Facile approach to obtain individual‐nanotube dispersion at high loading in carbon nanotubes/polyimide composites

A big challenge in making a composite lies in achieving individual‐nanotube dispersion of carbon nanotubes (CNTs) in a polymer matrix, without aggregation and entanglement and excellent interfacial adhesion between the CNTs and the polymers matrix. In this communication, using polyethylene glycol‐200, we successfully prepared CNT‐reinforced polyimide composites that exhibit individual‐nanotube dispertion in the matrix at high‐loading CNT's. The content of CNTs in a composite can reach 43 wt%. Copyright © 2007 John Wiley & Sons, Ltd.     

Short Twaron aramid fiber reinforced thermoplastic polyurethane

Mechanical, dynamic mechanical, and rheological behaviors of a short p‐aramid fiber reinforced thermoplastic polyurethane (TPU) have been studied in the range of 0–30 wt% of fibers. The tensile strength of the composite is improved slightly at higher fiber content with a minimum at around 10 wt% of fibers. The addition of fibers markedly reduces elongation at break and entails a steady increase in the elastic modulus, but decreases the wear resistance of the matrix. Storage modulus (E′) is increased and the shapes of loss tangent (tan δ) peaks point to a possible fiber–matrix interaction. Rheological studies show a power law behavior for all composites and increased viscosity with fiber loading. Study of the tensile and cryogenic fracture surfaces by scanning electron microscopy (SEM) indicates good correlation between the modes of failure and strength of the composites. The micrographs reveal good interfacial adhesion and extensive peeling and fibrillation of the fibers in the compounded and fractured composites. Theoretical models have been used to fit the experimental modulus data. Copyright © 2008 John Wiley & Sons, Ltd.     

STUDY OF THE MOLECULAR MOTION AND COMPATIBILITY IN AB-CROSSLINKED POLYMER BASED ON POLYURETHANE AND POLYSTYRENE-co-ACRYLIC ACID BY SOLID STATE HIGH RESOLUTION NMR

The ~(13)C T_(1s) of --CH_3 side group in PPU/P (St-co-AA), AB-crosslinked polymers (i. e.ABCP) was studied by using high resolution solid state NMR. The rotation motion of --CH_3 sidegroup in PPU was analyzed by means of the average spectral density functions of internal rota-tion. The results showed that the rotation of the --CH_3 side group is related closely to the com-patibility between the two components. The compatibility was studied by analyzing the protonspin-lattice relaxation in rotating frame, spin-spin relaxation and spin-diffusion. The resultsshowed that the hydrogen bonds between the components play a major role in determining thecompatibility. Through spin diffusion studying, the soft phase domain size was calculated. Bystudying proton spin-spin relaxation, the content of each component in each phase and that ofeach phase in the samples can be obtained. The result shows that the content of interphase is related closely to the compatibility.     

Effect of compatibilization on thermal degradation kinetics of HDPE-based composites containing cellulose reinforcements

Dynamic thermogravimetric analysis under nitrogen flow was used to investigate the thermal decomposition process of high-density poly(ethylene) (HDPE)-based composites reinforced with cellulose fibers obtained from the recycling of multilayer carton scraps, as a function of the cellulose content and the compatibilization. The Friedman, Flynn–Wall–Ozawa, and Coats–Redfern methods were used to determine the apparent activation energy (E _a) of the thermal degradation of the cellulose component into the composites. E _a has been found dependent on the cellulose amount and on the cellulose/polymer matrix interfacial adhesion. In particular, it has been evidenced an increase of the cellulose thermal stability as a consequence of the improved interfacial adhesion between the components in NFR composites.     

Morphology,rheological and crystallization behavior in non-covalently functionalized carbon nanotube reinforced poly(butylene succinate) nanocomposites with low percolation threshold

Multi-walled carbon nanotubes (CNTs) were non-covalently functionalized by surface wrapping of poly(sodium 4-styrenesulfonate) (PSS) with the aid of ultrasound. The functionalized CNTs were incorporated into poly(butylene succinate) (PBS) through solution coagulation to fabricate CNTs filled PBS nanocomposites. The morphologies of the PBS/CNT nanocomposites were studied by scanning electron microscope (SEM) and transmission electron microscope (TEM), and the effect of loading of functionalized CNT on the rheological behavior, electrical conductivity and mechanical properties of the nanocomposites was investigated systemically. SEM observation indicates that functionalized CNTs dispersed in PBS matrix without obvious aggregation and showed good interfacial adhesion with the PBS phase. TEM observation reveals that a CNT network was formed when the loading of CNTs increased from 0.1 to 0.3 wt%. Rheological investigation indicates the formation of a CNT network with a percolation threshold of only 0.3 wt%. Significant improvement in electrical conductivity occurred at CNT loading of 0.3 wt%, with the value of electrical conductivity increasing by six orders of magnitude compared to neat PBS. Differential scanning calorimetry indicates that the melt crystallization temperature of PBS was improved by ∼14 °C with addition of only 0.05 wt% functionalized CNTs. Tensile tests indicate that both the yield strength and Young's modulus of PBS were apparently reinforced by incorporation of functionalized CNTs, while the elongation at break was reduced gradually.     

Shape memory behavior of carbon nanotube‐reinforced trans‐1,4‐polyisoprene and low‐density polyethylene composites

Shape memory composites of trans‐1,4‐polyisoprene (TPI) and low‐density polyethylene (LDPE) with easily achievable transition temperatures were prepared by a simple physical blending method. Carbon nanotubes (CNTs) were introduced to improve the mechanical properties of the TPI/LDPE composites. The mechanical, cure, thermal, and shape memory properties of the TPI/LDPE/CNTs composites were investigated in this study. In these composites, the cross‐linked network generated in both the TPI and LDPE portions acted as a fixed domain, while the crystalline regions of the TPI and LDPE portions acted as a domain of reversible shape memory behavior. We found that CNTs acted as not only reinforced fillers but also nucleation agents, which improved the crystalline degree of the TPI and LDPE portions of the composites. Compared with the properties at the other CNT doses, the mechanical properties of the TPI/LDPE composites when the CNT dose was 1 phr were improved significantly, showing excellent shape memory properties (R_f = 97.85%, R_r = 95.70%).     

Effect of the Nanotube Radius and the Volume Fraction on the Mechanical Properties of Carbon Nanotube-Reinforced Aluminum Metal Matrix Composites

By using the advantages of carbon nanotubes (CNTs), such as their excellent mechanical properties and low density, CNT-reinforced metal matrix composites (MMCs) are expected to overcome the limitations of conventional metal materials, i.e., their high density and low ductility. To understand the behavior of composite materials, it is necessary to observe the behavior at the molecular level and to understand the effect of various factors, such as the radius and content of CNTs. Therefore, in this study, the effect of the CNT radius and content on the mechanical properties of CNT-Al composites was observed using a series of molecular dynamics simulations, particularly focusing on MMCs with a high CNT content and large CNT diameter. The mechanical properties, such as the strength and stiffness, were increased with an increasing CNT radius. As the CNT content increased, the strength and stiffness increased; however, the fracture strain was not affected. The behavior of double-walled carbon nanotubes (DWNTs) and single-walled carbon nanotubes (SWNTs) was compared through the decomposition of the stress–strain curve and observations of the atomic stress field. The fracture strain increased significantly for SWNT-Al as the tensile force was applied in the axial direction of the armchair CNTs. In the case of DWNTs, an early failure was initiated at the inner CNTs. In addition, the change in the elastic modulus according to the CNT content was predicted using the modified rule of mixture. This study is expected to be useful for the design and development of high-performance MMCs reinforced by CNTs.     

Effect of surface treatment with potassium permanganate on ultra-high molecular weight polyethylene fiber reinforced natural rubber composites

The effects of surface treatment using potassium permanganate on ultra-high molecular weight polyethylene (UHMWPE) fibers reinforced natural rubber (NR) composites were investigated. The results showed the surface roughness and the oxygen-containing groups on the surface of the modified fibers were effectively increased. The NR matrix composites were prepared with as-received and modified UHMWPE fibers added 0–6 wt%. The treated fibers increased the modulus and tensile stress at a given elongation. The tear strength increased with increasing fiber mass fraction, attained maximum values at 4 wt%. The hardness of composites exhibited continuous increase with increasing the fiber content. The dynamic mechanical tests showed that the storage modulus and the tangent of the loss angle were decreased in the modified UHMWPE fibers/NR composites. Several micro-fibrillations between the treated fiber and NR matrix were observed, which meant the interfacial adhesion strength was improved.     

Industrial cutting waste granite dust reinforced cardanol benzoxazine/epoxy resin hybrid composites for high-voltage electrical insulation applications

An attempt has been made to develop hybrid composites from benzoxazine monomer (C-ddm) hybridized with DGEBA epoxy resin (EP) and reinforced with varying weight percentages (20 wt%, 40 wt%, 60 wt%, 80 wt% and 100 wt%) of glycidoxypropyltrimethoxy- silane (GPTMS) functionalized granite dust (GD) obtained from industrial granite cutting and polishing process in order to utilize them for electrical insulation applications. The thermal stability of granite dust reinforced poly(EP-co-C-ddm) composites was studied by TGA analysis. Among the composites samples studied, 100 wt% GD reinforced poly(EP-co-C-ddm) composites possess better thermal stability than that of other neat matrices and composites. Among the composites prepared using varying weight percentages of functionalized GD reinforcement, it was observed that 80 wt% GD reinforced poly(EP-co-C-ddm) composites possesses better hydrophobic character than that of other neat matrices and composites. The value of LOI calculated for neat matrix (poly[EP-co-C-ddm]) and 20 wt%, 40 wt%, 60 wt%, 80 wt% and 100 wt% GD reinforced composites was found to be 22, 28, 34, 40, 43 and 45 respectively. The 80 wt% GD reinforced poly(EP-co-C-ddm) composites possess the higher values of tensile strength and flexural strength of 47 MPa and 140 MPa, respectively than those of their samples. The values of electrical surface resistivity and electrical volume resistivity of all the neat matrices and GD reinforced polybenzoxazine composites were found to be in the order of 10¹² and 10¹³ respectively. The values of dielectric strength obtained from break down voltage (BDV) for neat matrix [poly(EP-co-C-ddm)] and 20 wt%, 40 wt%, 60 wt%, 80 wt% and 100 wt% of GD reinforced poly(EP-co-C-ddm) composites are 15.0, 15.5, 16.5, 17.0, 17.0 and 17.0 kV/mm, respectively. Data obtained from thermal stability, hydrophobic behavior and dielectric studies it was inferred that the hybrid polymer composites developed in the present work can be conveniently used in the form insulators, sealants, adhesives and matrices where application demands at high-performance industrial and engineering applications.     

In situ Formation of Mildly Oxidized Graphene Oxide/Polydicyclopentadiene Composite and Reinforced Mechanical and Thermal Performances

A series of mildly oxidized graphene oxide (MOGO) reinforced polydicyclopentadiene composites (MOGO/polyDCPD) were prepared via the in situ polymerization of DCPD in the presence of MOGO using ring-opening metathesis polymerization (ROMP). The inter-crosslinking networks between MOGO and polyDCPD backbones formed the reinforced composite structures, examined qualitatively by swelling tests. Bending tests, DMA and TGA measurements were employed to study the optimal loading content of MOGO for achieving the best mechanical and thermal properties of MOGO/polyDCPD composites. The results showed that the maximum mechanical performance was achieved with 0.1 wt% of MOGO loading. Excess MOGO led to decreased mechanical properties due to the poor solubility and uneven distribution of MOGO in the polymer matrix, which was confirmed by SEM. Meanwhile, the thermal stability of MOGO/polyDCPD composites showed a similar trend. The decomposition temperature at 10 wt% weight loss was significantly increased compared with the unfilled polyDCPD, but decreased with composition of MOGO above 0.1 wt%. The addition of MOGO may not only inhibit the back-biting from the catalyst and the formation of low molecular weight oligomers in the polymer, but also covalently immobilize them on its flake.     

聚乳酸/凹凸棒土纳米复合材料的结构与性能

采用熔融复合方法制备了不同填料质量分数的聚乳酸/纳米凹凸棒土复合材料,纳米凹凸棒土的加入可以显著提高聚乳酸纳米复合材料的拉伸强度和断裂伸长率.扫描电镜结果表明,凹凸棒土粒子在复合材料中实现了均匀分散.DSC曲线在降温过程中出现明显结晶峰,说明纳米凹凸棒土对聚乳酸有一定的成核作用.当纳米凹凸棒填料含量>8%时,在聚合物基体中可形成完善的网络状结构.填料粒子作为体系中的物理缠结点使得复合材料熔体的应力松弛时间延长.红外谱图显示纳米凹凸棒土和聚乳酸分子间存在较强的相互作用.我们推测,纳米凹凸棒土的加入减少了PLA基体层的厚度,使其由三维应力转变为二维应变状态,导致最大切应力可以达到剪切屈服强度,产生剪切滑移形变带,使得呈现出韧性材料性质,有效提高了材料的断裂伸长率.     

Mechanical and thermal properties of Acacia leucophloea fiber/epoxy composites: Influence of fiber loading and alkali treatment

In this work, the influence of fiber content and alkali treatment on the mechanical and thermal properties of Acacia leucophloea fiber-reinforced epoxy composites was studied. Ten composite samples were fabricated by varying fiber content (5, 10, 15, 20, and 25 wt%); both untreated and treated fiber were soaked in a 5% NaOH solution for 45 min by using hand-layup method. The composite reinforced with 20 wt% treated fiber content exhibited better mechanical properties and thermal properties. Fourier transform infrared analysis, morphological analysis by atomic force microscope, and scanning electron microscope of composites were also performed.     

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.     

Ultrahigh Molecular mass Polyethylene/ Carbon Nanotube CompositesCrystallization and melting properties

Ultrahigh molecular mass polyethylene (UHMMPE) is filled with carbon nano-tubes (CNTs) by solution in the presence of maleic anhydride grafted styrene-(ethylene-co-butylene)-styrene copolymer (MA-SEBS) as a compatibilizer. The UHMMPE/CNT composites crystallized from melt were prepared at a cooling rate of 20°C min^-1. The melting and crystallization behaviors of UHMMPE/ CNT composites were investigated by differential scanning calorimetry. The results showed that onset melting temperature (T _m) and degree of crystallinity (X _c) of UHMMPE/CNT composites crystallized from solution are higher than those from melt due to the larger crystalline lamellar thickness. The onset crystallization temperature (T _c) of UHMMPE/CNT composites tends to shift to higher temperature region with increasing CNT content in the composites. Tm and Tc of UHMMPE phase in UHMMPE/CNT composites decrease with the addition of MA-SEBS. Moreover, the crystallization rate of UHMMPE phase in UHMMPE/CNT composite is increased due to the introduction of CNTs. MA-SEBS acts as compatilizer, enhances the dispersion of CNTs in the UHMMPE matrix. Thereby, the crystallization rate of UHMMPE phase in UHMMPE/CNT composite is further increased with the addition of MA-SEBS. This revised version was published online in August 2006 with corrections to the Cover Date.     

Comparison of the properties of waterborne polyurethane/multiwalled carbon nanotube and acid‐treated multiwalled carbon nanotube composites prepared by in situ polymerization

A series of waterborne polyurethane (WBPU)/multiwalled carbon nanotube (CNT) and WBPU/nitric acid treated multiwalled carbon nanotube (A‐CNT) composites were prepared by in situ polymerization in an aqueous medium. The optimum nitric acid treatment time was about 0.5 h. The effects of the CNT and A‐CNT contents on the dynamic mechanical thermal properties, mechanical properties, hardness, electrical conductivity, and antistatic properties of the two kinds of composites were compared. The tensile strength and modulus, the glass‐transition temperatures of the soft and hard segments (T_gs and T_gh, respectively), and ΔT_g (T_gh − T_gs) of WBPU for both composites increased with increasing CNT and A‐CNT contents. However, these properties of the WBPU/A‐CNT composites were higher than those of the WBPU/CNT composites with the same CNT content. The electrical conductivities of the WBPU/CNT1.5 and WBPU/A‐CNT1.5 composites containing 1.5 wt % CNTs (8.0 × 10⁻⁴ and 1.1 × 10⁻³ S/cm) were nearly 8 and 9 orders of magnitude higher than that of WBPU (2.5 × 10⁻¹² S/cm), respectively. The half‐life of the electrostatic charge (τ_1/2) values of the WBPU/CNT0.1 and WBPU/A‐CNT0.1 composites containing 0.1 wt % CNTs were below 10 s, and the composites had good antistatic properties. From these results, A‐CNT was found to be a better reinforcer than CNT. These results suggest that WBPU/A‐CNT composites prepared by in situ polymerization have high potential as new materials for waterborne coatings with good physical, antistatic, and conductive properties. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 3973–3985, 2005     

Model for thermal conductivity of composites with carbon nanotubes

This paper presents a model for evaluation of effective thermal conductivity for the composites with carbon nanotubes (CNT) having log-normal function of distribution of CNT, with direct effect over depolarization factor. The CNT are considered having cylindrical shape with L/d ratio very high. The model parameters are calculated in function of the data from literature. The influence of volume fraction of reinforced materials, of the aspect ratio of the particles included and of the ratio of the two thermal conductivities is presented.     

Flexural,impact, rheological and physical characterizations of POM reinforced by carbon nanotubes and paraffin oil

The paraffin oil dispersion technique innovated in the recent years to synthesize bulk polymer nanocomposite materials has a uniform dispersion. This research work aims to study the effect of added carbon nanotubes (CNTs) on flexural, impact and rheology behaviors of polyoxymethylene (POM) reinforced by 0–0.03 wt% of CNT using paraffin oil dispersion technique. The wettability and lamellar thickness were measured and rheological performance investigated using a parallel plate rheometer. The flexural and impact mechanical properties were also evaluated. The fracture surfaces were then examined by microscopy. The results showed that the energy to break, flexural strength and modulus increased proportionally with the addition of the amount of CNT in the matrix. For the rheology behavior, the viscosity decreased at the low percentage of CNT and then increased with increase in the percentage weight ratio of CNT in the POM matrix. It was also noted that the water contact angle rose with the increase the CNT percentages. Copyright © 2016 John Wiley & Sons, Ltd.     

Preparation and characterization of glass fiber–reinforced polyethylene terephthalate/linear low density polyethylene (GF‐PET/LLDPE) composites

Polyethylene terephthalate (PET) was melt blended with linear low density polyethylene (LLDPE) and subsequently compounded with glass fibers (GF) as reinforcements at percentages ranging from 15 to 45 wt% of LLDPE and 5 to 30 wt% of GF. Thermal, morphological, and mechanical properties of the prepared composites were investigated. It was found that compounding PET/LLDPE blends with GF would be beneficial in producing composites that are thermally stable with good mechanical properties. For example, the impact strength of the composites containing 85/15 wt% (PET/LLDPE) at relatively high loading of GF, ie, from 15 to 30 wt%, was higher than that of the GF‐reinforced neat PET. When increasing the percentage of LLDPE in the composites, the impact strength increased with increasing GF content, and this was also better than that of GF‐reinforced PET whose impact strength drastically decreased upon increasing the GF%. The improvement in mechanical properties of the composite, we suggest, should be correlated with the morphologies of the composites where the visualized interface adhesion tended to be better at higher loadings of both LLDPE and GF.     

Synthesis and characterization of fluorine functionalized graphene oxide dispersed quinoline-based polyimide composites having low-k and UV shielding properties

Polyimide nanocomposites having low-k and UV shielding properties have been developed using fluorine functionalized graphene oxide and bis(quinoline amine) based polyimide. The polyimide was synthesized using bis(quinoline amine) and pyromellitic dianhydride at appropriate experimental conditions, and its molecular structure was confirmed through various spectral analysis such as FTIR and NMR. The polyimide (PI) composites were prepared using bis(quinoline amine), pyromellitic dianhydride, and separately filled with 1, 5, 10 wt% of fluorinated graphene oxide (FGO) through in situ polymerization. The polymer composites were characterized using thermo gravimetric analysis (TGA), X-ray powder diffraction (XRD), and scanning electron microscopy (SEM). In addition, the water contact angle, dielectric behavior, and UV–Vis shielding behavior of FGO/PI composites were evaluated. The value of the water contact angle of the polyimide was increased with increment of FGO in the polyimide matrix. The highest water contact angle of polyimide composites observed 108° was obtained for 15 wt% FGO reinforced polyimide composite. The value of the dielectric constant for neat, 1, 5, and 15 wt% FGO reinforced polyimide composites was obtained as 4.5, 3.7, 2.6, and 2.0, respectively. It is also observed from by UV–Vis spectroscopy analysis that the FGO reinforced polyimide composites have good UV shielding behavior.     

Positive Temperature Coefficient Characteristics of Multi-walled Carbon Nanotube Filled Polyvinylidene Fluoride Nanocomposites

Composites of polyvinylidene fluoride (PVDF) and multi-wall carbon nanotubes (MWNT) were prepared by a melt mixing process. Temperature dependence of electrical properties of the nanocomposites was investigated for composites containing different amounts of MWNT. An obvious positive temperature coefficient was observed. It was found that resistivity of the composites was decreased with increasing MWNT content and the electrical percolation threshold was formed at 3 wt% MWNT, which were caused by the formation of conductive chains in the composites. The mechanism of the positive temperature coefficient behavior of the nanocomposites is discussed. The rheological results showed that the materials experience a fluid–solid transition at the composition of 2 wt%, beyond which a continuous MWNT network forms throughout the matrix leading to a percolated network structure, which further indictes the nanotubes were dispersed uniformaly, in the PVDF matrix.