Polarity Effect and Electromagnetic Radiation of Partial Discharge Accompanying Growth of Electrical Tree

We have investigated the characteristics of radiated electromagnetic (EM) waves from positive and negative partial discharges (PD) in epoxy resin and cross‐linked polyethylene. We found that there is a correlation among the EM level from PD, the positive PD current, and electrical trees. Therefore, the growth of an electrical tree produces a lot of positive PD. We have also investigated the characteristics of the frequency region of EM waves from PD in air, insulating oil, and liquid epoxy in addition to the above insulators. EM waves were detected in the frequency region of 40 MHz to 300 MHz from positive and negative PD in epoxy resin and cross‐linked polyethylene. EM waves were also detected in the frequency region of 40 MHz to 150 MHz from positive and negative PD in air. In the case of insulating oil and liquid epoxy, EM waves were detected in the frequency regions of 40 MHz to 150 MHz from positive PD, and 40 MHz to 250 MHz from negative PD. The frequency region differed depending on the material and the discharge polarity. Our investigation indicates that the cause is differences in electric field strength at the time of PD occurrence.     

APG压注工艺在中压互感器制造中的应用

介绍了环氧树脂自动压力凝胶(APG)工艺应用于中压互感器制造的基本原理,以及国内应用该工艺压注成型中压互感器的基本情况.     

含辣素衍生结构单体及其聚合物的合成、抑菌与抑藻性能

以取代芳烃和N-羟甲基丙烯酰胺为原料,采用傅克烷基化反应合成了四种含辣素衍生结构单体:4-羟基-2-甲基-5-甲硫基苄基丙烯酰胺(A)、2-羟基-4-丙烯酰胺甲基-5-甲硫基-6-甲基苄基丙烯酰胺(B)、3-丙烯酰胺甲基-2-羟基苯甲酰胺(C)和1-丙烯酰胺甲基-2-萘酚(D),并通过红外光谱(IR)和核磁氢谱(1 H NMR)对其结构进行了表征。抑菌实验结果表明化合物D对两种受试菌(金黄色葡萄球菌和大肠杆菌)的抑制活性最高,最小抑菌浓度均可达到0.187 5mg/mL,且D对两种受试藻(三角褐指藻和新月菱形藻)的抑制活性也最高。以四种化合物为功能单体合成出树脂,树脂对受试藻均具有较高的抑制活性,含化合物D的树脂的抑制活性最高,72h后抑制率均可达到50%以上。     

A novel bio‐based phthalonitrile resin derived from catechin: synthesis and comparison of curing behavior with petroleum‐based counterpart

The development of bio‐based thermosetting resins with good thermal stability can potentially afford sustainable polymers as replacements for petroleum‐based polymers. We report a practical route to a novel catechin‐based phthalonitrile resin precursor (CA‐Ph), which contains free phenolic hydroxyl groups that result in ‘self‐curing’ at elevated temperatures to afford a thermostable polymer. Comparison of the performance of this CA‐Ph resin with that of a conventional petroleum‐based bisphenol A phthalonitrile resin (BPA‐Ph; containing 5 wt% of the curing agent 4,4′‐diaminodiphenylsulfone) revealed that CA‐Ph exhibits a lower melting point and curing temperature. Cured CA‐Ph resin retains 95% of its weight at 520 °C under a nitrogen atmosphere, which compares favorably with results obtained for BPA‐Ph resin that retains 95% of its weight at a lower temperature of 484 °C. Kinetic results indicated that the curing reactions of both CA‐Ph and BPA‐Ph systems follow an autocatalytic mechanism. These results suggest that catechin is a useful bio‐based feedstock for the preparation of self‐curing and thermally stable phthalonitrile resins for advanced technological applications. © 2017 Society of Chemical Industry     

Improvement of the electrical resistivity of epoxy resin at elevated temperature by adding a positive temperature coefficient BaTiO_3-based compound

The DC electrical resistivity-temperature characteristic is an important property for insulating materials to operate at a high stress level. In order to improve the DC electrical resistivity at elevated temperature in a targeted way, a positive temperature coefficient(PTC) material(Ba Ti O3-based compound(BT60)) was selected as the filler in this paper, whose electrical resistivity has a PTC effect when the temperature exceeds its Curie temperature. The BT60 was treated with hydrogen peroxide and(3-Aminopropyl) triethoxysilane. Epoxy composites with different loadings of BT60 fillers(0 wt%, 0.5 wt%, and 2 wt% of epoxy) were prepared, denoted as EP-0, EP-0.5, and EP-2. It was shown that BT60 was able to maintain the DC breakdown strength when its loading was less than 2 wt% of epoxy. As the temperature exceeds 60 °C,BT60 will compensate for the negative temperature coefficient effect of epoxy resin to some extent. The electrical resistivity of EP-2 was improved by 55% compared with that of neat epoxy at 90 °C. It was found that the potential barrier at the grain boundary of BT60 and the deep traps in the interface between BT60 and the epoxy resin hinder the migration of carriers and thus increase the electrical resistivity of epoxy composite.     

Strengthen flame retardancy of epoxy thermoset by montmorillonite particles adhering phosphorus-containing fragments

Phosphaphenanthrene derivative tri-(3-DOPO-2-hydroxypropan-1-yl)-1,3,5-triazine-2,4,6-trione (TGD) and organo-modified montmorillonite (OMMT) were jointly introduced into the diglycidyl ether of bisphenol A cured by 4,4-diamino-diphenylmethane (EP) to investigate their flame retardant behaviors. With only addition of 0.5%OMMT and 2.5%TGD, epoxy thermoset achieved a limiting oxygen index value of 33.7% and passed UL 94 V-0 rating test. Compared with the combustion behaviors of 3%OMMT/EP and 3%TGD/EP, an obvious synergistic flame retardant effect between OMMT and TGD can be concluded in OMMT/TGD/EP. Meanwhile, the FTIR spectra of gas-phase and condensed-phase products further proved this synergistic effect working in a physical way. On one hand, the co-existence of hydroxyl-containing TGD enabled montmorillonite (MMT) particles to filtrate and adhere more smoke fragments. On the other hand, the co-action of MMT help the polar phosphorus-containing fragments from TGD better strengthened char layer, enhancing the barrier and protective effect of residue. The synergistic flame retardant effect from OMMT/TGD system endowed themselves with higher flame retardant efficiency, and epoxy thermoset with better flame retardant performance. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 47500.     

硅树脂添加量对氧化铝基陶瓷型芯性能的影响

以氧化铝粉末为基体,添加具有粘结性和一定陶瓷产率的硅树脂粉末,通过干压成型和无压烧结制备出氧化铝基陶瓷型芯,重点研究了硅树脂添加量对氧化铝基陶瓷型芯性能的影响。结果表明:硅树脂在裂解过程中会形成二氧化硅,二氧化硅与氧化铝基体发生反应形成新相莫来石。由于硅树脂在交联和裂解过程中会释放大量气体,导致烧结体失重,且气体的逸出会抑制由烧结引起的收缩,因此,随着硅树脂添加量增加,产生的气体量增加,烧结体的失重率增加,收缩率降低。硅树脂含量的增加使得烧结体的气孔率变大和体积密度减小,烧结体的室温抗弯强度逐渐减小。硅树脂的添加虽然降低了其室温强度,但是保证了陶瓷型芯的尺寸精度。     

Comparison of Canola and Soy Flour with Added Isocyanate as Wood Adhesives

Canola is widely grown in the northern latitudes for its vegetable oil, generating large quantities of residual, low value canola flour used as animal feed. The common wood adhesive poly(diphenylmethylene diisocyanate) (pMDI) should react with the wide variety of functional groups in proteins. Therefore, it would seem that canola flour with added pMDI could be an effective adhesive. Two main questions are addressed in this study: How do the wood adhesive properties of canola flour compare to the better-studied soy flour? How well do proteins, which contain an abundance of functional groups, cure with the very reactive pMDI? These questions were addressed using the small-scale adhesive strength test ASTM D-7998, with various adhesive formulations and bonding conditions for canola flour plus pMDI compared to soy adhesives. The more challenging wet cohesive bond strength was emphasized because the dry strengths were usually very good. Generally, soy adhesives were better than canola ones, as was the polyamidoamine-epichlorohydrin cross-linker compared to pMDI, but these generalizations can be altered by the conditions selected. Three-ply plywood tests supported the small-scale test results.     

预分散酚醛树脂硫化CIIR性能的研究

分别研究了预分散酚醛树脂HY-2045(预)、HY-2055(预)和SP-1055(预)对CIIR胶料硫化特性、力学性能及100℃×72h热空气老化性能的影响,并与原树脂HY-2045(原)、HY-2055(原)和SP-1055(原)的影响效果进行了对比。结果表明,与原酚醛树脂相比,预分散酚醛树脂在CIIR橡胶中的分散性、硫化胶拉伸强度和拉断伸长率均获得提高。加入SP-1055(预)可明显缩短CIIR胶料的t90;加入HY-2045(预)可使胶料的t10和t90延长,交联密度、硬度、100%定伸应力和拉伸强度均最小,拉断伸长率最大;加入HY-2055(预)可使胶料的t90延长,其他性能与加入SP-1055(预)的胶料相差不大。加入HY-2055(预)的硫化胶100℃×72h热空气老化后性能变化最小。