纳米炭黑分散方法和含量对低碳镁碳材料力学性能的影响

采用加KH-550偶联剂和高速搅拌的方法,将不同量的纳米炭黑N220均匀分散在酚醛树脂中,制成纳米炭黑-酚醛树脂复合结合剂,研究了纳米炭黑含量对复合结合剂黏度及其经1500℃炭化后碳结构的影响,并采用这些复合结合剂制备了w(C)=3%的低碳镁碳试样。研究了纳米炭黑含量(相对于酚醛树脂的质量分别为0、2.5%、5%、10%和15%)对低碳镁碳试样力学性能的影响,同时还与将纳米炭黑以预混合粉方式加入的低碳镁碳试样的力学性能进行了对比。结果发现:1)随着纳米炭黑含量的增加,复合结合剂的黏度迅速增大;2)纳米炭黑-酚醛树脂复合物经1500℃炭化后的碳结构呈光学同向性,但其微气孔数量减少,微气孔尺寸减小,碳结构的石墨化程度提高;3)随着纳米炭黑加入量的增加,低碳镁碳试样的常温抗折强度、高温抗折强度和常温耐压强度逐渐增大;4)将纳米炭黑直接分散在细粉中加入时,试样的常温抗折强度、高温抗折强度和常温耐压强度均比以纳米炭黑-酚醛树脂方式加入时差。     

碳纤维增强水泥/混凝土材料力学性能的若干研究

本文通过对水泥基体掺入碳纤维进行研究，得出了复合体抗压强度、劈拉强度与碳纤维掺量的关系。同时文中还利用聚丙烯腈纤维作对比研究，得出目前碳纤维作为增强体的优缺点，为碳纤维增强水泥基复合材料的推广应用提供更多的实验依据。     

Cure behaviour of epoxy resin matrices for carbon fibre composites

The cure behaviour of two resin formulations (with high and low curing agent content respectively) of an epoxy resin system, used as matrix for carbon fibre composites, was studied through calorimetric analysis. The aim of this work is to investigate the kinetics of this specific epoxy system in order to be able to choose a proper set of processing parameters which will give good composite material properties. The shape of the conversion curves gives evidence of the differences in the cure kinetics of the two systems. Furthermore, the values of the activation energies were determined both for formulation in the conversion range where vitrification occurs, following a phenomenological approach. These values give an indication of the differences in the curing mechanisms, when varying the content of curing agent. In particular, for both systems, the same reaction represents the onset of the cure process, ie the autocatalytic epoxy ring opening through addition reaction to the primary amine. This reaction dominates the entire cure process of the epoxy formulation at high curing agent content. Conversely, in the formulations with a low curing agent content, after depletion of the primary amines, different reactions may take place (with secondary amines and hydroxyl groups), depending on the cure temperature and the resin viscosity. © 1999 Society of Chemical Industry     

Preparation of polyetherimide/carbon fibre composites by a cataphoresis process

Preliminary results in this study show that it is possible to achieve a good Ultem 1000/carbon fibres covering by means of electrophoretical deposition. The expected amount of deposited polymer is well controlled and the deposited films have a good appearance. In this way a variety of carbon fibre composite materials can be manufactured. © 1999 Society of Chemical Industry     

Morphology,crystallization, and mechanical properties of poly(ethylene terephthalate)/multiwall carbon nanotube nanocomposites via in situ polymerization with very low content of multiwall carbon nanotubes

So far, the reported content of multiwall carbon nanotubes (MWNTs) in polymer/MWNTs nanocomposites is usually above 0.1 wt %. In this article, we will report our work on the study of the morphology, crystallization, and mechanical properties of poly(ethylene terephthalate) (PET)/MWNTs nanocomposites prepared by in situ polymerization with very low content of MWNTs (from 0.01 to 0.2 wt %). Well‐dispersed MWNTs with a big network throughout PET matrix were observed by SEM. The very small amount of MWNTs displayed a great nucleating effect on the PET crystallization. The crystallization temperature was improved for 6.4°C by using only 0.01 wt % MWNTs. The decreased chain mobility of PET by adding MWNTs was evident by the formation of imperfect or smaller/thinner crystallites with low melting temperature. An increased storage modulus was also achieved for the nanohybirds with MWNT content less than 0.05 wt %. Our result indicates that using very low content MWNTs (less than 0.1 wt %) is a simple way to achieve good dispersion, yet with remarkable enhancement for polymer/MWNTs modification. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 3695–3701, 2007     

Electrical, mechanical, and glass transition behavior of polycarbonate-based nanocomposites with different multi-walled carbon nanotubes

Five commercially available multi-walled carbon nanotubes (MWNTs), with different characteristics, were melt mixed with polycarbonate (PC) in a twin-screw micro compounder to obtain nanocomposites containing 0.25-3.0 wt.% MWNT. The electrical properties of the composites were assessed using bulk electrical conductivity measurements, the mechanical properties of the composites were evaluated using tensile tests and dynamic mechanical analysis (DMA), and the thermal properties of the composites were investigated using differential scanning calorimetry (DSC). Electrical percolation thresholds (p_cs) were observed between 0.28 wt.% and 0.60 wt.%, which are comparable with other well-dispersed melt mixed materials. Based on measurements of diameter and length distributions of unprocessed tubes it was found that nanotubes with high aspect ratios exhibited lower p_cs, although one sample did show higher p_c than expected (based on aspect ratio) which was attributed to poorer dispersion achieved during mixing. The stress-strain behavior of the composites is only slightly altered with CNT addition; however, the strain at break is decreased even at low loadings. DMA tests suggest the formation of a combined polymer-CNT continuous network evidenced by measurable storage moduli at temperatures above the glass transition temperature (T_g), consistent with a mild reinforcement effect. The composites showed lower glass transition temperatures than that of pure PC. Lowering of the height of the tanδ peak from DMA and reductions in the heat capacity change at the glass transition from DSC indicate that MWNTs reduced the amount of polymer material that participates in the glass transition of the composites, consistent with immobilization of polymer at the nanotube interface.     

Effect of short carbon fibre concentration on microstructure and mechanical properties of TiCN-based cermets

Short carbon fibre (C_f) reinforced TiCN-based cermets (C_f/TiCN composites) were produced by powder metallurgy method with pressureless sintering technology. The phase evolution, microstructure and fracture morphology of C_f/TiCN composites were investigated. The results showed that TiC, TiN, WC, Cr₃C₂ and Mo phases disappeared gradually and diffused into core and rim phases by dissolution–reprecipitation process, finally formed new hard TiCN core phases and complex compound (Cr, W, Mo, Ti)(CN) rim phases, with the sintering temperature increasing. The added C_f did not change the ‘core–rim’ microstructure but improved the mechanical properties of TiCN-based cermets. The C_f/TiCN composite containing 3?wt-% C_f achieved the best comprehensive mechanical properties, with fracture toughness and bending strength increasing by about 14.4% and 30.8%, respectively, when compared with the composite without C_f. Toughening and strengthening mechanisms of C_f/TiCN composite were concluded as crack deflection and branch, as well as the pull-out, fracture and bridging of carbon fibres.     

Mechanical and viscoelastic properties of butadiene–styrene thermoplastic and oxidized carbon fibre composites

The mechanical and dynamic properties of oxidized carbon fibre and butadiene–styrene thermoplastic elastomer (SBS) composites were studied as a function of the level of fibre oxidation and in comparison with the properties of composites reinforced with untreated commercial carbon fibre. As a general rule, fibre oxidation gives rise to materials with improved mechanical properties—greater tensile and tear strengths. The improvements accomplished depend on the degree of fibre oxidation. The effects of long exposure times to oxidizing agents were tested on the experimental samples, i.e. increase in the number of functional surface groups and loss in mechanical strength due to a decrease in the L/d ratio, properties which act in opposite directions in the composite. Storage modulus retention with increasing strain amplitude is directly proportional to the number of functional groups incorporated into the fibre surface, whereas at low strain amplitude it is proportional to fibre strength, measured in terms of the L/d ratio after processing. It is suggested that improved adhesion at the matrix–fibre interface is obtained through the functional groups of the oxidized fibre. As a consequence of fibre–matrix interface and at any frequency, the damping peak temperature is shifted towards higher ranges and at the same time the apparent activation energy of the relaxation process is observed to increase.     

Toughening of in situ polymerized cyclic butylene terephthalate by addition of tetrahydrofuran

A new method of toughening polymerized cyclic butylene terephthalate (pCBT) with tetrahydrofuran (THF) is proposed. The pCBT was prepared by in situ ring‐opening polymerization of a commercial cyclic butylene terephthalate, a cyclic form of poly(butylene terephthalate), in the presence of THF. In comparison to conventionally polymerized pCBT, the resultant material was found to be ductile, showing a strain at break of well above 100% in tensile tests. Other matrix properties, such as tensile modulus, tensile strength and glass transition temperature, were not significantly altered by the addition of THF. It was found that the presence of THF enhanced the polymerization reaction, resulting in an increased molecular weight and a narrowed molecular weight distribution. Moreover, remaining oligomers after polymerization were extracted by the THF and a toughened oligomer‐free pCBT was obtained. The influence of time and temperature on the long‐time toughening action of THF was studied. The results showed that samples became brittle after 3 months when subjected to a temperature of 80 °C, resulting in a reduction of the toughening action. Copyright © 2010 Society of Chemical Industry     

Effect of in situ grown SiC nanowires on microstructure and mechanical properties of C/SiC composites

Hexagonal-shaped SiC nanowires were in situ formed in C/SiC composites with ferrocene as catalyst in the densification process of polymer impregnation and pyrolysis. The effect of SiC nanowires on microstructure and properties of the composites were studied. The results show that the in situ formed SiC nanowires were hexagonal, mostly with diamer of about 250 nm, and grew by the vapor–liquid–solid (VLS) mechanism. The C/SiC composite with nanowires shows higher bulk density and flexural strength than the one with no SiC nanowires, and the high temperature flexural strength behavior of C/SiC composites with SiC nanowires was evaluated.     

Photoinduced cationic frontal polymerization of epoxy–carbon fibre composites

UV‐activated frontal polymerization was exploited for the preparation of epoxy–carbon fibre composites. The curing process was investigated showing the frontal behaviour, and the final properties of UV‐cured composites were compared with those of the same composites obtained by thermal curing in the presence of amine as hardener. The best curing formulations were designed, defining the photoinitiator‐to‐thermal initiator ratio, which was 1.5:1.5. It was observed that the presence of the carbon fibres induced an acceleration of the front velocity. By comparing the thermomechanical properties of the thermally cured composite and the same composite crosslinked using the frontal process, we could observe that the latter showed higher T_g value and lower σ_f. This was attributed to the formation of a different polymeric network structure. © 2019 Society of Chemical Industry     

Effect of carbon nanofiber functionalization on the in-plane mechanical properties of carbon/epoxy multiscale composites

In this work, vapor-grown carbon nanofibers (CNFs) were functionalized using an optimized route and dispersed in the matrix of carbon fabric-reinforced epoxy composites to develop multiscale carbon/epoxy composites. Functionalization was carried out through an oxidative treatment with a mixture of HNO₃/H₂SO₄ (1 : 3) using a combination of ultrasonication and magnetic stirring. Functionalized CNFs (F-CNFs) were characterized for their morphology, length, functional groups, and degradation due to oxidative treatment. The results showed that it was possible to efficiently functionalize CNFs without any degradation through proper selection of treatment duration. F-CNFs were dispersed homogeneously into the epoxy matrix using ultrasonication in combination with high-speed mechanical stirring. The incorporation of 0.1 wt % F-CNFs led to a 65% increase in Young's modulus and a 36% in tensile strength of neat carbon/epoxy composites. The fracture surfaces were studied using scanning electron microscopy to understand the property enhancement due to F-CNFs. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

碳/碳复合材料力学性能的研究进展

本文综述了碳/碳复合材料力学性能的研究进展,包括碳纤维、基体炭、界面性能、制备工艺及工艺参数等对碳/碳复合材料力学性能的影响。同时简单介绍了当今单向碳/碳复合材料力学性能的表征手段。希望对碳/碳复合材料力学性能的研究及应用提供帮助。     

The effect of carbon nanotube on the physical properties of poly(butylene terephthalate) nanocomposite by simple melt blending

Polyester nanocomposites based on poly(butylene terephthalate) (PBT) and carbon nanotube (CNT) were prepared by simple melt blending using a twin‐screw extruder. There is significant dependence of the thermal, rheological, and mechanical properties of the PBT nanocomposites on the concentration and dispersion state of CNT. The storage and loss moduli of the PBT nanocomposites increased with increasing frequency, and this enhancing effect was more pronounced at lower frequency region. The nonterminal behavior for the PBT nanocomposites was attributed to the nanotube–nanotube or polymer–nanotube interactions, and the dominant nanotube–nanotube interactions at high CNT content resulted in the formation of the interconnected network‐like structures of CNT in the PBT nanocomposites. The incorporation of a small quantity of CNT into the PBT matrix can substantially improve the mechanical properties, the heat distortion temperature, and the thermal stability of the PBT nanocomposites. The unique character of CNT dispersed in the PBT matrix resulted in the physical barrier effect against the thermal decomposition, leading to the improvement in the thermal stability of the PBT nanocomposites. This study also provides a design guide of CNT‐reinforced PBT nanocomposites with a great potential for industrial uses. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

石墨粒度对低炭镁炭砖性能的影响

以电熔镁砂和4种粒度(≤0.149mm、 ≤0.074mm、≤0.044mm和≤0.01mm)的天然鳞片 石墨为主原料,在石墨含量为4%的条件下,研究了 石墨粒度对低炭镁炭砖的物理性能、抗氧化性和热震 稳定性的影响。结果表明:用细石墨取代较粗石墨 (粒度≤0.149mm)制成的镁炭砖,其物理性能、抗氧 化性和热震稳定性都有了明显的改善,且都以加入粒 度≤0.074mm石墨的效果最好。其原因是细石墨的 加入改善了镁炭砖的基质结构。石　墨     

Influence of a cyclic butylene terephthalate oligomer on the processability and thermoelectric properties of polycarbonate/MWCNT nanocomposites

The thermoelectric properties of melt-processed nanocomposites consisting of a polycarbonate (PC) thermoplastic matrix filled with commercially available carboxyl (–COOH) functionalized multi-walled carbon nanotubes (MWCNTs) were evaluated. MWCNTs carrying carboxylic acid moieties (MWCNT-COOH) were used due the p-doping that the carboxyl groups facilitate, via electron withdrawing from the electron-rich π-conjugated system. Preliminary thermogravimetric analysis (TGA) of MWCNT-COOH revealed that the melt-mixing was limited at low temperatures due to thermal decomposition of the MWCNT functional groups. Therefore, PC was mixed with 2.5 wt% MWCNT-COOH (PC/MWCNT-COOH) at 240 °C and 270 °C. In order to reduce the polymer melt viscosity, a cyclic butylene terephthalate (CBT) oligomer was utilized as an additive, improving additionally the electrical conductivity of the nanocomposites. The melt rheological characterization of neat PC and PC/CBT blends demonstrated a significant decrease of the complex viscosity by the addition of CBT (10 wt%). Optical and transmission electron microscopy (OM, TEM) depicted an improved MWCNT dispersion in the PC/CBT polymer blend. The electrical conductivity was remarkably higher for the PC/MWCNT-COOH/CBT composites compared to the PC/MWCNT-COOH ones. Namely, the PC/MWCNT-COOH/CBT processed at 270 °C exhibited the best values with electrical conductivity; σ = 0.05 S/m, Seebeck coefficient; S = 13.55 μV/K, power factor; PF = 7.60 × 10⁻⁶μW/m K⁻², and thermoelectric figure of merit; ZT = 7.94 × 10⁻⁹. The PC/MWCNT-COOH/CBT nanocomposites could be ideal candidates for large-scale thermal energy harvesting, even though the presently obtained ZT values are still too low for commercial applications.     

The effect of poly(butylene succinate) content on the structure and thermal and mechanical properties of its blends with polylactide

Poly(butylene succinate) (PBS) and polylactide (PLA) were blended in a co‐rotating twin‐screw extruder with various contents of PBS from 0 to 100 wt%. The effect of PBS content on the thermal and mechanical properties of PBS/PLA blends was investigated by using DSC, softening point measurements, a Charpy impact test and tensile testing. The Fourier transform infrared spectra showed that the polymers are immiscible, but the addition of PBS could modify the PLA structure in PBS/PLA blends by changing the content of amorphous and crystalline phases. In addition, the cold crystallization temperature of PLA in blends decreases in comparison with pure PLA, which shows that PBS could have a plasticizing effect on PLA. This is confirmed by the results of DSC analysis. The mechanical properties of the blends depend on the percentage of PBS addition. Typically, the mechanical properties of PBS/PLA blends are intermediate between the properties of the polyesters from which they are obtained. However, in some cases unexpected changes in mechanical properties of the blends were observed. For example, the elongation at break for a PBS/PLA blend containing 10 wt% PLA is higher than for pure PBS. © 2019 Society of Chemical Industry     

The effect of fibre sizing and compatibilizer of polypropylene/poly(butylene terephthalate) blends on the mechanical and interphase properties of basalt fibre reinforced composites

The effect of basalt fibre sizing on the mechanical and interphase properties of fibre‐reinforced composites was studied. Two different chemical preparations of the fibre surface (PBT‐compliant and PP‐compliant) were used. The polymer matrix was prepared from polypropylene/poly(butylene terephthalate) (PP/PBT) immiscible polymer blend and the effect of different compatibilizers on the composite properties was evaluated. SEM hints at improved fibre adhesion to the polymer matrix when a PP‐compliant sizing is applied. SEM also reveals improved compatibilization effects when block copolymer instead of multiblock copolymer is used for the PP/PBT blend preparation. The pull‐out test was applied to quantitatively evaluate the interface adhesion between the fibres and matrices. It showed a high value of the interfacial shear strength between basalt fibres modified with PP‐compliant sizing and polymer blend compatibilized by block copolymer, thus confirming good adhesion. One possible explanation of such good mechanical properties can be related to the chemical interactions between functional groups, mainly maleic anhydride on basalt fibres and the polyolefin component (PP) of the polymer matrix. © 2017 Society of Chemical Industry