Modification of polyethylene by RF plasma in different/mixture gases

Herein, low-density polyethylene (LDPE) films were treated using radio-frequency plasma discharge in the presence of air, nitrogen, oxygen, argon, and their mixtures to introduce new chemical functionalities. The surface properties of treated LDPE were qualitatively and quantitatively characterized using various analytical and microscopic techniques. It was found that the optimum plasma treatment for LDPE occurs in the presence of air plasma at an exposure time of 120 s and 80 W of nominal power. The plasma formed layer had tendency to increasing thickness with increasing treatment time up to 60 s using air and oxygen and even more with inert gases. An aging study of plasma-treated LDPE samples stored in ambient air or water medium revealed the partial hydrophobic recovery.Funding: This publication was made possible by an Award JSREP07-022-3-010 from the Qatar National Research Fund (a member of The Qatar Foundation).Scopu

Improvement in properties of Ni-B coatings by the addition of mixed oxide nanoparticles

A comparison of properties of electrodeposited Ni-B and Ni-B-ZrO2-Al2O3 nanocomposite coatings is presented to explain the benefits of addition of mixed nanoparticles of ZrO2 and Al2O3 into Ni-B matrix. A comparative study of the properties of Ni-B and Ni-B-ZrO2-Al2O3 nanocomposite coatings in their as deposited condition indicates that the addition of mixed nanoparticles into Ni-B matrix has significant influence on its structural, surface, mechanical and electrochemical properties. Incorporation of mixed nanoparticles into Ni-B matrix shows significant grain refinement, substantial enhancement in mechanical properties and decent improvement in corrosion resistance. The improvement in mechanical properties can be attributed to grain refinement of Ni-B matrix and dispersion hardening effect of insoluble hard ceramic nanoparticles. Similarly, corrosion inhibition efficiency of binary Ni-B coatings is considerably improved which can be presumably regarded as the effect of formation of dense structure and decrease in active area of Ni-B matrix due to incorporation of mixed inactive nanoparticles. There is simultaneous improvement in mechanical and anti-corrosion properties of Ni-B coatings by the incorporation of mixed nanoparticles demonstrating usefulness of Ni-B-ZrO2-Al2O3 nanocomposite coatings for many applications.Scopu

Separation of water/oil emulsions by an electrospun copolyamide mat covered with a 2D Ti3C2Tx MXene

Purpose: Copolyamide 6,10 (coPA) electrospun mats were covered with multilayered (ML) and single-layered (SL) MXene (Ti3C2Tx) as a membrane for the separation of water/vegetable oil emulsions. Methods: Prepared membranes were characterized by atomic force microscopy (AFM), profilometry, the contact angle measurements of various liquids in air, and the underwater contact angle of vegetable oil. The separation efficiency was evaluated by measuring the UV transmittance of stock solutions compared to the UV transmittance of the filtrate. Results: The MXene coating onto coPA mats led to changes in the permeability, hydrophilicity, and roughness of the membranes and enhanced the separation efficiency of the water/vegetable oil emulsions containing 10, 100, and 1000 ppm of sunflower vegetable oil. It was found that membranes were highly oleophobic (>124°) under water, unlike in air, where the membranes showed high oleophobicity (<5°). The separation efficiency of water/oil emulsions for both types of covered membranes reached over 99%, with a surface coverage of 3.2 mg/cm2 Ti3C2Tx (for ML-Ti3C2Tx) and 2.9 mg/cm2 (for SL-Ti3C2Tx). Conclusions: The separation efficiency was greater than 98% for membranes covered with 2.65 mg/cm2 of ML-Ti3C2Tx, whereas the separation efficiency for membranes containing 1.89 and 0.77 mg/cm2 was less than 90% for all studied emulsion concentrations.This publication was supported by the Qatar University Collaborative Grant QUCG-CAM-19/20-2. The findings achieved herein are solely the responsibility of the authors. The publication of this article was funded by the Qatar National Library.Scopu

Piezoelastic PVDF/TPU Nanofibrous Composite Membrane: Fabrication and Characterization

Poly (vinylidene fluoride) nanofibers (PVDF NFs) have been extensively used in energy harvesting applications due to their promising piezoresponse characteristics. However, the mechanical properties of the generated fibers are still lacking. Therefore, we are presenting in this work a promising improvement in the elasticity properties of PVDF nanofibrous membrane through thermoplastic polyurethane (TPU) additives. Morphological, physical, and mechanical analyses were performed for membranes developed from different blend ratios. Then, the impact of added weight ratio of TPU on the piezoelectric response of the formed nanofibrous composite membranes was studied. The piezoelectric characteristics were studied through impulse loading testing where the electric voltage had been detected under applied mass weights. Piezoelectric characteristics were investigated further through a pressure mode test the developed nanofibrous composite membranes were found to be mechanically deformed under applied electric potential. This work introduces promising high elastic piezoelectric materials that can be used in a wide variety of applications including energy harvesting, wearable electronics, self-cleaning filters, and motion/vibration sensors

Electrically conductive, transparent polymeric nanocomposites modified by 2D Ti3C2Tx (MXene)

The electrically conductive, transparent, and flexible self-standing thin nanocomposite films based on copolyamide matrix (coPA:Vestamelt X1010) modified with 2D Ti3C2Tx (MXene) nanosheets were prepared by casting and their electrical, mechanical and optical properties and then, were investigated. The percolation threshold of the MXene filler within the coPA matrix was found to be 0.05 vol. %, and the highest determined electrical conductivity was 1.4 x 10(-2) Scm(-1) for the composite filled with 5 wt. % (1.8 vol. %) of MXene. The electrical conductivity of the as-prepared MXene was 9.1 Scm(-1), and the electrical conductivity of the MAX phase (the precursor for MXene preparation) was 172 Scm(-1). The transparency of the prepared composite films exceeded 75%, even for samples containing 5 wt. % of MXene, as confirmed by UV spectroscopy. The dynamic mechanical analysis confirmed the improved mechanical properties, such as the storage modulus, which improved with the increasing MXene content. Moreover, all the composite films were very flexible and did not break under repeated twisting. The combination of the relatively high electrical conductivity of the composites filled with low filler content, an appropriate transparency, and good mechanical properties make these materials promising for applications in flexible electronics.Qatar University Collaborative High Impact Grant [QUHI-CENG-18/19-1

Antimicrobial Modification of LDPE Using Non-thermal Plasma

Low-density polyethylene (LDPE) represents polymer having good chemical and physical characteristics for which it is widely used in many applications, such as biomedical and food packaging industry. This polymer excels by good transparency, flexibility, low weight and cost which makes it suitable material compared to non-polymer packaging materials. However, its hydrophobicity cause many limitations for antimicrobial activity which can result in absence of some characteristics required in food packaging applications. For that purpose, some researches have done experiments to modify the polymer surface to increase the surface free energy (hydrophilicity). This can be done by introducing some polar functional groups into the LDPE surface which will permit an increment of its surface free energy and so its wettability or adhesion without any disruption in its bulk properties [1]. One of the most preferable modification techniques is known as non-thermal radio-frequency discharge plasma, and it is preferred technique due to the ability to modify only thin surface layer leading to noticable improvement of the surface properties [2].Moreover, it represents environmentally friendly technique since it does not require the use of any hazardous chemicals or dangerous radiations and therefore non-thermal plasma is highly recommended for food packaging applications [1]. In addition, the surface modification of LDPE can lead to the enhancement of the antimicrobial activity, which was the main purpose of this research. Food packaging materials requires preventing any growth of bacteria, fungal, or any other microbial organisms for health and food safety. Some approved preservatives are commonly used directly in foods to preserve them form microorganisms growth and spoilage. Nowadays, some innovative ways are applied to graft acrylic acid on polymers surfaces [3] for biomedical applications to create an effective layer for an immobilization of antibacterial agents and this results in bacteria prevention on the LDPE surface. In this research, we focused on grafting of sorbic acid as one of the most commonly used preservatives in food and beverage for being safe, and effective in bacteria inhibition (whether pathogenic strains or spoilage kinds), molds, and yeasts [4]. It is also used in cosmetic industries since it has good compatibility with skin and it is easily usable [5]. For the potential enhancement of the antimicrobial efficiency, chitosan representing antimicrobial agent was used for the immobilization on sorbic acid created layer. Chitosan (a derivative of chitin polysaccharide) was chosen as a natural occurring antimicrobial agent (from crabs shrimps, and other sea shells [5]) that has strong and effective antimicrobial activity along with its nontoxicity, biofunctionality, biodegradability, and biocompatibility [6]. In this study, the LDPE surface was modified by several modification steps. The first step involved the modification of the LDPE surface by non-thermal radio-frequency discharge plasma as a radical graft initiator for the subsequently polymerization of sorbic acid containing double bonds. In the next step, grafting of sorbic acid was carried out immediately after plasma treatment allowing the interaction of plasma created radicals on LDPE surface with sorbic acid. Final step was focused on the immobilization of chitosan on grafted sorbic acid platform. Each modification step was analyzed by different analytical techniques and methods to obtain detailed information about the modification process. The surface parameters changes after modification of the LDPE surface, such as surface free energy (contact angles measurements), graft yield (gravimetric measurements) surface morphology (scanning electron microscopy and atomic force microscopy) and chemistry (Fourier transform infrared spectroscopy with attenuated total reflectance) were obtained allowing understanding the modification process.Qscienc

Piezoresponse, mechanical, and electrical characteristics of synthetic spider silk nanofibers

This work presents electrospun nanofibers from synthetic spider silk protein, and their application as both a mechanical vibration and humidity sensor. Spider silk solution was synthesized from minor ampullate silk protein (MaSp) and then electrospun into nanofibers with a mean diameter of less than 100 nm. Then, mechanical vibrations were detected through piezoelectric characteristics analysis using a piezo force microscope and a dynamic mechanical analyzer with a voltage probe. The piezoelectric coefficient (d33) was determined to be 3.62 pC/N. During humidity sensing, both mechanical and electric resistance properties of spider silk nanofibers were evaluated at varying high-level humidity, beyond a relative humidity of 70%. The mechanical characterizations of the nanofibers show promising results, with Young’s modulus and maximum strain of up to 4.32 MPa and 40.90%, respectively. One more interesting feature is the electric resistivity of the spider silk nanofibers, which were observed to be decaying with humidity over time, showing a cyclic effect in both the absence and presence of humidity due to the cyclic shrinkage/expansion of the protein chains. The synthesized nanocomposite can be useful for further biomedical applications, such as nerve cell regrowth and drug delivery. © 2018 by the authors. Licensee MDPI, Basel, Switzerland.NPRP from the Qatar National Research Fund (Qatar Foundation) [NPRP 7-1724-3-438

Piezoresponse, Mechanical, and Electrical Characteristics of Synthetic Spider Silk Nanofibers

This work presents electrospun nanofibers from synthetic spider silk protein, and their application as both a mechanical vibration and humidity sensor. Spider silk solution was synthesized from minor ampullate silk protein (MaSp) and then electrospun into nanofibers with a mean diameter of less than 100 nm. Then, mechanical vibrations were detected through piezoelectric characteristics analysis using a piezo force microscope and a dynamic mechanical analyzer with a voltage probe. The piezoelectric coefficient (d33) was determined to be 3.62 pC/N. During humidity sensing, both mechanical and electric resistance properties of spider silk nanofibers were evaluated at varying high-level humidity, beyond a relative humidity of 70%. The mechanical characterizations of the nanofibers show promising results, with Young’s modulus and maximum strain of up to 4.32 MPa and 40.90%, respectively. One more interesting feature is the electric resistivity of the spider silk nanofibers, which were observed to be decaying with humidity over time, showing a cyclic effect in both the absence and presence of humidity due to the cyclic shrinkage/expansion of the protein chains. The synthesized nanocomposite can be useful for further biomedical applications, such as nerve cell regrowth and drug delivery

Biotechnological production process and life cycle assessment of graphene

The aim of this study is to compare the graphene produced using a biotechnological method (Escherichia coli) with the graphene produced by Hummers' method (a chemical method) and to study the effect on the energy consumption and environment. The results indicated that the chemical reduction process has higher energy consumption, approximately 1642 Wh, than the energy consumption of the biotechnological reduction process, which is 5 Wh. The potential of global warming (GWP 100) improved by 71% using the biotechnological route for the production of graphene. Abiotic depletion, the photochemical ozone creation potential, and marine aquatic ecotoxicity potential were improved when the biological route was employed, compared with the chemical route. The eutrophication potential, terrestrial ecotoxicity, and ozone depletion layer changed very little since the main variables involved in the production of graphene oxide and waste management are the same. The biotechnological method can be considered a green technique for the production of graphene, especially given the reduction in the negative effects on global warming, abiotic depletion, the photochemical ozone creation potential, and the marine aquatic ecotoxicity potential