Cured Resin Systems Research Articles

Research on the formulation and performance of high-strength resin matrix T1 for wet winding

Aiming at the higher requirements on the performance of composite materials put forward by new specialized equipment, the development of new high-performance winding resin is carried out. First, basing on the epoxy curing system, the selection of the main resin has been completed, we select the appropriate curing agent according to the characteristics of the screened trifunctional glycidylamine epoxy resin and trifunctional alicyclic epoxy resin, the ratio is calculated and optimised, the curing system is established, and the design of the resin formulation system is completed. Second, according to the nature of the resin curing system, the toughening method is screened, and the synergistic enhancement of heat resistance and toughness of the resin is accomplished through the core-shell nano-toughening method. Finally, the glass transition temperature of the new high-performance winding resin T1 is 165.12°C, and the fracture toughness of the resin KIC can reach 1.74MPa-m1/2, and the annular tensile strength of the T1 resin-based T700 carbon fibre composites can reach 3500MPa, which meets the requirements of the design indexes of specialized equipment.

3D printing of electrically conductive and degradable hydrogel for epidermal strain sensor

Owing to superior electrical conductivity, stretchability, and biocompatibility, electrically conductive hydrogels have been widely applied in flexible wearable strain sensors. Generally, conductive fillers are required to be modified to enhance the dispersion stability in hydrogels, increasing the complexity of the experiment. Additionally, due to the intrinsic chemical and physical crosslinking networks, traditional hydrogels are not degradable, resulting in severe environmental pollution problems. Herein, we designed an electrically conductive and degradable hydrogel for the epidermal strain sensor through a facile digital light processing (DLP) three-dimensional (3D) printing technology. A three-step strategy of ultraviolet (UV) curing, ion sputtering, and water spraying was innovatively developed for alleviating the complexity and difficulty in preparing electronic-based hydrogels, and a mono-functional resin curing system was employed to endow hydrogels with promising degradability. This work opens a new path for the preparation of electrically conductive hydrogels and addresses the issues of environmental pollution caused by electronic waste.

Development and Evaluation of Large-Size Phase Change Proppants for Fracturing of Marine Natural Gas Hydrate Reservoirs

The stimulation method of the marine natural gas hydrate (NGH) reservoir through hydraulic fracturing has been proposed to resolve the problem of the low production capacity in the conventional development method of pressure drawdown. Nevertheless, due to the strong plasticity and high argillaceous siltstone content of the marine NGH reservoir, conventional small-particle-size proppant cannot form effective support for fractures after fracturing because of serious embedding in the reservoir. To solve this problem, the large-size phase change proppants were developed in this study. First, an epoxy resin curing system that can reduce curing time to 40 min in low temperature and humid environment was developed. Then, the epoxy resin and curing system was emulsified, and through the optimization of the emulsification process, the particle size of the proppant can be controlled in 0.5–4.5 mm and the cementation between the proppant particles during the curing process can be prevented. Finally, the proppant performances were evaluated. The performance evaluation shows that the cured proppants have regular structure and good compressive strength, and the emulsion proppants have good transport capacity. Their large sizes provide effective propping effects for fractures generated in weakly cemented clayey silt marine NGH reservoirs.

Study on an Epoxy Resin System Used to Improve the Elasticity of Oil-Well Cement-Based Composites

Oil-well cement-based materials have inherent brittleness; therefore, they cannot be directly used to seal oil and gas wells for a long time. To improve the elasticity of oil-well cement-based composites, a flexible epoxy resin system was developed. The flexibility, TG, and SEM of the cured resin system were evaluated. At the same time, the resin was added to oil-well cement-based materials to improve its elasticity. The compressive strength and elastic modulus of resin cement stone were tested, and the microstructure was analyzed by XRD, TG, and SEM/EDS. The results showed that the structure of the cured resin is compact, the thermal decomposition temperature is 243.9 °C, and it can recover its original shape after compression. At the curing age of 28 days, the compressive strength of cement-based composites containing 30% resin decreased by 26.7%, while the elastic modulus significantly decreased by 63.2%, and the elasticity of cement-based composites was significantly improved. The formation of hydration products (e.g., calcium silicate hydrate, and calcium hydroxide) in the resin cement slurry is obviously lower than that of pure cement, which is the reason for the decrease in compressive strength. The flexible structure of polymer particles and polymer film formed by epoxy resin is distributed inside the cement stone, which significantly improves the elasticity of oil-well cement-based composites. The results of this paper are helpful for the design of elastic cement slurry systems.

Zeolitic Imidazolate Frameworks as Latent Thermal Initiators in the Curing of Epoxy Resin.

The curing of a mixture of glycidyl phenyl ether (GPE) and hexahydro-4-methylphthalic anhydride (MHHPA) with zeolitic imidazolate frameworks (ZIFs)—ZIF-7, ZIF-8, ZIF-11, and ZIF-14—as latent thermal initiators has been critically evaluated. For ZIF-8 and ZIF-14, the % conversion values for GPE were 92 and 93%, respectively, for curing at 100 °C and for 1 h. With regard to the stability of ZIF-8 and ZIF-14 in the GPE-MHHPA mixture, the % conversion values for GPE were 11 and 12% for storage over 8 days at 25 °C. The ZIF-8 and ZIF-14 initiators exhibited excellent thermal latency for heating at 100 °C and showed good stability for storage at 25 °C. To evaluate the practicality of the resin curing system, the reactions of 2,2-bis(4-glycidyloxyphenyl)propane (DGEBA) and MHHPA with ZIFs were studied by differential scanning calorimetry. Prominent exothermic peaks for ZIF-8 and ZIF-14 were observed at 157 and 162 °C, respectively; by comparison, for the commercially available microencapsulated latent thermal initiators HX-3088 and HX-3722, the respective peak maxima were 177 and 181 °C, respectively. The exothermic peak maxima for ZIF-8 and ZIF-14 were lower than those for HX-3088 and HX-3722. The ZIF-8 and ZIF-14 initiators can be stored in precured epoxy resin at 25 °C and cured by lower temperatures compared with commercially-available initiators HX-3088 and HX-3722.

Optimal design and experimental investigation of teeth connection joint on a filament wound composite transmission shaft

Abstract For limited weight reduction and avoidance of composite damage caused by the press mounting of the traditional metal teeth press-fit joint, a novel teeth connection joint technique of the fiber wound composite transmission shaft was investigated by theoretical analysis, finite element simulation, and experiment verification. Based on the mechanics of composite materials, the expressions of equilibrium torsional stiffness and static torsional strength were derived. According to the three-dimensional Chang-Chang failure criterion, its finite element model of progressive damage analysis was established through the user material subroutine. Applying the fast curing resin system, a typical sample of the structure was prepared through co-curing for the static torsional strength test, and its failure details of the fracture surface were observed by using a scanning electron microscope, which confirmed the validity of theoretical and numerical results. Based on this, the influence of the ply method and geometric characteristics on the failure strength was studied, and the optimal design of the joint was realized by the genetic algorithm. Compared with the press-fit joint, this structure reduces weight by 70 % under the same joint strength, which provides a new way for the connection of the composite transmission shaft.

Influence of resin curing cycle on the deformation of filament wound composites by in situ strain monitoring

The residual stress of metal liners wrapped by composite materials has a significant influence on the service performance of rotating parts, such as flywheel rotors and motor jackets. However, the deformation of the liners, the flow of resins, and the temperature variation during the winding process make it difficult to predict and control this residual stress. In this paper, the process-induced strains were monitored online by a strain gauge with the help of a wireless strain meter. The evolution of this strain during the manufacturing process was fully discussed. A rapid curing resin system was used and its curing properties were tested by differential scanning calorimetry. The mechanical properties of the resin matrix and its composite were characterized. The effect of the curing cycle on the evolution of the residual strain was discussed in detail through comparative experiments. The experimental results show that the use of infrared radiation has a significant advantage regarding residual stress accumulation. This advantage is greater when carbon fiber is used than when glass fiber is used. The prestress in composites of glass fiber and carbon fiber increases by 5.9% and 41.7%, respectively, after cooling.

Orthogonal experimental analysis of the material ratio and preparation technology of single-component epoxy resin for asphalt pavement crack repair

This study conducts orthogonal experiments on a single-component epoxy resin curing system (SCECS) for repairing asphalt pavement cracks based on orthogonal table of L1837 to optimise its material proportion and preparation technology; slurry viscosity, curing of the tensile bond strength, tensile strength, and breaking elongation were adopted as the performance evaluation indices. The results showed that the mixing time, water volume, toughening agent amount, and curing agent amount are factors that have the most significant influence on the performance evaluation indices of the cured material. The optimal epoxy resin main agent, diluent and toughening agent ratio of epoxy resin base fluid is 1:2:3, the optimal PCA dosage is 20% of epoxy resin base fluid, and the optimal water dosage is 30% of the total amount of epoxy resin base fluid and PCA. The optimal preparation condition of the SCECS are 30% water consumption, 60 °C water temperature, 5 min stirring time, and 600 r/min stirring speed.

Preparation and curing behavior of latent 2‐PhIm‐PS microcapsule curing agent for epoxy resin

AbstractA core–shell microcapsule latent epoxy curing agent (2‐PhIm‐PS) is obtained by solvent evaporation method with 2‐phenyl imidazole (2‐PhIm) as the core material and polystyrene (PS) as the wall material. The microcapsule parameters, morphology, structure, curing behavior, and the mechanic properties of cured epoxy resin with this microcapsule latent curing agent were characterized through comparing with 2‐PhIm. The particle size distribution of the microcapsule is narrow, the average particle size is about 10.56 μm, and the core material content is 23%. The prepared 2‐PhIm‐PS microcapsule curing agent has excellent latent curing properties. It can completely cure epoxy resin E‐51 within 10 min at 130°C, and its latent period can be more than 40 days at room temperature. In addition, the curing kinetics of one‐component epoxy resin curing system (E‐51/2‐PhIm‐PS) composed of 2‐PhIm‐PS microcapsules and epoxy resin E‐51 is also studied by using Kissinger equation, Flynn–Wall–Ozawa and Crane formula. The results provide an outline for the evaluation on the applicability of the microcapsule curing agent of 2‐PhIm‐PS for epoxy resin.

Carborane-containing bismaleimide resins with excellent heat resistance and dimensional stability

Novel carborane-containing bismaleimides with excellent heat resistance and dimensional stability for advanced composites are presented. First, a new kind of carborane-containing mono-maleimido-terminated monomer 1-(4-tolyl)-2-(4-maleimido phenyl)- o-carborane (CB-MI) was synthesized and characterized by FT-IR and 1H-NMR. Then, it was used as a modifier for bismaleimide resin 4,4’-bismaleimidodiphenylmethane (BDM) with different weight fraction of CB-MI. The curing behavior and thermal property of the CB-MI/BDM resin systems were studied and presented here. Results displayed that a wide processing window and low curing temperature provided a good processability for the CB-MI/BDM resin system. Due to the effect of carborane groups, the char yield at 600°C of the cured resin systems tended to be increased with the addition of CB-MI. Moreover, the coefficient of thermal expansion of the resin was found to be reduced with the increase of CB-MI, indicative of a remarkable dimensional stability. This study might open up great opportunities for the preparation and design of various novel bismaleimides in a simple and feasible way and the resins with good thermal property and processability at the same time.

Characterization of moisture states and transport in MUF resin-impregnated poplar wood using low field nuclear magnetic resonance

In this study, the spin–spin relaxation time (T2) distributions of free water and bound water, as well as the moisture content (MC) profiles of MUF resin-impregnated poplar wood (Populous tomentosa) sample (RI) were investigated by low-field nuclear magnetic resonance, with the aim of providing insights into how MUF resin impregnation affects the moisture states and moisture transport in modified poplar wood during drying. The T2 curves demonstrated that the resin treatment did not increase the number of peaks in the T2 distributions, but affected the T2 value as compared to the control. Above the fiber saturation point (FSP), the T22 (corresponds to the free water in wood rays and wood fibers) of the RI sample exhibited an increase compared to the control, while the T23 (corresponds to the free water in the vessels) was almost unchanged. Below the FSP, a shorter T21 (corresponding to the bound water) of the RI sample was observed compared to the control. The drying curves and MC profiles indicated a significant difference in the moisture transport in the RI sample as compared to the control. The gradually cured resin system in the wood surface layer during drying provided a barrier for the transfer of water in the center layer toward to the surface, causing the resin curing reactions in the surface and core layers to be out of sync. Therefore, a more significant MC gradient was observed for the resin-impregnated sample.

Effect of Blending Modifications for Phenylethynyl-terminated Polyimides

A reactive diluent (ODA-PEPA) and a flexible phenylethynyl-terminated imide oligomer (PEI-PEPA) were designed and synthesized based on the 2,3,3’,4’-diphenyl ether tetracarboxylic acid dianhydride (a-ODPA), 3,4’-oxydianiline (3,4’-ODA), and 4-phenylethynylphthalic anhydride (PEPA). Solution blended systems with the addition of 5, 10, and 15 wt% ODA-PEPA to PEI-PEPA oligomer and their cured resin systems were prepared. Results showed that ODA-PEPA is semi-crystalline in nature. The Tg values of cured resins were improved from 273 °C to 280 °C by the addition of ODA-PEPA, due to the higher crosslink densities. In addition, rheological properties of blends showed lower melt viscosity and wider processing window, revealing improved melt processabilities for potential application in making advanced composites. The isothermal viscosity in 280 °C of PEI-PEPA containing 15 wt% ODA-PEPA reactive diluent decreased by two thirds, due to the low molecular weight of ODA-PEPA. The cured blends demonstrated high thermal stability and heat resistance. 5 wt% thermal decomposition temperatures (Td5) of the cured blends were above 549 °C and 547 °C in N2 and air atmosphere, respectively. The char yield reported at 800 °C in N2 atmosphere increased from 58.8% to 63.7 % with the addition of ODAPEPA. Meanwhile, the cured polyimides blends possessed good bond strength (> 9.3 MPa).

Shape recovery characteristics of shape memory cyanate ester/epoxy composite reinforced with calcium sulfate whisker

Purpose The purpose of this paper is to study the influence of calcium sulfate whiskers (CSWs) on the thermodynamic properties and shape memory properties of epoxy/cyanate ester shape memory composites. Design/methodology/approach To improve the mechanical properties of shape memory cyanate ester (CE)/epoxy polymer (EP) resin, high performance CSWs were used to reinforce the thermo-induced shape memory CE/EP composites and the shape memory CSW/CE/EP composites were prepared by molding. The effect of CSW on the mechanical properties and shape memory behavior of shape memory CE/EP composites was investigated. Findings After CSW filled the shape memory CE/EP composites, the bending strength of the composites is greatly improved. When the content of CSW is 5 Wt.%, the bending strength of the composite is 107 MPa and the bending strength is increased by 29 per cent compared with bulk CE/EP resin. The glass transition temperature and storage modulus of the composites were improved in CE/EP resin curing system. However, when the content of CSW is more than 10 Wt.%, clusters are easily formed between whiskers and the voids between whiskers and matrix increase, which will lead to the decrease of mechanical properties of composites. The results of shape memory test show that the shape memory recovery time of the composites decreases with the decrease of CSW content at the same temperature. In addition, the shape recovery ratio of the composites decreased slightly with the increase of the number of thermo-induced shape memory cycles. Research limitations/implications A simple way for fabricating thermo-activated SMP composites has been developed by using CSW. Originality/value The outcome of this study will help to fabricate the SMP composites with high mechanical properties and the shape memory CSW/CE/EP composites are expected to be used in space deployable structures.

Flame-retardancy, thermal and coating properties of P-containing poly-acrylate resin cured with MF resin

PurposeThe flammability of poly-acrylate (PA) resin is a major disadvantage in applications that require flame resistance. Many studies, including the authors’ previous study, have proved that covalent-incorporated phosphorous-containing (P-containing) monomer onto the PA resin can exhibit better flame resistance than that by an additive approach. However, other properties such as thermal stability, coating properties are still deteriorated. To further improve the flame-retardancy and other comprehensive properties of the P-containing PA resin, in this study, melamine formaldehyde(MF) resin was used not only as a curing agent to enhance the coating properties of the PA resin, but also as a nitrogen-containing (N-containing) resin to form a P-N synergistic effect and therefore further improve its flame retardancy.Design/methodology/approachEpoxy resin phosphorous acid-modified (EPPA-modified) PA (EPPA-PA) resin was first prepared and then using MF resin as curing agent. The flame retardancy of the cured resin was tested by the limiting oxygen index (LOI) and UL 94 methods. The thermal stability of the cured resin was studied by TGA. The coating technology such as adhesion property, pencil hardness and anti-solvent properties were characterized according to methods of International Standards ISO2409-1992, ISO 15184-1998 and ISO-15184-2012, respectively. The micro-char morphology of the char residue was observed by SEM.FindingsThe results showed that by using MF resin as curing agent has provided the PA resin with excellent coating properties and thermal stability, but also gave a P-N synergistic effect which has greatly enhanced the flame retardancy of the cured resin. The cured resin system containing only 1.7 Wt.% P content and 5.3 Wt.% N content can reach a LOI of 26.9 per cent and pass the V-0 rating in the UL-94 test.Research limitations/implicationsThis resin system releases formaldehyde due to the MF resin.Practical implicationsIt is expected that the large-scale production of this EPPA-PA resin cured by MF resin system will enable practical industrial applications.Originality/valueThis method for the synthesis of a P- and N-containing PA resin system is newfangled.

Preparation of a Novel Phosphorus-Nitrogen Containing Novolac Curing Agent for Epoxy Resin and flame-retardancy of its cured epoxy resin

ABSTRACTIn this study, DICY (dicyandiamide)-containing novolac (NN) was first prepared, and then DOPO (9,10-Dihydro-9-oxa-10-phosphaphenanthrene-10-oxide) was introduced to react with the unsaturated bonds from DICY to obtain a novel phosphorus-nitrogen-containing novolac resin (PNN), which was used as a curing agent for epoxy resins. The curing condition was confirmed by a non-isothermal curing kinetics study. The thermal stability and flame retardancy of the cured epoxy resin system were studied by thermogravimetric analysis (TGA), limited oxygen index (LOI) measurement, UL-94 test and cone calorimeter. The morphology of the burned chard residues was observed by Scanning electron microscopy (SEM). The results show that epoxy resin cured by the prepared PNN curing system presents excellent flame retardancy. The cured resin system, which contains only 1.31wt% phosphorus and 2.48wt% nitrogen, can achieve UL 94 V-0 rating.

Puncture properties of a hybrid continuous-discontinuous sheet moulding compound for structural applications

A novel two-step curing resin system and adapted moulding approach enables the manufacturing of hybrid continuous-discontinuous SMC in a one-shot process. Hybridization led to a significant increase of maximum force (+36%) and puncture energy (+35%) if specimens were punctured in a quasi-static manner. The effect of hybridization was less distinct under dynamic loading (increase of 13% and 7%, respectively), due to a negative rate dependency of the continuous carbon fibre SMC. An increase from 4.4·10−5 m∙s−1 to 4.4 m∙s− 1 resulted in a positive rate dependence of the hybrid SMC with increased maximum force (+33%) and puncture energy (+18%). Important failure mechanisms were inter-bundle and inter-fibre fracture of the continuous SMC and pseudo-delamination (intra-laminar) of the discontinuous component. Delamination took place at both considered loading rates but was more important if hybrid SMC was punctured in a dynamic manner.

Mechanical properties and damage evolution of a structural sheet molding compound based on a novel two step curing resin system

A novel two step curing resin system allows for the manufacturing of discontinuous, continuous and hybrid continuous-discontinuous sheet molding compound (SMC) with glass or carbon fibers. In this contribution, the discontinuous component of this innovative hybrid material, a structural glass or carbon fiber SMC, is characterized under quasi-static and dynamic loading conditions. Glass fiber SMC showed a positive loading rate sensitivity. For higher loading rates, maximum force and puncture energy increased significantly for charge (65%/67%) and flow region specimens (73%/64%). Carbon fiber SMC did not show a rate sensitivity. 1D flow of this material during compression molding leads to anisotropic mechanical properties due to fiber orientation. The microstructure of the material significantly influences damage evolution and failure, which was investigated by means of in-situ photography, SEM and μ-CT. The dominant failure mechanisms were interface failure and matrix cracking for the glass and the formation of inter-fiber fracture and inter-granular failure of pseudo-grain like microstructure for the carbon fiber SMC.

Synthesis and evaluation of catalytic curing behavior of novel nitrile-functionalized benzoxazine for phthalonitrile resins

In the present embodiment, bisphthalonitrile resin has been cured using synthesized novel bisphenyl nitrile-containing benzoxazine (NBZ) vis-a-vis traditional curing agents such as 4-(3′aminophenoxy)diphenyl sulphone (m-DDS) and amino-functionalized phthalonitrile (APN) to study the curing efficacy coupled with processing window and mechanism of curing. It has been established by FT-IR and DSC that NBZ molecules cure the bisphthalonitrile resin matrix by formation of free phenolic groups which act as nucleophile triggering the curing reaction through nitrile–nitrile addition polymerization reaction. Additionally, it has been seen that NBZ-catalyzed phthalonitrile resin curing system showed better processing window in comparison to m-DDS- and APN-catalyzed system. Considering the end-user applications, the NBZ- and m-DDS-cured resins have also been studied for their TG, DMA, water uptake, thermo-oxidative and dielectric properties.

Development of novel cardo-containing phenylethynyl-terminated polyimide with high thermal properties

A phenylethynyl-terminated reactive diluent [Card-4-phenylethynylphthalic anhydride (PEPA)], which contained fluorenyl cardo structures, was successfully synthesized and used as a modifier for flexible phenylethynyl-terminated imide oligomer (PEI-PEPA). The chemical structure, crosslink characterization, molecular weights, and thermal properties of the products were characterized. The imide systems with addition of 10, 20, 30, and 40 wt% Card-PEPA to PEI-PEPA (PEI-PEPA-Card) and their cured resin systems were prepared. The thermal curing behaviors of imide systems at different heating rates were analyzed by using differential scanning calorimetry. Thermal properties such as glass transition temperature (Tg) and char yield at 800°C of the resultant resin systems were studied by differential scanning calorimetry, dynamic mechanical analysis, and thermogravimetric analysis. The rheological properties were also investigated using a dynamic rheometry. These properties were found to be outstanding compared with pure PEI-PEPA. The uncured imide systems exhibited lower Tg and lower isothermal viscosity with addition of Card-PEPA. Furthermore, the Tg and char yield of the cured resin systems increased with addition of Card-PEPA. The cured resin systems containing 40 wt% Card-PEPA exhibited the highest Tg of 359°C and char yield at 800°C of 66.5%. Copyright © 2016 John Wiley & Sons, Ltd.

Carbon fiber-reinforced composites using an epoxy resin matrix modified with reactive liquid rubber and silica nanoparticles

Abstract Carbon fiber-reinforced composites are gaining importance and are about to play a very prominent role in automotive applications. In structural applications mainly epoxy resins are used as matrix materials. The properties of epoxy resins and laminates made thereof can be improved by tougheners like reactive liquid rubbers. Further improvements can be achieved by adding surface-modified silica nanoparticles, with 20 nm in size and a very narrow particle size distribution. In this study carbon fiber-reinforced laminates made from epoxy resins modified with reactive liquid rubber and silica nanoparticles have been prepared and investigated. A very fast amine cure of 15 min has been chosen to match industrial needs. Mechanical properties for bulk resins and laminates are compared and the mechanisms responsible for the property improvements are discussed. Structure property relationships between the neat resin fracture toughness and the interlaminar G Ic and G IIc of the reactive liquid rubber and silica nanoparticles modified resins were established. Tough laminates could be prepared. However, CAI performance of the hybrid laminates was slightly inferior as compared to the rubber-toughened laminates, most probably due to agglomerates of nanoparticles found in the cured resin systems. The reason for the nanoparticle aggregation was detected and their influence on laminate performance discussed.