Research

Sustained Release Agricultural Nanomaterials

As our society develops in size and quantity, the demand on resources increase in both intensity and density. In line with these, the world’s population grows higher each day and the agricultural spaces gets smaller each year. The world’s population is estimated to reach 9.3 billion by 2050. At this year, overall global food consumption is expected to double. In order to produce more food to feed a growing population with a smaller agricultural space, scientists need to find and adopt more efficient and sustainable production methods. At this context, pesticides are currently irreplaceable components of industrial agriculture despite their toxic hazards. Pesticides are chemical compounds that are used to control pests & insects in agricultural practices. Among them, insecticides are the most widely used products. Although there are natural alternatives to chemical insecticide agents, yet the natural products are far less effective than the conventionally used insecticides. Therefore, chemical insecticides are still a must in agricultural practices. The major problem with pesticide use is its excessive and indiscriminate use. According to a recent report, only 0.1% of the pesticides used in conventional agriculture reach the target species. The rest either accumulates on crop products, or contaminates the soil causing fertility loss in soil. Moreover, storage issues of pesticides also pose additional economical burdens. The trade-off in pesticide use is that, if no pesticide is used, agricultural production drops by 70%, if excessive pesticide is used, we lose fertile land and healthy production.

To overcome the major risks related with insecticide use, we have developed a sustained release insecticide product, where the active ingredient is loaded into naturally occurring nanotubes and extruded into polymeric films. Once encapsulated with nanotubes, active agent containing films slowly release the active ingredient. This way, excessive use of insecticides is prevented and cost issues related with indiscriminate use is solved. In addition, there will be no fertility loss in soil and healthy products are obtained, within the scope of sustainable agriculture.

Publications: S. Avaz Seven, OF Tastan, CE Tas, H Unal, IA Ince, YZ Menceloglu, Insecticide-Releasing LLDPE Films as Greenhouse Cover Materials, Materials Today Communications, 2019, In Press, Accepted Manuscript

Patent: YZ. Menceloglu, S. Avaz Seven, Kontrollü Salim Sağlayan Pestisit Yüklü Sera Örtüsü, Türk Patent Enstitüsü, 10-18774-A (Pending)

Awards: Deeptech Startup Competition Energy and Environment Category Winner and the Grand Winner at Hello Tomorrow Turkey, December 11, 2018. 

Super Absorbent Polymers

Super absorbent polymer (SAP) materials can absorb water 400-800 times of their weight by means of their highly hydrophilic network. Their absorbing and retaining features in water or aqueous solution offer industrial opportunities such as diapers performance improvement or agricultural applications. However, there are some problems related to SAPs with the current technology of diapers production. The thickness of disposal diapers is the main problem for the environment and consumers because of their restricted recyclable and inflexible structures. The reasons for that thickness are the limits of increasing the SAP/pulp ratio and absorption capacities of SAPs. In addition to that the rigid powder polymer structure of SAPs causes dusting and also makes it difficult to obtain uniform distribution of SAPs on the pulp surface. This project includes the synthesis of a super absorbent polymer and enhancing the swelling behavior of SAPs in different forms using different strategies. First, the absorption capacity of SAPs will be improved by tuning crosslinking degree. Second, interpenetrating polymer network is planned to enhance mechanical properties of SAPs. Third, preparing two different forms of SAPs; gel and gel coated on nonwoven surfaces to enhance the swelling behavior. SAPs prepared by different approaches will be tested in terms of their swelling and release behavior. The project offers thinner diapers with higher absorption capacities and make more eco-friendly and comfortable diapers.

Superhydrophobic Surfaces

The Lotus Effect: Thanks to nature... Inspired by the ever clean, highly water repellent surfaces of Lotus (Nelumbo Nucifera) leaves, our team has been working on producing similar, superhydrophobic surfaces via electrospinning/spraying. Such biological or synthetic surfaces are unique with their microscopically rough topographies comprising micron, sub-micron and nanometer scale features, which allow very limited contact area at the liduid-solid interface when combined with non-polar outermost surface chemistry. Corresponding outcomes are remarkably high advancing water contact angles varying generally between 150 and 180°, and relatively low threshold water sliding angles as low as 0°, or pinned droplets (despite the high advancing contact angles) depending on the geometry of the surface topography. For achieving the desired final properties, both the chemistry and the topography of the surface must be engineered, as our team has been realizing via co-polymer synthesis and electrospinning/spraying, respectively.

Our approach to copolymer design is straightforward; the monomer that will dominate the polymer backbone is selected according to the desired bulk properties of the final coating, and polymerized with a relatively low amount of a non-polar component (e.g. a fluorinated monomer or a crosslinker) which will dominate the outermost surface for minimizing the surface free energy. The coating is then formed from the copolymer via electrospinning/spraying. One example is solvent resistive superhydrophobic surfaces of copolymers having reactive groups such as isocyanate or epoxy, which can be crosslinked during or after electrospinning/spraying. Another example is perfectly hydrophobic surfaces, having practically no interaction with water (180° contact angles and 0° threshold sliding angles) achieved via a combination of self-assembly and particular electrospraying process control to form a dual scale roughness profile. We also perform theoretical investigation of the formation of topographical features. More than a decade of applied research has provided our group a solid capability to tune the wettability profile of a polymer surface using electrospinning/spraying.

K Acatay, E Simsek, C Ow‐Yang, YZ Menceloglu. Tunable, superhydrophobically stable polymeric surfaces by electrospinning. Angewandte Chemie International Edition, 2004, 43, 5210-5213.

E Simsek, K Acatay, YZ Menceloglu. Dual scale roughness driven perfectly hydrophobic surfaces prepared by electrospraying a polymer in good solvent–poor solvent systems. Langmuir, 2012, 28, 14192-14201.

E Ozden-Yenigun, E Simsek, YZ Menceloglu, C Atilgan. Molecular basis for solvent dependent morphologies observed on electrosprayed surfaces. Physical Chemistry Chemical Physics, 2013, 15, 17862-17872.

Green composite materials

Critical environmental and economical issues have been stimulating research in the mass production of sustainable materials for plastics market that favors low costs and high production rates for decades. Along with new industrial regulations and growing technological needs, green composite materials have attracted particular interest as promising alternatives to petrochemical based plastics and their composites. Using modular design approaches and processing techniques, we are interested in the production of high-performance green composites along with the recycling of natural and/or synthetic thermoset wastes to create new horizons for the mass production of sustainable materials towards solving the world-wide waste disposal problem. In this regard, our research mainly focuses on the production of Poly(lactic acid) (PLA) based composites with enhanced mechanical properties like stiffness, strength and impact resistance.

O Oguz, K Bilge, E Simsek, MK Citak, AA Wis, G Ozkoc, YZ Menceloglu, High-performance green composites of poly (lactic acid) and waste cellulose fibers prepared by high-shear thermokinetic mixing, Industrial & Engineering Chemistry Research 2017, 56 (30), 8568-8579

Polyurethane Based Nanocomposites

Thermoplastic polyurethanes, polyurethane-ureas, polyureas (TPUs) constitute one of the most important and versatile classes of thermoplastic elastomers. TPUs are segmented copolymers containing alternating hard and soft segments along a linear macromolecular backbone. Segmented TPUs generally display two-phase morphology, where hard segments act as reinforcing fillers in a continuous soft matrix. The soft segments in TPUs originate from hydroxyl or amine terminated oligomers with glass transition temperatures (Tg) well below room temperature, such as aliphatic polyethers and aliphatic polyesters, whereas the hard segments consist of diisocyanate and a chain extender such as a low molecular weight diol or diamine. Availability of a very large selection of hard and soft segment constituents and different synthetic techniques provide opportunities for the preparation of a wide range of TPU backbone structures. Each of the soft and hard segments provides different physical and chemical properties to the TPUs prepared from them. In general, two different approaches can be used to enhance the mechanical and thermal properties of TPUs; (I) alternating the molecular structure of polyurethane, (II) introducing inorganic filler to the polymer matrix. Our research mainly focuses on the investigation of critical design principles for the production of high performance TPUs in a close collaboration with Koc University. Along with this, we are particularly interested in the production of advanced functional nanocomposites consisting of TPU matrices and various inorganic fillers like silica nanoparticles. More specifically, the understanding of several interesting and challenging phenomena including glass transition, segmental dynamics, crystallization, micro-phase separation and polymer-filler interaction in such materials is of essential interest to our group.

N Sarier, R Arat, Y Menceloglu, E Onder, EC Boz, O Oguz, Production of PEG grafted PAN copolymers and their electrospun nanowebs as novel thermal energy storage materials, Thermochimica Acta, 2016, 643, 83-93

O Oguz, E Simsek, C Kosak Soz, O Kasli Heinz, E Yilgor, I Yilgor, YZ Menceloglu, Effect of filler content on the structure‐property behavior of poly (ethylene oxide) based polyurethaneurea‐silica nanocomposites, Polymer Engineering & Science, 2018, 58 (7), 1097-1107

O Oguz, SA Koutsoumpis, E Simsek, E Yilgor, I Yilgor, P Pissis, YZ Menceloglu, Effect of soft segment molecular weight on the glass transition, crystallinity, molecular mobility and segmental dynamics of poly(ethylene oxide) based poly(urethane–urea) copolymers, RSC Advances, 2017, 7 (65), 40745-40754

S Koutsoumpis, KN Raftopoulos, O Oguz, CM Papadakis, YZ Menceloglu, P Pissis, Dynamic glass transition of the rigid amorphous fraction in polyurethane-urea/SiO 2 nanocomposites, Soft matter, 2017, 13 (26), 4580-4590.

O Malay, O Oguz, C Kosak, E Yilgor, I Yilgor, YZ Menceloglu, Polyurethaneurea–silica nanocomposites: preparation and investigation of the structure–property behavior,  Polymer, 2013, 54, 20, 5310-5320.

E Yilgor, T Eynur, C Kosak, S Bilgin, I Yilgor, O Malay, Y Menceloglu, GL Wilkes, Fumed silica filled poly (dimethylsiloxane-urea) segmented copolymers: preparation and properties, Polymer, 2011, 52 (19), 4189-4198.

Z Hosgor, N Kayaman-Apohan, S Karatas, Y Menceloglu, A Gungor, Preparation and characterization of phosphine oxide based polyurethane/silica nanocomposite via non-isocyanate route, Progress in Organic Coatings, 2010, 69, 4, 366-375.

O Turunc, N Kayaman-Apohan, MV Kahraman, Y Menceloglu, A Gungor, Nonisocyanate based polyurethane/silica nanocomposites and their coating performance,  J Sol-Gel Sci Technol 2008 47: 290.

Phase Change Materials

Solid-solid phase change materials (SSPCMs) are crystalline solids that undergo phase changes from one lattice configuration to another by absorbing and releasing great amount of latent heat at well-defined temperatures below their melting points. The SSPCMs originate their remarkable performance from their configuration and the physical bonding that occurs between neighboring molecules in the crystalline solid. At low temperatures, the intermolecular physical attractions restrict molecular movement. At the phase transition temperature, a SSPCM absorbs an amount of energy and the physical bonds break, allowing the molecules to rotate and vibrate more freely in their lattice sites. When the material is cooled, the intermolecular physical bonds rebuild and the same amount of heat is released. The magnitude of physical attractions mainly affects the amount of energy absorbed and released throughout the solid-solid phase transition. By combining molecules of different structure in the same crystalline solid, the strength of physical bonding can be altered, thus phase transition temperature interval and heat storage capacity of a SSPCM can be modified. From this perspective, we are particularly interested in the production of novel phase change materials using polymer chemistry and modular processing approaches. Most recently, we developed thermo-regulating nano-webs composed of hollow nanofibres of PEG-g-PAN copolymers by means of coaxial electro-spinning for transforming the synthesized copolymers into the assemblies appropriate for numerous industrial areas such as textiles, packaging, solar energy systems, building envelopes and biomedical materials in a close collaboration with Istanbul Kultur University and Istanbul Technical University.

N Sarier, R Arat, Y Menceloglu, E Onder, EC Boz, O Oguz, Production of PEG grafted PAN copolymers and their electrospun nanowebs as novel thermal energy storage materials, Thermochimica Acta, 2016, 643, 83-93

Rheology of Cement

We develop superplasticizers for ordinary Portland cement (OPC) and calcium aluminate cement (CAC). Poly(carboxylate ether)-based superplasticizers (PCEs) are used to modify the viscosity, slump flow, and slump retention of cement mixtures.

From the first touch of water, CAC loses its flowability in less than 1 hour and commercially available superplasticizers are developed to cater the needs of OPC-based systems. The superplasticizer that we have developed for CAC is the first of its kind to address higher charge, surface development, and fast kinetics of this specialty cement (EP 3056476 A1, https://www.google.com/patents/EP3056476A1?cl=en). The pictures demonstrate the performance of superplasticizers—CAC system, top: with an incompatible superplasticizer, below: with the superplasticizer that we designed (SU-PCE). An addition of 0.4 wt% SU-PCE was enough to preserve the flowability of CAC in longer periods.

Stimuli Responsive Polymeric Materials

Shape memory applications are required to have the stimuli responsive materials with a few key structural and dynamic features that comprise reversible bonds and particular chain conformations under various conditions. Basically after a deflection from an equilibrium state at macroscopic level, such as mechanical deformation, the temporary state must be maintained through the recovery is triggered by an external stimuli in order to reach the original state. In shape memory applications, one of the main challenges is to develop advanced functional materials that are able to be accelerated by multiple stimuli. In the regard, we are particularly interested in the development of stimuli-responsive polymeric materials with tunable properties for shape memory applications. Our research mainly focuses on the production of heat and water activated shape memory polymers and their nanocomposites.

Electrospun Polymer /MWCNTs Nanofibers Reinforced and Toughened Composites

• Elif Ozden

The focus of this study is to investigate mechanical properties of multi-walled carbon nanotube (MWCNT) reinforced electrospun nanofibers in composites. Neat and MWCNT reinforced composite nanofibers of poly(styrene-co-glycidyl methacrylate) are produced by electrospinning. The process optimization for composite electrospun fibers is also investigated. An emprical relationship between polymer and MWCNT concentration and average fiber diameter is sought by response surface methodology (RSM). The nanofibers, are then embedded into epoxy matrix to form polymer composites. The experimental procedure was designed so as to observe the effects of GMA composition in structure and the effect of additional crosslinker agent by spraying method. The effect of neat and MWCNT reinforced nanofibers in the composites is reported in comparison to neat epoxy.

Application of Epoxy Based Carbon Nanotube Nano-Composites in Health Structural Monitoring Systems

• Shalima Shawuti

Carbon nanotubes (CNT) have been intensively investigated due to their mechanical, chemical, and electrical properties.1 CNTs are known as effective fillers in polymeric matrices which introduce strong materials at low loadings2,3 because of their excellent mechanical properties in combination with very high aspect ratio (as high as 1000 for multi walled carbon nanotubes (MWCNT)), which enables percolation of the filler at low MWCNT loading. It is also promising to use CNTs as additives in polymer blends for electrically conductive applications.3 The potential of CNTs for application as reinforcements, however, highly depends on the ability to disperse the nanotubes homogenously throughout the matrix and on the transfer of the mechanical load from the matrix to nanotube. Our current research includes improving dispersion of MWCNTs in epoxy-polymer matrix system by various methods. Synthesis of MWCNT/Epoxy composite films are synthesized via various processing methods, such as resin transfer mold and conventional open mold. Characterization of mechanical, electrical and thermal properties as well as solvent resistance are performed. REFERENCES 1. Xiong et al. Carbon 2006, 44, 2701. 2. Lu et al. Carbon 2007, 45, 2621 3. Cooper et al. Composites Sci. and Tech. 2002, 62, 1105

Development of Novel Materials for Proton Exchange Membrane Fuel Cells

• Burak Birkan, Cenk Gumeci

Fuel cells are electrochemical devices that convert the chemical energy of a reaction directly into electrical energy. Among them, proton exchange membrane fuel cells (PEMFC) deliver the highest power density, while offering low weight, cost, and volume. For these reasons, PEMFC’s are broadly applicable as an environmentally friendly energy source, but their larger-scale commercial use is limited due to poor ionic conductivities at low humidity and/or elevated temperatures, a susceptibility to chemical degradation at elevated temperatures, and finally, membrane cost. In response to all these factors, low cost, high proton-conducting, as well as mechanically and thermally stable PEM’s were produced by using the ATRP (Atom Transfer Radical Polymerization) technique in supercritical carbon dioxide (Sc-CO2) as the polymerization method for the synthesis of polymers with fluorinated backbones and ionic pendant groups on the side chain. Secondly, one of the most important components of PEMFC’s is the electrode, which typically consists of a Pt catalyst, either Pt black or Pt on a carbon support. The catalytic behavior of a precious metal is determined mainly by its distribution, the metal oxidation state, and sensitivity to the fuel quality. A unique process was developed, which involves producing nano-sized metal-supporting carbonfibers that could be used as the catalyst on electrodes at PEMFCs, thus increasing the catalytic material concentration by up to 0.2 mg catalytic material/cm2 area of the carbon fiber structure.

Production and Processing of Transparent Biodegradable Nanocomposites

• Funda Inceoglu

The environmental pollution from consumed plastics becomes very serious due to the increasing usage of the synthetic plastics, especially ones used in the packaging materials. With tighter environmental regulations and increasing waste disposal costs, plastic manufacturers are forced to seek new alternatives. One of the challenging ideas in this aspect is to increase the production and usage of biodegradable polymers (like starch, cellulose, lignin, poly(lactic acid), polyhydroxyalkanotes , etc.) with the goal of replacing non-biodegradable plastics, at least partially. However, biodegradable plastics cannot compete with conventional petroleum-based plastics because they alone are usually brittle and sensitive to water. Therefore, it must be combined with other materials, like synthetic polymers, to produce satisfactory plastic. The important question here is that "what is happening to the degradation rate of synthetic polymers in the environment after addition of natural biopolymer?" Recent studies have shown that when natural biopolymer is included in the synthetic one, the degradation rate of the synthetic polymer is also increasing. It was suggested that microbes first create pores on consumption of the biopolymer and increase the surface area of the composite. Increased surface area enhances oxygen-based reactions, which could increase synthetic polymer chain oxidation and susceptibility to biotic reactions . The main problem, however, in using natural polymer with synthetic polymer is the reduction of the mechanical and optical properties of the latter one with the addition of natural polymer. In our project, we are not only trying to prevent this drawback but also further enhance the mechanical strength of the composite material by the help of nano-science.

We use reactive twin screw extruder in order to modify polyolefins to provide compatibility between synthetic and natural polymers and to prepare biodegradable nanocomposite formulations.

Side Chain Liquid Crystalline Polycarbonate with a Chiral Backbone

• Yesim Muge Calik Sahin

The experimental demonstration of a novel and environmentally benign supercritical carbon dioxide(ScCO2) technique that sheds light on the design of an optically active side chain liquid crystalline poly(ether-carbonate) in a single-step reaction. Opticallyactive side chain liquid crystal polymers have attracted much attention due to the wide range of their potential applications, in particular in the fields of optics and electro optics. By a purposeful design of a chiral monomer and an understanding of the copolymerization mechanism in ScCO2 media simultaneously, we easily obtain highly stereoregular (isotactic), optically active polymers. The obtained copolymers exhibit another practical benefit by widening the mesomorphic temperature range compared to its acrylic analogues. This can be a good basis in the material design for preparing the practical materials suitable for device applications. Consequently, this work is important to the materials chemistry and to the synthesis community; it is the insightful combination of material processing and chemical design that not only enables the production of a valuable material, but also elucidates the advantages of ScCO2 application in terms of liquid crystallinity and the tacticity of the obtained polymer.

Intumescent Flame Retardant Synthesis for Coating Applications

• B. Kerem Goren, Funda Inceoglu

Apart from a few exceptions, most polymer materials are combustible. It is therefore necessary to modify these polymer materials to make them fire-retardant for many applications such as the construction, furniture, vehicle, or electronics industries. To satisfy regulations and standardized tests, organohalogen or organophosphorus compounds are added in large quantities as flameproofing agents to plastics. However, while organohalogen compounds themselves are non-toxic, they can release corrosive pyrolytic components that are a health hazard in the event of fire. Consequently, we are seeking safer alternative flame retardants by using materials such as metallic hydroxides. Unfortunately, their low activity requires usage in high concentrations, which negatively impacts the mechanical properties of the matrix into which they are incorporated. Flame retardants based on intumescency are preferred because of their moderate minimum effective concentration, which does not have a negative impact on the mechanical properties of the polymer matrix, in contrast to metal hydroxides. An intumescent system is active in the condensed phase and does not release corrosive and toxic gases while still maintaining flame retardancy. Moreover, intumescent systems evolve less corrosive gases, since nitrogen’s higher decomposition temperature is the main reason favoring their use in the cable jacketing industry. The main ingredients for an intumescent additive include an acid source, a carbon source, and a blowing agent. The solution employed here was the incorporation of a phosphorus- and nitrogen-containing intumescent additive into the polyethylene resins homogeneously, and the flame resistance of the resulting resin was demonstrated to meet the stand testing methods, the Limiting Oxygen Index (LOI) and the UL-94.

In-vitro and in-vivo Degradation of Non-woven Materials Prepared by Electrospinning

• Collaborative research with Dr. Piskin group of Hacettepe University, Ankara, Turkey

The aim of this study is to prepare non-woven materials from a biodegradable polymer, poly(ε-caprolactone) (PCL) by electrospinning. PCL was synthesized by ring-openning polymerization of ε-caprolactone in bulk using stannous octoate as the catalyst under nitrogen atmosphere. PCL was then processed into non-woven matrices composed of nanofibers by electrospinning of the polymer from its solution using a high voltage power supply. The effects of PCL concentration, composition of the solvent (a mixture of chloroform and DMF with different DMF content), applied voltage, and tipcollector distance on fiber diameter and morphology were investigated. The diameter of fibers increased with the increase in the polymer concentration and decrease in the DMF content significantly. Applied volatage and tip-collector distance were found critical to control “bead” formation. Elongation at break, ultimate strength and Young modulus were obtained from the mechanical tests, which were all increased by increasing fiber diameter. The fiber diameter influenced both in vitro degradation (performed in Ringer solutions) and in vivo biodegradation (conducted in rats) rates significantly. In vivo degradation was found to be faster than in vitro. Electrospun membranes were more hydrophobic than PCL solvent-casted ones, therefore their degradations were much slower.