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    Design of Highly Thermally Conductive Hexagonal Boron Nitride- Reinforced PEEK Composites with Tailored Heat Conduction Through-Plane and Rheological Behaviors by a Scalable Extrusion
    (Amer Chemical Soc, 2023) Gul, Saher; Arican, Selin; Cansever, Murat; Beylergil, Bertan; Yildiz, Mehmet; Okan, Burcu Saner
    The challenge of developing highly thermally conductive polymeric composites to meet the growing thermal management demands has recently attracted a lot of attention. To achieve a through-plane thermal conductivity higher than 2 W/mK, a high filler concentration within the poly(ether ether ketone) (PEEK) matrix is required, thus adding to the complexity of polymer processing. In this study, an optimized twin-screw extrusion melt compounding technique was developed by tuning the melt flow of unfilled PEEK, feeding zones, and process cycles for dispersion of hexagonal boron nitride (h-BN) in the PEEK polymer. The prepared composites demonstrated exceptionally high in-plane and through plane thermal conductivity of 12.451 and 2.337 W/mK, respectively, at 60 wt % h-BN loading. This improvement of thermal conduction in both directions can be attributed to two factors: (1) formation of through-thickness surface contacts between h-BN particles due to shear-driven exfoliation during compounding stage and (2) high degree of alignment of h-BN platelets achieved during molding stage. The calorimetric and thermogravimetric analyses indicated that the prepared composites possess enhanced crystallinity compared to unfilled PEEK and are thermally stable in elevated temperature ranges. The rheological characterization exhibited a progressive increase in viscosity and shear-thinning behavior of composite melts proportional to the h-BN concentration. Using the temperature and time-dependent rheological results, viscosity buildup profiles were constructed to outline allowable melt viscosity ranges for each composite composition. These profiles can be utilized to tailor the residence time of a composite melt by varying the filler concentration and process temperature during advanced manufacturing processes such as extrusion-based additive manufacturing and powder bed fusion. Hence, we provide a facile and industrially scalable method for development of h-BNfilled PEEK composites with high thermal dissipation characteristics aimed for thermal management in various harsh environment applications.
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    Engineering interfacial thermal transport through comparative analysis of electrospraying and dip coating of silanized h-BN for thermo-mechanical enhancement of CF/Epoxy composites
    (Elsevier Sci Ltd, 2025) Mehdipour, Mostafa; Dogan, Semih; Tabrizi, Arvin Taghizadeh; Bafqi, Mohammad Sajad Sorayani; Beylergil, Bertan; Yildiz, Mehmet; Okan, Burcu Saner
    The inherently low thermal conductivity of carbon fiber (CF) reinforced epoxy composites is mainly due to porosity and fabrication defects that interrupt thermal pathways. This study demonstrated a pathway to control heat in both out-of-plane and in-plane directions by incorporating hexagonal boron nitride (h-BN) as a thermally conductive agent and by configuring interface interactions on the CF and within the epoxy resin while evaluating physical and chemical interactions. Two integration techniques of dip coating and electrospraying were employed to apply h-BN, effectively creating robust h-BN layers on CF and dispersing neat or silane-modified hBN within the epoxy matrix by combining vacuum bag and hot compression processes to reduce void content. Electrospraying silane-modified h-BN onto carbon fiber, together with incorporating 20 wt% silane-modified hBN into the matrix, resulting in a total loading of 11 wt% in the composite-led to the highest out-of-plane thermal conductivity of 1.3 W/mK, representing a 166 % increase compared to CF reinforced into epoxy composite (CF+/ EP) with the out-of-plane thermal conductivity of 0.49 W/mK. Mechanically, the configuration using neat h-BN in both the matrix and dip-coated CF achieved a 127 % increase in flexural modulus and a 49 % improvement in Charpy impact strength versus unfilled CF/epoxy composites. Resizing the CF improved directional thermal conductivity in CF/epoxy composites by controlling porosity, achieving approximately an 81 % reduction in porosity when using silanized h-BN.
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    Experimental validation and numerical modeling of interfacial effects in silanized hexagonal boron nitride (h-BN) reinforced epoxy composites by tailoring silane concentration
    (Taylor & Francis Ltd, 2025) Mehdipour, Mostafa; Beylergil, Bertan; Yildiz, Mehmet; Okan, Burcu Saner
    This study investigates the use of h-BN particles as fillers, focusing on tailoring surface chemistry to enhance the thermal conductivity of epoxy composites. By enriching the interface between h-BN particles with amino-silane groups and the epoxy matrix through controlled surface modification, thermal performance, and interfacial bonding were improved. To achieve a high degree of functionalization, h-BN particles were oxygenated to 13.6 atomic percent (at. %) through thermal treatment, followed by reduction using 3-amino-propyl-3-ethoxy-silane (APTES), which increased the amino content by 3.5% at. % under optimized reaction conditions. During composite manufacturing, 10 wt.% functionalized h-BN particles were reinforced into the epoxy matrix, increasing bulk thermal conductivity by 53%, from 0.2 W/mK to 0.34 W/mK. Heat flux simulations with ANSYS confirmed the interface interactions and thermal performance, with silanized h-BN achieving the highest heat flux of 70 W/mm2, aligning well with experimental results. While silanization improved thermal conductivity by strengthening interfacial bonding between h-BN and the epoxy matrix, it introduced brittleness, making the composites stiffer and more fragile. However, the silanized h-BN composite showed a 57.14% increase in toughness compared to neat h-BN, while the highest flexural modulus of 4126 MPa was achieved with neat h-BN.
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    Influence of functionalized h-BN particle interphase and interface regulation with structural design on the directional thermal conductivity and mechanical performance of carbon fiber/epoxy composites
    (Elsevier Sci Ltd, 2025) Mehdipour, Mostafa; Dogan, Semih; Al-Nadhari, Abdulrahman; Bafqi, Mohammad Sajad Sorayani; Beylergil, Bertan; Yildiz, Mehmet; Okan, Burcu Saner
    This study highlights the importance of interfacial adhesion between carbon fiber (CF) and the epoxy matrix by adopting a novel approach that combines untreated and silane-treated h-BN in a multilayered structure. The interface was engineered by electrospraying h-BN particles, while the interphase was modified by incorporating up to 20 % h-BN into the epoxy matrix. The highest out-of-plane thermal conductivity of 2.31 W/mK, a 116 % increase compared to the reference value of 1.07 W/mK, was achieved by sizing CF with silanized h-BN through electrospraying, in conjunction with the 20 % h-BN-loaded epoxy matrix. Conversely, the incorporation of h-BN in the epoxy alone resulted in the best mechanical performance, with approximately a 46.4 % increase in elastic modulus, a 105 % improvement in flexural modulus, and a nearly 5 % increase in Charpy impact strength. Based on CT scan results, the resizing of CF fabrics improved directional thermal conductivity in CF/epoxy composites with controlled porosity.