Sharif Digital Repository

Since in a highly filled polymer, a major problem arises from non-uniformity of properties due to the poor dispersion of filler, the application of coupling agents have been directed to overcome this problem and also to enhance the mechanical performance of the composites by improving the adhesion at the interface. In this study, a comparison between two major coupling approaches is conducted: 1) Using PPgMA as a kind of compatibilizer which changes the nature of the matrix, 2) Using titanate coupling agent which takes action at the interface and reacts with hydroxyl groups at the inorganic filler surface, resulting in the formation of monomolecular layer on the inorganic surface to increase... 

X-ray diffraction and rheological measurements were used to characterize nanoparticle dispersion in LDPE/LLDPE/nanoclay hybrid nanocomposites. XRD patterns were interpreted with a novel distribution formula and rheological measurements were used to confirm the results. Results of these two methods indicated that increasing clay in all the prepared nanocomposites exhibited a significant improvement in filler-matrix interaction because of increasing the probability of polymer diffusion but further exfoliation need more compatibilizing situations. It seems that this mathematical method could be used for predicting the overall change in clay gallery d-spacing and the extent of... 

The network structure of styrene-butadiene rubber (SBR) in the presence of carbon black (CB) with two different structures and multi-walled carbon nanotubes (MWCNTs) was investigated. Swelling behaviour, tensile properties at various strain rates and cure kinetics were characterized. Experimental data were analysed using the Flory-Rehner model as well as the tube model theory. It is found that the network structure of CB-filled SBR follows a three-phase composite model including rigid particles, semi-rigid bound rubber and matrix rubber. This bound rubber is postulated to be critical for the mechanical and deformational properties, development of crosslinking density in matrix rubber and... 

In this work, solvent blending in combination with extruding are applied to provide polystyrene/silica nanocomposite specimens. Transmission electron microscope (TEM) and scanning electron microscope (SEM) show same nanoparticle dispersion in PS matrix in low to high filler loadings. Differential scanning calorimetry (DSC), dynamic mechanical thermal analyzer (DMTA) and thermogravimetric analyzer (TGA) were used to study the thermophysical characteristic of the nanocomposites in solid state. In addition, the melt state rheological behavior of the samples was investigated under constant and zero shear rates. Interestingly, different behaviors were detected in nanocomposites in low and high... 

Processing conditions and final mechanical properties of polymer nanocomposites are affected by their interfacial layers behavior. However, it is impossible to determine directly the properties of these layers by dynamic rheometry tests. In this work, the interfacial layers properties are evaluated for polystyrene containing silica nanoparticles by the concept of glass-transition temperature shift. The samples were prepared via solution-mixing method and dynamic rheometry was used to determine the viscoelastic behavior of filled polymers in the melt state. This initial step showed that addition of silica particles increased the glass-transition temperature. By preference, decrease in the... 

The reinforcing effect of high structure carbon black (HSCB) and multi-walled carbon nanotubes (MWCNTs) on natural rubber/styrene-butadiene rubber blend processed using mechanical mixing was comparatively investigated. In-depth analysis by dynamic mechanical analysis, the Eggers-Schummer model and Medalia's relationship showed that HSCB aggregates provided large internal pores leading to significant immobilized macromolecules in filled rubber. Additionally, a tubular immobilized rubber layer with a thickness of 8nm was estimated for the rubber/MWCNT system based on dynamic mechanical analysis data. The mechanical performance of the HSCB filled blend was higher than that of the MWCNT filled... 

The silanization of nanodiamond (ND) was successfully carried out by using the esterification reaction of hydrolyzed vinyltrimethoxysilane (VTS) in alcoholic solution. The surface carboxylic group of ND was first enhanced by thermal oxidation to increase the degree of esterification reaction. The extent of silane functionalization of ND was controlled by varying the weight ratio of VTS and oxidized ND (oxND), from 2:1 to 10:1 (w/w) in the functionalization reaction medium. Fourier transform infrared spectroscopy (FTIR) and thermogravimetric analysis (TGA) revealed that the highest degree of silanization occurred at VTS/oxND of 5:1 (w/w), while more silane concentrations resulted in... 

The effect of nanodiamond (ND) particles on the network structure and vulcanization kinetics of natural rubber (NR)/styrene-butadiene rubber (SBR) blend vulcanized by three different curing systems, namely conventional (CV), semi-efficient (SEV) and efficient (EV), was investigated. The filler dispersion, crosslink density, curing kinetics and reversion behavior were fully studied. The state of ND dispersion in the rubber matrix was investigated by the field emission scanning electron microscope (FESEM). Swelling experiments and tensile tests exhibited that upon incorporation of ND crosslink density of NR/SBR blend was enhanced significantly due to the large surface area of nano filler... 

This research investigates the flexural behavior of a polymer concrete beam/pile encased with carbon fiber sleeve. The mechanical properties of carbon fiber sleeves in tension and cement and polymer concrete in compression were determined. Polymer concrete beams were tested in flexure to determine the bending moment capacity. Then, the test results were compared to the theoretical model results. Finally, a parametric study was conducted to determine the influence of beam/pile parameters on the capacity of the element. Based on the investigation, carbon fiber sleeve filled with polymer concrete exhibits outstanding structural performance including ductility and bending capacity. © 2017 Taylor... 

A new refill friction spot welding process called Threaded Hole Friction Spot Welding (THFSW) was introduced to join AA5052 aluminum to short-carbon-fiber-reinforced polypropylene (PP-SCF) composite sheets. The process was based on filling of the pre-threaded hole by melted and re-solidified polymer. The results showed that THFSW was successful to join aluminum to polymer sheets and the hole was completely filled with melted polymer. Formation of a reaction layer composed mostly of Al, C and O as well as interlocking between the threaded hole and the re-solidified polymer were recognized as main bonding mechanisms. Maximum shear-tensile strength of the joints reached to ∼80 percent of the... 

The effect of a plasma electrolytic oxidation (PEO) pre-treatment on joining of AA 5052 aluminium alloy and polypropylene by friction stir spot welding (FSSW) is investigated using lap tensile shear tests. Two surface conditions of the AA 5052 alloy are compared, one with a PEO pre-treatment in a silicate-based electrolyte, another without any pre-treatment. The resultant specimens are examined by high resolution scanning electron microscopy, thermogravimetric analysis and attenuated total reflectance-infrared spectroscopy. The PEO treatment generated a thermally-insulating, porous ceramic coating, which has a highly porous, rough surface that is favourable for incorporating polypropylene... 

The effect of graphene (G) and graphene oxide (GO), used as the nanofiller in polymer nanocomposites (NC), on the structural and dynamic properties of polymer chains, has been studied by means of molecular dynamics (MD) simulations. Two polymers, i.e., poly(propylene) and poly(vinyl alcohol), are employed as matrices to cover a wider range of polymer–filler interactions. The local structural properties, e.g., density profile, average Rg, and end-to-end distance as well as dynamic properties, e.g., estimated translational and orientational relaxation times, of polymer chains are studied. In addition, the interaction energies are estimated between polymers and nanofillers for different hybrid... 

The aim of this paper is to investigate adhesion property between nano-layered filler and the polymer matrix using a combination of experimental and micromechanical models as well as the changes in yield strength and stiffness of a layered silicate-filled epoxy nanocomposite. The results indicate that addition of intercalated layered silicate particles increased Young's modulus and yield strength of the epoxy resin, although the increases in stiffness and yield strength are modest, 30% and 4%, respectively. In addition, experimental results were compared with predictive stiffening and strengthening models. The rule of mixtures provides an upper bound for the modulus in these materials, while... 

Shape memory polymers (SMPs) are a class of smart materials which can recover their shape even after many shape changes in application of an external stimulus. In this paper, flexural behavior of a composite beam, constructed of a corrugated part filled with SMPs, is studied. This composite beam is applicable in sensor and actuator applications. Since the corrugated profiles display higher stiffness-to-mass ratio in the transverse to the corrugation direction, the beams with a corrugated part along the transverse direction are stiffer than ones with a corrugated part along the length. Employing a developed constitutive model for SMPs and the Euler–Bernoulli beam theory, the behavior of the... 

This research investigates the flexural behavior of a polymer concrete beam/pile encased with carbon fiber sleeve. The mechanical properties of carbon fiber sleeves in tension and cement and polymer concrete in compression were determined. Polymer concrete beams were tested in flexure to determine the bending moment capacity. Then, the test results were compared to the theoretical model results. Finally, a parametric study was conducted to determine the influence of beam/pile parameters on the capacity of the element. Based on the investigation, carbon fiber sleeve filled with polymer concrete exhibits outstanding structural performance including ductility and bending capacity  

Mixed-matrix membranes (MMMs) are promising candidates for carbon dioxide separation. However, their application is limited due to improper dispersion of fillers within the polymer matrix, poor interaction of fillers with polymer chains, and formation of defects and micro-voids at the interface of both phases, which all result in the decline of the gas separation performance of MMMs. In this work, we present a new method to overcome these challenges. To this end, a series of MMMs based on polyethersulfone (PES) as the continuous polymer matrix and MIL-53-derived MOFs as the dispersed filler were prepared. FTIR-ATR, XRD, TGA, FESEM, and N2 adsorption/desorption analyses were employed to... 

Ground-source heat pumps, as the most environmentally friendly and energy-efficient air conditioning technology, suffer from a great required length of ground heat exchanger, partly arising from the low thermal conductivity of high-density polyethylene tubes commonly used in ground heat exchangers. In an attempt to find a replacement with an acceptable thermal conductivity for high-density polyethylene tubes, in this study, first, a comprehensive comparative study on fillers commonly used in thermally conductive polymer composites and resulting high-density polyethylene composites was conducted. Then, based on the advantages and disadvantages presented, an appropriate composite was selected... 

This paper aims to study the behavior of UPVC-confined columns reinforced with polypropylene fibers under axial compression. A sum of 42 column specimens has been tested, including 18 Unconfined Concrete Cylinders (UCC) and 24 confined Concrete-Filled UPVC Tube (CFUT) specimens. To investigate the sensitivity of these columns to various parameters, different levels of material volumes have been used, which include two concrete strengths of 40 and 50 MPa, two tube grades of PN6 and PN10, and three polypropylene fiber content of 0, 1 and 3 kg/m3 of the concrete mixture. The influence of each variable on the ultimate strength, ductility and confinement effectiveness of the specimens have been... 

Ammonium polyphosphate (APP) is one of the most widely used halogen-free flame retardant, added in various resins to improve the fire properties, such as flame and smoke spread ratings and LOI, of fiber-reinforced polymer (FRP) composites. This paper experimentally investigates the effects of using APP, as a fire-retardant filler, on mechanical properties (i.e. ultimate tensile, flexural, and bond strength) of glass fiber-reinforced polymer (GFRP) and carbon fiber-reinforced polymer (CFRP) composites. Based on two fiber types (i.e. carbon and glass) and three different APP mass fractions in resin (i.e. 0, 20, and 40% of total weight of matrix), six sets of specimens were prepared for each...