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.
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. //dx.doi.org/10.1016/j.polymer.2013.07.043
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.
//dx.doi.org/10.1016/j.polymer.2011.07.041
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.
//dx.doi.org/10.1016/j.porgcoat.2010.07.010
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.
Advanced composites have become indispensible resource in variety of fields including energy. They, for instance, have direct impact in the sector as the efficiency and performance of wind turbine based clean energy technology can be elevated by their optimal use. Nevertheless, advanced composites enable lighter structures for energy efficient vehicles of transportation without sacrificing the safety. Their undeniable potential calls engineers and scientists to push the boundaries of broad composites research and development for making them even more competitive and promising for stringent energy needs of the society. That is, we are urged to “think outside the box” practices with advancing manufacturing and characterization techniques and software specialized on composites as opposed to tradi-tional lay-ups, materials and production. In the context of multi-scale engineering of composites, a couple of THINKCOMPOSITE concepts that can be implemented in the design of wind turbine blades and structures of vehicles is explored.
Nano-Enhanced/Augmented Structural Compo-Sites
Figure: Enhanced mechanical properties by nanofibrous interlayers
The concept realized by nanofibrous inter-layers may find extensive use in nearly all light-weight structural applications, where advanced composites are necessary, such as in aerospace, automotive and energy. They can be easily incorporated into existing manufacturing processes and provide substantially enhanced properties, while the weight and thickness increase associated with interleaving is nearly negligible. Additionally, with the possibilities for combining the right selection of particles/fillers, the toughening performance can be further enhanced for both in- and out-of-plane loading conditions. Moreover, their full potential is even higher with multi-functional possibilities, such as tuning of mechanical, thermal and electrical properties by the right choices of nanofiber and filler combinations and proportions. With a complete understanding of impact on properties by using the nanofibrous interlayers, the opportunities are plentiful for developing characterization and scaled-up production capabilities and integration of the nanofibrous materials into conventional composite engineering design frameworks.
Design of and with Non-Crimp Fabric (NCF) as Building Blocks for Composites
Figure: Comparison of Tsai-Wu failure surfaces for laminates of traditional (0/45/90/-45) versus shallow angle (0/±25/0) and (0/25) stacks.
New generation non-crimp fabric (NCF) offers an attractively thin and lightweight building block alternative in the design of composite materials and structures. Pre-assembly of multiple plies of parallel fibers, each laying in a different orientation would not require crimping of the fibers and would enable a one-axis lay-up that can substantially reduce the labor, scrap and manufacturing costs. A state-of-the-art tow-spreading technique enables ply thickness to be reduced to as low as one-third of the typical commercial high quality pre-preg ply thickness. Bi-angle thin-ply NCF offers two different fiber orientations (with one being off-axis) and designing in anisotropic properties within the conventional one-axis ply thickness. In our quest for simultaneous weight and cost reduction at maximum performance of composite structures, the thin-ply bi-angle NCF building block incorporates the simultaneous design of anisotropic properties and structure, as opposed to more traditional composite designs, which typically imitate metals or materials with isotropic behavior.
Silicone-Based, Synthetic Tissue And Organ Models For Surgical Simulation
Lack of cadavers and fresh tissue/organ models hinders the quality of medical education; therefore, there is a need for a reliable and sustainable training medium for evergrowing number of medical students and personnel. In Akbulut research group, we design silicone-based surgical models that are engineered to simulate mechanical responses of real organs to incision, dissection, and suturing. Until now, we have developed skin, breast, and vascular models. Different suturing techniques, benign mass removal, and complicated oncoplastic surgery can be practiced on these models. We aim to improve the quality of surgical trainings via practical, affordable, and tactile simulation platform. This research resulted in a spinoff company, Surgitate, which now sells these models in several countries.
Figure: Enhanced mechanical properties by nanofibrous interlayers
Figure: Comparison of Tsai-Wu failure surfaces for laminates of traditional (0/45/90/-45) versus shallow angle (0/±25/0) and (0/25) stacks.
