Effect of Cure Conditions on the Generated Morphology and Viscoelastic Properties of a Poly(acrylonitrile–butadiene–styrene) Modified Epoxy–Amine System

Highly Toughened Nanostructured Self-Assembled Epoxy-Based Material—Correlation Study between Nanostructured Morphology and Fracture Toughness—Impact Characteristics

We present an efficient and effective method for preparing a novel self-assembled nanostructured material with high toughness and impact strength from a blend of di-glycidyl ether of bisphenol-A (DGEBA) and epoxidized poly(styrene-block-butadiene-block-styrene) (eSBS55) tri-block copolymer. The field emission scanning electron microscopy and transmission electron microscope results show the nanostructured morphological characteristics of the blends. This study achieved the highest fracture toughness, with a fracture toughness in the form of critical stress intensity factors (KIC) value of 2.54 MPa m1/2, in epoxy/block copolymer blends compared to previous works in the field. The impact strength also increased by 116% compared to neat epoxy. This is a major advancement in epoxy toughening due to the use of a single secondary phase. The resulting highly tough and impact-resistant material is a promising candidate for coating applications in industries such as flooring, building, aerospace, and automobiles.

Influence of dodecyl surfactants on the cross-linking, plasticization and damping behavior of epoxy novolac resins

A series of modified epoxy novolac resins (ENRs) were prepared by incorporating dodecyl chain surfactants with polar groups such as amine, carboxylic acid, phenol, resorcinol and benzene sulfonic acid. Except for the case of benzene sulfonic acid, no macrophase separation is seen in any of the modified ENRs. The addition of these dodecyl surfactants to ENR hinders the cross-linking reaction as revealed from their dynamic and isothermal DSC curing measurements and reduced glass transition temperatures (T_g). The cross-link density evaluated from the storage modulus (E') in the rubbery region using DMTA measurements is found to be low with the addition of surfactants in agreement with their plasticization behavior. The stiffness of the materials obtained at low temperatures showed a moderate increase for ENRs with carboxylic acid and phenol surfactants. Upon heating, their storage modulus drops at low temperatures compared to ENR supporting the mechanism of plasticization in them. This high value of E' for the plasticized material in the glassy phase is different from the generally known behavior. Such unusually high storage modulus together with increased 'd' spacing from the XRD results seems to indicate 'partial segmental confinement' of epoxy chains. It is believed that high damping obtained in these two materials is due to 'partial segmental confinement' of epoxy chains because of interaction with lauric acid and phenolic surfactants and the associated internal and interfacial friction in them. Dielectric relaxation measurements support the plasticization process based on the high dielectric loss and ionic conductivity in the surfactant modified ENR, as compared to the pristine ones.

Nanoscale chemical and mechanical heterogeneity of human dentin characterized by AFM-IR and bimodal AFM

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AFM-IR technique was used to detect the chemical heterogeneity of human dentin for the first time.

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The heterogeneity of mechanical properties of human dentin was explored by AFM AM-FM technique.

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A band at 1336 cm⁻¹ assigned to S Created by potrace 1.16, written by Peter Selinger 2001-2019 ]]>O stretching vibrations was found only in peritubular dentin.

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Peritubular dentin had a higher Young’s modulus (32.25 ± 4.67 GPa) than intertubular dentin.

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AFM-IR and AFM AM-FM are useful for understanding the mineral deposition mechanisms of dentin.

Human dentin, as an important calcified tissue in the body, plays significant roles in withstanding masticatory forces and has a complex hierarchical organization. Understanding the composition and ultrastructure of dentin is critical for elucidating mechanisms of biomineralization under healthy and pathological states. Here, atomic force microscope infrared spectroscopy (AFM-IR) and AFM-based amplitude modulation-frequency modulation (AM-FM) techniques were utilized to detect the heterogeneity in chemical composition and mechanical properties between peritubular and intertubular dentin at the nanoscale. AFM-IR spectra collected from peritubular and intertubular dentin contained similar vibrational bands in the amide regions (I, II and III), suggesting that collagen may exist in both structures. A distinctive band at 1336 cm⁻¹ indicative of SO stretching vibrations was detected only in peritubular dentin. AFM-IR imaging showed an uneven distribution of chemical components at different locations, confirming the heterogeneity of dentin. The Young’s modulus of peritubular dentin was higher, and was associated to a higher mineral content. This study demonstrated distinctive chemical and mechanical properties of peritubular dentin, implying the different development and mineralization processes between peritubular and intertubular dentin. AFM-IR is useful to provide compositional information on the heterogeneity of human dentin, helping to understand the mineral deposition mechanisms of dentin.

Synthesis of Benzene Tetracarboxamide Polyamine and Its Effect on Epoxy Resin Properties

Epoxy resins have found various industrial applications in high-performance thermosetting resins, high-performance composites, electronic-packaging materials, adhesives, protective coatings, etc., due to their outstanding performance, including high toughness, high-temperature performance, chemical and environmental resistance, versatile processability and adhesive properties. However, cured epoxy resins are very brittle, which limits their applications. In this work, we attempted to enhance the toughness of cured epoxy resins by introducing benzene tetracarboxamide polyamine (BTCP), synthesized from pyromellitic dianhydride (PMDA) and diamines in N-methyl-2-pyrrolidone (NMP) solvent. During this reaction, increased viscosity and formation of amic acid could be confirmed. The chemical reactions were monitored and evidenced using ¹H-NMR spectroscopy, FT-IR spectroscopy, water gel-phase chromatography (GPC) analysis, amine value determination and acid value determination. We also studied the effect of additives on thermomechanical properties using differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), dynamical mechanical analysis (DMA), thermomechanical analysis (TMA) and by measuring mechanical properties. The BTCP-containing epoxy resin exhibited high mechanical strength and adhesion strength proportional to the amount of BTCP. Furthermore, field-emission scanning electron microscopy images were obtained for examining the cross-sectional morphology changes of the epoxy resin specimens with varying amounts of BTCP.

Tetrafunctional epoxy as an all‐purpose modifier for homopolymerized bisphenol A diglycidyl ether

In some applications, homopolymerized epoxies, which offer better biocompatibility and lower water absorption than amine‐ and anhydride‐cured epoxy, are more preferable; however, using homopolymerized epoxy as matrix in composites still remains a challenge. Herein, homopolymerized bisphenol A diglycidyl ether curing systems with simultaneously improved tensile strength, impact strength, and glass transition temperature (Tg) were achieved by addition of small amounts of tetra‐functional epoxies (TFTEs) with different spacer lengths. Effects of spacer length in TFTE on thermal and mechanical properties were investigated. Results indicated that TFTE with the longest spacer length shows the best mechanical performance. In addition, effects of TFTE loading on thermal and mechanical properties were discussed. Compared with neat bisphenol A diglycidyl ether, addition of 5% tetraglycidyl‐1,10‐bis(triphenylmethane) decane leads to simultaneous improvements in tensile strength, impact strength, and Tg. Effects of thermal cycling on the mechanical properties were also reported. Results suggest that the modified homopolymerized epoxy shows good performances and could be used as matrix materials and possibly in some dental applications. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 46431.

Epoxy matrix toughness improvement via reactive bio-resin alloying

A facile solvent-less approach to toughen epoxy thermosets by means of a bio-based resin, that is, poly(furfuryl alcohol) (PFA; furan resin) is reported. The bio-resin PFA was firstly synthesized through polycondensation reaction of furfuryl alcohol as a bio-monomer and maleic anhydride as a catalyst. Different amounts of PFA were blended with diglycidyl ether of bisphenol A epoxy resin and cured by diethylenetriamine as a hardener, which simultaneously cross-linked both of the epoxy and PFA resins. The curing process was studied by Furrier transform infrared spectroscopy and differential scanning calorimetry. Scanning electron microscopy of the chemically cured blends revealed no phase separation. It was found remarkable increase in flexural modulus and strength of the neat and modified epoxies with increasing PFA content up to around 15%. Moreover, in comparison with neat epoxy, the epoxy-PFA thermosets showed 60% increase in critical stress intensity factor and 123% increase in critical strain energy release rate. In fact, chemical reaction of PFA-incorporated epoxy could toughen the epoxy matrix without sacrificing the flexural strength and modulus. Toughening was obtained through cross-link density reduction. As exhibited by dynamic mechanical thermal analysis, Tan δ and magnitude of β-relaxation were also increased for the epoxy-PFA alloys. Overall, this green, simple, concise and cost-effective approach was suggested for being considered to produce toughened epoxy thermosets in industrial scale.

Environmentally friendly high performance homopolymerized epoxy using hyperbranched epoxy as a modifier

A high performance, low cost, and environmentally friendly epoxy is demonstrated for the first time by copolymerizing a small amount of epoxide-terminated hyperbranched polyether with DGEBA.

A facile procedure to fabricate nano calcium carbonate–polymer-based superhydrophobic surfaces

A facile procedure to fabricate superhydrophobic surfaces based on nano calcium carbonate–polymer composites has been described.