Effects of graphene nanosheets on the dielectric,mechanical, thermal properties,and rheological behaviors of poly(arylene ether nitriles)

Poly(arylene ether nitriles) (PEN) containing various contents of graphene nanosheets (GNs) was prepared via solution‐casting method and investigated for their dielectric, mechanical, thermal, and rheological properties. For PEN/GNs nanocomposite with 5 wt % GNs, the dielectric constant was increased to 9.0 compared with that of neat PEN (3.1) and dielectric losses of all nanocomposites were in the range of 0.019–0.023 at 1 kHz. The tensile modulus and strength were increased about 6 and 14% with 0.5% GNs, respectively. The fracture surfaces of the all PEN/GNs nanocomposites revealed that GNs had good adhesion to PEN matrix. The thermal properties of the nanocomposites showed significant increase with increasing GN loading. For 5 wt % GNs‐reinforced PEN nanocomposite, the temperatures corresponding to a weight loss of 5 wt % (T_d5%) and 30 wt % (T_d30%) increased by about 20 and 13°C, respectively. Rheological properties of the PEN nanocomposites showed a sudden change with the GN fraction and the percolation threshold was about 1 wt % of GNs. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

EP/GNs/MWCNTs复合材料的导热性能

以多壁碳纳米管(MWCNTs)和石墨烯纳米微片(GNs)为导热填料,环氧树脂(EP)为基体采用溶剂和超声分散法,制备了EP/GNs/MWCNTs导热复合材料,并与EP/MWCNTs及EP/GNs复合材料的导热性能进行了对比。采用透射电子显微镜观察其微观结构,采用Hot Disk热导率测试仪测试其导热性能,采用差示扫描量热法和热重分析仪测试其耐热性及热稳定性。结果表明,MWCNTs和GNs共同作为EP导热填料时,相比于单组分填料(MWCNTs或GNs)更易形成导热网络;EP的热导率、玻璃化转变温度(Tg)和热分解温度均随着MWCNTs或GNs含量的增加而提高,其中,GNs更有利于提高EP的热导率和热分解温度,MWCNTs更有利于提高EP的Tg。在相同的导热填料含量下,相对于其中的任一单一填料,MWCNTs/GNs共同作用时,对热导率的提高有更显著的效果,且随着其中GNs比例的增加,热导率逐渐增大。当GNs和MWCNTs的体积分数分别为0.6%和0.4%时,EP/GNs/MWCNTs复合材料的热导率、Tg和起始分解温度分别为0.565 W/(m·K),152℃和316℃,分别比纯EP提高了132.5%,34.5%和8.2%。     

Mechanical,thermal, and rheological properties of graphene‐based polypropylene nanocomposites prepared by melt mixing

In this article, we describe the fabrication by melt mixing of graphene‐polypropylene nanocomposites and present the effect of graphene addition on some selected properties of polypropylene (PP). The graphene nanosheets (GNs) used as nano‐reinforcing agents were obtained through chemical reduction of graphene oxide by hydrazine hydrate. GNs were characterized and successfully dispersed into PP matrix to produce PP/GNs nanocomposites. The effects of GNs content on thermal, mechanical, and rheological properties were reported, and the obtained results were discussed in terms of morphology and state of dispersion and distribution of the GNs within the polymer matrix. Characterization by scanning electron microscopy and X‐ray diffraction of the nanocomposites has shown a relatively good dispersion of GNs in the polymer matrix, with the presence of only few aggregates. Increasing GNs content resulted in a significant increase in both mechanical and thermal properties with only few percent of GNs loading. Rheological behavior of the PP/GNs nanocomposites showed a Maxwellian‐like behavior for low GNs concentrations and a viscoelastic solid‐like behavior for GNs content exceeding the concentration of the percolation threshold. POLYM. COMPOS., 2012. © 2012 Society of Plastics Engineers     

Preparation and characterization of maleated polylactide-functionalized graphite oxide nanocomposites

Organically dispersible graphene nanosheets were fabricated by amine surfactant intercalated graphite oxide (GOAs) with ultrasonication below room temperature. Subsequently, GOAs filled nanocomposites of polylactide grafted with maleic anhydride (PLAgMA) were prepared directly by solution blending. The compatibilization effects provided by the functionalization of both constituents and their influence on the structure and properties of the final nanocomposites in different compositions were investigated. The interactions and structural morphology of the nanocomposites were examined by Fourier transform infrared spectroscopy, X-ray diffraction, scanning and transmission electron microscopy. Thermal, dynamic-mechanical and conductive properties of these nanocomposites were investigated as a function of GOAs content. The detailed morphological and X-ray diffraction results revealed that the degree of GOAs dispersion enhanced with maleated PLA. Study of the dynamic-mechanical properties showed that both the storage modulus G’ and the loss modulus G” are very sensitive to the microstructure of the nanocomposite. The thermal properties of the nanocomposites were significantly influenced by the GOAs content due to the shielding and nucleating effect of exfoliated layers. Both the thermal and electrical conductivities showed substantial improvements with increasing GOAs content. The overall results pointed to the compatibilization synergy of GO functionalization and PLA maleation.     

Thermal‐Insulation,Electrical, and Mechanical Properties of Highly‐Expanded PMMA/MWCNT Nanocomposite Foams Fabricated by Supercritical CO2 Foaming

Foaming behavior of poly(methyl methacrylate) (PMMA)/multi‐walled carbon nanotubes (MWCNTs) nanocomposites and thermally‐insulating, electrical, and mechanical properties of the nanocomposite foams are investigated. PMMA/MWCNT nanocomposites containing various amounts of MWCNTs are first prepared by combining solution and melt blending methods, and then foamed using CO₂. The foaming temperature and MWCNT content are varied for regulating the structure of PMMA/MWCNT nanocomposite foams. The electrical conductivity measurement results show that MWCNTs have little effect on the electrical conductivity of foams with large expansion ratio. Thermal conductivities of both solid and foamed PMMA/MWCNT nanocomposites are measured to evaluate their thermally insulating properties. The gas conduction, solid conduction, and thermal radiation of the foams are calculated for clarifying the effects of cellular structure and MWCNT content on thermal insulation properties. The result demonstrates that MWCNTs endowed foams with enhanced thermal insulation performance by blocking thermal radiation. Moreover, the compressive testing shows that MWCNTs improve the compressive strength and rigidity of foams. This research is essential for optimizing environmentally friendly thermal insulation nanocomposite foams with enhanced thermal‐insulation and compressive mechanical properties.     

Preparation and properties of polyurethane/multiwalled carbon nanotube nanocomposites by a spray drying process

A spray drying approach has been used to prepare polyurethane/multiwalled carbon nanotube (PU/MWCNT) composites. By using this method, the MWCNTs can be dispersed homogeneously in the PU matrix in an attempt to improve the mechanical properties of the nanocomposites. The morphology of the resulting PU/MWCNT composites was investigated by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). SEM and TEM observations illustrate that the MWCNTs are dispersed finely and uniformly in the PU matrix. X‐ray diffraction results indicate that the microphase separation structure of the PU is slightly affected by the presence of the MWCNTs. The mechanical properties such as tensile strength, tensile modulus, elongation at break, and hardness of the nanocomposites were studied. The electrical and the thermal conductivity of the nanocomposites were also evaluated. The results show that both the electrical and the thermal conductivity increase with the increase of MWCNT loading. In addition, the percolation threshold value of the PU composites is significantly reduced to about 5 wt % because of the high aspect ratio of carbon nanotubes and exclusive effect of latex particles of PU emulsion in dispersion. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Multiwalled carbon nanotubes‐reinforced isotactic polypropylene nanocomposites: Enhancement of crystallization and mechanical,thermal, and electrical properties

Multiwalled carbon nanotubes (MWCNTs)‐reinforced isotactic polypropylene (iPP) nanocomposites with low‐content of MWCNTs were fabricated using the melt‐cast techniques. The reinforced plastics were characterized by X‐ray diffraction (XRD) measurements, scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectroscopy, mechanical test, differential thermal analyses (DTA), and electrical tests. XRD studies exhibit the α‐crystal in the injection‐molded neat iPP with lamellar stacks having a long period of 150Å. Both the intensity of lamellar reflection and the thickness of long period increase with increasing the MWCNTs contents, indicating an enhancement of iPP crystallization by MWCNTs addition. This increase of lamellar thickness is analyzed to be consistent with that evaluated by DTA. SEM micrographs display larger MWCNTs aggregates with increasing amount of reinforcements and show a good adhesion between nanoparticles and iPP matrix. FTIR spectra reveal distinct chemical textures for the samples and confirm the existence of α‐crystal. Mechanical strengths, electrical conductivity, and dielectric constants are found to increase with increasing MWCNTs content, representing an improved performance of the nanocomposites. POLYM. COMPOS., 2012. © 2012 Society of Plastics Engineers     

Influence of graphite nanosheets on the structure and properties of PVC‐based nanocomposites

Polyvinyl chloride‐ (PVC)‐ based nanocomposites, containing graphite nanosheets (G), which may be used as electromagnetic wave absorbers was developed and investigated. The microstructure of polyvinyl chloride/graphite nanocomposites (PVC/G) were examined by means of X ‐ray diffraction, scanning electron microscopy (SEM), and thermal gravimetric analyses (TGA). SEM image reveals that the graphite nanosheets were well dispersed in the PVC matrix without agglomeration. Thermal stability of the PVC/G nanocomposites is improved as a result of inclusion of graphite nanosheets. The PVC/G nanocomposites were characterized to investigate the effect of dispersion of graphite nanosheets in PVC matrix. The dielectric spectroscopy of PVC/G nanocomposites in frequency range from 1 to 12 GHz has been performed. The results show that PVC/G nanocomposites exhibit high dielectric constant at the measured frequencies. Coefficient of attenuation and coefficient of reflection of PVC/G composites have been also examined in a frequency range from 1 to 12 GHz. The electromagnetic interference shielding effectiveness (EMI) depends on graphite volume fraction in the composite. The results show that the PVC/G represents a new class of conducting lightweight nanomaterial that can absorb electromagnetic waves at microwave frequency and may be promising for future commercial use. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Graphene/polypyrrole nanocomposites with high negative permittivity and low dielectric loss tangent

Graphene (GNs)/ polypyrrole (PPy) nanocomposites with different content of GNs prepared by in-situ polymerization possess negative permittivity in the range of test frequency. Importantly, the GNs/PPy nanocomposites also have low dielectric loss tangent. ATR and XRD tests showed that no significant change in chemical bond and crystallization is found in GNs/PPy nanocomposites. SEM analysis indicated that GNs/PPy nanocomposites form different morphologies with the increase of GNs content. The negative permittivity of GNs/PPy nanocomposites is mainly caused by the plasmon resonance of the free electrons. The variation of resistivity and negative permittivity are basically consistent, which reflects that the good conductivity of the nanocomposites is attribute to the plasmon resonance of free electrons. The moderate addition of GNs is beneficial to the development of permittivity to a great negative value and decrease the dielectric loss tangent. The negative permittivity is up to ?1.226?×?10⁵ and the dielectric loss tangent is reduce to 0.32 in GNs/PPy nanocomposites with 10?wt% GNs content. The negative permittivity and the low dielectric loss tangent in GNs/PPy nanocomposites is achieved in a wider frequency range 1–1000?MHz.     

Influence of nanoclays on electrical and morphological properties of thermoplastic polyurethane/multiwalled carbon nanotube/clay nanocomposites

Nanocomposites of thermoplastic polyurethanes (TPUs), multiwalled carbon nanotubes (MWCNTs) and clays were prepared via melt processing using polyether‐ and polyester‐based TPUs, MWCNTs, and organically modified nanoclays (Cloisite C30B and C25A). Coaddition of clays and MWCNTs to TPU nanocomposites increased their electrical conductivities above those without any clay. Nanoclay alone is shown to produce no effect on electrical conductivity. TEM results show that the coaddition of nanoclay affects the nanocomposite morphology by changing the MWCNT distribution. Clay C25A and MWCNTs were observed to form network structures in the nanocomposites, resulting in improved electrical conduction. Interaction between MWCNTs and clays as well as an increase in nanocomposite viscosity caused by the coaddition of clays may influence the morphology change. Most of the nanocomposites containing both MWCNTs and clay exhibited higher dielectric constants, indicating higher electrical conductivities. Tensile properties investigations confirmed the reinforcing effects of the MWCNTs and clays. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Cellulose acetate/multiwalled carbon nanotube nanocomposites with improved mechanical,thermal, and electrical properties

Cellulose acetate (CA)‐based nanocomposites with various contents of neat multiwalled carbon nanotube (MWCNT) or acid‐treated one (MWCNT‐COOH) are prepared via melt‐compounding method and investigated their morphology, thermal stability, mechanical, and electrical properties. SEM microphotographs reveal that MWCNT‐COOHs are dispersed uniformly in the CA matrix, compared with neat MWCNTs. FTIR spectra support that there exists a specific interaction between carboxyl groups of MWCNT‐COOHs and ester groups of CA, indicating good interfacial adhesion between MWCNT‐COOHs and CA matrix. Accordingly, thermal stability and dynamic mechanical properties of CA/MWCNT‐COOH nanocomposites were higher than those of CA/MWCNT composites. On the contrary, electrical volume resistivities of CA/MWCNT‐COOH nanocomposites are found to be somewhat higher than those of CA/MWCNT composites, which is because of the deterioration of graphene structures for MWCNT‐COOHs and the good dispersion of MWCNT‐COOHs in the CA matrix. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Dramatic improvement in mechanical properties of GNs‐reinforced HDPE nanocomposites

Graphite nanosheets (GNs) modified with sodium dodecyl benzene sulfonate (SDBS) was prepared and then incorporated into high‐density polyethylene (HDPE). The GNs/HDPE nanocomposites displayed pronounced enhancements of the mechanical properties. With a load of 10 wt % of the modified GNs, the nanocomposites exhibited an increase of about 290% in the elongation at break as well as an increase of about 14% in the elastic modulus in comparison with neat HDPE. Scanning electron microscopy (SEM) shows a notable microscopic orientation of the matrix and GNs in the strained nanocomposite specimen, which may play an important role in the dramatic increase in the elongation at break. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Physical properties of phenol-anchored multiwall carbon nanotube/epoxy nanocomposite

Surface functionalization of multiwall carbon nanotubes (MWCNTs) was carried out by introducing a ylide group containing anchored phenol structures. Epoxy nanocomposites filled with modified and pristine carbon nanotubes were prepared, and their mechanical, electrical, and thermal properties were evaluated. Mechanical properties such as tensile strengths and Young’s moduli of the epoxy nanocomposites increased significantly with the addition of the modified MWCNTs compared to the pristine MWCNTs, due to the strong interaction between the modified MWCNTs and the epoxy matrix. Scanning electron microscopy of the fractured epoxy systems revealed that the functionalized MWCNTs were finely dispersed in the matrix, as opposed to the pristine carbon nanotubes. The epoxy/functionalized MWCNT nanocomposite had a lower surface electrical resistance than the epoxy/pristine MWCNT nanocomposite, confirming the effect of functionalization.     

Preparation and characterization of melt‐blended graphene nanosheets–poly(vinylidene fluoride) nanocomposites with enhanced properties

Nanocomposites of poly(vinylidene fluoride) (PVDF) with chemically reduced graphene nanosheets (GNs) were prepared by melt mixing method and their structure and morphology characterized by SEM analysis. The addition of GNs in the PVDF matrix resulted in changes of the crystallization and melting behaviors. Furthermore, increasing GNs content led to improved thermal stability of the PVDF nanocomposites in air and nitrogen, as well as significant increase in tensile and flexural properties. The nanocomposites' rheological behavior is also affected by the GNs' content. Using oscillatory rheology to monitor the GNs' dispersion, it was found that as the GNs loading increase, the Newtonian behavior disappears at low frequency. This suggests a viscoelastic behavior transition from liquid‐like to solid‐like, with greater GNs content and more homogeneous dispersion resulting in a stronger solid‐like and nonterminal behavior. By using the melt mixing method to disperse GNs, the properties of PVDF are enhanced due to the better dispersion and distribution of GNs throughout the matrix. This improvement could broaden the applications for PVDF nanocomposites. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Polylactide/Polyethylene/Organoclay Blend Nanocomposites: Structure,Mechanical and Thermal Properties

Structure and physical properties of PLA/PE/organoclay with and without compatibilizer (PE-g-MA) with PLA as a matrix phase were investigated by X-ray diffraction, transmission electron microscopy, rheometric mechanical spectrometer, thermal gravimetric analysis, dynamic mechanical thermal analysis and Mechanical experiments. Two types of compatibilized-blend nanocomposites were prepared by two feeding orders: (1) simultaneous feeding, (2) PLA/organoclay-based master batch. The XRD results showed an intercalated structure for nanocomposites. The mechanical results demonstrated that presence of PE and compatibilizer improved the elongation at break, while organoclay enhanced Young's modulus. Thermogravimetric analysis showed that organoclays could retard the thermal decomposition process in the nanocomposites.     

熔融插层法制备聚乳酸/有机蒙脱土纳米复合材料及其性能研究

以新疆地产蒙脱土和聚乳酸为原料,通过熔融插层的方法制备了聚乳酸(PLA)/有机蒙脱土（OMMT）纳米复合材料。分别采用X射线衍射仪、扫描电子显微镜、透射电子显微镜、热重分析仪等对复合材料的微观结构、形貌及热稳定性进行了表征和分析。研究表明,PLA大分子链已经插入OMMT片层间,层间距明显增大,形成PLA/OMMT纳米复合材料,体系的相容性良好。PLA/OMMT纳米复合材料的热失重曲线移向高温端,其热分解温度提高。PLA/OMMT纳米复合材料的熔点、维卡软化点、冲击强度、拉伸强度、热稳定性均比PLA基体有明显的提高。PLA/OMMT纳米复合材料的降解性初步研究表明其是一种良好的生物可降解环保塑料。     

Study on the structure and properties of Poly(methylmethacrylate)/Polypyrrole-Graphene Oxide nanocomposites

In this paper Poly(methylmethacrylate)/Polypyrrole-Graphene Oxide (PMMA/PPy-GO) nanocomposites were prepared using in-situ chemical polymerization method and its structure and properties were studied. Fourier transform infrared (FTIR), X-ray diffraction (XRD), Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM) analysis confirmed that PPy nanopraticles covered the GO nanosheets surface and PMMA/PPy-GO nanocomposite were prepared successfully. The mechanical, electrical and thermal stability of the PMMA nanocomposites were also investigated using Tensile, Impact, Thermogravimetric analysis (TGA) and four-point probe methods. Correlation between direct morphological observation and final properties demonstrated that network structure formed by PPy-GOs in PMMA matrix. Tensile analysis showed that the addition of 0.4 wt % PPy-GO hybrids lead to 24.4 % enhancement in the Young’s modulus of PMMA compared to 5.0 % improvement that achieved at the same loading level of GO. Electrical conductivity measurement showed that dispersion of PPy-GO in PMMA matrix increased AC conductivity in the range of 8 orders of magnitude compared to PMMA. TGA analysis showed that the thermal stability of the PMMA nanocomposites improved over 20 ?C.     

Mechanical,thermal, and dielectric properties of poly(lactic acid)/chitosan nanocomposites

Poly(lactic acid) (PLA) loaded with various levels of chitosan nanoparticles (CsNP) (0–5.0%) were prepared by twin‐screw extrusion. The nanocomposites were investigated based on their morphology, thermal, mechanical and dielectric properties. The SEM morphology showed that CsNP was dispersed uniformly in the PLA matrix. Thermal analysis through DSC revealed that the cold crystallization temperature of PLA in the case of nanocomposites slightly decreased with increasing content of CsNP; indicating a limit nucleating effect of CsNP. TGA analysis revealed that the incorporation CsNP slightly decreased the thermal stability of the PLA matrix. The mechanical analysis indicated that the incorporation of the CsNP in the PLA matrix improved the elongation and the impact strength, but decreased the tensile strength. The dielectric properties of these materials have been investigated for the α‐relaxation process as a function of the temperature and frequency. The α‐relaxation process was analyzed with Vogel–Fulcher–Tamman and Havriliak–Negami models and fitting parameters and their evolution were obtained. POLYM. ENG. SCI. 56:987–994, 2016. © 2016 Society of Plastics Engineers     

Mechanical,thermal and electrical properties of multi‐walled carbon nanotube/aluminium nitride/polyetherimide nanocomposites

A series of polyimide‐based nanocomposites containing polyimide‐grafted multi‐walled carbon nanotubes (PI‐g MWCNTs) and silane‐modified ceramic (aluminium nitride (AlN)) were prepared. The mechanical, thermal and electrical properties of hybrid PI‐g MWCNT/AlN/polyetherimide nanocomposites were investigated. After polyimide grafting modification, the PI‐g MWCNTs showed good dispersion and wettability in the polyetherimide matrix and imparted excellent mechanical, electrical and thermal properties. The utilization of the hybrid filler was found to be effective in increasing the thermal conductivity of the composites due to the enhanced connectivity due to the high‐aspect‐ratio MWCNT filler. The use of spherical AlN filler and PI‐g MWCNT filler resulted in composite materials with enhanced thermal conductivity and low coefficient of thermal expansion. Results indicated that the hybrid PI‐g MWCNT and AlN fillers incorporated into the polyetherimide matrix enhanced significantly the thermal stability, thermal conductivity and mechanical properties of the matrix. Copyright © 2012 Society of Chemical Industry     

Thermophysical properties of foliated graphite/nickel reinforced polyvinyl chloride nanocomposites

A novel, polymer‐based foliated graphite/nickel nanocomposites with high thermal conductivity, mechanical properties, and low dielectric constant was developed. The network structure of polyvinyl chloride (PVC) reinforced foliate graphite and nickel nanoparticles (GN) were tested in terms of X‐ray diffraction (XRD), scanning electron microscope (SEM), energy dispersive x‐ray analysis (EDX), and thermal‐gravimetric analyses (TGA). Thermogravimetric analysis revealed a large improvement in the thermal stability of PVC/GN nanocomposites. Thermal conductivity and diffusivity of the composites increased with increasing GN content and temperature. The obtained experimental thermal conductivity result are compared with the existing theoretical models. The measured values of thermal conductivity were in excellent agreement with those calculated from the Agari model. In addition, specific heat, coefficient of thermal expansion (TEC), micro porosity, and crosslinking density (CLD) of composites were investigated. The mechanical properties such as tensile strength, tensile modulus, hardness, and elongation at break of the nanocomposites were improved with inclusion GN which is proportional to GN content. Finally, the dielectric properties of PVC/GN nanocomposites as a function of frequency have been investigated in details. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012