (PP/graphite) composites were prepared via blending granulated PP with maleic anhydride grafted PP and natural graphite. Electrical conductivity of prepared samples containing either 65, 70, or 75 wt% of graphite was measured and the most conductive sample containing 75 wt% of graphite was exposed to UV irradiation for 1 and 24 h or thermally treated at 170 °C for 1 h. The influence of thermal and UV exposure on the structural and electrical changes in such treated samples was studied. Local current measurements on the surface were made using scanning spreading resistance microscopy and morphology of the surface was studied by atomic force microscopy. X-ray diffraction analysis, infrared and Raman spectroscopy were also used for the structural characterization. Properties of treated and untreated samples are compared and differences are discussed.     

Comparative analysis of nanocomposites based on polypropylene and different montmorillonites

Nanocomposites of polypropylene (PP) were prepared by melt mixing using maleic anhydride modified polypropylene (PPg) and different organophilic montmorillonites (OMMT). The selected organo-modified clays differ in their initial particle size, amount and type of surfactant and/or their cation-exchange capacity. All composites have 80, 15 and 5 wt% of PP, PPg and OMMT, respectively. The materials were characterized using TGA, XRD, SEM and rotational rheometry. Cloisite 15A, Cloisite 93A, Nanomer I44 and a bentonite modified with octadecylammonium (B18) display intercalation and exfoliation after mixing and annealing and produce nanocomposites with different degrees of ‘solid-like’ rheological behavior. The composites based in Cloisite 15A and Nanomer I44, which use the same intercalant, show very similar phase structure and rheological response, regardless of the origin and initial characteristics of the clays. These nanocomposites are the most affected by the thermal history during rheological characterization in the molten state. On the other hand, Cloisite 10A and Cloisite 30B display collapse of the silicate layers after compounding with no evidence of exfoliation.     

Modification of PP by blending with PS and reactive polymers

In this paper a polypropylene (PP) resin with controlled rheology was selected as polymer matrix and modified by melt mixing with polystyrene (PS) which has certain processing compatibility with PP. The effect of the addition of polyperoxide (PPX), peroxide modified PS particles (PS‐PPX), and maleic anhydride (MAH) to the PP/PS blend during melt mixing on the rheological behavior and morphology of the PP/PS blends has been carefully studied.     

Preparing iPP/HDPE/CB functionally gradient materials: influence factors of components and processing

In this work, gradient materials with low electrical resistivity were prepared by compounding isotactic polypropylene (iPP)/high density polyethylene (HDPE) blends with carbon black (CB) through extruding and injection molding. Contact angle measurements and morphology measurements showed that the CB particles were selectively located in HDPE phase and the final composites had a gradient structure that the HDPE/CB phase exhibited different morphologies in the skin layer and core layer of the composites under different processing procedures. The main factors influencing the formation of the functional gradient materials (FGM), including screw speed during extruding, iPP types and CB contents were discussed. They affect the phase morphology by shear stress, the restoration of HDPE phase, and the viscosity ratio of polymer blends, respectively. In conclusion, iPP/HDPE/CB FGM could be formed easily in the composites blending with the iPP type with narrow molecular weight distribution (MWD) and higher CB content extruded at higher screw speed. The electrical properties of iPP/HDPE/CB composites were studied and the results showed that screw speed in extrusion significantly influenced the percolation curve and electrical property of the final composites. Copyright © 2011 John Wiley & Sons, Ltd.     

The role of interfacial compatibilization upon the microstructure and electrical conductivity threshold in polypropylene/expanded graphite nanocomposites

Attempts have been made to evaluate the effect of interface and degree of interfacial interaction upon electrical conductivity threshold in polypropylene/expanded graphite (PP/EG) nanocomposites, and dispersion state of graphite nanosheets. For this purpose, maleic anhydride grafted polypropylene (PPgMA) and maleic anhydride grafted EPDM (EPDMgMA) were used as compatibilizer. Nanocomposite samples containing 1–5 vol% of EG were prepared by melt mixing method using laboratory scale internal mixer. Characterization was carried out by using X‐ray diffraction (XRD), differential scanning calorimeter (DSC), thermo‐gravimetric analysis (TGA), scanning electron microscope (SEM), transmission electron microscope (TEM), and rheo‐mechanical spectroscopy (RMS). The conductivity measurements were carried out by using four point probe method according to ASTM D991. Results showed that the conductivity threshold is controlled by the extent of interfacial interaction between PP and EG. So, better conductivity was obtained using PPgMA as compatibilizer which causes higher level of interaction between PP and EG, and therefore better dispersion of the EG nanolayers in the polymer matrix. On the other hand, high levels of compatibilizers, especially EPDMgMA, caused formation of separated aggregates of EG shelled with the compatibilizer, which results in the reduction of conductivity of the nanocomposites. This finding has been verified by SEM, RMS, and conductivity measurements. Effects of EG nanolayers on crystalline structure and thermal decomposition temperature of the nanocomposites have also been investigated by DSC and TGA, respectively. Copyright © 2009 John Wiley & Sons, Ltd.     

Rheological and Structure Investigation of Melt Mixed Multi-Walled Carbon Nanotube/PE Composites

In this study a series of melt mixed multi-walled carbon nanotube (MWNT)/Polyethylene composites with several carbon nanotube (CNTs) concentrations were investigated. A good dispersion of the nanotubes in the matrix was seen using scanning electron microscopy. Melt rheological measurements in dynamic mode were used to estimate the percolation state of the CNTs within the polymer and to provide information about the structure of the CNT/polymer composites. The effect of nanotubes on the non-isothermal crystallization behaviour of the nanocomposites was also studied by differential scanning calorimetry.     

LDPE／CPE／炭黑三相复合导电体系的电学性能

研究了ＬＤＰＥ／ＣＰＥ／炭黑三相复合导电体系的导性能和电流－电压特性。实验结果表明复合体系具有明显的导电渗滤效应，在共混比ＬＤＰＥ／ＣＰＥ＞５０／５０时，导电性能随ＣＰＥ含量增加而显著提高，这主要是由于炭黑粒子在ＬＤＰＥ和ＣＰＥ两组分分中的分布不均匀性所致。     

Effect of PPO‐g‐MA on structures and properties of PPO/PA6/short glass fiber composites

Poly(2,6‐dimethyl‐1,4‐phenylene oxide)/polyamide 6 (PPO/PA6) blends were reactively compatibilized by maleic anhydride (MA) grafted PPO (PPO‐g‐MA) and reinforced by short glass fibers (SGF) via melt extrusion. An observation of the SGF‐polymer interface by scanning electronic microscope (SEM) together with etching techniques indicated that the PPO‐g‐MA played a decisive role in the adhesion of polymers to SGF. The rheological behavior was investigated by capillary rheometer, and the addition of PPO‐g‐MA, and SGF could increase the viscosity of the PPO/PA6 blends. The analysis of fiber orientation and distribution in the PPO/PA6/SGF composites showed PPO‐g‐MA favored to the random dispersion of SGF. The statistic analysis of SGF length showed that PPO‐g‐MA was helpful to maintain the fiber length during melt‐processing. For the composites at a given SGF content of 30 wt %, the addition of PPO‐g‐MA increased the tensile strength from 59.4 MPa to 97.1 MPa and increased SGF efficiency factor from 0.028 to 0.132. The experimental data were consistent with the theoretical predictions of the extension of Kelly‐Tyson model for tensile strength. The fracture toughness of the composites was investigated by single edge notch three‐point bending test. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 2188–2197, 2009