The effect of silica polymorphs on the thermomechanical properties of 0, 5, 10, and 20 wt % silica particles-reinforced-based poly(ethylene glycol) (PEG) composites have been studied as a function of temperature using dynamic mechanical analysis (DMA). The silica polymorphs exhibited quartz (Q), cristobalite (C), and amorphous (A) phases, which were obtained by processing natural silica sand. The DMA thermomechanical properties were determined in tensile (E) and shear (G) modes. The maximum storage moduli (E 0 and G 0 ) were achieved by samples with 20 wt % silica for all type of fillers. These values increased approximately 12 times for PEG/Q, 10 times for PEG/A, and 11 times for PEG/C composites compared to the pure PEG. Furthermore, the Poisson's ratio values of the composites were filler phase dependent, that is, 0.39-0.47 for PEG/Q, 0.15-0.18 for PEG/A, and somewhat anomalous for PEG/C composites.
Abstract. Degradation activation energy of PEG-Cristobalite composites was investigated using Dynamic Mechanical Analysis (DMA) instrument at multi-frequency shear mode. The applied frequencies were 1, 10, 100, and 200 Hz. The cristobalite of as much as 20% and 40% by weight was used as the filler of the composites, while PEG 4000 was the matrix. Results showed that additional of cristobalite improved the storage modulus (G') of the composites almost five times of the pure PEG 4000. Moreover, such addition and higher applied frequency shifted glass transition temperature (T g ) to higher values. Furthermore, the multi-frequency measurement provided the degradation activation energy of the samples, where the highest value was reached by the 40% sample, i.e. 571.4 kJ. This result implied that there was a certain energetic barrier from the filler that the structural units of polymer need to surmount collectively before its viscous flow occured. IntroductionResearch focus in modern polymeric materials includes thermal stability as well as physical and mechanical properties at high temperature. The thermal stability of polymers is connected not only with the initial degradation temperature (T g ) [1], but also, with dislocations due to mechanic and thermal treatment [2]. In particular, the apparent activation energy (E a ) is of great importance aspect of degradation of such materials [3].DMA technique is useful in characterizing polymer degradation as a function of frequency, temperature, time, stress or a combination of these parameters [4][5][6]. The dynamic mechanical responses of degradation are usually observed at temperatures near (or, in some cases, above) the melting point. As a result, the lifetime predictions based on these measurements can be determined. DMA response also depends on the physical or structural arrangement of phases such as interface, morphology and the nature of the constituents [4,5]. In particular, the effect of filler, fibre content, fibre orientation in fibre-reinforced composite materials has been extensively studied [7,8].Cristobalite is a metastable silica polymorph. It exists at room temperature but easily transformed into quartz at high temperature. There is no study on the utilization of cristobalite as a filler in a composite system. This phase is very unique since it exhibits a negative Poisson's ratio [9][10][11][12]. Materials with a negative Poisson's ratio (called auxetic material) have a counterintuitive behaviour of becoming wider when stretched and thinner when compressed [12]. This behaviour has many beneficial effects on the materials' macroscopic properties (e.g., increased indentation resistance, a
Crystallinity is an important parameter of thermoplastic polymers. Furthermore, crystallinity is closely related to processing conditions such as temperature and applied shear stress. However, determining the degree of crystallinity is very complicated because of the different interpretations of crystallinity according to each technique. In this paper, we analyze the crystallinity of polyethylene glycol-based composites using two instruments, i.e., X-Ray Diffraction (XRD) and wide-angle X-Ray Scattering (WAXS). The results showed that with the addition of 60 wt.% silica, the degree of crystallinity revealed by XRD was 81.24%, while WAXS showed a degree of crystallinity of 80.93%. In general, the crystallinity results obtained with WAXS were almost identical, only 0.31% different from the XRD results. This difference in results was due to more presence as a consequence of the broad amorphous halo and background instrumentation exhibited by the higher background from XRD. Thus, the instrument effect must first be removed from the XRD data and it is possible that the amorphous region of the sample will also be reduced and result in a slightly higher crystallinity. At the same time WAXS with the transmission technique will minimize the possibility of background instrumentation. Therefore, WAXS was recommended to analyze the crystallinity of polymer-based and amorphous materials.
Penelitian ini bertujuan untuk mengetahui pengaruh kristalinitas terhadap stabilitas termal komposit termoplastis dengan pengisi silika xerogel. Polimer yang digunakan adalah polietilena glikol (PEG 4000) yang merupakan polimer termoplastis. Silika xerogel diekstraksi melalui proses alkali fusion. Silika xerogel yang didapatkan menunjukkan fasa amorf melalui X-Ray Diffraction (XRD). Silika xerogel ditambahakan ke dalam PEG 4000 dengan komposisi yang bervariasi, yaitu, 0, 5, 10, dan 20%. Penambahan silika xerogel menurunkan tingkat kristalinitas komposit karena PEG murni merupakan material semikristalin. Melalui analisis termal menggunakan Thermogravimetric Analysis (TGA), pengaruh kristalinitas komposit tampak jelas pada daerah sebelum polimer mengalami transisi leleh. Namun, pada daerah dekomposisi (T>400C), pengaruh kristalinitas pada komposit tidak ada lagi. Hasil ini sangat menarik dikarenakan massa dekomposisi akhir menunjukkan nilai yang sama dengan komposisi silika xerogel yang ditambahkan, misalnya pada penambahan 20%, massa yang tersisa setelah dekomposisi adalah 20,77982 %. Oleh karenanya, analisis kristalinitas sangat mendukung hasil analisis termal dengan TGA pada komposit. Kata kunci:deformasi kristalografi TGA silika xerogel
Research about influence effect of activated activated carbon from oil palm empty fruit bunch to solar cell efficiency p-n junction layer Cu2O-TiO2 and direct of sunlight. The layer of Cu2O formed from copper (Cu) burned with temperature 550 ͦ C in 100 minutes. The solar cells are made with TiO2 layer composed of activated carbon from oil palm empty fruit bunch of 0%, 10%, 15%, dan 20%. The parameters of the solar cell can be obtained by measuring the short circuit (Isc), voltage open circuit (Voc), maximum power and Fill Factor (FF) with resitor value (R) 0-50 kΩ. The composed of TiO2 /activated carbon from oil palm empty fruit bunch analyzed using X-Ray Diffraction (XRD) and and Fourier Transform Infrared (FTIR) Spectrocopy. As a result addition of activated carbon from oil palm empty fruit bunch to solar cell efficiency is increase in the value, voltage and efficiency of solar cells. The results of the measurement of the highest efficiency of solar cells using a sun simulator and sunlight are found in variations of activated carbon 20%, with each efficiency values 0,043% and 0,0018%.
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