Study on the Structure of Peroxide Cross-Linked Polyethylene Pipes with Several Stabilizers

Cross-linked polyethylene (PEX) pipes used in hot water supply are required for high mechanical strength and high creep resistance at high temperature. Especially PEX-a pipes which are made by peroxide cross-linking have better performance, such as creep resistance and thermal shock resistance than the pipes made by the other cross-linking method. Because the PEX-a pipes indicate the higher cross-link degree as compared with the other PEX pipes. In this study, the PEX-a pipes which were mixed with several stabilizers were tested to evaluate the effects on cross-link degree and the oxygen induction time. And also they are evaluated with the chlorine aqueous solution by the performance of the long-term hydrostatic pressure test and the long-term hydro dynamic pressure test. As a result, it was found that the combination of antioxidants for PEX-a pipes plays an important role to prolong the oxygen induction time without inhibiting the cross-linking. From the results of the 1H pulsed NMR measurement over the melting point of polyethylene, it was found that each peroxide PEX pipe with different antioxidant combinations indicated the different proportion and crosslink density of cross-linked region, in addition, that these pipes had the effective structure of cross-linking for the hydrostatic and hydrodynamic pressure test with the chlorine aqueous solution. Therefore, it was considered to be useful results for studies of the stricture of cross-linking of polyethylene.

Construction of all-organic low dielectric polyimide hybrids via synergistic effect between covalent organic framework and cross-linking structure

Polyimide(PI)is a promising electronic packaging material,but it remains challenging to obtain an all-organic PI hybrid film with decreased dielectric constant and loss without modifying the monomer.Herein,a series of allorganic PI hybrid films were successfully prepared by introducing the covalent organic framework(COF),which could induce the formation of the cross-linking structure in the PI matrix.Due to the synergistic effects of the COF fillers and the cross-linking structure,the PI/COF hybrid film containing 2 wt%COF exhibited the lowest dielectric constant of 2.72 and the lowest dielectric loss(tanδ)of 0.0077 at 1 MHz.It is attributed to the intrinsic low dielectric constant of COF and a large number of mesopores within the PI.Besides,the cross-linking network of PI prevents the molecular chains from stacking and improves the fraction of free volume(FFV).The molecular dynamics simulation results are well consistent with the dielectric properties data.Furthermore,the PI/COF hybrid film with 5 wt%COF showed a significant enhancement in breakdown strength,which increased to 412.8 kV/mm as compared with pure PI.In addition,the PI/COF hybrid film achieve to reduce the dielectric constant and thermal expansion coefficient(CTE).It also exhibited excellent thermal,hydrophobicity,and mechanical performance.The all-organic PI/COF hybrid films have great commercial potential as next-generation electronic packaging materials.

Cross-Linked Hollow Graphitic Carbon as Low-Cost and High-Performance Anode for Potassium Ion Batteries

Large-scale and low-cost preparation of carbon-based potassium anode with long life and high capacity is one of the footstones for the development of potassium ion batteries(PIBs).Herein,a low-cost carbon-based material,cross-linked hollow graphitic carbon(HGC),is large scale synthesized to apply for PIBs anode.Its hollow structure can afford sufficient space to overcome the damage caused by the volume expansion of graphitic carbon(GC).While the cross-linked structure forms a compact interconnection network that allows electrons to rapid transfer between different GC frameworks.Electrochemical measurements demonstrated that the HGC anode exhibited low charge/discharge plateau(about 0.25 V and 0.1 V)and excellent specific capacity as high as 298 m A h g^(-1)at the current density of 50 m A g^(-1).And more important,after 200 cycles the capacity of HGC anode still shows 269 m A h g^(-1)(the decay rate of per cycle is only 0.048%).Meanwhile,the use of commercial traditional electrolyte(KPF_(6))and cheap raw materials that provide new hope for trying and realizing the large-scale production of PIBs based on carbon anode materials.

Preparation and characterization of genipin-cross-linked chitosan microparticles by water-in-oil emulsion solvent diffusion method

Chitosan (CS) microparticles with and without cross-linking were prepared by a water-in-oil emulsion solvent diffusion method without any surfactants. Aqueous CS solution and ethyl ace- tate were used as water and oil phases, respectively. Genipin was used as a cross-linker. Influ- ences of genipin ratios and cross-linking times on CS microparticle characteristics were investigated. Non-cross-linked and cross-linked CS microparticles were spherical in shape and rough in surface. Microparticle matrices showed porous structures. Surface roughness, mean par- ticle sizes and bulk density of CS microparticles increased and their dissolutions in acetic acid solution decreased when genipin ratio and cross- linking time increased.

Secondary structure characterization of mixed food protein complexes using microfluidic modulation spectroscopy(MMS)

Microfluidic modulation spectroscopy(MMS)has been recognised as a novel technology for producing high quality and reproducible data at a wide concentration range to characterise protein structure.In this study,the use of MMS for food applications was explored through the structural analysis of pea protein,whey protein,and pea/whey protein complexes prepared by transglutaminase cross-linking.MMS generated reproducible data with>99.5%repeatability in all protein samples.The cross-linking seemed to alter the structure of whey protein with isopeptide and hydrogen bond formation,more significantly than that of pea protein.The larger secondary and tertiary structural changes were observed with higher whey protein content in cross-linked pea/whey protein complex,which eventually increased the surface hydrophobicity.According to the second derivatives analysis by MMS,β-sheet and random coil increased andβ-turn decreased in the pea protein,whereasα-helix,β-sheet,andβ-turn decreased and random coil increased in the whey protein after cross-linking.In the pea/whey protein complex,β-turn shifted toβ-sheet due to cross-linking.There are some discrepancies between the relative secondary structure contents obtained from MMS data compared to the data acquired from circular dichroism.However,MMS has the considerable advantage of being able to directly measure original samples without significant dilution as required for circular dichroism measurements.This study provides evidence that MMS technology could be a robust technique to quantify the secondary structures of typical proteins in food with high reliability.

Preparation and characterization of cross-linked β-cyclodextrin polymer/Fe_3O_4 composite nanoparticles with core-shell structures

Cross-linkedβ-cyclodextrin polymer/Fe3O4 composite nanoparticles with core-shell structures were prepared via cross linking reaction on the surface of carboxymethylβ-cyclodextrin（CM-β-CD） modified Fe3O4 nanoparticles inβ-cyclodextrin alkaline solution by using epichlorohydrin as crosslinking agent.The morphology,structure and magnetic properties of the prepared composite nanoparticles were investigated by transmission electron microscopy（TEM）,Fourier transform infrared（FTIR） spectrometry,X-ray diffraction（XRD） measurement,thermogravimetric analysis（TGA） and Vibrating sample magnetometry （VSM）,respectively.

Study of Sorption Properties of Anion Exchangers with Long-Chained Cross-Linking Agents for Tungsten Hydrometallurgy

The macroporous anion exchangers with long-chained cross-linking agents were investigated for the tungsten recovery from salt solutions.The physical-chemical characteristics of these sorbents were studied by means of sorption-desorption experiment aswell as electron and IR-spectroscopy.The anion exchangers on the basis of macroporous copolymers of methylacrylate and divinyl-ester of diethyleneglycol or tetravinyl-ester of pentaerythritol possess the exchange capacity to tungsten 2--5 times greater than the porous anion exchangers on the basis of styrene and divinylbenzene,therefore they can be used for selective tungsten recovery from comulex salt solutions.

Preparation of Controllable Cross-Linking Polyethylene Foaming Materials and Their Properties

In order to prepare the polyethylene materials with controlling properties,we developed two kinds of controllable cross-linking polyethylene foaming system.2,5-dimethyl-2,5-bis (tert-butyl peroxy) hexane was used as cross-linking agent and TEMPO as cross-linking inhibitor,azodicarbonamide (AC) was used as foaming agent and citric acid as foaming promoter.The density,expansion ratio,cellular structure and mechanical property of these two kinds of controllable materials were studied.Experimental results show that,properties of these two kinds of materials appear similar trend:cellular size and expansion ratio are enlarged with the amount of cross-linking inhibitor or foaming promoter increasing,while density and mechanical strength appear decreasing trend.Through comparing those two material systems’ properties,cross-linking polyethelene foaming system with citric acid as foaming promoter has better properties.

Deciphering In-vivo Cross-linking Mass Spectrometry Data for Dynamic Protein Structure Analysis

Protein structure and protein-protein interactions(PPIs)are crucial for regulating cellular activities required for cell viability and homeostasis.Chemical cross-linking coupled with mass spectrometry(CXMS)has become a versatile tool providing insights into both protein structure with distance restraints and protein-protein interactions with interface sites.Cross-links as the most information-rich data in a CXMS experiment are responsible for the structural model validation and integrative modeling with high throughput and sensitivity.In this work,ensemble refinement of the existing protein structure against the in-vivo cross-linking distance restraints was performed for dynamic protein structure modeling and protein interaction binding interface building in the intracellular environment.These results indicate great potential of in-vivo CXMS data for providing a molecular basis of protein structural dynamics exploration and function performance.

The Influence of Pore Structures and Degree of Cross-Linking on Catalytic Properties of Aminomethyl Polystyrene Resin Supported Dendritic Copper Complexes

1 Introduction Immobilization of homogeneous catalysts onto polymer supports through covalent attachment has received wide attention because these materials offer advantage features of heterogeneous catalysis to homogeneous systems.The polymer-supported catalysts enhance their thermal stability,selectivity,recyclability and easy separation from reaction products leading to the operationally flexible[1-2].Such behaviour prompted us to know the effect of pore structures of polymer supporters on catalytic ...

ZnO纳米薄膜在竹材表面的生长及防护性能

在低温溶液反应体系下,通过晶种形成和晶体生长两步法在竹材表面培育ZnO纳米结构薄膜,应用场发射环境扫描电镜(FESEM)、X射线衍射仪(XRD)和X射线能谱仪(EDAX)对薄膜形态和结构进行表征,重点研究种子液浸渍时间对纳米薄膜形态及竹材防霉和抗光变色性能的影响.研究结果表明,在生长时间一定的前提下,竹材在种子液中经过0.5h、1h和2h的浸渍,其表面可形成壁厚为50～80nm的网状结构薄膜,使竹材的防霉性能和光稳定性得到显著改良;当种子液浸渍时间增加到4h,网状结构薄膜则被大量直径约700nm的ZnO圆片所覆盖,虽然此时竹材的防光变色性能保持不变,但防霉性能下降,表明纳米网状结构对于充分发挥ZnO防护性能起到重要作用.

表面活性剂减阻水溶液突扩流的阻力特性

为揭示胶束水溶液突扩流的减阻特性,实验研究了质量分数为1×10^(-4),2×10^(-4)的十六烷基三甲基溴化铵水溶液通过管径比为1:1.52的突扩的流动阻力行为.实验结果表明,在直管段最大减阻率都可达到70%的两给定质量分数的胶束水溶液,其突扩局部阻力系数,在较低雷诺数区域,较牛顿流体仅有10%～20%程度的降低,呈现局部低减阻特性;在较高雷诺数区域远大于牛顿流体,尤其当突扩进口流快失去减阻能力时,甚至接近牛顿流体的1.5倍,呈现明显的局部增阻行为.胶束水溶液减阻流,在突扩下游再次形成充分发展流所需的下游长度,远大于牛顿流体的7.8倍下游管径(45倍突扩台阶高度),流入突扩前完全失去减阻能力的质量分数为2×10^(-4)的胶束水溶液流,所需的突扩下游长度达到最大,约合158倍下游管径(920倍突扩台阶高度).通过胶束水溶液流变特性的实验分析认为,减阻水溶液突扩流的阻力行为与它的胶束网联结构的形成及松弛的时间特性密切相关.

网状结构高孔率泡沫钛的特性

网状泡沫钛属于弹脆性多孔材料,其压缩曲线的平台区为锯齿形,并在总体上呈缓慢增长的趋势;其平台区结束的极限应变较大,且密实化阶段的应力-应变曲线不是那么陡峭。采用浸浆烧结法制备获得了一种孔率在85%~90%之间、孔径分布在1~3 mm之间的网状泡沫钛。结果表明:该泡沫钛制品的热导率随着样品孔率的提高而明显地减小,且总体上具有良好的隔热性能,孔率为87%~89%的试样的室温热导率为0.4~0.8 W/(m·K)。此外,还测试该泡沫钛试样在200~6300 Hz声频范围内的吸声系数,发现其第一共振频率出现在4000 Hz左右,此时试样的吸声系数达到约0.9。

低密度竹纤维膨化材料的性能研究

该文通过对缓冲材料的微观结构和红外光谱分析,验证了其网状交联结构的存在性,并在此基础上对不同膨化倍数缓冲材料进行静态压缩试验、蠕变试验和四次压缩回弹试验,测定该材料的力学性能。试验结果表明,该缓冲材料的残余应变随膨化倍数的增加而逐渐提高,而其回弹厚度随膨化倍数的增加而逐渐减少;该缓冲材料的蠕变值早期快速提高,后期变化很小且呈直线趋势,卸载24 h后的残余应变在半h内急剧下降,而后逐渐趋于缓慢;该缓冲材料受到压缩后,孔隙收缩且形状发生较多的变化,即该材料的开放结构能够吸收一定外部能量。

PE-LD/CaCO_3/EVA复合材料性能的研究

分别探讨了重质碳酸钙（CaCO3）和乙烯-醋酸乙烯酯共聚物（EVA）的含量对低密度聚乙烯（PE-LD）/CaCO3／EVA三元复合体系的拉伸强度、断裂伸长率、冲击强度以及缺口冲击强度的影响，并结合试样冲击断面的扫描电镜照片，分析了复合材料力学性能变化的规律和原因。结果表明，当重质CaCO3含量为10％～20％、EVA含量为0．67％时，复合材料的力学性能最佳；当重质CaCO3含量为20％，EVA含量增加到1．33％～2．33％时，复合材料中树脂基体彤成的网状结构趋于完善，冲击强度达到最大值，而拉伸强度随EVA含量的增加变化不大。

有限元分析在钢网架屋盖结构设计中的应用研究

研究目的:研究ANSYS软件在钢网架屋顶结构设计中的适用性,分析钢网架结构设计参数的可行性。研究方法:用ANSYS软件建立钢网架屋顶结构的有限元模型,结合该结构的实际受力状态、材料特性、几何特性及边界条件等相关参数,对模型进行加载计算和求解。研究结果:通过对结构变形和内力两方面的检算,得到了钢网架屋顶结构的竖向变形值和结构中各杆件的轴力值。参照相关设计规范,该屋顶结构的变形和强度均满足规范要求。研究结论:有限元分析在检算钢网架屋盖结构设计参数的可行性方面比较适用,直接利用有限元软件ANSYS建立有限元模型,输入相关计算参数,然后划分网格、加载、求解,最终可提取需要的相关力学参数。类比本算例,可将有限元软件ANSYS作为辅助工具应用于其他工程结构的参数设计与力学检算中。

Semi-interpenetrating network anion exchange membranes based on quaternized polyvinyl alcohol/poly(diallyldimethylammonium chloride)

The semi-interpenetrating network anion exchange membranes(AEMs)based on quaternized polyvinyl alcohol(QPVA)and poly(-diallyldimethylammonium chloride)(PDDA)are synthesized.The chemical cross-linking structure is formed between hydroxyl groups of QPVA and aldehyde groups of glutaraldehyde(GA),which makes PDDA more stable embed in the QPVA matrix and also improves the mechanical properties and dimensional stability of AEMs.Due to the phase separation phenomenon of AEMs swelling in water,a microporous structure may be formed in the membrane,which reduces the transmission resistance of hydroxide ions and provides a larger space for the transfer of hydroxide ions,thus improving the conductivity.The ring structure of PDDA is introduced as a cationic group to transfer hydroxide ions,and shields the nucleophilic attack of the hydroxide ions through the steric hindrance effect,which improves alkaline stability.The hydroxide conductivity of semi-interpenetrating network membrane(QPVA/PDDA0.5-GA)is 36.5 mS cm^(-1) at 60℃.And the membrane of QPVA/PDDA0.5-GA exhibits excellent mechanical property with maximum tensile strength of 19.6 MPa.After immersing into hot 3 mol L^(-1) NaOH solutions at 60℃ for 300 h,the OHconductivity remains 78%of its initial value.The semi-interpenetrating network AEMs with microporous structure exhibit good ionic conductivity,mechanical strength and alkaline durability.

Highly integrated sulfur cathodes with strong sulfur/high-strength binder interactions enabling durable high-loading lithium-sulfur batteries

The development of high-sulfur-loading Li-S batteries is a key prerequisite for their commercial applications.This requires to surmount the huge polarization,severe polysulfide shuttling and drastic volume change caused by electrode thickening.High-strength polar binders are ideal for constructing robust and long-life high-loading sulfur cathodes but show very weak interfacial interaction with non-polar sulfur materials.To address this issue,this work devises a highly integrated sulfur@polydopamine/highstrength binder composite cathodes,targeting long-lasting and high-sulfur-loading Li-S batteries.The super-adhesion polydopamine(PD)can form a uniform nano-coating over the graphene/sulfur(G-S)surface and provide strong affinity to the cross-linked polyacrylamide(c-PAM)binder,thus tightly integrating sulfur with the binder network and greatly boosting the overall mechanical strength/conductivity of the electrode.Moreover,the PD coating and c-PAM binder rich in polar groups can form two effective blockades against the effusion of soluble polysulfides.As such,the 4.5 mg cm−2 sulfur-loaded G-S@PD-c-PAM cathode achieves a capacity of 480 mAh g−1 after 300 cycles at 1 C,while maintaining a capacity of 396 mAh g−1 after 50 cycles at 0.2 C when the sulfur loading rises to 9.1 mg cm−2.This work provides a system-wide concept for constructing high-loading sulfur cathodes through integrated structural design.

中西合璧峡谷回音 生生不息──论三峡工程淹没区传统聚落与民居的地域性特征

三峡地区山高平坝少，水系发达，自成一地理单元。独特的地理环境和历史上移民活动决定了这一地区聚落的分布和住民房屋形式与它地不同。沿江古场镇的分布主要受到转输贸易和煮盐业的影响，其布局受地形限制形成线性和网状结构．民居以穿斗式与南方天井式为主，大山的质朴与江河的畅快有机结合，表现出强烈的山地意识。这些构成了峡区极具特色的人──地地表景观。

有限元分析在钢网架屋盖结构设计中的应用研究

在介绍钢网架屋顶构造设计的基础上,利用ANSYS软件对结构进行了有限元建模、网格划分、加载与求解。通过对结构变形和内力两方面的验算,分析钢网架结构设计参数的可行性。