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Super-Toughened Fumed-Silica-Reinforced Thiol-Epoxy Composites Containing Epoxide-Terminated Polydimethylsiloxanes.

ABSTRACT: In response to the demand for high-performance materials, epoxy thermosetting and its composites are widely used in various industries. However, their poor toughness, resulting from the high crosslinking density of the epoxy network, must be improved to expand their application to the manufacturing of flexible products. In this study, ductile epoxy thermosetting was produced using thiol compounds with functionalities of 2 and 3 as curing agents. The mechanical properties of the epoxy were further enhanced by incorporating fumed silica into it. To increase the filler dispersion, epoxide-terminated polydimethylsiloxane was synthesized and used as a composite component. Thanks to the polysiloxane-silica interaction, the nanosilica was uniformly dispersed in the epoxy composites, and their mechanical properties improved with increasing fumed silica content up to 5 phr (parts per hundred parts of epoxy resin). The toughness and impact strength of the composite containing 5 phr nanosilica were 517 (±13) MJ/m³ and 69.8 (±1.3) KJ/m², respectively.

SUBMITTER: Bok G

PROVIDER: S-EPMC8347240 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Highly Toughened and Transparent Biobased Epoxy Composites Reinforced with Cellulose Nanofibrils.

Project description:Biobased nanofillers, such as cellulose nanofibrils (CNFs), have been widely used as reinforcing fillers for various polymers due to their high mechanical properties and potential for sustainable production. In this study, CNF-based composites with a commercial biobased epoxy resin were prepared and characterized to determine the morphology, mechanical, thermal, and barrier properties. The addition of 18?23 wt % of CNFs to epoxy significantly increased the modulus, strength and strain of the resulting composites. The addition of fibrils led to an overall increase in strain energy density or modulus of toughness by almost 184 times for the composites compared to the neat epoxy. The addition of CNFs did not affect the high thermal stability of epoxy. The presence of nanofibrils had a strong reinforcing effect in both glassy and glass transition region of the composites. A significant decrease in intensity in tan ? peak for the epoxy matrix occurred with the addition of CNFs, indicating a high interaction between fibrils and epoxy during the phase transition. The presence of highly crystalline and high aspect ratio CNFs (23 wt %) decreased the water vapour permeability of the neat epoxy resin by more than 50%.

| S-EPMC6523465 | biostudies-literature

Enhancing Thermo-Mechanical Properties of Epoxy Composites Using Fumed Silica with Different Surface Treatment.

Project description:The objectives of this study are to improve the thermal and mechanical properties of epoxy/fumed silica composite with different surface treatments of fumed silica. The addition of silica nanoparticles improved the thermal stability of the composite and slowed down the pyrolysis process. The crosslinking density and Tg of the epoxy/fumed silica composites increased because of the interfacial interaction between the PDMS-treated fumed silica particles and the epoxy matrix. The flexural strength of the epoxy nanocomposite was very high even at a low silica content because of the strong interactions between the PDMS-treated fillers and the epoxy matrix. These strong interfacial interactions originate from the attractive forces between the polymer and the filler. Therefore, the polymer nanocomposite containing the PDMS-treated fumed silica is shown to be sufficiently commercially promising.

| S-EPMC8400810 | biostudies-literature

Fatigue dataset of hybrid non-toughened and toughened epoxy adhesives.

Project description:In this article, four different structural epoxy adhesives such as SPABOND™ 820HTA (non-toughened), SPABOND™ 840HTA (toughened) adhesives, and their two hybrid combinations are fabricated using a manual mixing method. Quasi-static tensile experiments are conducted at standardized and high strain rates using ASTM D638-22 Type II specimens to investigate the strain rate effects on the tensile properties. Tensile-tensile fatigue experiments are performed using ASTM D638-22 Type I and Type II specimens to evaluate the impact of specimen geometry and toughening on fatigue life. The digital image correlation technique is utilized to obtain full-field strain data in these experiments. Technical data analysis, plotting, smoothing, filtering, and averaging are carried out using Origin ProⓇ and MATLAB R2021bⓇ. The obtained S-N curve data can be used to develop fatigue failure criteria and predict the behavior of wind turbine blade adhesive joints through finite element modeling.

| S-EPMC10749227 | biostudies-literature

Mechanism and Catalysis of Oxidative Degradation of Fiber-Reinforced Epoxy Composites.

Project description:Carbon fiber-reinforced polymer (CFRP) materials are widely used in aerospace and recreational equipment, but there is no efficient procedure for their end-of-life recycling. Ongoing work in the chemistry and engineering communities emphasizes recovering carbon fibers from such waste streams by dissolving or destroying the polymer binding. By contrast, our goal is to depolymerize amine-cured epoxy CFRP composites catalytically, thus enabling not only isolation of high-value carbon fibers, but simultaneously opening an approach to recovery of small molecule monomers that can be used to regenerate precursors to new composite resin. To do so will require understanding of the molecular mechanism(s) of such degradation sequences. Prior work has shown the utility of hydrogen peroxide as a reagent to affect epoxy matrix decomposition [1]. Herein we describe the chemical transformations involved in that sequence: the reaction proceeds by oxygen atom transfer to the polymer's linking aniline group, forming an N-oxide intermediate. The polymer is then cleaved by an elimination and hydrolysis sequence. We find that elimination is the slower step. Scandium trichloride is an efficient catalyst for this step, reducing reaction time in homogeneous model systems and neat cured matrix blocks. The conditions can be applied to composed composite materials, from which pristine carbon fibers can be recovered.

| S-EPMC6166884 | biostudies-literature

Fabrication of Woven Jute Fiber Epoxy Bio-Composites through the Epoxy/Thiol-Ene Photopolymerization Technique.

Project description:An eco-friendly epoxy/thiol-ene photopolymerization (ETEP) process was employed to prepare epoxy bio-composites using a commercial biobased epoxy resin and a woven jute fabric as reinforcement. In this process the components of the thiol-ene system, an allyl-functionalized ditertiary amine curing agent, a multifunctional thiol and a radical photoinitiator, were added to the epoxy resin to produce a polyether-polythioether crosslinked co-network. Moreover, the jute fibers were functionalized with thiol groups using the 3-mercaptopropyl (trimethoxysilane) with the purpose of creating a chemically bonded polymeric matrix/fiber system. The obtained bio-composites prepared with the thiol-functionalized cellulose fibers exhibited an increase up to 52% and 40% in flexural modulus and strength with respect to the non-functionalized counterparts. Under the three-point bending loadings, the composites displayed higher deformation at break and toughness due to the presence of polythioethers in the co-network. The prepared bio-composites developed in this work are excellent candidates to extend the use of cellulose fibers for structural applications.

| S-EPMC9824046 | biostudies-literature

Enhanced durability of carbon nanotube grafted hierarchical ceramic microfiber-reinforced epoxy composites.

Project description:As carbon nanotube (CNT) infused hybrid composites are increasingly identified as next-generation aerospace materials, it is vital to evaluate their long-term structural performance under aging environments. In this work, the durability of hierarchical, aligned CNT grafted aluminoborosilicate microfiber-epoxy composites (CNT composites) are compared against baseline aluminoborosilicate composites (baseline composites), before and after immersion in water at 25 °C (hydro) and 60 °C (hydrothermal), for extended durations (90 d and 180 d). The addition of CNTs is found to reduce water diffusivities by approximately 1.5 times. The mechanical properties (bending strength and modulus) and the damage sensing capabilities (DC conductivity) of CNT composites remain intact regardless of exposure conditions. The baseline composites show significant loss of strength (44 %) after only 15 d of hydrothermal aging. This loss of mechanical strength is attributed to fiber-polymer interfacial debonding caused by accumulation of water at high temperatures. In situ acoustic and DC electrical measurements of hydrothermally aged CNT composites identify extensive stress-relieving micro-cracking and crack deflections that are absent in the aged baseline composites. These observations are supported by SEM images of the failed composite cross-sections that highlight secondary matrix toughening mechanisms in the form of CNT pullouts and fractures which enhance the service life of composites and maintain their properties under accelerated aging environments.

| S-EPMC5695714 | biostudies-literature

Mechanical and Tribological Behavior of Functionally Graded Unidirectional Glass Fiber-Reinforced Epoxy Composites.

Project description:This paper aims to assess experimentally the mechanical and tribological behavior of conventional and functionally graded (FG) polymeric matrix composites reinforced with continuous glass fibers. The small punch test (SPT) and a pin-on-disc device were used in the present work to examine the mechanical and wear behavior, respectively. The hand lay-up technique was used in the present investigation to manufacture the conventional and FG composites. Various wooden looms with different nailed spacing were employed to manufacture the FG composites. According to test type, the FG composite is composed of four and ten layers, with a different glass fiber volume of fraction (Vf%) for each layer. In addition, the finite element simulation based on Hashin's failure criterion and cohesive zone modeling was used to show the progressive failure and give more explanation regarding the flexural behavior of such composites. The present results indicate that the wear rate of an FG composite could be affected by many factors, including the disk speed, applied load, the composite layers number, and average glass fiber volume fraction. On the other hand, the arrangement of layers in the composite materials by variation of Vf% for each layer can improve the wear rate and value of the ultimate load before the fracture of the composite material when subjected to SPT. The experimental and numerical results for all SPT specimens showed that the fracture of the SPT specimens began beneath the punch tip and grew along the fiber direction. The ultimate flexural capacity of FG composites increased by 30% compared with the conventional composites.

| S-EPMC9147567 | biostudies-literature

Novel Antibacterial and Toughened Carbon-Fibre/Epoxy Composites by the Incorporation of TiO2 Nanoparticles Modified Electrospun Nanofibre Veils.

Project description:The inclusion of electrospun nanofiber veils was revealed as an effective method for enhancing the mechanical properties of fiber-reinforced epoxy resin composites. These veils will eventually allow the incorporation of nanomaterials not only for mechanical reinforcement but also in multifunctional applications. Therefore, this paper investigates the effect of electrospun nanofibrous veils made of polyamide 6 modified with TiO2 nanoparticles on the mechanical properties of a carbon-fiber/epoxy composite. The nanofibers were included in the carbon-fiber/epoxy composite as a single structure. The effect of positioning these veils in different composite positions was investigated. Compared to the reference, the use of unmodified and TiO2 modified veils increased the flexural stress at failure and the fracture toughness of composites. When TiO2 modified veils were incorporated, new antibacterial properties were achieved due to the photocatalytic properties of the veils, widening the application area of these composites.

| S-EPMC6780269 | biostudies-literature

Delayed Thiol-Epoxy Photopolymerization: A General and Effective Strategy to Prepare Thick Composites.

Project description:Photoinduced thiol-epoxy click polymerization possesses both the characteristics and advantages of photopolymerization and click reactions. However, the photopolymerization of pigmented or highly filled thiol-epoxy thick composites still remains a great challenge due to the light screening effect derived from the competitive absorption, reflection, and scattering of the pigments or functional fillers. In this article, we present a simple and versatile strategy to prepare thick composites via delayed thiol-epoxy photopolymerization. The irradiation of a small area with a light-emitting diode (LED) point light source at room temperature leads to the decomposition of a photobase generator and the released active basic species can uniformly disperse throughout the whole system, including unirradiated areas, via mechanical stirring. No polymerization was observed at room temperature and therefore the liquid formulations can be further processed with molds of arbitrary size and desired shapes. It is only by increasing the temperature that base-catalyzed thiol-epoxy polymerization occurs and controllable preparation of thick thiol-epoxy materials can be achieved. The formed networks display excellent uniformity in different radii and depths with comparable functionality conversions, similar T g values, and thermal decomposition temperatures. The presented strategy can be applied to prepare thick composites with glass fibers possessing improved mechanical properties and dark composites containing 2 wt % carbon nanotubes.

| S-EPMC7331066 | biostudies-literature

Synthesis and Hydrophilicity Analysis of bis(propane-1,2-diol) Terminated Polydimethylsiloxanes (PDMSs).

Project description:Among silicone oligomers, polydimethylsiloxane (PDMS) is widely used industrially and has the advantage of improving the properties of other compounds, such as flame-retardant polyurethane (PU). However, as there are barriers to the synthesis of PU-grafted siloxane, owing to the polarity difference between isocyanate and PDMS, numerous research efforts are being aimed at improving the hydrophilicity of PDMS. To improve the hydrophilicity and reactivity of hydroxyl PDMS, bis(propane-1,2-diol)-terminated PDMS (G-PDMS-G) with four hydroxy (-OH) groups was synthesized through ring-opening addition to replace both ends of linear α,ω-hydroxyl PDMS (HO-PDMS-OH) with glycidol, resulting in hydrophilic PDMS rather than dihydroxy PDMS. In all cases of G-PDMS-G, the contact angle and viscosity both decreased by more than 20%, confirming the improved hydrophilicity. In particular, G-PDMS-G-3, which has the largest molecular weight, demonstrated the greatest decrease in viscosity and contact angle (33%).

| S-EPMC8836733 | biostudies-literature

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