Filled epoxy polymer couplings with “shape memory” effect

The effect of filling an epoxy polymer matrix with disperse and fibrous fillers on the change in the elastic deformation characteristics of polymers, particularly upon achieving the “shape memory” effect for union adhesive joints of pipelines, is considered.     

Effect of alkanolamines on properties of epoxy–anhydride compounds

Hot-cured epoxy compound based on ED-20 resin and isomethyltetrahydrophthalic anhydride was modified with alkanolamines of different structures. The influence exerted by the structure of alkanolamines on the structure and operation characteristics of modified epoxy–anhydride compounds was examined. Introduction of alkanolamines decreases the gel and cure times and enhances the operation properties of cured epoxy–anhydride compounds. The best products were obtained with alkanolamines derived from ethylenediamine. Their introduction into epoxy–anhydride compounds enhances by a factor of 1.5–2 the elasticity, tensile strength at uniform extension, and impact resilience of the cured formulations.     

Curing and thermomechanical properties of off-stoichiometric anhydride–epoxy thermosets

In the present work, we report the preparation and characterization of a new family of thermosets based on off-stoichiometric anhydride–epoxy formulations in the presence of an anionic initiator. Diglycidyl ether of bisphenol A (DGEBA) and hexahydro-4-methylphthalic anhydride (HHMPA) have been used as epoxy and anhydride comonomers, respectively, and 1-methylimidazole (1MI) has been used as anionic initiator. The isothermal curing kinetics and the thermal properties of the stoichiometric and the off-stoichiometric systems have been compared. The kinetics of the isothermal curing has been analyzed by differential scanning calorimetry (DSC) using an isoconversional method and the ?esták–Berggren equation to determine the activation energy, the frequency factor and the reaction orders. The materials obtained were characterized by DSC and dynamic mechanical analysis. Gelation during epoxy–anhydride condensation was determined by thermomechanical analysis. At the same curing temperature, the reaction is faster in the system with excess of epoxy groups. However, the glass transition temperatures of the partially cured stoichiometric system are greater. The gelation time of the off-stoichiometric system is shorter than that of the stoichiometric one. The results indicate that the dual-curing character of off-stoichiometric DGEBA/HHMPA thermosets with 1MI as anionic initiator makes them suitable for multistage curing processes with easy control of degree of cure and material properties in the intermediate stage and enhanced final material properties.

     

Studies on the cure parameters of cyanate ester–epoxy blend system through rheological property measurements

Thermosetting blend system of co-cured cyanate ester with epoxy resin is receiving importance for high technological applications because of its wide range of thermo-mechanical, rheological, and electrical properties. However, processing of these system warrant proper knowledge of the rheological behavior of the blend during the curing process. This article discusses the rheological behavior of the blend systems with respect to the pot life, gel time, gelation temperature and also evaluated fitting parameters for the prediction of gelation time and viscosity during the entire curing process from the isothermal rheological measurements.     

Catalytic curing of epoxy–anhydride binders under the action of azo compounds

Russian Journal of Applied Chemistry - A series of azo compounds were studied by differential scanning calorimetry as catalysts of the reaction of UP-643 epoxy–novolac resin with various...     

Structural characterization of protein–polymer conjugates for biomedical applications with small-angle scattering

Protein–polymer conjugates, typically consisting of one or more polymers covalently attached to a protein, are an increasingly common component in biotechnology. Polymers can increase circulation time, alter immune responses, and influence the self-assembly of proteins to which they are attached. To understand and take full advantage of the benefits that protein–polymer conjugates provide, there is a strong need for structural characterization of both the conjugates and their self-assembled structures. Although X-ray crystallography is suitable for determining protein structure, protein–polymer conjugates do not generally crystallize, requiring the use of alternative techniques. Small-angle scattering, with neutrons in particular, is one such technique. In this article, we review recent work in the area of protein–polymer conjugates and highlight the important role that structure plays. We then highlight shape-dependent and shape-independent approaches for structural characterization of protein–polymer conjugates and future directions in small-angle scattering interpretation. We conclude by introducing a new model that we suggest may be useful in the future to acquire more detailed structural properties.     

The shape of protein–polymer conjugates in dilute solution

Protein–polymer conjugation can significantly affect many different aspects of protein behavior, ranging from their solution properties to their ability to form solution and bulk nanostructured materials. An underlying fundamental question is how the molecular design affects the shape of the conjugate and, consequently, its properties. This work measures the molecular configuration of model protein–polymer conjugates in dilute solution using small-angle neutron scattering (SANS) and uses quantitative model fitting to understand the shape of the molecules. Form factor measurements of four model bioconjugates of the red fluorescent protein mCherry and the polymers poly(N-isopropylacrylamide), poly(hydroxypropyl acrylate), poly(oligoethylene glycol acrylate), and poly(ethylene glycol) show that these protein–polymer conjugates are well described by a recently developed scattering function for colloid–polymer conjugates that explicitly incorporates excluded volume interactions in the polymer configuration. In the regime where the protein does not exhibit strong interactions with the polymer, modeling the protein–polymer interactions using a purely repulsive Weeks–Chandler–Andersen potential also leads to a coarse-grained depiction of the conjugate that agrees well with its scattering behavior. The coarse-grained model can additionally be used for systems with varying protein–polymer interactions, ranging from purely repulsive to strongly attractive, which may be useful for conjugates with strong electrostatic or hydrophobic attractive interactions. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016, 54, 292–302     

Carbon nanotube–polyurethane shape memory nanocomposites with low trigger temperature

Ester-based polyurethane (PU) with low glass transition temperature was used to develop shape memory nanocomposites with low trigger temperature. Pristine carbon nanotubes (CNTs) and oxidized CNTs (ox-CNTs) were introduced by melt mixing to improve the mechanical and shape memory properties of the PU matrix. The dispersion of CNTs on the mechanical properties and shape memory behaviors of the nanocomposites were also investigated. The results show that better dispersion of ox-CNTs contributes to more stiffness effect below glass transition temperature (T_g) while lower storage modulus (E′) above T_g. The nanocomposites exhibit high shape fixity and recovery ratio above 98%. The ox-CNT/PU nanocomposite shows higher shape recovery ratio for the first cycle, faster recovery due to better dispersion of CNTs and have potential applications for controlling tags or proof marks in the area of frozen food. The trigger temperature can be tailored by controlling the T_g of the PU matrix or the content of the nanofillers.     

Thermodynamic characterization of aluminium corner of Al–Cu system with various Nd additions

Journal of Thermal Analysis and Calorimetry - The effect of various neodymium additions on the characteristic solidification temperatures and on the microstructure development of the...     

Effects of sensitizer length on radiation crosslinked shape–memory polymers

Shape–memory polymers (SMPs) are smart materials that can be designed to retain a metastable state and upon activation, recover a preprogrammed shape. In this study, poly(methyl acrylate) (PMA) is blended with poly(ethylene glycol) diacrylate (PEGDA) of various molecular weights in various concentrations and subsequently exposed to ionizing radiation. PEGDA sensitizes the radiation crosslinking of PMA, lowering the minimum absorbed dose for gelation and increasing the rubbery modulus, after crosslinking. Minimum dose for gelation, as determined by the Charlesby–Pinner equation, decreases from 25.57 kGy for unblended PMA to 2.06 kGy for PMA blended with 10.00 mole% PEGDA. Moreover, increase in the blend concentration of PEGDA increases the crosslinking density of the resulting networks. Sensitizer length, namely M_n of PEGDA, also affects crosslinking and final mechanical properties. Increase in the length of the PEGDA molecule at a constant molar ratio increases the efficacy of the molecule as a radiation sensitizer as determined by the increase in gel fraction and rubbery modulus across doses. However, at a constant weight ratio of PEGDA to PMA, shorter PEGDA chains sensitize more crosslinking because they have more reactive ends per weight fraction. Sensitized samples of PMA with PEGDA were tested for shape–memory properties and showed shape fixity of greater than 99%. Samples had a glass transition temperature near 28 °C and recovered between 97% and 99% of the induced strain when strained to 50%.     

Diffusion pack cementation of hafnium powder with halide activator on Ni–Ti shape memory alloy

The effect of a Hf chloride activator on the pack cementation of Hf powder on a Ni–Ti shape memory alloy wire was investigated. For this purpose, a Ni–Ti wire with a diameter of 0.5 mm was pack cemented in a powder mixture consisting of Hf and HfCl₄ powders at 1000 °C for 24 h. It was observed that Hf noticeably diffused into the Ni–Ti matrix with the aid of the HfCl₄ activator. The diffusion distance significantly increased as the amount of HfCl₄ activator increased. By the addition of 10 mass% HfCl₄, the martensite-to-austenite phase transformation start and finish temperatures increased from 12 to 142 °C and from 28 to 200 °C, respectively. The diffusion kinetics model was established based on Fick’s first law. It is suggested that 48 h of halide-activated pack cementation with 10 wt% HfCl₄ is necessary to increase the overall Hf content above 15 at.% throughout the Ni–Ti wire.     

Preparation and characterization of epoxy–silica networks chemically bonded through aminophenyl-trimethoxysilane

Epoxy–silica hybrids with interfacial bonding using aminophenyl-trimethoxysilane (APTMOS) have been prepared by the sol–gel process. In a sequential polymerization procedure the amine groups present on the APTMOS were used to partially cure diglycidyl ether of bisphenol-A (DGEBA) whereas the methoxy groups created silica-network simultaneously, through the sol–gel process. Complete curing and cross-linking were carried out later using curing agent jeffamine D-400 at higher temperature. The nature of silica network structure chemically bonded with the epoxy chains was studied by Fourier transformed infrared spectroscopy and the morphology of the hybrid through scattering electron and atomic force microscopies. The visco-elastic properties of the resulting hybrids were measured through dynamical thermal mechanical analysis. The effect of inter-phase bonding of the resulting hybrids and their thermal mechanical properties are compared with the similar DGEBA epoxy matrix where un-bonded silica network was produced from tetraethoxysilane. The properties of the hybrids using APTMOS show considerable improvement in thermal mechanical properties and the coefficient of thermal expansion is reduced in contrast to the un-compatiblized system.     

Study of martensite transformation and microstructural evolution of Cu–Al–Ni–Fe shape memory alloys

In this study, variations in the transformation temperature, crystal structure, and microstructure of the arc melted alloy having nominal composition of Cu–13%Al–4%Ni–4%Fe (in mass%) were investigated for two different treatment conditions, homogenized and heat treated at 950 °C for 1 h. For both conditions, transformation temperature of the alloy was examined by DSC and it was determined as ~200 °C, similar to the value for Cu–Al–Ni alloys given in the literature. The crystal structure of the martensite Cu–13%Al–4%Ni–4%Fe (in mass%) alloy was identified as 18R using XRD. By heat treatment performed at 950 °C, diffraction peaks become more distinct. The microstructure of the alloy was studied with the help of optical microscope as a result of which parallel martensite plates and precipitates were detected. Microhardness value of the alloy was found as 361 and 375 Hv for homogenized and heat-treated conditions, respectively.     

Comparative characteristics of cathodes with different catalytic systems in hydrogen–oxygen and hydrogen–air fuel cells with proton-conducting polymer electrolyte

The characteristics of low-temperature hydrogen–oxygen (air) fuel cell (FC) with cathodes based on the 50 wt % PtCoCr/C and 40 wt % Pt/CNT catalysts synthesized on XC72 carbon black and carbon nanotubes (CNT) are compared with the characteristics of commercial monoplatinum systems 9100 60 wt % Pt/C and 13100 70% Pt/C HiSPEC. It is shown that the synthesized catalysts exhibit a high mass activity, which is not lower than that of commercial Pt/C catalysts, a high selectivity with respect to the oxygen reduction to water, and a significantly higher stability. The characteristics of PtCoCr/C and Pt/CNT were confirmed by testing in the hydrogen—oxygen FCs. However, when air was used at the cathode, especially in the absence of excessive pressure, a voltage of FC with the cathode based on PtCoCr/XC72 is lower as compared with the commercial systems. Probably, this is associated with the transport limitations in the structure of trimetallic catalyst synthesized on XC72 carbon black due to the absence of mesopores. This drawback was eliminated to a large extent by raising the volume of mesopores as a result of application of mixed support (XC72 + CNT) and the use of only CNT for the synthesis of the monoplatinum catalyst. However, this did not eliminate another drawback, namely, a low platinum utilization coefficient in the cathode active layer as compared with that measured under the model conditions in the 0.5 M Н₂SO₄ solution. Therefore, further research is required to improve the structure of the catalytic systems, which are synthesized both on carbon black and nanotubes, while maintaining their high stability and selectivity.     

Welding dynamics in an atomistic model of an amorphous polymer blend with polymer–polymer interface

We consider an atomistic model of thermal welding at the polymer-polymer interface of a polyetherimide/polycarbonate blend, motivated by applications to 3D manufacturing in space. We follow diffusion of semiflexible chains at the interface and analyze strengthening of the samples as a function of the welding time t_w by simulating the strain–stress and shear viscosity curves. The time scales for initial wetting, and for fast and slow diffusion, are revealed. It is shown that each component of the polymer blend has its own characteristic time of slow diffusion at the interface. Analysis of strain–stress demonstrates saturation of the Young's modulus at t_w = 240 ns, while the tensile strength continues to increase. The shear viscosity is found to have a very weak dependence on the welding time for t_w > 60 ns. It is shown that both strain–stress and shear viscosity curves agree with experimental data.     

DSC analysis of Cu–Zn–Sn shape memory alloy fabricated via electrodeposition route

Cu–Zn–Sn shape memory alloy strips with composition range of 13.70–46.30 mass% Sn were fabricated by electrodepositing Sn on a shim brass surface and then subsequently annealed at a constant temperature of 400 °C for 120 min under flowing nitrogen. Subjecting the Sn-plated strips to differential scanning calorimetry (DSC) analysis revealed that the austenitic start (A _s) temperature was essentially constant at 225 °C while the martensite start (M _s) temperature was consistently within the 221.5–222 °C interval. Austenite to martensite phase transformation showed two distinct peaks on the DSC thermogram which can be attributed to the non-homogeneity of the bulk Cu–Zn–Sn ternary alloy. The latent heats of cooling and heating were found to increase with the mass% Sn plated on the shim brass. Effect of annealing temperature was also investigated wherein strips with an essentially constant composition of 26 mass% Sn were annealed at a temperature range of 350–420 °C for 120 min under flowing nitrogen. Varying the annealing temperature has no significant effect on the transformation temperatures of the ternary alloy.     

Effects of vanadium and cadmium on transformation temperatures of Cu–Al–Mn shape memory alloy

Cu-based quaternary shape memory alloys were extensively investigated alloy in last decade. In this study, Cu–Al–Mn, Cu–Al–Mn–V and Cu–Al–Mn–Cd shape memory alloys were produced by arc melting. We have investigated the effects of the alloying elements on the characteristic transformation temperatures, variations in structure and microstructure. The characterization of the transformation temperatures was studied by the differential scanning calorimetry. It was observed that the addition of the vanadium and cadmium decreases the characteristic transformation temperatures. The structural changes of the samples were studied by X-ray diffraction measurements and optical microscope observations. The crystal structure of the martensite Cu–Al–Mn, Cu–Al–Mn–V and Cu–Al–Mn–Cd shape memory alloys were identified as M18 at room temperature. The crystallite sizes of the alloys were determined. The microstructure of the alloy was studied with the help of optical microscope and V-type martensites with different orientations were detected. Microhardness value of the alloys were found between 194 and 211 Hv.     

Synthesis and characterization of novel multifunctional epoxy resin

A novel multifunctional epoxy resin was synthesized by polyphenol and epichlorohydrin.The structure and molecular weight ofthe multifunctional epoxy were characterized by FTIR and ESI-MS.DSC and DMTA were used to investigate the thermal propertyof multifunctional epoxy cured by DDS.The thermal resistance of the synthesized multifunctional epoxy was much better than astandard diglycidyl ether of bisphenol-A epoxy.     

Physico-chemical and pharmaceutical characterization of sulindac–proglumide binary system

Journal of Thermal Analysis and Calorimetry - Sulindac is a nonsteroidal anti-inflammatory drug with poor water solubility. This study presents a way to increase its dissolution rate while reducing...