具有负温度系数效应的导电硬质聚氨酯泡沫

采用高能球磨分散方法制备了稳定的聚合物多元醇/碳纳米管分散液,并通过原位聚合制备了导电聚氨酯（PU）/碳纳米管（CNTs）硬质泡沫复合材料。采用扫描电镜（SEM）表征了泡沫复合材料的结构,研究了CNTs含量对泡沫材料导电性的影响以及泡沫材料的负温度系数（NTC）效应,通过压缩测试考察了泡沫材料的力学性能。结果表明,CN...     

Piezoresistive and compression resistance relaxation behavior of water blown carbon nanotube/polyurethane composite foam

The in-situ bulk polycondensation process in combination with a ball milling dispersion process was used to prepare the water blown multiwall carbon nanotubes (CNT)/polyurethane (PU) composite foam. The mechanical properties, piezoresistive properties, strain sensitivity, stress and resistance relaxation behaviors of the composite foams were investigated. The results show that the CNT/PU composite foam has a better compression strength than the unfilled polyurethane foams and a negative pressure coefficient behavior under uniaxial compression. The resistance response of CNT/PU nanocomposites foam under cyclic compressive loading was quite stable. The nanocomposite foam containing a weight fraction of carbon nanotubes close to the percolation threshold presents the largest strain sensitivity for the resistance. The characteristic of resistance relaxation of CNT/PU composite foam is different from the stress relaxation due to the different relaxation mechanism. During compressive stress relaxation, the CNT/PU foam composites have excellent resistance recoverability while poor stress recoverability.     

一步法制备聚氨酯/碳纳米管复合泡沫材料及其性能

采用球磨法将碳纳米管分散到聚醚三元醇中,以水为发泡剂,采用一步法原位聚合制备了聚氨酯(PU)/碳纳米管(CNTs)复合泡沫材料,研究了发泡剂水的添加量和碳纳米管的含量对复合材料密度和性能的影响.结果表明,随水添加量的增加,泡沫材料的密度、压缩模量、拉伸模量以及断裂伸长率呈下降的趋势;碳纳米管的加入大幅度提高了材料的压缩...     

羧基碳纳米管增强酚醛泡沫的压缩性能及热性能

研究了羧基碳纳米管(CNT-COOH)增强酚醛泡沫复合材料的制备工艺、微观结构、压缩性能和热性能,并结合红外光谱和泡沫在不同压缩应变下的变形破坏形貌,探讨了CNT-COOH对酚醛泡沫的增强机制。结果表明,CNT-COOH作为异相成核剂,使酚醛泡沫泡孔的平均尺寸减小,泡孔密度增大; 随着酚醛泡沫中CNT-COOH含量增加,CNT-COOH/酚醛泡沫复合材料的压缩模量和压缩强度提高。红外分析表明,CNT-COOH可能未与酚醛泡沫发生固化反应。CNT-COOH/酚醛泡沫复合材料在不同压缩应变下的SEM分析表明,CNT-COOH位于泡孔的孔壁上,并通过CNT-COOH/酚醛泡沫的界面传载作用承受了一定载荷,增强了泡沫的力学性能。热重分析和垂直燃烧试验表明,CNT-COOH作为稳定剂,降低了泡沫的热降解速率,使其热稳定性和阻燃性能均略有提高。     

球磨对碳纳米管增强泡沫铝基复合材料压缩与吸能性能的影响

因碳纳米管（CNTs）具有优异的性能,被认为是金属基复合材料理想的增强体,因此如何制备得到CNTs增强体均匀分散的金属基复合材料一直是本领域的研究热点。本文通过原位化学气相沉积（CVD）、短时球磨和填加造孔剂的工艺成功制备了CNTs增强的泡沫铝基复合材料,着重研究了球磨过程对复合泡沫铝的微观形貌、压缩性能和吸能性能的影响规律。结果表明,随着球磨时间的延长,CNTs的分散性提高并逐步嵌入铝基体中,使复合泡沫铝的组织均匀性得到改善。相对于未球磨的含CNTs 3.0wt%的复合泡沫材料,当球磨时间增加至90 min时,复合泡沫铝的孔壁硬度、屈服强度和吸能能力分别提高了67%、126%和343%。     

Enhanced acoustic damping in flexible polyurethane foams filled with carbon nanotubes

Flexible polyurethane (PU) foams, with loading fractions of up to 0.2 wt% carbon nanotubes (CNTs), were made by free-rising foaming using water as blowing agent. Electron microscopy revealed an open cellular structure and a homogeneous dispersion of CNTs, although the incorporation of nanofiller affected the foaming process and thus the final foam density and cellular structure. The compressive response of the foams did not show an unambiguous improvement with CNT content due to the variable foam structure. However, dense films generated by hot pressing the foams indicated a significant intrinsic reinforcement of the polymer, even at low loadings of CNTs. Most significantly, CNTs were found to increase the acoustic activity monotonically at concentrations up to 0.1 wt%.     

Controlling bubble density in MWNT/polymer nanocomposite foams by MWNT surface modification

Polymer nanocomposite foams are promising substitutes for polymeric foams. Carbon nanotube/polymer nanocomposite foams possess high strength, low density, and can be made conductive. Creating polymer foams with controlled foam morphology is of great importance for controlling foam properties. The foam morphology is influenced by the foaming conditions and filler properties. For carbon nanotube/polymer composite foams, dispersion state and aspect ratio of the carbon nanotubes have been shown to influence the bubble density and bubble size. In the current study, the influence of carbon nanotube surface chemistry on the bubble density of multi-walled carbon nanotube/poly(methyl methacrylate), MWNT/PMMA, nanocomposite foams was investigated. The surface of the MWNTs with controlled aspect ratio was covalently modified with glycidyl phenyl ether (GPE). Surface modified MWNT/PMMA nanocomposite foams were produced using a supercritical carbon dioxide foaming process. At constant MWNT concentration, the bubble density of polymer nanocomposite foams filled with GPE surface modified MWNT was found to be several times higher than that of polymer nanocomposite foams filled with nitric acid treated MWNT. After the MWNTs were modified with GPE, the surface chemistry of the MWNT became the dominant factor in determining the bubble density while the MWNT aspect ratio became less influential.     

Si元素对碳纳米管增强铝基复合泡沫组织与性能的影响

针对金属基复合材料,添加合金元素是提升其综合性能的有效途径.本文通过高能球磨和填加造孔剂法,制备了添加Si元素的碳纳米管(CNTs)增强铝基(CNTs/Al-Si)复合泡沫,通过准静态压缩实验测试其压缩性能和吸能性能,进一步研究烧结温度和不同Si元素含量对CNTs/Al-Si复合泡沫微观组织、压缩性能和吸能性能的影响,...     

纳米碳管对泡沫炭的超临界发泡行为及其力学性能的影响机制

采用超声波?磁力搅拌的方法, 实现了纳米碳管(CNTs)在中间相沥青(MP)中的均匀分散, 并考察了CNTs对泡沫炭的超临界发泡行为及其压缩强度的影响. 研究结果表明: 在超临界发泡过程中, 处于过饱和状态的甲苯将优先在CNTs/MP固-液界面处成核, 进而不断扩散、聚集、膨胀和发泡, 导致泡沫炭孔结构的均一性得以提高; 当在中间相沥青中均匀分散3.5wt%的CNTs后, 所制泡沫炭的压缩强度由3.2MPa提高到4.7MPa, 升高了46.9%; CNTs良好的导热性能降低了基体碳在石墨化过程中的热应力差异, 使得微裂纹的数量减少, 并且其一维纳米结构使得石墨化泡沫炭的孔壁和韧带结构得以增强.     

Ultra-light,high flexible and efficient CNTs/Ti_3C_2-sodium alginate foam for electromagnetic absorption application

Ultra-light carboxylic functionalized multi-walled carbon nanotubes(CNTs-COOH) and Ti_3C_2 MXene hybrids modified sodium alginate(CNTs/Ti_3C_2-SA) based composite foams were prepared through ice-templated freeze-drying method. The microstructure of the synthesized CNTs/Ti_3C_2 hybrids and CNTs/Ti_3C_2-SA foams is characterized by the presence of CNTs inserted between MXene layers which prevents their restacking. The resultant CNTs/Ti_3C_2 hybrids exhibit a unique sandwich-like hierarchical structure. Scanning electron microscopy(SEM) images show that the CNTs/Ti_3C_2-SA foam exhibits a heterogeneous anisotropic microstructure and CNTs/Ti_3C_2 hybrids are homogeneously dispersed in the skeleton of the porous foam. In case that the content of the hybrids amounts 40 mg/cm3, the CNTs/Ti_3C_2-SA foam possesses excellent electromagnetic(EM) absorption performance with a minimum reflection coefficient(RCmin) as low as-40.0 d B. In case of a sample thickness of 3.95 mm, the RCminreaches-24.4 d B and the effective absorption bandwidth covers the whole X band from 8.2 to 12.4 GHz. A control test shows that, with the same absorbent content, the CNTs/Ti_3C_2-SA foam exhibits a far better EM performance than that of CNT-free Ti_3C_2-SA foam.     

Mesophase AR pitch derived carbon foam: Effect of temperature, pressure and pressure release time

For the carbon foam production, mesophase pitch pellets are heated up in a reactor in an aluminum mold to specified pressures and finally pressure released to obtain green carbon foam samples. The green foams were then stabilized and carbonized. The effects of various temperatures, pressures and pressure release times on production of carbons foams are investigated. The samples are subjected to SEM, mechanical testing, mercury porosimetry analysis and bulk density determination for characterization. For the processing temperatures of 553, 556, 566 and 573 K, the densities of the foams produced were 380, 390, 410 and 560 kg/m³ respectively. The compressive strengths of the respective samples were increased from 1.47, to 3.31 MPa for the lowest and highest temperatures. The processing pressures were 3.8, 5.8, 6.8 and 7.8 MPa. The bulk density and the compressive strength of the carbon foams produced were changed from 500 to 580 kg/m³, and 1.87 to 3.52 MPa for the lowest and highest pressures respectively. Pressure release times of 5 s, 80 s, 160 s and 600 s are used to produce different carbon foam samples. The densities and the comprehensive strengths measured for the highest and lowest pressure release times changed from 560 to 240 kg/m³ and 3.31 to 2.16 MPa respectively. The pore size distribution of all of the products changed between 0.052×10^-6m and 120×10^-6m. Increase in temperature and pressure increased the bulk density and compressive strength of the carbon foams. The mercury porosimetry results show % porosity increase with increasing temperature and pressure. On the other hand, increase in pressure release time decreased the bulk density, compressive strength of the carbon foam.     

碳纳米管增强开孔铝基复合泡沫的疲劳性能

采用原位化学气相沉积、短时球磨和填加造孔剂法相结合的工艺制备了碳纳米管(CNTs)/Al复合泡沫,研究了其在压缩-压缩循环载荷下的力学性能及失效机制。结果表明,CNTs/Al复合泡沫的应变-循环次数曲线经历线弹性、应变硬化及应变快速增长三个阶段。不同于泡沫铝的逐层坍塌变形失效模式,CNTs/Al复合泡沫疲劳失效的主要原因是大量剪切变形带的形成,试样出现快速的塑性变形。此外,CNTs含量为2.5wt%、孔隙率为60%的复合泡沫试样的疲劳强度相比于泡沫铝提高了92%。CNTs的均匀分布及增强相与基体材料之间良好的界面结合性保证了疲劳载荷能够以剪切力的形式从基体传递到CNTs上,使其充分发挥自身高强度、高韧性的特点,进而提高了疲劳性能。      

Carbon and glass hierarchical fibers: Influence of carbon nanotubes on tensile,flexural and impact properties of short fiber reinforced composites

Dense carbon nanotubes (CNTs) were grown uniformly on the surface of carbon fibers and glass fibers to create hierarchical fibers by use of floating catalyst chemical vapor deposition. Morphologies of the CNTs were investigated using scanning electronic microscope (SEM) and transmission electron microscope (TEM). Larger diameter dimension and distinct growing mechanism of nanotubes on glass fiber were revealed. Short carbon and glass fiber reinforced polypropylene composites were fabricated using the hierarchical fibers and compared with composites made using neat fibers. Tensile, flexural and impact properties of the composites were measured, which showed evident enhancement in all mechanical properties compared to neat short fiber composites. SEM micrographs of composite fracture surface demonstrated improved adhesion between CNT-coated fiber and the matrix. The enhanced mechanical properties of short fiber composites was attributed to the synergistic effects of CNTs in improving fiber–matrix interfacial properties as well as the CNTs acting as supplemental reinforcement in short fiber-composites.     

玻璃纤维增强体形式对酚醛泡沫性能的影响

针对酚醛泡沫脆性大、强度低等缺点,采用3种不同增强形式的玻璃纤维增强体,即短切玻璃纤维(SGF)、酚醛树脂浸渍固化的玻璃纤维针(GFN)及三维间隔连体织物,对酚醛泡沫进行增强.研究了纤维含量和纤维长度对酚醛泡沫压缩性能的影响规律,对比了不同增强形式纤维增强酚醛泡沫复合材料的压缩性能与保温性能.结果表明:当SGF长度为3 mm,与基体质量比为5%时,SGF增强酚醛泡沫的比压缩强度最佳,较纯泡沫的提高了21%;GFN(长度5 mm,与基体质量比为25%)增强酚醛泡沫的比强度提高8%;三维间隔连体织物增强酚醛泡沫的比强度虽略有下降,但其压缩强度(0.239 MPa)达到了承重类酚醛泡沫的要求.SGF和GFN增强的酚醛泡沫的热导率与纯酚醛泡沫的相比略有上升,但仍符合高效保温材料的要求;三维间隔连体织物增强酚醛泡沫的热导率上升明显.     

Comparison of tensile and compressive characteristics of vinyl ester/glass microballoon syntactic foams

The present study is focused on the synthesis and characterization of vinyl ester/glass microballoon syntactic foams. Tensile and compressive properties of vinyl ester matrix syntactic foams are characterized. Results show that the compressive strength and moduli of several syntactic foam compositions are comparable to those of the neat matrix resin. Due to the lower density of syntactic foams, the specific compressive properties of all compositions are higher than those of the neat resin. Similar trends are observed in the tensile properties. Mechanical properties of vinyl ester matrix syntactic foams are compared to well-documented mechanical properties of epoxy matrix systems. The comparison shows that low cost vinyl ester resins, which are extensively used in marine applications, can result in syntactic foams with comparable performance to epoxy matrix systems. In addition, tensile modulus is found to be 15–30% higher than the compressive modulus for all syntactic foam compositions. This difference is related to the possibility of particle fracture in the stress range where modulus is calculated in the compressive stress–strain curves.     

Characterization of rigid polyurethane foams containing microencapsulated Rubitherm? RT27. Part I

Rigid polyurethane foams (RPU foams) and phase change materials (PCMs) are widely used in buildings for thermal insulation and thermal storage, respectively. The combination of both materials could increase energy savings, leading to more energy efficient housing. In this work, PU foams were produced incorporating different percentages of microcapsules containing Rubitherm^? RT27. Microcapsules added to the foam had a high influence on the foaming process and also on the foam properties. It was observed that the increase of foam microcapsules content decreases the final foam height but increases its density and thermal energy storage (TES) capacity. On the other hand, an increase of the foam microcapsules content up to 5 wt% led to decrease the reduced compressive strength (RS) and modulus (RE) in 7 and 25%, respectively. Higher contents had a sharply negative impact on mechanical properties.     

碳纳米管类型对CNTs/Lyocell复合纤维结构与性能的影响

分别采用单壁碳纳米管（SWNTs）和多壁碳纳米管（MWNTs）这两种碳纳米管（CNTs）制备不同的CNTs/Lyocell复合纤维,探讨了碳纳米管类型对复合纤维的结构与性能的影响。结果表明,碳纳米管类型并未影响CNTs/Lyocell纤维的结晶结构,质量分数为1%的SWNTs或MWNTs在Lyocell基体中分布都比较...     

Alignment of carbon nanotubes and reinforcing effects in nylon-6 polymer composite fibers

Alignment of pristine carbon nanotubes (P-CNTs) and fluorinated carbon nanotubes (F-CNTs) in nylon-6 polymer composite fibers (PCFs) has been achieved using a single-screw extrusion method. CNTs have been used as filler reinforcements to enhance the mechanical and thermal properties of nylon-6 composite fibers. The composites were fabricated by dry mixing nylon-6 polymer powder with the CNTs as the first step, then followed by the melt extrusion process of fiber materials in a single-screw extruder. The extruded fibers were stretched to their maxima and stabilized using a godet set-up. Finally, fibers were wound on a Wayne filament winder machine and tested for their tensile and thermal properties. The tests have shown a remarkable change in mechanical and thermal properties of nylon-6 polymer fibers with the addition of 0.5?wt% F-CNTs and 1.0?wt% of P-CNTs. To draw a comparison between the improvements achieved, the same process has been repeated with neat nylon-6 polymer. As a result, tensile strength has been increased by 230% for PCFs made with 0.5% F-CNTs and 1% P-CNTs as additives. These fibers have been further characterized by DSC, Raman spectroscopy and SEM which confirm the alignment of CNTs and interfacial bonding to nylon-6 polymer matrix.     

空心球/铝基复合泡沫材料制备及性能研究

采用粉末冶金技术制备了不同孔隙率的空心球/铝基复合泡沫材料,对其进行T7热处理,并开展了不同孔隙率材料压缩性能及隔声性能的测试。结果表明,制备的泡沫材料中空心球均匀分布于基体内,且空心球与基体之间形成明显的过渡层;空心球/铝合金基复合泡沫材料的压缩应力-应变曲线呈现线弹性、应力平台、致密化3个阶段。随着孔隙率的增加,空心球/铝合金基复合泡沫材料的压缩峰值应力、平台应力及能量吸收能力均呈先上升后下降的变化趋势;随着孔隙率的增加,复合泡沫材料隔声性能逐渐下降。     

纤维增强发泡保温复合材料的制备与性能

为了增强玻化微珠/水泥发泡保温复合材料的力学性能和保温性能,通过掺加改性物理泡沫降低发泡保温复合材料的密度和导热系数,采用改性纤维对发泡保温复合材料进行增强。研究了纤维增强发泡保温复合材料的力学性能和耐水性能,并利用扫描电镜对试样内部微观形貌进行观察,探讨了改性泡沫和改性纤维对发泡保温复合材料的增强机制。结果表明,掺加泡沫明显降低了发泡保温复合材料的密度和导热系数,当泡沫掺量为1.05 mL/g时,试样密度和导热系数分别为186 kg/m³和0.056 W/（m·K）。泡沫改性可有效改善发泡保温复合材料的强度和软化系数,掺加改性泡沫试样的抗折强度、抗压强度和软化系数较掺加乳胶粉试样的分别提高了21.05%、21.43%和13.56%。改性纤维可显著提高发泡保温复合材料的强度和软化系数,掺加改性纤维试样的抗折强度、抗压强度和软化系数较掺加未改性纤维试样的分别提高了25.93%、13.51%和8.33%。