硅烷交联聚烯烃弹性体的接枝与交联

以乙烯-α烯烃共聚物(POE)接枝乙烯基硅烷制备硅烷交联弹性体,研究了POE的硅烷接枝反应、预交联和硅烷水解交联的影响因素。用红外光谱法对硅烷交联POE进行表征。用15 phr的聚丙烯与POE共混接枝乙烯基硅烷,水解制备改性弹性体,结果表明共混物具有较高的相对硅烷接枝率的同时,体系的加工流动性得到改善。当乙烯基三乙氧基硅烷(VTES)用量为5.0 phr、DCP为0.3 phr时,接枝料(T30S+DF610)具有较好的拉伸强度和断裂伸长率。     

硅烷接枝交联聚烯烃共聚物POE的研究

以过氧化二异丙苯(DCP)作为引发剂,使用哈克(HAAKE)流变仪研究了乙烯基三乙氧基硅烷(VTES)接枝交联不同型号的聚烯烃弹性体(POE)(TAFMER DF610、Vistamaxx 6202、Koattro KT-MR-05)的反应规律。结果表明,VTES以化学键接枝到POE分子链上。加工过程中扭矩变化和接枝交联的反应程度与POE的种类有直接关系,其中,DF610更容易预交联,接枝率较高;而Vistamaxx 6202和KT-MR-05在反应过程中产生降解,接枝率较低。对产品凝胶含量影响因素进行方差分析表明,水解前对凝胶含量影响严重的是DCP的含量,而水解后硅烷含量的变化对凝胶含量影响显著。     

PBT/官能化聚烯烃弹性体共混体系的力学性能与相形态

考察了马来酸酐接枝乙烯-辛烯共聚物（POE-g-MAH）和乙烯-丙烯酸甲酯-甲基丙烯酸缩水甘油酯三元共聚物（E-MA-GMA）对聚对苯二甲酸丁二醇酯（PBT）的增韧作用。结果表明,未接枝的POE弹性体对PBT缺口冲击韧性的改善作用不大。两种官能化聚烯烃弹性体（E-MA-GMA、POE-g-MAH）对PBT具有显著的增韧作用。当弹性体用量分别达到8．5％和10％以后,共混物都各自出现明显的脆／韧转变现象。这意味着在达到同样的冲击韧性时,PBT／E—MA—GMA共混体系的拉伸强度损失较小。SEM显示,PBT／E—MA—GMA共混体系中分散相具有更细微的分散,有效地诱导PBT基体产生银纹和剪切屈服,消耗大量的冲击能。     

聚丙烯／聚烯烃弹性体共混物非等温结晶动力学及力学性能研究

采用熔融共混法制备了聚丙烯(PP)/乙烯-辛烯弹性体(POE)共混物，在差示扫描量热仪上研究了PP及其共混体系降温过程的非等温结晶动力学，对所得数据分别用Jeziorny法和Mo法进行了处理，表明非等温结晶动力学参数Zc及Avrami指数n随冷却速率的增加而增加；对相同配比的共混物随着结晶度的增加，单位结晶时间里达到一定结晶度所需要的降温速率F(T)增大；当相对结晶度相同时，共混物需要的降温速率减小，所有这些均说明弹性体可作为聚丙烯结晶成核剂。另外，采用偏光显微镜研究了PP及其共混物的结晶形貌，测试了共混物的力学性能。结果表明，弹性体改性的共混物的结晶晶粒明显细化，共混物的冲击强度与断裂伸长率得到明显提高．韧性大幅度提高。     

Through Thickness Mechanical Properties of Chemical Vapor Infiltration and Nano‐Infiltration and Transient Eutectic‐Phase Processed SiC/SiC Composites

The through thickness (interlaminar) shear strength and trans‐thickness tensile strength of three different nuclear‐grade SiC/SiC composites were evaluated at room temperature by the double‐notched shear and diametral compression tests, respectively. With increasing densification of the interlaminar matrix region, a transition in failure locations from interlayer to intrafiber bundle was observed, along with significant increases in the value of the interlaminar shear strength. Under trans‐thickness tensile loading, cracks were found to propagate easily in the unidirectional composite. The 2D woven composite had a higher trans‐thickness tensile strength (38 MPa) because the failure mode involved debonding, fiber pull‐out and fiber failure.     

Polystyrene/Polyolefin Elastomer Blends Loaded with Halloysite Nanotubes: Morphological,Mechanical, and Gas Barrier Properties

Herein, a simple melt-blending method is utilized to disperse of halloysite nanotubes (HNTs) in polystyrene/polyolefin elastomer (PS/POE) blends. Based on morphological studies, the PS/POE/HNT nanocomposite containing up to 3 phr HNTs shows excellent nanofiller dispersion, while those filled with 5 phr HNTs exhibit nanofiller aggregation. To overcome the nanofiller aggregation issue, the polypropylene-grafted-maleic anhydride (PP-g-MA) compatibilizer is added to the PS/POE/HNT nanocomposite, which results in improved mechanical properties for the nanocomposite sheets. Furthermore, the addition of compatibilized HNTs to the PS/POE blends leads to decreased O₂ and N₂ gas permeabilities. Besides, incorporating POE, HNTs, and PP-g-MA leads to a decrease in water vapor transmission of PS. In the end, the experimentally-determined mechanical properties and gas permeabilities of the nanocomposite sheets are compared to those predicted by prevalent theoretical models, revealing a good agreement between the experimental and theoretical results. Molecular-dynamics simulations are also carried out to calculate the gas diffusion coefficients in the different sheets to further support the experimental findings in this study. Overall, the PS/POE/HNT/PP-g-MA nanocomposite sheets fabricated in this work demonstrate excellent mechanical and gas barrier properties; and hence, can be used as candidate packaging materials. However, the strength of the resulting PS/POE blend may be inferior to that of the virgin PS.     

Effects of Oxidation Curing of Polycarbosilane on Dielectric and Microwave Absorption Properties of PDCs‐SiC Ceramics

Polycarbosilane (PCS) was cured by oxidizing at different temperatures and pyrolyzed at 1000°C in vacuum. The dielectric properties of SiC ceramics were studied in X band. The ε′ and ε″ of SiC ceramics derived from oxidation‐curing PCS decreased to 4 and 0.35, respectively, which attribute to the decrease of free carbon content and order. SiC ceramic derived from PCS cured at 180°C showed that reflection loss was lower than ?10 dB in the frequency range from 8.2 to 11.3 GHz and the minimum value was ?26.7 dB at 9.6 GHz, which exhibits a promising prospect as microwave‐absorbing materials.     

Investigating the Mechanical Properties of RDX Crystals Using Nano‐Indentation

The shock sensitivity of RDX is of major interest for the development of insensitive munitions. Previous research has implied that internal defects that form within RDX crystals have a strong sensitising effect, increasing the probability of shock initiation. During the NATO Reduced sensitivity RDX Round Robin (R⁴) program the number of internal defects within RDX crystals of differing qualities were assessed by optical microscopy and a scoring system. The results suggested that RDX crystals with many internal defects were more sensitive. Studies investigating the mechanical properties of bulk RDX have shown that lots consisting of poorer crystals are weaker. This study investigates the mechanical properties of individual crystals from different RDX lots using nano‐indentation. It is shown that crystals with many internal defects have reduced modulus of elasticity, stiffness and prone to greater deformation under applied load. The results also show a correlation between these parameters and previously reported shock sensitivity data.     

Effect of Maleic‐Anhydride Grafting on the Physical and Mechanical Properties of Poly(L‐lactic acid)/Starch Blends

MA is grafted onto both PLLA and starch in an internal mixer in the presence of DCP in a one‐step reactive compatibilization process. The effect of maleation of MA on the physical and mechanical properties and morphology of the blends was assessed. The onset decomposition temperature of the PLLA/starch blends decreased as the starch content increases due to the lower thermal stability of starch and the low effect of the maleation reaction on the thermal stability of the blends. PLLA/starch blends without grafted MA showed higher crystallinity as the starch content increased. Reactive compatibilized blends with less than 20 wt% starch had higher storage modulus, indicating that the compatibility between the two phases was improved.

     

Effect of Nano‐Zirconia on the Mechanical and Biological Properties of Calcium Silicate Scaffolds

The calcium silicate (CaSiO₃) scaffolds added with 0, 10, 20, 30, and 40 wt% nano‐zirconia (nano‐ZrO₂) with controlable porous structure were fabricated via selective laser sintering. The effects of nano‐ZrO₂ content on the microstructure, crystalline phase, and mechanical and biological properties were investigated. The results showed that the compressive strength and fracture toughness of the scaffolds were enhanced by the addition of nano‐ZrO₂, and the phase transformation of monoclinic phase (m‐ZrO₂) into tetragonal phase (t‐ZrO₂) occurred, which was favorable for the reinforcing ability of ZrO₂ due to the stress‐induced phase transformation toughening mechanism. However, the excessive amount of nano‐ZrO₂ would cause undesired agglomeration, poor sinterability, and weak apatite‐forming ability. In vitro results showed that there were bone‐like apatite layer formation and MG‐63 cells attachment on the surfaces of the scaffolds, indicating the scaffolds possessed good biological properties.     

大陆扩大农业轮胎产品线

正美国《现代轮胎经销商》(www.moderntiredealer.com)2018年9月5日报道:大陆公司扩大农业轮胎产品线,新增采用新花纹块技术(lug technology)的先进子午线轮胎TractorMaster(见图1)。大陆称,TractorMaster轮胎继承了其2017年推出的Tractor70和Tractor85轮胎的一些特点,包括柔性N. flex胎体和专门开发的单钢丝圈胎圈技     

硫化体系对EPDM硫化胶力学性能的影响

考察了4,4′-二硫代二吗啉（DTDM）,N,N′-间苯撑双马来酰亚胺（HVA-2）,甲基丙烯酸镁与硫黄和过氧化二异丙苯（DCP）复合硫化体系对三元乙丙橡胶力学性能的影响。结果表明,与纯硫黄硫化胶相比,DTDM/HVA-2/S复合硫化体系的EPDM硫化胶拉断伸长率及压缩永久变形均较小,而拉伸强度、定伸应力和硬度均较大,耐老化性能较好。甲基丙烯酸盐可明显提高硫黄、过氧化物硫化EPDM硫化胶的交联密度、拉伸强度、定伸应力和拉断伸长率。在甲基丙烯酸镁/炭黑/EPDM胶料中添加等量S i69改性白炭黑和石蜡油后,硫化胶各项力学性能都有明显提高,定伸应力和硬度保持较低水平,耐热空气老化性能有所改善。     

真空搅拌水泥基材料的物理力学性能和孔结构

混凝土的孔隙率越低,其强度越高.混凝土中的孔通常来自于搅拌引气和水的蒸发两个方面.现行各种提高混凝土强度的措施都不能完全消除搅拌引{气带来的孔隙.提出真空搅拌混凝土技术,并通过试验验证了该技术的作用效果.当水泥浆、纤维素醚改性水泥浆和超高性能混凝土三种水泥基材料搅拌时的真空度从0降低到-0.096 MPa时,它们的流动度都减小,表观密度和抗压强度都增加,其中水泥浆的抗压强度增加9.6％,纤维素醚改性水泥浆的抗压强度增加85％,超高性能混凝土的抗压强度增加30.8％.相对于常规搅拌,在接近绝对真空(真空度为-0.096 MPa)条件下搅拌,超高性能混凝土在700～1100 nm处的孔数量峰值消失,在7～11 nm处的孔数量峰值大幅降低.真空搅拌工艺可以成为提高水泥基材料强度和调控水泥基材料孔结构的一种新技术.     

Curing Viscosity of HTPB‐Based Binder Embedding Micro‐ and Nano‐Aluminum Particles

Aluminum is used as a metal fuel in energetic materials for the improvement of propulsion performance and density. Both nano‐sized and micrometer‐sized activated powders represent valuable options in order to improve metal combustion properties, each possessing advantages and drawbacks. These ingredients bear peculiar properties (namely, higher specific surface, coatings, or surface characteristics) which generate high mixing viscosity once suspended in a polymer as well as altered mechanical properties of the final product. Four different powders dispersed in a polymer binder are taken into consideration and the evolution of viscosity in time during the curing process is investigated. The suspending medium is represented by a mixture of hydroxyl‐terminated polybutadiene (HTPB), isophorone diisocyanate (IPDI) and dioctyl adipate (DOA). Viscosity was measured for 5 h on samples under isothermal curing at 60 °C. Non‐isothermal DSC kinetic analyses were also performed using the Kissinger method. It was found that, for the test conditions, a size reduction of metal particles slowed down the increment rate of curing viscosity while some peculiar coatings, such as fatty acids, introduced opposite trends.     

Nano‐/Microscale Investigation of Tribological and Mechanical Properties of Epoxy/MWNT Nanocomposites

The effects of MWNT content and aspect ratio on the properties of epoxy‐based nanocomposites are investigated using nanoindentation and nanoscratch methods. The Halpin‐Tsai model for predicting the elastic modulus and hardness is modified to include the effective aspect ratio factor. The modified model predicts the experimental results more accurately. The frictional behavior is investigated and a new equation is proposed that correlates the ploughing friction with the plasticity index. The dispersion state of MWNTs and the surface features of residual grooves are investigated using scanning electron micrographs and AFM profiles. The mechanisms of improvements in the properties are also discussed.

     

Effect of High‐Energy Vibromilling on Interfacial Interaction and Mechanical Properties of PVC/Nano‐CaCO3 Composites

Summary: The effects of interfacial interaction between nano‐CaCO₃ and PVC on mechanical properties and morphology of PVC/nano‐CaCO₃ composites were studied. Nano‐CaCO₃ was treated with vibromilling in the presence of PVC and coupling agents. The mechanical properties of PVC/treated nano‐CaCO₃ are remarkably improved. Transmission electron microscopy results revealed that vibromilled nano‐CaCO₃ particles are well dispersed in PVC matrix with good homogeneity and well adhered to PVC matrix. Molau test indicated that chemical reaction between newly formed surface of nano‐CaCO₃ and PVC or coupling agent took place. Theoretical calculation results show that the interfacial interaction between PVC and nano‐CaCO₃ are substantially improved through vibromilling treatment of nano‐CaCO₃ in the presence of PVC and coupling agent.

Molau test results of the samples in THF.     

硅烷偶联剂对玻璃纤维生产工艺及力学性能的影响

研究了A-1100和A-187两种硅烷偶联剂对玻璃纤维拉丝成型工艺、络纱工艺、原丝硬挺度与玻璃纤维及其复合材料界面性能的不同影响。结果显示:A-1100浸润剂体系更有利于玻璃纤维的拉丝成形,拉伸强度更高;相比之下A-187生产的玻璃纤维原丝更加柔软,具有更优的加工性能,粗纱毛羽极少;此外,在环氧树脂-酸酐体系中,涂覆含A-187浸润剂的纤维复合材料具有更高的界面剪切强度和湿态强度保留率。     

Investigations on Material and Mechanical Properties,Air‐Permeation Behavior and Filtration Performance of Mullite‐Bonded Porous SiC Ceramics

A theoretical relation between processing parameters and porosity (29–56%) of mullite‐bonded porous SiC ceramics was derived and validated with experimental data. Porosity‐dependent variation of fracture strength (9–34 MPa) and elastic modulus (7–28 GPa) was explained by the minimum solid area model. At room temperature, the Darcian, k₁ (1.2 × 10^?13–1.6 × 10^?12 m²) and the non‐Darcian, k₂ (4.6 × 10^?9–2.7 × 10^?7 m) permeability coefficients showed linear variation with porosity. Tests conducted up to 650°C indicated an increase in k₁ with temperature and a reverse trend for k₂. Airborne NaCl nanoparticle filtration tests showed good performance of SiC ceramics with fractional collection efficiency of >99% at 46–56% porosity levels.     

The Effect of Mixing on the Mechanical Properties of Hyaluronan‐Based Injectable Hydrogels

A method for determining the correlation between the mixing of two reactive polymers and the structural and mechanical properties of the formed hydrogels is presented. Rheological measurements show that insufficient mixing gives rise to soft and not fully crosslinked hydrogels while excessive mixing beyond gel point results in weaker hydrogels due to potential breakage of their 3D network. Furthermore, the hydrogels swell significantly more in cell culture medium than in phosphate‐buffered saline, attributed to interactions with additional molecules such as proteins. Thus, moderate mixing gives rise to the most homogenous and mechanically stable hydrogels and the choice of medium e.g., for release experiments, should be consistent in order to avoid unnecessary variations in the data caused by different swelling profiles.

     

聚氨酯微孔弹性体的合成及力学性能研究

以聚酯多元醇POL-2016、聚醚多元醇PPG-330N、异氰酸酯MT和MDI-100LL、交联剂乙二醇和TMP等为主要原料,采用半预聚法制备聚氨酯微孔弹性体。研究了多元醇的种类及质量比、游离NCO的质量分数、交联剂和固化剂的质量比、及异氰酸酯的质量比对聚氨酯微孔弹性体力学性能的影响,发现当m(POL-2016)／m(PPG-330N)=60／40、NCO质量分数为6％-6．5％时,弹性体综合性能较佳。