Mohammad Reza Saeb

Cure Kinetics of Epoxy Nanocomposites Affected by MWCNTs Functionalization: A Review

The current paper provides an overview to emphasize the role of functionalization of multiwalled carbon nanotubes (MWCNTs) in manipulating cure kinetics of epoxy nanocomposites, which itself determines ultimate properties of the resulting compound. In this regard, the most commonly used functionalization schemes, that is, carboxylation and amidation, are thoroughly surveyed to highlight the role of functionalized nanotubes in controlling the rate of autocatalytic and vitrification kinetics. The current literature elucidates that the mechanism of curing in epoxy/MWCNTs nanocomposites remains almost unaffected by the functionalization of carbon nanotubes. On the other hand, early stage facilitation of autocatalytic reactions in the presence of MWCNTs bearing amine groups has been addressed by several researchers. When carboxylated nanotubes were used to modify MWCNTs, the rate of such reactions diminished as a consequence of heterogeneous dispersion within the epoxy matrix. At later stages of curing, however, the prolonged vitrification was seen to be dominant. Thus, the type of functional groups covalently located on the surface of MWCNTs directly affects the degree of polymer-nanotube interaction followed by enhancement of curing reaction. Our survey demonstrated that most widespread efforts ever made to represent multifarious surface-treated MWCNTs have not been directed towards preparation of epoxy nanocomposites, but they could result in property synergism.

Antibacterial glass-ionomer cement restorative materials: A critical review on the current status of extended release formulations

Glass-ionomer cements (GICs) have been widely used for over forty years, because of their desirable properties in dentistry. The most important advantages of the GICs are associated with their ability to release long-term antimicrobial agents. However, GICs used as restorative materials have still lots of challenges due to their secondary caries and low mechanical properties. Recent studies showed that the fluoride-releasing activity of conventional GICs is inadequate for effectual antibacterial conservation in many cases. Therefore, many efforts have been proposed to modify the antibacterial features of GICs in order to prevent the secondary caries. Particularly, for achieving this goal GICs were incorporated into various biomaterials possessing antibacterial activities. The scope of this review is to assess systematically the extant researches addressing the antibacterial modifications in GICs in order to provide with an authoritative, at the same time in-depth understanding of controlled antibacterial release in this class of biomaterials. It also gives a whole perspective on the future developments of GICs and challenges related to antibacterial GICs.

Biowaste chicken eggshell powder as a potential cure modifier for epoxy/anhydride systems: competitiveness with terpolymer-modified calcium carbonate at low loading levels

Biowaste chicken eggshell (ES) powder was applied as a potential cure modifier in epoxy/anhydride systems. Cure behaviour and kinetics of composites filled with very low content (0.1 wt% based on epoxy resin) of ES, calcium carbonate (CaCO3), and terpolymer-modified fillers, mES and mCaCO3, were discussed comparatively. Surface analysis was performed by X-ray photoelectron spectroscopy. Cure kinetics was investigated by differential (Friedman) and integral (Ozawa and Kissinger–Akahira–Sunose) isoconversional methods using dynamic differential scanning calorimetry (DSC) data. Overall, protein precursors naturally existing in the structure of pristine ES facilitated crosslinking of epoxy and hardener of anhydride with functional groups resulting from terpolymer attachment to CaCO3 particles. Accelerated/hindered cure was observed depending on the filler type and surface characteristics, as investigated via the autocatalytic/non-catalytic nature of reactions and comparison of activation energy values of four types of composites. An enhanced cure was identified for composites containing untreated ES, which could be inferred on account of the lower competitive cure of carboxyl groups in the terpolymer backbone with epoxy compared to peptide groups existing in microporous pristine ES. On the other hand, mCaCO3 revealed low values of activation energy compared to pristine CaCO3, but still of the same order as ground biowaste ES.

Mechanical, rheological, and thermal behavior assessments in HDPE/PA-6/EVOH ternary blends with variable morphology

The mechanical, rheological, and thermal properties of various binary and ternary blends based on polyamide 6 (PA-6), high-density polyethylene (HDPE), and poly vinyl alcohol (EVOH) with variable morphology were comprehensively studied to give a perspective on interfacial adhesion situation. In this regard, transitions in the phase morphology of ternary systems were traced by means of scanning electron microscopic investigations, varying the type of matrix and composition in the minority phase. Theoretical and experimental analyses of impact and tensile properties provided support for the compatibilizing action of EVOH on HDPE/PA-6 immiscible blends. Rheological and thermal studies were also performed to make a broader image on the interphase region in ternary systems with core-shell and individually-dispersed minor domains. The most interesting finding was that there is a tendency for PA-6 to partially encapsulate HDPE domains within the EVOH continuous phase. This is roughly supported by SEM micrographs, but yield stress measurements placed too much emphasis on the morphological status.

SEBS-g-MAH as a Reactive Compatibilizer Precursor for PP/PTT/SEBS Ternary Blends: Morphology and Mechanical Properties

This article highlights the effect of using maleic anhydride-assisted SEBS compatibilizer precursor on the morphology and mechanical properties of the polypropylene (PP)/poly (trimethylene terephthalate) (PTT)/poly(styrene-b-(ethylene-co-butylene)-b-styrene) (SEBS) 70/15/15 ternary blends. In all ternary blends, the amounts of PP and PTT, respectively as the matrix and the primary minor components were kept constant at 70 and 15 wt%; in turn, the amount of constituent polymers within the secondary minor phase containing reactive maleic anhydride grafted SEBS (SEBS-g-MAH) and nonreactive SEBS was changed. The mentioned compatibilizing system was first melt-blended in a co-rotating twin screw extruder and then added into the blend. Theoretical models were also employed to make a comparison with experimental values obtained from morphology characterization through the ternary systems. Accordingly, it is found that the blend containing only non-reactive SEBS exhibited fine dispersion of core-shell particles; however, by diminishing SEBS to SEBS-g-MAH weight ratio, the morphology changed from the pure core-shell to a multi-phase system consisting of both core-shell and detached particles. Eventually, this transition in the phase morphology caused some consequences and/or advantages on the mechanical properties, so that the blend consisting of 50/50 weight ratio of SEBS/SEBS-g-MAH exhibited the minimum value of modulus; in contrast, the impact strength of that sample was considerably higher than that of neat PP specimen. These alterations in mechanical properties could be ascribed to the formation of some especial microstructures, in another word, the impact of particle size and particle size distribution, which has been well-established through scanning electron micrographs.

The Crystallinity Behavior of Polyethylene/Clay Nanocomposites Under the Influence of Water-Assisted Melt Blending

High-density polyethylene (HDPE)/clay nanocomposites were prepared via water-assisted and conventional melt blending. The influence of exfoliated/intercalated domains on crystallinity of nanocomposites was then investigated. X-ray diffraction and electron microscopy evidenced for enhanced intercalation and partial exfoliation of clay platelets pursuing rheological measurements. The methane permeability of water-injected nanocomposites was lower compared to melt-blended specimens implying the influence of intercalated domains. A theoretical/experimental analysis was performed to roughly determine the lamellar thickness distribution of the crystalline regions. Contribution of clay platelets to crystallization mechanisms was indicative of clay impact as heterogeneous nucleating agent, whereas mechanical properties were dependent on interface situation.

High-performance epoxy-based adhesives reinforced with alumina and silica for carbon fiber composite/steel bonded joints

Epoxy-based adhesives reinforced with silica and alumina fillers (20, 40, and 60 phr) were prepared and successfully applied for lap-joint bonding of carbon fiber composite with steel. The mechanical properties of adhesives were assessed as different cure temperatures to find optimum cure temperature. Morphology of the reinforced epoxy adhesives was observed by optical microscopy to disclose the interplay between composite properties and distribution fashion of the silica and alumina fillers within the epoxy matrix. Thermal stability and interfacial interaction situation were explored by thermogravimetric and Fourier transform infrared spectroscopy analyses, respectively. Rheological behavior of the composite samples was also studied. Lap shear test was an indication for a considerable improvement of about 12% and 20%, compared to unfilled epoxy/hardener systems, for composites containing 60 phr of alumina and silica, respectively. However, the presence and population of voids in case of samples cured at elevated temperature deteriorated lap shear strength. Of note, the storage and loss modulus of the latter adhesive have been increased by 797% and 472%, respectively. Thermal stability on the basis of initial degradation temperature and char yield (> 500℃) of the assigned adhesive under N2 and air have also been enhanced. Higher performance of silica-based adhesives was mechanistically and morphologically discussed on the bedrock of formation of a 3D inter-connected network of filler particles.

The Influence of NBR-g-GMA Compatibilizer on the Morphology and Mechanical Properties of Poly (ethylene terephthalate)/Polycarbonate/NBR Ternary Blends

The work aims to study the role of NBR-g-GMA compatibilizer on the morphology and mechanical characteristics of PET/PC/NBR ternary blends. The compatibilizer content and amount of constitutive polymers are changed to correlate morphology development with mechanical properties. Various ternary samples are prepared using a twin-screw extruder whereat weight percent of rubbery dispersed phase (NBR+NBR-g-GMA) is changed. Analyzing the morphology of produced samples and interpretation of mechanical properties corroborated the role of the mentioned factors on the type of morphology and also the size of both individual and composite domains in these sorts of ternary blends. Based on this attempt, the mechanical properties of 50/50 blends of NBR/NBR-g-GMA, showed maximum toughness value compared to pure PET specimen. Also, the results revealed that by increasing the rubber content, the rodlike structures were disappeared; besides, toughness was increased. On the contrary, by increasing PC content, rodlike structures have seen by morphological study; however, core-shell droplets formed in the blend structure caused enhancing the impact strength and reducing Youngs modulus. Ultimately, the ternary blend of 63/7/30 of PET/PC/ (NBR+NBR-g-GMA) revealed the best mechanical properties due to proper interaction between the PET matrix and rubbery domains in the presence of reactive compatibilizer.

Agarose-based biomaterials for tissue engineering

Agarose is a natural polysaccharide polymer having unique characteristics that give reason to consider it for tissue engineering applications. Special characteristics of agarose such as its excellent biocompatibility, thermo-reversible gelation behavior and physiochemical features support its use as a biomaterial for cell growth and/or controlled/localized drug delivery. The resemblance of this natural carbohydrate polymer to the extracellular matrix results in attractive features that bring about a strong interest in its usage in the field. The scope of this review is to summarize the extensive researches addressing agarose-based biomaterials in order to provide an in-depth understanding of its tissue engineering-related applications.

Competitive removal of heavy metal ions from squid oil under isothermal condition by CR11 chelate ion exchanger

Heavy metal ions (HMIs) are serious threats to the environment. Sub-critical water treatment was used to mimic contamination of squid oil in aqueous, metal-soap and oil phases. Isothermal adsorption of HMIs (Cu2+, Pb2+, Cd2+ and Zn2+) was studied from aqueous phase to oil phase (493, 523, 548, and 573K) for solutions with different initial concentration of HMIs was studied. Decomposition of glycerides into fatty acids was favored at high subcritical temperatures, with metal-soap phase showing the highest chelation ability toward Cu2+ (96%, isotherm 573K). The removal-ability of HMIs from contaminated oil was performed by CR11 chelate ion exchanger, showing facilitated removal from metal-soap and oil phases at low temperatures compared to general-purpose PEI-chitosan bead and PEI-chitosan fiber sorbents. The chelation behavior of Pb2+ and Cd2+ was the same in the OIL, with maximum values of 5.7×10-3 (mol/l) and 5.0×10-3 (mol/l) at 573K, respectively. By contrast, concentration of Zn2+ ion showed a slight increase with increasing temperature due to electrostatic forces between Zn2+ and active sites of glycerides in oil phase. For oil solution, the selectivity of adsorption for CR11, especially for Zn2+, was at least five-fold larger compared to PEI-chitosan bead and PEI-chitosan fiber adsorbents.