Synthesis and properties of macromer-grafted polymers for noncovalent functionalization of multiwalled carbon nanotubes

We prepared macromer-grafted polymers (MGPs) containing suitable polymer side chains for improving solubility and pyrene units for improving adsorption on multiwalled carbon nanotube (MWCNT) surfaces, and demonstrated that these MGPs act as MWCNT solubilizers that improve solubility of MWCNTs in typically poor solvents such as alkanes and that improve flowability of polymer/MWCNT composites. The polydimethylsiloxane (PDMS)-MGPs, synthesized using PDMS macromers and pyrene-containing monomers, improved solubility of MWCNTs not only in chloroform but also in hexane, which is a poor solvent for MWCNTs. Moreover, the addition of PDMS-MGP-adsorbed MWCNTs (MWCNT/PDMS-MGPs) to epoxy resin monomers or polybutylene terephthalate (PBT) drastically reduced the viscosity of the obtained epoxy resin monomer/MWCNT/PDMS-MGP mixtures and PBT/MWCNT/PDMS-MGP composites in comparison to the epoxy resin monomer/MWCNT mixtures and PBT/MWCNT composites, respectively. The viscosity of PBT/MWCNT/PDMS-MGP composites including ?1 vol% of MWCNTs, in particular, was almost equal to that of pristine PBT.     

The thermal characteristics of epoxy resin: Design and predict by using molecular simulation method

Trial-and-error approaches for experimentally designing and optimizing the polymer matrix for advanced composites are time-consuming and expensive. The simulation for curing behavior and structure–property relationships of epoxy resins can provide a guideline for designing resin matrix which will possess desirable properties. So far there are few reports in which the accuracy of the molecular simulation for the different amine-epoxy systems are addressed. In this paper, an atomistic modeling technique was used to theoretically investigate the curing and thermal transition behavior of two epoxy resin matrices containing amine curing agent with different chemical structures i.e. diaminodiphenyl methane (DDM)/diglycidyl-4,5-epoxycyclohexane-1,2-dicarboxylate (TDE85) and diaminodiphenyl sulfone (DDS)/TDE85 to give help for designing high heat-resistant epoxy matrix. The simulated results successfully predicted that the reaction process was catalyzed in the early stage of the curing and the slight modification in the diamine structure resulted in significant change in the curing and glass transition behavior of epoxy resin. As the bridging group of diamine changed from methylene to sulphone, the reactivity of diamine toward epoxy declined and the glass transition temperature increased from about 190 °C to about 230 °C. This simulated method presented a good agreement with experimental data, and can be used to design and predict high performance resin matrix for advanced composites.     

Pseudoreinforcement effect of multiwalled carbon nanotubes in epoxy matrix composites

The carbon nanotube possesses outstanding physical properties. Theoretically, adding carbon nanotubes into a polymer matrix can remarkably improve the mechanical properties of the polymer matrix. In the present work, a series of composites was prepared by incorporating multiwalled carbon nanotubes (MWNTs) into an epoxy resin. The influences of MWNT content and curing temperature on the flexural properties of the epoxy resin were investigated. The results showed that a very low MWNT content should be used to ensure homogeneous dispersion of MWNTs in the epoxy matrix. A higher MWNT content may lead to deteriorated mechanical properties of the composites because of the aggregation of MWNTs. A decline in the flexural properties of the neat epoxy resin with increasing curing temperature was found. However, under the same curing conditions, improvement in flexural properties was observed for the composite with the low MWNT content and a mild curing temperature. The improvement was far beyond the predictions of the traditional short‐fiber composite theory. In fact, this improvement should be attributed to the retarding effect of MWNTs on the curing reaction of epoxy matrix. Therefore, the improvement in the flexural properties was only a pseudoreinforcement effect, not a nano‐reinforcement effect of the MWNTs on the epoxy resin. Perhaps, it is better for MWNTs to be used as functional fillers, such as electrical or thermal conductive fillers, than as reinforcements. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 3664–3672, 2006     

Impact of water absorption on the creep performance of epoxy/microcrystalline cellulose composites

Recently, considerable effort has been made to study cellulose/epoxy composites. However, there is a gap when it comes to understanding the post-conditioning anomalous effect of moisture uptake on their mechanical and dynamic-mechanical properties, and on their creep behavior. In this work, up to 10.0 wt% microcrystalline cellulose (MCC) was incorporated into epoxy resin by simple mixing and sonication. Epoxy/MCC composites were fabricated by casting in rubber silicone molds, and rectangular and dog-bone test specimens were produced. The moisture uptake, dynamic mechanical, chemical, tensile, and creep behavior were evaluated. The incorporation of MCC increased the water diffusion coefficient. The changes in storage modulus and glass transition temperature, combined with Fourier-transform infrared spectroscopy analysis, evidenced that water sorption in epoxies causes both plasticization and additional resin crosslinking, although the latter is prevented by the addition of MCC. The creep strain of the composites increased by 60% after conditioning, indicating that plasticization induced by water sorption plays an important role in the long-term properties of the composites.     

Material systems for rapid manufacture of composite structures

A manufacturing process is described that builds complex composite parts using a layered building process in which each layer of pre‐preg composite is laid and cured as the build progresses. In order to employ on‐line curing without molds, resin technologies that provide fast curing at room temperature—ultraviolet curable and epoxy/polyamide—were investigated. UV‐curable resins were tested for their ability to “shadow” cure by exposing carbon fiber composites to ultraviolet light to determine if the cure propagated from areas directly exposed to areas under fibers. Though ultraviolet curing showed advantages in cure time and low volatile production, very minimal “shadow” curing was achieved. A low temperature curing epoxy/polyamide mixture was tested for the effects of cure temperature, cure time, and mix ratio on the final degree of cure (%DOC) and glass transition temperature (T_g). Layers were made using different resin mixtures, partially cured, and used to build layered parts to determine curing characteristics during the lay‐up process. In the epoxy/polyamide mixtures, mix ratio had little effect on the reaction rate but did affect the T_g. A kinetic model was established for the resin epoxy/polyamide system for optimizing processing conditions during fabrication. However, the model failed to correctly predict the fabrication. The reaction of the material was different during the fabrication process than during the isothermal cure due to the presence of oxygen. During the build process, the degree of cure in each layer increased significantly over the prestaged degree of cure in less time than theoretically predicted. However, the final resin properties, such as T_g, were still below the specifications for high performance parts.     

Low-temperature fast curable behavior and properties of bio-based carbon fiber composites based on resveratrol

Environmentally friendly materials are an integral part of sustainable chemistry, and bio-based polymer composites are an important class of materials. The manufacture of composites is expected to reduce or even eliminate the use of adjuvants, considering the importance of reducing energy consumption and avoiding health and environmental risks. In this study, a phenyl-containing, polyfunctional, bio-based epoxy resin (TGER) was synthesized, and carbon fiber-reinforced, bio-based epoxy resin composites were fabricated by vacuum-assisted resin infusion using two aromatic amine curing agents, 4,4′-diaminodiphenylmethane (DDM) and 3,3′-diethyl-4,4′-diaminodiphenylmethane (DEDDM). Curing reactions and rheological behavior studies showed that TGER had higher curing reactivity toward DDM and DEDDM than to diglycidyl ether of bisphenol A (DGEBA) and possessed good processability. The results indicated that the resveratrol-based epoxy resin displayed low-temperature fast curing properties. The evaluation of the mechanical properties of the carbon fiber composites showed that the flexural strengths of CF/TGER/DDM and CF/TGER/DEDDM were 520 and 628 MPa, respectively. The initial decomposition temperature of CF/TGER composites is above 200°C. Furthermore, the carbon fiber–reinforced biopolymers possess excellent heat resistance. Therefore, carbon fiber-reinforced, resveratrol-based epoxy resin composites are promising candidates as alternatives to petroleum-based high-performance carbon fiber composites.     

兆瓦级风力发电机叶片用环氧树脂

针对兆瓦级风机叶片用纤维/环氧复合材料的特殊要求,开展了适用于真空辅助灌注(VARTM)工艺的环氧基体树脂的国产化研究。采用国产环氧树脂与实验室自制的稀释剂制备环氧树脂与胺类固化剂配合使用,通过示差扫描量热分析,IR光谱,力学性能,耐热性、粘度及吸水性测试等研究了环氧树脂与固化剂配比对其工艺和固化物性能的影响,获得了初始粘度低、粘度对温度不敏感、操作时间长的环氧基体树脂,其树脂浇注体的拉伸性能、弯曲性能均优于国外环氧树脂固化体系,可满足兆瓦级风机叶片用高性能复合材料的使用需求。     

Influence of the Stoichiometric Ratio on the Curing Kinetics and Mechanical Properties of Epoxy Resin Cured with a Rosin-Based Anhydride

Bio-based alternatives for petroleum-based epoxy resin curing agents, such as maleopimaric acid (MPA), are indispensable for sustainable fiber reinforced polymer composites with thermosetting matrices. However, previous investigations disregarded the importance of choosing the right stoichiometric ratio R between the anhydride groups in the rosin-based curing agent and the epoxy groups in the resin. Therefore, the influence of R on the curing kinetics and mechanical properties of an epoxy resin cured with a rosin-based anhydride is studied. Here, Fourier-transform infrared spectroscopy (FT–IR) indicates that for R ⩾ 0.9 unreacted anhydride groups are present in the thermoset. Consequently, the network density decreases and the glass transition temperature T_g drops by about 40 °C. On the other hand, the steric hindrance of unreacted functional groups for R ⩾ 0.9, increases the flexural modulus and the reduced network density improves fracture toughness. The results indicate that the best R for overall high mechanical performance and good processability is preferably low (R ⩽ 0.7). Here, a low R results in a high T_g and good processability due to a low viscosity. However, the latency of the mixtures is low and therefore, the mixtures are not fit for processing via prepreg technology.     

Effect of polymeric additives on properties of glass–bisphenol A dicyanate laminate composites

The polycyanurate network matrix derived from the thermal, dibutyl tin dilaurate catalyzed polymerization of bisphenol A dicyanate was modified in their glass–laminate composites with different linear polymeric additives bearing pendant phenol, cyanate, and epoxy functions. The mechanical properties and fracture energy for delamination of the glass–laminate composites were estimated as functions of the backbone structure and concentration of the various additives. The effect of altering the nature or concentration of the functional group for a given backbone structure of the additive was examined in some cases. Except for the epoxy functional acrylic polymer, all other systems adversely affected the fracture energy for delamination of the composites due to either plasticization or embrittlement of the matrix. With the exception of the styrene‐hydroxyphenyl maleimide (SPM) copolymer, the other modifiers impaired the mechanical properties and adversely affected the thermomechanical profile of the composites. In the cases of the phenol functional acrylic polymer and its cyanate derivative, plasticization of the matrix by the partly phase‐separated additive, which eased the fiber debonding, appears to be responsible for the impairment of the mechanical properties. The high glass transition temperature SPM copolymer enhanced the resin–reinforcement interaction through dipolar interactions induced by the hydroxyl groups, which resulted in amelioration of the mechanical properties. However, its possible coreaction and formation of a brittle, homogeneous phase with the polycyanurate was conducive for poor damage tolerance. The SEM analysis of the fractured composites showed that in the elastomers fiber debonding is the major cause for delamination. Although the presence of SPM led to a stronger interphase, failure occurred either in the brittle matrix or through fiber breakage. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 75–88, 2000     

Laboratory investigation of the properties of asphalt modified with epoxy resin

Epoxy asphalts were prepared by mixing styrene–butadiene–styrene (SBS) modified asphalt with epoxy resin. The curing process and morphology of epoxy asphalts were characterized by infrared spectroscopy and fluorescent microscope, respectively. The effects of epoxy resin contents, ratio of curing agent to epoxy resin and curing temperature on properties of epoxy asphalt were investigated. Results indicated that epoxy resin and epoxy asphalt showed similar curing efficiency. Epoxy asphalts can be cured at 120 or 60°C and its viscosity at 120°C can meet the demands of asphalt mixture mixing and paving. The chemical reaction of epoxy resin in epoxy asphalt is slow and reaction occurs not only with the curing agent but also carboxylic acid in epoxy asphalt. The microstructure of epoxy asphalt transforms from the dispersed structure to networks structure with epoxy resin content increasing and phase transition starts when 30 wt % epoxy resin present in asphalt. The softening point and tensile strength of epoxy asphalt increased with epoxy resin contents increasing. The softening point and tensile strength of epoxy asphalt were markedly improved when epoxy resin content was more than 30 wt %, which is attributed to formation of continuous structure of epoxy resin. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

用红外光谱法研究环氧树脂基体的固化特性

用红外光谱法研究了芳纶抗弹复合材料中改性Ｆ－４６环氧树脂基体的固化特性,用环氧基团相对浓度的变化速率表征环氧树脂基体的固化反应速率。研究了环氧树脂基体的固化反应速率随固化剂含量、固化反应温度的变化规律;根据固化反应过程中环氧树脂基体的环氧基、酯基和醚基等各活性基团相对浓度的变化情况,探讨了环氧树脂基体的固化反应机理。     

Preparation of Epoxy Resin Based on 1,5-Naphthalenediol and Its Application in Carbon Fiber-Reinforced Composites

A series of new epoxy resin base on 1,5-naphthalenediol were prepared to produce the heat-resistant carbon fiber-reinforced composites. The structures of the epoxy resins were characterized by Fourier Transform Infrared (FTIR) spectroscopy and Gel Permeation Chromatography (GPC) analyses. Dynamic curing behavior was investigated using Differential Scanning Calorimetry (DSC). The physical properties of the cured polymers were evaluated with Dynamic Thermal Mechanical Analyses (DMTA) and Thermogravimetric Analyses (TGA). The results showed that the cured polymer exhibited a higher glass transition temperature (T_g) of 251.1°C and better thermal stability. Such properties make the resin highly promising for heat-resistant composite applications.     

The effect of hygrothermal fatigue on physical/mechanical properties and morphology of neat epoxy resin and graphite/epoxy composite

The effect of moisture absorption, desorption, and thermal spiking on the physical/mechanical properties of TGDDM/DDS epoxy resin was investigated and compared to the Gr/Ep composite. The mechanism of moisture diffusion in the neat resin was described on the morphological level. The diffusion rate of moisture in epoxy resin was found to depend on the mobility of molecular chains within an inhomogeneous epoxy network. Two well-known concepts of plasticization of amorphous polymers, the lubricity theory and the gel theory, were invoked to describe the interactions between the absorbed moisture and the resin network. Slight permanent changes in properties of the neat resin were observed after one absorption-desorption cycle. In the thermal spiking experiment, only the spiking temperature above the glass transition of the moisture saturated epoxy resins changed their internal structure and produced very small (thin) microcracks. By comparison with the neat epoxy resin, the Gr/Ep composites contain the reinforcement-matrix boundary region, characterized by the highest restrictions to molecular mobility. The absorbed moisture during the static hygrothermal fatigue cannot effectively plasticize this region. But during thermal spiking, the formation of microcracks is observed within the reinforcement-matrix boundary region as well as an increase in the moisture content.     

Synthesis and application of thermal latent initiators of epoxy resins: A review

Epoxy resin, which is extensively used in civil and industrial applications, shows excellent comprehensive performance, especially as a polymer matrix used in fiber-reinforced composites. A thermal latent initiator, used as an epoxy curing agent, has high storage stability and is widely applied in the preparation of epoxy-based blends and fiber-reinforced composites. In this review, the basic properties of epoxy resins and commonly used curing agents are discussed while progress on the synthesis of thermal latent initiators is reviewed in detail. Moreover, the curing mechanisms, thermal stability, and mechanical properties of epoxy resins with thermal latent initiators are also discussed.     

聚醚酰亚胺/环氧树脂体系的固化及相分离行为研究

环氧树脂固化物本征的低韧性是限制其在复合材料应用的主要缺点之一。利用高性能热塑性树脂聚醚酰亚胺(PEI)与环氧树脂共混,系统研究了PEI在环氧树脂中的溶解行为、固化行为以及相分离行为。溶解试验表明:PEI与环氧齐聚物具有良好的相互溶解性;同时,PEI的加入降低了环氧树脂固化反应的活化能,但并没有改变其固化反应的机制。扫描电镜结果显示:随着PEI含量的增加,环氧/PEI浇铸体的相形貌从明显的分散颗粒相结构演变为双连续相结构和反转相结构。     

一种侧链型液晶聚合物与环氧树脂共混改性研究

设计并合成了一种侧链型液晶聚合物（SLCP），用红外光谱（FTIR），差示扫描量热分析（DSC）和偏光显微镜（POM）对聚合物结构和液晶性能进行表征，探讨其对环氧树脂共混物力学性能的影响，并分析共混物的微相分离结构，结果表明，用T31作固化剂时SLCP对环氧树脂有较好的增强增韧效果，在强度和玻璃化温度不降低的情况下断裂伸长度比未改性固化物最大提高2．6倍，但用三乙醇胺作固化剂时SLCP对环氧树脂改性效果不明显。     

纳米粒子改性环氧树脂玻璃化转变温度的研究

采用示差扫描量热分析(DSC)研究了纳米A l2O3粒子改性的环氧树脂基体玻璃化转变温度与纳米粒子含量之间的关系以及纳米粒子含量对改性体系固化剂用量的影响。结果表明,随着纳米粒子含量的提高,改性树脂的玻璃化转变温度逐渐下降,由纯树脂的224℃下降到182.5℃(纳米粒子用量30%,固化剂添加量70%)。并且纳米粒子的加入会影响树脂基体的固化反应。达到玻璃化转变温度峰值时的固化剂用量并非按照改性体系中环氧树脂含量等当量比加入,而是与纳米粒子含量有关,纳米粒子含量越高,达到玻璃化转变温度峰值时固化剂用量越少。     

Asphaltene/polymer composites: Morphology,compatibility, and rheological properties

In this study, we investigate the use of asphaltene, a natural waste product that is inevitably formed during heavy oil processing, as a filler in polymer composites. The focus of this work is on the compatibility of various asphaltenes, featuring different polarities, with several polymers, including polypropylene (PP), polystyrene (PS), polymethyl methacrylate (PMMA), and polycarbonate (PC). The Hansen solubility parameters were plotted to predict the compatibility of polymers with different asphaltenes. Then, polymer composites were prepared by two common techniques: melt mixing and solution mixing. The dispersion state of the asphaltenes in each polymer was investigated by using imaging and rheological techniques. This work showed that the network structure of the asphaltenes and, thus, the final properties of the composites can be controlled by the polarity of asphaltenes, mixing technique, and melt viscosity of the polymer. For instance, more polar asphaltene (Asph P) produced smaller aggregates in PMMA, which has a higher polar solubility parameter than PP or PS. At 2.5 wt.% of asphaltene, Asph P showed 26% and 177% larger asphaltene agglomerates in PP and PS, respectively, than the less polar asphaltene (Asph Al). PS/asphaltene and PMMA/asphaltene composites prepared by the solution mixing method exhibited better dispersion compared to their melt-mixed counterparts. In melt-mixed composites, the dispersion quality of the asphaltene was better for polymers with higher melt viscosity. Thus, a careful choice of polymer, asphaltene, and preparation conditions can be used to tune the properties of asphaltene/polymer composites.     

Intercalation of epoxy resin in organically modified montmorillonite

Various methods of preparation of epoxy resin/clay mixtures, before the addition of the crosslinking agent and curing to form epoxy‐based polymer layered silicate (PLS) nanocomposites, have been investigated to determine their effect on the nanostructure. Organically modified montmorillonite clay was used, and the mixtures were prepared by both simple mixing and solvent‐based methods. X‐ray diffraction shows that intercalation of the resin into the clay galleries occurs for all clay loadings up to 25 wt % and for both preparation methods, but the dispersion of the clay in the resin, observed by optical microscopy, is significantly better for the solvent preparation method. Differential scanning calorimetry (DSC) shows that the intercalated resin has the same molecular mobility as the extra‐gallery resin, but suggests that the intercalated resin does not penetrate completely into the galleries. Prolonged storage of the resin/clay mixtures at room temperature leads to changes in the DSC response, as well as in the response to thermogravimetry, which are interpreted as resulting from homopolymerization of the epoxy resin, catalyzed by the onium ion in the modified clay. This confirms and explains the earlier observation of Benson Tolle and Anderson (J Appl Polym Sci 2004, 91, 89) that “conditioning” of the resin/clay mixtures at ambient temperature has a significant effect when the crosslinking agent is subsequently added, and indicates that the preparation method has important consequences for the nanostructure development in the PLS nanocomposites. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102:3751–3763, 2006     

热固性环氧树脂形状记忆效应研究

将新型的高分子固化剂与环氧树脂(EP)进行共混,经适度交联固化后制备出一种具有较低玻璃化转变温度(Tg)的无定型EP体系,并对该EP固化体系的力学性能、形状记忆特性和动态力学性能等进行了研究。结果表明:适度交联固化的EP体系具有良好的形状记忆特性,固化剂用量是影响该形状记忆体系综合性能的主要因素;其最大形变恢复率均为100%,形变恢复速率基本上随固化剂用量增加而增大,最大形变恢复速率为0.023 s-1;形变固定率随固化剂用量增加而减小,当w(固化剂)=37.5%或54.5%时,形变固定率为100%或96%。