Effects of surface modification on rheological and mechanical properties of CNT/epoxy composites

Despite superior properties of carbon nanotubes (CNTs), physical properties of the CNT/epoxy composites are not improved significantly because interfacial bonding between the CNTs and the polymer matrix is weak. CNTs were treated by an acidic solution to remove impurities and modified subsequently by amine treatment or plasma oxidation to improve interfacial bonding and dispersion of nanotubes in the epoxy matrix. The functional groups on the surface of treated CNTs were investigated by X-ray photoelectron spectroscopy. The surface modified CNTs were embedded in the epoxy resin by ultra-sonication and the cured nanotube containing composites were characterized by field emission scanning electron microscopy. Rheological properties of nanotube containing epoxy resin and mechanical properties of the modified CNT/epoxy composites were improved because the modification of CNTs improved dispersion and interaction between the CNT and the epoxy resin.     

Effect of rheological behavior of epoxy during precuring on foaming

In this study, the effect of rheological behavior of epoxy during precuring on foaming was investigated. Dynamic time sweep test of epoxy/curing agent (100/1, w/w) was conducted. The viscosities as a function of time showed extremely rapid increase from the order of 10²–10³ to 10⁶Pa · s at a certain time, followed by slow increase of the viscosities. Dynamic frequency sweep test of precured epoxy with curing agent was conducted at 90°C. The critical gelation time was obtained by using rheological criterion proposed by Winter and Chambon. We found that the slopes of G′(ω) and G″(ω) decreased with increasing precuring time. Correspondingly, tan δ showed a change from negative to positive slope at a critical time. By using the results, the critical gelation time was determined as t = 895–935 s. Samples of epoxy/curing agent/blowing agent (100/1/0.5) were precured for 960–1620 s. And then precured samples were foamed at 230°C for 300 s to decompose chemical blowing agent. The formed bubble size distribution becomes sharp with increase of the precuring time. There are roughly two sizes of bubbles when precured for relatively short time (t < 1080 s) before foaming: large bubbles (>100 μm) and small ones (?30 μm). On the other hand, foams precured for long time (t > 1200 s) before foaming, large bubbles disappear, and the average diameter of the bubble becomes small while the porosity is low. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Fracture and toughening behavior of aramid fiber/epoxy composites

The effect of short Aramid fibers on the fracture and toughening behavior of epoxy with high glass transition temperature has been studied. Fine dispersion of the fibers throughout the matrix is evidenced by optical microscopy. Compared with neat epoxy resin, the fracture toughness (K_IC) of the composites steadily increases with increasing fiber loading, indicating that addition of Aramid fibers has an effective toughening effect to the intrinsically brittle epoxy matrix. Scanning electron microscopy (SEM) indicates that formation of numerous step structures for fiber‐filled epoxy systems is responsible for the significant toughness improvement. SEM and transmitted optical microscopy show that fiber pullout and fiber breakage are the main toughening mechanisms for the Aramid fiber/epoxy composites. POLYM. COMPOS. 26:333–342, 2005. © 2005 Society of Plastics Engineers.     

Preparation of epoxy composites with CTAB‐modified BN and MWCNTs

In this study, multi‐walled carbon nanotubes (MWCNTs) and boron nitride (BN) were functionalized with cetyltrimethylammonium bromide (CTAB) at both pH 5.5 and pH 11. These MWCNT‐CTAB and BN‐CTAB particles used to prepare the composites were dispersed in a bisphenol A (DGEBA)‐type epoxy resin (ER) system at room temperature. The TGA analysis showed that the BN composite can significantly improve the thermal stability of neat ER at temperatures above 400 °C. The curing degrees of the nanocomposites were calculated to be approximately the same values as neat ER using the Beer–Lambert law from FTIR spectra. The best electrical conductivity of the composites obtained was 3.10 × 10⁻³ S/cm for ER/MWCNT‐CTAB (pH 5.5). The surface hardness, Young's modulus, and tensile strength of the composites were examined. The surface hardness values of the ER/MWCNT‐CTAB composites were higher than those of the other composites. The composite morphology was characterized using X‐ray diffraction (XRD) and scanning electron microscopy (SEM). POLYM. COMPOS., 37:3423–3432, 2016. © 2015 Society of Plastics Engineers     

含氟活性稀释剂对环氧树脂流变性能的影响

为解决环氧树脂的高粘度给成型带来的困难,用NXS-11A型旋转粘度计研究了含氟活性稀释剂对环氧树脂体系的流变性能的影响。研究结果表明,含氟活性稀释剂/环氧树脂体系在常温(35℃)时为牛顿型流体;常温下,环氧树脂体系粘度随含氟活性稀释剂添加量的增加下降显著,当氟活性稀释剂添加6%时,其粘度约可下降50%;但温度较高时,粘度随含氟活性稀释剂添加量的增加下降缓慢。随着含氟活性稀释剂的增加,环氧树脂体系的流动活化能明显下降。     

多壁碳纳米管/有机硅改性环氧树脂复合材料的研制

以有机硅改性EP(环氧树脂)为聚合物基体、经强碱处理及硅烷偶联剂表面改性的MWCNTs(多壁碳纳米管)为功能性填料,采用原位聚合法制备了MWCNTs/有机硅改性EP复合材料。研究结果表明:经表面改性处理后的MWCNTs可在聚合物基体中良好分散,当w(MWCNTs)=0.6%(相对于有机硅改性EP质量而言)时,复合材料的拉伸强度(86.03 MPa)、弯曲强度(154.07 MPa)相对最大,并且比表面未改性的MWCNTs体系分别提高了17.12%、8.19%。     

Thermomechanical properties and rheological behavior of biodegradable composites

The effect of type and content of fillers on the thermal, mechanical, and rheological behavior of the commercial biodegradable polyester product, Ecovio® (BASF) is analytically studied. Ecovio® is basically a blend of poly(butylene adipate‐terephthalate) (PBAT) copolyester (Ecoflex®, BASF) and polylactide (PLA). Two different types of fillers (nanosilica particles and micro‐sized wood‐flour), at various weight fractions were used for this purpose. The role of these fillers on the thermomechanical performance of Ecovio® was investigated in terms of several experimental techniques including scanning electron microscopy (SEM), differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), creep, tensile testing, and single cantilever bending. The rheological behavior has been systematically analyzed, providing additional evidence about the dispersion quality and the interfacial effects between nanofillers and matrix. One of the findings of this work is that the presence of PBAT in the blend (PLA/PBAT) enhances the compatibility of the polymer matrix with both fillers and their dispersion quality. POLYM. COMPOS., 35:1140–1149, 2014. © 2013 Society of Plastics Engineers     

Comparative study on electrical properties of orientated carbon nanotubes/epoxy composites

The percolation threshold of carbon nanotubes (CNTs)/epoxy resin composites was simulated in the Bruggeman' Effective‐Medium Theory based on experiment. Both distinct percolation effect and low percolation threshold in the aligned CNTs/epoxy composites were predicted. With the CNTs loading larger than the percolation threshold, the critical exponent of CNTs/epoxy composites rises rapidly with the increase of aspect ratio of CNTs. It is shown that the electrical conductivity of composites presents distinct aeolotropism, the percolation threshold is sensitive relative to the tiny change of the orientation factor, the aspect ratio, and the structure of CNTs in the composites matrix. The simulated results are consistent with the experimental results basically, and the discrepancy between simulated results and experimental results has been interpreted reasonably. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Preparation and properties of MWCNTs/poly(acrylonitrile‐ styrene‐butadiene)/epoxy hybrid composites

Poly(acrylonitrile‐styrene‐butadiene) (ABS) was used to modify diglycidyl ether of bisphenol‐A (DGEBA) type epoxy resin, and the modified epoxy resin was used as the matrix for making multiwaled carbon tubes (MWCNTs) reinforced composites and were cured with diamino diphenyl sulfone (DDS) for better mechanical and thermal properties. The samples were characterized by using infrared spectroscopy, pressure volume temperature analyzer (PVT), thermogravimetric analyzer (TGA), dynamic mechanical analyzer (DMA), thermo mechanical analyzer (TMA), universal testing machine (UTM), and scanning electron microscopy (SEM). Infrared spectroscopy was employed to follow the curing progress in epoxy blend and hybrid composites by determining the decrease of the band intensity due to the epoxide groups. Thermal and dimensional stability was not much affected by the addition of MWCNTs. The hybrid composite induces a significant increase in both impact strength (45%) and fracture toughness (56%) of the epoxy matrix. Field emission scanning electron micrographs (FESEM) of fractured surfaces were examined to understand the toughening mechanism. FESEM micrographs reveal a synergetic effect of both ABS and MWCNTs on the toughness of brittle epoxy matrix. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

PAM-g-PVA/MWCNTs导电复合材料的制备及表征

以硝酸铈胺-PVA为氧化还原引发体系,制备了丙烯酰胺接枝聚乙烯醇（PAM-g-PVA）聚合物,采用共混法,在接枝聚合物中掺杂多壁碳纳米管制备了PAM-g-PVA/MWCNTs气敏传感导电薄膜材料,研究了在不同饱和蒸气中的气敏响应性。结果表明,导电薄膜在乙酸乙酯、正丙醇饱和有机溶剂蒸气中显示负蒸气系数效应（NVC）,在丙酮和盐酸饱和蒸气中为正气系数效应（PVC）,但随着电阻的增加,导电薄膜在盐酸饱和蒸气中呈现负蒸气系数效应。     

滑石粉粒径及含量对PVC/滑石粉复合体系动态流变行为的影响

考察了滑石粉粒径及含量对PVC/滑石粉复合体系动态流变行为的影响。结果表明:随着滑石粉的粒径减小、含量增加,PVC/滑石粉复合体系的黏度和模量增加,损耗因子减小,van Gurp-Palmen曲线向高复合模量方向移动。     

Hybridization effects on tensile and bending behavior of aramid/basalt fiber reinforced epoxy composites

In this study, the mechanical properties of aramid/basalt hybrid composite laminates were determined, and the effects of hybridization on the mechanical properties were investigated. To examine the effect of hybridization, the mechanical properties of aramid/basalt hybrid composite laminates were compared with those of aramid/epoxy and basalt/epoxy non‐hybrid composite laminates. The mechanical properties, tensile and flexural, of composite laminates were determined by performing uniaxial tensile and three‐point bending tests. The results showed that the employment of basalt fibers for partial substitution of aramid fibers in the composite laminate could provide improvements in the tensile and flexural properties. Furthermore, the results of three‐point bending tests were found that the employment of basalt fibers on compressive side across the thickness of composite laminates were realized significant improvement for flexural properties in comparison to the employment of basalt fibers on tensile side. POLYM. COMPOS., 38:1144–1150, 2017. © 2015 Society of Plastics Engineers     

Dynamic mechanical study of epoxy,epoxy/glass,and glass/epoxy/wood hybrid composites aged in various media

It was proposed and subsequently established that wrapping of red oak wood crossties with epoxy impregnated glass fiber composites will impart longer service life and better stiffness and strength characteristics to these hybrid ties than conventional ones and will help them better withstand environmental extremes. The objective was to understand the degrading effects of aqueous (distilled water), saline (NaCl), acidic (HCl), and alkaline (NaOH) solutions, as well as accelerated aging and freeze/thaw cycling environments on the dynamic and static mechanical properties of these hybrid materials (i.e., wood, wrapped with fiber reinforced resin) and their components. Also micrographs of composite samples, obtained through scanning electron microscopy (SEM), were studied to determine the failure mechanism of composite specimens aged in different environments. Results showed that immersion in aging media lowered the glass transition temperature (T_g) and enhanced apparent phase separation in the samples because of polymer plasticization. In water immersion, the T_g and the stiffness increased with time owing to continued resin curing. At ambient temperature, sustained load had little effect on the mechanical behavior of the aged samples. The extent of degradation was the least for samples aged in salt solution. Soaking in room‐temperature acid solution was most damaging to pure red oak wood samples. Six‐cycle aging did not damage the neat resin or the hybrid samples, whereas it damaged pure wood specimens. Therefore, the composite wrapping around the wood core of the hybrid sample protected it sufficiently, thereby preventing damage to the hybrid specimen during the aging process. POLYM. COMPOS., 2009. © 2008 Society of Plastics Engineers     

A high temperature X-ray diffraction study of the influence of MWCNTs on the thermal expansion of MWCNT/Ni composites

The inclusion of multiwall carbon nanotubes (MWCNTs) into metallic matrices is expected to improve their electrical and mechanical performance. This work analyses the lattice thermal expansion behavior of MWCNT-reinforced Ni composites in order to understand the influence of CNTs on their thermomechanical properties. The lattice thermal expansion coefficient (CTE) of the composites was estimated from X-ray diffraction measurements as a function of the temperature. The MWCNT-reinforced composites show higher lattice CTE (up to 12%) compared to pure Ni. This behavior is mainly produced by the expansion mismatch between the matrix and the reinforcements. We suggest three main mechanisms that explain the behavior of the CTE of metallic matrices in presence of MWCNT. These mechanisms correlate to the anchoring effect observed in previous macroscopic measurements of thermal expansion carried out on the same system.     

Influence of wood flour loading on tribological behavior of epoxy composites

A series of wood flour (WF) filled epoxy composites consisting of five samples were prepared by varying the concentration of WF in step of 10 wt%. These samples were characterized for its wear behavior in abrasive and sliding wear modes to study the influence of WF. It was observed that specific wear rate (k₀) of all the composites decreased with increasing load in sliding wear mode. Specific wear rate was of the order of 10⁻¹⁰ m³/Nm in abrasive wear mode and ∼10⁻¹⁴ m³/Nm in sliding wear mode. Composite containing 40 wt% WF exhibited the lowest specific wear rate in abrasive wear mode. While composite containing 20 wt% WF exhibited lowest specific wear rate in sliding wear mode. This was attributed to the fact that in abrasive wear mode, the wear debris consisting of mainly WF particles was maximum for 10 wt% composite and minimum for 40 wt% composite. In sliding wear mode, the exposed WF particles caused maximum roughening of steel counterface in the case of composite containing higher concentration of WF particles. Hence, they exhibited a higher value of specific wear rate. POLYM. COMPOS., 2008. © 2008 Society of Plastics Engineers     

Recycling of carbon/epoxy composites

The recycling of carbon fibers from carbon/epoxy composites was attempted with a solvent method in nitric acid solutions. Gel permeation chromatography and gas chromatography/mass spectrometry showed that the epoxy resin could entirely decompose into low‐molecular‐weight compounds, and the main components of the dissoluble decomposed compounds were 2,4‐dinitrophenol and 2‐nitro‐4‐carboxylphenol. Electron probe microscopy showed no damage to the recycled carbon fibers. The single‐fiber tension strength loss of the recycled carbon fibers was 1.1% under the following conditions: a decomposition temperature of 90 °C, a nitric acid solution concentration of 8M, and a ratio of the sample weight to the nitric acid solution volume of 6 g:100 mL. Through orthogonal experimentation, the recycling conditions for the carbon/epoxy composites were examined. The best combination was a decomposition temperature of 90°C, a nitric acid solution concentration of 8M, and a ratio of the sample weight to the nitric acid solution volume of 4g:100 mL. This method could liquefy raw materials for rocket engine shells reinforced with carbon fibers. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 95: 1912–1916, 2004     

Viscoelastic behavior of epoxy/carbon fiber/Zno nano‐rods hybrid composites

The insufficient viscoelastic resistance of fiber reinforced plastics can be retrofitted by the addition of more rigid nano fillers to the polymer matrix. In this study, carbon fibers plies were grafted with zinc oxide (ZnO) nano‐rods and the hybridized reinforcement was utilized in laminated composites. Flexural creep tests were carried out using dynamic mechanical analysis (DMA) and the time/temperature superposition principle was employed for accelerated testing. To verify the applicability of TTPS, prolonged stress relaxation tests were also carried out in flexural mode. Data from the DMA flexural creep tests revealed that the whiskerization of carbon fibers with ZnO nano rods reduced the creep compliance by 23% at elevated temperatures and prolonged durations. Also, the relaxation data confirmed the applicability of TTPS to these hybrid composites. The stress relaxation modulus improved by 65% in comparison to composites based on neat carbon fibers. POLYM. COMPOS., 36:1967–1972, 2015. © 2014 Society of Plastics Engineer     

Tribological behavior of epoxy composites containing reactive SiC nanoparticles

The present article evaluated the sliding wear behaviors of epoxy and its composites filled with SiC nanoparticles. Polyglycidyl methacrylate (PGMA) and a copolymer of glycidyl methacrylate and styrene were grafted onto the nanoparticles as a measure of surface pretreatment, respectively. The grafted polymers were selected because the epoxide groups on PGMA would take part in the curing reaction of epoxy resin and covalently connect the nanoparticles with the matrix, while styrene acted as a copolymerized monomer to adjust the amount of the reactive groups of the grafted macromolecular chains, and hence the compatibility between the grafted polymers and the matrix. In comparison to the composites filled with untreated nano‐SiC particles, the composites with the grafted nano‐SiC exhibit improved sliding wear resistance and reduced frictional coefficient owing to the chemical bonding at the filler/matrix interface. The results were analyzed in terms of structure‐properties relationship of the composites. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 2608–2619, 2007     

定向碳纳米管/高密度聚乙烯复合材料体系流变行为的研究

对定向碳纳米管进行酸化处理以后，采用机械共混法制备了定向碳纳米管／高密度聚乙烯复合材料，利用毛细管流变仪研究了高密度聚乙烯和定向碳纳米管／高密度聚乙烯复合材料的流变行为．讨论了剪切应力、剪切速率、温度以及定向碳纳米管的加入对体系流变行为的影响。结果表明：高密度聚乙烯和定向碳纳米管／高密度聚乙烯复合材料都属于假塑性流体．高密度聚乙烯的非牛顿性要大于定向碳纳米管／高密度聚乙烯复合材料；随剪切速率和剪切应力的增大及温度的升高．熔体表现粘度均减小；随着定向碳纳米管含量的增加，定向碳纳米管／高密度聚乙烯复合材料的表观粘度先减小后增大。     

Effect of functionalization on the thermo-mechanical and electrical behavior of multi-wall carbon nanotube/epoxy composites

The effect of the functionalization of multi-wall carbon nanotubes (MWCNTs) on the structure, the mechanical and electrical properties of composites was investigated. Samples based on epoxy resin with different weight percentage of MWCNTs or COOH-functionalized carbon nanotubes (MWCNT–COOH) were prepared and characterized. Dynamic-mechanical thermal analysis shows that the storage modulus increases with the addition of MWCNTs, whereas a constant value or even a weak reduction was observed for functionalized nanotubes. Two phases were suggested in the composites with MWCNT–COOH, both by dynamic-mechanical properties and by water transport. Chemical functionalization of MWCNTs increases the compatibility with the epoxy matrix due to the formation of an interface with stronger interconnections. This, in turn, causes a significant decrease in the electrical conductivity of this type of composite with respect to the untreated MWCNTs which can be explained in terms of tunnelling resistance between interacting nanotubes.