Epoxy Polymer Research Articles

Microscopic deformation and failure modes of high‐functionality epoxy resins from bond breaking molecular dynamics simulations and experimental investigation

AbstractThe material behavior of the API‐60 epoxy resin was investigated using atomistic molecular dynamics simulations. In this study, a hybrid, reactive force field (M‐GAFF2), which combined Morse and harmonic bond potentials from GAFF2, was developed to understand the elastic/plastic response of the cured epoxy polymer. We found that elastic deformation was caused by epoxy network rearrangement at low strain while plastic deformation was observed by stretching and breaking covalent bonds after the yield point. Ab initio calculations at the CASPT2(2,2)/6‐311+G** level of theory were performed to compute parameters for M‐GAFF2. These are necessary for breaking covalent bonds in the epoxy network backbone when they are deformed. The M‐GAFF2 was effective in revealing the ductile‐like deformation behavior of the crosslinked epoxy polymer at the microscopic level, including elastic/plastic deformations and progressive failure. The effect of testing temperature at 300 and 400 K and degree of cure (DoC) on tensile properties such as Young's modulus, ultimate strength, and failure strain was evaluated to verify the feasibility of the M‐GAFF2 in different thermodynamic constraints. This new approach is easy to use for nonequilibrium MD simulations and computationally efficient for studying the microscopic deformation and failure behavior of thermosetting polymers at the atomistic scale.

Fully recyclable and high-performance carbon fiber composites based on thermoplastic epoxy polymer

In this paper, a linear and highly polymerized thermoplastic epoxy (TPE) is treated as the matrix to prepare the fully recyclable and high performance carbon fiber reinforced TPE composites (CFRTPE). The TPE is synthesized from bisphenol A epoxy and aniline through a simple polymerization process, whose mechanical and thermal properties (tensile strength: 65 MPa, tensile modulus: 2.3 GPa, initial decomposition temperature: 365.4 °C) are comparable to that of traditional bisphenol A epoxy based thermoset. The CFRTPE composites samples could be prepared by prepreg through molding and vacuum bag method with the mild conditions (180 °C for 20 min). The mechanical and thermomechanical properties testing results show that the CFRTPE could achieve comparable and even better mechanical performance compared with the reference specimen and literature reports. Most importantly, both the full-length CFs and TPE of CFRTPE composites could be recycled conveniently and rapidly at room temperature without damaging the morphologies and mechanical properties, which indicates promising potential for practical applications.

Mechanical Evaluation on Carbon/Basalt Fiber-Reinforced Hybrid Polymer Matrix Composite

This work is about making hybrid composite materials out of carbon fiber mats and basalt fiber mats that are 40% reinforced with a 60% epoxy polymer matrix. Traditional hand layup has been used for the fabrication process to make five laminates of these two fibers. The mechanical properties of the hybrid composite were evaluated by measuring its tensile strength, flexural strength, impact energy, and hardness. The results showed that adding more carbon fiber layers to the composite made a big difference in its mechanical properties. In sample A, the tensile strength is 280 MPa, the flexural strength is 247 MPa, and the basalt fiber can keep more impact energy of 24 J in sample E, along with the carbon fiber and epoxy matrix. A scanning electron microscope was used to figure out how carbon/basalt fiber composite laminates break down.

Chemical structure change of lignin extracted from bamboo biomass by maleic acid

Maleic acid (MA) is an effective solvent for lignin extraction from raw biomass under mild conditions through acidolysis and hydrophobic interaction. To improve the valorization of lignin, the lignin extracted with MA was subjected to successive organic solvent fractionation to make the narrow Mw and Mn distribution and the homogeneity structure of lignin fragments. After successive organic solvent fractionation, the dispersity index (Đ) of lignin reduced from 2.86 to 1.25, and the purity and homogeneity were greatly improved. The phenolic hydroxyl content of lignin extracted by ethyl acetate was the highest (2.45 mmol/g), and the aliphatic-OH concentration was the lowest (0.65 mmol/g). While the βO4 bonds were partially cleaved, more hydrophobic substrates with CC linkages were recovered by ethyl acetate. Lignin fragments with a variety of main structures and functional groups were obtained effectively with successive fractionation. This method supplied broad prospects for the preparation of lignin and its applications in epoxy resin, rubber, thermoplastic additives and polymer raw materials.

3D Printing of Frontal-polymerized Multiscale Epoxy Thermoset and Composites

Epoxy thermosets and their composites demonstrate an intensive application due to their high strength, chemical resistance, and lightweight while the conventional manufacturing methods are very difficult to fabricate complex geometry and also time-consuming and energy-intensive. Frontal polymerization based in-situ curing provides an alternative efficient way in the additive manufacturing of epoxy thermosets with both design and manufacturing freedom. However, low reactivity of epoxy resins makes it difficult to integrate frontal polymerization of epoxy resin into energy-efficient additive manufacturing. Carbon nanotubes (CNTs) catalyzed frontal polymerization of epoxy resins afforded a new way to free-form manufacturing of epoxy thermosets with low energy consumption and design flexibility. In this paper, frontal curing of epoxy resins was tuned by CNT catalysation and then integrated to fast printing of multiscale epoxy composites. Specifically, discontinuous CNTs and continuous carbon fibers (c-CF) were integrated to print frontal-cured multiscale epoxy composites. The mechanical tests indicated that the CNTs/c-CF/epoxy thermosets composites demonstrated a tensile strength of 1.2GPa while the CNTs/epoxy thermosets only showed a tensile strength of around 50 MPa. The young’s modulus of the CNTs/c-CF/Epoxy thermosets reached 95 GPa, around 9-fold higher than that of the CNTs/Epoxy thermosets. This emerging technology provides a new direction for thermosets and composites manufacturing.

Design and Investigation of Dynamic Properties of the Developed Glass-Jute-CGS Fiber Reinforced Hybrid Epoxy Polymer Composites for High-Performance Applications

Abstract In the current investigation, hybrid polymer composites developed using alkali treated Calotropis Gigantea stem fibers (CGS) as well as jute (J) and glass (G) fibers with different weight percentages are incorporated into the epoxy matrix. The dynamic characteristics for the inclusion of CGS fibers with glass-jute fiber reinforced epoxy-based laminates were determined experimentally. Here, three different sets of laminates, namely G-CGS-J-CGS-G, G-J-CGS-J-G, and G-CGS-CGS-CGS-G, were fabricated by means of the hand lay-up method. In addition, different weight percentages (wt. %) of CGS fibers, 0 wt. %, 5 wt. %, 10 wt. %, 15 wt. %, 20 wt. %, and 25 wt. %, were incorporated in the glass-jute fiber reinforced epoxy resin. The various analytical characterization results confirm that the incorporation of CGS fibers in the glass-jute fiber reinforced epoxy resin enhances the dynamic properties of the glass-jute fiber reinforced epoxy-based laminates, such as storage modulus, loss modulus, and tanδ values. The morphology of the fractured specimens due to the damage mechanisms was observed using a scanning electron microscope. Further, it was observed that the highest improvement in dynamic properties was achieved for the G-J-CGS-J-G hybrid laminate with 20 wt. % incorporated CGS fibers. The maximum storage modulus was observed in the G-J-CGS-J-G laminate of 8.263 Pa, with a loss modulus of 7.345 Pa and tanδ of 0.433 for 20 wt. % of CGS fibers. From the overall results, it was concluded that the hybrid laminate with 20 wt. % incorporated CGS fibers could be used for high-performance automobile interior applications.

Influence Of Dewaxing on Mechanical properties of kapok fiber-reinforced polymer composite

The low density, lightweight, easy processing and biodegradability nature of Natural fiber-reinforced polymer composite have gained enough attention from many researchers and scientists. Kapok Fiber (Ceiba pentandra) is a natural cellulosic fiber have a hollow microtubular structure and a high degree of hollowness. The hand lay-up technique has been adopted for kapok fiber-reinforced epoxy polymer composite fabrication with different fiber loading(2, 3, 4, 5, 6 and 7 wt %). The mechanical strength of kapok fiber-reinforced polymer epoxy composite is investigated through the flexural and tensile test. The best flexural and tensile performance is observed at 5 wt% loading of kapok fiber. To increase compatibility between fiber and epoxy matrix dewaxing process is adopted. The effect of dewaxing on cellulose crystallinity, crystallinity size, surface morphology, elemental composition and functional groups of fiber are studied. The roughness of the fiber surface increases after dewaxing due to the partial removal of non-cellulosic compounds like lignin, pectin, wax and some oily substances. The increase in fiber surface roughness and cellulose crystallinity index by chemical treatment made a strong interlocking at the fiber-matrix interface. The effect of dewaxing on mechanical strength is also studied to fabricate the composite for the benefit of society.

Effect of zirconia nanoparticles modified by silane coupling agent on some properties of epoxy coating

Effect of zirconia nanoparticles (zirconia NPs/ZrO2 NPs) modified by 3 wt.% (glycidyloxypropyl) triethoxysilane – GPTES (m-ZrO2 NPs) on some properties of epoxy coating such as mechanical properties, thermal stability and anti-corrosion performance was investigated. The obtained results indicated that the addition of zirconia nanoparticles to epoxy coating could enhance the properties of this coating. The addition of 2 wt.% of pure ZrO2 NPs (u-ZrO2 NPs) to the epoxy matrix could increase the mechanical properties (hardness and adhesion to the steel substrate) by approximately 10 %, the onset temperature of thermal degradation of the epoxy/u-ZrO2 NPs coating was 4.4 oC higher, and the anti-corrosion performance of epoxy coating was improved in comparison with the neat epoxy coating. Organically modified ZrO2 NPs had higher improvement for epoxy coating’s properties than pure ZrO2 NPs. The epoxy coating filled with m-ZrO2 NPs had 19.7 % higher in relative hardness, 88.73 % more in adhesion to steel substrate, 25.6 oC higher in the onset temperature of thermal degradation, and higher anti-corrosion performance in comparison with the epoxy coating filled with 2 wt.% of pure zirconia nanoparticles. The cross-section FESEM images of the epoxy/m-ZrO2 NPs coating showed that m-ZrO2 NPs could regularly disperse in epoxy polymer matrix while unmodified zirconia nanoparticles (u-ZrO2 NPs) were agglomerated to big cluster in the epoxy coating. This was the reason for the high performance of the epoxy coating filled with zirconia NPs modified by GPTES.

Evaluation of dry sliding wear behavior of abaca/glass fiber hybrid composite for tribological applications

Abaca is a high-strength natural fiber whose tribological behavior in epoxy polymer composite is unexplored to date. This paper aims to study the mechanical and dry sliding wear behavior of abaca fiber (A) and glass fiber (G) reinforced epoxy laminate composites with various stacking sequences. Symmetrically oriented laminate composites were fabricated in different stacking sequences (AAAA, AGAG, AGGA, and GAAG) using hand lay-up technique. Mechanical characterization is carried out as per ASTM standards. It is found that GAAG hybrid composite possesses maximum tensile strength (101.05 MPa). Meanwhile, AGAG composite shows maximum flexural strength (190.15 MPa) and interlaminar shear strength (5.97 MPa). Abrasive wear behavior of the composites is investigated by performing the test on a pin-on-disc tribo tester as per the ASTM G99 standard under dry sliding conditions. Tribological results indicate that hybridization of abaca and glass fiber into an epoxy matrix enhances the wear properties significantly. Maximum wear resistance is observed with AGGA-layered hybrid composite. The reduction in volumetric wear of AGGA composite is found to be lower than neat epoxy by 86.51%. However, the frictional force of AGGA composite increased by 54.17%. Furthermore, the morphology of fractured and worn-out surfaces is studied using a scanning electron microscope. It is inferred that failure is mainly due to the development of micro-cracks on both fiber and matrix, combined with fiber fragmentation, plowing, and debonding.

Flexible epoxy‐dispersed liquid crystal membranes of intrinsic thermal conductivity with high voltage orientation molding

AbstractFlexible epoxy‐dispersed liquid crystal membranes (EDLC‐v membranes) with high thermal conductivity were successfully prepared by using of high voltage orientation molding. Liquid crystal monomer (LCM) was uniformly dispersed into flexible epoxy polymers cured by trimethylolpropane tris(3‐mercaptopropionate) (TTMP) or pentaerythritol tetra(3‐mercaptopropionate) (PETMP). In‐plane thermal conductivity (TC//) of EDLC‐v membranes reached to 1.47 W m−1 K−1 with LCM content of 30 wt%, which was 5.65 times higher than that of epoxy polymers without LCM (0.26 W m−1 K−1). In addition, the tensile strength and elongation at break of EDLC‐v membranes were up to 27.9 MPa and 92.8%, respectively. The main reasons for high TC// and flexibility of EDLC‐v membranes are molecular chains' ordered arrangement, crosslinking in epoxy polymers, hydrogen bond interaction, and high voltage orientation molding. This work provided a new and feasible way to prepare intrinsic high thermal conductive polymer materials, as well as flexible epoxy polymers.

Advances in Nonfouling and Antimicrobial Coatings: Perspectives for the Food Industry

Microbial cross-contamination represents a significant burden to public health and food wasted due to microbial spoilage. Despite established protocols for cleaning and sanitizing surfaces and advances in antimicrobial and nonfouling coatings research, the persistence of pathogenic and spoilage microorganisms remains a challenge in food manufacturing. Specifically, the design and application of antimicrobial and nonfouling coatings in nonfood contact regions of food manufacturing facilities remain an area of research need as these regions are known microbial growth niches. In this review, we survey the state-of-the-art antimicrobial and nonfouling technologies compatible with polyurethane and epoxy coatings suitable for Zone 2/3 regions, such as drain ditches and equipment framework. The properties of polyurethane and epoxy coatings are discussed, followed by a detailed survey of antimicrobial and nonfouling compounds suitable for incorporation into polyurethane and epoxy polymerization chemistries. Challenges and opportunities in the application of antimicrobial and nonfouling coatings to Zones 2/3 are discussed, with an emphasis placed on the design of effective application studies.

Dynamic Mechanical Analysis of Banyan/Ramie Fibers Reinforced with Nanoparticle Hybrid Polymer Composite

Natural fibers are an increasing potential alternative to synthetic fibers in recent research, due to their unique properties and weight ratio in composite materials. In this work, the banyan mat and ramie mat are used as reinforcement phase and the epoxy polymer is used as matrix material, and granite nanoparticles are used as filler for making composite laminates. The two phases of reinforcing and matrix were taken at an equal ratio of 50% in each, and the conventional hand layup process was fabricated making five different sequences of laminates. In this analysis, the dynamical mechanical properties of this hybrid composite are identified with the erratic weight ratio of banyan mat and ramie mat fabrics. The results revealed the maximum storage modulus is 1580 MPa at 93.8°C and a loss modulus of 298 MPa at 93.8°C in sample A, 12% more storage modulus, 17% more loss modulus was obtained in sample A compared to sample B, and 29% E ′ and 27% E ″ more compared to sample E and also using storage modulus, loss modulus, damping factor are the viscoelastic behavior which can reveal the glass transition temperature of hybrid composite laminates by conducting dynamic mechanical analysis, and SEM test was used to identify the failure mode of hybrid composite.

Investigating the transfer of toughness from rubber modified bulk epoxy polymers to syntactic foams

Syntactic foams are lightweight, high specific strength materials used in the aerospace and naval industries. Their utility is limited by their brittleness. The epoxy polymer matrix in an epoxy/hollow glass microsphere (GMS) syntactic foam was modified using carboxyl-terminated butadiene-acrylonitrile (CTBN) rubber with the aim to increase fracture toughness. The microstructure and fracture properties were investigated, and compared to CTBN modified bulk epoxy polymers. The formation of complex CTBN microstructures was responsible for the increase in fracture energy, from 193 J/m2 for the unmodified syntactic foam, to 296 J/m2 at 12 wt% CTBN modification. However, this increase is much smaller than for the CTBN modification of bulk epoxy polymers, where an increase from 101 J/m2 to 1112 J/m2 was measured for the same CTBN concentration. There is little toughness transfer from the bulk epoxy polymers to the syntactic foams, attributable to small interstitial regions between the GMS, restricting plastic zone size. A statistical approach to the analytical modelling of fracture energy in the bulk epoxy polymers highlights the importance of considering the underlying distribution of rubber particle and void sizes. The increase in fracture energy achieved in this work can increase the overall usefulness of syntactic foams in structural applications.

Materials to Mitigate the Urban Heat Island Effect for Cool Pavement: A Brief Review

The urban heat island (UHI) effect has a significantly negative impact on the living environment in urban areas. Asphalt pavement is one of the most widely used infrastructures that absorbs solar energy, which leads to the UHI effect and premature failure. As a result, cool pavement technology has been rapidly developed in recent years to mitigate the UHI effect originating from asphalt pavement. Although several outstanding review articles have analyzed previous studies on cool pavement technologies, very few review articles have focused on how to design and expand cool pavement technology from a materials perspective. In this mini-review article, the theoretical and practical factors of the solar reflective coatings and phase-change materials, which are significantly dependent on the design of new materials, have been summarized. The main challenges and potential problem-solving ideas have been presented. In a cool pavement, the solar reflective coatings are composed of epoxy resin or acrylic polymer matrix filled with solar reflective nanoparticles, such as TiO2, SiO2, ZnO, Al2O3, or Fe2O3. The main challenges of the solar reflective coatings are the spalling of the coating polymers from the asphalt pavement surface and the dispersion of the solar reflective nanoparticle in the polymer matrix. Most importantly, it is critical to harmonize the balance between the bonding strength, aging rate, solar reflectance, curing requirements, mechanical properties, and durability of the solar reflective coating. For the nanofillers, the cost of the filler materials, the balance between UV, visible light, and near-infrared reflectance and the dispersion status of the nanofillers in the polymer matrix are the primary factors that must be concerned. For the phase-change materials (PCMs), the interaction between the asphalt and the PCMs, the decomposition of the PCMs, the toxicity of the PCMs, the distribution status of the PCMs in the asphalt matrix, and the cost are the main factors that have to be considered in constructions. This review article can not only provide basic knowledge for the development of new solar reflective pavement materials but also serve as a guide for practical applications of cool pavement in the field.

Graphitic carbon-rich oil fly ash as effective reinforcements to enhance the mechanical, thermal, and radiation shielding properties of high-grade epoxy polymer

Herein, we enhanced the epoxy resin's mechanical, thermal, and radiation shielding properties by introducing graphitic heavy oil fly ash (HOFA) to produce composite sheets at various weight fractions of HOFA, namely, 0, 10, 20, and 30 wt%. The morphology, chemical group functions, mechanical properties, thermal properties, and the X-ray and neutron shielding properties of the produced epoxy resin/HOFA composite sheets were rigorously tested. The SEM images showed a uniform distribution for the HOFA particles in the polymer matrix. The FTIR spectra revealed a new peak of C=C bounds, suggesting that the epoxy resin/HOFA composites were tightly bounded through these functional sites. The mechanical results showed that Young's modulus and stiffness were enhanced gradually by increasing the HOFA weight fraction; for instance, Young's modulus increased by ∼20% compared with neat epoxy. The hardness obtained by the nanoindentation test was also significantly enhanced by around 25% by increasing the HOFA weight fraction. The observed micro scratch confirmed these mechanical enhancements. The thermal conductivity and diffusivity were slightly increased by increasing the load of HOFA, but this was combined with an apparent increase in the value of the char yields, suggesting improvements in the thermal properties. The X-ray shielding results showed increases in the linear attenuation coefficients and decreases in the half-value layer, indicating better shielding properties; no effects were detected in the neutron shielding while HOFA addition. These results clearly demonstrated the possibility of reinforcing the epoxy resin thermal, mechanical, and radiation shielding properties using the waste HOFA material to be a valuable and economical material used in polymer composite applications, such as constructions, piping, and automobiles.

Elevated temperature mechanical behavior of nano Al2O3 embedded interpenetrating polymer network/glass fiber composites

AbstractTwo methods of enhancing the mechanical performance of glass fiber reinforced polymer (GFRP) composites, namely the formation of an interpenetrating polymer network (IPN) of two thermoset polymers (epoxy and vinyl ester) and the addition of nanofillers (nano Al2O3) have been implemented simultaneously. The content of nano Al2O3 (0.1, 0.4, and 0.7 wt% of the polymer matrix) in the glass fiber reinforced epoxy‐vinyl ester IPN (GEVIPN) composite significantly affected its mechanical performance. Incorporation of 0.1 wt% nano Al2O3 in GEVIPN composite exhibited 17.69% and 27.64% improvement in flexural strength and toughness, respectively. Additionally, when the composites were subjected to elevated temperature testing, their mechanical performance was drastically affected. However, the test results revealed that nano Al2O3/GEVIPN composites possessed significantly improved mechanical degradation resistance at elevated temperatures. This new composite material could be utilized as structural materials in the civil, automotive, and marine industries. Dynamic mechanical thermal analysis was performed to assess the composites' thermomechanical behavior. Fractography analysis of tested samples revealed the underlying phenomena, which dictate the mechanical performance at each testing temperature. A constitutive deformation model assessed the reliability of this new material at ambient and elevated test temperatures.

Optical properties of novel luminescent nacre‐like epoxy/graphene nanocomposite coating integrated with lanthanide‐activated aluminate nanoparticles

Nacre structure has aragonite polygonal tablets, tessellated to generate separate layers, and exhibits adjacent layers and tablets within a layer bonded by a biopolymer. Herein, we report the development of nacre-like organic/inorganic hybrid nanocomposite coating consisting of epoxy tablets as well as rare-earth activated aluminate and graphene oxide tablet/tablet interfaces. The lanthanide-activated aluminate was prepared by the high temperature solid-state approach followed by the top-down technology to provide the phosphor nanoparticles (PNPs). Graphene oxide nanosheets were prepared from graphite. The prepared epoxy/graphene/phosphor nanocomposites were applied onto mild steel. Covalent bonds were formed between epoxy polymer chains resin and graphene oxide nanosheets. Those interface interactions results in tough surface, high tensile strength, and excellent durability. The usage of phosphor in the nanoparticle form guaranteed no agglomerations were produced throughout the hardening procedure by allowing better distribution of PNPs in the nacre-like matrix. The generated nacre-like substrates displayed reversible fluorescence. The excitation of the white colored nacre-like coats at 367 nm results in a green emission band at 518 nm as designated by CIE Lab and photoluminescence spectra. Various analysis methods were utilized to inspect the surface structure and elemental composition of the nacre-like coats. An improved hydrophobicity and mechanical characteristics were detected with increasing the phosphor concentration. Due to the astonishing characteristics of the prepared nacre-like composite paint, both ceramics and metals can benefit from the current simple strategy.

Impregnation methods for quantitative analyses of the gas diffusion layer in proton exchange membrane fuel cells

Microstructural analysis is central to understand and predict the performance and degradation of proton exchange membrane fuel cell (PEMFC) materials. Advanced electron and x-ray 3-D microscopy methods are needed to characterize the reticulate structures forming the catalyst, gas diffusion layer/ microporous layers. The high-throughput dual beam scanning electron microscope allows the 3-D imaging of such layers with a spatial resolution in the range of a few nm. However, for accurate quantitative analyses, impregnation of the porous sample is required to mitigate artefacts due to milling and pore-through effect, and provide sufficient contrast between the material phases for image segmentation. This study investigates an impregnation method based upon the addition of Cobalt (II) acetylacetonate nanoparticles in an epoxy polymer resin. The results were compared with conventional methods using commercial resins stereology on sections polished by focused ion beam (FIB). The results indicate the appropriateness of the newly proposed method, providing adequate contrast for accurate image segmentation. An Energy Dispersive X-ray (EDX) analysis was included to obtain an information about the composition, which can be used for further improvements of the resin.

Strategic Role of Carbon Nanotube Functionalization on the Multifunctional Properties of Structural Epoxy Nanocomposites

AbstractCarbon nanotubes (CNT) have received great attention as nanofillers for epoxy structural nanocomposites, due to their rare combination of mechanical, electrical, thermal properties, and others. Furthermore, the surface of the carbon nanotubes can be easily transformed with a variety of characteristic atoms or groups of atoms conferring specific and desired properties. Different kinds of functionalization (covalent and non‐covalent) can be performed. A very recent and hopeful strategy capable of modifying the surface of carbon nanotubes, without endangering their structural integrity, is the non‐covalent modification of CNT walls with specific molecules that show a marked similarity with the graphitic structure of carbon nanotubes. The aim of this work is to enhance the interactions of CNT with epoxy matrices to allow much better nanofiller dispersion within the epoxy polymer through carbon nanotube modification. The obtained results highlight that the performed functionalizations are suitable for designing carbon‐based nanocomposites with improved structural and functional properties. Specific surface modifications of CNT walls are carried out using supramolecular chemistry specialized in non‐covalent interactions.These weak and reversible forces act advantageously by activating the self‐repairing functionality in the nanofilled resins.The morphology of nanodomains and the interfacial interactions between nanocharge and hosting resin are investigated by Tunneling Atomic Force Microscopy (TUNA). The nanocomposite performance is strongly affected by the performed functionalization.

The anisotropy of bonded ferrite magnets obtained by centrifugal casting in magnetic field

• The orientation of bonded magnets in an external magnetic field depends on the powder particle size. • For powders composed of multidomain particles, the orientation occurs in the circumferential direction. • The orientation of the powder occurs in a way that leads to a minimization of the energy. Bonded magnets were produced by centrifugal casting of a powder mixture comprising a magnetically hard material (strontium ferrite) and a chemically hard polymer (epoxy resin) in an external, constant magnetic field perpendicular to the axis of rotation. The tests were carried out for commercial strontium ferrite powder, with micrometre-sized particles. At 5% and 10% powder content by volume, the magnets exhibited a gradient structure, i.e. the proportion of magnetic powder was highest at the surface and decreased towards the sample’s axis. At higher powder content, the viscosity of the slip was high enough to prevent particles to move over significant distances, and no marked change in the proportion of ferrite in the sample volume was observed. Measurements of the magnetic properties in the characteristic directions of the cylindrical sample (radial, axial and circumferential) showed that the powder particles tend to align their easy axis with the axis of the cylinder, i.e. perpendicular to the direction of the magnetic field. These results indicate that the magnetization anisotropy obtained is different from that described in earlier work, where strontium ferrite powder with a particle size above 100 μm was oriented circumferentially (the easy axis was perpendicular to the radius and axis of the cylinder). These differences are due to the different proportion of single and multidomain particles in the two powders and to the different mechanisms of their remagnetization. The results are explained on the basis of the presented model assuming that the single domain particles rotate in such a way that their remagnetization during mould centrifugation is achieved by rotating the magnetization vector in a plane perpendicular to the easy axis, which minimises the energy loss in this process.