Unreacted Epoxy Research Articles

Exploring the Impact of Molecular Structure on Curing Kinetics: A Comparative Study of Diglycidyl Ether of Bisphenol A and F Epoxy Resins.

Epoxy resins are essential for various applications, and their properties depend on the curing reactions during which epoxy and amine compounds form the network structure. We here focus on how the presence or absence of two methyl groups in common epoxy bases, diglycidyl ether of bisphenol A and F (4,4'-DGEBA and 4,4'-DGEBF), affects the curing kinetics. The chemical reactions of both 4,4'-DGEBA and 4,4'-DGEBF, when cured with the same amine, were monitored by Fourier-transform infrared (FT-IR) spectroscopy and differential scanning calorimetry (DSC). Despite no difference in the reactivity of epoxy groups between 4,4'-DGEBA and 4,4'-DGEBF, the initial curing reaction was slower for the latter. This delay for the 4,4'-DGEBF system was attributed to intermolecular stacking, which hindered the approach of unreacted epoxy groups to amino groups and vice versa. This conclusion was drawn from the results obtained through ultraviolet (UV) spectroscopy, wide-angle X-ray scattering (WAXS), density functional theory (DFT) calculation, and all-atom molecular dynamics (MD) simulation.

Investigation of the kinetics of heat treatment of epoxy polymers

The study examines the effect of the concentration of modifiers (BDI) on the annihilation characteristics of cured epoxy polymers using the positron annihilation method. The results show that both the concentration and size of microcavity defects decrease, which can be explained by the formation of densely sewn areas due to the production of additional bridges. The supramolecular structure of the formed epoxy polymer is discussed, with the identification of several distinct areas, including polymer globules formed by stacking chains of simple polyester macromolecules around polymerization centers, and the interglobular space consisting of the ends of macro chains and low molecular weight products. The end groups of polymerization-cured epoxy polymers, such as double bonds of the vinylidene type, hydroxyl and unreacted epoxy groups, create conditions for the splitting of BDI in the interglobular space. The study also demonstrates that at optimal concentrations of modifiers, there is a decrease in the radius and concentration of micropore defects, as well as a general decrease in the proportion of free volume. The curing processes of epoxy polymers and their heat treatment in the presence of modifiers are investigated, with BDI having a significant effect on the formation of the epoxy polymer structure.

Molecular Simulations and Network Analyses of Surface/Interface Effects in Epoxy Resins: How Bonding Adapts to Boundary Conditions.

In this study, we unravel the atomic structure of a covalent resin near boundaries such as surfaces and composite constituents. For this, a molecular simulation analysis of epoxy resin hardening under various boundary conditions was performed. On the atomic level of detail, molecular dynamics simulations were employed to study crosslinking reactions and self-organization of the polymer network within nm scale slab models. The resulting structures were then coarsened into a graph theoretical description for connectivity analysis of the nodes and combined with characterization of the node-to-node vector orientation. On this basis, we show that the local bonding of epoxy resins near interfaces tends to avoid under-coordinated linker sites. For both epoxy–vacuum surface models and epoxy–silica/epoxy cellulose interfaces, we find almost fully cured polymer networks. These feature a local increase in network linking lateral to the surface/interface, rather than the dangling of unreacted epoxy groups. Consequently, interface tension is low (as compared to the work of separating bulk epoxy), and the reactivity of the resin surface appears negligible.

Study on Irradiation Effect of Insulating Materials for Fusion Superconducting Magnet: Effect of Low-temperature Irradiation

The purpose of this study is to investigate the change in dielectric performance in the direction of parallel to layers due to the difference in γ-ray irradiation temperature, irradiation atmosphere, and absorbed dose. γ-ray was irradiated using a 60Co source at room temperature, in liquid nitrogen, and in liquid nitrogen temperature gas atmosphere in the absorbed doses of 0, 5, and 10 MGy, respectively, and the dielectric breakdown tests were conducted at room temperature using a high-voltage breakdown tester. To investigate the mechanism of the change in dielectric strength, the density and electron spin resonance (ESR) measurements of the specimens were carried out. After irradiation at room temperature, the dielectric strength increased slightly with the increase in the absorbed dose. The reason for this may be that the molecular density increased due to the promotion of cross-linking reaction by recombination of molecules and reaction of unreacted epoxy groups by γ-ray irradiation. After irradiation in liquid nitrogen, the dielectric strength decreased significantly at 10 MGy, while after irradiation in liquid nitrogen temperature gas atmosphere, the dielectric strength slightly decreased with the increase in absorbed dose. These results suggest that, at low temperature, the freezing of molecular motion limits the movement of radicals generated by irradiation, and that the decomposition reaction is dominant against the crosslinking reaction.

Self-Healing of Epoxy-Loaded Halloysite Nanotubes/Polysulfone Nanocomposite Membrane

Self-healing composites are smart materials that can be fabricated through the dispersion of tubular nanofillers loaded with appropriate healing agents in a polymeric matrix. In this study, polysulfone (PSf) containing epoxy-loaded halloysite nanotubes (e-HNTs) were successfully fabricated via non-induced phase separation (NIPS) method at varying concentrations. Fourier Transform Spectroscopy (FTIR) analysis showed that epoxy (healing agent) and amine (hardener) were successfully loaded into the lumen of the HNT through the observed functional groups of the epoxy system along the HNT spectrum. The tensile strength of the loaded membranes compared to their unloaded counterpart slightly decreased due to the possible embrittlement of the unreacted epoxy. However, the membranes with epoxy-loaded HNTs garnered lower wettability on average due to the hydrophobic character of the epoxy system, which is a preferable trait for smart coatings. The self-healing capability of the membranes with 5% filler (loaded and unloaded) was investigated by scratch test and Scanning Electron Microscopy (SEM). The result revealed a high tendency of healing for the epoxy-infused nanocomposite film.

Biphasic polylactide/polyamide 6,10 blends: Influence of composition on polyamide structure and polyester crystallization

Blends with different ratios of polylactide and polyamide 6,10 (PA610) have been prepared by melt-mixing using a Brabender mixer equipment. Previously, a rheologically modified polylactide (PLAREx) was obtained through reactive extrusion using a multifunctional epoxide agent. It was expected that unreacted epoxy groups of PLAREx were able to improve the compatibility between the two polymers. SEM observations revealed a logical dependence of the morphology of immiscible phases with composition, and more interestingly a co-continuity at relatively low PA content (around 50%) was detected. This result contrasts with previous observations performed with non-modified PLA.Confined PA domains increased with the PA content and hardly crystallized at the typical crystallization temperature of the pure PA (195 °C). Synchrotron X-ray diffraction studies indicated that a PA crystallization at a lower temperature close to 120 °C was enhanced and led to a pseudohexagonal γ phase that differs from the characteristic layered structure of PA610. SAXS data revealed also that well differentiated lamellar entities could be assigned at both immiscible polymer phases. Clear differences were observed in the spherulitic morphologies attained under isothermal melt crystallization experiments. Results indicated that the texture of PLAREx spherulites was modified by the presence of PA. Compatibilization of PA molecules on the crystal lamellar boundaries of PLAREx led to an enhancement of the lamellar twisting frequency. Optical microscopy results also indicated that the crystal growth rate of PLAREx increased by the incorporation of PA, but in contrast this had an adverse effect on the nucleation process.

Covalent immobilization of recombinant Citrobacter koseri transaminase onto epoxy resins for consecutive asymmetric synthesis of L-phosphinothricin.

Transaminase responsible for alienating prochiral ketone compound is applicable to asymmetric synthesis of herbicide L-phosphinothricin (L-PPT). In this work, the covalent immobilization of recombinant transaminase from Citrobacter koseri (CkTA) was investigated on different epoxy resins. Using optimum ES-105 support, a higher immobilized activity was obtained via optimizing immobilization process in terms of enzyme loading, coupling time and initial PLP concentration. Crucially, due to blocking unreacted epoxy groups on support surface with amino acids, the reaction temperature of blocked immobilized biocatalyst was enhanced from 37 to 57°C. Its thermostability at 57°C was also found to be superior to that of free CkTA. The Km value was shifted from 36.75mM of free CkTA to 39.87mM of blocked immobilized biocatalyst, demonstrating that the affinity of enzyme to the substrate has not been apparently altered. Accordingly, the biocatalyst performed the consecutive synthesis of L-PPT for 11 cycles (yields>91%) with retaining more than 91.13% of the initial activity. The seemingly the highest reusability demonstrates this biocatalyst has prospective for reducing the costs of consecutive synthesis of L-PPT with high conversion.

Glutathione-responsive multifunctionalizable hydrogels via amine-epoxy “click” chemistry

A novel glutathione-responsive hydrogel was synthesized through catalyst-free epoxy-amine ‘click’ chemistry using PEG-diamine and a redox-responsive diepoxy crosslinker. The chain length of PEG-diamine component was varied to modulate the physical characteristics of thus obtained hydrogels. Hydrogels exhibited degradation upon treatment with glutathione, as evident through visually apparanet gel disolution and rheological measurements. The unreacted epoxy and newly formed hydroxyl groups post-gelation were used as reactive handles to functionalize the hydrogels, as demonstrated through attachment of different fluorescent probes. Finally, it was also established that these hydrogels provide an efficient platform for ligand-directed biomolecular immobilization through anchoring of a fluorescently labelled protein onto the hydrogels.

Preparation and characterization of dual-curable off-stoichiometric amine-epoxy thermosets with latent reactivity

A new family of dual-curable poly(hydroxyamine)-poly(ether) thermosets based on off-stoichiometric amine-epoxy formulations has been prepared and characterized. The first curing stage was a self-limiting click epoxy-amine polycondensation with an excess of epoxides and the second stage was an anionic homopolymerization of the unreacted epoxy groups, initiated by a latent base. The curing process was sequential with storage stable intermediate materials. The latency of these partially-cured intermediate materials was established not only by a thermally activated base generator, but also by the vitrification of the formulations. The intermediate and final materials exhibit a wide range of properties depending on the relative contribution of both curing stages. Intermediate materials can either be shape conformable solids, or liquids that are applicable as adhesives. Fully cured materials exhibit shape-memory effect.

Synthesis and characterization of PAA microgels using multifunctional epoxy cross-linkers with a new cross-linking mechanism via a precipitation polymerization method

Polyacrylic acid (PAA) microgels were prepared by a free radical precipitation polymerization method. Initially, epoxy type cross-linkers were used to prepare PAA microgels by the precipitation polymerization method. Different types of multifunctional cross-linkers such as ethylene glycol diglycidyl ether (EGDGE), Triphenylol methane triglycidyl ether (TMTGE) and 4,4′- Methylenebis(N,N-diglycidyl aniline) (MBDGA) were used as bi-, tri- and tetra-functional cross-linkers, respectively. Epoxy type cross-linkers are able to cross-link PAA by reaction between the –COOH groups of PAA and the epoxide groups of the cross-linkers. Some of the epoxy rings do not react with acid groups of PAA chains during the polymerization stage; unreacted epoxy rings can be reacted during the sample drying time, a stage we designated as the ‟post-curing stage”. The effect of cross-linker concentration and its functionality on the behaviors of samples (i.e., swelling capacity, gel content, glass transition temperature and rheological properties) were investigated. A new relationship between average molecular weight of two successive cross-links ( Mc) and epoxy concentration ([epoxy]) was defined. The microgel properties, such as rotational viscosity and rheological properties, were compared with those of microgels prepared by divinyl type cross-linkers. Our results show that microgels synthesized by this novel mechanism have higher rheological properties (at low shear rate, strain and frequency) than those synthesized by conventional methods. These behaviors can be due to the increase in polymer side chains of the polymer network generated by this new cross-linking method.

Development of a photocurable glass-fiber reinforced epoxy-amine/thiol-ene composite

This work reports a rapid and efficient method to prepare photocurable glass-fiber reinforced epoxy composites. The curing agent for the developed epoxy photocurable systems is a tertiary tetramine functionalized with six allyl groups. The tertiary amine groups induce the anionic polymerization of the epoxy groups to produce the corresponding polyethers. At the same time the double bonds of the curing agent react with an added multifunctional thiol by means of the thiol-ene mechanism, forming polythioethers. These polythioethers affect the reactivity of the system because once formed they are basic enough to anionically polymerize the unreacted epoxy groups. Moreover, the flexibility of the polythioethers improves the toughness of the polyethers derived from the epoxy resin as demonstrated by the impact resistance determinations. When this epoxy-amine/thiol-ene system was tested to prepare glass fiber reinforced epoxy composites, completely cured specimens were obtained with modulus of approximately 25,000–29,000 MPa. The heat released during the thiol-ene photopolymerization contributes to completely cure the composite.

Preparation and characterization of UV/thermal dual-curable polyurethane acrylate adhesive for inertial confinement fusion experiment

A new type of polyurethane acrylate (APUE) oligomer, which contains both acrylic and epoxy group in its molecular structure, was synthesized. UV/thermal dual-curable adhesives were prepared using various contents of APUE oligomers, reactive diluent, photoinitiators and thermal-curing agent. The curing behaviors of the dual-curable adhesives were investigated using photo-DSC, on-line FT-IR spectroscopy, the determination of gel fraction and dynamic mechanical thermal analysis (DMTA). The reaction rate and extent of UV curing were studied and found to be strongly dependent on the concentration of C=C bonds in the APUE oligomers. The gel fraction was also evaluated as a function of C=C bond concentration, demonstrating that gel fraction increased with increasing C=C bond contents in the APUE oligomers. Moreover, when the dual-curable adhesive was thermally-cured, the gel fraction was largely improved, due to the thermal-curing agent initiating the unreacted epoxy groups to allow the formation of further crosslinking. The adhesion strength at −196°C increased with increasing C=C bond content. The latent thermal-curing agent contributed to the enhancement of the adhesion strength.

Effect of the addition of multi-walled carbon nanotubes on the thermomechanical properties of epoxy resin

The influence of multi-walled carbon nanotubes (MWCNTs) on thermosetting epoxy is examined using dynamic mechanical analysis, thermogravimetric analysis, and differential scanning calorimetry (DSC). Specimens are prepared with loadings of 0.1 and 1 wt% MWCNTs which are dispersed in the resin using two different dispersion methods. While the storage modulus of the specimens is improved, both the glass transition temperature and the thermal stability are reduced by the addition of MWCNTs with both effects being greater for the higher MWCNT loading, for both dispersion systems. The DSC results additionally indicate that the level of residual unreacted epoxy increases progressively with the addition of the nanotubes. This finding is considered as confirmation that the MWCNTs obstruct crosslinking of the epoxy resin. POLYM. COMPOS., 2015. © 2015 Society of Plastics Engineers

Design of New Camelina Oil‐Based Hydrophilic Monomers for Novel Polymeric Materials

AbstractTriglyceride‐based monomers represent a competitive alternative to petrochemical resources in the macromolecular compounds area. In the current study, several types of hydrophilic camelina oil (CO)‐based monomers were synthesized using tunable experimental protocols that involve three different steps: first—conversion of the double bonds into epoxy rings, second—partial opening of the epoxy rings and methacrylic groups grafting and last—opening of the unreacted epoxy rings and hydrophilic units attaching. 1H‐NMR, 13C‐NMR and FTIR spectroscopy demonstrate the success of the CO functionalization with polymerizable and hydrophilic moieties—polyethylene glycol units—with different molecular weights, exhibiting self‐emulsifiable properties. Several bulk and emulsion polymerization tests were performed for the synthesized monomers and their ability to build polymer networks using different photo‐chemical procedures (using visible and UV radiations respectively) was demonstrated, without additional surfactants. FTIR spectroscopy indicates the polymerization success by the disappearance of the specific bands assigned to the double bonds from methacrylic groups and thermogravimetric analysis demonstrates that the emulsion polymerization leads to materials with an improved thermostability.

Novel cross-linking mechanism for producing PAA microgels synthesized by precipitation polymerization method

A series of new cross-linkers, ethylene glycol diglycidyl ether (EGDGE), with new cross-linking mechanism, was utilized to prepare cross-linked poly(acrylic acid) microgels by precipitation polymerization method. All of the epoxy rings do not react with –COOH groups of PAA chains during polymerization stage; therefore, the unreacted epoxy rings would be reacted after polymerization stage (during sample drying time), which was named as “post curing stage.” The effect of cross-linker concentration, time, and temperature of post curing stage on the samples behaviors (i.e., swelling capacity, gel content, glass transition temperature, and rheological properties) were investigated. A new relationship between gelation rate in the post curing stage and epoxy content was defined. Also a relationship between average molecular weight of two successive cross-links (Mc), epoxy concentration ([epoxy]), and temperature of post curing stage (T pc ) was suggested. The microgel properties such as the rotational viscosity and rheological properties (that was synthesized by this novel cross-linking method) were compared to that of microgels that were synthesized by divinyl-type cross-linkers (trimethylol propane triacrylate (TMPTA)). The results show that the microgel properties which were synthesized by novel cross-linking mechanism are better than that of microgel properties by conventional cross-linking method.

Immobilization of lipase on epoxy-activated Purolite® A109 and its post-immobilization stabilization

In this study, Purolite® A109, polystyrenic macroporous resin, was used as immobilization support due to its good mechanical properties and high particle diameter (400μm), which enables efficient application in enzyme reactors due to lower pressure drops. The surface of support had been modified with epichlorhydrine and was tested in lipase immobilization. Optimized procedure for support modification proved to be more efficient than conventional procedure for hydroxy groups (at 22°C for 18h), since duration of procedure was shortened to 40min by performing modification at 52°C resulting with almost doubled concentration of epoxy groups (563μmolg−1). Lipase immobilized on epoxy-modified support showed significantly improved thermal stability comparing to both, free form and commercial immobilized preparation (Novozym® 435). The highest activity (47.5IUg−1) and thermal stability (2.5 times higher half-life than at low ionic strength) were obtained with lipase immobilized in high ionic strength. Thermal stability of immobilized lipase was further improved by blocking unreacted epoxy groups on supports surface with amino acids. The most efficient was treatment with phenylalanine, since in such a way blocked immobilized enzyme retained 65% of initial activity after 8h incubation at 65°C, while non-blocked derivative retained 12%.

Covalent Immobilization of Alcohol Dehydrogenase (ADH2) from Haloferax volcanii: How to Maximize Activity and Optimize Performance of Halophilic Enzymes

Alcohol dehydrogenase from halophilic archaeon Haloferax volcanii (HvADH2) was successfully covalently immobilized on metal-derivatized epoxy Sepabeads. The immobilization conditions were optimized by investigating several parameters that affect the halophilic enzyme-support interaction. The highest immobilization efficiency (100%) and retention activity (60%) were achieved after 48h of incubation of the enzyme with Ni-epoxy Sepabeads support in 100mM Tris-HCl buffer, pH 8, containing 3M KCl at 5°C. No significant stabilization was observed after blocking the unreacted epoxy groups with commonly used hydrophilic agents. A significant increase in the stability of the immobilized enzyme was achieved by blocking the unreacted epoxy groups with ethylamine. The immobilization process increased the enzyme stability, thermal activity, and organic solvents tolerance when compared to its soluble counterpart, indicating that the immobilization enhances the structural and conformational stability. One step purification-immobilization of this enzyme has been carried out on metal chelate-epoxy Sepabeads, as an efficient method to obtain immobilized biocatalyst directly from bacterial extracts.

Synthesis of bio‐based polyurethanes from epoxidized soybean oil and isopropanolamine

AbstractEpoxidized soybean oil (ESO) and isopropanolamine were used to synthesize a new polyol mixture for preparation of bio‐based polyurethanes. The chemical synthetic route for reaction of ESO with isopropanolamine was analyzed by 1H‐NMR. The results suggested that both ester groups and epoxy groups in ESO had reacted with amino group of isopropanolamine through simultaneous ring‐opening and amidation reactions. Epoxy groups in various situations exhibited different reactivity, and the unreacted epoxy groups were further opened by hydrochloric acid. The synthesized polyol mixture had high hydroxyl number of 317.0 mg KOH/g. A series of polyurethanes were prepared by curing the synthesized polyol mixture with 1,6‐diisocyanatohexance along with different amount of 1,3‐propanediol (PDO) as chain extender. Tensile tests showed that yield strengths of the polyurethanes ranged from 2.74 to 27.76 MPa depending on the content of PDO. Differential scanning calorimetry analysis displayed one glass transition temperature in the range of 24.4–28.7°C for all of the polyurethane samples, and one melt peak at high content of PDO. Thermogravimetric analysis showed that thermal degradations of the polyurethanes started at 240–255°C. In consideration of simple preparation process and renewable property of ESO, the bio‐based polyurethane would have wide range of applications. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

Synthesis of reactive soybean oils for use as a biobased thermoset resins in structural natural fiber composites

AbstractBiobased thermosets resins were synthesized by functionalizing the triglycerides of epoxidized soybean oil with methacrylic acid, acetyl anhydride, and methacrylic anhydride. The obtained resins were characterized with FTIR, 1H‐NMR, and 13C‐NMR spectroscopy to confirm the functionalization reactions and the extent of epoxy conversion. The viscosities of the methacrylated soybean oil resins were also measured for the purpose of being used as a matrix in composite applications. The cross‐linking capability was estimated by UV and thermally initiated curing experiments, and by DSC analysis regarding the degree of crosslinking. The modifications were successful because up to 97% conversion of epoxy group were achieved leaving only 2.2% of unreacted epoxy groups, which was confirmed by 1H‐NMR. The 13C‐NMR confirms the ratio of acetate to methacrylate methyl group to be 1 : 1. The viscosities of the methacrylated soybean oil (MSO) and methacrylic anhydride modified soybean oil (MMSO) were 0.2 and 0.48 Pas, respectively, which indicates that they can be used in resin transfer molding process. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

Study of factors related to performance improvement of self-healing epoxy based on dual encapsulated healant

Our earlier work developed epoxy based self-healing composites with embedded dual microcapsules, which contain unreacted epoxy as the polymerizable component and mercaptan and tertiary amine catalyst as the hardener, respectively. Self-healing was allowed to proceed rapidly, offering attractive repair effectiveness. To give full play to the healing agent, influences of a series of factors on healing chemistry of the composites were studied in this paper. It was found that strong alkality of the catalyst, high activity of mercaptan, and low viscosity of the encapsulated epoxy prepolymer ensured high healing efficiency and rate of healing. In addition, matching of the microcapsules' sizes and fractions was critical for keeping stoichiometric ratio of the components at the damage areas, as required by the mechanism of the healing reaction (i.e. addition polymerization). Homogeneous dispersion of the capsules under proper stirring speed led to timely contacts between the healant fluids flowing out of the fractured capsules. Larger microcapsules favored filling of the cracks in terms of larger amount of the released healing agent, while smaller ones facilitated mixing and interdiffusion of the ingredients. The results provided key data for optimizing the self-healing system.