Thermal and Fire Behavior of a Bio-Based Epoxy/Silica Hybrid Cured with Methyl Nadic Anhydride

Nanoindentation Response of Structural Self-Healing Epoxy Resin: A Hybrid Experimental-Simulation Approach

In recent years, self-healing polymers have emerged as a topic of considerable interest owing to their capability to partially restore material properties and thereby extend the product's lifespan. The main purpose of this study is to investigate the nanoindentation response in terms of hardness, reduced modulus, contact depth, and coefficient of friction of a self-healing resin developed for use in aeronautical and aerospace contexts. To achieve this, the bifunctional epoxy precursor underwent tailored functionalization to improve its toughness, facilitating effective compatibilization with a rubber phase dispersed within the host epoxy resin. This approach aimed to highlight the significant impact of the quantity and distribution of rubber domains within the resin on enhancing its mechanical properties. The main results are that pure resin (EP sample) exhibits a higher hardness (about 36.7% more) and reduced modulus (about 7% more), consequently leading to a lower contact depth and coefficient of friction (11.4% less) compared to other formulations that, conversely, are well-suited for preserving damage from mechanical stresses due to their capabilities in absorbing mechanical energy. Furthermore, finite element method (FEM) simulations of the nanoindentation process were conducted. The numerical results were meticulously compared with experimental data, demonstrating good agreement. The simulation study confirms that the EP sample with higher hardness and reduced modulus shows less penetration depth under the same applied load with respect to the other analyzed samples. Values of 877 nm (close to the experimental result of 876.1 nm) and 1010 nm (close to the experimental result of 1008.8 nm) were calculated for EP and the toughened self-healing sample (EP-R-160-T), respectively. The numerical results of the hardness provide a value of 0.42 GPa and 0.32 GPa for EP and EP-R-160-T, respectively, which match the experimental data of 0.41 GPa and 0.30 GPa. This validation of the FEM model underscores its efficacy in predicting the mechanical behavior of nanocomposite materials under nanoindentation. The proposed investigation aims to contribute knowledge and optimization tips about self-healing resins.

Functional cellulose-derived epoxy cross-linked with BADGE resin to construct high-performance epoxy composites

The development of equipped bio-based epoxy materials has been gaining much attention recently. Nevertheless, finding the balance between the structure and properties of materials remains a significant challenge. In this work, cellulose-based epoxy (PHPCEP) with "soft" and "hard" cooperative structures was designed and demonstrated to endow bisphenol A diglycidyl ether (BADGE) with excellent toughness, heat resistance, mechanical strength, glass transition temperature, thermal stability, and solvent resistance. When 5 wt% PHPCEP was incorporated into BADGE composites, the resulting materials exhibited the maximum flexural strength (121.9 MPa) and tensile strength (71.4 MPa), a high glass transition temperature (148.3 °C), and 10 wt% PHPCEP/BADGE demonstrated the highest impact strength (70.5 kJ/m2). These figures are 18.8 %, 16.1 %, 21.5 %, and 254.3 % higher than the corresponding values of neat BADGE. The results of dynamic mechanical properties and heat degradation of the cured specimens also suggest that PHPCEP/BADGE materials have superior stiffness and toughness than neat BADGE, which could be attributed to the strong interaction between PHPCEP and BADGE, delivering better thermal stability for the composites compared to the pristine resin. Considering the remarkable effect, this work provides an effective way of highly efficient utilization of abundant cellulose and a high-performance additive for composite materials.

Recent advancement in synthesizing bio-epoxy nanocomposites using lignin, plant oils, saccharides, polyphenols, and natural rubbers: A review

Due to environmental issues, production costs, and the low recycling capability of conventional epoxy polymers and their composites, many science groups have tried to develop a new type of epoxy polymers, which are compatible with the environment. Considering the precursors, these polymers can be produced from plant oils, saccharides, lignin, polyphenol, and natural resins. The appearance of these bio-polymers caused to introduce a new type of composites, namely bio-epoxy nanocomposites, which can be classified according to the synthesized bio-epoxy, the used nanomaterials, or both. Hence, in this work, various bio-epoxy resins, which have the proper potential for application as a matrix, are completely introduced with the synthesis viewpoint, and their characterized chemical structures are drawn. In the next steps, the bio-epoxy nanocomposites are classified based on the used nanomaterials, which are carbon nanoparticles (carbon nanotubes, graphene nanoplatelets, graphene oxide, reduced graphene oxide, etc.), nano-silica (mesoporous and spherical), cellulose (nanofibers and whiskers), nanoclay and so on. Also, the features of these bio-nanocomposites and their applications are introduced. This review study can be a proper guide for developing a new type of green nanocomposites in the near future.

Sol-Gel Approach for Fabricating Silica/Epoxy Nanocomposites

This review focuses on the opportunities provided by sol-gel chemistry for the production of silica/epoxy nanocomposites, with significant representative examples of the "extra situ" approach and an updated description of the "in situ" strategy. The "extra situ" strategy enables the creation of nanocomposites containing highly engineered nanoparticles. The "in situ" approach is a very promising synthesis route that allows us to produce, in a much easier and eco-friendly manner, properly flame-retarded silica/epoxy nanocomposites endowed with very interesting properties. The review highlights the recently proposed mechanism of nanoparticles formation, which is expected to help to design the synthesis strategies of nanocomposites, changing their composition (both for the nanoparticle and matrix nature) and with in situ-generated nanoparticles possibly more complex than the ones obtained, until today, through this route.

Recent advances in the development of green furan ring-containing polymeric materials based on renewable plant biomass

Fossil resources are rapidly depleting, forcing researchers in various fields of chemistry and materials science to switch to the use of renewable sources and the development of corresponding technologies. In this regard, the field of sustainable materials science is experiencing an extraordinary surge of interest in recent times due to the significant advances made in the development of new polymers with desired and controllable properties. This review summarizes important scientific reports in recent times dedicated to the synthesis, construction and computational studies of novel sustainable polymeric materials containing unchanged (pseudo)aromatic furan cores in their structure. Linear polymers for thermoplastics, branched polymers for thermosets and other crosslinked materials are emerging materials to highlight. Various polymer blends and composites based on sustainable polyfurans are also considered as pathways to achieve high-value-added products.

Curing Regime-Modulating Insulation Performance of Anhydride-Cured Epoxy Resin: A Review

Anhydride-cured bisphenol-A epoxy resin is widely used in the support, insulation and sealing key components of electrical and electronic equipment due to their excellent comprehensive performance. However, overheating and breakdown faults of epoxy resin-based insulation occur frequently under conditions of large current carrying and multiple voltage waveforms, which seriously threaten the safe and stable operation of the system. The curing regime, including mixture ratio and combination of curing time and temperature, is an important factor to determine the microstructure of epoxy resin, and also directly affects its macro performances. In this paper, the evolution of curing kinetic models of anhydride-cured epoxy resin was introduced to determine the primary curing regime. The influences of curing regime on the insulation performance were reviewed considering various mixture ratios and combinations of curing time and temperature. The curing regime-dependent microstructure was discussed and attributed to the mechanisms of insulation performance.

Synthesis of SiO2 Nanoparticle Epoxy Resin Composite and Silicone-Containing Epoxy Resin for Coatings

Due to its unique properties, including strong adhesion force, high heat resistivity, high insulation properties, and strong mechanical properties, epoxy resin is the most commonly used material for a variety of applications, including adhesives, electronic devices for coatings, and somewhere as a matrix for reinforcement of composites as a fiber network. To boost their properties, different other materials are also inserted in their structure and made its composites; silicon is one of them. Corrosion is serious for marine equipment and causes economic loss. To overcome such issues, different types of coating materials are developed. In this review, current methods for coatings of different materials using a silicon dioxide epoxy nanocomposite are discussed in diversity with the currently followed synthetic routes for the preparation of nanosilica epoxy composites and enhanced properties.

Solvent-Free One-Pot Synthesis of Epoxy Nanocomposites Containing Mg(OH)2 Nanocrystal-Nanoparticle Formation Mechanism

Epoxy nanocomposites containing Mg(OH)₂ nanocrystals (MgNCs, 5.3 wt %) were produced via an eco-friendly "solvent-free one-pot" process. X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), and thermogravimetric analysis (TGA) confirm the presence of well-dispersed MgNCs. HRTEM reveals the presence also of multisheet-silica-based nanoparticles and a tendency of MgNCs to intergrow, leading to complex nanometric structures with an intersheet size of ∼0.43 nm, which is in agreement with the lattice spacing of the Mg(OH)₂ (001) planes. The synthesis of MgNCs was designed on the basis of a mechanism initially proposed for the preparation of multisheet-silica-based/epoxy nanocomposites. The successful "in situ" generation of MgNCs in the epoxy via a "solvent-free one-pot" process confirms the validity of the earlier disclosed mechanism and thus opens up possibilities of new NCs with different fillers and polymer matrix. The condition would be the availability of a nanoparticle precursor soluble in the hydrophobic resin, giving the desired phase through hydrolysis and polycondensation.

Co-immobilization of Cellulase and β-Glucosidase into Mesoporous Silica Nanoparticles for the Hydrolysis of Cellulose Extracted from Eriobotrya japonica Leaves

Fungal cellulases generally contain a reduced amount of β-glucosidase (BG), which does not allow for efficient cellulose hydrolysis. To address this issue, we implemented an easy co-immobilization procedure of β-glucosidase and cellulase by adsorption on wrinkled mesoporous silica nanoparticles with radial and hierarchical open pore structures, exhibiting smaller (WSN) and larger (WSN-p) inter-wrinkle distances. The immobilization was carried out separately on different vectors (WSN for BG and WSN-p for cellulase), simultaneously on the same vector (WSN-p), and sequentially on the same vector (WSN-p) in order to optimize the synergy between cellulase and BG. The obtained results pointed out that the best biocatalyst is that prepared through simultaneous immobilization of BG and cellulase on the same vector (WSN-p). In this case, the adsorption resulted in 20% yield of immobilization, corresponding to an enzyme loading of 100 mg/g of support. 82% yield of reaction and 72 μmol/min·g activity were obtained, evaluated for the hydrolysis of cellulose extracted from Eriobotrya japonica leaves. All reactions were carried out at a standard temperature of 50 °C. The biocatalyst retained 83% of the initial yield of reaction after 9 cycles of reuse. Moreover, it had better stability than the free enzyme mixture in a wide range of temperatures, preserving 72% of the initial yield of reaction up to 90 °C.

Silica Meets Tannic Acid: Designing Green Nanoplatforms for Environment Preservation

Hybrid tannic acid-silica-based porous nanoparticles, TA-SiO2 NPs, have been synthesized under mild conditions in the presence of green and renewable tannic acid biopolymer, a glycoside polymer of gallic acid present in a large part of plants. Tannic acid (TA) was exploited as both a structuring directing agent and green chelating site for heavy metal ions recovery from aqueous solutions. Particles morphologies and porosity were easily tuned by varying the TA initial amount. The sample produced with the largest TA amount showed a specific surface area an order of magnitude larger than silica nanoparticles. The adsorption performance was investigated by using TA-SiO2 NPs as adsorbents for copper (II) ions from an aqueous solution. The effects of the initial Cu2+ ions concentration and the pH values on the adsorption capability were also investigated. The resulting TA-SiO2 NPs exhibited a different adsorption behaviour towards Cu2+, which was demonstrated through different tests. The largest adsorption (i.e., ~50 wt% of the initial Cu2+ amount) was obtained with the more porous nanoplatforms bearing a higher final TA content. The TA-nanoplatforms, stable in pH value around neutral conditions, can be easily produced and their use would well comply with a green strategy to reduce wastewater pollution.

Suitability and Sustainability of Anti-Graffiti Treatments on Natural Stone Materials

Graffiti vandalism represents an aesthetic and structural phenomenon of degradation both for buildings and cultural heritage: the most used sprays and markers can permeate the stone materials exposing them to degradation. Hence, great attention is being currently devoted to new non-invasive chemical approaches to face this urgent problem. This work is aimed at deeply examining the effects of some of the most sustainable chemical protective methods on the physical properties of natural building materials (e.g., tuff and limestone) by testing two commercial anti-graffiti products. It was found that the nanotechnological product Ector (E) was more effective than Nord Resine (NR) in anti-graffiti applications even if its permanent character hinders its application to the cultural heritage. Conversely, the less performant NR could be used in this field due to its sacrificial behavior, according to the guidelines of the Italian Ministry of Cultural Heritage and Activities and Tourism. The findings highlight the importance of developing new sustainable methods for the preservation of cultural and building materials from vandal graffiti, which should combine the high hydrophobia, the ecological characteristics, and the effectiveness of E, with the sacrificial properties of NR.

Structure and Bottom-up Formation Mechanism of Multisheet Silica-Based Nanoparticles Formed in an Epoxy Matrix through an In Situ Process

Organic/inorganic hybrid composite materials with the dispersed phases in sizes down to a few tens of nanometers raised very great interest. In this paper, it is shown that silica/epoxy nanocomposites with a silica content of 6 wt % may be obtained with an "in situ" sol-gel procedure starting from two precursors: tetraethyl orthosilicate (TEOS) and 3-aminopropyl-triethoxysilane (APTES). APTES also played the role of a coupling agent. The use of advanced techniques (bright-field high-resolution transmission electron microscopy, HRTEM, and combined small- and wide-angle X-ray scattering (SAXS/WAXS) performed by means of a multirange device Ganesha 300 XL+) allowed us to evidence a multisheet structure of the nanoparticles instead of the gel one typically obtained through a sol-gel route. A mechanism combining in a new manner well-assessed knowledge regarding sol-gel chemistry, emulsion formation, and Ostwald ripening allowed us to give an explanation for the formation of the observed lamellar nanoparticles.

Polymer Adsorbents vs. Functionalized Oxides and Carbons: Particulate Morphology and Textural and SurfaceCharacteristics

Various methods for morphological, textural, and structural characterization of polymeric, carbon, and oxide adsorbents have been developed and well described. However, there are ways to improve the quantitative information extraction from experimental data for describing complex sorbents and polymer fillers. This could be based not only on probe adsorption and electron microscopies (TEM, SEM) but also on small-angle X-ray scattering (SAXS), cryoporometry, relaxometry, thermoporometry, quasi-elastic light scattering, Raman and infrared spectroscopies, and other methods. To effectively extract information on complex materials, it is important to use appropriate methods to treat the data with adequate physicomathematical models that accurately describe the dependences of these data on pressure, concentration, temperature, and other parameters, and effective computational programs. It is shown that maximum accurate characterization of complex materials is possible if several complemented methods are used in parallel, e.g., adsorption and SAXS with self-consistent regularization procedures (giving pore size (PSD), pore wall thickness (PWTD) or chord length (CLD), and particle size (PaSD) distribution functions, the specific surface area of open and closed pores, etc.), TEM/SEM images with quantitative treatments (giving the PaSD, PSD, and PWTD functions), as well as cryo- and thermoporometry, relaxometry, X-ray diffraction, infrared and Raman spectroscopies (giving information on the behavior of the materials under different conditions).