Chemical surface modification of glass beads for the treatment of paper machine process waters

Adsorption of detrimental contaminants on a solid sorbent is proposed to remove these contaminants from process waters to increase water recycling and reduce effluent loads in the papermaking industry. A self-assembly process of attaching (covalent grafting) cationic aminosilane molecules to glass beads was investigated. The existence and the hydrolytic stability of self-assembled monolayers and multilayers were confirmed by X-Ray Photoelectron Spectroscopy and contact angle measurements. Effects of reaction time and curing on aminosilane layer structures are also discussed. The curing step after silanization seems to be crucial in the hydrophobization of the quaternary ammonium silane coated onto glass beads, and curing could affect the final chemical structure of the ammonium groups of grafted organosilane. Results indicated that modified glass beads have a strong hydrophobicity, which is attributed to the hydrophobic property of the longest carbon chain grafted onto the glass surface. Adsorption of a model contaminant (stearic acid) onto chemically modified glass beads was determined using colloidal titration. Hydrophobic interactions could be the main driving force involved between the long carbon chains of stearic acid and the carbon chains of the aminosilane layers on glass bead surfaces. Finally, self-assembly processes applied onto glass beads may have two promising applications for papermaking and self-cleaning systems.     

Characterization of conductive composite films based on TEMPO-oxidized cellulose nanofibers and polypyrrole

Abstract  

In this article, conductive composite films based on TEMPO-oxidized cellulose nanofibers (TOCN) and polypyrrole (PPy) were synthesized in situ by a Chemical Polymerization Induced Adsorption Process of pyrrole on the surface of TOCN in aqueous medium. Resulting composite films were investigated by X-ray photoelectron spectroscopy, scanning, and transmission electron microscopy, N₂ gas adsorption analysis, thermogravimetric analysis, mechanical tests, and conductivity measurements in the ambient air. Our results showed a stable, flexible, and highly electrically conductive composite film in which PPy nanoparticles coated the surface of the TOCN network. In addition, the advantage in using the famous material, TOCN, is clearly due to the presence of carboxylate (COOH/COO⁻Na⁺) and hydroxyl (OH) moieties on the surface of TOCN. These reactive moieties could enhance the adsorption process of positively charged PPy backbone during polymerization. TEM observations demonstrated the formation of a PPy coat along the surface of the cellulose nanofibers having a diameter of about 90 nm which is relatively higher compared to the initial diameter of pure TOCN (~9 nm). Despite the physical and chemical treatment of TOCN during polymerization, the micrometric length of the cellulosic nanomaterial was maintained. In addition, the incorporation of polyvinyl alcohol as an additive in the TOCN/PPy composite seems to enhance the flexibility of composite films (bent up to 180°) without losing the high electrical conductivity. Finally, because of the high conductivity and good mechanical properties of the TOCN/PPy composite films obtained in this work, they can be used as a promising material in applications of sensors, flexible electrodes, and other fields requiring electrically conductive flexible films.     

Experimental and theoretical study of an integrated thermoelectric–photovoltaic system for air dehumidification and fresh water production

The main objective of this study is to present an integrated thermoelectric–photovoltaic renewable system to dehumidify air and produce fresh water. The system is combined with a solar distiller humidifying ambient air to enhance distillate output to meet the specified fresh water needs for a residential application. A model is developed to simulate the air dehumidification process using thermoelectrically cooled TEC channels. Experiments were performed to validate the developed model results. It is found that the model predicted well the variation in the air temperature along the channel with a maximum relative error in air temperature less than 2.4%. In addition, the simulation model predicted well the amount of water condensate produced by the integrated system with a maximum relative error of 8.3%. An optimization problem is formulated to design and set the integrated system optimal operation to produce 10 L of fresh water per day meeting the fresh water needs of a typical residential. Using five TEC channels of a length of 1.2 m and an area of 0.07 × .05 m² integrated with 1.2‐m² solar distiller that recirculates a constant air mass flow rate of 0.15 kg s^?1 is capable of meeting water demand when air mass flow rate through each TEC channel is optimally set at 0.0155 kg s^?1. The associated optimal electrical current input to the TEC modules varied depending on the month and is set at 2.2 A in June, 2.1 A in July and 2.0 A in August, September and October. Copyright © 2011 John Wiley & Sons, Ltd.     

Fabrication of polymer waveguides between two optical fibers using spatially controlled light-induced polymerization

A new method for the fabrication of polymer waveguides between two optical fibers using a spatially controlled photopolymerization is reported. By taking advantage of the self-guiding effect of light through a photopolymerizable medium, polymer waveguides perfectly aligned with the fiber cores and strongly anchored to their surfaces are fabricated. The process is characterized by following in situ the coupling efficiency of a nonactinic laser source. Examples of waveguides exhibiting good coupling efficiency and high flexibility are given. By selecting the suitable monomers and adjusting the photonic parameters, the optical and mechanical waveguide properties (diameter, length, refractive index, rigidity, and flexibility) can be controlled in view of optical sensor applications.     

Study of the hydrophobization of TEMPO-oxidized cellulose gel through two routes: amidation and esterification process

In this paper, we studied the hydrophobization of TEMPO-oxidized cellulose gel (TOCgel) by covalent coupling of long carbon chains via esterification and amidation processes. In this context, amidation process was achieved by covalent coupling of stearylamine (SA) on the carboxyl moieties of TOCgel using carbodiimide and hydroxysuccimide as catalyst and amidation agent. In parallel, esterification process was realized by grafting of alkyl ketene dimer (AKD) on the hydroxyl groups of TOCgel in the presence of 1-methylimidazole as a promoter. The grafting state of the final products obtained under heterogeneous conditions was confirmed by fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), thermogravimetric analysis (TGA), transmission and scanning electron microscopy, and contact angle measurement (CAM). The hydrophobic behavior of the obtained products was discussed based on the results of CAM and absorption rate of water drop in their film surface. FTIR and XPS results indicated the formation of amide bonding for the SA-g-TOCgel (amidation), and β-keto ester linkages for the AKD-g-TOCgel (esterification). As confirmed by CAM, the both chemical treatments enhanced the transition hydrophilic/hydrophobic behavior of the TOCgel fibers. It appeared also that CA values of grafted samples showed a slightly greater hydrophobicity of AKD-g-TOCgel (115° ± 2°) relatively to SA-g-TOCgel (102° ± 2°). However, the absorption rate of water drop seems to be relatively faster for AKD-g-TOCgel than for SA-g-TOCgel. Indeed, the water resistance of amidation product could be due to the high graft efficiency obtained (46.3 %) in comparison with that of the esterification product (30 %). In parallel, this result was confirmed by the dispersion test of modified TOCgels in hexane solvent which indicated clearly the high stable dispersion of SA-g-TOCgel obtained through the amidation process. Moreover, TGA result demonstrated that the thermal stability was found to be slightly higher for SA-g-TOCgel than for AKD-g-TOCgel. Finally, the excellent hydrophobic properties of modified TOCgel material could be suitable to be used as reinforcement for nonpolar polymer matrices in industrial applications.     

Year-round numerical simulation of a parabolic solar collector under Lebanese conditions: Beirut case study

A detailed thermal and optical numerical model is developed to simulate the performance of a small-scale parabolic collector having an evacuated receiver line with selective coating, taking into account different energy balances and interactions with the surrounding. An analytical model is developed to estimate the direct, diffuse and global solar radiation intensities on inclined surfaces. The collector performance model was validated using published experimental data. A year-round dynamic simulation for the collector performance under Beirut climatic conditions was carried out with an economic and environmental analysis. The outlet water temperature could reach a maximum of 114°C in July and 52°C in December by employing a collector of about 6 m² aperture area with 0.01 kg/s water flow rate. The maximum daily thermal energy production is attained in July with 22.267 kWh while January exhibits the lowest thermal energy production with 6.704 kWh per day with a maximum thermal efficiency of 72%.     

Modelling and testing of a hybrid solar‐biomass ORC‐based micro‐CHP system

Expanders employed recently in organic Rankine cycle (ORC)‐based systems suffer from key problems including excessive working fluid leakage, thermal losses, low isentropic efficiency and high cost. The majority of the units available in the market are for medium and large‐scale applications (>100 kW) with no commercial micro‐scale expanders available and applicable for ORC units for residential and building applications. Moreover, the majority of the studies conducted on ORC expanders employed HFC and HCFC working fluids which have high global warming potential leading to negative environmental impacts. In this study, a micro‐scale CHP system based on the ORC technology is theoretically and experimentally investigated to provide the thermal needs and part of the electrical demands for residential applications. An innovative design for a hybrid ORC‐based micro‐CHP system is proposed using a biomass boiler and a solar concentrator to run the CHP system providing more reliable and clean operation compared to conventional natural gas‐driven units. The micro‐CHP system employs a new type small‐scale scroll expander with a compact design, integrating the generator and the turbine in a single unit. A numerical model was developed using the Engineering Equation Solver (EES) software to simulate the thermodynamic behaviour of the ORC unit predicting the thermal and electrical performance of the overall CHP system. In addition, an experimental setup was built to test the whole ORC–CHP system performance under different conditions, and the effect of various operational parameters on the system performance has been presented using an environmentally friendly HFE7100 working fluid. The maximum electric power generated by the expander was in the range of 500 W at a pressure differential of about 4.5 bars. The attained expander isentropic efficiency was over 80% at its peak operating conditions with no fluid leakage observed. Being mass‐produced with low cost in the automotive industry along with the high isentropic efficiency and the leakage‐free performance, the proposed compact scroll expander represents a potential candidate to be used in the development of micro‐scale ORC–CHP units for building applications. Copyright © 2013 John Wiley & Sons, Ltd.     

Oriented crystallization of isotactic polystyrene in films prepared by friction transfer

The ability to orient polymer chains by applying external forces opens up the possibility to obtain polymeric surfaces with ordered structures. Here, we employed a friction-transfer approach by moving a pin of isotactic polystyrene (i-PS) across a smooth silicon counterface at controlled velocity, pressure and temperature which led to the deposition of a molecularly thin layer of highly oriented i-PS chains. The observed morphology of the resulting film (ribbons oriented in the sliding direction) indicated that the transferred molecules were highly oriented. This was confirmed after isothermal crystallization which led to the formation of so-called “shish-kebab” crystals aligned in the sliding direction. Thus, after crystallization all polymers were preferentially oriented with their chain axis in the shearing direction. Our results strongly suggest that by extending the polymer chain conformations in the shearing direction we can introduce a significant reduction of the nucleation barrier. Accordingly, friction transfer allows to align not only the transferred polymer chains but also the subsequently forming crystalline domains within the transferred films.