Polymers

Research

19 pages, 6283 KiB

Open AccessArticle

Flexural and Viscoelastic Properties of FRP Composite Laminates under Higher Temperatures: Experiments and Model Assessment

by Getahun Tefera, Sarp Adali and Glen Bright

Polymers 2022, 14(11), 2296; https://doi.org/10.3390/polym14112296 - 5 Jun 2022

Cited by 4 | Viewed by 2552

Abstract

This study investigates an experimental and analytical study on the flexural, failure, and viscoelastic properties of hybrid and non-hybrid composite laminates at increasing temperatures and frequencies. Carbon, glass, and hybrids of the two fibre materials with stacking sequences of [0/90]_s were considered, [...] Read more.

This study investigates an experimental and analytical study on the flexural, failure, and viscoelastic properties of hybrid and non-hybrid composite laminates at increasing temperatures and frequencies. Carbon, glass, and hybrids of the two fibre materials with stacking sequences of [0/90]_s were considered, and specimens were prepared via the resin transfer moulding method. Three-point bending and dynamic mechanical analysis tools were used. The failure surfaces of the laminates were examined using a scanning electron microscope. The results indicated that the flexural strength, modulus, and strain at failure of all groups of laminates decreased as the temperature increased. In particular, the storage modulus, damping factor, flexural strength, and flexural modulus properties of all groups of laminates increased as the hybrid ratio decreased on each targeted temperature and frequency test. However, the strain at failure increased as the hybrid ratio increased. Additionally, results obtained from the scanning electron microscope images confirmed that combinations of delamination and debonding failure modes were observed on the stacking sequences of [0]_s and [90]_s layers of bidirectional laminates. Finally, a comparison between the storage modulus results of all groups of laminates was conducted with three empirical models. The empirical model developed by Gibson et al. provided the most accurate prediction for all groups of laminates in the targeted temperature and frequency range. The predictions using the remaining empirical models were broadly similar. Further work is needed to optimise the empirical parameters and minimise the errors. Full article

(This article belongs to the Special Issue Advanced Epoxy-Based Materials II)

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19 pages, 49539 KiB

Open AccessArticle

Mechanical Behavior of GFRP Laminates Exposed to Thermal and Moist Environmental Conditions: Experimental and Model Assessment

by Getahun Tefera, Sarp Adali and Glen Bright

Polymers 2022, 14(8), 1523; https://doi.org/10.3390/polym14081523 - 9 Apr 2022

Cited by 13 | Viewed by 2498

Abstract

This paper presents an experimental and analytical study about the mechanical response at a different temperature on glass fiber-reinforced polymer laminates. The effect of different environmental conditions on compressive, tensile, stiffness, and viscoelastic behavior (storage modulus, loss modulus and damping ratio) of laminates [...] Read more.

This paper presents an experimental and analytical study about the mechanical response at a different temperature on glass fiber-reinforced polymer laminates. The effect of different environmental conditions on compressive, tensile, stiffness, and viscoelastic behavior (storage modulus, loss modulus and damping ratio) of laminates were investigated. Before testing, laminates were preserved in a deep freezer at −80 °C, −20 °C, 0 °C, and room temperature (25 °C) for up to 60 days. Results confirmed that temperatures ranging from −80 to 50 °C, which were below the glass transition temperature of the epoxy resin, did not significantly affect the compressive, tensile, and stiffness performance of all laminates. When the testing temperature increased to 100 °C, the properties were decreased significantly due to the damaging of the fiber/matrix interface. Additionally, results obtained from dynamic mechanical analyses tests showed a drop-in storage modulus, high peaks in loss modulus and high damping factor at the glass transition region of the epoxy resin. The highest storage modulus, two phases of glassy states and highest damping ratio on the −80/G group of laminates were obtained. The accuracy of experimental results was assessed with empirical models on the storage modulus behavior of laminates. The empirical model developed by Gibson et al. provided accurate estimates of the storage modulus as a function of temperature and frequency. The remaining empirical models were less accurate and non-conservative estimations of laminates stiffness. Full article

(This article belongs to the Special Issue Advanced Epoxy-Based Materials II)

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17 pages, 5270 KiB

Open AccessArticle

Influence of Epoxy Resin Curing Kinetics on the Mechanical Properties of Carbon Fiber Composites

by Isidro Cruz-Cruz, Claudia A. Ramírez-Herrera, Oscar Martínez-Romero, Santos Armando Castillo-Márquez, Isaac H. Jiménez-Cedeño, Daniel Olvera-Trejo and Alex Elías-Zúñiga

Polymers 2022, 14(6), 1100; https://doi.org/10.3390/polym14061100 - 9 Mar 2022

Cited by 26 | Viewed by 4370

Abstract

In this study, the kinetic parameters belonging to the cross-linking process of a modified epoxy resin, Aerotuf 275-34™, were investigated. Resin curing kinetics are crucial to understanding the structure–property–processing relationship for manufacturing high-performance carbon-fiber-reinforced polymer composites (CFRPCs). The parameters were obtained using differential [...] Read more.

In this study, the kinetic parameters belonging to the cross-linking process of a modified epoxy resin, Aerotuf 275-34™, were investigated. Resin curing kinetics are crucial to understanding the structure–property–processing relationship for manufacturing high-performance carbon-fiber-reinforced polymer composites (CFRPCs). The parameters were obtained using differential scanning calorimetry (DSC) measurements and the Flynn–Wall–Ozawa, Kissinger, Borchardt–Daniels, and Friedman approaches. The DSC thermograms show two exothermic peaks that were deconvoluted as two separate reactions that follow autocatalytic models. Furthermore, the mechanical properties of produced carbon fiber/Aerotuf 275-34™ laminates using thermosetting polymers such as epoxies, phenolics, and cyanate esters were evaluated as a function of the conversion degree, and a close correlation was found between the degree of curing and the ultimate tensile strength (UTS). We found that when the composite material is cured at 160 °C for 15 min, it reaches a conversion degree of 0.97 and a UTS value that accounts for 95% of the maximum value obtained at 200 °C (180 MPa). Thus, the application of such processing conditions could be enough to achieve good mechanical properties of the composite laminates. These results suggest the possibility for the development of strategies towards manufacturing high-performance materials based on the modified epoxy resin (Aerotuf 275-34™) through the curing process. Full article

(This article belongs to the Special Issue Advanced Epoxy-Based Materials II)

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30 pages, 16232 KiB

Open AccessArticle

Low-Velocity Impact Behavior of Foam Core Sandwich Panels with Inter-Ply and Intra-Ply Carbon/Kevlar/Epoxy Hybrid Face Sheets

by Stanley Samlal and R. Santhanakrishnan

Polymers 2022, 14(5), 1060; https://doi.org/10.3390/polym14051060 - 7 Mar 2022

Cited by 14 | Viewed by 3773

Abstract

Sandwich composites are extensively employed in a variety of applications because their bending stiffness affords a greater advantage than composite materials. However, the aspect limiting the application of the sandwich material is its poor impact resistance. Therefore, understanding the impact properties of the [...] Read more.

Sandwich composites are extensively employed in a variety of applications because their bending stiffness affords a greater advantage than composite materials. However, the aspect limiting the application of the sandwich material is its poor impact resistance. Therefore, understanding the impact properties of the sandwich structure will determine the ways in which it can be used under the conditions of impact loading. Sandwich panels with different combinations of carbon/Kevlar woven monolithic face sheets, inter-ply face sheets and intra-ply face sheets were fabricated, using the vacuum-assisted resin transfer process. Instrumented low-velocity impact tests were performed using different energy levels of 5 J, 10 J, 20 J, 30 J and 40 J on a variety of samples and the results were assessed. The damage caused by the modes of failure in the sandwich structure include fiber breakage, matrix cracking, foam cracking and debonding. In sandwich panels with thin face sheets, the maximum peak load was achieved for the inter-ply hybrid foam core sandwich panel in which Kevlar was present towards the outer surface and carbon in the inner surface of the face sheet. At an impact energy of 40 J, the maximum peak load for the inter-ply hybrid foam core sandwich panel was 31.57% higher than for the sandwich structure in which carbon is towards the outer surface and Kevlar is in the inner surface of the face sheet. The intra-ply hybrid foam core sandwich panel subjected to 40 J impact energy demonstrated a 13.17% higher maximum peak load compared to the carbon monolithic face sheet sandwich panel. The experimental measurements and numerical predictions are in close agreement. Full article

(This article belongs to the Special Issue Advanced Epoxy-Based Materials II)

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10 pages, 2190 KiB

Open AccessArticle

Experimental and Digimat-FE Based Representative Volume Element Analysis of Dye-Mixed Colored Resin and Carbon Fiber

by Jee-Hyun Sim, Dong-Hyeon Yeo, Hyun-Sung Yoon, Seong-Hun Yu, Do-Hyun Lee and Jin-Seok Bae

Polymers 2022, 14(5), 1028; https://doi.org/10.3390/polym14051028 - 4 Mar 2022

Cited by 1 | Viewed by 3104

Abstract

Recently, the automobile industry has demanded weight reduction, so research on materials is being actively conducted. Among this research, carbon fiber-reinforced composite materials are being studied a lot in the automobile industry due to their excellent mechanical properties, chemical resistance, and heat resistance. [...] Read more.

Recently, the automobile industry has demanded weight reduction, so research on materials is being actively conducted. Among this research, carbon fiber-reinforced composite materials are being studied a lot in the automobile industry due to their excellent mechanical properties, chemical resistance, and heat resistance. However, carbon fiber-reinforced composite materials have disadvantages, in that they are not free from color selection, and have weak interfacial bonding strength. In this study, a colored epoxy resin was prepared by mixing epoxy—which is a thermosetting resin according to the pigment concentration (0.1, 0.3, 0.5, 1.0 wt%)—and curing shrinkage. Thermal expansion characteristics were analyzed and the concentration of 0.5 wt% pigment showed the lowest shrinkage and thermal expansion characteristics. In addition, to measure the interfacial shear strength (IFSS) of the carbon fiber and the colored epoxy resin, the IFSS was obtained by performing a microdroplet debonding test, and the strength of the pigment concentration of 0.5 wt% was reduced to a relatively low level. Through these experiments, it was determined that an epoxy resin in which 0.5 wt% pigment is mixed is the optimal condition. Finally, using the composite material modeling software (Digimat 2020.0), the representative volume element (RVE) of the meso-scale was set, and interfacial properties of carbon fibers and colored epoxy resins were analyzed by interworking with general-purpose finite element analysis software (Abaqus CAE). Full article

(This article belongs to the Special Issue Advanced Epoxy-Based Materials II)

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13 pages, 4839 KiB

Open AccessArticle

Preparation of a Novel Organic Phosphonic Acid Intercalated Phosphate Tailings Based Hydrotalcite and Its Application in Enhancing Fire Safety for Epoxy Resin

by Huali Zhang, Lingzi Jin, Hanjun Wu, Zhenyue Zhang, Junxia Yu, Wenjun Zhang, Yi Pan and Zhiquan Pan

Polymers 2022, 14(4), 725; https://doi.org/10.3390/polym14040725 - 14 Feb 2022

Cited by 6 | Viewed by 2316

Abstract

Phosphate tailings (PTs) are solid waste, which is produced by phosphate flotation. In this work, PTs were used as raw materials for the preparation of diethylenetriamine pentamethronic acid (DTPMP) intercalated trimetal (Ca-Mg-Al) layered double hydroxides (TM-DTPMP LDHs) by co-precipitation method. TM-DTPMP LDHs were [...] Read more.

Phosphate tailings (PTs) are solid waste, which is produced by phosphate flotation. In this work, PTs were used as raw materials for the preparation of diethylenetriamine pentamethronic acid (DTPMP) intercalated trimetal (Ca-Mg-Al) layered double hydroxides (TM-DTPMP LDHs) by co-precipitation method. TM-DTPMP LDHs were characterized by X-ray diffraction, fourier-transform infrared spectroscopy, scanning electron microscopy, differential thermal gravimetric analysis, X-ray photoelectron spectroscopy and applied as a flame retardant to improve the fire safety of epoxy resin (EP). The results showed that the composite materials exhibited obvious layered structure. After intercalation, layer spacing increased from 0.783 to 1.78 Å. When the amount of TM-DTPMP LDH in EP was 8%, the limitted oxygen index of the composite material increased from the original 19.2% to 30.2%. In addition, Cone calorimeter (CC) and Raman spectrum results indicated that with the addition of TM-DTPMP LDHs, the value of heat release rate peak (pHRR) and total heat release (THR) were reduced by more than 43% and 60%, while the value of smoke formation rate (pSPR) and the total smoke production (TSP) decreased nearly 64% and 83%, respectively. The significant reduction in the release of combustion heat and harmful smoke during EP combustion may be attributed to the synergistic flame-retardant effect between hydrotalcite and DTPMP. This work exhibited great potential for the green recycling of PTs and the enhancement of the fire safety of EP. Full article

(This article belongs to the Special Issue Advanced Epoxy-Based Materials II)

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14 pages, 4832 KiB

Open AccessArticle

Internal Polymerization of Epoxy Group of Epoxidized Natural Rubber by Ferric Chloride and Formation of Strong Network Structure

by Kriengsak Damampai, Skulrat Pichaiyut, Subhradeep Mandal, Sven Wießner, Amit Das and Charoen Nakason

Polymers 2021, 13(23), 4145; https://doi.org/10.3390/polym13234145 - 27 Nov 2021

Cited by 19 | Viewed by 2627

Abstract

In this work, studies are carried out to understand the crosslinking reaction of epoxidized natural rubber (50 mol% epoxy, ENR-50) by metal ion namely ferric ion (Fe³⁺, FeCl₃, ferric chloride). It is found that a small amount of FeCl [...] Read more.

In this work, studies are carried out to understand the crosslinking reaction of epoxidized natural rubber (50 mol% epoxy, ENR-50) by metal ion namely ferric ion (Fe³⁺, FeCl₃, ferric chloride). It is found that a small amount of FeCl₃ can cure ENR to a considerable extent. A direct interaction of the ferric ion with the epoxy group as well as internal polymerization enable the ENR to be cured in an efficient manner. It was also found that with the increased concentration of FeCl₃, the crosslinking density of the matrix increased and therefore, the ENR offers higher mechanical properties (i.e., modulus and tensile strength). In addition, the glass transition temperature (t_g) of ENR vulcanizate is increased with increasing concentration of FeCl₃. Moreover, the thermal degradation temperature (T_d) of the ENR-FeCl₃ compound was shifted toward higher temperature as increasing concentration FeCl₃. Full article

(This article belongs to the Special Issue Advanced Epoxy-Based Materials II)

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15 pages, 7250 KiB

Open AccessArticle

Investigations on Epoxy-Carbamate Foams Modified with Different Flame Retardants for High-Performance Applications

by Simon T. Kaysser, Christian Bethke, Isabel Fernandez Romero, Angeline Wo Weng Wei, Christian A. Keun, Holger Ruckdäschel and Volker Altstädt

Polymers 2021, 13(22), 3893; https://doi.org/10.3390/polym13223893 - 11 Nov 2021

Cited by 2 | Viewed by 2274

Abstract

In transport sectors such as aviation, automotive and railway, materials combining a high lightweight potential with high flame retardant properties are in demand. Polymeric foams are suitable materials as they are lightweight, but often have high flammability. This study focuses on the influence [...] Read more.

In transport sectors such as aviation, automotive and railway, materials combining a high lightweight potential with high flame retardant properties are in demand. Polymeric foams are suitable materials as they are lightweight, but often have high flammability. This study focuses on the influence of different flame retardants on the burning behavior of Novolac based epoxy foams using Isophorone Diamine carbamate (B-IPDA) as dual functional curing and blowing agent. The flame retardant properties and possible modifications of these foams are systematically investigated. Multiple flame retardants, representing different flame retardant mechanisms, are used and the effects on the burning behavior as well as mechanical and thermal properties are evaluated. Ammonium polyphosphate (APP), used with a filler degree of 20 wt.% or higher, functions as the best performing flame retardant in this study. Full article

(This article belongs to the Special Issue Advanced Epoxy-Based Materials II)

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12 pages, 9535 KiB

Open AccessArticle

Parametric Analysis of Epoxy/Crumb Rubber Composite by Using Taguchi—GRA Hybrid Technique

by Kiran Shahapurkar, Venkatesh Chenrayan, Belay Brehane Tesfamarium, Manzoore Elahi M. Soudagar, Nazia Hossain, Ali A. Rajhi, Sagr Alamri, Ibrahim M. Alarifi, Pavan Shahapurkar, M. A. Mujtaba, M. C. Kiran and Gulam Mohammed Sayeed Ahmed

Polymers 2021, 13(19), 3441; https://doi.org/10.3390/polym13193441 - 7 Oct 2021

Cited by 9 | Viewed by 2370

Abstract

Effect of parameters affecting solid particle erosion of crumb rubber epoxy composite is investigated. Five important process parameters—impact velocity, impingement angle, standoff distance, erodent size, and crumb rubber content—are taken into consideration. Erosion rate and erosion efficiency are included as the chief objectives. [...] Read more.

Effect of parameters affecting solid particle erosion of crumb rubber epoxy composite is investigated. Five important process parameters—impact velocity, impingement angle, standoff distance, erodent size, and crumb rubber content—are taken into consideration. Erosion rate and erosion efficiency are included as the chief objectives. The Taguchi coupled gray relational analysis type statistical model is implemented to study interaction, parameters’ effect on responses, and optimized parameters. ANOVA and regression model affirmed impingement angle and crumb rubber content play a significant role to minimize the erosion. Validity of the proposed model is justified with the standard probability plot and R² value. A confirmation experiment conducted with A₂B₂C₃D₃E₃ condition registers noticeable enhancement in GRG to the tune of 0.0893. Full article

(This article belongs to the Special Issue Advanced Epoxy-Based Materials II)

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12 pages, 3268 KiB

Open AccessArticle

Effect of Silica Nanoparticles Blocked with Epoxy Groups on the Crosslinking and Surface Properties of PEG Hydrogel Films

by Junyoung Park, Nahee Kim, Kevin Injoe Jung, Soomin Yoon, Seung Man Noh, Joona Bang and Hyun Wook Jung

Polymers 2021, 13(19), 3296; https://doi.org/10.3390/polym13193296 - 27 Sep 2021

Cited by 5 | Viewed by 2613

Abstract

Silica nanoparticles (G-SiNPs) blocked with 3-glycidoxypropyl trimethoxysilane (GPTS) were newly applied to hydrogel films for improving film coating properties and to distribute the epoxy groups on the film surface. The effects of the content of epoxy-functionalized G-SiNPs on the crosslinking features by photo-induced [...] Read more.

Silica nanoparticles (G-SiNPs) blocked with 3-glycidoxypropyl trimethoxysilane (GPTS) were newly applied to hydrogel films for improving film coating properties and to distribute the epoxy groups on the film surface. The effects of the content of epoxy-functionalized G-SiNPs on the crosslinking features by photo-induced radical polymerization and the surface mechanical properties of the hydrogel films containing poly(ethylene glycol) dimethacrylate (PEGDMA) and glycidyl methacrylate (GMA) were investigated. The real-time elastic modulus of various PEG hydrogel mixtures with prepared particles was monitored using a rotational rheometer. The distribution of epoxy groups on the crosslinked film surface was directly and indirectly estimated by the elemental analysis of Si and Br. The surface mechanical properties of various hydrogel films were measured by nano-indentation and nano-scratch tests. The relationship between the rheological and surface properties of PEG-based hydrogel films suggests that the use of small amounts of G-SiNPs enhances the surface hardness and crosslinked network of the film and uniformly distributes sufficient epoxy groups on the film surface for further coating applications. Full article

(This article belongs to the Special Issue Advanced Epoxy-Based Materials II)

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15 pages, 5976 KiB

Open AccessArticle

Fabrication of Diaminodiphenylmethane Modified Ammonium Polyphosphate to Remarkably Reduce the Fire Hazard of Epoxy Resins

by Feiyue Wang, Jiahao Liao, Long Yan and Hui Liu

Polymers 2021, 13(19), 3221; https://doi.org/10.3390/polym13193221 - 23 Sep 2021

Cited by 18 | Viewed by 2820

Abstract

A novel diaminodiphenylmethane (DDM) modified ammonium polyphosphate (APP) flame retardant, DDP, was successfully synthesized via ion-exchange reaction. DDP was introduced into epoxy resins (EPs) to reduce flammability. A comparable level of DDP exerts better flame-retardant and smoke suppression efficiencies in EP than APP. [...] Read more.

A novel diaminodiphenylmethane (DDM) modified ammonium polyphosphate (APP) flame retardant, DDP, was successfully synthesized via ion-exchange reaction. DDP was introduced into epoxy resins (EPs) to reduce flammability. A comparable level of DDP exerts better flame-retardant and smoke suppression efficiencies in EP than APP. An EP blend containing 15 wt% DDP displays a limiting oxygen index (LOI) value of 37.1% and a UL 94 V-0 rating, and further exhibits a 32.3% reduction in total heat release and a 48.0% reduction in total smoke production compared with pure EP. The presence of DDP greatly facilitates char formation during combustion, and the char mass from thermal decomposition of an EP blend is 37.8% smaller than that of an EP blend containing 15 wt% DDP at 800 °C. The incorporation of DDP into EP blends has a smaller impact on the glass transition temperature and tensile strength than those of a comparable level of APP. This reflects the better compatibility of DDP with the EP matrix compared with that for APP. Full article

(This article belongs to the Special Issue Advanced Epoxy-Based Materials II)

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16 pages, 4722 KiB

Open AccessArticle

Characterization of Cure Behavior in Epoxy Using Molecular Dynamics Simulation Compared with Dielectric Analysis and DSC

by Shuang Yan, Wolfgang Verestek, Harald Zeizinger and Siegfried Schmauder

Polymers 2021, 13(18), 3085; https://doi.org/10.3390/polym13183085 - 13 Sep 2021

Cited by 13 | Viewed by 3281

Abstract

The curing behavior of a thermosetting material that influences the properties of the material is a key issue for predicting the changes in material properties during processing. An empirical equation can describe the reaction kinetics of the curing behavior of an investigated material, [...] Read more.

The curing behavior of a thermosetting material that influences the properties of the material is a key issue for predicting the changes in material properties during processing. An empirical equation can describe the reaction kinetics of the curing behavior of an investigated material, which is usually estimated using experimental methods. In this study, the curing process of an epoxy resin, the polymer matrix in an epoxy molding compound, is computed concerning thermal influence using molecular dynamics. Furthermore, the accelerated reaction kinetics, which are influenced by an increased reaction cutoff distance, are investigated. As a result, the simulated crosslink density with various cutoff distances increases to plateau at a crosslink density of approx. 90% for the investigated temperatures during curing time. The reaction kinetics are derived according to the numerical results and compared with the results using experimental methods (dielectric analysis and differential scanning calorimetry), whereby the comparison shows a good agreement between experiment and simulation. Full article

(This article belongs to the Special Issue Advanced Epoxy-Based Materials II)

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17 pages, 4706 KiB

Open AccessArticle

Analysis of the Electrical and Thermal Properties for Magnetic Fe₃O₄-Coated SiC-Filled Epoxy Composites

by Jiale Wu, Yiran Zhang, Yangzhi Gong, Kun Wang, Yun Chen, Xupeng Song, Jun Lin, Boyang Shen, Shaojian He and Xingming Bian

Polymers 2021, 13(18), 3028; https://doi.org/10.3390/polym13183028 - 7 Sep 2021

Cited by 11 | Viewed by 2477

Abstract

Orderly arranged Silicon carbide (SiC)/epoxy (EP) composites were fabricated. SiC was made magnetically responsive by decorating the surface with iron oxide (Fe₃O₄) nanoparticles. Three treatment methods, including without magnetization, pre-magnetization and curing magnetization, were used to prepare SiC/EP composites [...] Read more.

Orderly arranged Silicon carbide (SiC)/epoxy (EP) composites were fabricated. SiC was made magnetically responsive by decorating the surface with iron oxide (Fe₃O₄) nanoparticles. Three treatment methods, including without magnetization, pre-magnetization and curing magnetization, were used to prepare SiC/EP composites with different filler distributions. Compared with unmodified SiC, magnetic SiC with core-shell structure was conducive to improve the breakdown strength of SiC/EP composites and the maximum enhancement rate was 20.86%. Among the three treatment methods, SiC/EP composites prepared in the curing-magnetization case had better comprehensive properties. Under the action of magnetic field, magnetic SiC were orderly oriented along the direction of an external field, thereby forming SiC chains. The magnetic alignment of SiC restricted the movement of EP macromolecules or polar groups to some extent, resulting in the decrease in the dielectric constant and dielectric loss. The SiC chains are equivalent to heat flow channels, which can improve the heat transfer efficiency, and the maximum improvement rate was 23.6%. The results prove that the orderly arrangement of SiC had a favorable effect on dielectric properties and thermal conductivity of SiC/EP composites. For future applications, the orderly arranged SiC/EP composites have potential for fabricating insulation materials in the power electronic device packaging field. Full article

(This article belongs to the Special Issue Advanced Epoxy-Based Materials II)

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11 pages, 1976 KiB

Open AccessCommunication

Reaction Mechanism and Mechanical Property Improvement of Poly(Lactic Acid) Reactive Blending with Epoxy Resin

by Krittameth Kiattipornpithak, Nanthicha Thajai, Thidarat Kanthiya, Pornchai Rachtanapun, Noppol Leksawasdi, Yuthana Phimolsiripol, David Rohindra, Warintorn Ruksiriwanich, Sarana Rose Sommano and Kittisak Jantanasakulwong

Polymers 2021, 13(15), 2429; https://doi.org/10.3390/polym13152429 - 23 Jul 2021

Cited by 21 | Viewed by 4438

Abstract

Polylactic acid (PLA) was melt-blended with epoxy resin to study the effects of the reaction on the mechanical and thermal properties of the PLA. The addition of 0.5% (wt/wt) epoxy to PLA increased the maximum tensile strength of PLA (57.5 MPa) to 67 [...] Read more.

Polylactic acid (PLA) was melt-blended with epoxy resin to study the effects of the reaction on the mechanical and thermal properties of the PLA. The addition of 0.5% (wt/wt) epoxy to PLA increased the maximum tensile strength of PLA (57.5 MPa) to 67 MPa, whereas the 20% epoxy improved the elongation at break to 12%, due to crosslinking caused by the epoxy reaction. The morphology of the PLA/epoxy blends showed epoxy nanoparticle dispersion in the PLA matrix that presented a smooth fracture surface with a high epoxy content. The glass transition temperature of PLA decreased with an increasing epoxy content owing to the partial miscibility between PLA and the epoxy resin. The Vicat softening temperature of the PLA was 59 °C and increased to 64.6 °C for 0.5% epoxy. NMR confirmed the reaction between the -COOH groups of PLA and the epoxy groups of the epoxy resin. This reaction, and partial miscibility of the PLA/epoxy blend, improved the interfacial crosslinking, morphology, thermal properties, and mechanical properties of the blends. Full article

(This article belongs to the Special Issue Advanced Epoxy-Based Materials II)

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14 pages, 3939 KiB

Open AccessArticle

Probabilistic Assessment of Fracture Toughness of Epoxy Resin EPOLAM 2025 Including the Notch Radii Effect

by Adrián Álvarez-Vázquez, Miguel Muñiz-Calvente, Pelayo Fernández Fernández, Alfonso Fernández-Canteli, María Jesús Lamela-Rey and José María Pintado

Polymers 2021, 13(11), 1857; https://doi.org/10.3390/polym13111857 - 3 Jun 2021

Cited by 1 | Viewed by 2573

Abstract

Many design scenarios of components made of polymer materials are concerned with notches as representative constructive details. The failure hazard assessment of these components using models based on the assumption of cracked components leads to over-conservative failure estimations. Among the different alternative approaches [...] Read more.

Many design scenarios of components made of polymer materials are concerned with notches as representative constructive details. The failure hazard assessment of these components using models based on the assumption of cracked components leads to over-conservative failure estimations. Among the different alternative approaches proposed that are based on the apparent fracture toughness,

K_{c}^{N}

is considered. In so doing, the current deterministic underlying concept must be replaced by a probabilistic one to take into account the variability observed in the failure results in order to ensure a reliable design. In this paper, an approach based on the critical distance principle is proposed for the failure assessment of notched EPOLAM 2025 CT samples with each different notch radii (

ρ

) including a probabilistic assessment of the failure prediction. First, each apparent fracture toughness is transformed into the equivalent fracture toughness for

ρ = 0

based on the critical distances theory. Then, once all results are normalized to the same basic conditions, a Weibull cumulative distribution function is fitted, allowing the probability of failure to be predicted for different notch radii. In this way, the total number of the specimens tested in the experimental campaign is reduced, whereas the reliability of the material characterization improves. Finally, the applicability of the proposed methodology is illustrated by an example using the own experimental campaign performed on EPOLAM 2025 CT specimens with different notch radii (

ρ

). Full article

(This article belongs to the Special Issue Advanced Epoxy-Based Materials II)

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14 pages, 6700 KiB

Open AccessArticle

Improved Copper–Epoxy Adhesion by Laser Micro- and Nano-Structuring of Copper Surface for Thermal Applications

by Mario Mora, Hippolyte Amaveda, Luis Porta-Velilla, Germán F. de la Fuente, Elena Martínez and Luis A. Angurel

Polymers 2021, 13(11), 1721; https://doi.org/10.3390/polym13111721 - 24 May 2021

Cited by 8 | Viewed by 3413

Abstract

The objective of this work is the enhancement of metal-to-metal bonding to provide high thermal conductivity together with electrical insulation, to be used as heat sinks at room and cryogenic temperatures. High thermal conductive metal (copper) and epoxy resin (Stycast 2850FT) were used [...] Read more.

The objective of this work is the enhancement of metal-to-metal bonding to provide high thermal conductivity together with electrical insulation, to be used as heat sinks at room and cryogenic temperatures. High thermal conductive metal (copper) and epoxy resin (Stycast 2850FT) were used in this study, with the latter also providing the required electrical insulation. The copper surface was irradiated with laser to induce micro- and nano-patterned structures that result in an improvement of the adhesion between the epoxy and the copper. Thus, copper-to-copper bonding strength was characterized by means of mechanical tensile shear tests. The effect of the laser processing on the thermal conductivity properties of the Cu/epoxy/Cu joint at different temperatures, from 10 to 300 K, is also reported. Using adequate laser parameters, it is possible to obtain high bonding strength values limited by cohesive epoxy fracture, together with good thermal conductivity at ambient and cryogenic temperatures. Full article

(This article belongs to the Special Issue Advanced Epoxy-Based Materials II)

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23 pages, 54074 KiB

Open AccessArticle

The Structure, Morphology, and Complex Permittivity of Epoxy Nanodielectrics with In Situ Synthesized Surface-Functionalized SiO₂

by Mohammed Mostafa Adnan, Inger-Emma Nylund, Aleksander Jaworski, Sverre Hvidsten, Marit-Helen Glomm Ese, Julia Glaum and Mari-Ann Einarsrud

Polymers 2021, 13(9), 1469; https://doi.org/10.3390/polym13091469 - 1 May 2021

Cited by 7 | Viewed by 2931

Abstract

Epoxy nanocomposites have demonstrated promising properties for high-voltage insulation applications. An in situ approach to the synthesis of epoxy-SiO₂ nanocomposites was employed, where surface-functionalized SiO₂ (up to 5 wt.%) is synthesized directly in the epoxy. The dispersion of SiO₂ was [...] Read more.

Epoxy nanocomposites have demonstrated promising properties for high-voltage insulation applications. An in situ approach to the synthesis of epoxy-SiO₂ nanocomposites was employed, where surface-functionalized SiO₂ (up to 5 wt.%) is synthesized directly in the epoxy. The dispersion of SiO₂ was found to be affected by both the pH and the coupling agent used in the synthesis. Hierarchical clusters of SiO₂ (10–60 nm) formed with free-space lengths of 53–105 nm (increasing with pH or SiO₂ content), exhibiting both mass and surface-fractal structures. Reducing the amount of coupling agent resulted in an increase in the cluster size (~110 nm) and the free-space length (205 nm). At room temperature, nanocomposites prepared at pH 7 exhibited up to a 4% increase in the real relative permittivity with increasing SiO₂ content, whereas those prepared at pH 11 showed up to a 5% decrease with increasing SiO₂ content. Above the glass transition, all the materials exhibited low-frequency dispersion effect resulting in electrode polarization, which was amplified in the nanocomposites. Improvements in the dielectric properties were found to be not only dependent on the state of dispersion, but also the structure and morphology of the inorganic nanoparticles. Full article

(This article belongs to the Special Issue Advanced Epoxy-Based Materials II)

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15 pages, 2671 KiB

Open AccessArticle

Dielectric Properties of BaTiO₃–Epoxy Nanocomposites in the Microwave Regime

by Hsin-Yu Yao, Yi-Wen Lin and Tsun-Hsu Chang

Polymers 2021, 13(9), 1391; https://doi.org/10.3390/polym13091391 - 25 Apr 2021

Cited by 15 | Viewed by 3529

Abstract

We synthesized BaTiO₃–epoxy nanocomposites (particle size < 100 nm) with volume fractions up to 25 vol. %, whose high-frequency complex permittivity was characterized from 8.2 to 12.5 GHz. The maximum dielectric constant approaches 9.499 with an acceptable loss tangent of 0.113. [...] Read more.

We synthesized BaTiO₃–epoxy nanocomposites (particle size < 100 nm) with volume fractions up to 25 vol. %, whose high-frequency complex permittivity was characterized from 8.2 to 12.5 GHz. The maximum dielectric constant approaches 9.499 with an acceptable loss tangent of 0.113. The dielectric loss gradually saturates when the particle concentration is higher than 15 vol. %. This special feature is an important key to realizing high-k and low-loss nanocomposites. By comparing the theoretical predictions and the experimental data, four applicable effective-medium models are suggested. The retrieved dielectric constant (loss tangent) of 100-nm BaTiO₃ nanopowder is in the range of 50–90 (0.1–0.15) at 8.2–12.5 GHz, exhibiting weak frequency dispersion. Two multilayer microwave devices—total reflection and antireflection coatings—are designed based on the fabricated nanocomposites. Both devices show good performance and allow broadband operation. Full article

(This article belongs to the Special Issue Advanced Epoxy-Based Materials II)

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