LEE- Malzeme Bilimi ve Mühendisliği-Yüksek Lisans

Bu koleksiyon için kalıcı URI

http://hdl.handle.net/11527/19376

Gözat

Yazar "Cebeci, Hülya" ile LEE- Malzeme Bilimi ve Mühendisliği-Yüksek Lisans'a göz atma
  • Öge
    Evaluation of thermal, rheological, and dynamic mechanical properties of CNT reinforced PEI and PEEK composites
    (Graduate School, 2022) Kaygınok, Fulden ; Cebeci, Hülya ; 729354 ; Department of Materials Science and Engineering
    In this study, the effect of multiwall carbon nanotube (CNT) reinforcement on viscoelastic properties of polyetherimide (PEI) and polyether ether ketone (PEEK) polymers was investigated by oscillator rheology and dynamic mechanical analysis (DMA) method. CNT reinforced PEI and PEEK composites were produced using a specially designed twin-screw extruder at 1, 3, and 5 wt.% at 210 rpm and 360 °C and 380 °C for CNT/PEI and CNT/PEEK composites, respectively. Thermogravimetric (TGA) and differential scanning calorimetry (DSC) analyzes were performed to examine the thermal properties of the samples. It was observed that the decomposition temperatures in PEI samples showed two-stage decomposition depending on the aromatic group and non-aromatic group decomposition at approximately 529 °C and 564 °C, and their thermal stability was found as about up to 400 °C, whereas in PEEK samples, decomposition occurred in a single step due to ether and ketone groups and their thermal stability was found as about up to 550 °C. Also, a residual weight of around 50% in PEI and PEEK samples was at 800 °C. It was seen that CNT did not significantly affect the thermal stability of polymers. In addition, CNT almost did not change the glass transition temperature of polymers (Tg), but it increased the crystal ratio by acting as the nucleation factor for PEEK composites, and the highest crystal ratio was obtained from 1 wt.% CNT/PEEK composite as 29%. The morphological analysis revealed that CNT reinforced PEI and PEEK composites were fabricated homogeneously without any agglomerations. Rheology analysis showed that the linear viscoelastic region (LVR) narrowed with CNT, that is, the critical strain decreased, which was explained as evidence of the formation of a brittle solid network in the structure. Also, the critical strain has an exponential dependence on the volume fraction of the CNT as -1.76 and -1.40 for PEI and PEEK, respectively. On the other hand, the frequency-dependent results in LVR showed that the storage modulus of both polymers increased and the frequency dependence decreased with the increase in the amount of CNT. The frequency dependence of the storage modulus was exponentially 0.7 and 1.57 for neat PEI and PEEK, and these values were calculated as 0.32 and 0.27 at 1 wt.% CNT reinforcement, respectively. The decrease of frequency dependency and sudden increase in 1 wt.% CNT reinforcement was interpreted as an indication of the structure change, and the rheological percolation threshold was determined below 1 wt.% CNT reinforcement was also proved by drawing Cole-Cole plots that are a clear representation for the transition from the liquid-like to the solid-like structure. Additionally, the complex viscosity increased with CNT in both polymers and they changed the behavior from Newtonian to shear-thinning in the low-frequency region and shear-thinning behavior became dominant with 1 wt.% CNT reinforcement.