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
