Inorganic Porous Materials Based Epoxy Self-Healing Coatings

The long-term stability of protective coating for metal is critically important for structural applications [1, 2]. Self-healing ability extend the service life of protective coatings leading to a significant reduction in maintenance cost for oil and gas pipe lines and structural parts in civil and construction industry. Recently, the self-healing technology based on healing agent loaded containers has been receiving attention [3, 4]. The incorporation of self- healing agent loaded containers into polymer matrix can be carried out using existing blending techniques. Hence, this technology facilitate large-scale application of self-healing materials [5]. Different micro or nano containers has been used for the storage and release of self-healing agents upon specific corrosion triggering conditions (e.g. on pH change) or upon mechanical damage [6]. Polymer capsules, polymer nanofibers, hollow glass bubbles, hollow glass fibers etc. were used by the researchers to load the healing agent inside their cavity. The inorganic particles with nano cavity offers large surface area, high pore volume and good stability favorable for the storage of the healing agents. Moreover, the usage of inorganic nanomaterials as reservoirs for healing agent can eliminate the tedious encapsulation process. The present study aims to use inorganic nanotubes and mesoporous silica as containers for healing agents in epoxy coating. The ability of Halloysite nanotubes (HNT), titanium dioxide (TiO2) nanotube and mesoporous silica to load and release the healing agents are investigated and compared their performance. Among them, Halloysite nanotubes are naturally occurring clay mineral. Meanwhile, TiO2 nanotube and mesoporous silica are synthesised in laboratory and characterised using scanning electron microscopic (SEM), transmission electron microscopic (TEM) techniques and Brunauer-Emmett-Teller (BET) surface area analysis. The morphology of the nanotubes and mesoporous silica are shown in Fig. 1 (in supporting file). In this study, the epoxy pre-polymer and hardener are used as healing agents. Containers loaded with epoxy and hardener can provide a repair system with matching chemical entity with host epoxy coating. Both epoxy encapsulated nanotubes (either Halloysite or TiO2 nanotubes) and amine immobilized mesoporous silica are incorporated into epoxy, followed by the addition of diethylenetriamine curing agent. The mixture is coated on the metal with an average thickness of 300 ?m. The controlled epoxy coatings are also prepared without nanotube and mesoporous silica. Epoxy coating loaded with encapsulated Halloysite nanotubes and immobilized mesoporous silica is abbreviated as 'EP/HNT/SiO2' and the one loaded with encapsulated TiO2 nanotubes and immobilized mesoporous silica is abbreviated as 'EP/ TiO2/SiO2'. The self-healing ability of the scratched coatings is monitored by electrochemical impedance spectroscopy (EIS) in definite time intervals for 5 days. Both EIS bode plots and tafel polarization curves are analysed to observe the self-healing ability of the coatings. For the scratched controlled epoxy coating, after an immersion time of 24 hours, the impedance curve drop to its minimum value over the entire frequency range and on further immersion period the impedance curve remains its minimum value. However, in the case of self-healing coatings, the initially declined impedance value recovers in successive days. The recovery in low frequency impedance values (at 0.01 Hz), which is a direct reflection of the recovery of corrosion resistance of the coating are evaluated. While EP/TiO2/SiO2 coating recovered 57% of its anticorrosive property, the EP/HNT/SiO2 coating recovered only 0.026%. This results suggest that the nature of the nanotubes affect the amount and rate of healing agent released into the scratched area from the tube lumen which itself affect the self-healing ability of the coating. SEM is also used to observe the healed scratches on the coatings. After 96 hours of immersion in 3.5 wt% NaCl solution, the scratches in EP/TiO2/SiO2 self-healing coatings are found to be almost covered. The results confirm the effective self-healing ability of the EP/TiO2/SiO2 coating in which the released epoxy pre-polymer from nanotube lumen get contact with the amine hardener immobilized in mesoporous silica and cross-link to cover the scratch. Acknowledgment: This abstract was made possible by PDRA grant # PDRA1-1216-13014 from the Qatar national research fund (a member of Qatar foundation).qscienc

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

Electrospun PVDF graphene oxide composite fibre mats with tunable physical properties

This article is aimed at a basic physical characterization of electrospun PVDF/graphene oxide (GO) composite non-woven fibre mats. The morphological characterization of the prepared fabrics was performed via SEM investigations. Introduction of the GO during the electrospinning process caused significant changes in the crystalline structure of PVDF, and a transformation from α- to β-crystalline phases was achieved. Addition of the GO particles into PVDF did not only improve the thermal stability of the polymer, but also acted as a reinforcing filler, giving rise to improved dynamic moduli and tensile strength. The dielectric properties were evaluated over a broad frequency range, and it was confirmed that the presence of small amounts of GO had little effect on the dielectric properties of the PVDF, since the GO has a dielectric character similar to that of the PVDF. © 2016, Springer Science+Business Media Dordrecht.QUST-CAM-FALL-14/15-1, QU, Qatar University; QUST, Qingdao University of Science and TechnologyCollege of Arts and Sciences at Qatar University [QUST-CAM-FALL-14/15-1

Halloysite Nanotube as Multifunctional Component in Epoxy Protective Coating

The current research explores the use of halloysite nanotube as a multifunctional filler in epoxy coating for carbon steel. Epoxy monomer loaded halloysite was incorporated into epoxy coating along with amine hardener immobilized mesoporous silica. The waterproofing, self-healing, anticorrosive abilities, and stability under weathering of the coating were evaluated. The halloysite nanotubes are able to impart better waterproofing property to the coating. The released epoxy monomer encapsulated inside the halloysite cavity upon reaction with amine curing agent immobilized in mesoporous silica recovers the damage and thereby facilitates self-healing in epoxy coating. Apart from offering healing ability to the coating, the halloysite nanotubes are able to protect the coatings for a longer period from severe weathering conditions.Scopu

Improvement of aluminum/polyethylene adhesion through corona discharge

Polyethylene (PE) is often used in several industrial applications including the building, packaging and transport industries. Aluminum (Al) is widely used in different applications in the automotive, railway, aeronautic, and naval industries because of its excellent mechanical and chemical properties. Laminates prepared from Al and PE lead to an enhancement in physical and mechanical properties. These materials play a main role in the packaging and building sectors, such as in TetraPak containers and aluminum composite panels. The main problem observed is associated with the adhesion between polymers and metals. This research focused on investigating the enhancement in the adhesion of the PE/Al laminate using the corona discharge. The corona treatment of the surfaces led to a significant increase in the adhesion of the PE/Al laminate as a result of improved surface properties confirmed by peel test measurements. Moreover, the positive effect of the corona treatment in combination with a primer on the improvement of adhesion characteristics was observed too. Different analytical techniques were employed to characterize the effect of the corona treatment on the improvement in adhesion of PE/Al. A significant increase in wettability was confirmed by the measurement of contact angles. Changes in the surface morphology of the PE and Al surface, after the corona treatments at different operating conditions, were observed using atomic force microscopy (AFM) and scanning electron microscopy (SEM). In addition, x-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR) were used to analyze changes in chemical composition after the corona discharge effect on PE and Al surfaces.This publication was made possible by an Award JSREP 07-022-3-010 from the Qatar National Research Fund (a member of The Qatar Foundation). The statements made herein are solely the responsibility of the authorsScopu

Graphene and graphitic derivative filled polymer composites as potential sensors

Graphite and numerous graphitic-derived micro- and nano-particles have gained importance in current materials science research. These two-dimensional sheets of sp(2)-hybridized carbon atoms remarkably influence the properties of polymers. Graphene mono-layers, graphene oxides, graphite oxides, exfoliated graphite, and other related materials are derived from a parental graphite structure. In this review, we focus primarily on the role of these fillers in regulating the electrical and sensing properties of polymer composites. It has been demonstrated that the addition of an optimized mixture of graphene and or its derivatives to various polymers produces a record-high enhancement of the electrical conductivity and achieved semiconducting characteristics at small filler loading, making it suitable for sensor manufacture. Promising sensing characteristics are observed in graphite-derived composite films compared with those of micro-sized composites and the properties are explained mainly based on the filler volume fraction, nature and rate of dispersion and the filler polymer interactions at the interface. In short, this critical review aims to provide a thorough understanding of the recent advances in the area of graphitic-based polymer composites in advanced electronics. Future perspectives in this rapidly developing field are also discussed

Eco-Friendly Synthesis of Graphene Oxide Reinforced Hydroxypropyl Methylcellulose/Polyvinyl Alcohol Blend Nanocomposites Filled with Zinc Oxide Nanoparticles for High-k Capacitor Applications

Polymer/inorganic nanocomposites comprising of hydroxypropyl methylcellulose and polyvinyl alcohol as a polymer matrix and unique combination of graphene oxide and zinc oxide nanoparticles as fillers have been prepared using colloidal processing technique and characterized using various analytical methods. The dielectric properties of the nanocomposites are investigated using impedance analyzer. The nanocomposites show improvement in the dielectric properties compared to hydroxypropyl methylcellulose/polyvinyl alcohol (50/50) blends, which results from the homogeneous dispersion of fillers into the polymer matrix. The results indicate that these nanocomposites have a potential to meet the technological demands of high-k dielectrics and/or embedded capacitors.Scopu