Thermal Properties and Crystallite Morphology of Nylon 66 Modified with a Novel Biphenyl Aromatic Liquid Crystalline Epoxy Resin

In order to improve the thermal properties of important engineering plastics, a novel kind of liquid crystalline epoxy resin (LCER), 3,3′,5,5′-Tetramethylbiphenyl-4,4′-diyl bis(4-(oxiran-2-ylmethoxy)benzoate) (M1) was introduced to blend with nylon 66 (M2) at high temperature. The effects of M1 on chemical modification and crystallite morphology of M2 were investigated by rheometry, thermo gravimetric analysis (TGA), dynamic differential scanning calorimetry (DSC) and polarized optical microscopy (POM). TGA results showed that the initial decomposition temperature of M2 increased by about 8 °C by adding 7% wt M1, indicating the improvement of thermal stability. DSC results illustrated that the melting point of composites decreased by 12 °C compared to M2 as the content of M1 increased, showing the improvement of processing property. POM measurements confirmed that dimension of nylon-66 spherulites and crystallization region decreased because of the addition of liquid crystalline epoxy M1.     

Curing Behavior,Kinetics and Thermal Properties of o-Cresol Formaldehyde Epoxy Resin Modified by Liquid Crystalline Epoxy Resin

The curing kinetics of a bi-component system of o-cresol-formaldehyde epoxy resin (o-CFER) modified by liquid crystalline p-phenylene di[4-(2,3-epoxypropyl) benzoate] (p-PEPB), with 4,4-diamino-diphenyl ether (DDE) as a curing agent, was investigated by nonisothermal differential scanning calorimetry (DSC) method. The relationship between apparent activation energy, Ea, and the conversion α was obtained by the isoconversional method of Ozawa. A molecular reaction mechanism is proposed. The results show that the values of Ea in the initial stage are higher and tend to decrease slightly with the reaction progress. The primary amines have a higher Ea than secondary amines. The average curing Ea of o-CFER/p-PEPB/DDE system is 61.64 KJ/mol. These curing reactions can be described by a model proposed by ?esták and Berggren, which includes two parameters of m and n. Parameters such as reaction orders were evaluated using the ?esták-Berggren (S-B) equation and the following kinetic equation: dα/dt = Aexp(?Ea/RT)α ^m (1 ? a) ⁿ . The curing behavior of the system was studied by polarized optical microscopy (POM) and torsional braid analysis (TBA). The compatibility of the p-PEPB and o-CFER system is very good. Temperature of mechanical loss peak is higher by 63°C than the common o-CFER epoxy resin, when the weight ratio of p-PEPB with o-CFER is 4:100.     

环氧树脂/液晶双马来酰胺复合材料的研究

以液晶双马来酰亚胺(IA)为改性剂,制备了 IA 质量含量不同的环氧树脂(EP)/IA 复合材料体系,用冲击强度仪、扫描电镜、热变形温度仪、热失重仪等测试手段对复合材料的力学性能和热性能进行测试分析。结果表明,复合材料的冲击强度均有所提高,当 IA 的含量为0.8%(质量分数,下同)时,冲击强度提高了5.3 kJ/m~2;当 IA 含量为1.5%时,复合材料的热变形温度较纯 EP 提高了12℃,失重5 %时的温度(T₅)提高了57℃,失重50%时的温度(T₅₀)提高了45℃。     

热致性液晶聚合物种类对环氧树脂性能的影响研究

利用自行合成的多种热致性高分子液晶聚合物对CYD -12 8环氧树脂进行共混改性 ,用FTIR方法研究了液晶聚合物对环氧树脂固化反应程度的影响 ,用DSC、TGA研究了液晶聚合物对环氧树脂固化物Tg 和热失重温度的影响 ,测试了共混物的力学性能 ,并用扫描电镜观察了共混物冲击断面的形貌。结果表明 :端基含有活性反应基团的液晶聚合物可以提高固化反应程度、提高固化物的韧性和强度 ,同时还使固化物的Tg 和热失重温度提高 ,SEM观察表明 ,加入液晶聚合物的材料断裂面面积增大 ,逐渐出现韧性断裂的特征。     

芳香酯基液晶环氧树脂的合成

以对羟基苯甲酸和对苯二酚为原料,用对甲苯磺酸共沸催化法合成对羟基苯甲酸对苯二酚酯;再由对羟基苯甲酸对苯二酚酯与4-溴环氧丁烷进行反应合成酚酯型液晶环氧物质4-(2-(环氧乙烷基)乙氧基)苯甲酸-4-(2-(环氧乙烷基)乙氧基)苯酚酯。研究该化合物与4,4’-二氨基二苯甲烷(DDM)固化反应的固化特性及固化物的力学性能,并对其结构以及固化行为和固化物的形态进行了表征。结果表明该液晶环氧树脂与DDM交联聚合的网络保持了较好的液晶织态,聚合物具有较好的综合性能。     

苯胺甲基笼型倍半硅氧烷改性环氧树脂的性能

研究了苯胺甲基笼型倍半硅氧烷(PAM-POSS)/环氧树脂(E-44)/MeTHPA/TEA体系的固化反应及其热性能,并考察了固化杂化树脂的力学性能。结果表明:随着PAM-POSS含量的增加,杂化树脂的冲击强度和弯曲强度呈先增大后下降的趋势,当PAM-POSS质量分数为10%时,冲击强度和弯曲强度达到最大值。     

Flame Retardancy and Mechanical Properties of Bio‐Based Furan Epoxy Resins with High Crosslink Density

This work outlines an interesting approach to bioepoxy resins from sustainable 2,5‐bis((oxiran‐2‐ylmethoxy)methyl)furan (BOF). The 3,3′‐diamino diphenyl‐sulfone (33DDS) and 4,4′‐diamino diphenyl‐sulfone (44DDS) are employed as hardeners. For comparison, petro‐based networks from diglycidyl ether of bisphenol A (DGEBA) are developed as well. The systematic analyses suggest that the BOF/DDS networks show higher crosslink densities and mechanical properties than DGEBA/DDS thermosets. Remarkably, an attractive multilayer tubular microstructure is fabricated in the BOF/44DDS thermosets, and it greatly enhances the mechanical performance. Apart from that, BOF/DDS composites exhibit excellent flame retardancy. Especially, for BOF/44DDS, the self‐extinguishment happens in 7 s. The fire retardant mechanism confirms that a low heat release rate and heat release capacity as well as a compact char layer occur in the pyrolysis of BOF/DDS. Thus, the BOF/DDS exhibits superior performance over its DGEBA counterparts and meets a wide variety of requirements in engineering.     

原位聚合芳香型聚氨酯／环氧树脂共混材料的动态力学性能研究

以自制的芳香型二元醇为原料，用原位聚合的方法制备了芳香型聚氨酯厮氧树脂共混材料。系统地研究了二元醇含量对共混材料动态力学性能、冲击性能的关系。结果显示，对环氧树脂增韧的同时，低温下的储能模量基本上没有降低，玻璃化转化温度有所提高，体系为均相体系。     

Influence of Catalyst Content on the Thermal and Mechanical Properties of Epoxy Resins Initiated by a Cationic Latent Thermal Catalyst at Elevated Temperatures

The effect of catalyst content on the thermal and mechanical properties of diglycidyl ethers of bisphenol A (DGEBA)/BPH system was investigated at elevated temperatures. The contents of the catalyst, N‐benzylpyrazinium hexafluoroantimonate (BPH), examined were 0.5, 1, and 3 wt.‐% and the elapsed heating time was varied from 0 to 1 024 h. As a result, the thermal‐oxidative resistance and mechanical properties, including flexural strength, elastic modulus in flexure, and impact strength showed a maximum value at 1 wt.‐% BPH. By increasing the elapsed time to 4 h, the thermal and mechanical properties of the specimens were also improved. These results showed that the internal structure of the epoxy system was stabilized and post‐cured as the elapsed time increased, resulting in an improvement of the thermal and mechanical properties of the specimens.

Impact strength of the DGEBA/BPH system as a function of BPH content and elapsed heating time.     

Curing and Morphology Studies of Thermosets from Blends of a Main Chain Liquid Crystalline Polyester and Diepoxide/Diamine

Summary: Blends of the commercial liquid‐crystalline polyester Rodrun LC‐3000 (60–90 wt.‐%) with a bisphenol A‐diglycidyl ether based diepoxide (DOW D.E.R.330) and an aromatic diamine (MCDEA) prepared in a twin‐screw extruder have been compression‐moulded and cured either isothermally at 260 °C or in a temperature ramp between 160 and 230 °C. The blends were investigated with SEM and thermal analysis (DSC, DMTA). Blends with 80% Rodrun and less cured at 260 °C and the blend containing 60% Rodrun cured in a temperature ramp showed macro‐phase separation followed by reaction‐induced micro‐phase separation (RIPS) both in the Rodrun‐rich and in the epoxy‐rich macro‐separated phases. Blends containing 90, 80 and 70% Rodrun moulded at 160 °C and cured in the temperature ramp showed only RIPS and a morphology rather similar to that of the uncured blends that was most likely co‐continuous; the blend with 90% Rodrun cured at 260 °C showed RIPS and a dispersed epoxy phase in a Rodrun matrix. Phase composition has been determined by extraction of the soluble fraction and chemical analysis.

SEM showing the reaction induced micro‐phase separation for sample REA90/10i.     

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.     

Curing behavior and thermal and mechanical properties enhancement of tetraglycidyl‐4,4′‐diaminodiphenylmethane/4,4′‐diaminodiphenylsulfone using a liquid crystalline epoxy

A thermosetting resin system, based on tetraglycidyl‐4,4′‐diaminodiphenylmethane, has been developed via copolymerization with 4,4′‐diaminodiphenylsulfone in the presence of a newly synthesized liquid crystalline epoxy (LCE). The curing behavior of LCE‐containing resin system was evaluated using curing kinetics method and Fourier transform infrared spectroscopy. The effect of LCE on the thermal and mechanical properties of modified epoxy systems was studied. Thermogravimetric analysis indicated that the modified resin systems displayed a high T_0.05 and char yield at lower concentrations of LCE (≤5 wt%), suggesting an improved thermal stability. As determined using dynamic mechanical analysis and differential scanning calorimetry, the glass transition value increased by 9.7% compared to that of the neat resin when the LCE content was 5 wt%. Meanwhile, the addition of 5 wt% of LCE maximized the toughness with a 175% increase in impact strength. The analysis of fracture surfaces revealed a possible effect of LCE as a toughener and showed no phase separation in the modified resin system, which was also confirmed by dynamic mechanical analysis. © 2016 Society of Chemical Industry     

Curing Kinetics of Liquid Crystalline Epoxy Resins Based on Bisphenol-S Mesogen with DDE by Nonisothermal DSC Data

The curing kinetics for a system of Sulfonyl bis(4,1-phenylene)bis[4-(2,3-epoxypro pyloxy)benzoate] (p-SBPEPB) with 4,4′-diaminodiphenyl ether (DDE) were investigated by nonisothermal differential scanning calorimetry (DSC). The dependencies of the apparent activation energy Ea and the conversion α during overall curing reaction were revealed by Ozawa's method. The results shown the Ea decreased drastially from 107 to 75 KJ/mol with α in the initial stages (α = 0–20%), the average apparent activation energy Ea of p-SBPEPB/DDE is 82.81 KJ/mol and was relatively constant in the 0.5 to 0.9 conversion interval. Some parameters were evaluated using the two kinetic models of ?esták–Berggren (S-B) equation and JMA model. The liquid crystalline (LC) phase had formed and was fixed in the system during the curing process.     

一种高温环氧树脂的工艺及力学性能

对比研究了国产MERICAN 3768和国外CYCOM 890 RTM两种高温环氧树脂的工艺性和力学性能。同时选取典型航空结构,采用双轴向碳纤维织物和真空灌注工艺制备了对比零件。结果表明,国产MERICAN 3768树脂的浸润性、流变固化特性和力学性能均与国外CYCOM 890 RTM树脂相当,均具有优异的工艺性和力学性能,与纤维匹配性好,满足航空应用对树脂的要求。     

Synthesis and characterization of the two novel liquid crystalline epoxy resins based on bisphenol‐s mesogen

Two novel liquid crystalline epoxy resins (LCER) based on bisphenol‐S mesogen, 4,4′‐Bis‐(2,3‐epoxypropyloxy)‐sulfonyl bis(1,4‐phenylene) (p‐BEPSBP) and sulfonyl bis(4,1‐phenylene) bis[4‐(2,3‐epoxypropyloxy)benzoate] (p‐SBPEPB), were synthesized. Their liquid crystalline behavior and structure were characterized by Fourier transmittance infrared ray (FTIR), differential scanning calorimetry (DSC), ¹HNMR, polarized optical microscopy (POM) and X‐ray diffraction (XRD). The results show that p‐BEPSBP is a kind of thermotropic liquid crystal and has a smectic mesophase with a melting point (T_m) at 165°C; the p‐SBPEPB is a kind of nematic mesophase with the temperature range of 155–302°C from the T_m to the clearing point T_i. The curing behaviors and texture of the liquid crystalline epoxy resins with 4,4′‐diaminodiphenyl ether (DDE) were also studied by DSC and some kinetic parameters were evaluated according to the Ozawa's method. The dynamic mechanical properties of curing products were also investigated by torsional braid analysis (TBA), and the results suggest that the dynamic mechanical loss peak temperature (T_p) of p‐BEPSBP/DDE and p‐SBPEPB/DDE is 120 and 130°C, respectively. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Synthesis,Morphology, and Viscoelastic Properties of Polyhedral Oligomeric Silsesquioxane Nanocomposites with Epoxy and Cyanate Ester Matrices

Octaaminophenyl(T₈)POSS [1, (C₆H₄NH₂)₈(SiO_1.5)₈] and dodecaaminophenyl(T₁₂)POSS [2, (C₆H₄NH₂)₁₂(SiO_1.5)₁₂] were synthesized, characterized and then incorporated into two types of thermoset resins: (1) the bisphenol-F-based cyanate ester resin, PT-15, and (2) epoxy (Epon 828, Shell Chemical Corp.)/4,4′-diaminodiphenylmethane (DDM) resin, respectively, to make two series of nanocomposites. The sum of amino groups in both DDM and POSS were held in a 1:1 mole ratio to the epoxy groups. EPON-828/1/DDM and EPON-828/2/DDM composites (78.63/0/21.37, 77.48/5/17.52, 76.34/10/13.66, 74.05/20/5.95 and 72.28/27.72/0 wt/wt/wt compositions for both series) were prepared. PT-15/1 and PT-15/2 composites (99/1, 97/3 and 95/5 wt/wt compositions for both types) were also prepared. These nanocomposites were characterized by transmission electron microscopy (TEM), dynamic mechanical analysis (DMA), solvent extraction and FT-IR. In all systems, POSS 1 and 2 were chemically bound into the resin matrix and phase-separated POSS particle domains were not observed. Incorporation of both 1 and 2 can dramatically elevate the high temperature bending storage moduli, E′, of epoxy resins.     

An Excellent Intrinsic Transparent Epoxy Resin with High Flame Retardancy: Synthesis,Characterization, and Properties

In this paper, a novel multifunctional, liquid, and colorless curing agent, namely DPTA, is prepared through diphenylphosphinic chloride (DPPC) and tetraethylenepentamine (TEPA). Different measurements confirm that the DPTA is prepared successfully and the cured DPTA‐EPs simultaneously display excellent flame retardancy and transparency. The resulting DPTA‐EP system reaches high optical transmittance up to 90% within the visible region. Meanwhile, the introduction of the flame‐retardant groups in DPTA‐EP does not deteriorate the mechanical behaviors compared with that of reference sample TEPA‐EP. More importantly, with only 15 wt% DPTA addition, the resulting DPTA‐EP with 1.6 mm passes UL‐94 V‐0 rating, and limiting oxygen index reaches 29.0%. Moreover, the peaks of heat release rate and total smoke production of DPTA‐EP are largely reduced by 43.1% and 58.8%, respectively, further verifying the excellent smoke‐suppression efficiency and flame retardancy. The analyses from both cone calorimeter (CC) and thermogravimetric (TG) results suggest that the satisfactory flame retardancy of cured DPTA‐EP dominates in the gaseous phase. The earlier release of large amount of non‐combustion gas and phosphorus containing groups improve the flame‐retardant efficiency.     

水处理容器湿法缠绕用环氧树脂体系

设计了一种适合水处理容器湿法缠绕使用的环氧树脂体系，该体系在室温有较长的凝胶期，粘度低，可在室温下凝胶、固化，在80℃固化良好。树脂浇铸体力学性能优良，与玻璃纤维之间粘结良好，NOL环复合材料力学性能好，产品爆破强度高。结果表明，纤维强度转化率较高，该环氧树脂体系完全满足水处理容器缠绕使用。     

一种新型环氧树脂潜伏性固化剂二苯基双胍的合成与性能

设计并合成了一种环氧树脂潜伏性固化剂二苯基双胍。采用FTIR和1HNMR表征了固化剂的化学结构,并通过DSC分析得到环氧树脂与固化剂的最佳质量配比为5∶1,固化活性实验及凝胶实验分析得到最佳固化温度为130℃,储存期为室温下30 d,拉伸实验分析了固化物的抗拉强度可达38.07 MPa,采用TG测试得到固化物的热分解温度超过270℃。结果表明,与双氰胺环氧树脂固化体系相比,该固化剂和环氧树脂有更好的相容性,潜伏性良好,其固化温度降低30℃以上,固化物有更优异的力学性能和良好的热稳定性。     

Lignin Epoxy Composites: Preparation,Morphology, and Mechanical Properties

A novel route to lignin epoxy composites is developed through covalent incorporation of depolymerized lignin epoxide into amine‐cured epoxy matrix. The partially depolymerized lignin is first epoxidized with epichlorohydrin and the resultant depolymerized lignin epoxide shows decreased solubility in common organic solvents. When dispersed in epoxy matrix and cured, the depolymerized lignin epoxide is integrated into epoxy networks in the form of submicron aggregates. The resulting lignin epoxy composites show improved mechanical properties compared with neat epoxy. At a loading content of 1.0 wt% of degraded lignin epoxide, the Young's modulus and the critical stress intensity factor (K_IC) of the composite increase by 10% and 25%, respectively, in comparison with those of neat epoxy, while the glass transition temperature is little changed. This method presents a promising way to convert wasteful lignin to an alternative epoxy monomer and effective additive in epoxy composites.