Epoxidized soybean oil modified using fatty acids as tougheners for thermosetting epoxy resins: Part 1

A series of bio-rubber (BR) reactive tougheners for thermosetting epoxy resins was prepared by grafting renewable saturated fatty acids of different chain lengths (C6-C14) onto epoxidized soybean oil (ESO) at varying molar ratios. The tunable nature of the BR systems derives from the architecture and functionality of naturally occurring molecules. Control of BR reactivity and molecular weight by varying the degree of grafting and the chain length of the fatty acid was demonstrated. The BR-toughened samples were prepared by blending BRs with diglycidyl ether of bisphenol A (DGEBA), Epon 828, and stoichiometrically curing the mixture using an aromatic amine hardener, diethyl toluene diamine (Epikure W). Fracture surface morphology studies showed that tuning of phase separated particle sizes was possible depending on the BR type and weight fraction. The resulting toughening effect was evaluated by measuring the fracture toughness of control and toughened polymer samples. The use of BRs significantly improved the critical strain energy release rate and critical stress intensity factor values of thermosetting polymer samples without significantly reducing T_g and modulus. In addition to toughening and adding renewable content to petroleum-based thermosetting epoxy systems these new tougheners have low viscosity compared to common alternatives and aid ease of processing.     

Synergistic improvement of mechanical and thermal properties in epoxy composites via polyimide microspheres

Achieving synergetic improvements of mechanical strength, toughness, and thermal stability of epoxy resin has been a crucial but very challenging issue. Herein, to explore a new solution for circumventing this issue, polyimide microspheres were successfully prepared through the inverse nonaqueous emulsion process, and the structure, size distribution and morphologies of polyimide (PI) microspheres were comprehensively investigated. Then the PI microspheres were incorporated in epoxy resin matrix to systematically investigate the mechanical and thermal properties of obtained epoxy/PI microspheres composites. It was found that the PI microspheres can not only enhance the mechanical strength of epoxy resin, but also significantly improve the toughness. Specially, the epoxy-based composites containing 3 wt% PI microspheres exhibit a 47% increase in tensile strength, while the G_IC and Charpy impact strength increase by 106% and 200%, respectively. The toughing mechanism of epoxy/PI microspheres composites was discussed. Moreover, the PI microspheres can also endow the epoxy resin with excellent thermal stability and heat resistance. Thus, this work may open a new opportunity to synergistically enhance the mechanical and thermal properties of epoxy-based composites and may also give some valuable inspiration for the rational design of other high-performance thermosetting composites.     

Enhanced wear resistance of ultra-high molecular weight polyethylene fibers by modified-graphite oxide

A simple and feasible method to enhance the wear resistance of ultra-high molecular weight polyethylene (UHMWPE) fibers was reported. The graphite oxide (GO) prepared using improved Hummer's method was surface modified with hexadecylamine to improve its compatibility with UHMWPE. Combined with well-dispersion of modified-GO (m-GO) in dichloromethane and the fact that the viscosity of UHMWPE suspension can be decreased by dichloromethane, the well dispersed m-GO/dichloromethane was added into UHMWPE suspension to improve m-GO dispersion in UHMWPE fibers. Finally, UHMWPE fibers with different m-GO concentration were prepared using gel spinning technology. The effect of m-GO concentration on the structure and properties of modified UHMWPE fibers were investigated. The results indicated that the melting temperature and crystallinity of m-GO modified UHMWPE fibers increased with increasing of m-GO concentration, while the fiber's crystal sizes and orientation increased, thus the tensile strength of m-GO modified UHMWPE fibers remained almost undamaged. The introduction of m-GO is beneficial to the formation of smooth transfer film on fiber's surface, which enhanced the self-lubrication of UHMWPE fibers. Compared with pure UHMWPE fiber, the UHMWPE fiber containing 1.5 wt% m-GO had enhanced wear resistance by 55.4% and still maintained high tensile strength of 29.98 cN dtex⁻¹.     

基于STM32的可穿戴式无线体域网信息监测系统设计与实现

针对传统疾病诊疗模式中疾病监护实时性差的缺点,以低功耗、高速STM32处理器为核心,设计一款可穿戴式无线体域网信息监测系统.系统由无线传感网络、中央监测模块和手机终端组成,具有实时采集、数据存储、无线传输和监测人体生命体征信 息的功能.测试结果表明,系统运行稳定,性能指标均达到系统设定要求,应用于医疗监测可起到实时监护、早期预防的作用.     

LCC-HVDC送端电网等值方案研究

大规模新能源经电网换相高压直流输电(LCC-HVDC)送出时,极易引发送端电网暂态过电压.通过建立LCC-HVDC及送端等值电网电磁暂态仿真模型,可以详细分析其暂态过电压特性,进而优化其控制策略.目前,针对LCC-HVDC送端电网等值的相关研究较少.结合工程需求,给出一种适用于LCC-HVDC送端电网的等值方案.首先,根据主干网各梯级断面点节点残压大小与LCC-HVDC电气耦合强弱的关系,提出一种基于节点残压的内部系统主干网确定方法.该方法在快速确定内部系统范围的同时,可有效避免等值过程中可能因人为因素而引起的等值误差;然后,以梯级断面点为依据划分拓扑区域,以等值前后各拓扑区域电气特性一致为原则,提出内部系统中包括新能源电源在内的等值电源、负荷及变压器等元件的详细参数确定方法;最后,给出LCC-HVDC送端电网多端口戴维南等值方法,简化了外部系统.基于国内某LCC-HVDC送端电网等值方案实际算例,验证了所提等值方案的有效性.     

基于机械力化学的热固性塑料再资源化

针对热固性塑料再资源化困难的问题,提出了热固性塑料机械力化学法回收的工艺流程,对热固性酚醛树脂进行超细粉碎回收,分析了机械力对酚醛树脂物化性质的影响,将再生粉末和聚氯乙烯按照比例混合后模压成再生板材,并对再生板材的表面形貌和力学性能进行表征测试。结果表明,粉碎腔内流场处于紊流状态,颗粒间相互混掺,运动无序且应力场分布不均,材料受到反复的挤压、摩擦、冲击等形式的机械力作用,产生的内应力使部分交联键发生断裂,材料恢复了部分塑性成型的能力,回收的再生粉末颗粒和聚氯乙烯之间有较强的结合力,制备的再生板材具有较好的力学性能,其拉伸强度为3.78~19.02 MPa,弯曲强度为11.72~36.85 MPa,可以实现较为理想的回收再利用。     

聚酰胺6扩链改性及其超临界CO2模压发泡研究

以扩链剂KL–E4370、抗氧剂1010对线型尼龙6(PA6)进行改性,制备出具有高熔体强度的改性PA6材料。采用固态发泡的发泡方法,通过超临界CO₂模压发泡制备相应发泡材料。通过差示扫描量热仪,流变仪来表征改性材料的可发泡性,并通过扫描电子显微镜来观测发泡材料的泡孔形貌。探究不同工艺条件对PA6泡沫泡孔结构的影响,分析了不同泡孔结构对发泡材料力学性能的影响。在饱和压力为10~20 MPa、发泡温度为223~231℃的范围内制备的PA6泡沫泡孔直径在18.3~143.6μm之间,泡孔密度为7.42×10⁶~1.75×10⁹个/cm³,发泡倍率为5.6~22.4。所得PA6泡沫的拉伸强度为1.5~5.8 MPa,断裂伸长率为22%~51%,压缩强度为0.03~2.47 MPa。     

计及直流微电网扰动抑制的残差动态分散补偿控制策略

针对直流微电网电能质量问题与环流问题,提出一种计及直流微电网扰动抑制的残差动态分散补偿控制策略.此策略在直流下垂控制的基础上,首先分析直流微电网扰动问题及并联状态下的环流问题;其次建立Buck型与Boost型多DC-DC变换器并联的状态空间模型,推导基于残差的变换器动态分散补偿结构,该结构直接在电压环输出端进行补偿,通过扰动抵消计算补偿控制器Q*(s).采用小信号稳定性分析方法证明本文补偿结构的稳定性;最后基于RTDS搭建数字物理实验平台,以相同与不同类型变换器并联为例进行实验验证.该结构能够加快分布式电源及公共负荷投切时直流母线电压动态响应速度,有效地抑制了环流影响和交流侧不平衡情况引起的直流母线电压二倍工频扰动,维持了电压的一致性,保证了母线电压的稳定,有助于实现分布式电源的"即插即用"技术.     

离心铸造铸铁排水管生产中的一些问题

针对离心铸造铸铁排水管生产过程中存在的问题，如设备选型、涂料的影响，麻坑、针孔等铸造缺陷的产生原因等进行了分析和探讨。只要铸造生产工艺合理、涂料性能合适，即使是简易型离心铸管机也可生产出无铸造缺陷的高质量铸管。涂料性能与涂料使用方法强烈影响铸管表面质量和管模使用寿命。铸管外表面麻坑、针孔等缺陷的主要影响因素是涂料本身的性能和涂料使用工艺，铸管内表面龟纹等铸造缺陷的主要影响因素是铁水质量。     

单─银精矿提取银的技术

某单─银矿经浮选所得精矿（％）：Ａｇｌ～２，Ｃｕ≈１，Ｐｂ４～７，ＣａＯ＋ＭｇＯ３０～３５，Ｓ４～７，Ｃ８～９。研究了氰化、硫脲、氨浸等方案对该精矿浸出效果，并从浸出指标等因素进行比较，认为焙烧─预浸─氨浸方案较好，银浸出率＞９７％，铜浸出率９５％。