聚丙烯腈/钠基蒙脱土纳米复合材料的结构和性能研究

采用乳液聚合法制备了聚丙烯腈/钠基蒙脱土(Na-MMT)纳米复合材料,并通过湿法纺丝得到了Na-MMT纳米复合腈纶纤维.用X射线衍射仪表征了纳米蒙脱土在腈纶基体中的分散情况,并用热重分析法和电子单纱强力仪对纤维的热稳定性能和力学性能进行了表征.结果表明,通过乳液分散聚合法,层状蒙脱土剥离,并均匀分散在聚丙烯腈基体中,与不舍蒙脱土的腈纶纤维相比,Na-MMT纳米复合腈纶纤维的热稳定性能和力学性能得到明显提高.     

Epoxy based nanocomposites with fully exfoliated unmodified clay: mechanical and thermal properties

The unmodified clay has been fully exfoliated in epoxy resin with the aid of a novel ultrafine full-vulcanized powdered rubber. Epoxy/rubber/clay nanocomposites with exfoliated morphology have been successfully prepared. The microstructures of the nanocomposites were characterized by means of X-ray diffraction and transmission electron microscopy. It was found that the unmodified clay was fully exfoliated and uniformly dispersed in the resulting nanocomposite. Characterizations of mechanical properties revealed that the impact strength of this special epoxy/rubber/clay nanocomposite increased up 107% over the neat epoxy resin. Thermal analyses showed that thermal stability of the nanocomposite was much better than that of epoxy nanocomposite based on organically modified clay.     

Highly ordered hierarchical poly(ethylene oxide)-b-polystyrene/organoclay nanocomposites

A lamellar forming poly(ethylene oxide)-b-polystyrene (PEO-b-PS)/organoclay nanocomposite with a unique hierarchical structure has been fabricated, by casting solution blends of the block copolymer and organoclay, with subsequent annealing at 180 °C for 8 h under uniaxial constraint. PEO-b-PS provided the nanocomposite lamellar structure with a slightly increased long period. Lamellar layers of the nanocomposite block copolymer were oriented parallel to the film plane. Fully exfoliated clay platelets were localized mostly in the aligned PEO layers, and all platelets were found to be parallel to the interface between PEO and PS layers. PEO crystals in the nanocomposite were oriented with the c-axis perpendicular to the phase-separated layers. The orientation function degree of the PEO crystals within the nanocomposite was lower than that of the crystals within the neat block copolymer.     

Crystallization behavior of organo-nanoclay treated and untreated kraft fiber–HDPE composites

Both non-isothermal and isothermal crystallization behaviors of neat HDPE and organo-nanoclay treated and untreated kraft fiber–high density polyethylene (HDPE) or HDPE–maleic anhydride polyethylene (MAPE) composites were analyzed using differential scanning calorimetry (DSC). The isothermal crystallization process was studied by the Avrami model. The crystallization patterns and organo-nanoclay distribution was characterized by X-ray diffraction (XRD). It was found that both organo-nanoclay treated and untreated kraft fibers could act as nucleating agent for the HDPE polymer when the fiber length was comparatively small. All composites crystallized much faster than the neat HDPE, while their crystallinity levels were lower. The organo-nanoclay treatment of kraft fibers made the crystallinity level lower, but the nucleation rate increased in the composites compared to the untreated kraft fiber–HDPE composites. But both the crystallinity level and the nucleation rate of the composites were increased by adding MAPE compatibilizer to the composites. MAPE increased the d-spacing of the organo-nanoclay layers in the composites and resulted in exfoliated clay platelets when the fiber loading was as high as 40 wt%.     

化学处理和吸湿水对剑麻纤维及其与树脂界面性能的影响

使用KMnO₄、NaOH、阻燃剂、硅烷对剑麻纤维进行表面处理。采用单丝拉伸和微脱粘方法分别测试了剑麻纤维的拉伸性能及其与改性丙烯酸酯、环氧树脂的界面性能,考察了吸湿水对剑麻纤维表面形貌、拉伸性能及其与树脂界面粘结的影响,分析了相应的破坏模式。结果表明,经过表面化学处理后剑麻纤维的拉伸强度和模量均有不同程度的下降,其中经KMnO₄和硅烷处理后,纤维拉伸强度下降了44%,经NaOH处理后其拉伸强度降低了27%,阻燃剂处理对剑麻性能的影响不明显。表面化学处理还会降低剑麻纤维与改性丙烯酸酯的界面粘结强度,其下降的幅度与纤维拉伸强度下降程度不一致,阻燃剂处理的剑麻/改性丙烯酸酯的界面强度最低,仅为2.0 MPa,较未处理剑麻纤维复合体系下降了80%。经硅烷处理后,剑麻纤维的吸水率下降,吸水后其拉伸性能保留率高于未处理剑麻纤维。湿态条件下未处理剑麻纤维与环氧树脂的界面强度为6.6 MPa,高于硅烷处理剑麻/环氧树脂的界面强度,其断口形貌表明硅烷处理可导致微纤之间的弱粘结,从而降低了剑麻纤维自身及其与树脂的界面性能。     

PBO纤维表面空气冷等离子体改性

采用等离子体处理方法对PBO(聚对苯撑苯并二 口 恶 唑)纤维表面进行改性。用XPS和AFM测试分析等离子处理时间对PBO纤维表面组成和表面形貌的影响规律;首次采用浸润性测试和IR测试分析等离子体处理前后纤维浸润性和表面官能团的变化。用Microbond测试方法表征了纤维与树脂基体的界面剪切强度,并用SEM观察微复合材料破坏形貌。结果表明:等离子体处理后纤维浸润性得到改善,纤维表面苯环上引入了很多羟基。等离子体处理最佳条件下(170 W,10 min),纤维表面粗糙度最大,纤维表面O元素含量最大, O/C比率提高了50.5 %, IFSS值提高了64.7 %。     

高性能有机纤维单丝复合体系界面粘结性能实验研究

采用单丝复合体系多次断裂法,通过对纤维单丝断点数的统计及其断点形貌的分析,考察了PBO纤维、芳纶Twaron纤维、超高分子量聚乙烯纤维(UHMWPE)3种高性能有机纤维与韧性环氧基体的界面剪切强度;并对比考察了界面剪切强度与对应复合材料单向板层间剪切强度之间的关系;结合XPS、SEM等手段分析了有机纤维表面物理化学特性对界面剪切强度的影响。结果表明,Twaron/环氧的界面剪切强度高于PBO/环氧,UHMWPE/环氧的界面粘结弱,该方法不能测试;上述体系界面剪切强度与对应的复合材料单向板层间剪切强度变化趋势是一致的;表面化学活性高的纤维对应的界面剪切强度高。     

氩气低温等离子体处理对PBO纤维的表面改性

采用低温等离子体表面处理技术对聚苯撑苯并二口恶唑(PBO)纤维表面进行改性.选用氩气作为处理气氛,研究了气压、功率和处理时间等参数对纤维表面性质的影响.采用FT-IR和SEM等方法对处理前后纤维表面化学结构及形态结构进行了表征,并通过单丝拔出试验测定了改性前后PBO纤维与环氧树脂基体的界面剪切强度(IFSS),对纤维与树脂的界面粘结性进行了初步评价.同时,采用液滴形状法对纤维表面亲水性进行了表征.通过研究发现,经低温氩气等离子处理后,PBO纤维表面亲水性增强,PBO纤维/环氧树脂的IFSS较未处理样品提高了42%.     

Long-term moisture effects on the interfacial shear strength between surface treated carbon fiber and epoxy matrix

In recent years, carbon fiber reinforced polymer (CFRP) composites have found increasing applications in marine and offshore area, where the CFRP components are subjected to a persistent attack of moisture. The performance degradation of composites under those critical service conditions becomes a key issue. In this work, silane coating and multiwalled carbon nanotubes were applied on carbon fibers to enhance the fiber/matrix interfacial bonding strength. The long-term effects of moisture on the interfacial shear strength (IFSS) of the composites in underwater environments, such as de-ionized water and simulated seawater, have been studied using single fiber microbond method. The silane coating and carbon nanotube-modified silane coating are found to contribute 14.5% and 26.3% increase in IFSS of the CFRP in dry air, and well maintain this improvement during a 120-day immersion test in de-ionized water and simulated seawater.     

The effect of heat treatment temperature on the interfacial shear strength of C/C composites

This paper investigates the effect of heat treatment temperature on the interfacial shear strength (IFSS) of carbon/carbon composites reinforced with polyacrylonitrile-based fibers. A series of single fiber push-out tests were performed on specimens heat treated at 1800, 2100, and 2400 °C, using a nanoindenter with a flat ended conical tip. The microstructure was characterized using polarized light and transmission electron microscopy and the debonded fiber/matrix interface was examined using scanning electron microscopy. Wavelet analysis of the load–displacement data was used as an additional tool to investigate the initiation and progression of debonding. Compared to 1800 °C, heat treatment at 2400 °C was associated with a decrease in IFSS, from 12 to 7 MPa. Transmission electron microscopy study showed that the microstructure of the fiber/matrix interphase remained amorphous even with heat treatment at 2400 °C. The decrease in the IFSS can be partly attributed to the reorganization of the graphene sheets in the matrix in the vicinity of fiber/matrix interphase. The thermal expansion mismatch between fiber and pyrocarbon matrix is another possible reason for the observed decrease in the IFSS.     

A study of the mechanical properties of short natural-fiber reinforced composites

The degree of fiber–matrix adhesion and its effect on the mechanical reinforcement of short henequen fibers and a polyethylene matrix was studied. The surface treatments were: an alkali treatment, a silane coupling agent and the pre-impregnation process of the HDPE/xylene solution. The presence of Si–O–cellulose and Si–O–Si bonds on the lignocellulosic surface confirmed that the silane coupling agent was efficiently held on the fibres surface through both condensation with cellulose hydroxyl groups and self-condensation between silanol groups.

The fiber–matrix interface shear strength (IFSS) was used as an indicator of the fiber–matrix adhesion improvement, and also to determine a suitable value of fiber length in order to process the composite with relative ease. It was noticed that the IFSS observed for the different fiber surface treatments increased and such interface strength almost doubled only by changing the mechanical interaction and the chemical interactions between fiber and matrix.

HDPE-henequen fiber composite materials were prepared with a 20% v/v fiber content and the tensile, flexural and shear properties were studied. The comparison of tensile properties of the composites showed that the silane treatment and the matrix-resin pre-impregnation process of the fiber produced a significant increase in tensile strength, while the tensile modulus remained relatively unaffected. The increase in tensile strength was only possible when the henequen fibers were treated first with an alkaline solution. It was also shown that the silane treatment produced a significant increase in flexural strength while the flexural modulus also remained relatively unaffected. The shear properties of the composites also increased significantly, but, only when the henequen fibers were treated with the silane coupling agent. Scanning electron microscopy (SEM) studies of the composites failure surfaces also indicated that there is an improved adhesion between fiber and matrix. Examination of the failure surfaces also indicated differences in the interfacial failure mode. With increasing fiber–matrix adhesion the failure mode changed from interfacial failure and considerable fiber pull-out from the matrix for the untreated fiber to matrix yielding and fiber and matrix tearing for the alkaline, matrix-resin pre-impregnation and silane treated fibers.     

Effect of superheated steam treatment of carbon fiber on interfacial adhesion to epoxy resin

To elucidate the effect of superheated steam (SHS) treatment of carbon fiber on the adhesion to epoxy resin and surface states, virgin unsized carbon fiber was exposed to SHS with or without N₂ in the temperature range of 500–800 °C. The interfacial shear strength (IFSS) between the carbon fiber and epoxy resin was successfully improved by SHS treatment with N₂, and the IFSS of fiber treated above 700 °C was the same as or higher than that of a commercial sized fiber. SHS treatment without N₂ resulted in an increase of total acidic groups on the fiber surface accompanied with the increase of phenolic hydroxyl groups, whereas that with N₂ resulted in a simultaneous increase of total acidic and basic functional groups. The significant improvement in the IFSS after SHS treatment with N₂ is considered to be due to the increase of basicity on the fiber surface.     

Interfacial shear strength of a glass fiber/epoxy bonding in composites modified with carbon nanotubes

In recent years, carbon nanotubes (CNTs) grown on fibers have attracted a lot of interest as an additional reinforcing component in conventional fiber-reinforced composites to improve the properties of the fiber/matrix interface. Due to harsh growth conditions, the CNT-grafted fibers often exhibit degraded tensile properties. In the current study we explore an alternative approach to deliver CNTs to the fiber surface by dispersing CNTs in the fiber sizing formulation. This route takes advantage of the developed techniques for CNT dispersion in resins and introduces no damage to the fibers. We focus on unidirectional glass fiber/epoxy macro-composites where CNTs are introduced in three ways: (1) in the fiber sizing, (2) in the matrix and (3) in the fiber sizing and matrix simultaneously. Interfacial shear strength (IFSS) is investigated using single-fiber push-out microindentation. The results of the test reveal an increase of IFSS in all three cases. The maximum gain (over 90%) is achieved in the composite where CNTs are introduced solely in the fiber sizing.     

Structure–property relationships in biaxially deformed polypropylene nanocomposites

Semi-solid forming processes such as thermoforming and injection blow moulding are used to make much of today’s packaging. As for most packaging there is a drive to reduce product weight and improve properties such as barrier performance. Polymer nanocomposites offer the possibility of increased modulus (and hence potential product light weighting) as well as improved barrier properties and are the subject of much research attention. In this particular study, polypropylene–clay nanocomposite sheets produced via biaxial deformation are investigated and the structure of the nanocomposites is quantitatively determined in order to gain a better understanding of the influence of the composite structure on mechanical properties. Compression moulded sheets of polypropylene and polypropylene/Cloisite 15A nanocomposite (5 wt.%) were biaxially stretched to different stretching ratios, and then the structure of the nanocomposite was examined using XRD and TEM techniques. Different stretching ratios produced different degrees of exfoliation and orientation of the clay tactoids. The sheet properties were then investigated using DSC, DMTA, and tensile tests .It was found that regardless of the degree of exfoliation or orientation, the addition of clay has no effect on percentage crystallinity or melting temperature, but it has an effect on the crystallization temperature and on the crystal size distribution. DMTA and tensile tests show that both the degree of exfoliation and the degree of orientation positively correlate with the dynamic mechanical properties and the tensile properties of the sheet.     

甲基丙烯酰氧基倍半硅氧烷改性碳纤维/聚芳基乙炔复合材料界面性能

利用微脱粘法、三点弯曲法、扫描电镜（SEM）、力调制模式原子力显微镜（AFM）和动态力学热分析（DMTA）研究了甲基丙烯酰氧基倍半硅氧烷（Methacryl-POSS）涂层改性前后的碳纤维增强的聚芳基乙炔（PAA）复合材料的界面性能。用Wilhelmy法研究了处理前后的碳纤维与PAA树脂的浸润性。结果表明: POSS涂层处理后的碳纤维表面粗糙度增大,与PAA树脂的浸润性提高;复合材料的界面剪切强度提高了36%,层间剪切强度提高了50%。DMTA图谱表明, POSS涂层改性后,复合材料的玻璃化转变温度提高了12℃,损耗因子降低了53%,表明复合材料的界面粘接性能得到大幅度的改善。      

Influence of functionalized carbon nanofibers on the single carbon fiber–epoxy matrix interface

Amine-functionalized carbon nanofibers (A-CNFs) were deposited on the surface of individual sized carbon fibers using electrophoretic deposition (EPD), and the average interfacial shear strength (IFSS) was determined using the single fiber fragmentation test in conjunction with Weibull analysis. The IFSS decreased by 25% for fibers acting as the negative electrode in water without CNFs, and the impact of agglomerates on IFSS estimation is discussed. Further, a 187% IFSS increase was achieved for fibers undergoing a two-stage A-CNF EPD approach.     

Effects of thermal histories on interfacial properties of carbon fiber/polyamide 6 composites: Thickness,modulus, adhesion and shear strength

Interface thickness and modulus of carbon fiber (CF) reinforced polyamide 6 (PA 6) composites with different thermal histories are characterized as 331–394 nm and 0.24–0.30 times to fiber modulus, respectively. Transverse fiber bundle (TFB) test is firstly employed for evaluating semi-crystalline PA 6 interfacial adhesion. TFB Failure mechanisms are schematically given. Besides enhanced molecular entangling on fiber surface, increased matrix toughness is also found to have a great effect on improved TFB results. Droplet micro-debonding results show that decreasing cooling rate and increasing annealing temperature both decrease interfacial shear strength (IFSS) though residual PA 6 on carbon fiber surface increases. In the end, the above data are normalized together with some previous measured parameters. It shows that quenching of the CF/PA 6 composites and subsequent annealing are shown to give similar results as slow cooling. Relationships between each other are also discussed.     

Measurement and analytical validation of interfacial bond strength of PAN-fiber-reinforced carbon matrix composites

Carbon/carbon composites are well suited to high-friction applications due to their excellent mechanical and thermal properties. Since interfacial shear strength is critical to composite performance, characterization of fiber/matrix interface is a crucial step in tailored design of composites. This article presents a hybrid experimental/analytical study to evaluate the interfacial shear strength (IFSS) of PAN-fiber-reinforced carbon matrix composites. Microstructure was studied by light and high-resolution transmission electron microscopy (HRTEM). A series of push-out tests were conducted to examine the fiber/matrix debonding process. The residual fiber displacement was confirmed by scanning electron microcopy (SEM). The validity of the calculated IFSS value was demonstrated by a simplified analytical approach, where the components contributing to the measured displacement were analyzed considering the mechanics of the indentation. The method described in this article has been successfully used for determining the IFSS of PAN-fiber-reinforced carbon matrix composites.     

Grafting Low Contents of Branched Polyethylenimine onto Carbon Fibers to Effectively Improve Their Interfacial Shear Strength with an Epoxy Matrix

The mechanical properties of carbon fiber (CF) reinforced composites are greatly dependent on the interfacial strength between the CFs and matrix. To improve the interfacial adhesion of carbon fiber/epoxy composites, branched polyethylenimine (PEI) is grafted onto the CFs treated in a mixed acid at optimized process time. The chemical compositions and bonds of functionalized CFs are characterized by thermal gravimetric analysis, Fourier‐transform infrared, and X‐ray photoelectron spectroscopy. The surface structures and morphologies of various CFs are analyzed by Raman spectroscopy and scanning electron microscopy, respectively. Microbond test is adopted to evaluate the interfacial shear strength (IFSS) between the CFs and epoxy matrix. The results show that the CFs modified by low molecular weight PEI are better than those modified by high molecular weight PEI. The IFSS of PEI modified CFs can reach a maximum of 107.2 ± 14.3 MPa at a low functionalization degree compared with 78.1 ± 11.6 MPa of unmodified CFs. The branched structure and high density of active amine groups on the PEI chains are responsible for the improved interfacial strength.     

Controlled synthesis of train-structured montmorillonite/layered double hydroxide nanocomposites by regulating the hydrolysis of polylactic acid

Two-dimensional nanosheets obtained by exfoliation can assemble into new functional nanomaterial. One of the critical challenges is developing an efficient method to make the layered composite complete exfoliation, and another is regulating and controlling nanosheets assembly to obtain the nanocomposite with specific structure. In this article, the platelets of layered double hydroxides (LDH) and montmorillonite (MMT) are exfoliated completely and efficiently in polylactic acid (PLA) by melting blend for 10 min, and the monolayers of MMT or LDH can store stably in PLA for a long time. A new well-organized layered nanocomposite containing the nanosheets of LDH and MMT was gained by being exfoliated and assembling. The structure of MMT/LDH nanocomposite not only holds a periodically alternating structure, but also possesses a train structure, and the formation mechanism of train structure is proposed at the first time; furthermore, the structure of MMT/LDH could be regulated and controlled. Fortunately, even being exfoliated and assembled, MMT nanosheet or LDH nanosheet was not destroyed. The MMT/LDH nanocomposite with expectant structure can be obtained by this efficient and environmentally friendly method, and this method may easily be extended to other layered materials.