Multifunctional Epoxy Research Articles

Multifunctional epoxy composites modified with a graphene nanoplatelet/carbon nanotube hybrid

AbstractEpoxies are a class of thermoset polymers which find use in high performance applications. However, epoxies are inherently brittle and are poor conductors of electricity, which limits their ability to be employed in functional applications. Carbon nanomaterials have attracted considerable attention as filler materials, due to their combination of outstanding properties. In the present work, an epoxy polymer was modified with a hybrid nanofiller, consisting of graphene nanoplatelets (GNPs) and carbon nanotubes (CNTs) at a mass ratio of 9:1, using three‐roll milling. Addition of 1 wt% resulted in an increase of eight orders of magnitude in the electrical conductivity and a 182% increase in the fracture energy, GIC, of the epoxy. CNTs contributed greatly in the reduction of the percolation threshold, which was 10 times lower than that of conventional GNP/epoxy composites, while the increase in toughness was entirely attributed to the GNPs, predominantly through the mechanism of crack deflection. The toughening contribution of the hybrid nanofiller was theoretically calculated using analytical modeling, which showed excellent agreement between the predicted and experimental values of GIC.

Effect of multi-functional epoxy chain extender on the weathering resistance performance of Poly(butylene adipate-co-terephthalate) (PBAT)

In this research work, both natural weathering and artificial weathering processes were carried out to investigate the effects of multi-functional epoxy chain extender (Joncryl ADR 4370) content on the degradation and the mechanical properties and molecular weight of poly(butylene adipate-co-terephthalate) (PBAT). The carboxyl end-groups of PBAT decreased significantly with an increase in ADR content from 0 to 1.5 wt%. Similarly, the molecular weight of PBAT initially increased and then decreased because of the formation of a crosslinked network structure under the influence of excessive chain extenders. The main degradation mechanism of PBAT during the natural and artificial weathering process is photo-degradation and hydrolyzation. The degradation rate of PBAT increased with increasing content of chain extender, as hydroxyl groups facilitate the water attack on the ester bonds of PBAT. In contrast, the higher content of chain extender presented the lower loss velocity of the tensile strength. This is mainly because the more ADR content, the more crosslinking network structures will be formed during the melting extrusion which can slow down the decrease of tensile strength. Hence, it is indicated that the crosslinking structure has more effect on tensile strength than that of hydrolysis effect during degradation. According to the analysis and study on the performance changes of PBAT/ADR materials under the conditions of long-term natural weathering (360d) and artificial weathering (600 h), this work provides theoretical guidance to produce PBAT mulching films with excellent performance.

Microcellular foaming of poly(lactic acid) branched with food‐grade chain extenders

AbstractThis study evaluated the effectiveness and efficiency of two food‐grade multifunctional epoxies chain extenders (CE) in branching PLA and improving its foamability. Both CE grades were effective in branching PLA causing increased end mixing torque, shear, elongational viscosities, molecular weight but decreased crystallinity of poly(lactic acid) (PLA) with CE content, due to chain entanglements. CE with low epoxy equivalent weight (EEW) was more efficient than the counterpart with high EEW due to its high reactivity. Neat PLA foams showed poor cell morphology with areas without nucleated cells and had a low expansion, owing to its low elongational viscosity. By contrast, there was a considerable change in the morphology of the PLA foam structure caused by its branching. Chain‐extended PLA foams had uniform cell morphology with a high void fraction (up to ~85%) and expansion ratio (an eightfold expansion over unfoamed PLA) due to their high elongational viscosities, suggesting that melt properties of branched PLA were appropriate for optimum cell growth and stabilization during foaming. Overall, CE with low EEW was the most effective grade and 0.25% the optimum content that provided appropriate melt viscosity to produce PLA foams with a homogeneous structure, fine cells, high void fraction, high volume expansion ratio, and cell‐population density.

Synthesis and performance of flexible epoxy resin with long alkyl side chains via click reaction

AbstractEpoxy resin is a thermosetting polymer with excellent performance and wide application. However, it suffers from low toughness and high brittleness because of its high crosslink density. To overcome these disadvantages, this study synthesizes a toughened, flexible, and hydrophobic epoxy resin (DGEBDBP) by introducing a flexible segment into the polymer network via a thiol‐ene click reaction. The cured flexible epoxy resin is obtained by mixing E44, DGEBDBP, and polyamide curing agents of varying contents. The long alkyl side chains significantly improve the mechanical properties and hydrophobicity of the cured epoxy resin. The sample containing 75% DGEBDBP and 25% E44 achieve the highest breaking elongation that was nine times that of pure E44, the highest compressive strength of 112.8 MPa, and the highest contact angle of 101.4°. The introduction of side chains through the thiol‐ene click reaction can provide a simple and effective method for designing and preparing multifunctional epoxy resins.

Evolution of cell morphology from sub-macroscale to nanoscale in modified thermoplastic polyether ester elastomer via supercritical CO2 foaming

Modified thermoplastic polyether ester elastomer (TPEE) foams with the cell size from sub-macroscale to nanoscale were prepared by solid-phase batch foaming in the presence of supercritical CO2 (scCO2). Multifunctional epoxy chain extender (CE) with the functionality of 9 was incorporated into TPEE to form a moderate crosslinking structure. The rheological property and crystallization behavior of modified TPEE were investigated, and then the cell morphologies of as-prepared TPEE foams were analyzed. It was found that the introduction of branching and crosslinking structure led to an increased melt viscosity and a reduction of crystallinity of TPEE. Moreover, it was identified that the rheological property dominated the foamability at high foaming temperature of 185 °C, and then the fine sub-macroscale cells were seen. Conversely, the change of crystallization behavior mainly affected the evolution of cell morphology at low foaming temperature of 160 °C, and the foams with nano and/or micro cells are obtained. As a result, a series of TPEE foams with the cell morphology from sub-macroscale to nanoscale could be achieved by adjusting the crosslinking degree of modified TPEE and the temperature of supercritical CO2 foaming.

The synergic effect of microcapsules and titanium nanoparticles on the self-healing and self-lubricating epoxy coatings: A dual smart application

In the present study, the multi-functional smart epoxy coatings were fabricated by incorporating the 15 wt.% microcapsules containing the linseed oil and various percentage of nano-TiO2 (4, 8, 12 and 16 wt.%). The self-healing and self-lubricating abilities of these nanocomposite coatings were investigated by corrosion and wear tests. The obtained results showed that the smart coating containing the 16 wt.% nano-TiO2 had the best function in the corrosion media, due to healing a scratch in form of layer by layer. By using the microscopically analysis, it was found that the linseed oil acted as lubricant agent in the wear test. Adding 4 wt.% nano-TiO2 had the negative effect on the anti-wear properties, due to forming the nanocomposite debris. However, by increasing the percentage of nano-TiO2 up to 12 wt.%, the anti-wear properties had the enhancing trend. Improving the mechanical function of coatings, forming the nano-TiO2/linseed oil self-suspense and trapping the debris by capsule containers were the characterized mechanisms for improving the anti-wear properties. It was also realized that the formation of nano-TiO2/epoxy skin on the surface of microcapsules and agglomeration of nanoparticles had the negative effect on the wear properties of smart coatings.

Super toughened and highly ductile PLA/TPU blend systems by in situ reactive interfacial compatibilization using multifunctional epoxy‐based chain extender

AbstractThis study investigates the influence of using multifunctional epoxy Joncryl ADR 4468 chain extender (CE) on the properties of various polylactide (PLA)/thermoplastic polyurethane (TPU) (75 wt/25 wt) blend systems. The blends were based on two different TPU grades with ether‐ and ester‐based soft segment as the dispersed phase (i.e., TPUether and TPUester) and an amorphous and a semicrystalline PLA grades as the matrix (i.e., aPLA and scPLA). PLA appeared to be more compatible with the TPUester, which caused the enhancement of the impact strength and strain at break values of the blends more remarkably. The dynamic rheological experiments also confirmed that the CE revealed a better reactivity with TPUester than TPUether. This further enhanced the interfacial compatibility between the PLA and TPUester and thereby dramatically improved the impact strength and ductility of the PLA/TPUester blends, specifically those with 0.5 wt% CE. Meanwhile, aPLA as the matrix reflected the TPUs toughening effect more efficiently than scPLA. This was due to the possible shrinkage caused by the crystallization of scPLA matrix, which could deteriorate the interfacial interactions between the phases in the corresponding blends.

Development of Multi-Functional Hybrid Carbon-Based Nano-Reinforced Epoxy Adhesives

In an effort to expand the insulating behavior of adhesives, incorporated nano-sized fillers, such as multi-walled carbon nanotubes (MWCNTs) and graphene nanoplatelets (GNPs), are usually selected. Including both MWCNTs and GNPs into polymers is assumed to have complementary influence (synergy), providing a new research area. Nevertheless, limited studies have been carried out towards this hybrid direction, as it is challenging to achieve a uniform distribution of both fillers into the polymer matrix. In this work, the addition of MWCNTs and GNPs into the epoxy adhesives has been studied to increase their thermal and electrical conductivity without diminishing their mechanical properties. Three types of nano-reinforced adhesives were developed by using: 1) 2%wt. MWCNTs, 2) 8%wt. GNPs and 3) 1%wt. MWCNTs and 8%wt. GNPs. The production of nano-reinforced adhesives was achieved by using a three-roll milling technique, while during the experimental characterization single lap shear tests, thermal and electrical conductivity measurements were performed. According to the results, the introduction of nano-particles caused significant increases in electrical and thermal conductivity. MWCNTs in content of 2%wt. showed the highest improvement in the electrical conductivity (9 orders of magnitude), while GNPs in content of 8%wt. recorded the highest increase (207%) in the thermal conductivity of nano-reinforced adhesives. Finally, it was observed that the hybrid system successfully contributed to the development of a multi-functional epoxy adhesive with improved thermal and electrical properties without significantly compromising its mechanical properties.

A multifunctional epoxy structural adhesive with superior flexibility, damping and durability

In this work, we introduced MCA with a flexible long chain into epoxy resin, and the elongation at break of MCA cured epoxy resin was over 200%.

Thermal stability enhancement of poly(hydroxybutyrate-co-hydroxyvalerate) through in situ reaction

ABSTRACT Poly(hydroxybutyrate-co-hydroxyvalerate) (PHBV) has recently caught more and more attention due to its renewability, good mechanical and barrier properties, as well as marine biodegradability. However, the severe thermal degradation during processing is a major drawback and limits its application. In this work, the thermal stability of PHBV during melt-processing was investigated by incorporating reactive agents. Various contents of Di(tert-butylperoxyisopropyl)benzene (DB), Triallyl isocyanurate (TAIC) and multi-functional epoxy chain extender (ECE) were used. The mixing torque, mechanical and thermal properties were studied. The results revealed that the mixing torque of PHBV gradually decreased during 10 min of melting time and eventually dropped to 2 N.m. Upon adding ECE, the mixing torque slightly increased but still decreased during 10 min period. For the system consisting of DB/TAIC or DB/TAIC/ECE, the mixing torque reached the equilibrium and their values were roughly twofold higher than PHBV alone. The possible crosslinking reaction and torque reversion were predominantly observed when adding high contents of DB and TAIC. 1 H NMR spectra suggested the reaction of DB/TAIC and PHBV. Young’s modulus and tensile strength of system consisting of DB at 0.3 phr, TAIC at 0.1 phr and ECE at 0.5 phr increased from 1440 and 40.4 MPa to 1803 and 55.5 MPa, respectively. TGA thermograms showed that the onset temperature and inflection point were improved when adding DB/TAIC and ECE. From the findings, it indicated that the combination of DB/TAIC and ECE was one of the simplest and effective ways to improve the melt viscosity without sacrificing the mechanical properties.

Characterization of a tetrafunctional epoxy-amine coating for corrosion protection of mild steel

Epoxy resins are one of the most widely used thermosetting materials in industrial and practical applications because they exhibit excellent mechanical, thermal, and dielectric performance at commodity volume and cost. In particular, multifunctional epoxies—dense and cross-linked structured resins—are used as molding compounds, sealants, and protective coatings for many barrier-related applications. In this work, we used a tetrafunctional epoxy-amine resin as a coating for mild steel and used electrochemical impedance spectroscopy (EIS) to investigate its protection performance in a 3.5 wt % NaCl solution. The results indicate that the coating was able to resist corrosion and maintain a very high impedance modulus for more than 30 d of continuous exposure to the NaCl solution. Different resistance behaviors, as indicated by EIS, were observed for the coatings with artificially introduced damage. The coating also showed high thermal resistance and good adhesion to mild steel surfaces. This tetrafunctional epoxy-amine resin could effectively function as a high performance and corrosion resistant coating material for semiconductor, aerospace, and marine applications.

Enhancing the loading and swelling capacity of cellulose crystal through difunctional and multifunctional epoxy crosslinkers and the effects on the elasticity and plasticity: A computational study

Cellulose is known to have wide industrial applications because of its natural abundance and possibility of enhancing its physical properties through modification with crosslinkers. This study considers the impacts of the difunctional long chain and multifunctional epoxy crosslinkers. Strong agreement was observed between the computed and experimental properties which include low porosity, higher network, compactness and elasticity of multifunctional over the difunctional long-chain epoxy modified cellulose (called hydrogels). These consequentially affect the dynamic fluctuation of cellulose, plasticity, glass temperature, viscosity and conductivity. Hydrogels that were experimentally found to have higher porosity, swelling and loading ability were also observed to have stronger water interaction and gas absorption. The multivariance analysis and partial least squares (PLS) established a good relationship between the experimental and computational results. The general order of gases diffusion through the hydrogels is N2 > CH4 > O2 > CO2 with some slight variation in the specific hydrogels.

Polyhedral oligomeric silsesquioxane/epoxy coatings: a review

Nowadays, there is a need for a paradigm shift in material selection for surface coatings so as to meet the requirements of advanced systems. Polyhedral oligomeric silsesquioxanes (POSS) are three-dimensional networks with a silica-like core covered by an organic shell, a promising nanosized structure for organic coatings. The use of POSS structures in coating materials has experienced an almost erratic period over the past decade, mainly because of the synthesis of POSS being exclusive and, to some extent, expressive. However, there has been a big return to the use of POSS in coatings during the last years. Epoxy is best known for its versatility of usage as an organic coating. Hybrid organic–inorganic POSS nanostructures with unique properties are a complement to the epoxy for coating applications. The tailorable compatibility and considerable reactivity of POSS molecules towards organic groups have made them promising candidates for emerging multifunctional epoxy coatings. In this sense, the focus of this review is placed on POSS/epoxy nanocomposite coatings. The thermal, mechanical, anti-corrosion and dielectric properties of POSS/epoxy coatings have been comprehensively studied and discussed.

Film Blowing of Linear and Long-Chain Branched Poly(ethylene terephthalate).

Film blowing of Poly(ethylene terephthalate) (PET) is challenging due its inherently low melt viscosity and poor melt strength. In this study, it is shown how the rheological properties of a commercial PET can be altered by reactive extrusion using either pyromellitic dianhydride (PMDA) or a multifunctional epoxy (Joncryl® ADR 4368) as chain extender, in order to improve the processing behavior during film blowing. The modified materials were characterized by shear and elongation rheometry and relevant processing characteristics, like melt pressure, bubble stability, and film thickness uniformity, were used to assess the influence of the type of modifier on processing and product performance. It is shown that PMDA is useful to increase the melt strength which leads to an improved bubble stability, while epoxy modified PET shows a reduced drawability that can cause problems at high take-up ratios. On the other hand, the epoxy modifier indicates a pronounced strain hardening during elongational deformation, and therefore leads to a better film thickness uniformity compared to the neat PET and the PET modified with PMDA. The differences with respect to processing performance are discussed and ascribed to the molecular structure of the materials.

Improvement in Toughness of Poly(ethylene 2,5-furandicarboxylate) by Melt Blending with Bio-based Polyamide11 in the Presence of a Reactive Compatibilizer

The objective of this study was to improve the toughness of bio-based brittle poly(ethylene 2,5-furandicarboxylate) (PEF) by melt blending with bio-based polyamide11 (PA11) in the presence of a reactive multifunctional epoxy compatibilizer (Joncryl ADR®-4368). The morphological, thermal, rheological, and mechanical properties of PEF/PA11 blends were investigated. Compared with neat PEF, the toughness of PEF/PA11 blend was not improved in the absence of the reactive compatibilizer due to the poor compatibility between the two polymers. When Joncryl was incorporated into PEF/PA11 blends, the interfacial tension between PEF and PA11 was obviously reduced, reflecting in the fine average particle size and narrow distribution of PA11 dispersed phase as observed by scanning electron microscopy (SEM). The complex viscosities of PEF/PA11 blends with Joncryl were much higher than that of PEF/PA11 blend, which could be ascribed to the formation of graft copolymers through the epoxy groups of Joncryl reacting with the end groups of PEF and PA11 molecular chains. Thus, the compatibility and interfacial adhesion between PEF and PA11 were greatly improved in the presence of Joncryl. The compatibilized PEF/PA11 blend with 1.5 phr Joncryl exhibited significantly improved elongation at break and unnotch impact strength with values of 90.1% and 30.3 kJ/m2, respectively, compared with those of 3.6% and 3.8 kJ/m2 for neat PEF, respectively. This work provides an effective approach to improve the toughness of PEF which may expand its widespread application in packaging.

Multifunctional epoxy composites with highly flame retardant and effective electromagnetic interference shielding performances

Multifunctional epoxy composites with low flammability, high ablation resistance, superior electrical conductivity and outstanding electromagnetic interference (EMI) shielding performances are prepared by a two-step procedure. The first step involves pyrolysis of lignin-resorcinol-glyoxal pre-polymer into carbon foams, while the second step is infiltrating flame retardant epoxy resins (FREP) into the highly porous carbon foams. SEM images show that the three-dimensional network microstructure of carbon foams is integrally preserved during infiltration by the epoxy resins, which could serve as an effective pathway for electron transport. For the flame-retardant carbon foam/epoxy (FREP-CF) composite, a UL-94 V-0 classification is achieved. In the cone calorimeter measurement, the peak heat release rate and the total heat release of the FREP-CF composite are reduced by 64% and 37%, respectively, compared to those of the original epoxy resin. The FREP-CF composite can resist approximately 1000 °C flame for 10 min with the temperature on the back side lower than 200 °C, which is much better than the EP-CF composite. Additionally, a notable electrical conductivity of 216 S/m and a superior EMI shielding effectiveness of 33.5 dB are achieved for the FREP-CF composite. This multifunctional epoxy composite enables it a promising candidate for electronics, aerospace and transportation applications.

Damping assessment of new multifunctional epoxy resin for aerospace structures

The increasing demand for more advanced materials, particularly in the aerospace field, has led to the development of carbon-fiber-reinforced composite manufactured employing different kinds of nanoparticles. The reinforcement with Carbon Nanotubes (CNTs) allows the modulation of several characteristics of the composite, which becomes suitable for more extreme operating conditions. Furthermore, the incorporation of CNTs in polymeric matrices of composite materials allows them to be electrically conductive, and hence suitable for developing self-responsive/self-protective materials characterized by a combination of properties strongly requested for replacing the traditional composites. In addition, detection of specific electrical properties can be used to develop self health-monitor composites subjected to damages due to static and dynamic loads. For instance, damage detection through conductivity measurements offers many advantages when compared to traditional glass fiber optic sensors. In fact, because of their high cost, it is not possible to create a dense network of these fibers to inspect large parts of the composite and especially if the damage spreads in the material without crossing the fiber. Therefore, the use of carbon nanotubes may provide an effective solution to overcome the described limitation. As part of an intensive research activity aimed at studying the performance of innovative smart resins, in this article, the authors show the outcomes related to some of the dynamic properties of the developed resins. Relevant results related to the enhancement of dissipative phenomena have been found in formulation modified with elastomeric phase e CNTs.

Inorganic-organic gel electrolytes with 3D cross-linking star-shaped structured networks for lithium ion batteries

Abstract Inorganic–organic electrolytes with 3D cross-linking star-shaped structured networks (3D-GPEs), consisting of multifunctional epoxy POSS and rich EO unites, are proposed for lithium ion batteries. Here, multifunctional epoxy POSS, epoxy and amino monomers containing rich EO units are chosen to build tough and compact 3D network membranes as host polymer to guarantee fast ion transport through epoxy ring-open polymerization with no initiator or no small molecule by-products generating. The electrochemical properties of 3D-GPEs and the performances of Li/LiFePO4 cells assembled with 3D-GPEs were investigated. As a result, the ionic conductivity of 3D-GPEs containing POSS is up to 2.35 × 10−3 S cm−1 at room temperature, which is almost two times than that of the GPEs without POSS. The electrochemical windows of the 3D-GPEs containing POSS are wide up to 5.25 V, indicating excellent electrochemical stability. The Li/3D-GPEs/LiFePO4 batteries exhibit good cycling performance and high rate capability. Moreover, Li/LiFePO4 cells assembled with 3D-GPEs containing POSS deliver higher discharge capacity. The discharge capability of LiFePO4/ 3D-GPE/Li is 148 mAh g−1 with excellent capacity retention after 80th cycle at 0.1C at room temperature.

Improving the Toughness and Thermal Resistance of Polyoxymethylene/Poly(lactic acid) Blends: Evaluation of Structure-Properties Correlation for Reactive Processing.

The study focuses on the development of polyoxymethylene (POM)/poly(lactic acid) (PLA) blends with increased impact and thermal resistance. The study was conducted in two phases; in the first part, a series of unmodified blends with PLA content of 25, 50, and 75 wt.% was prepared, while the second part focused on the modification of the PLA/POM (50/50) blends. An ethylene/butyl acrylate/glycidyl methacrylate terpolymer (E/BA/GMA) elastomer (EBA) was used to improve the impact strength of the prepared blends, while reactive blending was used to improve interfacial interactions. We used a multifunctional epoxy chain extender (CE) as the compatibilizer. Static tensile tests and notched Izod measurement were used to evaluate the mechanical performance of the prepared samples. The thermomechanical properties were investigated using dynamic mechanical thermal analysis (DMTA) analysis and heat deflection temperature (HDT)/Vicat softening temperature (VST) methods. The crystallinity was measured using differential scanning calorimetry (DSC) and wide-angle X-ray diffraction (WAXS) measurements, while the rheology was evaluated using a rotational rheometer. The paper also includes a structure analysis performed using the SEM method. The structural tests show partial miscibility of the POM/PLA systems, resulting in the perfect compatibility of both phases. The impact properties of the final blends modified by the EBA/CE system were found to be similar to pure POM resin, while the E modulus was visibly improved. Favorable changes were also noticeable in the case of the thermomechanical properties. The results of most of the conducted measurements and microscopic observations confirm the high efficiency of the reaction for PLA as well as for the modified POM/PLA mixtures.

Anderson-type polyoxometalate-based hybrid with high flame retardant efficiency for the preparation of multifunctional epoxy resin nanocomposites

Transition metal oxides based catalytic carbonization have been proved to be a promising way to enhance polymer flame retardancy, but finding better way to introduce organic phosphorus and transition metal oxide hybrids into polymer matrix to form nanocomposites is still a great challenge. In this work, an organic phosphorus and metal oxide hybrid compound named P–MnMo6 was prepared through combining 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) with polyoxometalate (POM). The as-prepared P–MnMo6 had a center of [MnMo6O18]3- and was used as the precursor of transition metal oxides to improve the flame retardancy of epoxy resin (EP). With the aid of the organic modification, the addition of P–MnMo6 not only maintained the transparency of EP but also enhanced the dynamic mechanical properties. Notably, the thermogravimetric analysis showed that the char yield of EP/P–MnMo6 composite increased significantly. Besides, epoxy with 8 wt% addition of P–MnMo6 passed the vertical burning grade (UL-94) V-0 rating with the limiting oxygen index (LOI) value of 30.4%. Cone calorimeter test indicated the peak heat release rate of EP/P–MnMo6-4 decreased by 41%. Meanwhile, smoke products and CO were greatly suppressed. In addition, the potential flame retardancy mechanism of P–MnMo6 in epoxy matrix was proposed.