Category: Solutions with Graphene

Protecting concrete

Posted on | by Energeia Graphenemex

Protecting concrete:

additives and coatings for greater durability in construction

“The compressive strength test is usually the most used parameter as an indicator of concrete quality; however, its value does not determine its durability by itself, that is, in addition to mechanical resistance, permeability and chemical resistance also influence its useful life”

The permeability of concrete is understood as the passage of water and aggressive ions through the capillaries between the aggregates and the cement paste; this is a complex phenomenon and depends above all on the atomic structure of the penetrating ions. One of the most harmful substances for concrete are chloride ions, these can be present from the beginning in the fresh mix, that is, dissolved in the aggregates, additives or in the water, or permeate from the outside, this being the case that exposes the greatest risk of corrosion. Although in general it can be said that the durability of concrete against atmospheric agents depends fundamentally on its permeability to water, while the durability with respect to aggressive salts, both for concrete and for reinforcement, depends on its resistance to the entry of chlorides. by different ways.

“The penetrability of the chlorides is manifested mainly by the diffusion of the ions in the concrete, rather than by the penetration of the entire solution into the samples. That is, the penetration of chlorides does not depend solely on the permeability of the water”

To protect concrete against corrosion, there are two main types of products: on the one hand, there are additives for fresh concrete mixes whose function is to act on the metal surface, canceling the anodic or cathodic reaction or both, and on the other, there are coatings. for the protection of hardened concrete. However, whatever the product used, anticorrosion protection is usually temporary, especially when the structures are subject to movements, loads or temperatures that could affect the performance of the protection or barrier placed.

In the previous article entitled Towards sustainable construction, we discussed the importance of the key nanometric component in the resistance of cement, known as hydrated calcium silicates (C-S-H) or tobermorite gel, and it’s interesting interaction with graphene oxide (GO) nanoparticles, a nanometric structure derived from graphite and of recent interest for the development of more resistant, durable and environmentally friendly structures.

GO is formed by nanometric sheets of carbon atoms linked in a hexagonal pattern and by a series of oxygenated groups anchored to its surface that facilitates its dispersion in water and combining with other materials, for example, with the nanoparticles present in cement (C-S-H).

In this regard, international studies show that the shape and surface chemistry of GO allow it to act as a platform to accelerate the hydration of cement and promote the creation of large amounts of C-S-H particles, from the formation of a new GO/ bond. C-S-H. This strong interaction gives rise to a denser network of interlocking cement crystals which, in addition to favoring the mechanical properties of the structures, also acts as a barrier against the infiltration of water through the capillary pores, but with an effect that last longer than currently available additives. This property is extremely important for the durability of concrete and for the prevention of alkali-silica reaction (ASR), an expansion reaction that occurs in the presence of moisture between alkaline cement paste and reactive amorphous silica causing cracks.

Electrical resistivity and corrosion rate Another important test for concrete is electrical resistivity and is defined as the resistance of a material to the passage of electrical charges; its measurement in concrete is a common test to identify the presence of moisture, as well as to predict the initiation period of corrosion in reinforced concrete based on the inverse relationship between electrical resistivity and ion diffusivity. That is, the higher the resistivity, the less movement of electrical charges caused by a lower porosity. The participation of graphene oxide nanoparticles in this property has also been evaluated in different studies that confirm that the GO/C-S-H interaction produces a more compact or less porous concrete that, in addition to reducing water and ion permeability, also limits the movement of electrical charges providing greater anticorrosive protection of metallic concrete structures.

Energeia Fusion (Graphenemex®), the leading Mexican company in Latin America in the research and production of graphene materials, for more than 10 years has been given the task of materializing the benefits of graphene on a scientific basis to turn it into real applications. Thus, after a long journey of research and with results comparable to those reported by various international studies regarding the use of graphene oxide in different products, including concrete, in 2018 it managed to launch Graphenergy Construcción®, the first additive on the market. for concrete with graphene oxide in the world; a multifunctional water-based additive that contributes to improve different properties of cement-based structures with a single application, such as:

  1. Remodeling of the microstructure of the cement paste with better interfacial bond GO/C-S-H,
  2. Better compactness of the cement,
  3. Less movement of electric charges,
  4. Decrease in the crack extension process,
  5. Significant reductions in the rate of calcium hydroxide handling,
  6. Greater mechanical resistance by improving its microstructure,
  7. Greater durability of the structures due to improvements in impermeability, resistance to chloride penetration and reduction of penetration depth.

It is important to remember that these effects may vary since, in addition to the type of graphene or graphene oxide used, the final properties of cement-based structures also depend on factors such as the water-cement ratio, degree of compaction of the mixture; the characteristics of cement, aggregates, additives, among others, but with proper management and monitoring of graphene additives, the results can be very interesting.

Drafting: EF/DHS

Sources

  1. Ultrahigh Performance Nanoengineered Graphene- Concrete Composites for Multifunctional Applications. Adv. Funct. Mater. 2018; 28: 1705183;
  2. The role of graphene/graphene oxide in cement hydration. Nanotechnology Reviews. 2021;10(1): 768;
  3. Experimental study of the effects of graphene nanoplatelets on microstructure and compressive properties of concrete under chloride ion corrosión. Construction and Building Materials, 2022; 360, 129564;
  4. Effect Of On Graphene Oxide the Concrete Resistance to Chloride Ion Permeability. IOP Conf. Ser. 2018: Mater. Sci. Eng. 394 032020;
  5. Effects of graphene oxide on early-age hydration and electrical resistivity of Portland cement paste. Constr Build Mater. 2017; 136, 506;
  6. Recent progress on graphene oxide for next-generation concrete: Characterizations, applications and challenges. “J. Build. Eng. 2023; 69, 106192;
  7. Graphene nanoplatelet reinforced concrete for self-sensing structures – A lifecycle assessment perspective. J. Clean. Prod. 2019; 240, 118202;
  8. Graphene opens pathways to a carbon-neutral cement industry. Science Bulletin. 2021; 67;
  9. Reinforcing Effects of Graphene Oxide on Portland Cement Paste. J. Mater. Civ. Eng. 2014; A4014010-1;
  10. A review on the properties, reinforcing effects, and commercialization of nanomaterials for cement-based materials. Nanotechnology Reviews 2020; 9: 303–322, 10;
  11. Permeabilidad a los cloruros del hormigón armado situado en ambiente marino sumergido. Revista Ingeniería de Construcción. 2007; 22: 1, 15;
  12. Penetrabilidad del hormigón al agua y a los iones agresivos como factor determinante de su durabilidad. Materiales de Construcción, 1973; 23: 150;
  13. La resistividad eléctrica como parámetro de control del hormigón y de su durabilidad. Revista ALCONPAT, 2011; 1(2),90;
  14. Portland cement blended with nanoparticles. Dyna, 2007; 74:152, 277;
  15. Improvement in concrete resistance against water and chloride ingress by adding graphene nanoplatelet. Cem concr res, 2016; 83: 114

Towards a sustainable construction

Posted on | by Energeia Graphenemex

Towards a sustainable construction:

how graphene oxide increases the resistance of concrete and favors the reduction of CO2 emissions

The investigation of new technologies for the cement and concrete industry is not only limited to improving its durability, but also to seeking strategies to control its influence on climate change, taking as a background that this industry is the third largest source of emissions of carbon dioxide (CO2) and that the global challenge for 2030 is to reduce these emissions by at least 16%.

Nanotechnology

Nanotechnology for the cement industry is not a new concept, in fact, cement is considered a nanostructured material because 50 to 60% of its composition consists of nanoparticles of approximately 10 nm known as hydrated calcium silicates (C-S-H). or tobermorite gel. This important nanometric component is the foundation for the development of new formulations applying other nanoparticles such as Nano Silica (n. SiO2), Nano Titanium Oxide (n. TiO2), Nano Ferric Oxide (n. Fe2O3), Nano Aluminum Oxide or alumina (n. Al2O3), Clay Nanoparticles and Carbon Nanoparticles, such as carbon nanotubes, graphene nanoparticles or graphene oxide.

“C-S-H fills the empty spaces in the cement, improves the density, cohesion, impermeability and resistance of the cement”

Graphene oxide (GO) is a carbon nanoparticle obtained from the oxidation and exfoliation of graphite. Its well-known mechanical and impermeability properties, combined with a nucleating and densifying effect on the microstructure of cement, captured the attention of scientists and industries when they discovered that the use of low concentrations of this nanomaterial allows the development of more resistant, durable, and friendly structures with the environment.

“GO promotes the formation of C-S-H to improve and accelerate cement hydration through a new chemical bond”

How does GO interact with cement?

Although it is perfectly documented that C-S-H is responsible for 60 to 80% of the strength of cement, recent research has shown that GO further favors these results and that it is not exclusive to improve mechanical strength, but also contributes with other properties such as impermeability, anticorrosiveness and/or thermal insulation. The benefits that GO brings to cement itself or to cement-based materials are attributed to the interaction between the carboxyl groups (COOH) of GO with the C-S-H of the cement to form strong GO/C-S-H chemical bonds. This occurs in the following way, when the cement comes into contact with water, it dissolves and releases large amounts of ions; On the other hand, GO, by presenting a large surface area and good capacity to increase the mobility of Ca2+ ions in the cement paste, GO allows them to be adsorbed on it. In other words, GO acts as a platform to enhance the nucleation or promotion effect to form a large number of C-S-H particles (fig. 1), a phenomenon that ultimately facilitates the hydration process at an early age and which in turn leads to the formation of denser, more resistant and less permeable microstructures.

“Hydration is the process by which cement reacts chemically in the presence of water, develops binding properties and becomes a bonding agent.”

Fig. 1. Schematic representation of the interaction of the cement paste in the presence of graphene and graphene oxide.
Taken from: Nanotechnology Reviews (2021), vol. 10, no. 1,768

Mechanical resistance vs. lower CO2 emissions

The compressive strength test is the most common measure to control the quality of concrete and, therefore, it is also the most widely used technique to evaluate the effect of GO on these structures. According to tests carried out in the laboratory, the presence of GO in the concrete can exceed 50% of the expected resistance, while field evaluations report improvement fluctuations in the range of 5% to 50%. This variation is due to the fact that, in addition to the type of GO and dosage studied, like any concrete structure, the resistance also depends on factors such as the water-cement ratio, the degree of compaction of the mix; the characteristics of the cement, aggregates and additives; the age of the concrete; the temperature and hygrometry of the curing environment. However, these values are attractive enough to be used not only in the design of more resistant structures, but also with lower cement content to contribute to the reduction of CO2 emissions. In fact, in 2019 a study carried out by researchers from the University of Cambridge revealed that, if the addition of graphene nanoparticles managed to reduce just 5% of the cement in the concrete mix, its effect on global warming would be reduced by one 21%”.

Due to the foregoing and, from the 21st Conference of the Parties to the United Nations Framework Convention on Climate Change (COP 21) held in 2015, which concluded with the adoption of the Decision and the Paris Agreement that, from 2020 promotes low-carbon development to keep the global temperature rise below 2°C, companies from countries such as England, Spain, the United States, Vietnam and Mexico have accelerated their efforts to promote the benefits of graphene nanotechnology in favor of the environment.

Energeia Fusion, the leading Mexican company in Latin America in the production of graphene materials and the development of applications, in 2018 launched Graphenergy Construcción®, the first additive for concrete with graphene oxide in the world; a multifunctional water-based additive that contributes to improving different properties of cement-based structures with a single application. Likewise, in the short term it hopes to have a graphene-reinforced cement available and contribute to achieving environmental commitments.

Sources

  1. Ultrahigh Performance Nanoengineered Graphene- Concrete Composites for Multifunctional Applications. Adv. Funct. Mater. 2018, 28, 1705183;
  2. The role of graphene/graphene oxide in cement hydration. Nanotechnology Reviews. 2021;10(1): 768;
  3. Experimental study Construction and Building Materials, 2022, 360, 129564;
  4. Effect Of On Graphene Oxide the Concrete Resistance to Chloride Ion Permeability. IOP Conf. Ser. 2018: Mater. Sci. Eng. 394 032020;
  5. Effects of graphene oxide on early-age hydration and electrical resistivity of Portland cement paste. Constr Build Mater. 2017, 136, 506;
  6. Recent progress on graphene oxide for next-generation concrete: Characterizations, applications and challenges. “J. Build. Eng. 2023, 69, 106192;
  7. Graphene nanoplatelet reinforced concrete for self-sensing structures – A lifecycle assessment perspective. J. Clean. Prod. 2019, 240, 118202;
  8. Graphene opens pathways to a carbon-neutral cement industry. 2021, Science Bulletin 67;
  9. Reinforcing Effects of Graphene Oxide on Portland Cement Paste. J. Mater. Civ. Eng. 2014. A4014010-1;
  10. A review on the properties, reinforcing effects, and commercialization of nanomaterials for cement-based materials. Nanotechnology Reviews 2020; 9: 303–322, 10;
  11. Permeabilidad a los cloruros del hormigón armado situado en ambiente marino sumergido. Revista Ingeniería de Construcción. 2007, 22, 1, 15;
  12. Penetrabilidad del hormigón al agua y a los iones agresivos como factor determinante de su durabilidad. Materiales de Construcción, 1973, 23, 150;
  13. La resistividad eléctrica como parámetro de control del hormigón y de su durabilidad. Revista ALCONPAT, 2011, 1(2),90;
  14. Portland cement blended with nanoparticles. Dyna, 2007, 74, 152, 277

The graphene additive for concrete

Posted on | by Energeia Graphenemex

The graphene additive for concrete:

a revolutionary thermal insulator in construction

In recent years, the construction industry is looking formward to improve the properties of mortar and concrete, to increase their durability, especially in structures exposed to aggressive or extreme environments. Among the properties that are sought to improve, is the resistance to compression, the resistance to compression tension, as well as to reduce cracking. With the increase in the volume of concrete in civil engineering projects, more attention has been paid to the thermal cracks that occur. Experimentation has shown that during the hydration process of the mortar and/or concrete, heat is generated due to the exothermic reactions that occur. Poor heat dissipation causes a gradient between the interior of the mass and its surface, which generates internal stresses and can lead to cracking or thermal cracking in the concrete.

Nowadays, graphene oxide (GO), a graphene precursor material, has attracted a lot of attention because it is an insulating material, with low thermal property and has extraordinary mechanical properties. GO has a large surface area (2600 m2/g) and the presence of oxygenated groups gives it unique properties that make it easily dispersed in water, making it an ideal nanomaterial for the development of concrete additives.

Although the mechanical properties of cement-based compounds and structures are important in building infrastructure, the thermal insulation property is very important to reduce energy consumption for air conditioning and heating in buildings. Therefore, GO is a good candidate due to its low thermal conductivity properties. Thermal conductivity is defined as the ability of a material to transfer heat. It is the phenomenon by which heat spreads from high-temperature areas (warmer) to colder areas within the material. In the case of GO, the presence of holes and functional groups on the GO surface cause local stress or instability, resulting in a reduction in thermal conductivity of up to 2 to 3 orders of magnitude (<100 W/m-K). In the GO, the propagation of heat flux occurs in the vacant regions (voids) and in the oxygenated functional groups of the GO surface (Figure 1). When a heat flux attempts to traverse the GO through some defect or vacancy, the heat flux not only propagates out of plane, but also disturbs the heat flux around the basal plane gap.

Figure 1. Schematic image of graphene oxide (GO) sheet with vacancy or defect defects
and randomly distributed oxygenated functional groups.

Recent investigations have reported the improvement of the thermal insulation properties of cement-based composite materials by adding different concentrations of GO, as well as the effect of GO on increasing compressive strength and greater impermeability to chloride ions. and water in concrete. The incorporation of GO decreased microcracking, the porosity of the material (decreases the volume of pores) and improved compaction. GO sheets become a barrier to crack propagation, which improves mechanical properties. The compressive strength of the specimens of the compounds with GO concentrations of 0.05% by weight increased by up to 18.7% and 13.7% at a curing age of 7 and 28 days, respectively. In the case of the evaluations of the thermal properties of the compounds, the thermal conductivity was 0.578 W/m K for the specimen without GO (control) and 0.490 W/m K for the compound with 0.1 % by weight of GO, while that the thermal diffusivity values oscillate between 0.38× 10-6 and 0.33× 10-6 m2/s (Figure 2). Thermal conductivity decreases with increasing GO content due to low conductivity or excellent insulating effect of GO sheets and good interactions between mortar and GO sheets. Generally, material with thermal conductivity values of less than 0.250 W/m K is known as a thermal insulator. Therefore, the thermal insulation of the mortar is improved in the compounds with the incorporation of GO.

Figure 2. a) Comparative graphs of the compressive strength of the compounds at different concentrations of GO at the curing age of 3, 7, 21, 28 and 77 days. b) Thermal conductivity and diffusivity of the compounds, at the curing age of 7 days.

Energeia -Graphenemex® developed and sells an admixture for concrete with graphene oxide (Graphenergy Construction). A nanotechnological additive that improves mechanical resistance, impermeability and provides an antimicrobial effect to any cement-based material. The additive can also manage to reduce the final number of pores in the set product, which translates into a more compact product and greater impermeability to the passage of water, improving the protection against corrosion of steel cores in concrete.

The thermal insulation property of the additive can achieve a reduction in the temperature of concrete-based structures, infrastructure, or buildings to a more comfortable temperature inside (up to 3 °C), reducing energy consumption for air conditioning and/or or heating in buildings.

References

  1. Janjaroen, Khammahong. The Mechanical and Thermal Properties of Cement CAST Mortar/Graphene Oxide Composites MaterialsInt J Concr Struct Mater (2022).
  2. Yi Yang, Jing Cao y col.Thermal Conductivity of Defective Graphene Oxide: A Molecular Dynamic Study. Molecules 2019, 24, 1103.
  3. Guojian Jing, Zhengmao Ye y col. Introducing reduced graphene oxide to enhance the thermal properties of cement composites. Cement and Concrete Composites 109 (2020) 103559.

Graphene and nanomedicine: the perfect combination for improved health

Posted on | by Energeia Graphenemex

Graphene and nanomedicine:

the perfect combination for improved health

Part III. Dentistry- Implantology

The application of nanotechnology in nanomedicine is based on the fact that most biological molecules, from DNA, amino acids and proteins to constituents such as hydroxyapatite and collagen fibrils, among others, exist and function at the nanometric scale.

Nanometer (nm): millionth of 1 millimeter.

Graphene materials are two-dimensional (2D) sheet-shaped carbon nanoparticles that have gained popularity in the field of biomedical sciences not only for their incredible mechanical, thermal, electrical, optical, and biological properties, but also for their ability to transfer these properties to other materials allowing the possibility of creating new compounds with advanced characteristics. In Odontology, and particularly in relation to implantology, this transfer of properties has opened numerous lines of research with great expectations due to the interesting synergistic effect between infection control and its regenerative capacity.1

Nanoparticle: particle that measures between 1 and 100 nm.

Graphene as a new strategy for the design and manipulation of dental implants and tissue regeneration. Taken from Tissue Eng Regen Med. 2017; 14(5):481

What are the problems that graphene could solve?

Osseointegration

One of the main concerns after the placement of an implant is the failure of its osseointegration. This can occur because instead of bone cells growing at the bone-implant interface, fibrous tissue grows that does not allow implant stabilization. An alternative to favor site conditions where cell interactions will occur is modification of the implant surface by physical or chemical methods to create nanoporosities that increase surface area and favor cell activity. 2

Osseointegration: Firm, stable, and long-lasting connection between an implant and the surrounding bone. Its success depends on biological and systemic factors of the patient, in addition to the characteristics of the implant.

In the case of graphene materials, in addition to their extensive and extremely thin surface area one atom thick, another of their added values is the cloud of electrons that surrounds them, and the presence of some oxygenated groups allows them to interact with proteins serum to form a focal adhesion. In other words, the hydrophobic/hydrophilic nature of these nanomaterials in combination with the roughness of the surface contributes to the interaction with proteins and later with cells, acting as a scaffold to promote the growth, differentiation, and anchorage of bone cells in the implant, paving the way for a stable and predictable osseointegration with a better projection of useful life.3,4

The regenerative impact of graphene materials lies in their great ability to adsorb proteins, creating a layer between cells and the surfaces of the materials to promote cell adhesion and proliferation.1

Infection control

Another cause for implant failure is the appearance of peri-prosthetic or peri-implant infections; to avoid them, it is common to use techniques such as antibiotic impregnation, local drug delivery systems, and the coating of implants with titanium nanotubes, silver nanoparticles, or polypeptide nanofilms for the controlled release of antibiotics.5 However, the worrying increase of antibiotic resistance has made these strategies less and less effective.

Graphene materials, in addition to their biocompatibility, have intrinsic antimicrobial properties with advantages over traditional antibiotics as they have less chance of developing microbial resistance. Odontology has been exploring these effects for several years on bioceramic materials such as alumina and zirconium, metals such as titanium, restorative materials such as glass ionomer, and polymeric materials such as polymethyl methacrylate (PMMA), to name a few. In general, the antimicrobial mechanisms accepted for these nanostructures are: 1) physical damage to the membrane, 2) oxidative stress, 3) inactivation by electron withdrawal, 4) isolation against the passage of nutrients and finally, 5) in the case of coatings, control of hydrophobicity and surface energy can also prevent cell attachment with low affinity and prevent biofilm formation.6,7

Biofilm: Layer of microorganisms that grow and adhere to the surface of a natural structure such as teeth (dental plaque) or artificial such as a medical device (intravascular catheters).

In 2021, a group of scientists from the University of Gwangju, Korea, published a study in which they coated zirconium implants with graphene oxide using the argon plasma method. Their results reported that this modification reduced by 58.5% the presence of Streptococcus mutans, the bacterium with the greatest influence on the formation of dental plaque and dental caries, agreeing with a significant reduction in biofilm thickness of 43.4%. In addition to the antimicrobial effect, they also showed a statistically significant increase of 3.2% and 15.7% in the proliferation and differentiation of bone cells.8 These results are consistent with what was reported by the Jiao Tong University, Shanghai, on a hybrid material of titanium with graphene. synthesized by the spark plasma sintering (SPS) technique. Similarly, the research demonstrated an interesting decrease in the formation of multibacterial biofilms composed of Streptococcus mutans, Fusobacterium nucleatum and Porphyromonas gingivalis, accompanied by an improvement in the activity of human gingival fibroblasts, one of the most important cell groups involved in healing.9 In addition to the synergy between infection control and its regenerative capacity, other studies related to dental implantology are also focusing their attention on the mechanical properties for the design of new implants or restorative materials. 10-12

Energeia-Graphenemex, the pioneering Mexican company in Latin America in the research and development of applications with graphene materials, throughout its 10-year career has overcome numerous scientific and commercial challenges to reach the market with products for different industries. And being aware that to reach the health sector it is essential to carry out exhaustive evaluations, kindly invites all those companies and/or research centers that are interested in continuing to explore the benefits of graphene materials and laying increasingly solid foundations on their safe use for biomedical applications.

Drafting: EF/DHS

References

  1. ¿Can Graphene Oxide Help to Prevent Peri-Implantitis in the Case of Metallic Implants? Coatings 2022, 12, 1202.
  2. New design of a cementless glenoid component in unconstrained shoulder arthroplasty: a prospective medium term analysis of 143 cases. Eur J Orthop Surg Traumatol 2013. 23(1):27–34 7.
  3.  European Journal of Orthopaedic Surgery & Traumatology (2018) 28:1257
  4. Graphene-Based Biomaterials for Bone Regenerative Engineering: A Comprehensive Review of the Field and Considerations Regarding Biocompatibility and Biodegradation. Adv. Healthc. Mater. 2021, 2001414.
  5. Nanotechnology and bone regeneration: a mini review. 2014 Int Orthop 38(9):1877–1884 /1. European Journal of Orthopaedic Surgery & Traumatology (2018) 28:1257
  6. Graphene: ¿An Antibacterial Agent or a Promoter of Bacterial Proliferation? iSciencie. 2020.  23, 101787
  7. Graphene: The game changer in dentistry. IP Annals of Prosthodontics and Restorative Dentistry 2022;8(1):10
  8. Antibacterial Activity of Graphene Depends on Its Surface Oxygen Content.
  9. Direct-Deposited Graphene Oxide on Dental Implants for Antimicrobial Activities and OsteogenesisInt. J. Nanomedicine 2021 :16 5745
  10. Graphene-Reinforced Titanium Enhances Soft Tissue Seal. Front. Bioeng. Biotechnol. 2021. 9:665305.
  11. Graphene-Doped Polymethyl Methacrylate (PMMA) as a New Restorative Material in Implant-Prosthetics: In Vitro Analysis of Resistance to Mechanical Fatigue. J. Clin. Med. 2023, 12, 1269.
  12. Mechanical Characterization of Dental Prostheses Manufactured with PMMA–Graphene Composites. Materials 2022, 15, 5391
  13. Fabrication and properties of in situ reduced graphene oxide-toughened zirconia composite ceramics. J. Am. Ceram. Soc. 2018, 101, 8

Innovation in the production of composite materials: the use of graphene in pultrusion

Posted on | by Energeia Graphenemex

Innovation in the production of composite materials:

the use of graphene in pultrusion

Fiber-reinforced polymeric composites are widely used in the aerospace, automotive, naval, and wind power generation sectors due to their lightweight properties and high mechanical strength. These materials are a booming alternative to replace other materials such as metals.

At present there are different methods for the manufacture of fiber-reinforced composites, among which the pultrusion method stands out. A highly efficient and automated method that allows control of process parameters (greater precision and accuracy), reducing variability in the production of parts.

Pultrusion is a production process for reinforced materials where two components can be distinguished, the matrix or continuous phase and the reinforcement or discontinuous phase. The matrix acts as a bonding agent, in which the reinforcement is embedded. The function of the matrix is to transfer the load to the fibers, keep the fibers in their position, prevent the propagation of cracks, provide physical and chemical properties of the composite and also define the temperature range that the composite material can withstand. The matrix is thermosetting or thermosetting (unsaturated polyester, epoxy resins or vinyl-ester resins). On the other hand, the reinforcement has the purpose of adding some property that the matrix does not have, such as increasing mechanical resistance, rigidity, resistance to abrasion or improving its performance when exposed to high temperatures. The reinforcement efficiency is greater, the smaller the size of the particles or the diameter of the fiber and the more homogeneously they are distributed in the matrix. The most used fibers are glass, carbon and aramid due to their high tensile strength.

The pultrusion process (Figure 1) is continuous and is used to manufacture parts with a constant cross section, such as poles, rods, automotive moldings, etc. In the first feeding stage, the reinforcing fibers go through a perforated plate for alignment, then they go through a pre-molding where a fabric is added to reinforce the fiber. Later, in the second stage, the fibers are impregnated with liquid resin and go to a pre-forming stage where the fibers are oriented before entering the mold. In the third stage (molding), the cross section of the part is shaped, and the resin is hardened by applying heat. During the application of heat in the mold, there are three phases: pre-heating of the matrix and reinforcement, activation of the polymerization catalyst and curing of the material. The profile then exits the mold as a thermoset material and passes into a continuous traction mechanism that pulls the material at a constant speed (fourth stage)). Finally, in the fifth stage, a disk saw cuts the profile to the desired length. The profile of the reinforced composite obtained is a completely rigid material, which does not soften and is insoluble with the ability to withstand high temperatures.

Figure 1. General scheme of the pultrusion process: (1) Feeding, (2) Impregnation, (3) Molding, (4) Traction device and (5) Saw (Cutting).

Currently, the main applications of this process are focused on the manufacture of materials for construction, transport, and consumables, for example: vehicle construction, thermal insulation, cable ducts, covers and grids for water treatment plants, beam profiles, building facades, windows, bridges, stairs, among others.

However, there are still limitations in this technology, the low chemical interaction of the fiber with the matrix (resin) leads to a weak interface bond strength between both phases (low chemical adhesion), which makes the behavior of interlaminar shearing and performance of composite materials is not entirely satisfactory. In other words, if the matrix is brittle, spontaneous rupture can be generated. This behavior makes it possible to measure the resistance to interlaminar shearing. Depending on the type of break, the resistance of the matrix material or the quality of the fiber-matrix bond can be characterized.

In recent years, it has been reported that the introduction of functionalized graphene oxide (GO) on the surface of the fibers is an effective method to improve the interfacial properties of composite materials, since the large surface area of graphene oxide allows covering the surface of the fibers, increasing the strength of the chemical bond between the fiber and the matrix, thus improving the mechanical resistance of the reinforced composites. In addition, graphene oxide helps to improve the resistance to interlaminar fracture of the composite material, inhibiting the initiation and propagation of cracks.

The addition of graphene oxide to reinforced polymeric composites offers numerous advantages for the development of advanced materials in a wide variety of applications due to its large surface area, which has a strong impact on mechanical strength properties, greatly improving properties such as modulus, toughness, and fatigue. On the other hand, graphene oxide can provide compounds with greater resistance to fire. Its efficiency is associated with the fact that graphene oxide has a strong barrier effect, high thermal stability, and great surface absorption capacity, which are favorable for effectively reducing heat and mass transfer.

Currently, Energeia – Graphenemex®, a leading Mexican company in Latin America in the research and production of graphene materials for the development of applications at an industrial level, sells graphene and graphene oxide that can be incorporated or dispersed in any matrix (resin) during the pultrusion process and with them improve the mechanical properties of the profiles or products.

The incorporation of graphene materials (graphene, graphene oxide) in the pultrusion process, provide improvements in the characteristics of the final product, which include:

  • Greater tensile strength. Tensile strength can increase up to 30% compared to a standard profile without graphene.
  • Production of lighter weight profiles since graphene allows the weight of the product to be reduced without affecting its mechanical properties.
  • Profiles with higher modulus of elasticity.
  • Greater resistance to corrosion and fire-retardant properties.
  • Greater resistance to fractures or fissures.

References

  1. Yuxin He, Qiuyu Chen. Effect of multiscale reinforcement by fiber surface treatment with polyvinyl alcohol/graphene oxide/oxidized carbon nanotubes on the mechanical properties of reinforced hybrid fiber composites. Composites Science and Technology 204 (2021).108634.
  2. Jonas H. M. Stiller, Kristina Roder, David Lopitz. Combining Pultrusion with carbonization: Process Analysis and materials properties of CFRP. Ceramics 2023, 6. 330-341.
  3. Dittrich B, Wartig K-A, Hofmann D, Mu¨lhaupt R, Schartel B. Flame retardancy through carbon nanomaterials: carbon black, multiwall nanotubes, expanded graphite, multi-layer graphene and graphene in polypropylene. Polym Degrad Stab 98:1495.

The safety of graphene in human health: what science says about it

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The safety of graphene in human health:

what science says about it

Part II. Are graphene materials safe for humans?

The family of graphene materials comprises a wide range of two-dimensional (2D) carbon nanostructures in the form of sheets that differ from each other by the particularities derived from the production method or by the innumerable functionalizations that can be performed after its obtaining. In 2022, Nature magazine, one of the most important scientific journals in the world, published a study in which 36 products from graphene suppliers from countries such as the United States, Norway, Italy, Canada, India, China, Malaysia and England were analyzed, concluding that graphenes represent a heterogeneous class of materials with variable characteristics and properties, whether mechanical, thermal, electrical, optical, biological, etc., which can be transferred to a large number of three-dimensional (3D) compounds to modify or create new products.

“Undoubtedly, graphene and nanotechnology in general continue to be controversial issues as they confront us with a world that is difficult to see and understand, but with simply amazing effects”

Are graphene materials safe?

Graphene materials promise to be an important tool within biomedical technologies. In principle, its benefits can be used for the design of diagnostic elements such as sensors and devices for images up to neural interfaces, gene therapy, drug delivery, tissue engineering, infection control, phototherapy for cancer treatment, bioelectronic and dental medicine, among other. But for them to be truly used in this type of technology, their interactions with the biological environment must first be understood or, failing that, ensure that their presence does not alter the natural environment of the cells. In this sense, numerous studies have been carried out with the different forms, presentations, and available concentrations of graphene whose findings have gradually paved the way for its safe use in biomedical technologies:

i) Graphene materials in their free form. In in vitro tests, exposure of human lung epithelial cells to graphene sheets at concentrations lower than 0.005 mg/ml did not cause significant changes in their morphology or adhesion,2,3 nor was cytotoxic activity identified in stem cells derived from adipose tissue. human, periodontal ligament and dental pulp exposed to 0.5 mg/ml of GO,4 even and understanding a possible dose-size dependent effect, other investigations report safe concentrations below 40 mg/ml or, that do not exceed 1, 5% w/v. 5-8

Finally, one of the most recent in vivo studies published by the University of Manchester, United Kingdom, on the pulmonary response of mice exposed to graphene oxide (GO) in the respiratory tract, did not identify significant damage or pulmonary fibrosis at 90-day follow-up. These results provide solid grounds for the safety of these nanostructures without underestimating basic safety measures, such as avoiding their inhalation.9 Likewise, scientists from the University of Trieste, Italy, analyzed the impact of graphene materials on the skin, reporting low toxicity on cells.10

“It is unlikely that graphene materials in their free form are used to be in contact with the biological environment, they are generally functionalized or immobilized in other materials to develop an application”

ii) Functionalized graphene materials. Functionalization is the term that refers to the chemical modification of a nanomaterial to give it a “function”, that is, to facilitate its incorporation with other compounds or to benefit its biocompatibility and better direct its use by anchoring functional groups, molecules, or nanoparticles. A study published in the journal Nature Communications on graphene bioapplications highlights the importance of its functionalization with amino groups to make it more compatible with human immune cells.11,12

“The most common functionalization of graphene is the anchoring of oxygenated groups on its surface, this material is known as graphene oxide”

iii) Immobilization in polymers. The use of graphene materials as nano-filling for plastics, resins, coatings, etc., is the most common way in which these nanostructures are used. For the biomedical sector, its immobilization in polymers has shown good biocompatibility and stimulation of cell proliferation; antimicrobial activity and improvement of the mechanical properties of polymers, being classified as excellent candidates for the manufacture of bone fixation devices, molecular scaffolds, orthopedic implants, or dental materials.13-15

Given the great potential of graphene materials in health sciences, but also due to the many questions about their safety, an international research team from the European Graphene Flagship project, led by EMPA (German acronym for the Federal Institute for Testing and Materials Research), conducted a study to assess the potential health effects of graphene materials immobilized within a polymer; the results showed that the graphene particles released from said polymeric compounds after abrasion induce insignificant effects.16

“It is reassuring to see that this study shows negligible effects, confirming the viability of graphene for mass applications. Andrea C. Ferrari, Graphene Flagship Science and Technology Officer.” 17,18

Energeia-Graphenemex, the pioneering Mexican company in Latin America in the research and development of applications with graphene materials, throughout its 10-year career has overcome numerous scientific and industrial challenges to reach the market with products for industrial use. In 2018, it began to explore the antimicrobial capabilities of its products with excellent results in vitro and in a relevant environment; currently, and in conjunction with other research centers, it is carrying out evaluations to explore the potential of its materials as nano-reinforcement of biopolymers.

Drafting: EF/DHS

References

  1. Cytotoxicity survey of commercial graphene materials from worldwide. npj 2D Materials and Applications (2022) 6:65
  2. Biocompatibility of Pristine Graphene Monolayers, Nanosheets and Thin Films. 2014, 1406.2497.
  3. Preliminary In Vitro Cytotoxicity, Mutagenicity and Antitumoral Activity Evaluation of Graphene Flake and Aqueous Graphene Paste. Life 2022, 12, 242
  4. Biological and physico-mechanical properties of poly (methyl methacrylate) enriched with graphene oxide as a potential biomaterial. J Oral Res 2021; 10(2):1
  5.  Graphene substrates promote adherence of human osteoblasts and mesenchymal stromal cells. Carbon. 2010; 48: 4323–9
  6. Multi-layer Graphene oxide in human keratinocytes: time-dependent cytotoxicity. Prolifer Gene Express Coat 2021; 11:1
  7. Cytotoxicity assessment of graphene-based nanomaterials on human dental follicle stem cells. Colloids Surf B Biointerfaces. 2015; 136:791
  8. Arabinoxylan/graphene-oxide/nHAp-NPs/PVA bionano composite scaffolds for fractured bone healing. 2021. J. Tissue Eng. Regen. Med. 15, 322.
  9. Size-Dependent Pulmonary Impact of Thin Graphene Oxide Sheets in Mice: Toward Safe-by-Design. Adv. Sci. 2020, 7, 1903200
  10. Differential cytotoxic effects of graphene and graphene oxide on skin keratinocytes. 2017. Sci Rep 7, 40572
  11. Amine-Modified Graphene: Thrombo-Protective Safer Alternative to Graphene Oxide for Biomedical Applications. ACS Nano 2012, 6, 2731
  12. Single-cell mass cytometry and transcriptome profiling reveal the impact of graphene on human immune cells. Nature Communications, 2017, 8: 1109,
  13. In-vitro cytotoxicity of zinc oxide, graphene oxide, and calcium carbonate nano particulates reinforced high-density polyethylene composite. J. Mater Res. Technol. 2022. 18: 921
  14. Graphene-Doped Polymethyl Methacrylate (PMMA) as a New Restorative Material in Implant-Prosthetics: In Vitro Analysis of Resistance to Mechanical FatigueJ. Clin. Med. 2023, 12, 1269
  15. High performance of polysulfone/ Graphene oxide- silver nanocomposites with excellent antibacterial capability for medical applications. Matter today commun. 2021. 27
  16. Hazard assessment of abraded thermoplastic composites reinforced with reduced graphene oxide. J. Hazard Mater. 2022. 435. 129053
  17. https://www.empa.ch/web/s604/graphene-dust
  18. https://www.graphene-info.com/researchers-asses-health-hazards-graphene-enhanced-composites

Graphene in protection against electromagnetic radiation

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Graphene in protection

against electromagnetic radiation

The development of communication technology together with electronic devices has generated great concern regarding the electromagnetic radiation emitted by these technologies.

Electromagnetic radiation is a type of electromagnetic field, that is, a combination of oscillating electric and magnetic fields, which propagates through space carrying energy from one place to another. Electromagnetic radiation can manifest itself in various ways, such as radio waves, microwaves, infrared radiation, visible light, ultraviolet radiation, X-rays or gamma rays and correspond to different wavelengths, ranging from kilometers (radio waves) to the order of picometers (gamma rays). The full range of wavelengths is what is called the electromagnetic spectrum (Figure 1.).

Figure 1. Electromagnetic spectrum.

Electromagnetic radiation can be high frequency (radiation from mobile and wireless telephones, radio frequencies, TV waves, microwaves, radar, satellite signals, Wi-Fi, Bluetooth) and low frequency (fields generated by cables or electrical consumers).

Heat and electromagnetic radiation (EM radiation) are unavoidable by-products in electronic devices, especially those that operate at high frequencies. As electronic devices get smaller, they operate at higher and higher frequencies, generating even more heat and electromagnetic waves.

High frequency electromagnetic radiation not only degrades the devices themselves (producing heat), but also tends to interfere with neighboring electronic devices and most importantly, it has an adverse effect on human health as it can cause many diseases, such as leukemia, miscarriages, and brain cancer.

Therefore, the blocking or protection (shielding) against electromagnetic radiation could be one of the solutions to minimize health risks and for the protection of electronic equipment and/or devices. Metals are natural electromagnetic blocking materials, capable of reflecting electromagnetic waves due to their free electrons, which explains their high electrical conductivity and low penetration depth. However, their heavy weight, cost and the susceptibility of metals to corrosion make their use limited if not impossible.

The use of conductive coatings or paints to block electromagnetic radiation is the most viable option to solve the problem. Graphene is currently the most revolutionary nanotechnological additive in the coatings industry. Because graphene has extraordinary properties, which include high electrical conductivity, high thermal conductivity, and mechanical resistance. In addition, it possesses other distinctive properties, including gas impermeability, chemical resistance, antibacterial potential, and large surface area.

The electrical conduction capacity and thermal conductivity of graphene can be exploited in the formulation of shielding coatings against EM radiation, since graphene forms a continuous network along the surface of the coating, creating homogeneous films that block radiation. electromagnetic radiation while dissipating excess heat. In recent studies, it has been reported that the incorporation of carbon-based nanostructures, such as graphene in coatings or paints, allows the development of coatings with high electrical conductivity for shielding or protection against electromagnetic interference (EMI). The way to act with respect to high frequency electromagnetic waves is by refraction. Electromagnetic waves will bounce (reflect) off the treated surface similar to the effect of a mirror with respect to light (See Fig. 2). The barrier-effect in the propagation could be attributed to the contribution coming from the reflection capacity, the absorption and multiple internal reflections. The shielding efficiency increases with the addition of a higher concentration of graphene in the polymeric matrix of the coating. These graphene coatings can block more than 99.98% of high-frequency electromagnetic radiation.

Figure 2. Percentage of Reflection, absorption and transmission of pristine epoxy (a) and epoxy with graphene (b).
Taken from Adv. Electron. Mater. 2019, 5. 1800558

These coatings against electromagnetic radiation can act for both high frequency and low frequency, with an excellent quality of attenuation (decrease in intensity of signals or electric waves) of up to 38 dB, with one hand, and 47 dB if applied. two hands.

Energeia – Graphenemex®, a leading Mexican company in Latin America in research and production of graphene materials for the development of applications at an industrial level, through its Graphenergy line, is constantly researching and developing new multifunctional coatings and currently has for sale a wide range of nanotechnological coatings with graphene. Shielding coatings against electromagnetic radiation are currently being developed and evaluated. Coatings with high electrical conductivity, to reduce high and low frequency electrical fields respectively. These coatings will also offer anticorrosive and antimicrobial protection. In addition, to provide high resistance to wear, resistance to UV rays, impermeability and extraordinary adhesion.

Referencias

  1. Suneel Kumar Srivastava, Kunal Manna, Recent advancements in the electromagnetic interference shielding performance of nanostructured materials and their nanocomposites: a review, Journal of Materials Chemistry A, 10.1039/D1TA09522F, 10, 14, (7431-7496), (2022).
  2. Kargar, F., Barani, Z., Balinskiy, M., Magana, A. S., Lewis, J. S., Balandin, A. A., Adv. Electron. Mater. 2019, 5, 1800558.
  3. Seul Ki Hong et al 2012 Nanotechnology 23 455704.
  4. Lekshmi Omana, Anoop Chandran*, Reenu Elizabeth John, Runcy Wilson. Recent Advances in Polymer Nanocomposites for Electromagnetic Interference Shielding: A Review. Omega 2022, 7, 30, 25921–25947

Graphene: The next revolution in biomedical applications

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Graphene:

The next revolution in biomedical applications

Part I. Tissue Engineering

Advances in medicine have reached levels unimagined until recently. Among them, tissue engineering has an important participation. With it is possible to combine cells, biomaterials and biologically active molecules with the aim of repairing or replicating tissues or organs with a function similar to that of the original structure. In principle, biomaterials are used as molecular scaffolds to act as a three-dimensional (3D) support or guide for the anchoring and growth of the cells that will be in charge of forming the new tissue.

The first molecular scaffolds were designed with natural materials such as collagen, glycosaminoglycans (GAGs), chitosan, and alginates; then with artificial compounds such as polylactic acid (PLA), polyglycolic acid (PGA), poly(lactic-co-glycolic) acid (PLGA), polyurethanes (PUs), polytetrafluoroethylene (PTFE), polyethyleneterephthalate (PET); bioceramics such as hydroxyapatite (HA) and tricalcium phosphate; metals such as stainless steel, chrome-cobalt alloys (Co-Cr) or titanium alloys (Ti) and recently, new research is oriented towards the use of nanotechnology.

The relationship between nanotechnology and tissue engineering is due to the fact, that the extracellular matrix (ECM) that helps cells unite and communicate with each other, is made up of a network of nanometer-sized fibers made up of bioactive molecules. It is at this point where nanotechnology opens new possibilities for regenerative medicine, since it has been proven that the use of materials that act on the same nanometric scale as the ECM favors mimicking the physiological environment of the organism to stimulate cell growth and differentiation in a more natural environment.

Among the most studied nanomaterials in recent years are graphene materials, which consist of nanometric sheets of carbon atoms organized in two-dimensional (2D) hexagonal networks. Among the most interesting properties for tissue engineering are: its large surface area, mechanical resistance, thermal conductivity, biocompatibility and finally, an extraordinary ability to share its properties with other materials to improve their original characteristics.

For example, the use of graphene materials within the 3D architecture of certain biopolymers in tests carried out on heart, liver, bone, cartilage, and skin tissues has shown substantial improvements in their physicochemical, mechanical, electrical and biological properties, achieving excellent response. for stem cell adhesion and differentiation.

In 2022, the Andaltec technology center (Spain) reported the development of a material from polymers derived from graphene by 3D printing with great potential for the regeneration of muscle tissue. They demonstrated that in the presence of graphene derivatives, cells contract and expand without an external stimulus, therefore, it has great potential for use in regenerative medicine.

On the other hand, the Division of Postgraduate Studies and Research (DEPeI) on Odontology, UNAM and the National School of Higher Studies (ENES) León Unit, Mx., through a study published in J Oral Res 2021 supports the possibilities of graphene oxide (GO) in the design of biomaterials for dental use. The results of the research carried out with Graphenemex® GO samples, concluded that this nanomaterial in combination with polymethylmethacrylate (PMMA), in addition to improving its physical-mechanical properties, also demonstrated good compatibility and an interesting stimulation of cell proliferation when being evaluated on cultures with gingival-fibroblasts, dental-pulp-cells and human osteoblasts.

In 2020, researchers from the University of Malaga (Spain) published another study that identified GO as the ideal material for regenerative medicine. The study carried out on an animal model, showed high biocompatibility of different types of graphene oxide with dopaminergic cells, favoring their maturation and protecting them from the toxic conditions of Parkinson’s disease. These results postulate GO as an adequate scaffold to test new drugs or develop constructs for cell replacement therapy of Parkinson’s disease.

Despite the large amount of research on the interactions of graphene materials with biological media, there is still a long way to go to have these biomaterials available and in clinical operation. Energeia- Graphenemex, the pioneering Mexican company in Latin America in the research and development of applications with graphene materials, in collaboration with other companies and research centers, seeks to contribute with science to understand these interactions in a security framework, to lay solid foundations on the use of graphene nanotechnology in the biomedical sector for the benefit of society.

Drafting: EF/DHS

References

  1. Graphene and its derivatives: understanding the main chemical and medicinal chemistry roles for biomedical applications. J Nanostructure Chem, 2022, 12:693
  2. Biological and physico-mechanical properties of poly (methyl methacrylate) enriched with graphene oxide as a potential biomaterial. J Oral Res 2021; 10(2):1
  3. Graphene-Based Antimicrobial Biomedical Surfaces. ChemPhysChem 2021, 22, 250
  4. Functionalized Graphene Nanoparticles Induce Human Mesenchymal Stem Cells to Express Distinct Extracellular Matrix Proteins Mediating Osteogenesis. Int J Nanomed 2020:15 2501
  5. Graphene Oxide and Reduced Derivatives, as Powder or Film Scaffolds, Differentially Promote Dopaminergic Neuron Differentiation and Survival. Front. Neurosci., 21 December 2020. Sec. Neuropharmacology Volume 14
  6. International Journal of Nanomedicine 2019:14 5753
  7. Biocompatibility Considerations in the Design of Graphene Biomedical Materials. Adv. Mat. Interfaces 2019, 6, 1900229
  8. Graphene based scaffolds on bone tissue engineering. Bioengineered, 2018, 9:1, 38
  9. When stem cells meet graphene: Opportunities and challenges in regenerative medicine. Biomaterials, 2018, 155, 236
  10. Graphene-based materials for tissue engineering. Adv. Drug Deliv. Rev. 2016,105, 255

Chapter 92 e: Tissue Engineering, Anthony Atala. 2023 McGraw Hill.

Improve safety with flame retardant polymeric compounds with graphene oxide

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Improve safety with flame retardant polymeric compounds

with graphene oxide

Polymeric compounds (engineering plastics) are widely used in the automotive, construction, food, aerospace and other sectors. Its use is based on the weight/resistance ratio, physical stability, chemical resistance and corrosion resistance.

However, most polymers, due to their nature, are flammable and combustible. That is, they are materials that catch fire quickly when exposed to fire, undergoing degradation, Veo complicadoand releasing heat to later start the propagation of the flames. During the combustion of polymers, they release smoke (soot) and toxic gases that are a danger to the safety of human life and property.

Four key components are involved during the combustion of polymeric materials: heat, oxygen, fuel, and free radical reaction. Flame retardancy of polymeric composites can be achieved by inhibiting or perturbing one or more of these components.

In recent years, multiple investigations have been carried out to develop additives that help inhibit or reduce the flammability of polymers, these additives are known as flame retardants.

Conventional flame retardants can be classified into two main categories, based on their components: inorganic flame retardants and organic flame retardants. The first include hydroxide, metal oxide, phosphate, silicate among others. They have excellent thermal stability, are non-toxic, are low cost and do not produce pollution. However, inorganic flame retardants are limited by high loading, low compatibility, and aggregation. On the other hand, organic flame retardants include flame retardants containing halogens, phosphorous, phosphorous-nitrogen, etc. The latter have high efficiency and good compatibility with polymers. Their main disadvantage is that they are restricted because they can release toxic gases and be harmful during combustion, endangering the health of people and the environment.

Graphene oxide (GO) is currently the most novel nanomaterial for use as a flame retardant because it exhibits high efficiency as a retardant with low loads and is non-toxic. Its efficiency is associated with the fact that graphene oxide has a strong barrier effect, high thermal stability and great surface absorption capacity, which are favorable for reducing heat and mass transfer.

Graphene-based flame retardants can improve the flame resistance of polymers by inhibiting the two key terms: heat and fuel. More specifically, graphene oxide can function as a flame retardant in different synergistic ways.

  1. First of all, GO has a unique two-dimensional layer structure and can promote the formation of a continuous dense layer of carbon during the combustion process. Carbon can act as a physical barrier to prevent heat transfer from the heat source and delay the escape of products (pyrolysis) from the polymeric substrate.
  2. Second, GO has a large specific surface area and can effectively adsorb flammable volatile organic compounds or hinder their release and diffusion during combustion.
  3. Third, GO contains abundant reactive oxygen-containing groups (carboxyl group at the edges, as well as epoxy and hydroxyl groups at the basal planes in the sheets). For example, oxygen-containing groups can undergo decomposition and dehydration at low temperatures, thus absorbing heat and cooling the polymeric substrate during combustion. Meanwhile, the gases generated by dehydration can dilute the oxygen concentration around the ignition periphery, decreasing the risk of fire spread.
  4. It can also modify the rheological behavior of the polymer and prevent its dripping, thus hindering the release and diffusion of volatile decomposition products through the ”maze effect” and affecting the flame retardancy of compounds (for example, modifying the UL-94 classification, oxygen index (OI) and time to ignition (TTI).

In studies carried out, it has been found that the incorporation of functionalized graphene oxide (5% by weight) in Polypropylene (PP) increased the Young’s modulus and the elastic limit of PP by 53% and 11%, respectively. While in the results of the flammability test (UL-94), it indicates that the presence of GO produces a change in the behavior of the melt and prevents the material from dripping.

On the other hand, the preparation of polymeric compounds in melt blending (extrusion) of Polystyrene/GO have been reported, where it was found that GO (5%) can promote carbonization on the polymer surface (layer of carbonized material). and inside, the presence of a load or filler that presents high resistance to heat and contributes to the formation of carbon residues, improving the flame resistance of polystyrene-based compounds.

Currently Energeia – Graphenemex®, a leading Mexican company in Latin America in research and production of graphene materials for the development of applications at an industrial level, through its Graphenergy Masterbatch line, has developed a wide range of masterbatches with graphene oxide, based on various polymers, such as PP, HDPE, LDPE, PET and PA6.

The incorporation of graphene and graphene derivatives (GO) to polymeric matrices has allowed the development of polymeric compounds with better mechanical properties, greater thermal stability, gas barrier capacity and reduced flammability of polymeric compounds.

References

  1. Han Y, Wu Y, Shen M, Huang X, Zhu J, Zhang X. Preparation and properties of polystyrene nanocomposites with graphite oxide and graphene as flame retardants. J Mater Sci 48:4214.
  2. Hofmann D, Wartig K-A, Thomann R, Dittrich B, Schartel B, Mu¨lhaupt R. Functionalized graphene and carbon materials as additives for melt-extruded flame retardant polypropylene. Macromol Mater Eng 298:1322.
  3. Dittrich B, Wartig K-A, Hofmann D, Mu¨lhaupt R, Schartel B. Flame retardancy through carbon nanomaterials: carbon black, multiwall nanotubes, expanded graphite, multi-layer graphene and graphene in polypropylene. Polym Degrad Stab 98:1495.