Effects of carbon blacks on electrical properties of EPDM compounds

The correlations between mechanical and electrical properties of ethylene propylene diene terpolymer (EPDM) compounds and carbon black types and levels applied are studied. Tensile strength increases with an increase of the carbon black, especially for carbon black with higher surface area. Tracking resistance of EPDM compounds improves when a small amount of relatively nonconductive carbon blacks are added to EPDM compounds, whereas conductive carbon blacks decrease both dielectric properties and tracking resistance of EPDM compounds. Possible reasons for these results are discussed. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 2540–2546, 2000     

Synthesis and properties of styrene–EPDM–vinyl acetate graft polymer

The styrene–EPDM–vinylacetate (SEV) graft polymer, which linked respectively the styrene (St) unit and vinylacetate the (VAc) unit to the ethylene–propylene–diene terpolymer (EPDM) backbone was synthesized by two‐step graft polymerizations: First the graft polymerization of VAc onto EPDM was carried out, and then St was added successively in the prepolymerized solution and further polymerized for a given period to obtain SEV. The effects of concentration of EPDM and an initiator, mole ratio of VAc to St, polymerization time, temperature, and solvent were examined on the graft polymerizations. The synthesized graft polymers (SEVs) that have different contents of St or VAc were identified by Fourier transform IR spectrum. The highest graft ratio has been obtained by 10 wt % of EPDM, 1.0 mole ratio of VAc to St, and 1.0 wt % of BPO in toluene for 48 h at 70°C. The glass transition temperature of SEV is lower than that of poly(vinyl acetate) (PVAc) and polystyrene (PS). The thermal stability of SEV is higher than that of PVAc, PS, and the acrylonitrile–butadiene–styrene (ABS) resin. The tensile strength of SEV was improved as compared with that of EPDM. The light resistance and weatherability of SEV were better than those of ABS. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 2296–2304, 2000     

Incorporation effects of fluorinated side groups into polyimide membranes on their physical and gas permeation properties

The effects of incorporation of fluorinated alkyl side groups into polyimide membranes were investigated in terms of their physical and gas permeation properties. Four polyimides with fluorinated side groups and four polyimides without the side groups were prepared by polycondensation of 2‐(perfluorohexyl)ethyl‐3, 5‐diamino benzoate (PFDAB) and m‐PDA with four aromatic dianhydrides (6FDA, ODPA, BTDA, and PMDA), respectively. It was found that the incorporation of fluorinated side groups into the polyimide membranes decreased their surface free energies (T_gs), solubility parameters, and fractional free volume (FFV)s and therefore, enhanced the permeabilities for CO₂, O₂, N₂, and CH₄ gases but reduced the selectivities for CO₂/ CH₄, O₂ /N₂, CO₂/N₂ gas pairs depending upon the structure of dianhydride monomers. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 2756–2767, 2000     

Gold nanoparticle-assisted delivery of brain-derived neurotrophic factor to cerebral organoids

Gold nanoparticle(AuNP)-assisted delivery of proteins/drugs to cells or in vivo systems has long been studied.However,their interaction with in vivo mimicking o...     

Crystallization kinetics of poly(ethylene terephthalate) with thermotropic liquid crystalline polymer blends

The isothermal and dynamic crystallization behaviors of polyethylene terephthalate (PET) blended with three types of liquid crystal polymers, i.e., PHB60–PET40, HBA73–HNA27, [(PHB60–PET40)–(HBA73–HNA27) 50 : 50], have been studied using differential scanning calorimetry (DSC). The kinetics were calculated using the slope of the crystallization versus time plot, the time for 50% reduced crystallinity, the time to attain maximum rate of crystallization, and the Avrami equation. All the liquid crystalline polymer reinforcements with 10 wt % added accelerated the rate of crystallization of PET; however, the order of the acceleration effect among the liquid crystalline polymers could not be defined from the isothermal crystallization kinetics. The order of the effect for liquid crystalline polymer on the crystallization of PET is as follows: (PHB60–PET40)–(HBA73–HNA27) (50 : 50); HBA73–HNA27; PHB60–PET40: This order forms the dynamic scan of the DSC measurements. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 67:1383–1392, 1998     

Effect of orientation on the biodegradability of uniaxially stretched aliphatic copolyester films

The effects of uniaxial drawing conditions on the orientation of aliphatic copolyester films were investigated by using both Fourier transform infrared-attenuated total reflection (FTIR-ATR) dichroism and wide angle X-ray diffraction (WAXD) methods. The results showed that orientation in uniaxially drawn films was determined by the drawing rate and drawing temperature. At higher drawing rates and higher drawing temperatures, higher orientation was obtained due to a large deformation of spherulites. The WAXD patterns of drawn films exhibited the preferential orientation of lamellar crystallites. The results of microbial degradation indicated that development of crystalline orientation evidently depressed biodegradability of samples. Video microscopy observations revealed that the degree of orientation played a dominant role in determining the rate of surface erosion. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 64: 1999–2006, 1997     

铸石骨料高强度混凝土力学及抗冲磨性能

针对水工泄水建筑物过流面混凝土的冲刷磨损和空蚀破坏问题,采用铸石作为粗骨料,部分替代玄武岩骨料或完全替代玄武岩骨料,制备高强抗冲磨混凝土,研究了铸石高强抗冲磨混凝土的抗压强度和轴向拉伸性能,并采用水下钢球法和缩放型空蚀发生器研究了铸石粗骨料对混凝土抗冲磨防空蚀性能的影响,结果表明,铸石粗骨料可显著提高混凝土的抗压强度,提升幅度可超过50％,铸石粗骨料对混凝土的轴向抗拉强度、抗拉弹性模量和极限拉伸值等性能的提升效果不明显,提升幅度基本在10％以内,铸石粗骨料显著提升了混凝土的抗冲磨性能,水下钢球法抗冲磨强度可提升55％,抗空蚀强度提升62％.     

高层建筑地基基础和桩基础土建施工技术探讨

在高层建筑工程的具体建设施工过程中,地基基础及基床基础的土建施工是保障整体工程质量与安全的关键.因此,随着高层建筑工程施工数量与规模的不断扩大,其地基基础及桩基础的土建施工技术也开始受到社会的广泛关注.基于此,对高层建筑工程具体施工过程中的地基基础及桩基础施工技术进行分析,以此提升工程质量,保障工程安全.     

Fatigue damage study of cold metal transition fusion-brazed aluminium/steel dissimilar joints

ABSTRACT

An aluminium/steel CMT-welded joint is mainly composed of fusion zone (FZ), interfacial intermetallic compound (IMC) zone, and heat-affected zone (HAZ). IMC and FZ are the weakest link in the welded joint. The fatigue fracture indicates that the lattice distortion caused by the lattice mismatch of Fe₂Al₅ and Fe is more likely to engender dislocation slipping and cracks easily nucleate during the fatigue testing. The hysteresis loop is shifted to the right, which indicating that the specimen experiences a ratcheting effect. In the high-stress condition, the cyclic hardening induced by the ratcheting strain is much stronger than that in the lower stress condition, which improves the fatigue life of the materials.