Reaction‐induced phase separation and resulting thermomechanical and surface properties of epoxy resin/poly(ethylene oxide)–poly(propylene oxide)–poly(ethylene oxide) blends cured with 4,4′‐diaminodiphenylsulfone

We investigated the phase separation, cure kinetics and thermomechanical properties of diglycidyl ether of bisphenol‐A/4,4′‐diaminodiphenylsulfone/poly(ethylene oxide)–poly(propylene oxide)–poly(ethylene oxide) (PEO–PPO–PEO) triblock copolymer (TBCP) blends. Fourier transform infrared spectroscopy, differential scanning calorimetry, and atomic force microscopy revealed that the blends exhibited heterogeneous phase morphology in which the TBCP formed dispersed domains in epoxy matrix, due to reaction induced phase separation. A fraction of phase‐separated PEO phase underwent partial crystallization whereas another fraction formed interphases between the dispersed domains and epoxy matrix. Moreover, the dispersed PEO chains improved the compatibility and interfacial adhesion between the matrix and domains and, consequently, significantly improved the mechanical properties of epoxy resin. Furthermore, the thermal degradation studies and contact angle measurements disclosed that the dispersed domains were well protected by the epoxy matrix. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44406.     

Polyoxymethylene/polyurethane/alumina ternary composites: Structure,mechanical, thermal and dielectric properties

Ternary composites composed of polyoxymethylene (POM), polyurethane (PU), and boehmite alumina were produced by melt blending with and without latex precompounding. Latex precompounding served for the predispersion of the alumina particles. The related masterbatch (MB) was produced by mixing the PU latex with water‐dispersible boehmite alumina. The dispersion of the alumina was studied by transmission and scanning electron microscopy techniques (TEM and SEM, respectively) and discussed. The crystallization of POM was inspected by means of differential scanning calorimetry (DSC) and polarized optical microscopy (DSC and polarized light microscopy, respectively). The mechanical and thermomechanical properties of the composites were determined in uniaxial tensile, dynamic‐mechanical thermal analysis (DMTA), short‐time creep tests (performed at various temperatures), and thermogravimetric analysis (TGA). The melt flow of the composites was characterized in a plate/plate rheometer. In addition, the dielectric response of the nanocomposites was investigated by means of broadband dielectric spectroscopy at an ambient temperature. The composites produced by the MB technique outperformed the direct melt (DM) compounded composites in respect to the thermal and mechanical characteristics. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Improved mechanical and thermal properties of spent coffee bean particulate reinforced poly(propylene carbonate) composites

Using biodegradable polypropylene carbonate (PPC) as the polymer matrix and 5 to 25?wt% content of spent coffee bean powder (SCBP) as filler, completely biodegradable composite films of PPC/SCBP were prepared. These composite films were characterized by polarized optical microscopy (POM), Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), thermogravimetric analysis, differential scanning calorimetry (DSC), and tensile tests. The POM images indicated the uniform distribution of the SCBP in the composites. The FTIR spectra indicated that the PPC structure was retained by the composite films. The XRD analysis found that the composite films had lower crystallinity than the PPC due to the presence of amorphous hemicellulose containing SCBP. A significant enhancement in thermal stability of the filler reinforced composite was noticed which was more than 30% of the PPC matrix due to the presence of polyphenols in SCBP. A maximum increase of 35% of tensile strength was observed with the addition of 20?wt% SCBP filled composite films. These biodegradable composite films with higher thermal stability and tensile strength can be considered for packaging applications.     

Failure Mode Analyses of Reinforced Concrete Beams Strengthened in Flexure with Externally Bonded Fiber-Reinforced Polymers

As existing structures age or are required to meet the changing demands on our civil infrastructure, poststrengthening and retrofitting are inevitable. A relatively recent technique to strengthen reinforced concrete (RC) beams in flexure uses fiber-reinforced polymer (FRP) strips or sheets glued to the tension side of the beam. A number of researchers have reported that the failure mode of an FRP-strengthened RC beam can change from the desired ductile mode of an underreinforced beam to a brittle one. This paper analyzes the effects of this strengthening technique on the response and failure modes of a reference RC beam. A nonlinear RC beam element model with bond-slip between the concrete and the FRP plate is used to study how the failure mechanism of simply supported strengthened RC beams is affected by the following parameters: plate length, plate width, plate stiffness, and loading type. The beam geometry is kept constant. The parametric studies confirm the experimentally observed results according to which the most commonly observed failure modes due to loss of composite actions are affected by the plate geometric and material properties. In addition, distributed loads (difficult to apply in an experimental test) may not be as sensitive to plate debonding in the region of maximum bending moment as are beams subjected to point loads.     

Rheological and thermal properties of poly(ethylene oxide)/multiwall carbon nanotube composites

Poly(ethylene oxide) (PEO) based nanocomposites were prepared by the dispersion of multiwall carbon nanotubes (MWCNTs) in aqueous solution. MWCNTs were added up to 4 wt % of the PEO matrix. The dynamic viscoelastic behavior of the PEO/MWCNT nanocomposites was assessed with a strain‐controlled parallel‐plate rheometer. Prominent increases in the shear viscosity and storage modulus of the nanocomposites were found with increasing MWCNT content. Dynamic and isothermal differential scanning calorimetry studies indicated a significant decrease in the crystallization temperature as a result of the incorporation of MWCNTs; these composites can find applications as crystallizable switching components for shape‐memory polymer systems with adjustable switching temperatures. The solid‐state, direct‐current conductivity was also enhanced by the incorporation of MWCNTs. The dispersion level of the MWCNTs was investigated with scanning electron microscopy. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Poly (butylene terephthalate)/silica nanocomposites prepared from cyclic butylene terephthalate

Poly (butylene terephthalate) (PBT)/silica nanocomposites were compounded from cyclic butylene terephthalate (CBT) resin with very low melt viscosity via high-speed stirring and subsequent in situ polymerization. The effect of silica nanoparticles on the properties of CBT and its polymer composites has been studied. It was shown that the well-dispersed silica nanoparticles, even in small content (1–2 wt.%), result in the dramatic extension of the polymerization process of CBT resin. The flexural properties of polymerized PBT nanocomposites, including modulus, yield strength and failure strain, was improved significantly with the incorporation of silica nanoparticles.     

Effect of Various Chemical Treatments of Prosopis juliflora Fibers as Composite Reinforcement: Physicochemical,Thermal, Mechanical,and Morphological Properties

ABSTRACT

The present environmental regulations enforced by the government authorities have made the investigators around the globe to make use of more and more green materials particularly in composite systems. In this context, natural fibers play an important role and proven to be excellent reinforcements in polymer matrices. However, these natural fibers have got one major limitation: their incompatible hydrophilic behavior which affects their bonding with hydrophobic matrixes. Researchers over the years have come up with several fiber surface modification processes to overcome this defect. So, in this present study, the effect of various chemical treatments like alkaline, benzoyl peroxide, potassium permanganate, and stearic acid on Prosopis juliflora fibers has been discussed. These various chemical treatments on the fiber surfaces impacted on their structure, composition, and properties which were discovered through chemical analysis, Fourier transform-infrared, X-ray diffraction, thermogravimetric analysis, differential scanning calorimetry, scanning electron microscopy, and tensile testing.     

Size effects in two-dimensional layered materials modeled by couple stress elasticity

In the present study, the effect of material microstructure on the mechanical response of a two-dimensional elastic layer perfectly bonded to a substrate is examined under surface loadings. In the current model, the substrate is treated as an elastic half plane as opposed to a rigid base, and this enables its applications in practical cases when the modulus of the layer (e.g., the coating material) and substrate (e.g., the coated surface) are comparable. The material microstructure is modeled using the generalized continuum theory of couple stress elasticity. The boundary value problems are formulated in terms of the displacement field and solved in an analytical manner via the Fourier transform and stiffness matrix method. The results demonstrate the capability of the present continuum theory to efficiently model the size-dependency of the response of the material when the external and internal length scales are comparable. Furthermore, the results indicated that the material mismatch and substrate stiffness play a crucial role in the predicted elastic field. Specifically, the study also addresses significant discrepancy of the response for the case of a layer resting on a rigid substrate.     

Effects of Indium Content on Microstructural,Mechanical Properties and Melting Temperature of SAC305 Solder Alloys

The present study investigated the effects of indium (In) addition on the microstructure, mechanical properties, and melting temperature of SAC305 solder alloys. The indium formed IMC phases of Ag₃(Sn,In) and Cu₆(Sn,In)₅ in the Sn-rich matrix that increased the ultimate tensile strength (UTS) and the hardness while the ductility (% EL) decreased for all In containing solder alloys. The UTS and hardness values increased from 29.21 to 33.84 MPa and from 13.91 to 17.33 HV. Principally, the In-containing solder alloys had higher UTS and hardness than the In-free solder alloy due to the strengthening effect of solid solution and secondary phase dispersion. The eutectic melting point decreased from 223.0°C for the SAC305 solder alloy to 219.5°C for the SAC305 alloy with 2.0 wt% In. The addition of In had little effect on the solidus temperatures. In contrast, the liquidus temperature decreased with increasing In content. The optimum concentration of 2.0 wt % In improved the microstructure, UTS, hardness, and eutectic temperature of the SAC305 solder alloys.     

Raw and chemically treated bio-waste filled (Limonia acidissima shell powder) vinyl ester composites: Physical,mechanical, moisture absorption properties,and microstructure analysis

The rapid growth of environmentally sustainable and eco-friendly materials tends to the utilization of biowastes as filler in polymer matrix composites. The particulate composite with improved wettability of fillers and advanced approach can evolve polymer composites that exhibit promising applications in packaging, automobile, marine, construction, and aerospace. In the present work, one of the biowaste fillers were synthesized from Limonia acidissima shells via a top-down approach (pulverizing) and the surfaces were chemically modified using sodium hydroxide (NaOH) before they were used as fillers in vinyl ester polymer composites by different weight percentage (0, 5, 10, 15, and 20 wt%). The prepared particulate composites were characterized by mechanical properties, moisture absorption behavior, and morphology. At different filler loading the tensile strength, tensile modulus, flexural strength, flexural modulus, impact strength, hardness, density, and moisture intake tests were performed. The results reveal that the properties increased for composites filled with alkaline treated fillers for the same filler loading and found to be higher at filler loading of 15 wt%. The morphological analysis confirms the better interfacial bonding between alkali-treated particles and matrix due to the removal of non-cellulose materials from the surface of the particles.