Study on sepiolite‐reinforced polymeric nanocomposites

Epoxy nanocomposites reinforced by nano‐sized sepiolite are investigated. Sepiolite particles and the nanocomposites were characterized by SEM, TEM, XRD, and IR. The level of reinforcement is assessed from impact strength and flexural strength. It is shown that significant improvement in mechanical property is obtained for all reinforced nanocomposites and the addition of 1% sepiolite appears to be an optimum blend ratio. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci, 2006     

Influence of porosity on the mechanical behaviour of single phase β-TCP ceramics

Processing and mechanical behaviour of fine grained (diameter ≈0.5–3 µm) and pure β-TCP materials with different levels of porosity (up to 19%) is described. Pores with diameters, d₅₀ ≈13–14 µm were formed fromcorn starch during sintering. Comprehensive mechanical characterisation –Young´s modulus, strength and toughness– has been done paying special attention to toughness determined in stable fracture tests. The dependence of Young´s modulus and strength with porosity was well fitted to the minimum solid area models while toughness values did not. The competitive processes occurring during fracture impede the degradation of toughness associated to the decrease in Young´s modulus as porosity increases. Materials present similar values of the critical energy release rate G_IC, which describes crack initiation. A maximum of the specific fracture energy, G_F, which averages crack propagation, has been obtained for the material with the highest porosity.     

Anisotropy in nanocellular polymers promoted by the addition of needle‐like sepiolites

This work presents a new strategy for obtaining nanocellular materials with high anisotropy ratios by means of the addition of needle‐like nanoparticles. Nanocellular polymers are of great interest due to their outstanding properties, whereas anisotropic structures allow the realization of improved thermal and mechanical properties in certain directions. Nanocomposites based on poly(methyl methacrylate) (PMMA) with nanometric sepiolites are generated by extrusion. From the extruded filaments, cellular materials are produced using a two‐step gas dissolution foaming method. The effect of adding various types and contents of sepiolites is investigated. As a result of the extrusion process, the needle‐like sepiolites are aligned in the machine direction in the solid nanocomposites. Regarding the cellular materials, the addition of sepiolites allows one to obtain anisotropic nanocellular polymers with cell sizes of 150 to 420 nm and cell nucleation densities of 10¹³–10¹⁴ nuclei cm^?3 and presenting anisotropy ratios ranging from 1.38 to 2.15, the extrusion direction being the direction of the anisotropy. To explain the appearance of anisotropy, a mechanism based on cell coalescence is proposed and discussed. In addition, it is shown that it is possible to control the anisotropy ratio of the PMMA/sepiolite nanocellular polymers by changing the amount of well‐dispersed sepiolites in the solid nanocomposites. © 2019 Society of Chemical Industry     

Enhancing toughness of low‐density polyethylene filaments through infusion of multiwalled carbon nanotubes and ultrahigh molecular weight polyethylene

We report enhancement in fracture strain and toughness of low‐density polyethylene by infusing multiwalled carbon nanotubes (MWCNT) and a second‐phase polymer; ultrahigh molecular weight polyethylene (UHMWPE). Infusion of MWCNT improved strength and modulus by about 23 and 57%, respectively, but reduced fracture strain (～45%) and toughness (～36%). UHMWPE was then dispersed as a minor phase, and the resulting nanocomposites showed a 55% increase in toughness without any loss of strength or modulus. The loading of MWCNT and UHMWPE was 2 and 8% by weight, respectively. Nanocomposites were in the form of filaments and were extruded through a melt extrusion process. Differential scanning calorimetry and X‐ray diffraction studies revealed increase in crystallinity and crystallite size. Scanning electron microscope micrographs showed sliding of polymer interfaces and changes in fracture process. Strain hardening experiments also showed improvement in strength and modulus but reduction in toughness. POLYM. ENG. SCI., 2011. © 2010 Society of Plastics Engineers.     

Characterization of the fracture behavior and viscoelastic properties of epoxy-polyamide coating reinforced with nanometer and micrometer sized ZnO particles

The mechanical and viscoelastic properties of an epoxy-polyamide coating containing nano and micro sized ZnO particles were studied. The nanocomposites were prepared at different loadings of the nano sized ZnO particles. The composites were also prepared using micro sized ZnO particles at different lambdas (lambda (λ) = PVC/CPVC). The optical properties of each nanocomposite were studied by UV–vis technique. Dynamic mechanical thermal analysis (DMTA) and micro-Vickers were used to investigate the mechanical properties of the composites. The viscoelastic properties of the composites were studied by a tensile test. The fracture morphologies of the composites were studied by a scanning electron microscope (SEM). An increase in Tg together with a decrease in cross-linking density of the composites was obtained when the coating was reinforced with the micro sized ZnO particles. On the other hand, the Tg and cross-linking density of the composites were decreased using nano sized ZnO particles. It was also found that, the Young's modulus and the fracture energy of the coating were decreased using micro and nano sized ZnO particles. The greater toughness as well as fracture energy of the composite was obtained when it was reinforced with the nano sized ZnO particles. The curing behavior of the epoxy coating was affected in the presence of the micro and nano sized ZnO particles.     

Toughening of unmodified polyvinylchloride through the addition of nanoparticulate calcium carbonate and titanate coupling agent

PVC/CaCO₃ polymer nanocomposites of differing compositions were produced using a two‐roll mill and compression molding. In all formulations, 0.6 phr of titanate was incorporated to assist dispersion during processing. The morphology was observed using transmission electron microscopy, and the static and dynamic mechanical and fracture properties were determined. Fracture toughness examination was performed according to strain energy release test method. The presence of nanometer‐sized CaCO₃ particles led to a slight decrease in the tensile strength but improved the impact energy absorption, storage modulus, and fracture toughness. The use of titanate coupling agent softened the polymer matrix and reduced the matrix's modulus. Fracture surface examinations by scanning electron microscopy showed that the coupling agent improved particle–matrix bonding and inhibited void formation around the particles. Finite element analysis suggested that the improved particle–matrix bonding reduced the matrix's plasticity around the particles, which decreased the toughening efficiency of the composites. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Nanocellular Polymers with a Gradient Cellular Structure Based on Poly(methyl methacrylate)/Thermoplastic Polyurethane Blends Produced by Gas Dissolution Foaming

Graded structures and nanocellular polymers are two examples of advanced cellular morphologies. In this work, a methodology to obtain low‐density graded nanocellular polymers based on poly(methyl methacrylate) (PMMA)/thermoplastic polyurethane (TPU) blends produced by gas dissolution foaming is reported. A systematic study of the effect of the processing condition is presented. Results show that the melt‐blending results in a solid nanostructured material formed by nanometric TPU domains. The PMMA/TPU foamed samples show a gradient cellular structure, with a homogeneous nanocellular core. In the core, the TPU domains act as nucleating sites, enhancing nucleation compared to pure PMMA and allowing the change from a microcellular to a nanocellular structure. Nonetheless, the outer region shows a gradient of cell sizes from nano‐ to micron‐sized cells. This gradient structure is attributed to a non‐constant pressure profile in the samples due to gas desorption before foaming. The nucleation in the PMMA/TPU increases as the saturation pressure increases. Regarding the effect of the foaming conditions, it is proved that it is necessary to have a fine control to avoid degeneration of the cellular materials. Graded nanocellular polymers with relative densities of 0.16–0.30 and cell sizes ranging 310–480 nm (in the nanocellular core) are obtained.     

Toughening epoxies with halloysite nanotubes

An experimental attempt was made to characterize the fracture behaviour of epoxies modified by halloysite nanotubes and to investigate toughening mechanisms with nanoparticles other than carbon nanotubes (CNTs) and montmorillonite particles (MMTs). Halloysite-epoxy nanocomposites were prepared by mixing epoxy resin with halloysite particles (5 wt% and 10 wt%, respectively). It was found that halloysite nanoparticles, mainly nanotubes, are effective additives in increasing the fracture toughness of epoxy resins without sacrificing other properties such as strength, modulus and glass transition temperature. Indeed, there were also noticeable enhancements in strength and modulus for halloysite-epoxy nanocomposites because of the reinforcing effect of the halloysite nanotubes due to their large aspect ratios. Fracture toughness of the halloysite particle modified epoxies was markedly increased with the greatest improvement up to 50% in K_IC and 127% in G_IC. Increases in fracture toughness are mainly due to mechanisms such as crack bridging, crack deflection and plastic deformation of the epoxy around the halloysite particle clusters. Halloysite particle clusters can interact with cracks at the crack front, resisting the advance of the crack and resulting in an increase in fracture toughness.     

Toughened nylon66/nylon6 ternary nanocomposites by elastomers

The elastomer toughening of PA66/PA6 nanocomposites prepared from the organic modified montmorillonite (OMMT) was examined as a means of balancing stiffness/strength versus toughness/ductility. Several different formulations varying in OMMT content were made by mixing of PA6 and OMMT as a master‐batch and then blending it with PA66 and different elastomers in a twin screw extruder. In this sequence, the OMMT layers were well exfoliated in the nylon alloy matrix. The introduction of silicate layers with PA6 induced the appearance of the γ crystal phase in the nanocomposites, which is unstable and seldom appears in PA66 at room temperature and it further affected the morphology and dispersion of rubber phase resulting in much smaller rubber particles. The incorporation of POE‐g‐MA particles toughened the nanocomposites markedly, but the tensile modulus and strength were both reduced. Conversely, the use of OMMT increased the modulus but decreased the fracture toughness. The nanocomposites exhibited balanced stiffness and toughness. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Improvement in interfacial shear strength and fracture toughness for carbon fiber reinforced epoxy composite by fiber sizing

Carbon fiber was sized by a thermoplastic polymer solution mixed with a compatible amine monomer. The effect of sizing agent on tensile strength was studied by single fiber strength testing. Interfacial properties of re‐sized carbon fiber/epoxy composite were investigated, with special emphasis on the improvement in both interfacial shear strength and interfacial fracture toughness. The interfacial fracture toughness of composites was characterized by calculating the effective interphase fracture energy rate through the information obtained from the force–displacement curve in the micro‐bond test. Fracture topography of micro‐bond specimen was observed to discuss the interfacial fracture mechanism. POLYM. COMPOS., 35:482–488, 2014. © 2013 Society of Plastics Engineers     

Morphology and mechanical properties of dual‐curable epoxyacrylate hybrid composites

A dual‐curable epoxyacrylate (EA) oligomer with one epoxide group and one vinyl group at each end was synthesized for the application as adhesive sealant in the liquid crystal display panels. However, after UV and thermal cure, the EA resin was brittle with a poor resistance to crack initiation and propagation. Liquid rubbers with different functional end groups were thus tried as toughening agents for the EA resin. Among all the rubber‐toughened EAs, the EA‐V5A5 added with vinyl‐terminated and amino‐terminated butadiene‐acrylonitrile copolymers (VTBN and ATBN) each at 5 phr had the highest fracture toughness, tensile strength, and elongation at break but a lower initial modulus. To raise the modulus, submicron‐sized silica particles (∼170 nm) with surface vinyl functional groups were further added to the EA‐V5A5 to prepare the hybrid composites. Because of interfacial chemical bonding provided by the surface vinyl functional groups, both modulus and fracture toughness were increased by adding silica particles, without any appreciable decrease in extensibility. For the hybrid composite at 20 phr silica particles, the initial modulus, fracture toughness, and fracture energy were raised by 10.3, 100, and 267%, respectively, when compared to the neat epoxyacrylate. Owing to their strong interfacial bonding, the increase of fracture toughness was mainly due to the crack deflection and bifurcation on silica particles, in addition to the rubber particle bridging and tearing as evidenced by SEM pictures on the fracture surface. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41820.     

Mechanical Properties of Magnesia–Spinel Composites

The mechanical properties of magnesia–spinel composite ceramics, which are candidate materials for supporting solid oxide fuel cells, have been measured as a function of porosity (up to 30%) and temperature (up to 900°C). The theory for the ring-on-ring test has been re-examined to resolve an inconsistency in the literature.
The Young's modulus shows an exponential dependence on porosity that is in agreement with the expectation of minimum solid area models. Fracture toughness, fracture energy, and flexural strength are all approximately proportional to Young's modulus.
The mechanical properties are not greatly dependent on temperature, but there is a detectable increase in fracture toughness with temperature, which could be due to some limited plasticity.     

Toughening of bone cement using nanoparticle: The effect of solvent

Drawbacks of poly(methyl methacrylate) (PMMA)‐based bone cement as a grouting agent for in vivo fixation of orthopedic and dental implants such as considerable low mechanical strength have been improved using nanotechnology. Bone cement‐layered silicate nanocomposites have been prepared without any heat treatment in the presence of polar (dimethyl formamide, DMF) and nonpolar (benzene) solvents. Solvents have been removed completely from the bone cement after its preparation. Nanostructure is very much dependent on the solvent used for nanocomposite preparation, and benzene‐based nanocomposites are highly intercalated, whereas DMF‐based nanocomposites do not exhibit intercalation. Thermal stability of bone cement has improved in the presence of nanoclays. The relative enhanced interaction in case of benzene‐based nanocomposites has been shown through FTIR and UV–vis studies. The significant improvement in modulus and toughness of bone cement has been demonstrated in the presence of minimum amount of nanoclay for benzene‐based nanocomposites, whereas no change in modulus and reduced toughness have been observed for DMF‐based nanocomposites. The decrease of contact angle has been witnessed with increasing nanoclay concentration indicating better hydrophilic materials suitable for biomedical applications for greater cell growth. The reason for varying property enhancement in different solvents has been discussed considering the polarity effect and interactions. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Effects of perfluoroether concentration and curing protocol on morphology and mechanical properties of toughened TGDDM/MNA resin systems

Previous published work has shown that hydroxyl terminated perfluoroether oligomers can be suitably modified and functionalised to make them miscible with epoxy resins in the uncured state. The reaction conditions can adjusted to induce phase separation either through spinodal decomposition to produce an IPN type morphology, or by nucleation and growth if a dispersed-particle microstructure is required.In the present work we examine the relative toughening enhancement efficiency of the two possible heterophase morphologies. Both systems show a sigmoidal increase in fracture toughness, with increasing concentration of the perfluoroether modifier. However, this takes place at much lower modifier concentrations for the systems with a particulate morphology (about 3.5% w/w) than for IPN systems (about 7.5% w/w). The maximum fracture toughness achievable for the two systems, on the other hand, is very similar and coincides with the concentration at which co-continuous phases are formed.These differences in morphology, however, are not reflected in the variation of modulus and compressive yield strength with increasing concentration of perfluoroether modifier, in so far as both systems exhibit a gradual and small reduction in property with increasing concentration. Furthermore, the dynamic mechanical spectra of the two systems are very different, but the changes resulting from increasing the concentration of toughening agent are relatively small in either case.Nanoindentation tests indicate that it is the local plasticity, brought about by the presence of the softer perfluoroether phase, which is responsible for the enhancement of fracture toughness. This is corroborated by AFM examinations, which reveal local plastic deformations in the regions surrounding the softer particles.     

Zirconium nitride nano-particulate reinforced Alon composites: Fabrication, mechanical properties and toughening mechanisms

Aluminium oxynitride (Alon) exhibits excellent stability, high rigidity and good thermal shock resistance, but it has relatively low strength and poor fracture toughness. The aim of this investigation was to develop a new type of zirconium nitride (ZrN) nano-particulate reinforced Alon composites via a change of ZrO₂ nano-particles during sintering. A reduction of porosity and grain size was observed in the composite. With increasing amount of ZrN nano-particles up to 2.7%, the relative density, hardness, Young's modulus, flexural strength, and fracture toughness all increased. When the ZrN nano-particles exceeded 2.7%, while the flexural strength and fracture toughness decreased slightly, the density, hardness and Young's modulus continued to increase. Different toughening mechanisms including crack bridging, crack branching and crack deflection were observed, thus effectively increasing the crack propagation resistance and leading to a considerable improvement in the flexural strength and fracture toughness of the composites.     

Simultaneous improvement in strength,toughness, and thermal stability of epoxy/halloysite nanotubes composites by interfacial modification

This work investigated the effect of silane modification of halloysite nanotubes (HNTs) on the mechanical properties of epoxy/HNTs nanocomposites. Three kinds of silane coupling agents, including 3‐(2‐aminoethyl)‐aminopropyltrimethoxysilane (AEAPS), (3‐glycidyloxypropyl)‐trimethoxysilane (GPTMS), and octyltriethoxysilane (OTES), were employed. It was shown that the modified HNTs exhibited a better dispersion in the epoxy matrix compared with pristine one. Because of strong interfacial interaction between AEAPS modified HNTs and the epoxy matrix, the nanocomposites exhibited the highest glass transition temperature and modulus among all the samples. On the other hand, AEAPS and GPTMS modified HNTs/epoxy nanocomposites showed enhanced tensile strength and toughness. The toughing mechanisms were identified by the SEM micrographs of the fracture surfaces of the different kinds of samples. In this study, simultaneous enhancement of strength, toughness, and thermal stability of epoxy by the modified HNTs provides a novel approach to produce high‐performance thermosets. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43249.     

Theoretical and experimental determination of tensile properties of nanosized and micron‐sized CaCO3/PA66 composites

The objective of this research was to investigate the probability of reinforcing Polyamide66 (PA66) with both micron‐sized and nanosized calcium carbonate (CaCO₃) particles. For this purpose, micron‐sized and nanosized CaCO₃ particles were used as fillers to prepare microcomposites (conventional composites) and nanocomposites via a polymer solution method. The microcomposites and nanocomposites were found to have higher modulus and lower strength than neat PA66. Also, nanocomposites had higher modulus and strength than microcomposites. Theoretical prediction of elastic modulus was carried out using Rule of mixtures, Guth, Nicolais–Narkis, Hashin–Shtrikman, and Halpin–Tsai equations. Calculated results show that these equations cannot predict the results accurately for the work carried out. However, these models can be used with confidence for the prediction of elastic modulus as experimental data are higher than the calculated values. POLYM. COMPOS., 2009. © 2008 Society of Plastics Engineers     

Toughening of unmodified polyvinylchloride through the addition of nanoparticulate calcium carbonate

PVC/CaCO₃ polymer nanocomposites of differing compositions were produced using a two-roll mill and compression molding. The morphology was observed using transmission electron microscopy, and the static and dynamic mechanical and fracture properties determined. The presence of nanometer-sized CaCO₃ particles led to a slight decrease in the tensile strength but improved the impact energy, the storage modulus and the fracture toughness. Fracture surface examination by scanning electron microscopy indicated that the enhanced fracture properties in the nanocomposites were caused by the assisted void formation at the particles. This hypothesis is supported by a microstructure-based finite element modeling based upon elastic-plastic deformation around a weakly bonded particle. Hence, this provides an explanation of both the uniaxial tensile behavior and enhanced toughness of the nanocomposites.     

Microstructural,mechanical, and thermal characteristics of recycled cellulose fiber‐halloysite‐epoxy hybrid nanocomposites

Epoxy hybrid‐nanocomposites reinforced with recycled cellulose fibers (RCF) and halloysite nanotubes (HNTs) have been fabricated and investigated. The dispersion of HNTs was studied by synchrotron radiation diffraction (SRD) and transmission electron microscopy (TEM). The influences of RCF/HNTs dispersion on the mechanical properties and thermal properties of these composites have been characterized in terms of flexural strength, flexural modulus, fracture toughness, impact toughness, impact strength, and thermogravimetric analysis. The fracture surface morphology and toughness mechanisms were investigated by SEM. Results indicated that mechanical properties increased because of the addition of HNTs into the epoxy matrix. Flexural strength, flexural modulus, fracture toughness, and impact toughness increased by 20.8, 72.8, 56.5, and 25.0%, respectively, at 1 wt% HNTs load. The presence of RCF dramatically enhanced flexural strength, fracture toughness, impact strength, and impact toughness of the composites by 160%, 350%, 444%, and 263%, respectively. However, adding HNTs to RCF/epoxy showed only slight enhancements in flexural strength and fracture toughness. The inclusion of 5 wt% HNTs into RCF/epoxy ecocomposites increased the impact toughness by 27.6%. The presence of either HNTs or RCF accelerated the thermal degradation of neat epoxy. However, at high temperature, samples reinforced with RCF and HNTs displayed better thermal stability with increased char residue than neat resin. POLYM. COMPOS. 2012. © 2012 Society of Plastics Engineers     

Influence of porosity on mechanical properties of tetragonal stabilized zirconia

3YSZ specimens with variable open porosity (1–57%) were fabricated, and the stiffness, strength and fracture properties (fracture toughness and R-curve) were measured to investigate their potential use as support structures for solid oxide fuel or electrolysis cells. The ball-on-ring test was used to characterize Young's modulus and Weibull strength. The variation of fracture toughness with porosity was investigated and modelled using the results from fracture mechanical testing. A distinct R-curve behaviour was observed in dense 3YSZ specimens, in samples with a porosity around 15% and in some of the highly porous samples (porosities ～45%) reflecting a transformation toughening in the material. For the most porous samples, the “R-curve behaviour” disappeared and subcritical crack growth was observed. The studies indicate that even highly porous 3YSZ structures (porosities exceeding 40%) are feasible supports for SOFC/SOECs from a mechanical point of view.