Preparation,structure, and property of polyoxymethylene/carbon nanotubes thermal conducive composites

Polyoxymethylene (POM)/multiwalled carbon nanotubes (MWNTs) nanocomposites were prepared through a simple solution‐evaporation method assisted by ultrasonic irradiation. To enhance the dispersion of MWNTs in POM, MWNTs were chemically functionalized with PEG‐substituted amine (MWNT‐g‐PEG), which exhibited strong affinity with POM due to their similar molecular structure. The thermal conductivity and the mechanical properties of the composites were investigated, which showed that the thermal conductive properties of POM were improved remarkably in the presence of MWNTs, whereas reduced by using MWNT‐g‐PEG due to the heat transport barrier of the grafted‐PEG‐substituted amine chain. A nonlinear increase of the thermal conductivity was observed with increasing MWNTs content, and the Maxwell‐Eucken model and the Agari model were used for theoretical evaluation. The relatively high effective length factor of the composite predicted with mixture equation indicated that there were few entangles of MWNTs for the samples of MWNT‐g‐PEG in the composites. The mechanical strength of the composites can be improved remarkably by using suitable content of such functionalized MWNTs, and with the increase of the aliphatic chain length of PEG‐substituted amine, the toughness of the composites can be enhanced. Transmission electron microscope result indicated that MWNT‐g‐PEG exhibited strong affinity with POM and a good dispersion of MWNTs was achieved in POM matrix. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 905–912, 2010     

注塑温度对POM/TPU共混物分散相及力学性能的影响

研究了注塑温度对聚甲醛(POM)/热塑性聚氨酯弹性体(TPU)共混物形态结构和力学性能的影响.实验结果表明,注塑温度影响POM基体相与TPU分散相的粘度比,195℃时两者粘度相当,在剪切流动过程中,TPU可在POM基体中形成条状分散相,可吸收较多的冲击能并阻止银纹的生长以及裂纹的产生,从而较大幅度提高共混物的缺口冲击强度.     

Effect of ionomers on mechanical properties, morphology, and rheology of polyoxymethylene and its blends with methyl methacrylate-styrene-butadiene copolymer

Two ionomers, ethylene-methacrylic acid copolymer ionized with sodium cation (EMA-Na) and zinc cation (EMA-Zn), were employed as impact modifiers to prepare blends with polyoxymethylene (POM) via a melt extrusion. A copolymer of methyl methacrylate-styrene-butadiene (MBS) used as a co-impact modifier was also incorporated into the blends. The mechanical properties, thermal properties, morphology, and rheology were studied. A moderate toughening was observed for POM/ionomer binary blends, which was attributable to the rubbery natural and good adhesion of the ionomers. EMA-Zn exhibited a much better toughening effect than EMA-Na because of its higher elasticity and stronger interaction with POM. The incorporation of the ionomers into POM/MBS blends resulted in an improvement of mechanical properties, which was attributable to the compatibilizing effect of ionomer on POM/MBS blending system. The observation of scanning electron microscopy demonstrated that the finer phase domains were caused by incorporation of ionomers, which, acting as a compatibilizer as well as an impact modifier, reduced the interfacial tension and improved the interfacial adhesion between the phases. Differential scanning calorimetry investigation indicated that the presence of ionomer in the blends disturbed the crystallization of POM and resulted in a decrease in the crystallinity of POM. The evaluation of melt flow index revealed an increase in viscosity of the blends by incorporation of the ionomers, which was caused the ionic interaction between POM and the ionomers.     

Electrical and melt rheological characterization of PC and co‐continuous PC/SAN blends filled with CNTs: Relationship between melt‐mixing parameters,filler dispersion,and filler aspect ratio

Electrical and melt rheological properties of melt‐mixed polycarbonate (PC) and co‐continuous PC/poly(styrene–acrylonitrile) (SAN) blends with carbon nanotubes (CNTs) are investigated. Using two sets of mixing parameters, different states of filler dispersion are obtained. With increasing CNT dispersion, an increase in electrical resistivity near the percolation threshold of PC–CNT composites and (PC + CNT)/SAN blends is observed. This suggests that the higher mixing energies required for better dispersion also result in a more severe reduction of the CNT aspect ratio; this effect was proven by CNT length measurements. Melt rheological studies show higher reinforcing effects for composites with worse dispersion. The Eilers equation, describing the melt viscosity as function of filler content, was used to fit the data and to obtain information about an apparent aspect ratio change, which was in accordance with measured CNT length reduction. Such fitting could be also transferred to the blends and serves for a qualitatively based discussion. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2018 , 56, 79–88     

Preparation and properties of natural rubber composites reinforced with pretreated carbon nanotubes

In order to achieve dramatic improvements in the performance of rubber materials, the development of carbon nanotube (CNT)‐reinforced rubber composites was attempted. The CNT/natural rubber (NR) nanocomposite was prepared through solvent mixing on the basis of pretreatment of CNTs. Thermal properties, vulcanization characteristics, and physical and mechanical properties of the CNT/NR nanocomposites were characterized in contrast to the carbon black (CB)/NR composite. Through the addition of the CNTs treated using acid bath followed by ball milling with HRH (hydrated silica, resorcinol, and hexamethylene tetramine) bonding systems, the crystallization melting peak in differential scanning calorimetry (DSC) curves of NR weakened and the curing rate of NR slightly decreased. Meanwhile, the over‐curing reversion of CNT/NR nanocomposites was alleviated. The dispersion of the treated CNTs in the rubber matrix and interfacial bonding between them were rather good. The mechanical properties of the CNT‐reinforced NR showed a considerable increase compared to the neat NR and traditional CB/NR composite. At the same time, the CNT/NR nanocomposites exhibited better rebound resilience and dynamic compression properties. The storage modulus of the CNT/NR nanocomposites greatly exceeds that of neat NR and CB/NR composites under all temperature regions. The thermal stability of NR was also obviously improved with the addition of the treated CNTs. Copyright © 2008 John Wiley & Sons, Ltd.     

Polypropylene/carbon nanotube magnetic composites obtained using carbon nanotubes from sawdust

Magnetic polypropylene (PP) nanocomposites with different loadings (from 0.5 to 20 wt %) of carbon nanotubes with iron (CNT‐Fe) were fabricated using the melt‐mixing method. The carbon nanotubes were synthesized by pyrolysis of sawdust from the furniture industry. The morphological characterization shows homogenous dispersion of the filler in the polymer matrix. The addition of only 0.5 wt % CNT‐Fe already results in ferromagnetic behavior in the diamagnetic polymer matrix. The thermal properties were investigated using thermogravimetric analysis and differential scanning calorimetry. The results show an increase in the maximum degradation, crystallization, and melting temperatures of the nanocomposites compared with neat PP. The nanocomposites showed improvement in terms of mechanical and oxygen permeability properties. A very significant result of the work is the high remnant magnetization and coercivity values of the nanocomposites at room temperature whereas most of the works on similar systems show magnetic properties only at very low temperatures.     

Dispersion of multiwalled carbon nanotubes in a rubber matrix using an internal mixer: Effects on rheological and electrical properties

The dispersion of multiwalled carbon nanotubes (CNTs) in an ethylene propylene rubber matrix was investigated using an internal mixer. Poly(ethylene‐co‐polyvinyl acetate) (EVA) statistic copolymer was used as a dispersing agent. The effects of the concentration of the dispersing agent and the matrix viscosity on the quality of the dispersion of 1 wt % of CNTs were studied by using microscopy and rheology in the melt state. It was demonstrated that the dispersion is governed principally by the viscosity of the matrix. As expected, better dispersion was observed when the matrix exhibited a lower viscosity. The influence of the filler content on the rheological and electrical properties is presented. A Cross model with a yield stress is proposed to describe the rheological behavior of these materials, which exhibit a viscoelastic solid behavior from 1 wt % CNT content. Electrical measurement data indicate that the electrical percolation threshold was 2.9 wt %. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 49: 1597–1604, 2011     

Effect of Oil Palm and Jute Fiber Treatment on Mechanical Performance of Epoxy Hybrid Composites

In this work, oil palm empty fruit bunch (EFB) and jute fibers were treated with 2-hydroxy ethyl acrylate (2-HEA) to improve interfacial bonding of oil palm EFB and jute fibers with epoxy matrix. Hybrid composites were fabricated by incorporation of modified oil palm EFB and jute fibers into an epoxy matrix by the hand lay-up technique. Mechanical (flexural and impact) and morphological properties of modified hybrid composites were measured. Results indicated that flexural and impact properties of modified fiber–reinforced hybrid composites improved as compared to untreated hybrid composites due to better fiber/matrix interfacial bonding, which was confirmed by scanning electron microscopy. We confirmed that treated oil palm/jute hybrid composite may be fabricated by advanced techniques such as resin transfer molding, extrusion, and injection molding for industrial applications in the automotive sector.     

Mechanical,thermal, and morphological properties of powder coating waste reinforced acetal copolymer

The present study investigates the individual effects of three different thermosetting waste materials, used as fillers, on the mechanical, thermal and flow properties of acetal copolymers (POM). Different amounts ranging from 5% to 30% by weight of hydrolyzed powder coating recyclates were mixed as filler material in POM. The matrix and the fillers were first dry-mixed and then compounds were prepared through melt extrusion. The resulting compounds were cooled, granulated, and then standard tensile test bars were produced through use of an injection-molding machine. We investigated the mechanical and thermal properties of test specimens, and tensile strength, bending strength and impact strength were evaluated as a function of type and amount of filler material in the POM matrix. In addition, the change in melt flow index of POM/filler mixtures was determined, before and after extrusion. Furthermore, the morphology of the specimens was examined via electron microscopy. The results of this investigation are encouraging and present an innovative approach to reutilize hydrolyzed electrostatic powder coating wastes with thermoset structures as fillers in acetal copolymers.     

EFFECT OF PROCESSING METHOD ON THE IMPACT STRENGTH OF POM/TPU/CaCO3 TERNARY COMPOSITES

Polyoxymethylene （POM）/elastomer/filler ternary composites were prepared, in which thermoplastic polyurethane （TPU） and inorganic filler, namely, CaCO3, were used to achieve balanced mechanical properties of POM. The dispersion and phase morphology of POM/elastomer/filler composites were found to depend largely on processing method, CaCO3 content in masterbatch and the filler size. Two processing methods were employed to prepare POM/elastomer/filler ternary composites. One is called the one-step method, in which elastomer and the filler directly melt blended with POM matrix. The other is called the two-step method, in which the elastomer and the filler were mixed to get masterbatch first, which was then melt blended with pure POM of different content. The effect of phase morphology and processing method on impact strength was investigated. It was found that the two-step method results in an increase in impact strength but not for the one-step method. Additionally, the impact strength of POM ternary composites decreases with the increase in the size of CaCO3 particles.     

Poly(lactic acid)/poly(butylene succinate)/calcium sulfate whiskers biodegradable blends prepared by vane extruder: Analysis of mechanical properties,morphology, and crystallization behavior

Ternary blends of PLA/PBS/CSW with different weight fractions were prepared using a vane extruder. The mechanical properties, morphology, crystallization behavior and thermal stability of the blends were investigated. For the PLA/CSW blend, the tensile strength decreased, the flexural strength and modulus increased compared with pure PLA. For PBS, the addition of CSW had little influence on the mechanical properties. For the ternary blends PLA/PBS/CSW, the tensile strength, flexural strength and modulus decreased compared with pure PLA, while the elongation at break and the impact strength increased significantly. The brittle-ductile transition of the blends took place when the PBS weight fraction reaching 30 wt%. As a soft component in the blends, PBS was beneficial to improve the tensile ductility and the toughness of PLA. SEM measurements reveal that PLA/PBS/CSW blends were immiscible. When the weight fraction of PBS was 50 wt%, significant phase separation was observed, and CSW had preferential location in the PBS phase of the blend. DSC measurement and POM observation reveal that CSW had a heterogeneous nucleation effect on PLA and PBS matrix. The addition of PBS improved the crystallization of PLA and the thermal resistance of the PLA/PBS/CSW blends significantly.     

Mechanical and thermal properties of epoxy/silicon carbide nanofiber composites

The silicon carbide (SiC) nanofibers (0.1, 0.25, and 0.5 phr), produced by self‐propagating high‐temperature synthesis (SHS), are used to reinforce the epoxy matrix cured with an anhydride hardener. Morphological studies reveal a better dispersion of SiC nanofibers and a good level of adhesion between nanofiber and the matrix in composites with lower (0.1 and 0.25 phr) nanofiber loading. The flexural studies show that a maximum increase in flexural properties is obtained for composites with 0.25 phr SiC nanofiber. The fracture toughness of epoxy is found to increase with the incorporation of SiC nanofibers, and 0.25 phr SiC nanofiber loading shows maximum fracture toughness value. The possible fracture mechanisms that exist in epoxy/SiC nanofiber composites have been investigated in detail. Thermogravimetric analysis reveals that SiC nanofibers are effective fillers to improve the thermal stability of epoxy matrix. Copyright © 2014 John Wiley & Sons, Ltd.     

Evaluating the effect of addition of nanodiamond on the synergistic effect of graphene-carbon nanotube hybrid on the mechanical properties of epoxy based composites

Addition of carbon nanotubes (CNT) to Graphene (Gr) is seen to have synergistic effect as reinforcement to polymer matrix. This is possible as CNTs inhibit stacking of Gr sheets, thus providing larger surface area nanophase to get bonded with polymer matrix and providing mechanical support through load sharing and crack growth inhibition. However, tube like morphology and high aspect ratio of CNT often lead to entanglement, which restricts their effect in exfoliating Gr. The aim of the present study is to investigate the potential of ND in improving the synergistic effect of Gr-CNT hybrid as a reinforcement to epoxy matrix. This study utilizes the power of ultrasonication technique, which is very simple and scalable, for dispersing and incorporating nanofillers into epoxy matrix. Addition of ND to Gr-CNT epoxy composite improved the tensile strength from ~46% with 0.5 wt% (75Gr:25ND) to ~51% with 0.8 wt% (25Gr:25CNT:50ND) as compared to neat epoxy. While the fracture toughness improved from ~140% with 0.5 wt% (25Gr:75CNT) to 165% with 0.8 wt% (25Gr:50CNT:25ND). Fractured surfaces of composites revealed improved dispersion and strong interfacial interaction with addition of ND to Gr-CNT hybrid. NDs attaches to the surface of Gr inhibit the stacking of Gr sheets by restricting π-π stabilization. NDs also help in bridging the ends of CNTs together into long chains, thereby increasing the aspect ratio of the fiber like reinforcement. This increases the total available surface area of CNTs and Gr, to interact with epoxy matrix, improves the overall efficiency of Gr-CNT hybrid as a reinforcement, resulting into improvement in mechanical properties of the composite structure.     

Synthesis,characterization, processability,mechanical properties,flame retardant,and oil resistance of chlorinated acrylonitrile butadiene rubber

Novel chlorinated acrylonitrile butadiene rubber (Cl‐NBR) was prepared from NBR by the alkaline hydrolysis of chloroform by using phase‐transfer catalysis. The formation of Cl‐NBR was monitored by ¹H‐NMR, UV‐Vis, and Fourier transform infrared spectroscopic techniques. The percentage of chlorine attached to the rubber chain was estimated by Volhard method. The effect of polar groups on the structural and thermal properties of Cl‐NBR was analyzed by scanning electron microscopy, X‐ray diffraction analysis, differential scanning calorimetry, and thermogravimetric analysis studies. The flame retardant, oil resistance, cure behavior, and mechanical properties of chlorinated elastomer were also analyzed. The proton NMR revealed the attachment of chlorine in the backbone of NBR with new chemical shift values. The C‐Cl stretching of chlorinated NBR was confirmed from Fourier transform infrared. The UV spectrum also supported the formation of chlorinated unit in the NBR chain through the shifts and broadening of absorption peaks. The X‐ray diffraction analysis pattern indicated a decrease in the amorphous domain of NBR with an increase in the level of chemical modification. The increased glass transition temperature obtained from differential scanning calorimetry confirms the increased molecular rigidity of the chlorinated NBR and thermal transitions increased with increase in the level of chemical modification. The thermal stability of Cl‐NBR decreased with an increase in chlorine content. The flame and oil resistance of Cl‐NBR was greatly higher than pure NBR due to the increased polarity of modified rubber. The superior tensile strength of Cl‐NBR (4 times higher than pure NBR) and higher oil resistance find applications in pump diaphragms, aircraft hoses, oil‐lined tubing, and gaskets materials with the excellent flame resistant property.     

Effect of modified carbon nanotube on physical properties of thermotropic liquid crystal polyester nanocomposites

Polymer nanocomposites based on a very small quantity of carbon nanotube (CNT) and thermotropic liquid crystal polymer (TLCP) were prepared by simple melt blending using a twin-screw extruder. Morphological observations revealed that modified CNT was uniformly dispersed in the TLCP matrix and increased interfacial adhesion between the nanotubes and the polymer matrix. The enhancement of the storage and loss moduli of the TLCP nanocomposites with the introduction of CNT was more pronounced at low frequency region, and non-terminal behavior observed in the TLCP nanocomposites resulted from the nanotube-nanotube and polymer-nanotubes interactions. There is significant dependence of the mechanical, rheological, and thermal properties of the TLCP nanocomposites on the uniform dispersion of CNT and the interfacial adhesion between CNT and TLCP matrix, and their synergistic effect was more effective at low CNT content than at high CNT content. The key to improve the overall properties of the TLCP nanocomposites depends on the optimization of the unique geometry and dispersion state of CNT and the interfacial interactions in the TLCP nanocomposites during melt processing. This study demonstrate that a very small quantity of CNT substantially improved thermal stability and mechanical properties of the TLCP nanocomposites, providing a design guide of CNT-filled TLCP composites with as great potential for industrial use.     

A Review Featuring Fabrication,Properties and Applications of Carbon Nanotubes (CNTs) Reinforced Polymer and Epoxy Nanocomposites

Carbon nanotubes (CNTs) have long been recognized as the stiffest and strongest man-made material known to date.In addition,their high electrical conductivity has roused interest in the areas of electrical appliances and communication related applications.However,due to their miniature size,the excellent properties of these nanostructures can only be exploited if they are homogeneously embedded into light-weight matrices as those offered by a whole series of engineering polymers.In order to enhance their chemical affinity to engineering polymer matrices,chemical modification of the graphitic sidewalls and tips is necessary.The mechanical and electrical properties to date of a whole range of nanocomposites of various carbon nanotube contents are also reviewed in this attempt to facilitate progress in this emerging area.Recently,carbonaceous nano-fillers such as graphene and carbon nanotubes (CNTs) play a promising role due to their better structural and functional properties and broad range of applications in every field.Since CNTs usually form stabilized bundles due to van der Waals interactions,they are extremely difficult to disperse and align in a polymer matrix.The biggest issues in the preparation of CNTs reinforced composites reside in efficient dispersion of CNTs into a polymer matrix,the assessment of the dispersion,and the alignment and control of the CNTs in the matrix.An overview of various CNT functionalization methods is given.In particular,CNT functionalization using click chemistry and the preparation of CNT composites employing hyperbranched polymers are stressed as potential techniques to achieve good CNT dispersion.In addition,discussions on mechanical,thermal,electrical,electrochemical and applications ofpolymer/CNT composites are also included.     

Processing and Characterization of Polypropylene Filled with Multiwalled Carbon Nanotube and Clay Hybrid Nanocomposites

Nanocomposites reinforced with hybrid fillers of carbon nanotubes (CNTs) and clays were developed, aiming at enhancing the dispersion of nanofillers with balanced mechanical properties while lowering the cost of the final product. Polypropylene-based nanocomposites were prepared by the master batch dilution technique with varying combinations of CNTs and clays as fillers by using commercially available highly concentrated master batches of polypropylene/organoclays and polypropylene/multiwalled carbon nanotubes using high-shear twin-screw extrusion. Their mechanical and morphological properties were then evaluated. It was shown that the addition of hybrid filler to polypropylene enhanced the ductility and flexural properties of nanocomposites, confirming the synergistic effect of nanofillers as a multifunctional fillers. The novelty of this work lies in the synergy arising from the combination of two nanofillers with unique dimensions and aspect ratios as well as different dispersion characteristics, which have not been specifically considered previously.     

Effect of dispersion and selective localization of carbon nanotubes on rheology and electrical conductivity of polyamide 6 (PA6), Polypropylene (PP), and PA6/PP nanocomposites

Nanocomposites were prepared by adding 1–3 vol % multiwalled carbon nanotubes (MWCNTs) to polyamide 6 (PA6), polypropylene (PP), and their co‐continuous blends of 60/40 and 50/50 volume compositions. Because of the good interaction and interfacial adhesion to the PA6, nanotubes were disentangled and distributed evenly through nanocomposites containing PA6. In contrast, lack of active interactions between the matrix and the CNTs resulted in poor tube dispersion in PP. These observations were then verified by studying the rheology and electrical conductivity of their respective nanocomposites. Absence of percolated CNT clusters and possible wrapping of the tubes by PA6 resulted in low electrical conductivity of PA6/CNT nanocomposites. On the other hand, despite the weak dispersion of the tubes, electrical conductivities of PP/CNT nanocomposites were much higher than all other counterparts. This could be the result of good three‐dimensional distribution of the agglomerated bundles and secondary aggregation of tubes in PP. Adding CNTs to blends of PA6/PP (60/40 and 50/50) resulted in almost full localization of carbon nanotubes in PA6, leading to their higher effective concentration. At the same CNT loadings, the blend nanocomposites had three to seven orders of magnitude higher electrical conductivity than pure PA6. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015 , 53, 368–378     

Multiwalled carbon nanotubes reinforced poly (ether‐ketone) nanocomposites: Assessment of rheological,mechanical, and electromagnetic shielding properties

This study investigates the effect of multiwalled carbon nanotubes (MWCNTs) content on rheological, mechanical, and EMI shielding properties in Ka band (26.5‐40 GHz) of poly (ether‐ketone) [PEK] prepared by melt compounding using twin screw extruder. Transmission electron microscopy (TEM) and field emission gun scanning electron microscopy (FEG‐SEM) studies were adopted to identify dispersion of nanotubes in PEK matrix. TEM and SEM images showed uniform dispersion of MWCNTs in PEK/MWCNT composites even at loading of 5 wt%. The rheological studies showed that the material experiences viscous (fluid) to elastic (solid) transition at 1 wt% loading beyond which nanotubes form continuous network throughout the matrix which in turn promotes reinforcement. Additionally, Van‐Gurp Palmen plot (phase angle vs complex modulus) and values of damping factor further confirm that the material undergoes viscous to elastic transition at 1 wt% loading. This reinforcement effect of nanotubes is reflected in enhanced mechanical properties (flexural strength and flexural modulus). Flexural strength and flexural modulus of PEK showed an increment of 17% upon incorporation of 5 wt% of MWCNTs. Total shielding effectiveness (SE_T) of −38 dB with very high shielding effectiveness due to absorption (SE_A ~ −34 dB) was observed at 5 wt% loading of MWCNTs in PEK matrix in the frequency range of 26.5‐40 GHz (Ka band).     

聚丙烯/凹凸棒石纳米复合材料的制备与性能研究

以聚丙烯(PP)为聚合物基体,天然凹凸棒石(ATP)为无机组分,经过氧化聚乙烯对ATP表面进行包覆处理,用熔融共混的方法制备了PP/ATP纳米复合材料.扫描电镜结果显示,经本方法处理后的ATP在PP基体中分散较为均匀.ATP棒晶簇直径最佳分散尺寸能达到20~40 nm,比未处理ATP在基体中的棒晶簇直径小10 nm以上;XRD测试表明,未处理ATP和处理后的ATP均有使PP晶粒细化的作用,同时不改变PP的α晶型;DSC结果显示,ATP的加入提高了PP的结晶温度和结晶度,说明ATP有一定的成核作用.通过对复合材料的力学性能测试发现,经过处理的ATP制备的复合材料力学性能优于未处理ATP复合材料对PP力学性能的改善.其中ATP与氧化聚乙烯固含量的质量比为2∶1,ATP含量为3 wt%时复合材料力学性能达到最好.缺口冲击强度比纯PP最高提高了83%,提高幅度显著;经过处理的ATP制备的复合材料拉伸强度提高了6%~11%;弯曲强度提高了33%~45%;弯曲模量提高了90%~106%.