Center for Advanced Materials

The performance of cement mortar reinforced with varying percentages of treated bundled date palm fibers is investigated to appraise their feasibility for structural and non-structural applications. The study first entailed the evaluation of two different alkali pre-treatments at varying concentrations by subjecting treated and untreated bundled fibers to tensile testing. The suitable pre-treatment was then adopted while casting cement mortar mixes. The physical properties of fresh mortar was studied through setting times and, for mortar mixes cured up to 28 days, through parameters such as drying shrinkage and water absorption. The unconfined compressive strengths, split tensile strengths as well as the flexural strengths of the cured mortar mixes at two different ages were undertaken to assess their mechanical properties; while the durability was gauged based on their sulfate resistance for up to a period of four months.

The inhibition efficiency of the stearamidopropyl dimethylamine (SAPDA) surfactant for the corrosion of API X120 steel in a 0.5 M HCl solution at different temperatures was investigated using different electrochemical and microscopy techniques. The kinetics and thermodynamic parameters were discussed. The overall results showed that SAPDA significantly decreased the corrosion rate of API X120 steel with an inhibition efficiency of approximately 99% at an inhibitor concentration of 136 μmol L −1. It was revealed that the adsorption of the SAPDA surfactant on the API X120 steel surface followed Langmuir's adsorption isotherm. Polarization studies indicated that SAPDA is chemi/physisorbed on the steel surface. Quantum chemical calculations, using the density functional theory, were applied to better understand the relationship between the inhibitor efficiency and its molecular structure.

The impact of AEO7 surfactant on the corrosion inhibition of carbon steel (C-steel) in 0.5 M HCl solution at temperatures between 20 °C and 50 °C was elucidated using weight loss and different electrochemical techniques. The kinetics and thermodynamic parameters of the corrosion and inhibition processes were reported. The corrosion inhibition efficiency (IE%) improved as the concentration of AEO7 increased. In addition, a synergistic effect was observed when a concentration of 1 × 10 −3 mol L −1 or higher of potassium iodide (KI) was added to 40 µmol L −1 of the AEO7 inhibitor where the corrosion IE% increased from 87.4% to 99.2%. Also, it was found that the adsorption of AEO7 surfactant on C-steel surface followed the Freundlich isotherm. Furthermore, electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization measurements indicated that AEO7 was physically adsorbed on the steel surface. The surface topography was examined using an optical profilometer, an atomic force microscope (AFM), and a scanning electron-microscope (SEM) coupled with an energy dispersion X-ray (EDX) unit. Quantum chemical calculations based on the density functional theory were performed to understand the relationship between the corrosion IE% and the molecular structure of the AEO7 molecule. Carbon steel (C-steel) is extensively utilized as a construction material in different industrial fields due to its high mechanical properties and low cost. It exists in most industrial infrastructures such as heat exchangers, reactors, drums, boilers and tubings 1,2. In oil and gas industries, sulfuric and hydrochloric acids are commonly utilized as pickling acids for the oil wells acidification and the removal of undesirable scales such as rust or mill-scale from steel or any ferrous alloys at elevated temperatures. However, pickling acids are highly corrosive and their aggressiveness needs to be suppressed by adding suitable corrosion inhibitors in small ranges 3-5. For these reasons, an intensive attention is paid for the corrosion of steel in different aggressive corrosion media 6-11. Excellent corrosion inhibition properties are exhibited using inhibitors comprising electronegative atoms such as oxygen, sulfur, phosphorous and/or nitrogen as well as aromatic rings. Recently, eco-friendly biodegradable natural materials show perfect corrosion inhibition efficiencies as well as cost effectiveness. For instance, polymers , possessing polar functional groups such as hydroxyl, carboxylic and amino groups, manifest good corrosion inhibition in different corrosive media because they have a high affinity towards metallic surfaces 12-16. For decades, surfactants are used in an extensive range of applications, from cleaning purposes such as shampoos, soap and detergents to industrial uses, namely, additives in coatings, concrete mixtures and paints. Moreover, researchers investigate the surfactant-flooding phenomenon in order to enhance the oil recovery. Furthermore, surfactants are utilized as corrosion inhibitors for several metals in the oil and gas production 17-20. There are four types of surfactants: anionic, cationic, nonionic and amphoteric. The ethoxylated fatty alcohols surfactants are one of the most common nonionic surfactants that are used in the detergent industry and for an eco-friendly applications 21,22. Nevertheless, their corrosion inhibition effectiveness is not yet well exploited especially in acidic environments 23,24. For instance, Abdallah has investigated the effect of the numbers of ethylene oxide units of ethoxylated fatty alcohols, on the corrosion of zinc in 0.5 M HCl. It was found that to the corrosion inhibition increase with increasing the concentration and the number of ethylene oxide units per molecule. Inhibition was

Motivated with sustainability and economic factors, there is a rapid increase in the use of recycled asphalt pavement (RAP) material in the construction of new asphalt pavements. This necessitates the development of better understanding of the interaction between recycled and virgin binders, as well as studying the influence of this interaction on the properties of the blended binder. This paper provides in-depth evaluation of these properties at various scales using chemical, mechanical and rheological tests. This study involved the use of binders with different proportions of RAP (0, 15, 25, 35 and 100%). The chemical characterization of these binders was carried out using Fourier Transform Infrared Spectroscopy (FTIR), and the results showed that higher peak levels of C@O and S@O bonds were observed with the increase in RAP binder content. Atomic Force Microscopy (AFM) imaging of these binders showed that the surface roughness increased with an increase in RAP content especially when the RAP proportion exceeded 25%. The multiple stress creep recovery (MSCR) test was used to measure the rutting resistance, and the linear amplitude sweep test (LAS) was used to evaluate the fatigue resistance. There was slight improvement in rutting resistance with an increase in RAP content; however, the fatigue resistance degraded with the addition of RAP. The moduli/stiffness of virgin, RAP and blended binders was determined using Dynamic Shear Rheometer (DSR), Nanoindentation (NI), and AFM. The moduli obtained from these three techniques increased exponentially and at similar rates up to 25% of RAP. However, the dynamic modulus from DSR increased at a higher rate than the nano-scale moduli at higher RAP contents. This finding suggests that the nano-scale interactions were not influenced by the increase in RAP content as the DSR measurements of dynamic modulus and fatigue life values imply. The nano-scale understanding of blended binder offers opportunities for better engineering and accommodation of RAP in asphalt mixtures.

Thermal characterization of Phase Change Materials (PCMs) compose of linear low-density polyethylene (LLDPE), paraffin wax (W) with a melting point of 25 °C, and expanded graphite (EG), that are highly effective in thermal energy storage systems in the building industry, is reported. Thermal investigation of PCMs with various compositions of LLDPE, W and EG has been performed by nonconventional transient guarded hot plane technique (TGHPT) and compared with conventional Differential Scanning Calorimetry (DSC) measurements. An excellent agreement in determination of thermal characteristics by both methods was found. The highest values of the total amount of stored energy, sensible heat for solid and liquid states (Q total , Q s (solid) and Q s (liquid), respectively) were found for the PCMs with composition LLDPE/W/EG = 40/50/10 and 35/50/15 w/w/w. Moreover, thermal conductivity and diffusivity of PCMs have been significantly improved by adding EG. Additionally, life cycle assessment was performed to evaluate the environmental impact of three different materials as glass wool, rock wool and PCM used with brick wall.

An adaptation of the fracture toughness test method, the J-integral technique, is described within the general framework of polymer fracture behavior. It is shown that there is a strong interaction between different morphological parameters in the way they affect the fracture behavior of isotactic polypropylene (iPP). The fracture toughness decreases with increasing crystallinity at a fixed spherulite size. The fracture toughness also decreases slightly with increasing spherulite size at a constant crystallinity, but this may not be a pure spherulite size effect. The use of a nucleating agent results in a very fine spherulitic structure but facilitates crack growth and reduces the material toughness beyond the crack initiation stage. This suggests that the material behavior is dictated by the increase in crystallization temperature caused by the presence of the nucleating agent and not by the change in spherulite size.

The influence of adding waste wax, produced as a by-product of the low density polyethylene manufacturing process, on the thermal and mechanical properties of three types of polyethylene (PE), high-density polyethylene (HDPE), linear low-density polyethylene (LLDPE) and low-density polyethylene (LDPE), with 10, 20, 30 and 40 wt.% was investigated. Polymerwax mixing was effective with no apparent leakage of the wax during sample preparation, which was evident from the agreement between the theoretical and experimental values of enthalpy for all types of PE. The wax dispersion in the matrix strongly depends on the percentage of wax added to the polymer and the molecular structure of the polymer. It was found that increasing the wax content enhances the phase separation. LDPE undergoes less phase separation due to its highly branched structure composed of a network of short and long chain branches. The wax has no pronounced plasticising effect on the polymer. This is clearly manifested in LDPE as no change in the melting temperature occurred. LLDPE and HDPE were slightly affected by a high concentration of wax (30% and 40%). This is due to the non-uniform distribution of short chain branching along the LLDPE and HDPE main chains, which can interact with the wax structure.

Artificial aging of Shape Stabilized Phase Change Materials (SSPCM) based on linear low density polyethylene (LLDPE) and paraffin wax (W) modified with various amounts of expanded graphite (EG) was investigated and reported in this paper. It was found that EG not only strongly suppresses leakage of paraffin wax from the material over time but also significantly improves the photo oxidation stability. The increase in the melting point of wax incorporated within LLDPE matrix during aging was observed whereas the specific melting enthalpy of the paraffin wax decreased. This is mainly caused by the leakage of paraffin wax from the blends. The melting of neat LLDPE decreased during aging whereas its specific enthalpy of melting increased. Addition of EG led to the prolonged photo-oxidation stability of materials, as confirmed by Carbonyl Index measurements.

Composites of Linear Low Density Polyethylene (LLDPE) and Graphene Nanoplatelets (GNPs) were processed using a twin screw extruder under different extrusion conditions. The effects of screw speed, feeder speed and GNP content on the electrical, thermal and mechanical properties of composites were investigated. The inclusion of GNPs in the matrix improved the thermal stability and conductivity by 2.7% and 43%, respectively. The electrical conductivity improved from 10-11 to 10-5 S/m at 150 rpm due to the high thermal stability of the GNPs and the formation of phonon and charge carrier networks in the polymer matrix. Higher extruder speeds result in a better distribution of the GNPs in the matrix and a significant increase in thermal stability and thermal conductivity. However, this effect is not significant for the electrical conductivity and tensile strength. The addition of GNPs increased the viscosity of the polymer, which will lead to higher processing power requirements. Increasing the extruder speed led to a reduction in viscosity, which is due to thermal degradation and/or chain scission. Thus, while high speeds result in better dispersions, the speed needs to be optimized to prevent detrimental impacts on the properties.

This contribution is focused on the Mullins effect in polyethylene. An ultra-low-density polyethylene with 0.15 crystal content, a low-density polyethylene with 0.3 crystal content and a high-density polyethylene with 0.72 crystal content are subjected to cyclic stretching over a large strain range. Experimental observations are first reported to examine how the crystal content influences the Mullins effect in polyethylene. It is found that the cyclic stretching is characterized by a stress-softening, a hysteresis and a residual strain, whose amounts depends on the crystal content and the applied strain. A unified viscohyperelastic-viscoelastic-viscoplastic constitutive model is proposed to capture the polyethylene response over a large strain range and its crystal-dependency. The macro-scale polyethylene response is decomposed into two physically distinct sources, a viscoelastic-viscoplastic intermolecular part and a viscohyperelastic network part. The local inelastic deformations of the rubbery amorphous and crystalline phases are considered by means of a micromechanical treatment using the volume fraction concept. Experimentally-based material kinetics are designed by considering the Mullins effect crystaldependency and are introduced into the constitutive equations to capture the experimental 2 observations. It is shown that the model is able to accurately reproduce the Mullins effect in polyethylene over a large strain range. The inherent deformation mechanisms are finally presented guided by the proposed constitutive model.

Natural aging of shape-stabilized phase change materials containing linear low density polyethylene (LLDPE), paraffin wax and expanded graphite (EG) in Qatari climate has been studied. It was found that expanded graphite significantly improved the performance of prepared SSPCMs in multiple ways. Firstly, EG suppressed leakage of paraffin wax from the compact shape of SSPCMs. The addition of 15 wt% of EG to shape stabilized phase change materials (SSPCMs) containing 50 wt% of wax caused a decreasing in the leakage of wax by 50% over 210 days of natural aging. Secondly, \expanded graphite enhanced the photochemical stability of the blends; this was confirmed by FTIR analysis, where carbonyl index decreased with EG content.

The influence of two types of graphene nanoplatelets (GNPs) on the physicomechanical properties of linear low-density polyethylene (LLDPE) was investigated. The addition of these two types of GNPs-designated as grades C and M-enhanced the thermal conductivity of the LLDPE, with a more pronounced improvement resulting from the M-GNPs compared to C-GNPs. Improvement in electrical conductivity and decomposition temperature was also noticed with the addition of GNPs. In contrast to the thermal conductivity, C-GNPs resulted in greater improvements in the electrical conductivity and thermal decomposition temperature. These differences can be attributed to differences in the surface area and dispersion of the two types of GNPs.