Preparation and properties of styrene ethylene butylene styrene / polypropylene thermoplastic elastomer powder for selective laser sintering 3D printing

As one of the most important thermoplastic elastomer materials, the application of styrene ethylene butylene styrene (SEBS) in selective laser sintering (SLS) has not been reported. In this study, SEBS and polypropylene (PP) are blended and then pulverized at low temperatures. We find that SEBS with high molecular weight and styrene segment content is difficult to melt and flow under laser irradiation, which is not suitable for SLS 3D printing. SEBS with low molecular weight can be printed, and its tensile properties can reach 2.1Mpa and 134% elongation at break. We test the enhanced absorption effect of two different infrared absorbers and find that graphene (GE) can enhance absorption mainly rely on its special structure to increase the optical path of the laser. The absorption enhancement effect of each enhancer rises first and then decreases. 0.4‰ addition of GE can bring 22.5% enhancement. With the enhancement of GE, we get a product of 2.8 MPa tensile strength and 176% elongation at break.     

Enzymatic degradability and release properties of graphene oxide/silk fibroin nanocomposite films

The structure evolution of silk fibroin (SF) in the nanocomposite films with graphene oxide (GO) was investigated and related to the enzymatic degradability and release property. The interaction with GO was found to induce conformation transition of SF from random coil to β-sheet. However, the surface binding constrained the rearrangement of the silk chains, leading to a decrease of β-sheet when GO content was more than 1.0%. The crystal structure of SF played a key role in the degradation of GO/SF composites. The preferential degradation of the hydrophilic blocks resulted in a faster degradation of SF films with higher β-sheet content. The addition of GO to SF matrix led to a slower release and a reduction of the burst release of RhB, the model compound. The release profile was well fitted to the Rigter–Peppas equation, from which the characteristic constant decreased and the diffusional exponent increased with increasing GO content but quickly leveled off when GO content was more than 1.0%. Degradation of the composites had little influence on the characteristic constant of RhB release, however, led to an increased diffusional exponent, which was more evident for the composites with higher β-sheet content.     

Ultrahigh molecular weight polyethylene with improved crosslink density,oxidation stability,and microbial inhibition by chemical crosslinking and tea polyphenols for total joint replacements

Highly crosslinked ultrahigh molecular weight polyethylene (UHMWPE) stabilized by vitamin E (VE) is widely applied in artificial joints as the bearings. Despite the approval, there is a discord that VE lowers the crosslinking efficiency, limiting its use at high concentration. In this work, we aim to obtain highly crosslinked and oxidation resistant UHMWPE through the conjunction of tea polyphenol and chemical crosslinking. We hypothesized that highly incorporated tea polyphenol with multiple reactive sites can ameliorate crosslinking efficiency of chemical crosslinked UHMWPE in comparison to VE. Epigallocatechin gallate (EGCG) as representative tea polyphenol was incorporated into UHMWPE at high concentration (2–8 wt%), followed by chemical crosslinking with 2 wt% organic peroxide. Unlike VE/UHMWPE blends as the control, chemical crosslinking achieved an increasing trend in crosslink density of EGCG/UHMWPE blends with increasing antioxidant concentration. High concentration of EGCG also enhanced the oxidation stability of UHMWPE. Intriguingly, EGCG endowed UHMWPE with an excellent antimicrobial property, which was inefficient in VE/UHMWPE. Cell viability was hardly affected by the high loaded antioxidant and peroxide. The chemically crosslinked UHMWPE blended with EGCG is proved to be a reasonable, cost effective and realistic alternative for use in artificial joints.     

Catechol-containing waterborne polyurethane adhesive inspired by mussel proteins

A series of waterborne polyurethane (PDMAPU) containing catechol group were prepared by double-bond random copolymerization of terminated double bond polyurethane prepolymer with modified acrylamido dopamine under thermal initiation. This kind of mussel-like waterborne polyurethane adhesive is inspired by marine mussel, as well as it is environment-friendly and used in bonding of leather. FTIR and ¹H NMR proved the successful introduction of catechol group into polyurethane matrix. Oxidative cross-linking between catechol unit and molecular chain in PDMAPU structure, the thermal stability and crystallization ability of PDMAPU was significantly improved. The increase of the particle size of PDMAPU emulsion showed that the introduction of catechol group changed the microstructure of polyurethane and enhanced the cross-linking degree. The water resistance of polyurethane emulsion was further improved. Compared with PU without catechol group, the peel strength of leather substrate adhered by PDMAPU emulsion increased from 0.42 to 1.93 MPa, which indicated that PDMAPU has better bonding properties with leather. The bidentate hydrogen bond formed with catechol group as the reaction sites is considered to be the key reason for the adhesion of mussel-like polyurethane adhesive to hydrophilic substrates. This work provides an alternative to prepare environment-friendly high performance adhesive for hydrophilic substrates.     

含电动汽车充电的配电网运行可靠性评估算法

现有方法难以对不同充电状态下的配电网运行状态进行准确评估,为此设计含电动汽车充电的配电网运行可靠性评估算法.通过计算配电网运行情况与配电网元件使用状态,实现配电网运行可靠性评估指标的选取.同时,设定充电周期,计算电动汽车充电功率,并将此作为评估参考因素之一.采用模拟法构建评估模型,将运行可靠性评估指标与电动汽车充电功率融入此模型中,实现对含电动汽车充电的配电网运行可靠性的评估.算例测试结果表明,在慢充和快充状态下的评估计算响应时间明显低于现有方法,并且评估结果的准确性较高.算法更适用于电动汽车配电网运行状态的评估.     

调压连接方式对暂态传递电压的影响

500kV单相自耦中压无载调压的变压器,当调压绕组与低压绕组相邻、中压截波入波时,会在低压到铁心之间感应出很高的冲击传递电压,本文使用波过程仿真的方法,对比了不同的调压连接方式下低压到铁心之间传递电压的变化,进而得出调压的最优连接方案.     

轰运飞机气动元件综合测试台的设计

本文较系统地介绍了测试台气动系统和CAT系统的设计。该测试台一方面功能齐全、可靠性高、操作方便，另一方面软件部分较为完善优越，运行速度较快，使得数据的采集、处理实现了计算机自动化，是航空气动元件比较理想的测试设备。     

Cu对Al-Zn系a1／（a1＋a2）边界走向的影响

对平衡处理(300℃～340℃)后的Al-Zn及Al-Zn加Cu合金a1相成分进行了电子探针微区分析。确定了Cu对a1 a2溶解度间隙形状，即a1/(a1 a2)边界走向的影响。该边界随着Cu含量的增加，向低Zn侧偏移，而不是此前所确定的向高Zn侧偏移。这一结果支持近年的热力学计算结果，溶解度间隙呈“隧道形”，而不支持根据实测相图推测的“钟罩形”。     

低碳Si-Mn系TRIP钢的热处理工艺对组织的影响

低碳Si-Mn系TRIP钢有着复杂的显微组织，主要由多边形铁素体（F）＋无碳贝氏体（B）＋残留奥氏体（AR）组成。本试验采用了彩色金相法，并结合X－ray衍射、SEM和TEM等手段研究了低碳Si-Mn系TRIP钢显微组织与工艺的关系，发现随着两相区退火温度的升高，最终显微组织中铁素体基体体积分数变小，并且贝氏体量增多，残留奥氏体的稳定性呈起伏式变化；在贝氏体转变区的等温温度过高或过低，均使最终显微组织中残留奥氏体体积分数减少；在贝氏体转变区等温时，所形成贝氏体表现出粒状的特征。     

纳米晶镁铝水滑石／聚乙烯复合阻燃料的制备

采用共混法制备聚乙烯／镁铝水滑石纳米复合材料。XRD、SEM、TEM和性能测试表明：镁铝水滑石纳米晶体分散在聚乙烯基体中，且有少部分发生插层；阴离子表面活性剂对水滑石的处理效果要优于偶联剂；pH值对处理效果有一定影响；镁铝水滑石阻燃剂填充聚乙烯体系阻燃效果，要优于填充A1（OH）3阻燃剂。