Relationship between the material properties and fatigue crack‐growth characteristics of natural rubber filled with different carbon blacks

An investigation of the influence of different types of carbon black on fatigue crack‐growth behavior was undertaken. Fatigue tests were carried out on edge‐notched specimens under cyclic tension loading. A power‐law dependency between the crack‐growth rate and tearing energy was obtained. Natural rubber (NR) filled with N330 (the mean diameter is 30 nm) carbon black possessed the lowest values of exponent b and constant B (the two crack growth parameters determined from cyclic crack growth testing), which denoted the strongest resistance to crack growth at a given tearing energy. Strain‐induced crystallization was investigated by the modified Mooney–Rivlin equation and showed the earliest appearance and strongest ability of the crystallization of the NR/N330 composite at the largest amount of bound rubber. The study on the viscoelastic properties by dynamic mechanical analysis confirmed that the NR/N330 composite had the largest viscoelastic contribution, which was attributed to the viscoelastic dissipation in the viscoelastic region in front of the crack tip. All of these results confirm the best crack‐propagation resistance of NR filled with N330. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Crack growth resistance of natural rubber reinforced with carbon nanotubes

Carbon nanotubes (CNTs)/natural rubber (NR) composites are prepared through ultrasonically assisted latex mixing combined with a two-roll mixing process, and their crack growth behavior is examined to evaluate their fatigue properties. CNTs/NR shows a reinforcement of crack growth resistance compared to unfilled NR. The measurements of the tearing energy and the hysteresis loss show that CNTs/NR exhibits more energy dissipation than NR. Also, strain-induced crystallization (SIC) around the crack tip of CNTs/NR and NR composite was examined at different fatigue strains. CNTs positioned at the crack tip led to a crack branching at low fatigue strain, which is responsible for the improvement of the crack growth resistance of CNTs/NR. However, the inclusion of CNTs renders NR higher crystallinity and larger crystallization zones in front of the crack tip at high fatigue strains, which allows more energy dissipation during crack growth. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48447.     

Effects of hybrid filler networks of carbon nanotubes and carbon black on fracture resistance of styrene‐butadiene rubber composites

In this study, influences of hybrid filler networks of carbon nanotubes (CNTs) and carbon black (CB) on fracture resistance of styrene‐butadiene rubber (SBR) composites were well investigated. The spherical CB was partially substituted by fibrous CNTs in two different ways: unequal replacement (1 phr CNTs replacing 4 phr CB) and equal replacement (1 phr CNTs replacing 1 phr CB). The J‐integral tests were employed to evaluate the crack initiation and propagation resistance. The strain amplification and distribution near the crack tip was measured by digital image correlation to explore the fracture resistance mechanism. Results revealed that the fracture resistance was effectively improved by unequal replacement. Meanwhile, for unequal replacement, higher content of CNTs resulted in a weaker strain amplification factor and larger amplification area near the crack tip, which contributed to the improved fracture resistance. However, opposite trends were observed for equal replacement. A synergistic effect in fracture resistance of SBR composites between CB and CNTs was realized for unequal replacement. POLYM. ENG. SCI., 56:1425–1431, 2016. © 2016 Society of Plastics Engineers     

Effect of silane coupling agent on the fatigue crack propagation of silica‐filled natural rubber

Based on the real‐time crack tip morphology monitoring, the influence of silane coupling agent (SCA) on the crack‐growth behavior of silica‐filled natural rubber (NR) was analyzed. By using SCA, silica particles can be well dispersed and a filler–matrix network can be formed, which leads to lower crack‐growth rate. Results indicate that a dosage of 5 wt % (with respect to silica loading) is the optimal content. The real‐time observation and scanning electron microscopy (SEM) analysis proved that thin ligaments and dimples with homogeneous distribution appear on the crack tip. These crack tip morphologies reflect the low crack‐growth rate. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41980.     

Crack growth of natural rubber filled with functionalized silica particles

In the present work, functionalized liquid isoprene rubber (FLIR) was used to improve the filler dispersion and filler–rubber interaction in the silica filled natural rubber system. By the infrared spectra and scanning electron microscopy, it was proved that the FLIR was successfully grafted on the silica and the functionalized silica was dispersed in the NR matrix homogeneously. Based on the real‐time crack tip morphology monitoring method, the influence of FLIR on the crack growth behavior of NR filled with silica was analyzed. By the adding of FLIR, the crack resistance of the natural rubber embedded with functionalized silica is remarkably increased. When the weight ratio of FLIR to silica is 3:10, the NR composite has the best crack resistance. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 42972.     

A highly oriented poly(3,4‐ethylenedioxythiophene) film: Facile synthesis and application for supercapacitor

A single crystal poly(3,4‐ethylenedioxythiophene) (PEDOT) film with highly oriented arrangement has been fabricated from an aqueous solution by a novel unipolar pulse electropolymerization method. Film formation mechanism was proposed based on the in situ mass change during electropolymerization process measured by the electrochemical quartz crystal microbalance. The compositions, morphology and crystal structure of the fabricated films are characterized by Fourier transfer infrared spectroscopy, scanning electron microscopy, and X‐ray diffraction, respectively. It is found that the prepared PEDOT film on carbon nanotubes (CNTs)‐modified electrode with a spongy dendritic structure possesses outstanding electroactivity, high specific capacitances (239.1 F?g^?1, including the specific capacitances of CNTs which is 21.4 F?g^?1), and excellent cycling stability with 7.3% decay from its initial capacitance over 10,000 cycles. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43418.     

Influence of carbon nanotubes with different functional groups on the morphology and properties of PPO/PA6 blends

Carbon nanotubes with different functional groups were prepared and then incorporated into the poly(2,6‐dimethyl‐1,4‐phenylene oxide)/polyamide 6 (PPO/PA6) blend via melt blending. The influence of different carbon nanotubes on the morphology and properties of the blend was studied. The results show that addition of pristine CNTs, CNTs‐OH, CNTs‐NH₂ leads to the evolution of the phase structure of PPO/PA6 (mass ratio: 60/40) blend from sea‐island to cocontinuous, whereas incorporation of CNTs‐COOH does not change the blend morphology due to serious aggregation of the carbon nanotubes. Incorporating different CNTs into PPO/PA6 blend increases the tensile modulus and storage modulus of the blends, whereas decreases slightly the tensile strength. At the same time, the glass transition temperatures (T_g) of PA6 and PPO are enhanced. ΔT_g, the gap between the T_g of PA6 and PPO, decreases with the addition of carbon nanotubes due to the stronger interaction of carbon nanotubes with PA6 than PPO. A similar tendency was found in the storage modulus (G′) and complex viscosity (η*) of the composites. The dispersion state of different carbon nanotubes and their interaction with polymer components are different, which causes the different confinement effect to the macromolecular chains. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

炭黑/煤矸石/碳纳米管复合填料体系对天然橡胶性能的影响研究*

利用硝酸氧化法对碳纳米管(CNTs)进行纯化,并用环氧天然橡胶(ENR)进行改性处理。结合胶质量分数测定结果表明, ENR用量15%(质量)时效果最佳。采用胶乳凝聚法制备CNTs/天然橡胶(NR)母料。煤矸石粉(CG)经高温煅烧和表面改性处理。 将CNTs/天然橡胶(NR)母料、CG和炭黑(CB)通过机械混炼法与天然橡胶及配合剂混合,制备CB/CG/CNTs/NR复合材料,并对复合材料进行硫化特性及物理机械性能。结果表明： CNTs延迟硫化效应明显;相比炭黑,CG对硫化具有促进作用。硫化特性和甲苯溶胀法测定结果表明,在填料份数相同的条件下,单独由CB填充的NR有最大的交联密度,CNTs对交联密度影响不明显。物理机械性能测试结果表明,当CG：CB：CNTs=17.5:16.5:1(Phr)时,NR硫化胶的300%定伸应力和扯断伸长率明显高于单独由CB填充NR,而拉伸强度与之接近,复合填料样填充NR具有较好的综合性能。扫描电镜测试结果表明,复合填料在NR基体中分布均匀。     

Reinforcement role of carbon nanotubes,Part I: High‐performance epoxy resin

The reinforcement role of single‐walled carbon nanotubes (SWCNT) in a high‐performance epoxy resin is studied in this article, with the emphasis on the deformation and load transfer mechanism. Tensile tests show that introducing carbon nanotubes (CNTs) into the epoxy resin changes the tensile strength of the material, and that the increase of Young's modulus is in good agreement with the increasing of glass transition temperature (T_g) measured by differential scanning calorimetry (DSC). Residual strains in CNTs induced during curing process have been investigated both experimentally and theoretically. Raman spectroscopy study shows that load transfers more efficiently in tension than in compression. The Raman shifts of deformed CNTs under repeated loading indirectly reveals that the load can be further transferred via friction after debonding fully occurs. Thin epoxy layers were observed on the pull out ends of CNTs, which implies the existence of the immobilized epoxy layer between CNTs and bulk epoxy. POLYM. COMPOS., 36:2212–2219, 2015. © 2014 Society of Plastics Engineers     

Failure analysis of carbon black filled styrene butadiene rubber under fatigue loading conditions

Abstract

The present paper deals with the fatigue crack growth in a carbon black-filled styrene butadiene rubber (CB-SBR) under fully relaxing loading conditions. More precisely, it is devoted to the determination of the scenario of crack growth. For that purpose, an original ‘microcutting’ technique, previously applied by the authors on natural rubber (NR), is used to observe microscopic phenomena involved in fatigue crack growth thanks to scanning electron microscopy (SEM). Results show that the crack tip grows following a tearing line by generating ligaments; it explains the differences between fatigue responses of crystallisable and non-crystallisable rubbers during crack propagation. So, contrary to crystallisable elastomers such as NR, the microstructure of SBR is similar at crack tip and in the bulk material, and the crack tip does not resist crack propagation. Moreover, the morphology of fracture surfaces only depends on particles encountered by the fatigue crack during its propagation.     

High‐performance natural rubber latex composites developed by a green approach using ionic liquid‐modified multiwalled carbon nanotubes

The effect of multiwalled carbon nanotubes (MWCNTs) modified by a hydrophilic ionic liquids (ILs), including 1‐ethyl‐3‐methylimidazolium bromide and 1‐hexyl‐3‐methylimidazolium bromide, was studied. The obtained water‐suspensible carbon nanotubes (CNTs) were still homogeneously distributed in water a month after sonication. The microstructural development of filler networks and the uniform dispersion of MWCNTs in the presence of IL were analyzed by TEM. The apparent physical (cation–π/π–π) interaction between the MWCNTs and the IL was characterized by Raman spectroscopy, DSC, and TGA. Furthermore, high‐performance composites of natural rubber latex (NRL) and CNTs modified with IL were obtained by the liquid latex blending method. The CNTs were homogeneously distributed in the matrix and CNT–ILs improved the fatigue resistance and mechanical properties of the NRL/CNT–IL composites. This study demonstrates a simple and eco‐friendly approach to develop multifunctional advanced materials based on IL‐modified MWCNT elastomer composites. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46588.     

Enhanced fatigue life of carbon nanotube‐reinforced epoxy composites

The effects of carbon nanotube (CNT) inclusion on cyclic fatigue behavior and the residual mechanical properties of epoxy composites after different degrees of fatigue have been studied. Tension–tension cyclic fatigue tests were conducted at various load levels (25–50 MPa) to establish the relationship between stress and the number of cycles to failure (S–N curves). The residual strength and modulus were measured after loading at 30 MPa for 5000, 15,000, and 25,000 cycles. The incorporation of a small amount of CNTs increased the fatigue life of epoxy in the high‐cycle, low‐stress‐amplitude regime by 1550%. Micrographs indicate the key mechanisms for enhancement in fatigue life such as CNT crack‐bridging and pullout. POLYM. ENG. SCI., 52:1882–1887, 2012. © 2012 Society of Plastics Engineers     

碳纳米管/NR复合材料的硫化特性

对机械混合制备的碳纳米管(CNTs)／NR复合材料硫化性能进行研究。结果表明，与炭黑补强胶料相比，加入CNTs后，NR胶料的焦烧时间略有延长，硫化返原现象减轻。应用几种不同工艺预处理的CNTs进行试验发现，除经混酸氧化处理CNTs对NR硫化产生明显迟滞效应外，其它几种CNTs填充胶料的硫化特性变化不大。应用CNTs填充橡胶材料，混炼胶中硫黄的用量应适当增大。     

In situ preparation of polyimide/amino‐functionalized carbon nanotube composites and their properties

In order to improve the dispersion of carbon nanotubes (CNTs) in polyimide (PI) matrix and the interfacial interaction between CNTs and PI, 4,4′‐diaminodiphenyl ether (ODA)‐functionalized carbon nanotubes (CNTs‐ODA) were synthesized by oxidation and amidation reactions. The structures and morphologies of CNTs‐ODA were characterized using Fourier transform infrared spectrometer, transmission electron microscopy, and thermal gravimetric analysis. Then a series of polyimide/amino‐functionalized carbon nanotube (PI/CNT‐ODA) nanocomposites were prepared by in situ polymerization. CNTs‐ODA were homogeneously dispersed in PI matrix. The influence of CNT‐ODA content on mechanical properties of PI/CNT‐ODA nanocomposites was investigated. It was found that the mechanical properties of nanocomposites were enhanced with the increase in CNT‐ODA loading. When the content of CNTs‐ODA was 3 wt%, the tensile strength of PI/CNT‐ODA nanocomposites was up to 169.07 MPa (87.11% higher than that of neat PI). The modulus of PI/CNTs‐ODA was increased by 62.64%, while elongation at break was increased by 66.05%. The improvement of the mechanical properties of PI/CNT‐ODA nanocomposites were due to the strong chemical bond and interfacial interaction between CNTs‐ODA and PI matrix. POLYM. COMPOS., 35:1952–1959, 2014. © 2014 Society of Plastics Engineers     

Compressive residual thermal stress induced crack deflection in carbon nanotube-doped carbon/carbon composites

Introducing carbon nanotubes (CNTs) by electrophoretic deposition (EPD) is a promising method to improve the strength and toughness of carbon/carbon (C/C) composites. Herein, a new reinforcing mechanism called “compressive residual thermal stress (RTS) induced crack deflection” has been reported. Concretely, CNTs, with different loading content, were introduced by EPD method. Results showed that the CNT content had little influence on CNT-induced matrix refinement. However, the strength of the CNT-doped C/C composites increased with the rising content of CNTs and cracks could only deflect when the CNT interface reached a certain thickness. A theory based on compressive RTS induced crack deflection was built to interpret this discrepancy. Tensile stress existed at the interface in pure C/C composites, while compressive stress occurred and increased with the rising thickness of the CNT interface, which were verified by finite element analysis and Raman test. Calculation revealed that compressive stress exceeded 30 MPa at the crack tip could make the crack deflection happen more easily since it released more strain energy than penetration.     

Sensing of damage in carbon nanotubes and carbon black‐embedded epoxy under tensile loading

In situ sensing of damage in epoxy embedded separately with carbon nanotubes (CNTs) and carbon black (CB) microparticles is investigated under quasi‐static uniaxial tensile loading. Three different weight fractions of CNTs (0.1, 0.3%, and 0.5%) and one‐weight fraction of CB (10%) are used to generate a conductive network in epoxy. A modified four circumferential ring probes technique is employed and a constant current was applied through the outer probes. The resulting voltage drop between the inner probes is measured using a high‐resolution electrometer‐based system to determine the resistance change associated with nonlinear deformation, damage initiation, and growth in the material. As the generated conductive network is different with changing weight fractions of CNTs, the resulting electrical response was identified to be significantly different between composites. The nonlinear deformation associated with the unfolding of entangled polymer chains and further straightening of them, decreased the distance between neighboring CNTs, resulting in improved electron hopping. For CB‐embedded epoxy, a very high percentage increase in resistance is noticed when compared to CNTs case owing to induced microcracks associated with agglomerated CB particles. POLYM. COMPOS., 2012. © 2012 Society of Plastics Engineers     

Production of a cellular structure in carbon nanotube/natural rubber composites revealed by nanomechanical mapping

Composites based on an elastomer, natural rubber (NR), and pristine multiwalled carbon nanotubes (MWCNTs) were prepared using a two-roll mill mixer. The high shear stress produced a homogeneous dispersion of CNTs in the NR matrix. Using an atomic force microscopy nanomechanical mapping technique, the structure and nanoscale mechanical properties of the resulting composites were investigated in term of CNT loading. Topography, elastic modulus, and adhesive energy distribution maps of the materials were obtained at the same point and at the same time in a single scan. Such maps were used to identify and characterize the CNT, NR, and mechanical interfacial regions formed around the CNTs. The mechanical interfacial regions together with the CNTs divide the elastomer matrix into small “cells”. We claim that the cellular structure is produced in the CNTs/NR composites.     

Poly(vinylidene fluoride)–polyacrylonitrile blend flat‐sheet membranes reinforced with carbon nanotubes for wastewater treatment

In this reported study, poly(vinylidene fluoride) (PVDF) and polyacrylonitrile (PAN) blend flat‐sheet membranes were prepared via a phase‐inversion method with various loadings of multiwalled carbon nanotubes. The effects of the carbon nanotubes (CNTs) on the performance and morphology of the PVDF–PAN composites were investigated via tests of the pure water flux and rejection of bovine serum albumin, scanning electron microscopy, atomic force microscopy, Fourier transform infrared spectroscopy, X‐ray diffraction, thermogravimetric analysis, and contact angle (CA) analysis. The experimental results demonstrate that the CNTs contributed to the improvement of the flux and hydrophilicity of the membranes. The maximum value of the flux was 398.1 L m^?2 h^?1, and the value of CA for the composite membranes was found to be 48°. In addition, the results of the mechanical properties tests illustrate that the brittleness and plasticity of the hybrid membranes were greatly improved by the presence of the CNTs. The flux recovery ratio was maintained at 75%; this demonstrated that the PVDF–PAN membranes enhanced with the CNTs possessed good antifouling performance. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46155.