Processing and characterization of polyethylene-based composites

Thermoplastic matrix polymer composites have gained commercial success in the semistructural and structural applications. Polyethylene (PE) is one of the most versatile and widely used thermoplastics in the world because of its excellent properties like toughness, near-zero moisture absorption, excellent chemical inertness, low coefficient of friction, ease of processing and unusual electrical properties. This review is designed for comprehensive source of PE-based polymer composites research, including structure and classification of PE manufacturing/processing techniques for PE composites, and it also described different characterization methods for PE composites. Differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) characterization methods were used to describe the thermal properties of PE composites. Morphological studies were explained by using scanning electron microscope (SEM), transmission electron microscope (TEM) and atomic force microscope (AFM) techniques. Rheological properties and dynamic mechanical analysis (DMA) are also discussed in this review. X-ray diffraction (XRD) characterization was described in this review to explain crystallinity in PE composites. Hence, this review offers a comprehensive discussion on processing and characterization of PE-based composites

Anti-microbial Activity Of Graphene Oxide Against Bacteria And Fungi

Graphene Oxide (GO) is a promising material for various applications. The team prepared GO from graphite and studied the interaction with different microorganisms. Anti-microbial properties were detected for the prepared GO. Anti-microbial activities of GO was tested against one eukaryotic fungi (Candida albicans) two prokaryotic bacteria Gram-negative bacilli (Escherichia coli ATCC 41570 and Pseudomonas aeruginosa ATCC 25619) and two prokaryotic bacteria Gram-positive cocci (Streptococcus feacalis 19433 and Staphylococcus aureus ATCC 11632). Spectrophotometer was used to measure the growth as an indirect method, viable cell counting was used as direct method. Readings were taken at successive incubated times. Results revealed that GO exhibited stronger antibacterial and anti-fungal activity against the used bacteria and fungi species. Acknowledgements: This research was made possible by NPRP grant (NPRP5-039-2-014) from the Qatar National Research Fund (a member of Qatar Foundation). The statement made herein are solely the responsibility of the author.qscienc

Designing piezoelectric nanogenerator from PVDFHFP nanocomposite fibers containing cellulose nanocrystals and Fedoped ZnO

Self-powering devices harvest energy from the environment and perform based on a maintenance free approach. These materials are of utmost significance as they solve the problems associated with the energy crisis and management, to greater extends. Advances in material science and the design of various polymer nanocomposites developed many self-powering devices that are flexible, sensitive, less power consuming and of low cost. The semi-crystalline polymer, poly vinylidene fluoride (PVDF) and its co-polymers are notable for mechanical energy harvesting because of the typical crystalline phases in their structure. Various nanoparticles are added to such polymers to enhance their dielectric and piezoelectric properties as well. Since the alignment of crystalline phases improve the energy harvesting properties, techniques such as electrical poling are practiced to enhance their applicability. Among various alignment procedures, electrospinning stands as unique since the high voltage applied to the polymer solution generates nanofiber scaffolds in perfect alignments. The present work aims to develop electrospun composite fibers in nano-dimensions for designing self-powering nanogenerators. The co-polymer of PVDF, polyvinylidene fluoride hexa fluoropropylene (PVDF-HFP) was used as the base polymer and the iron-doped zinc oxide (Fe-ZnO) and cellulose nanocrystals (CNC) as the filler reinforcements. Fe-ZnO nanostructures were obtained by hydrothermal synthesis method from the ZnO precursor, while the CNC were synthesized following the acid hydrolysis of cellulose microfibers. The optimized concentration of 20 wt.% was used for obtaining the electrospun fibers of neat PVDF-HFP and various concentrations of nanoparticles were mixed with this base solution. Simple solvent mixing was employed using the acetone/DMF solvent mixture to prepare the composite solutions prior to electrospinning. The electrospinning conditions were also optimized by varying the applied voltage, tip to collector distance and speed of the rotating collector. Nice fibers were obtained at a voltage of 12-13 eV and rotating collector speed of 200 rpm. Composites of CNC with PVDF-HFP, Fe-ZnO with PVDF-HFP and the hybrid material of CNC/Fe-ZnO with PVDF-HFP were prepared and properties were investigated. All the fibers were tested for the morphology, structural, thermal and dielectric properties. The mechanical energy harvesting was performed using an assembled set up containing a frequency generator, shaker and data acquisition system. At 2 wt. % of the nanofillers, the PVDF-HFP/CNC generated about 2 V, the PVDF-HFP/Fe-ZnO generated about 4 V and the hybrid nanocomposite containing both nanoparticles generated about 6 V. The filler synergy plays a major role in regulating the material properties and here the combined effect of the piezoelectric performance of the cellulose nanocrystals and the modified ZnO nanoparticles enhanced the mechanical energy harvesting capability of the final nanocomposite. A nanogenerator is designed based on the developed polymer nanocomposite fibers and the piezoelectric performance on various conditions of stretching, pressing and twisting were also investigated. In all the cases the hybrid composite showed notable performance substantiating its application in designing self-powered nanogenerators. The dielectric properties of the hybrid material showed many fold increase in its dielectric constant, making it useful in electrical energy storage. In short, the designed device by electrospinning technique is highly useful in adding to the energy management and is environmentally safe and of good efficiency.qscienc

Mussel-mimicking sulfobetaine-based copolymer with metal tunable gelation, self-healing and antibacterial capability

In the present study, the sulfobetaine-based copolymer bearing a dopamine functionality showed gel formation adjusted by the application of metal salts for gelation and various values of pH. Normally, the liquid-like solution of the sulfobetaine-based copolymer and metal cross-linkers is transformed to a gel-like state upon increasing the pH values in the presence of Fe3+ and Ti3+. Metal-induced coordination is reversible by means of the application of EDTA as a chelating agent. In the case of Ag+ ions, the gel is formed through a redox process accompanied with the oxidative coupling of the dopamine moieties and Ag0 particle formation. Mussel-mimicking and metal-dependent viscoelastic properties were observed for Fe3+, Ti3+, and Ag+ cross-linking agents, with additionally enhanced self-healing behavior in comparison with the covalently cross-linked IO4 − analogues. Antibacterial properties can be achieved both in solution and on the surface using the proper concentration of Ag+ ions used for gelation; thus, a tunable amount of the Ag0 particles are formed in the hydrogel. The cytotoxicity was elucidated by the both MTT assay on the NIH/3T3 fibroblast cell line and direct contact method using human dermal fibroblast cell (F121) and shows the non-toxic character of the synthesized copolymer. © 2017 The AuthorsQatar University [QUUG-CAM-2017-1]; Ministry of Education, Youth and Sports of the Czech Republic - Program NPU I [LO1504]; Maersk Oil R&TC Qatar project; Qatar National Research Fund (Qatar Foundation) [9 - 219-2-105

Vibration sensing systems based on poly(Vinylidene fluoride) and microwave-assisted synthesized zno star-like particles with controllable structural and physical properties

This study deals with the effect of zinc oxide (ZnO) star-like filler addition to the poly(vinylidene fluoride) (PVDF) matrix, and its effect on the structural and physical properties and consequences to the vibration sensing performance. Microwave-assisted synthesis in open vessel setup was optimized for the preparation of the star-like shape of ZnO crystalline particles. The crystalline and star-like structure was confirmed by X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy-dispersive spectroscopy (EDX). Furthermore, the PVDF-based composites were prepared using a spin-coating technique from solution. An investigation of the transformation of the α crystalline phase to the β crystalline phase of the neat PVDF matrix and with various filler concentrations was performed using Fourier-Transform infrared (FTIR) spectroscopy, which shows an enhanced β-phase from 44.1% to 66.4% for neat PVDF and PVDF with 10 wt.% of particles, respectively. Differential scanning calorimetry (DSC) measurements and investigation showed enhanced crystallinity and melting enthalpy of the composite systems in comparison to neat PVDF, since ZnO star-like particles act as nucleating agents. The impact of the filler content on the physical properties, such as thermal and dynamic mechanical properties, which are critical for the intended applications, were investigated as well, and showed that fabricated composites exhibit enhanced thermal stability. Because of its dynamic mechanical properties, the composites can still be utilized as flexible sensors. Finally, the vibration sensing capability was systematically investigated, and it was shown that the addition of ZnO star-like filler enhanced the value of the thickness mode d33 piezoelectric constant from 16.3 pC/N to 29.2 pC/N for neat PVDF and PVDF with 10 wt.% of ZnO star-like particles. © 2020 by the authors. Licensee MDPI, Basel, Switzerland.Qatar National Research Fund (a member of the Qatar Foundation) [NPRP-6-282-2-119]; Czech Science FoundationGrant Agency of the Czech Republic [19-17457S]; Ministry of Education, Youth and Sports of the Czech Republic-DKRVO [RP/CPS/2020/003

Nicotinamide-based supergelator self-assembling via asymmetric hydrogen bonding NH⋯OC and H⋯Br− pattern for reusable, moldable and self-healable nontoxic fuel gels

Hypothesis: Development of highly efficient low-molecular weight gelators (LMWGs) for safe energy storage materials is of great demand. Energy storage materials as fuel gels are often achieved by construction of hybrid organic frameworks capable of multiple noncovalent interactions in self-assembly, which allow tuning required properties at the molecular level by altering individual building blocks of the LMWG. However, LMWGs have limited rechargeable capability due to their chemical instability. Experiments: We designed, synthesized and characterized a novel, bio-inspired chiral gemini amphiphile derivative 1 containing N-hexadecyl aliphatic tails from quaternized nicotinamide-based segment and bromide anion showing supergelation ability in water, alcohols, aprotic polar and aromatic solvents, with critical gel concentrations as low as 0.1 and 0.035 wt% in isopropanol and water, respectively. Findings: Nanostructural architecture of the network depended on the solvent used and showed variations in size and shape of 1D nanofibers. Supergelation is attributed to a unique asymmetric NH⋯OC, H⋯Br− hydrogen bonding pattern between H-2 hydrogens from nicotinamide-based segment, amide functional groups from chiral trans-cyclohexane-1,2-diamide-based segment and bromide ions, supporting the intermolecular amide–amide interactions appearing across one strand of the self-assembly. Gels formed from 1 exhibit high stiffness, self-healing, moldable and colorable properties. In addition, isopropanol gels of 1 are attractive as reusable, shape-persistent non-toxic fuels maintaining the chemical structure with gelation efficiency for at least five consecutive burning cycles. © 2021 Elsevier Inc.Chemical Institute, Slovak Academy of Sciences [IRCC-2020004]; Slovak Research and Development AgencySlovak Research and Development Agency [APVV-17-0324]; Ministry of Education of the Slovak Republic [1/0712/18, 1/0145/20]; European Union's Horizon 2020 research and innovation programme [810701]; Ministry of Education, Youth and Sports of the Czech Republic-DKRVO [RP/CPS/2020/003]; Qatar National Library; Qatar University [IRCC-2020004]RP/CPS/2020/003; Univerzita Komenského v Bratislave; Horizon 2020 Framework Programme, H2020: 810701; Slovenská Akadémia Vied, SAV: IRCC-2020-004; Ministerstvo Školství, Mládeže a Tělovýchovy, MŠMT; Ministerstvo školstva, vedy, výskumu a športu Slovenskej republiky; Qatar University, QU; Agentúra na Podporu Výskumu a Vývoja, APVV: APVV-17-0324; Vedecká Grantová Agentúra MŠVVaŠ SR a SAV, VEGA: 1/0145/20, 1/0712/18; Horizon 202

Preparation and characterization of urea-formaldehyde microcapsules filled with paraffin oil

Paraffin oil was encapsulated in a urea–formaldehyde polymer shell by in situ polymerization. The effect of modifying the fabrication parameters, specifically the emulsifier, the core material concentration, the stirring rate, and the pH, on the resulting microcapsules was characterized by FTIR, SEM, particle size analysis and TGA. The stiffness and the mechanical stability during mixing of the microcapsules were also evaluated. It was found that the ethylene maleic anhydride copolymer (EMA)-based microcapsules are smaller, harder and have an increase in yield of 15 % or more compared to the polyvinyl alcohol (PVA)-based microcapsules. Both EMA- and PVA-based microcapsules have good thermal stability up to 400 °C. Smaller EMA-based microcapsules require a higher force, up to 0.96 N, to be 80 % deformed.Scopu

A new experimental device and inverse method to characterize thermal properties of composite phase change materials

A new experimental device has been developed in order to characterize the phase change material (PCM) thermal properties (thermal conductivity k, sensible and latent heat thermal energy storage, cp and Lf) in the solid phase, during the solid–liquid transition and in the liquid phase. It allows to measure cylindrical samples of maximum 60 mm radius and 10 mm thick. A typical measurement consists in imposing a vertical temperature gradient through the PCM sample driven by a heat source, monitoring during the experiment time all the boundary conditions (temperatures and heat fluxes) and measuring temperature evolution in three locations within the PCM sample. In this work, we will focus only on the solid thermal conductivity characterization. These experiment data are used to solve the inverse heat conduction problem by applying the conjugate gradient method and finally, to determine the PCM thermal properties. Two types of composite PCM have been thermally characterized: paraffin mixed with synthetic graphite (Timrex SFG75) and paraffin mixed with graphite waste.NPRP grant # 4-465-2-173 from the Qatar National Research Fund (a member of Qatar Foundation)Scopu

Mechanical Properties of Gamma Irradiated TiO\u3csub\u3e2\u3c/sub\u3eNPs/MWCNTs/LDPE Hybrid Nanocomposites

This work investigates the impact of ϒ-irradiation on the mechanical properties of titanium oxide nanoparticles (TiO2NPs)/multi-walled carbon nanotubes (MWCNTs) hybrid low-density polyethylene (LDPE) nanocomposites. Hybrid LDPE nanocomposite films prepared using melt mixing technique were exposed to different doses of ϒ-radiation, ranging from 5 to 50 kGy. The tensile strength was diminished after TiO2NP or MWCNT addition, then increased with a further increase in the carbon nanotube (CNT) content. This behavior can be ascribed to stress transfer between the filler and the LDPE network. Besides, the tensile strength was enhanced after exposure to a dosage of 5 and 25 kGy of ϒ-radiation, then followed by a decline when exposed to 50 kGy, especially in the case of hybrid films due to the degradation and cross-linking of LDPE chains caused by ϒ-radiation. Because of the absorbance and antioxidant effects of CNTs, the CNT addition retarded the degradation of LDPE networks and decreased the catalytic activity of TiO2NPs to activate degradation upon radiation exposure. Therefore, the tensile strength was retained after exposure to a dose of 50 kGy of ϒ-radiation, especially in case of less TiO2NPs and more CNTs filled hybrid films. Furthermore, the % of the total elongation at break is decreased after incorporating MWCNTs. The % of the total elongation at break after exposure to a dosage of 25 kGy was reduced as a result of chain scissions and molecular weight decrease. Young’s modulus of the irradiated composites was lower than without irradiation. This effect was more significant for neat LDPE and TiO2NPs filled LDPE films, whereas MWCNTs had some stability effects on the nanocomposites