高分子量聚全氟乙丙烯(Fs-46)耐辐照性质的研究

本文针对聚全氟乙丙烯(Fs-46)树脂的耐辐照性质, 对照研究了普通Fs-46树脂与分子量大于20万Fs-46树脂的耐辐照及抗热老化性质。在190±2℃饱和水蒸汽0.2~3.0kPa压力下, 经(γ-射线(1×10^6库仑)照射后, 再于200℃经4320小时的热老化模拟试验, 后者机械强度基本不变, 前者的机械强度明显下降。结果表明分子量大于20万的Fs-46树脂具有比普通树脂Fs-46更好的耐辐照和抗热老化性能。     

共聚结构和分子量对热塑性聚酰亚胺树脂熔融与耐热性能的影响

基于具有刚性主链结构的4,4'-(六氟亚异丙基)双邻苯二甲酸酐/对苯二胺(6FDA/p-PDA)树脂体系, 通过共聚引入间苯二胺(m-PDA)、 4,4'-二氨基-2,2'-双三氟甲基联苯(TFDB)和9,9'-双(4-氨基苯基)芴(BAFL)等主链刚性且兼具大自由体积特性的芳香二胺, 以非反应性封端剂邻苯二甲酸酐(PA)对分子量进行调控, 设计制备了系列分子量可控的热塑性聚酰亚胺(TPI)树脂. 系统研究了共聚结构和分子量对TPI树脂熔融性能和耐热性能的影响, 构建了聚合物的聚集态结构与树脂熔融性能的对应关系, 并对树脂的室温和高温力学性能进行了评价. 研究结果表明, 大自由体积的芳香二胺共聚结构的引入可有效降低分子链堆砌密度, 增大聚合物的自由体积, 从而赋予树脂良好的熔融性能. 降低设计分子量可进一步改善树脂的熔融加工性. 这类具有刚性主链结构的TPI树脂兼具优异的耐热性能和力学性能, 树脂的玻璃化转变温度在308~338 ℃之间, 以TFDB和BAFL共聚制备的TPI-C-25K和TPI-D-25K树脂表现出高强高韧的特性, 拉伸和弯曲强度分别超过120 MPa和190 MPa, 断裂伸长率大于8.2%, 并且在250 ℃高温下表现出良好的耐热稳定性.     

高透明抗冲聚苯乙烯树脂的辐射合成与性能表征

以过氧化苯甲酰为引发剂,采用苯乙烯、甲基丙烯酸甲酯为共聚单体,先经本体自由基预聚合,再经γ辐照聚合法合成甲基丙烯酸甲酯 苯乙烯共聚物(MS)树脂.系统研究了吸收剂量和剂量率对MS树脂的分子量及其分布的影响,同时研究了树脂的化学结构、热性能、透过率和力学性能.结果表明,辐射合成的MS树脂是一种无规共聚物,具有很好的光学性能,较好的韧性和强度.     

高性能光催化降解聚乙烯薄膜的研究

利用酸性蓝BGA染料敏化的纳米TiO2作为光催化剂, 与低密度聚乙烯(LDPE)树脂复合制备了具有可见光催化降解性能的复合塑料薄膜. 采用SEM、FTIR、VHX-100数码显微镜和高温凝胶渗透色谱(HTGPC)等分析技术系统地研究了该塑料薄膜在紫外光和太阳光照射下的降解性能. 探讨了塑料薄膜在光辐照前后的力学性能、质量和分子量变化规律. 研究结果表明, 该薄膜在经紫外线照射5 d后质量损失达到17.6％, 数均分子量由21800降低为5900; 经太阳光照射48 d后质量损失达到12.5％, 分子量降为8100. 辐照后薄膜拉伸强度和断裂伸长率显著降低, 羰基含量升高.     

氨基硅油改性碳纤维/环氧树脂复合材料的耐老化性能

通过在复合树脂基体中引入氨基硅油进行改性,制备了不同氨基硅油含量的碳纤维/环氧树脂复合材料,在湿热环境下进行老化实验后,通过动态热机械分析(DMA)、热重分析(TGA)、拉伸性能测试、扫描电镜(SEM)及接触角测定等方法研究氨基硅油对于碳纤维/环氧树脂复合材料热力学性能、力学强度保持率和耐水性能的改善效果。实验结果表明,经老化实验后含氨基硅油材料的抗拉强度保持率最高提升了13.23%。当氨基硅油含量为8 wt%时,复合材料表面接触角均值大于90~o。氨基硅油对环氧树脂基体的改性可改善碳纤维/环氧树脂复合材料的耐湿热老化性能。     

耐紫外光老化CO2共聚物的合成与性能

CO₂基塑料(PPC)是通过CO₂与环氧丙烷共聚所得的生物降解高分子,由于PPC的耐紫外老化性能较差,随紫外线的照射不仅PPC的相对分子质量快速下降,且其拉伸强度和断裂伸长率等力学性能也迅速降低,而农用地膜长期处于紫外线照射的环境中,因此亟待改善PPC的耐紫外老化性能。 本文设计合成了含紫外吸收基团的单体2-羟基-4(2,3-环氧丙氧基)二苯甲酮(HEB),与CO₂和环氧丙烷进行三元共聚制备了耐紫外光老化的CO₂共聚物(PPCH)。 在保证PPCH相对分子质量不低于5.0×10⁴的前提下,PPCH中HEB单元的摩尔分数最高可达0.32%,相应地其玻璃化转变温度(T_g)和起始热分解温度(T_d-5%)分别为26.7和216.9 ℃,拉伸强度达到30.97 MPa。 普通PPC经过240 h的紫外辐照后,其数均相对分子质量下降了67.8%,相应地其拉伸强度和断裂伸长率分别下降了10.1%和40.1%。 即使PPCH中的HEB摩尔分数仅为0.06%,经过240 h辐照后其数均相对分子质量仅下降了6.2%,相应地其拉伸强度和断裂伸长率也仅分别下降了1.7%和13.3%,证明PPCH具有较强的耐紫外老化性能,原因在于其主链含有HEB单元,对紫外光具有较好的吸收性能。 PPCH的紫外吸收性能随HEB单元在聚合物中含量的增加而增强,因此随着共聚物中引入的HEB单元含量增加,PPCH的相对分子质量和力学性能的保持率均得到了大幅度提高。 另一方面,对PPCH共聚物与相同二羟基二苯甲酮(BP)含量的PPC/BP共混物进行120 h的50 ℃热水萃取实验,PPCH显示出稳定的紫外光吸收性能,而PPC/BP共混物的紫外吸收性能随热水萃取时间的增长而快速下降,表明三元共聚反应能够有效解决普通共混物面临的小分子紫外吸收剂的外迁移问题。     

基于二氧化碳共聚物的紫外光固化高分子材料的制备与性能

普通低分子量的二氧化碳共聚物由于预聚体中含有较多的亲水性端羟基, 在紫外光辐照下不能交联而降低材料的耐水性. 为降低亲水性端羟基对材料耐水性的影响, 本文利用锌钴双金属氰化物(Zn-Co DMC)催化剂实现了CO₂与4-乙烯基环氧环己烷、 环氧环己烷的三元无规共聚, 制备出分子量在40000以上, 含C=C双键的脂环族聚碳酸酯; 采用四(3-巯基丙酸)季戊四醇酯为固化剂, 基于紫外光诱导的双键-巯基点击反应制备了紫外光固化高分子材料. 研究发现, 在5.0 mJ/cm²的紫外光辐照剂量下即可制备出高透明硬化涂层, 在可见光(400~750 nm)波段内透光率达到97.5%, 铅笔硬度达到3H, 对马口铁等基体附着力达到0级. 值得指出的是, 该紫外光固化薄膜的玻璃化转变温度超过110 ℃, 与双酚A型环氧树脂相当, 而且不含苯环等结构, 具有更优异的耐紫外光老化性能.     

环境温度对紫外辐照HDPE结构与性能的影响研究

采用元素、XPS、GPC分析，凝胶和力学性能测定，研究了空气中不同环境温度下紫外辐照官能化HDPE的结构、粘着性以及紫外辐照官能化HDPE对HDPE/聚乙烯醇(PVA)体系的增容作用。实验结果表明，提高环境温度可显著提高引入C-O、C(=O)O和C=O等含氧基团的速度。在相同辐照时间下，随环境温度提高，辐照HDPE的分子量下降、分子量分布变宽以及剥离强度提高的幅度增大，并在70℃时产生凝胶。较高环境温度下辐照的HDPE对HDPE/PVA共混体系有较好增容作用，在HDPE/PVA(83/17)体系中加入10%(质量分数)的70℃环境温度下辐照24h的HDPE，共混物的拉伸屈服强度和缺口冲击强度分别从30.8MPa和110J/m提高到34.9MPa和142J/m。     

聚富马酸丁二酯的水热老化行为研究

研究了聚富马酸丁二酯(PBF)的水热老化行为,采用凝胶渗透色谱法(GPC)、力学性能测试,示差扫描量热法(DSC)和全反射红外光谱(ATR-FTIR)研究了老化过程中PBF的分子量、力学性能、热性能和表面化学基团含量的变化.研究结果表明,PBF在30℃下具有良好的耐老化性能.温度对PBF老化行为的影响显著,水热老化温度升至60℃,PBF各项力学性能急剧下降,老化20天后样品在水中断裂并形成碎片,力学性能完全丧失,同时数均分子量下降了50%.80℃水热老化5天,样品即断裂并形成碎片,失去结构的完整性,数均分子量下降了87%.老化过程中碳碳双键的含量未发生明显变化,老化降解的机理是水的增塑、溶胀以及酯键水解,聚合物分子链断裂,分子量下降.     

天然橡胶/石墨烯纳米复合材料的制备及耐核辐射性能

采用乳液共混和原位还原法制备了天然橡胶(NR)/还原氧化石墨烯(RGO)纳米复合材料,研究了γ射线辐照对复合材料力学性能和热稳定性的影响.研究结果表明,RGO以少数几层堆叠片层结构均匀分散于NR基体中.RGO的加入可显著提高NR的力学性能和热稳定性,加入质量分数为0.6%的RGO可使材料拉伸强度由(22±1.4)MPa提升至(25±1.1)MPa,质量损失50%对应的温度(T50)升高6.4℃.经200 k Gy的γ射线辐射后,纯NR的拉伸强度和T50分别下降了75%和4.5℃,而NR/RGO-0.6%复合体系仅分别下降了56%和1.2℃.揭示了RGO提高材料耐辐射性能的机理,由于RGO可捕捉猝灭因辐射产生的自由基,从而减弱了辐射老化降解和交联反应的发生.     

顺铂耐药的分子机制

顺铂被广泛用于多种类型的实体肿瘤的临床治疗.DNA是顺铂的主要靶点,顺铂结合会导致DNA损伤并诱发细胞凋亡.然而,顺铂化疗常常受到内在的和获得性的耐药性的限制.在过去30多年里,大量的研究致力于对顺铂耐药性的理解,并且提出了几种导致顺铂耐药性的分子机制.这些机制显示顺铂的耐药性具有多因素特征.本文系统描述和讨论了顺铂的耐药性机制,包括细胞内药物积累的减少,药物去活作用的增强,DNA修复作用,DNA损伤反应和凋亡通路的变化以及一些间接信号通路的调控影响.     

DSC Studies of rhododendron hybrids frost resistance

The DSC method was used to study phase transitions in Rhododendron L. leaf tissues caused by temperatures below the freezing point of water. The curves show several stages of water crystallisation, demonstrating that these processes do not occur simultaneously in various types of cell organelles. Temperatures and enthalpies of the phase transitions were determined and significant changes were found in the DSC curves when the sample was repeatedly subjected to sub-zero temperature cooling and heating. Also, frost resistance of the same rhododendron taxons was studied by conductometric analysis and the DSC results were compared with the data from other laboratory studies.     

Scratch resistance and weatherfastness of uv-curable clearcoats

UV-cuing has found an increasing number of industry allocations over the past decade due to its unique benefits, e.g. solvent free formulations, high cure speed and low temperature processing. In addition to these benefits two additional properties of uv-cured coatings are of today's interest, especially in the automotive industry: scratch resistance and resistance against chemicals. One of the most important requirements for a broad use of uv-curable coatings in the coating industry is that coatings are stable against degradation caused by atmospheric influences since coatings for outdoor use are subject to especially harsh weathering conditions, e.g. uv-light, oxygen, moisture and air pollutants. This weathering leads to a degradation of the polymeric binder. Clearcoats containing photoinitiators based on bis-acylphosphinoxide (“BAPO”) and a combination of hydroxyphenyl-s-triazine uv-absorber and a sterically hindered amine as a light stabilizer package show a very good curing behavior as well as an improved weatherfastness over a long period of time and a good scratch and chemical resistance.     

High scratch and etch resistance by optimized cross-linking chemistry and density

Target of development in the field of modern automotive clear coats is the combination of high etch and high scratch resistance. For high etch resistance the cross-linking chemistry is the key factor. The property scratch resistance is mainly influenced by the cross-linking density and the flexibility of chains between netpoints. By combining these parameters high etch and scratch resistant clear coats can be formulated. As a representative example an optimized clear coat based on epoxy/acid cross-linking chemistry is discussed. The ways to achieve high cross-linking density are shown.     

Superhydrophobic ceria on aluminum and its corrosion resistance

Superhydrophobic ceria on the aluminum substrate was fabricated, and its corrosion resistance was investigated by different techniques. For example, the so‐obtained superhydrophobic sample was immersed into the NaCl aqueous solution, and the variations in the surface wettability as well as the surface morphology were monitored; potentiodynamic polarization in the NaCl aqueous solution was adopted to evaluate its electrochemical corrosion resistance; a droplet of the aqueous solution HCl was dripped onto the superhydrophobic surface, and the corrosion process as well as the surface morphology after corrosion was monitored. The experimental results showed that the superhydrophobic ceria possessed a good corrosion resistance because of the entrapped air in the solid/liquid interface. Copyright © 2016 John Wiley & Sons, Ltd.     

Effect of mechanical pre-conditioning on fracture resistance of polypropylene

The effect of externally applied mechanical pre-conditioning,i.e.pre-impact treatment,on the fracture resistance was investigated for polypropylene(PP).Impact strength was obtained via notched and/or unnotched samples.It has been shown that the pre-impact treatment is favorable to the improvement of the fracture resistance.The impact strength increases linearly with the applied pre-impact energy.Both optical and SEM results show that there are at least two possible mechanisms for the improvement of the fracture resistance.One is the crack blunting effect which is introduced to notched sample by pre-impact treatment,reducing the sensitivity of PP to the applied notch.The other is the formation of large amount of microvoids induced by pre-impact treatment,which changes the stress distribution and induces intensive plastic deformation of PP at the second impact measurement,leading to the improvement of the fracture resistance.     

Thermal stability and flame resistance of polypyrrole-coated PET fibres

Electro-conducting doped polypyrrole was deposited by in situ oxidative polymerisation on PET non-wovens. Thermal properties were evaluated by means of DSC and TG in nitrogen and air. Flame resistance tests reveal that coated PET fibres resist to direct contact with fire. By thermal analysis, it was found that PPy reduces the temperature at which thermo-oxidative degradation of PET occurs. Polypyrrole-coated PET non-wovens were heated above the melting point of PET for 30 min. After the heating the fibres become brittle and frail, but SEM observations revealed that they maintained their fibrous shape. A loss of chlorine was found because of intense heating.     

Observation of negative differential resistance in diketopyrrolopyrrole-based copolymer films

Remarkable and repeatable negative differential resistance (NDR) phenomenon was observed in a metal-polymer-metal structure diode based on bishexyloxy-divinyl-benzene-alt-diketopyrrolopyrrole (C6DPPPPV),a type of donor-acceptor (D-A) conjugated copolymer.Thickness dependence of the devices implied that the observed NDR characteristics were bulk-controlled.The device performance was considered to depend on the slow trapping and releasing processes related to the local deep states,which was enhanced by the gr...     

Weathering resistance of halogen-free flame retardance in thermoplastics

The influence of weathering on the fire retardancy of polymers is investigated by means of a cone calorimeter test, before and after artificial weathering. The surface degradation was monitored using different techniques (ATR-FTIR, microscopy, colour measurement). Different kinds of polymeric materials were chosen, all as they are used in practice: polycarbonate (PC) blends, polyamide (PA) and polypropylene (PP) flame-retarded with arylphosphate, melamine cyanurate (MC) and intumescent formulation based on ammonium polyphosphate (APP), respectively.All samples show material degradation at the surface due to weathering. No significant weathering influence occurs on the flame retardancy when it is a bulk property, as was observed for aryl phosphates in PC blends and MC in PA. When the fire retardancy is dominated by a surface mechanism, dependence on the duration of weathering is detected: for intumescent formulations based on ammonium APP in PP, a worsening in the formation of the intumescent network was observed.     

Determination of lanthanum and cerium in cmsx-4 nickel-based superalloys by inductively coupled plasma mass spectrometryEI北大核心CSCD

CMSX-4 is the second-generation nickel-based single crystal superalloy used widely in the world. The oxidation resistance and corrosion resistance of CMSX-4 alloy can be improved by adding trace lanthanum (La), cerium (Ce) and other rare earth elements. A method for the simultaneous determination of La and Ce in CMSX-4 nickel-based superalloy by wet dissolution-inductively coupled plasma mass spectrometry was established. The sample was heated and dissolved under normal pressure by aqua regia and hydrofluoric acid, and the interference of fluorine ion was eliminated by using perchloric acid. The amount of dissolved acid and the digestion conditions were optimized. The limits of detection were 0.23 μg/g for La and 0.85 μg/g for Ce under optimized conditions. The spiked recoveries were 95.0%–98.9% with the relative standard deviations of 1.3%–3.9%, which can meet the requirements of accurate and rapid determination of La and Ce in CMSX-4 nickel-based superalloy. © 2023, Youke Publishing Co.,Ltd. All rights reserved.