A New DOPO-Eugenol Adduct as an Effective Flame Retardant for Epoxy Thermosets with Improved Mechanical Properties

The development of efficient green flame retardants is an important way to realize more sustainable epoxy thermosets and downstream materials.In this work,a monoepoxide is synthesized through O-glycidylation of eugenol,and then reacted with DOPO(9,10-dihydro-9-oxa-10-phosphophenanthrene-10-oxide)to obtain a new bio-based flame retardant,DOPO-GE.DOPO-GE is blended with a bisphenol A epoxy prepolymer exhibiting good compatibility and DDS(4,4′-diaminodiphenylsulfone)is used as the curing agent to afford epoxy thermosets.Although DOPO-GE leads to the reduced glass transition temperature of the thermosets,the storage modulus increases considerably.The DOPO-GE-modified thermosets exhibit the high thermal stability with the onset thermal decomposition temperature in nitrogen and air exceeding 300℃.When the phosphorus content in the thermoset is 1.0%,the residual yield of the thermosets at 750℃ in nitrogen increases from 13.9%to 30.6%,due to the increased charring ability.More interestingly,when the phosphorus content is only 0.5%,the limiting oxygen index is as high as 30.3%with UL94 V0 achieved.Cone calorimeter results reveals the significantly decreased heat release rate,total heat release,mass loss and total smoke production.Furthermore,DOPO-GE can notably improve the flexural strength,flexural modulus and fracture toughness,whereas the shear and impact strength are reduced to varied extents.In short,DOPO-GE can be obtained via a facile way,and shows the good flame-retardant effect on the epoxy thermosets with an application potential.

A Vanillin-Derived,DOPO-Contained Bisphenol as a Reactive Flame Retardant for High-Performance Epoxy Thermosets

Quest for bio-based halogen-free green flame retardant has attracted many concerns in recent years.Herein a reactive functional flame retardant containing phosphorus VDP is synthesized from vanillin,9,10-dihydro-9-oxa-10-phosphophene-10-oxide(DOPO)and phenol via a facile way.VDP is characterized with^(1)H NMR,^(31)P NMR,FTIR and Time of Flight Mass Spectrometry,and used as a new reactive flame retardant for bisphenol epoxy thermosets.Thermogravimetry analysis shows that when the VDP loading is only 0.5P%(based on phosphorus content),the residue increases from 14.2%to 21.1%at 750℃ in N_(2)compare with neat DGEBA.Correspondingly,the limit oxygen index increased to 29.6%,and flame retardancy reaches UL-94 V0 grade.Micro combustion calorimetry(MCC)and cone calorimetry analyses demonstrate that VDP can significantly lower flammability of the epoxy thermoset.With only 0.5P%of VDP,the heat release rate,total heat release rate and smoke production are reduced markedly.At the same time,the mechanical properties of the modified epoxy thermosets are also improved.The impact strength increases by 34%and the flexural strength increased by 23%,with 1.5P%of VDP.In short,VDP not only improves the flame retardancy,but also improves the mechanical properties of the epoxy thermosets.

Spreading and Curing Behaviors of a Thermosetting Droplet-Silicone on a Heated Surface

Thermosetting materials are widely used as encapsulation in the electrical packaging to protect the core electronic components from external force, moisture, dust, and other factors. However, the spreading and curing behaviors of such kind of fluid on a heated surface have been rarely explored. In this study, we experimentally and numerically investigated the spreading and curing behaviors of the silicone(OE6550 A/B, which is widely used in the light-emitting diode packaging) droplet with diameter of ~2.2 mm on a heated surface with temperature ranging from 25 ℃ to 250 ℃. For the experiments, we established a setup with high-speed camera and heating unit to capture the fast spreading process of the silicone droplet on the heated surface. For the numerical simulation, we built a viscosity model of the silicone by using the Kiuna’s model and combined the viscosity model with the Volume of Fluid(VOF) model by the User Defined Function(UDF) method. The results show that the surface temperature significantly affected the spreading behaviors of the silicone droplet since it determines the temperature and viscosity distribution inside the droplet. For surface temperature varied from 25 ℃ to 250 ℃, the final contact radius changed from ~2.95 mm to ~1.78 mm and the total spreading time changed from ~511 s to ~0.15 s. By further analyzing the viscosity evolution of the droplet, we found that the decreasing of the total spreading time was caused by the decrease of the viscosity under high surface temperature at initial spreading stage, while the reduction of the final contact radius was caused by the curing of the precursor film. This study supplies a strategy to tuning the spreading and curing behavior of silicone by imposing high surface temperature, which is of great importance to the electronic packaging.

PREPARATION AND PROPERTIES OF THERMOSETTING ACRYLIC COATINGS USING TITANIUM-OXO-CLUSTER AS A CURING AGENT

Thermosetting acrylic coatings were prepared by using carboxyl acid group-containing acrylic oligomer and curing with titanium-oxo-clusters which were first pre-hydrolyzed from titanium n-butoxide.The curing ability of the titanium-oxo-cluster was examined using a microdielectric analytical(DEA)curing monitor,Fourier transformed infrared spectroscopy(FTIR),and Soxhlet extraction experiments,and the properties of the resulted coatings were investigated with pendulum hardness tester,dynamic mechanical analysis(DMA),thermogravimetric analysis(TGA)and ultraviolet-visible spectrometer.The effect of titania-oxo-cluster in leading acrylic oligomers to form thermosetting acrylic coatings was confirmed.An increasing pendulum hardness and modulus of acrylic coatings with increasing titania content was observed, which resulted from the increment of crosslinking degree rather than of the titania content.The thermosetting acrylic/titania coatings also showed better thermal stability and higher UV-blocking properties than those coatings using organic curing agent.

Chemical and Morphological Surface Modification of Epoxy Based Thermosets

Recently developed low fluorine containing polymers are advanced materials which confer advantageous properties to surfaces at a lower cost than conventional fluoropolymers (like PTFE), and are also more easily processable. Fluoropolymer surfaces are characterized by a low surface energy, high oleo and hydrophobicity, low coefficients of friction, among many other properties. This makes them desired materials in microelectronics, antifogging, antifouling and medical applications, to name a few. Fluorinated compounds are not easily coupled with macromolecules or common organic systems, and great efforts are made to compatibilize fluorinated species with hydrocarbon polymers. In this work, two chemical routes were explored in order to incorporate perfluorinated alkyl chains in an epoxy-amine based thermoset. On one side, a perfluoroalkyl thiolated molecule was used as a stabilizing ligand for silver nanoparticles, which were incorporated in the matrix polymer. On the other hand, fluorinated chains containing epoxy functionalities, were used as the matrix modifier. In the first case, fluorinated chains covering the nanoparticles, were mixed with the matrix, while in the second case, the fluoroalkyl chains were chemically linked to the network. Fluorine migration to the air—polymer interface was confirmed by X-Ray photoelectron spectroscopy (XPS). The materials hydrophobicity was then studied in terms of their contact angle with water (CA), as a function of the surface composition and the topography. Scanning electron microscopy (SEM) and atomic force microscopy (AFM), operated in moderate and light tapping modes, were used to morphologically describe the surfaces. An exhaustive surface analysis was made in order to explain the different hydrophobicity grades found.

Preparation of carbon brushes with thermosetting resin binder

Carbon brushes with a resin binder were prepared according to an industrial process and the effects of the molding pressure, grains size and cure temperature on the properties of brush samples were discussed. The results show that the bulk density, bending strength and Rockwell hardness increase, while resistivity decreases with increasing molding pressure. Cure temperature has much more influence on the properties of brushes than molding pressure and grains size. Isothermal differential scanning calorimetry(DSC) was used to estimate the degree of cure of resin binder and a novel method of using the true density to measure the degree of cure of resin binder was presented and discussed briefly. Based on optimal process parameters carbon brushes were manufactured, durability tests for brushes were carried out on an alternate current motor and scanning electron microscope(SEM) was adopted to observe the morphology of worn surface of brushes. The results show that a luster oxide film can be formed on the surface of brushes and their service life reaches 380 h.

Molecular design of recyclable thermosetting polyimide and its composite with excellent mechanical and tribological properties

Recyclability of thermosetting polymers and their composites is a challenge for alleviating environmental pollution and resource waste.In this study,solvent-recyclable thermosetting polyimide(PI)and its composite were successfully synthesized.The tensile strength,elongation at break,and Young’s modulus of PI are 108.70±7.29 MPa,19.35%±3.89%,and 2336.42±128.00 MPa,respectively.The addition of reduced graphene oxide(RGO)not only enhances the mechanical properties of PI but also endows it with excellent tribological properties.The PI illustrates a high recycling efficiency of 94.15%,but the recycled composite exhibits inferior mechanical properties.The recycling and utilization of PI and its composite are realized through imine bonds(-C=N),which provides new guidance for solving the problem of environmental pollution and resource waste and is potential application in the field of sustainable tribology.

Thermosetting resin modified asphalt:A comprehensive review

Thermosetting resins have advantages such as high strength,corrosion resistance,and aging resistance,and have excellent prospects for practical application as asphalt modifiers.In order to promote the research of thermosetting resin modified asphalt,to provide direction for its further research,this paper reviews the research progress of thermosetting resin modified asphalt in recent years.The material composition,modification mechanism,and curing behavior of epoxy asphalt,thermosetting polyurethane modified asphalt,unsaturated polyester modified asphalt,and other thermosetting resin modified asphalts are overviewed.Different types of thermosetting resin modified asphalt have different performances,the performance advantages of different thermosetting resin modified asphalts are summarized.At the same time,the existing problems in thermosetting resin modified asphalt and further research directions are provided.Encouraging researchers to produce thermosetting resin modified asphalts using waste or bio-based materials,and to study the recycling technologies and life cycle assessment of thermosetting resin modified asphalt.This paper provides a reference for the study of thermosetting resin modified asphalt.

热塑型聚酰亚胺的制备及其粘接性能研究

为了改善两层型挠性覆铜板(2L-FCCL)中热塑型聚酰亚胺(TPI)对热固型聚酰亚胺(PI)薄膜和铜箔的粘接性,本文选用具有柔性结构的芳香二酐单体和芳香或脂环的二异氰酸酯单体通过一步反应制备得到TPI样品,然后将其直接涂覆在表面经过预处理的商品化热固型PI薄膜上得到复合膜,最后经过高温热压得到相应的2L-FCCL。通过观察所得TPI反应液的状态并进行DSC测试,选定了有机溶剂可溶且Tg为226.5℃的TPI-8;然后通过TGA、TMA和拉伸试验测得TPI-8的2%热分解温度(T2%)为464℃、50~200℃的热膨胀系数(CTE)为64.25×10^(-6)℃^(-1)、拉伸强度为64.52MPa、弹性模量为1.75 GPa、断裂伸长率为62%,并通过FTIR对其化学结构进行了确认;最后分别研究了两种热固型PI薄膜的碱水预处理时间对所得FCCL粘接性能的影响,发现其中SPI膜经60℃碱水处理1 min和3 min后得到的FCCL90°剥离强度(90°PS)≥0.7 N/mm且最大值达到0.94 N/mm,而UPI膜经同样热碱水处理1~7 min后得到的FCCL 90°PS均≤0.6 N/mm。因此,采用本方法可一步快速简单的制备可溶解且热学性能、力学性能、尺寸稳定性较好的TPI,同时其对铜箔以及表面经过碱水预处理的SPI具有较好的粘接性能,满足FCCL相关标准的要求。

基于香草醛的热固性树脂研究进展

香草醛是一种可由木质素磺酸盐生产的单芳香化合物,其化学结构独特,已成为生物基材料领域研究热点。本文首先介绍了基于香草醛的热固性高分子材料包括环氧树脂、苯并噁嗪、酚醛树脂、丙烯酸树脂等研究进展,着重论述了基于香草醛特征结构进行化学转化以及制备交联结构产物的过程。进而,本文总结了含有动态共价键的香草醛基热固性材料研究进展。香草醛的醛基有利于缩醛、亚胺、硫缩醛等动态化学基团的引入,而通过交联体系的选择可有效引入动态二硫键、D-A加成键及β-羟基酯基团。在总结香草醛基热固性材料的特点及发展应用的基础上,本文展望了香草醛基热固性树脂在原料获取、产品制备、回收利用及有效降解等方面可持续性所面临的挑战。

纤维增强热固性树脂基复合材料成型过程数值模拟研究进展

纤维增强热固性树脂基复合材料在高端制造领域应用广泛,其固化过程涉及树脂流动、固化反应发生、残余应力引发固化变形等多个步骤。数值模拟纤维增强热固性树脂基复合材料的工艺成型过程是一个多场耦合的复杂问题,建立完善的数值模拟方法用来预测其成型过程中的固化行为对于工艺类型选择、工艺参数设计和复合材料构件性能优化具有重要的理论与实践意义。本文归纳了数值模拟纤维增强热固性树脂基复合材料成型过程的主要研究进展,并讨论了不同数值模型的适用条件,通过分析同一问题不同模型的适用条件可以为复合材料固化工艺及参数设计的选择提供指导。提升精度和降低成本是数值模型迭代优化的主要研究方向。在此基础上,本文对数值模拟纤维增强热固性树脂基复合材料成型过程进行了总结,并认为未来可以从复合材料的树脂流动多尺度建模、机器学习与材料基因组方法在复合材料的构件优化设计中的应用和残余应力对复合材料的性能及使用寿命的影响等方面开展研究。

Three-dimensional Cure Simulation of Stiffened Thermosetting Composite Panels

Stiffened thermosetting composite panels were fabricated with co-curing processing.In the co-curing processing,the temperature distribution in the composite panels was nonuniform.An investigation into the threedimensional cure simulation of T-shape stiffened thermosetting composite panels was presented.Flexible tools and locating tools were considered in the cure simulation.Temperature distribution in the composites was predicted as a function of the autoclave temperature history.A nonlinear transient heat transfer finite element model was developed to simulate the curing process of stiffened thermosetting composite panels.And a simulation example was presented to demonstrate the use of the present finite element procedure for analyzing composite curing process.The glass/polyester structure was investigated to provide insight into the nonuniform cure process and the effect of flexible tools and locating tools on temperature distribution.Temperature gradient in the intersection between the skin and the flange was shown to be strongly dependent on the structure of the flexible tools and the thickness of the skin.

可回收热固性环氧树脂及其玻纤增强复合材料性能研究

为了研究可回收环氧树脂R与风电叶片中常规环氧灌注树脂的区别,采用真空灌注工艺制备了玻璃纤维增强可回收热固性复合材料,对比分析了树脂之间的材料性能以及其复合材料之间的力学性能。结果表明,可回收树脂R的粘度与常规灌注树脂相近,适用期长于常规灌注树脂,适用于风电叶片的真空灌注工艺;放热峰出现时间略早于常规灌注树脂,有利于减少生产工时;其本体性能、复合材料力学性能与常规灌注树脂大体相当;可回收树脂R与常规灌注树脂的之间具有良好的界面性能,表明该树脂可以通过先制备部件然后整体灌注成型的方式制造大型复合材料制件。

Tailoring the Properties of Diels-Alder Reaction Crosslinked High-performance Thermosets by Different Bismaleimides

A series of Diels-Alder reaction cross-linked thermosets with recyclability and healability were prepared from furan-containing aromatic polyamide and bismaleimides with different chemical structures.The structures of synthesized bismaleimides were confirmed by 1 H nuclear magnetic resonance(1 H-NMR)spectroscopy;their reversible cross-linking with the furanic polyamide was further detected by 1 H-NMR technique and sol-gel transition behavior.The dynamic mechanical analysis and tensile test revealed the variable thermal and mechanical properties of thermosets cross-linked by different bismaleimides and with different molar ratios of maleimide group to furan group(Ima/fur).The tensile test also demonstrated that the better recyclability and solvent-assisted healability of thermosets cross-linked could be achieved by more flexible bismaleimides.This work is expected to provide valuable information for design of recyclable and healable high-performance thermosets with desired properties.

二阶热固性环氧沥青桥面铺装黏层黏结性能试验研究

该文以宜昌伍家岗长江大桥为工程依托,针对铺装结构中RA沥青混凝土与高黏高弹SMA沥青混凝土层间的二阶热固性环氧沥青材料的不同洒布量、不同第一阶段固化时间、不同养护时间、不同服役温度下的界面抗剪与拉拔强度以及洒布量对耐剪切疲劳性能的影响开展研究。研究结果表明:随着二阶热固性环氧沥青洒布量的增加,黏结与抗剪强度提高,结构耐剪切疲劳性能增强,施工环境温度为25~35℃时,二阶热固性环氧沥青黏结层与高黏高弹SMA的施工间隔建议44~52 h,施工完成后封闭养护时间应大于7 d,二阶热固性环氧沥青黏层可实现组合铺装结构的25℃抗剪强度≥3.8 MPa,拉拔强度≥1.7 MPa,60℃抗剪强度≥1.7 MPa,拉拔强度≥0.9 MPa,研究结果对二阶热固性环氧沥青材料在桥面铺装工程中的应用具有指导意义。

玻纤网覆盖下不同外墙保温材料火灾行为研究

为探究玻璃纤维网对热固性、热塑性外墙保温材料燃烧性能的影响,采用锥型量热仪进行燃烧实验研究,并对燃烧产生的各项参数进行分析。结果表明,玻璃纤维网会增大保温板材的点燃时间、热释放速率、生烟速率等相关参数。热固性材料的部分火灾行为受玻璃纤维网的影响较为明显,但在引燃性和火灾传播性能方面所受影响较小。热塑性材料中,玻璃纤维网对于XPS的引燃性、释热性、火灾传播性能及EPS的生烟性影响较大。玻璃纤维网使PUF、EPS的火灾增长指数小幅度降低,有抑制火焰蔓延的作用。

Synthesis of renewable isosorbide-based monomer and preparation of the corresponding thermosets

Two kinds of difunctionalized isosorbide derivatives containing norbornene groups were designed and synthesized by a facile one-step reaction under mild conditions.~1H NMR spectroscopy confirmed the chemical composition and differential scanning calorimetry（DSC） revealed the distinct curing behaviors between conventional petroleum-based dicyclopentadiene（DCPD） and synthesized renewable isosorbided-based monomer（ISN）. In contrast to DCPD, ISN was low viscous liquid at room temperature and had even higher reactivity to perform ring-opening metathesis polymerization（ROMP） in the presence of Grubbs＇ catalyst. Due to the presence of flexible and elastic Si–C long chains, the cured poly（ISN） thermosets not only had good mechanical properties but also exhibited much higher storage modulus at the rubbery state in comparison with traditional poly（DCPD）.

Highly Soluble Phenylethynyl-terminated Imide Oligomers and Thermosetting Polyimides Based on 2,2′3,3′-Biphenyltetracarboxylic Dianhydride

The properties of a series of imide oligomers were characterized according to their molecular weights, solubility, and thermal and rheological properties. This series of imide oligomers was synthesized via a two-step method using 2,2′,3,3′-biphenyltetracarboxylic dianhydride(3,3′-BPDA) and aromatic diamines as the monomers, and 4-phenylethynyl phtlialic anhydride(PEPA) as the end-capping agent. The imide oligomers based on 3,3′-BPDA showed excellent solubility in low boiling point solvents and low melt viscosity, which were attributed to their unique bent architectures. High-performance thermosetting polyimides were produced from these oligomers via thermal crosslinking of the phenylethynyl groups. The mechanical and thermal properties of the thermosets were studied using tensile testing, dynamic mechanical thermal analysis(DMTA), and thermogravimetric analysis(TGA). The 3,3′EPDA-based thermosets exhibited excellent thermal properties, with glass transition temperatures of up to 455℃, and 5% mass loss temperatures of up to 569℃ in air. The thermosets based on 3,3-BPDA showed superior thermal properties compared to those derived from TriA-X series oligomers.