Development of Polypyrrole/Epoxy Composites as Isotropically Conductive Adhesives

As a possible replacement for lead bearing solders, metal filled isotropically conductive adhesives (ICAs) have shown a lot of potential recently. But still they have to come a long way and overcome their limitations like low impact strength and moisture instability. The current paper attempts to address the limitations of these ICAs by using intrinsically conducting polymer as a filler in place of metals. Conducting polymer (CP) polypyrrole (PPy) was incorporated as a filler in an epoxy/anhydride (EP) system and its application as an isotropic conductive adhesive was studied. PPy was synthesized by chemical polymerization using dodecyl-benzene sulphonic acid (DBSA) as dopant. The composites with varying PPy concentrations were studied for curing behavior and thermal degradation properties using DSC and TGA, respectively. The composites show good impact properties and conductivity at very low filler concentrations. SEM observations established that PPy particles were dispersed in the epoxy matrix uniformly. The overall characteristics of these conductive adhesives establish that they can be used as conductive adhesives in the electronics industry.     

On the Use of Silver Plated Nano Aluminum Nitride and Silver Plated Chopped Carbon Fiber to Prepare Electrically Conductive Adhesives with High Thermal Conductivity

To satisfy the high electrical and thermal conductivity required for the development of microelectronic products, silver plated aluminum nitride (Ag/AlN) and silver plated chopped carbon fiber (Ag/CF) were added into an acrylate resin to prepare electrically conductive adhesives (ECAs) with high thermal conductivity. The Ag/AlN was prepared by subjecting AlN to an electroless silver plating using a Pb-free activation method. The Ag/AlN has good electrical and thermal conductivity compared to the AlN without treatment. When the weight fraction of Ag/AlN is 45 ωt%, the electrical conductivity of ECAs based on acrylate resin filled with Ag/AlN is 1.5 S/cm, and the thermal conductivity reaches 2.1 W/(m · K). With the addition of 3 ωt% Ag/CF as supplement filler, the electrical conductivity has a sharp increase to 17.8 S/cm because of the formation of conductive networks in the ECAs. However, the shear strength has an apparent loss, falling from 4.2 to 1.1 MPa.     

Effect of Nanoclay on the Mechanical,Thermal, and Water Absorption Properties of an UP-toughened Epoxy Network

Unsaturated polyester (UP)-toughened epoxy nanocomposites were prepared, and their effective mechanical and thermal properties were studied. Two types of organo-modified montmorillonite (OMMT) clays were used to prepare the nanocomposites. X-ray diffraction (XRD) and transmission electron microscopy (TEM) analysis showed the formation of exfoliated silicate layers in the UP-toughened epoxy matrix. Mechanical tests revealed that nanocomposites (containing 1 wt% OMMT clay) showed an increase in tensile strength to 13.8%, flexural strength to 10%, and impact strength to 4% compared with an UP-toughened epoxy blend. The effect of different heating rates on the curing behavior of UP-toughened epoxy nanocomposites was investigated using non-isothermal differential scanning calorimetry. The data were interpreted using the Kissinger and Flynn–Wall–Ozawa models to find the curing reaction parameter. The water uptake behavior for nanocomposites increased with the addition of OMMTs. Scanning electron microscopy micrographs indicated morphological changes in the impact fractured samples of UP-toughened epoxy nanocomposites.     

Characterization and material model definition of toughened adhesives for finite element analysis

Some toughened adhesives used for structural joints are characterised by non-linear behaviour prior to failure that may significantly influence the entire joint response. The determination of appropriate and accurate material models for use in analysis and design phases covering both nonlinearities and final material rupture constitutes one of the main challenges for the utilisation of adhesives and for offering designers the same confidence level as that offered by other joining techniques.The present research proposes the utilisation of both elasto-plastic and continuum damage models as a combination that can fully reproduce the mechanical response of toughened adhesives in finite element (FE) analysis. In this context, the Drucker-Prager exponential model has demonstrated to provide accurate fits with the nonlinearities of these materials, allowing the real plastic behaviour of the adhesives to be adjusted in the computational models with a high degree of correlation. On the other hand, a continuum damage model has been proposed to simulate the final material failure process introducing a displacement-based damage parameter into the constitutive equation of the damaged material. The definition of the parameters associated with the mentioned models has been carried out through the execution of an experimental programme combining traction and torsion tests, described in the present paper as part of the study developed. The research is finally completed with an experimental and FE analysis of a specific bonded joint that allows the operation of the material model to be checked in a real application.     

氰酸酯/环氧树脂泡沫塑料的制备与性能表征

采用两步法,以双酚A型氰酸酯和双酚A型环氧树脂为主要原料制备了一种新型的氰酸酯/环氧树脂泡沫塑料。利用傅里叶变换红外光谱、扫描电子显微镜、动态热机械分析仪、差示扫描量热分析和热失重分析等分别对氰酸酯/环氧树脂泡沫塑料的化学结构、泡沫泡孔结构和热力学性能进行了表征。结果表明,氰酸酯/环氧树脂泡沫已固化完全,观察不到2 272 cm–1/2 236 cm–1处的氰酸酯基团吸收峰和913 cm–1处的环氧基团吸收峰。氰酸酯/环氧树脂泡沫塑料为闭孔结构,泡孔均匀且基本上呈规则的球形;力学性能优异,比压缩强度为10.22 MPa·cm3/g;玻璃化转变温度为223℃,失重5%的分解温度为309℃,具有优良的耐热性。     

新型环氧树脂固化剂的合成与表征

在无水碳酸钾和强极性非质子有机溶剂中,采用2,2-双(4-羟基苯基)丙烷(BHPP)和2,4-二硝基氯苯(24DNCB)为主原料,通过缩合反应得到2,2-双[4-(2,4-二硝基苯氧基)苯基]丙烷(BDNPPP);在钯/炭、水合肼和有机溶剂的作用下,BDNPPP被进一步还原,得到了新型环氧固化剂2,2-双[4-(2,4-二氨基苯氧基)苯基]丙烷(BDAPPP),并对其进行了系统的表征。     

Design,Realization, and Characterization of Advanced Adhesives for Joining Ultra‐Stable C/C Based Components

The aim of this work is to develop high‐performance adhesives to join carbon fiber reinforced composites (C/C) for use in aerospace applications; in order to guarantee sound mechanical strength, a low coefficient of thermal expansion, and ease of application on large components. Several different adhesive formulations, based on phenolic or cyanate‐ester resins (charged with the maximum experimentally feasible amount of carbon‐based fillers), are developed and tested. The measurements of the lap shear strength at room temperature of the C/C joined by means of one phenolic and one cyanate ester‐based resin demonstrates that these formulations are the most suitable for the given application. A complete characterization, by means of viscosimetry, dilatometry, and thermal gravimetric analysis, coupled with gas analysis by means of mass spectroscopy, confirms that the phenolic‐based formulation is the most promising joining material. A nano‐indenter is used to obtain its Young modulus and hardness, both inside the joint and as a bulk cured adhesive.     

Influence of Composition,Humidity, and Temperature on Chemical Aging in Epoxies: A Local Study of the Interphase with Air

The developing chemical depth profile in an epoxy adhesive bulk (with varying amine content) is monitored during aging by FTIR microspectroscopy on sample cuts prepared with low angle microtomy. Three aging regimes are applied in order to separate the role of temperature and water: dried or moist air (90% rel. humidity) at 60°C and dried air at 120°C for up to 300 days. Quantitative evaluation of the IR spectra shows: thermo-oxidative aging (= dried air) is controlled by the diffusion of atmospheric oxygen. It affects a gradient region of more than 200 μm in depth. At given aging time, the depth profiles depend on temperature, humidity, and on the epoxy-amine ratio. Humidity mainly affects the IR band intensities. The plasticizing effect of water promotes the loss of small network fragments. At 120°C, autoxidation of α-CH₂ at ether and amine groups and the oxidative attack on tertiary amines dominate aging. At 60°C in dried air, these processes proceed only very slowly. In the case of amine excess, aging is extended by the additional oxidation of primary and secondary amines to carbonyls. Carbonyls undergo consecutive reactions, especially in the presence of water. Hence, increasing temperature does not simply accelerate the aging mechanisms but it reduces their selectivity and changes their hierarchy. Thus, the long-term aging behavior at moderate temperatures cannot be predicted safely from accelerated aging tests.     

Epoxy/montmorillonite nanocomposites: influence of organophilic treatment on reactivity, morphology and fracture properties

Two different alkylammonium modified montmorillonites have been dispersed in epoxy network precursors in order to study the influence of the organophilic treatment on the reactivity and cure behavior of the networks, on the morphology of the final composites and on their elastic and fracture properties. An increase in the interplatelet distance during curing of the network (in addition to the initial swelling by the network precursors) is possible when the competition between cure kinetics, diffusion kinetics and interactions between network precursors and organophilic montmorillonite allows it. Network structure is not modified and a catalytic effect of the organoclays has been demonstrated. Correlation between morphologies and mechanical properties reveals that exfoliated nanocomposites lead to interesting stiffness improvements. However, intercalated nanostructures can lead to very interesting stiffness/toughness balance for glassy epoxy networks without lowering their glass transition temperature. This suggests that stiffness and toughness improvements might not be ruled by the same kind of morphologies.     

Novel Biodegradable pH/Thermosensitive Hydrogels: Part 1. Preparation and Characterization

A series of biodegradable and pH/thermosensitive hydrogels based on monomethoxyl poly(ethylene glycol) (MPEG), poly(?-caprolactone) (PCL), methylacrylic acid (MAA), and N-Isopropylacrylamide (NIPAAm) were prepared by UV-initiated free radical polymerization method. Swelling behavior and hydrolytic degradable behavior in aqueous medium with different pH values and pH/thermosensitivity of the hydrogels were studied in detail. The prepared biodegradable pH/thermo-sensitive hydrogels based on PCL, MPEG, MAA, and NIPAAm may have great potential application in smart drug delivery system.     

Novel composite sandwich structure from green materials: Mechanical,physical, and biological evaluation

Flax and Jute fabrics were used as reinforcements with polyester resin to form composite skins while poplar particleboard was used as a core for making composite sandwich structures by applying vacuum assisted resin transfer molding (VARTM) technique. Mechanical, physical, and biological properties of these novel composite sandwich structures were evaluated. The results showed that the proposed engineered panels have superior mechanical properties that are suitable for different structural applications compared with conventional particleboards. When compared with the control panels, significant enhancement on Modulus of elasticity (MOE) and Modulus of rupture (MOR) were achieved. On the other hand, the results indicated that the proposed panel composites exhibit better dimensional stability compared with poplar particleboard control panels. In addition, the proposed composite sandwich structures proved resistant against the decay fungi after 12 weeks of fungal exposure. Obviously, the developed composite panels could be used in a wide variety of applications. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42253.     

新型2-巯基苯并咪唑银/硬脂酸银(AgMBM/AgSt)的制备、表征及其在PTG材料中的成像性能研究

分别以硬脂酸银(AgSt)为本体、2-巯基苯并咪唑(MBM)为修饰剂,合成了一种新型的2-巯基苯并咪唑银/硬脂酸银(AgMBM/AgSt)复合结构颗粒.利用红外光谱仪(FTIR)、透射电子显微镜(TEM)、X射线衍射仪(XRD)以及热重-差示扫描量热仪(TG-DSC)对复合颗粒的微观结构、形貌、晶型以及热相变行为进行了表征,研究了AgMBM/AgSt作为光敏热成像(PTG)材料银源时的成像性能.结果表明,AgMBM/AgSt由本体AgSt以及其表面负载的AgMBM小颗粒构成.与本体AgSt相比,AgMBM/AgSt在80℃附近出现新的热相变峰,其热分解温度也有所降低.当AgMBM/AgSt为银源时,PTG材料的热显影密度显著增加,而灰雾仍然保持较低水平.     

一种新型环己烯合成环氧环己烷催化剂的制备及表征

针对现有固载型相转移催化剂制备过程中存在的问题,对环己烯合成环氧环己烷工艺进行了改进。在固载型过氧化磷钨杂多酸季铵盐PSC的制备中,对质子酸N的选用和磷酸的加入方式以及原料配比等问题进行了重新优化,并对优化工艺后制备的催化剂结构进行表征和性能实验。结果表明,改进后的催化剂制备工艺,不仅提高了原料钨酸的利用率,简化了操作,降低了成本,而且所制备的催化剂使用多次后仍能保持较高的催化活性及稳定性。     

Functional Characterization and Synthetic Application of Is2-SDR,a Novel Thermostable and Promiscuous Ketoreductase from a Hot Spring Metagenome

In a metagenome mining-based search of novel thermostable hydroxysteroid dehydrogenases (HSDHs), enzymes that are able to selectively oxidize/reduce steroidal compounds, a novel short-chain dehydrogenase/reductase (SDR), named Is2-SDR, was recently discovered. This enzyme, found in an Icelandic hot spring metagenome, shared a high sequence similarity with HSDHs, but, unexpectedly, showed no activity in the oxidation of the tested steroid substrates, e.g., cholic acid. Despite that, Is2-SDR proved to be a very active and versatile ketoreductase, being able to regio- and stereoselectively reduce a diversified panel of carbonylic substrates, including bulky ketones, α- and β-ketoesters, and α-diketones of pharmaceutical relevance. Further investigations showed that Is2-SDR was indeed active in the regio- and stereoselective reduction of oxidized steroid derivatives, and this outcome was rationalized by docking analysis in the active site model. Moreover, Is2-SDR showed remarkable thermostability, with an apparent melting temperature (T_M) around 75 °C, as determined by circular dichroism analysis, and no significant decrease in catalytic activity, even after 5 h at 80 °C. A broad tolerance to both water-miscible and water-immiscible organic solvents was demonstrated as well, thus, confirming the potential of this new biocatalyst for its synthetic application.     

Superoxide Dismutase as a Novel Macromolecular Nitric Oxide Carrier: Preparation and Characterization

Nitric oxide (NO) is an important molecule that exerts multiple functions in biological systems. Because of the short-lived nature of NO, S-nitrosothiols (RSNOs) are believed to act as stable NO carriers. Recently, sulfhydryl (SH) containing macromolecules have been shown to be promising NO carriers. In the present study, we aimed to synthesize and characterize a potential NO carrier based on bovine Cu,Zn-superoxide dismutase (bSOD). To prepare S-nitrosated bSOD, the protein was incubated with S-nitrosoglutathione (GSNO) under varied experimental conditions. The results show that significant S-nitrosation of bSOD occurred only at high temperature (50 °C) for prolonged incubation time (>2 h). S-nitrosation efficiency increased with reaction time and reached a plateau at ~4 h. The maximum amount of NO loaded was determined to be about 0.6 mol SNO/mol protein (~30% loading efficiency). The enzymatic activity of bSOD, however, decreased with reaction time. Our data further indicate that NO functionality can only be measured in the presence of extremely high concentrations of Hg²⁺ or when the protein was denatured by guanidine. Moreover, mildly acidic pH was shown to favor S-nitrosation of bSOD. A model based on unfolding and refolding of bSOD during preparation was proposed to possibly explain our observation.     

Tetragonal Nanocrystalline Barium Titanate Powder: Preparation, Characterization, and Dielectric Properties

Nanocrystalline tetragonal-BaTiO₃ powder was prepared using a hydrothermal method, under moderate conditions, and with a high precursor concentration. Characterization via X-ray diffractometry and differential scanning calorimetry confirmed that the average particle size and tetragonal content of the prepared powder were 70 nm and 80%, respectively. The sintered sample made from the prepared powder had a room-temperature dielectric constant of 6900, which was high for BaTiO₃.     

A Novel Precursor for Preparation of Silver Nanoparticles: Synthesis, Characterization and Crystal Structure of Ag(PPh3)2(2-pyCOO)

A novel silver complex, Ag(PPh₃)₂(2-pyCOO)·0.5H₂O·0.5C₂H₆O, was prepared from Ag(CH₃COO)(PPh₃)₂ and 2-pyridinecarboxylic acid and after characterization by elemental analysis, infrared, ¹H and ³¹P NMR spectroscopes, and X-ray crystallography, was used as a precursor for the preparation of silver nanoparticles. The silver nanoparticles were obtained by thermolysis of the silver complex at 350 °C in the presence of oleic acid as a surfactant. Resulting silver nanoparticles were characterized by X-ray powder diffraction (XRD) and scanning electron microscopy (SEM). The formation of silver nanoparticles with an average size of 60 nm and spherical morphology was confirmed by SEM. Bulk silver particles were obtained instead of silver nanoparticles when thermolysis of the silver complex was carried out in the absence of oleic acid.     

含钛介孔SiO2 催化剂的合成及其催化性能

分别以廉价硅酸钠与正硅酸乙酯为硅源,通过复合模板剂制备了介孔二氧化硅,并利用吸附相反应技术合成了TiO2/SiO2复合催化剂。用X射线衍射(XRD)、红外谱图分析(FT-IR)等手段对其结构进行了表征,通过苯酚的羟基化反应考察了催化剂的催化性能。     

Span 60 as a Microsphere Matrix: Preparation and in Vitro Characterization of Novel Ibuprofen-Span 60 Microspheres

Microspheres are a potential delivery system for controlled and sustained drug release. Polymeric microspheres are commonly prepared by the solvent evaporation technique whereas waxy microspheres by the melt dispersion technique. The goal of this study was to prepare a surfactant (Span 60)—Ibuprofen microspheres using both techniques. Ibuprofen‐Span 60 microspheres were fabricated with different drug to polymer weight ratios of 3:1, 1:1 and 1:3 and characterized by particle size, in vitro dissolution, infrared spectroscopy, x‐ray diffraction and scanning electron microscopy. The actual drug content increased with increasing the concentration of anti‐aggregating agent (polyvinylpyrolidone). The actual drug content and drug encapsulation efficiency was markedly higher in case of microspheres prepared by a solvent evaporation technique compared to that prepared by a melt dispersion one using the same theoretical drug content. The microspheres were spherical with irregular surfaces. The in vitro release showed no burst effect and incomplete drug release. The rate and total drug released from the microspheres prepared by a solvent evaporation technique are higher than those prepared by using the melt dispersion technique. FTIR rolled out the chemical changes of the drug in Span 60 microspheres. The X‐ray diffraction pattern of the microspheres prepared by using a solvent evaporation technique showed a decrease in the drug crystallinity. The drug crystallinity in microspheres prepared by the melt dispersion technique decreased with increasing the theoretical drug content. The drug entrapment mechanism is responsible for the changes in drug physicochemical properties and in vitro release.