Search Results
Abstract
The addition of suitable cross-linking agents with norbornene-based monomers has significant effects on the thermal properties of the resulting polymers formed by olefin metathesis. Ethylidene norbornene (ENB) and endo-dicyclopentadiene (endo-DCPD) were mixed separately with various loadings of three different cross-linking agents and then polymerized with the addition of Grubbs’ catalyst. The polymerization kinetics and resulting glass transition temperature (T g) of the systems were evaluated by differential scanning calorimetry (DSC). The addition of the first cross-linking agent, norbornadiene (CL-1), to both endo-DCPD and ENB resulted in decreasing glass transition temperatures with increasing concentrations. In contrast, the addition of the other two cross-linking agents (CL-2 and CL-3), which were both custom synthesized bifunctional norbornyl systems, to both endo-DCPD and ENB resulted in a monotonic increases in T g with cross-linker concentration. By tailoring the loading of these custom cross-linking agents, the properties of these polymer systems can be controlled for various applications, including self-healing composites.
, having the isocyanate-to-hydroxy (NCO/OH) ratio greater than 1. In this paper, we studied to use cross-linking agents, including trimethylolpropane (TMP) and 1-aminopropyltriethoxy silane (APTS), in the synthesis of lignin-based polyurethane to enhance
−1 ) was added as a cross-linker agent; TEMED (3.21 μmol mL −1 ) was added as a reaction catalyst; and PS (3.38 μmol mL −1 ) was added as a reaction initiator. After homogenization, the solution was purged by N 2 bubbling for 25 min, and the material
Abstract
A method, based on the measurement of the 
-photopeak at 332 keV arising from a124Sn(n, )125mSn reaction, has been developed for the rapid measurement of Sn at concentrations of 
20 
g g–1, present as the cross-linking agent, in explosive charges. The method is comparative, and has a limit of detection of 0.6 g g–1 and a precision of 5% RSD. The method requires no sample preparation and is economical in effort.
Abstract
The kinetics of free-radical cross-linking polymerization of methyl methacrylate (MM) in the presence of poly[2-(10-undecenoyloxy)ethyl methacrylate] (PUDEM) as a macromolecular cross-linker has been isothermally examined within the temperature range from 85-100°C using the differential scanning calorimetry (DSC). The activation energy found for this reaction, E a=89.3 kJ mol-1, exceeds slightly the literature values of activation energy obtained for the mass polymerization of MM without any cross-linking agent. The activation energy has been also determined by the isoconversion method. It has been found that E a decreases with the increase in the conversion, which may indicate a change in the reaction mechanism.
Abstract
Hydrogels, in general, can be used as a compliant surface in prosthesis of human synovial joints due to their biocompatible characteristics. In this work, different hydrogels were prepared from two aqueous solutions of PVAL (15 and 20 mass/mass%) by chemical reactions using citric acid as a cross-linking agent and by electron beam (EB) irradiation with doses from 25 to 100 kGy. The hydrogels were evaluated by their mechanical properties through indentation creep test, thermal properties by differential scanning calorimetry (DSC), and also equilibrium water content (EWC).
Abstract
Liquid organic peroxides (LOPs) have been widely used as initiators of polymerization, hardening, or cross-linking agents. We evaluated a beneficial kinetic model to acquire accurate thermokinetic parameters to help preventing runaway reactions, fires or explosions in the process environment. Differential scanning calorimetry was used to assess the kinetic parameters, such as kinetic model, reaction order, heat of reaction (ΔH d), activation energy (E a), frequency factor (lnk 0), etc. The non-isothermal and isothermal kinetic models were compared to determine the validity of the kinetic model, and then applied to the thermal hazard assessment of commercial package contaminated with LOPs. Simulations of a 0.5-L Dewar vessel and 25-kg commercial package were performed. We focused on the thermal stability of different liquid system properties for LOPs. From the results, the optimal conditions were determined for avoiding violent heat effects that can cause a runaway reaction in storage, transportation, and manufacturing.
Pectinex Ultra SP-L, a commercial pectinase with fructosyl-transferase (FTF) activity, is able to catalyze the production of short chain fructooligosaccharides (FOS). It was immobilized onto an anion exchange resin by a combined method. The optimal biocatalyst/matrix ratio (16.7 g enzyme solution/g dry support) as well as the most favourable conditions of the immobilization: the concentration of cross-linking agent (0.125%) and the time of chemical fixation (15 min) have been determined. The temperature and pH optima of the solid-phase biocatalyst have been found 53 °C and 5.6, respectively. It showed almost no decrease in its activity during 12 reaction cycles. Based on these results, lab-scale synthesis experiments have been carried out for fructooligosaccharide production under the determined optimal operational conditions.
Abstract
The thermal stability of sheepskin collagen cross-linked with chrome sulfate and mimosa (MI)–oxazolidine (OZ), respectively, had been researched in this experiment. All samples’ shrinkage temperatures (T s) are determined by a special T s-testing-apparatus and denaturation temperatures (T d) are determined by the differential scanning calorimetry. The relations between the modified collagens containing moisture and their hydrothermal stability, T s or T d, were studied. The results show that the cross linking agents can enhance the thermal stability of modified collagen whose T s are 109.8 and 110.6 °C for collagen treated with chrome and MI–OZ, respectively. When the samples contain 25–71.9% moisture for chrome leather and 20–71.1% for leather treated with MI–OZ, the hydrothermal stability will decrease with the increase of moisture. It was found that the difference between T s and T d of collagen modified by chrome is more obvious than that of collagen modified with MI–OZ. And when the moisture of chrome leather exceeds 55%, T d cannot express thermal stability of modified collagen as a substitute for T s, and the moisture is 40% for leather tanned with MI–OZ.
Abstract
Solid bisphenol-A epoxy resin (DGEBA) of medium molecular mass was cured using o-tolylbiguanide (TBG) as cross-linking agent. In order to improve the kinetics of the reactive system, two Lewis acid catalysts (erbium(III) and ytterbium(III) trifluoromethanesulfonates) were added in proportions of 1 phr. The kinetic study was performed by dynamic scanning calorimetry (DSC) and the complete kinetic triplet (E, A and g(α)) determined. The kinetic analysis was performed with an integral isoconversional procedure (model-free), and the kinetic model was determined by the Coats-Redfern method and through the compensation effect (IKR). All the systems followed the m=1.5/n=0.5 isothermal curing model simulated from non-isothermal experiments. The addition of a little proportion of ytterbium or erbium triflates accelerated the curing process. In order to extract further information about the role of the lanthanide triflates added to epoxy/TBG systems, the kinetic results were compared with our previous kinetic studies made on DGEBA/lanthanide triflates initiated systems.
