Amine Hardener Research Articles

Subtle variations in the structure of crosslinked epoxy networks and the impact upon mechanical and thermal properties

ABSTRACTPresented here is an investigation of the structure–property relationships of crosslinked networks using three bi‐functional glycidyl ether aromatic epoxy resins, two bi‐aryl and one tri‐aryl, cured with bi‐ and tri‐aryl amines. Subtle changes to the monomer chemistry including changing aromatic substitution patterns from meta to para, methylene to isopropyl and isopropyl to ether were explored. Changing an epoxy resin backbone from methylene to isopropyl enhances backbone rigidity thus increasing glass transition temperature (Tg), yield strength, and strain despite reducing modulus. Changing meta‐substitution to para increases Tg and yield strain while leaving strength unaffected and reducing modulus. Changing isopropyl linkages to ether reduces modulus, strength, Tg, and yield strain reflecting increased molecular flexibility. Using three instead of two aromatic rings increases the molecular weight between crosslinks thereby decreasing Tg and yield strain while increasing modulus and strength. Despite the complexities of multiple systems for varying epoxy resins and amine hardeners, the effect upon network properties is explained in terms of short‐ and long‐range molecular and segmental mobility, crosslink density, and equilibrium packing density. © 2020 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020, 137, 48874.

АНАЛІЗ АМІННИХ ЗАТВЕРДЖУВАЧІВ КЛЕЮ МЕТОДОМ рН-МЕТРИЧНОГО ТИТРУВАННЯ В СЕРЕДОВИЩІ МІЦЕЛ ДОДЕЦИЛСУЛЬФАТУ НАТРІЮ

One of the primary tasks in the development of amine hardeners for adhesive and epoxy resins is the control of amino group quantities in their composition. The main parameter that indicates the rate of the polymerization reaction and characterizes the quality of the hardener is the amine number. It is determined by the number of primary and secondary amino groups contained in the hardener molecule, because these functional groups are involved in reactions with epoxy resins. The most common methods of analysis of amine hardeners are mainly based on titration in organic solvents and require a procedure of derivatization of primary and secondary amino groups using formaldehyde and acetic anhydride. The search for a simple, cheap and environmentally friendly alternative to such titrimetric methods is still ongoing. In this paper on the example of industrial samples of polyamide PO-300, polyethylene polyamine (PEPA) and diethylenetriamine (DETA) shows the prospects of using the method of pH-metric titration in water-micellar medium of sodium dodecylsulfate (SDS) to determine the content of primary and secondary amino groups in the adhesive hardeners. According to the developed techniques, working solutions of PO-300, PEPA and DETA were prepared by dissolving their exact mass in 20 ml of 2.0 M SDS solution. The values of PO-300, PEPA and DETA samples were 0.1040 g, 0.0225 g and 0,0200 g, respectively. Titration of the obtained solutions was performed with 0.05 M HCl solution. The percentage of primary amino groups, calculated on the basis of the obtained differential titration curves, is equal to 5,56% for PO-300, 23,6% for PEPA and 31,6% for DETA. The content of secondary amino groups in PO-300, PEPA and DETA samples is 3,03%, 15,0% and 19,6%. Founded amine number for PO-300, PEPA and DETA is well correlated with data declared by the manufacturer and equals to 302, 1381 and 1890, respectively. Unfortunately, it was not possible to establish the presence and quantity of tertiary amino groups in the samples of adhesive hardeners by this technique. The effect of cationic surfactant cetylpyridinium chloride, nonionic Triton X-100 and anionic surfactant SDS on the value of the pH jump of diethylenetriamine (DETA) was also studied. It was found that anionic SDS has the greatest differentiating effect on the acid-base properties of amino groups DETA in comparison with other studied surfactants. At that, the primary amino groups are titrated in the first place.

Identifying the properties of epoxy composites filled with the solid phase of wastes from metal enterprises

The article addresses the issue related to the disposal of dust from steel industry as a reinforcing filler for epoxy composites. The polymer composition of welding that has been developed and studied includes epoxy dian oligomer, amine hardener and the filler – finely dispersed waste of metals. Polyethylene polyamine was used as a hardener in order to improve heat resistance and strength characteristics. Manganese triacetate was used in order to decrease the temperature and reduce the time of curing. The possibility was established to dispose of finely dispersed metal-containing waste from metallurgical production to be used a filler for epoxy composites of cold curing. It was revealed that the optimal content of dusts from foundries in the composite is at the level of 45–60 %. At this content, there is the highest impact resistance at the level of 40–50 MPa and a softening temperature in the range of 170–190 °С. It was established that at an increase in the amount of a filler from 40 % to 70 %, the cross-linking degree increases by 88 % to 98 %, respectively. However, at the content of the filler less than 45 % or exceeding 60 %, the impact resistance of the resulting composites decreases. At the content of a filler in the composite less than 45 %, the cause of low values of impact resistance and softening temperature could be the low cross-linking degree, less than 90 %. A decrease in these properties of composites at the content of the filler exceeding 60 % could be associated with the formation of a heterogeneous structure of filler. In the compositions with the highest performance characteristics, there is an optimized content of the filler and catalyst. Using a hardener and a curing catalyst in quantities of 3–3.5 and 1.5–2 %, respectively, makes it possible to shorten curing time by up to 2 hours. In general, the resulting epoxy composites are superior in their performance to known cold-curing analogs. The dependences of impact resistance, softening temperature, and cross-linking degree on the content of waste in the composite were derived, which make it possible to calculate the optimal formulation for composites depending on the required properties

Amine-Functionalized TiO2 Nanoparticles Covalently Loaded into Epoxy Networks via Thermal and Microwave Curing Processes

TiO2 nanoparticles were surface modified by NH2-functionalized organic moieties, and then chemically loaded into diglycidyl ether of bisphenol A-derived epoxy networks. Amine functionalization of these organically modified nanoparticles allowed them to have an efficient participation in the curing processes. Alongside the main amine hardener, i.e., 3,3′-dimethyl-4,4′-diaminodicyclohexylmethane, the aminated TiO2 played the role of a new inorganic co-hardener. Thermal and microwave-assisted curing processes resulted in epoxy-based composites incorporated by uniformly dispersed TiO2 nanoparticles. Diffuse reflectance ultraviolet-visible spectra showed that unlike the neat synthesized counterparts, TiO2-loaded epoxy composites have significant absorption in the visible range of 400–700 nm. According to the results obtained from atomic force microscopy technique, it was found that the microwave-assisted curing process results in a smoother surface in comparison with the thermal one. Transmission electron microscopy obviously demonstrated that the average size of the loaded particles is below 50 nm. Thermogravimetric analysis of the TiO2-containing epoxy networks revealed that the resulted composites are thermally decomposed through a simple one-step process at about 360 °C. Dynamic mechanical thermal analysis profiles indicated that no agglomeration of the nanoparticles occurs during the curing processes of the epoxy resin, and the incorporated nanoparticles somewhat limit the segmental motions of the polymer chains.

Bio-based unidirectional composite made of flax fibre and isosorbide-based epoxy resin

Abstract Ultrasound-assisted synthesis of diglycidyl ethers of isosorbide (DGEI) with different epoxy equivalent weight (EEW) with isophorone diamine (IPD) hardener have been performed. Interestingly, it was found that one specific epoxy formulation exhibits high reactivity with amine hardener inducing high glass transition and indentation stiffness. Associated with flax fibres, this new bio-based resin has made it possible to develop performing and promising unidirectional biocomposites with characteristics comparable to commercial petroleum-based epoxy resins.

Synthesis and characterization of amine hardener filled microcapsules for self-healing composite applications

Materials experience microcracks during service conditions and thus might not fulfil their functionality. Hence there is a necessity to develop a method which enhances the functionality of the material without affecting its inherent properties. Self-healing of materials through microencapsulation repairs microcracks and extends the service life of material. In this work, amine hardener encapsulated polymethyl methacrylate (PMMA) microcapsules were synthesized using oil-in -water solvent evaporation technique. Various process parameters such as surfactant concentration, operating temperature, agitation speed and core to shell ratio were investigated to get the desired morphology and healing agent content. The challenges faced during the synthesis of microcapsules were reported. It was observed that solvent evaporation rate, stirring duration, surfactant type and concentration have an impact on the agglomeration of capsules. The molecular architecture, thermal stability and surface morphology of the microcapsules were characterized by Fourier-transform Infrared spectroscopy (FT-IR), Thermogravimetric analysis (TGA) and Scanning Electron Microscope (SEM) respectively. Core content of the capsules was evaluated by solvent extraction method and the capsules average size and size distribution were reported. The effect of different surfactants and their combinations such as Polyvinyl Alcohol (PVA), Tween 80 and (Tween 80 + PVA) on the microcapsules synthesis were reported. This study also reported the influence of surfactant concentration on the microcapsule shell thickness, which is a critical parameter in evaluating structural healing efficiency. Developed microcapsules ability to release core content and repair micro cracks was verified qualitatively with 3D optical microscope.

The Gradient of Dynamic Mechanical Characteristics across the Thickness of Epoxy Polymers during Environmental Exposure

Temperature dependences of dynamic modulus of elasticity and dynamic loss modulus of four compositions of epoxy polymers based on 2,2-di-(4-hydroxyphenyl) propane and a cycloaliphatic amine hardener in an initial state and after 3, 6, 9, and 12 months of exposure on an open bench under conditions of moderately warm climate of Gelendzhik. A glass transition temperature determined during a transition from a glassy state to a highly elastic one of epoxy polymers proved to be sensitive to the polymer composition, an amount of sorbed moisture and duration of exposure. Postcuring of polymers, masked by a plasticizing effect of moisture, is discovered. The glass transition temperature of exposed epoxy polymers changes unevenly across the thickness of specimens. Properties of a surface layer facing the sun (on the front side) change to the greatest extent. Methods of dynamic mechanical analysis have good sensitivity and informativeness for a study of non-uniformity of climatic aging across the thickness.

Synthesis of Pluri-Functional Amine Hardeners from Bio-Based Aromatic Aldehydes for Epoxy Amine Thermosets.

Most of the current amine hardeners are petro-sourced and only a few studies have focused on the research of bio-based substitutes. Hence, in an eco-friendly context, our team proposed the design of bio-based amine monomers with aromatic structures. This work described the use of the reductive amination with imine intermediate in order to obtain bio-based pluri-functional amines exhibiting low viscosity. The effect of the nature of initial aldehyde reactant on the hardener properties was studied, as well as the reaction conditions. Then, these pluri-functional amines were added to petro-sourced (diglycidyl ether of bisphenol A, DGEBA) or bio-based (diglycidyl ether of vanillin alcohol, DGEVA) epoxy monomers to form thermosets by step growth polymerization. Due to their low viscosity, the epoxy-amine mixtures were easily homogenized and cured more rapidly compared to the use of more viscous hardeners (<0.6 Pa s at 22 °C). After curing, the thermo-mechanical properties of the epoxy thermosets were determined and compared. The isophthalatetetramine (IPTA) hardener, with a higher number of amine active H, led to thermosets with higher thermo-mechanical properties (glass transition temperatures (Tg and Tα) were around 95 °C for DGEBA-based thermosets against 60 °C for DGEVA-based thermosets) than materials from benzylamine (BDA) or furfurylamine (FDA) that contained less active hydrogens (Tg and Tα around 77 °C for DGEBA-based thermosets and Tg and Tα around 45 °C for DGEVA-based thermosets). By comparing to industrial hardener references, IPTA possesses six active hydrogens which obtain high cross-linked systems, similar to industrial references, and longer molecular length due to the presence of two alkyl chains, leading respectively to high mechanical strength with lower Tg.

Divanillin-Based Aromatic Amines: Synthesis and Use as Curing Agents for Fully Vanillin-Based Epoxy Thermosets.

Bio-based aromatic diamines from vanillin substrate were successfully synthesized and characterized. These amines, i.e., methylated divanillylamine (MDVA) and 3,4-dimethoxydianiline (DMAN), were then tested as curing agents for the design of bio-based epoxy thermosets. The epoxy thermosets obtained from these novel vanillin-based amines exhibited promising thermomechanical properties in terms of glass transition temperature and char residue.

PEG-based epoxy and epoxy/silica networks: Thermal, mechanical, and thermo-mechanical investigations

A diglycidyl ether resin and an amine hardener, both based on polyethylene glycol (PEG) were synthesized and utilized for preparing new epoxy thermosetting materials. Two popular monomers, i.e. diglycidyl ether of bisphenol A (DGEBA) and/or isophorone diamine (IPDA) were also utilized. Three transparent and rubber-like films were fabricated through one combinational and two non-combinational manners. In the combinational manner, diglycidyl ether of PEG (DGEPEG) and DGEBA with equal moles were cured with equal moles of amine-functionalized PEG (APEG) and IPDA. In the non-combinational manners, at one time, the PEG-based resin was cured with IPDA hardener, and at the other time, DGEBA resin was cured with PEG-based amine hardener. Stoichiometric amounts of epoxy resin and amine hardener were used in all of the curing processes. Three epoxy/silica nanocomposites with silica-loading of 5.0 wt%, and with the same epoxy matrices were also synthesized similarly. Silica nanoparticles were organically modified and amine-functionalized prior to use. The neat epoxy networks and their silica-loaded nanocomposites were characterized by FT-IR, and FE-SEM techniques. The structure and composition of the six networks obtained significantly affect their thermal, mechanical, and thermo-mechanical behaviors. These influencing factors were fully investigated by thermogravimetric analysis, tensile testing, and dynamic mechanical analysis.

Optimization of the Curing and Post-Curing Conditions for the Manufacturing of Partially Bio-Based Epoxy Resins with Improved Toughness.

This research deals with the influence of different curing and post-curing temperatures on the mechanical and thermomechanical properties as well as the gel time of an epoxy resin prepared by the reaction of diglycidyl ether of bisphenol A (DGEBA) with an amine hardener and a reactive diluent derived from plants at 31 wt %. The highest performance was obtained for the resins cured at moderate-to-high temperatures, that is, 80 and 90 , which additionally showed a significant reduction in the gel time. This effect was ascribed to the formation of a stronger polymer network by an extended cross-linking process of the polymer chains during the resin manufacturing. Furthermore, post-curing at either 125 or 150 yielded thermosets with higher mechanical strength and, more interestingly, improved toughness, particularly for the samples previously cured at moderate temperatures. In particular, the partially bio-based epoxy resin cured at 80 and post-cured at 150 for 1 h and 30 min, respectively, showed the most balanced performance due to the formation of a more homogeneous cross-linked structure.

Modified of the Epoxy Coatings by Polyaniline

An actual problem is searching of new pathways of increase of anticorrosion properties of an organic coating. In the field of practice and the theory of metal protection from corrosion recently there were novel trends. One of them – making and examination of the conducting polymers inhibiting corrosion of many metals. Influence of the amine hardener modified by polyaniline (PANi) on anticorrosion properties of epoxy coatings in various corrosion-active mediums was studied. The polarization studies have shown that the introduction of PANI in the epoxy polymer coating reduces the corrosion current density. Using electrochemical impedance spectroscopy has established that coatings containing of PANI, are less permeable due to its hydrophobic. It was showed, that PANi it can be used for increase of anticorrosion properties of manufacturing epoxy primer.

Resilience of Adhesive Compounds in Water—Salt Media

The resilience of adhesive compounds in water—salt media was shown experimentally to depend on the nature of the bonding surfaces, as well as on the chemical peculiarities of adhesives. Unlike compounds based on epoxy resins and anhydride hardeners, adhesive compounds based on epoxy resins and aliphatic amine hardeners are unsteady in water-salt media. The resilience of systems on the basis of polyurethane adhesives to the water-salt environment is sensitive to the adhesive structure and may vary in a very broad range.

Toughening of Epoxy Resin: The Effect of Water Jet Milling on Worn Tire Rubber Particles.

In this work a cycloaliphatic amine-cured epoxy (EP) resin was modified by micron-scale rubber particles (RP). Nominal RP, in sizes of 200 and 600 µm respectively, were produced using worn truck tires and ultra-high-pressure water jet cutting. The RP were dispersed into the EP resin using different mixing techniques (mechanical, magnetic, and ultrasonic stirring) prior to the introduction of the amine hardener. The dispersion of the RP was studied using optical light microscopy. A longer mixing time reduced the mean size of the particles in the EP compounds. Static (tensile and flexural), dynamic (unnotched Charpy impact), and fracture mechanical (fracture toughness and strain-energy release rate) properties were determined. The incorporation of the RP decreased the stiffness and strength values of the modified EPs. In contrast, the irregular and rough surface of the RP resulted in improved toughness. The fracture toughness and strain-energy release rate were enhanced up to 18% owing to the incorporation of 1% by weight (wt%) RP. This was traced to the effects of crack pinning and crack deflection. Considerably higher improvement (i.e., up to 130%) was found for the unnotched Charpy impact energy. This was attributed to multiple cracking associated with RP-bridging prior to final fracture.

Properties and Technology of Applying Metal Coatings to Carbon Tape

The results of evaluating the adhesion strength and mechanical characteristics of elementary filaments used to make LUP carbon tape after metal plating the tape with titanium and stainless steel are presented. The thickness of these coatings is determined by atomic force microscopy and also by measuring the diameter of filaments before and after metal plating. Two types of single-layer coatings are considered – titanium grade VT1-0 and stainless steel grade 12X18H10T, as well as a two-layer coating consisting of a layer of titanium with a layer of stainless steel on top. To determine the adhesive strength using the pull-out method, a binder was used based on epoxy resin and an amine hardener.

Kinetic Analysis of the Curing of a Partially Biobased Epoxy Resin Using Dynamic Differential Scanning Calorimetry.

This research presents a cure kinetics study of an epoxy system consisting of a partially bio-sourced resin based on diglycidyl ether of bisphenol A (DGEBA) with amine hardener and a biobased reactive diluent from plants representing 31 wt %. The kinetic study has been carried out using differential scanning calorimetry (DSC) under non-isothermal conditions at different heating rates. Integral and derivative isoconversional methods or model free kinetics (MFK) have been applied to the experimental data in order to evaluate the apparent activation energy, Ea, followed by the application of the appropriate reaction model. The bio-sourced system showed activation energy that is independent of the extent of conversion, with Ea values between 57 and 62 kJ·mol−1, corresponding to typical activation energies of conventional epoxy resins. The reaction model was studied by comparing the calculated y(α) and z(α) functions with standard master plot curves. A two-parameter autocatalytic kinetic model of Šesták–Berggren [SB(m,n)] was assessed as the most suitable reaction model to describe the curing kinetics of the epoxy resins studied since it showed an excellent agreement with the experimental data.

FEATURES OF THE COPPER(II) CARBONATE INFLUENCE ON AN INFLAMMABILITY OF EPOXY-AMINE COMPOSITES

Introduction. Inflammation susceptibility and the nature of combustion are one of the most important characteristics for the parametrization of the fire hazard of polymer materials. Because ignition is the occurrence process of the persistent flame near the surface of the material, which is preceded by the process of propagation of the flame front on its surface, the predisposition to ignition of the polymer materials plays an important role in the aspect of initiation of fires. A comparative evaluation of inflammation susceptibility of substances of different nature was carried out basing the determination of the ignition point and self-ignition point.&#x0D; Purpose. The work aims to determine the peculiarities of the influence of copper(II) carbonate on the increase of ignition point and self-ignition point of epoxy-amine composites.&#x0D; Metods. The experimental determination of the ignition point and self-ignition point was carried out according to all-Union State Standard 12.1.044-89 (4.7, 4.9 items). Toward this end, three samples of the test material were prepared with a weight of 3 g. Before testing, samples were conditioned in air.&#x0D; Results. Data on the effect of copper(II) carbonate on the value of ignition point and self-ignition point of the epoxy-amine composites indicate that the epoxy-amine-based composite, cured by the traditional amine hardener (PEPA), has lowest temperature of the ignition and self-ignition. The temperture values of ignition and self-ignition increase as the content of copper(II) carbonate increases in the composite, measuring up a maximum value at 80 g of CuCO3 per 100 g of binder. It is proved that the reason for the increase of the ignition temperature and self-ignition temperature of the modified epoxy-amine composites is the appearance of strong coordination bonds that are formed due to the chemical binding of the combustible polyethylenepolyamine with the non-combustible inorganic salt (with copper(II) carbonate). The measured values of the ignition point and self-ignition point of the amine hardener (PEPA) of the epoxy-diane oligomer indicate that it is able to ignite at temperature 136ºC, and self-ignite at temperature 393ºС. After forming the chelate complex, the coordinated PEPA turns into a practically non-combustible substance.&#x0D; Conclusion. Consequently, the main factor that affects to make difficulty of ignition of organic nitrogen-containing substances is the efficient chemical binding N atoms of the combustible amine molecules with d-metal atom of the non-combustible inorganic salt, which is accompanied by the formation of sufficiently strong coordination bonds of the Cu(ІІ)¬N type. The resistance to ignition of the modified polymeric composites will depend on the binding strength of the copper(II) salt with an amine hardener. The mechanism of the fire retardant influence of the d-metal salts on combustion of the epoxy-amine-based composites consists in this. So, copper(II) compounds, in particular copper(II) carbonate, can successfully be used as the fire retardant additives enabling of efficiently lowering the fire hazard of synthetic polymers based on epoxy-amine composites.

Effect of Kenaf Alkalization Treatment on Morphological and Mechanical Properties of Epoxy/Silica/Kenaf Composite

The mechanical performance of silica modified epoxy at various concentration of sodium hydroxide for surface treatment of multi-axial kenaf has been analyzed. Epoxy resin with amine hardener was modified with silica powder at 20 phr and toughened by treated kenaf fiber that immerses in various concentrations of sodium hydroxide (NaOH) ranging from 0% to 9% of weight. The composite was analyzed through differential scanning calorimetry (DSC) to ensure complete curing process. The mechanical properties of the composites were analyzed through flexural test, Charpy impact test and DSC to ensure the complete curing process. DSC analysis results show epoxy sample was completely cured at above 73°C that verifies the curing temperature for preparation for the composite. Hence, 3% NaOH treated composite exhibits the best mechanical properties, with 10.6 kJ/m2 of impact strength, 54.1 MPa of flexural strength and 3.5 GPa of flexural modulus. It is due to the improvement of fiber-matrix compatibility. Analysis by SEM also revealed that a cleaner surface of kenaf fiber treated at 3% NaOH shown cleaner surface, thus, in turn, improve surface interaction between fiber and matrix of the composite. The composites produced in this work has high potential to be used in automotive and domestics appliances.

Basalt fiber reinforced polymers with improved thermal and mechanical properties by combination of twin polymerization with epoxide chemistry

Fiber reinforced polymers (FRPs) require a good match of fiber reinforcement and polymer matrix facilitating excellent thermal and mechanical properties. This contribution combines the mineral fibers glass and basalt with a novel silicatic hybrid polymer matrix formed during twin polymerization of 2‐(3‐Amino‐n‐propyl)‐2‐methyl‐4H‐1,3,2‐benzodioxasiline (APSI) as a novel amine hardener and the bisphenol A‐based epoxide BADGE. The resulting ternary hybrid material consists of a nanostructured and crosslinked epoxide, phenolic resin and polydialkylsiloxane network. In comparison to conventionally cured BADGE with IPDA (isophorone diamine), the glass and basalt fiber reinforced twin polymers showed a retarded combustion with a higher residual mass after oxidation. Moreover, the reinforcing effect with glass respective basalt was pronounced in case of APSI cured BADGE. The increased inorganic ratio in the composites due to in situ formation of polysiloxane species seems to affect beneficially FRPs thermal and mechanical properties by increasing the stiffness by 25% and the storage modulus by 260%. POLYM. COMPOS., 40:3115–3121, 2019. © 2018 Society of Plastics Engineers

Study of Coatings Derived from the Copolymer of Vinylidene Fluoride and Hexafluoropropylene

A study has been carried out on the swelling of a copolymer of vinylidene fluoride and hexafluoropropylene in organic solvents. The optimal conditions for dissolving this fluoroelastomer were determined. Vulcanization of the fluorocopolymer was carried out using amine hardeners, namely, m-xylylenediamine and 3-aminopropyltriethoxysilane. A mechanism was proposed for the hardening of the copolymer. The effects of these hardeners on the coating properties were compared.