1 ICPMSE 2015 : 17th International Conference on Polymer Materials Science and Engineering Istanbul, Turkey, July 29-30, 2015 Authors : H.BABOU, R. FERHOUM, B. AMERATE and M. ABERKANE Laboratoire (LE2M), University Mouloud MAMMERI of Tizi-Ouzou, Algeria Thermal ageing effect on mechanical behavior of Polycarbonate

2 Resume this work is devoted to the experimental study of thermal ageing effect on the mechanical and microstructural behavior of polycarbonate (PC). A simple compression tests, micro-hardness and an IRTF analysis were completed in order to characterize the response of material on specimens after ageing at a temperature of order 100 C° and for serval maintain durations 72, 144 and 216 hours. These investigations showed a decrease of the intrinsic properties of polycarbonate (Young modulus, yield stress, etc.); the superposition of spectra IRTF shows that the intensity of chemical connections C=C, C-O, CH 3 and C-H are influenced by the duration of thermal ageing; in addition, an increase of 30% of micro-hardness was detected after 216 hour of ageing. Introduction The industrial polymeric materials, such as glassy polymer, are increasingly useful, this due to their low cost production, and to the mechanics, physics and thermics properties which are have these materials. Many researches has worked in this context to better understanding the evolution of properties of such as materials in serial extensive conditions such as temperature, UV irradiation, chemical attacks, mechanical stress, etc. In this paper, we focused on the characterization of the effects of thermal ageing on the mechanical behavior and microstructural of polycarbonate, our objective is to understand the mechanisms of thermal ageing on polycarbonate. Matériau et procédure expérimentale - the material of study is Polycarbonate Bisphénol A (PC), glassy polymer with a good stiffness and transparence, the properties of PC are resumed in the table below: Table 1: properties of Polycarbonate

3 - The thermal ageing of the polycarbonate specimens was completed at temperature of order 100 °C for three maintain durations (72, 144 and 216 hours). - Uniaxial compression tests have been completed with strain rate in order of 10- 2, the specimens has a size of 4.4x8x8 mm 3. Results Figure 5: IRTF spectra at virgin state and after degradations Figure 2: Evolution of mechanical properties of PC: a) Yield stress b) Plastic flow stress Figure 4: Evolution of micro-hardness Figure 1: Stress-strain curves in a virgin state and after thermal ageing

4 Interpretation Mechanical behavior at virgin state: We focused initially in compression test on virgin specimens (figure 1, black line). At the beginning we notes a reversible nonlinear viscoelastic behavior caused by the rotation of intermolecular segments ends with a yield point; witch are followed by a plastic stage, this phenomenon is due to the molecular chains alignment; once the molecular chains become entirely oriented, a hardening appear and increase until the crushing of specimen. Mechanical behavior after thermal ageing: The evolution of mechanical behavior before and afterwards ageing showed in figure 1, this result affirm the existence of degradation on material under the effect of high temperature. Indeed a decrease of yield stress, plasticity and hardness observed, Quantify it showed in figure 2 a) and b) the evolution of yield stress and plastic flow stress respectively, the change of these properties is go up to 14 MPa for the yield stress and 15 MPa for plastic flow stress from virgin state to 216 hours of thermal aging. hardness analyses In figure 4, we can see an increase in order of 30 %, 21 HK at virgin state against 29 HK at 216 hours of ageing. This evolution of the micro-hardness was allotted to molecular rearrangements causing a thickening of the polycarbonate. Analyse par spectroscopie IRTF The figure 5 reproduces the chemical structure behavior with spectra IRTF of material. This result illustrate the thermal aging effect on the microstructure by decreasing of intensity of all of chemical links of polycarbonate (Co, CH3, C=C and CH). We can explain the phenomena by cuts of chains and the formation of various products of oxidation.

5 Conclusion In the present study, we characterized the thermal ageing effects on the mechanical behavior and microstructure of polycarbonate, at 100 °C and for three maintain times (72, 144 and 216 hours). To achieve results, simple tests of compression, of micro-hardness measurements, and an analysis IRTF were reproduced. This investigation showed a degradation of our material, it have founded a significant fall of the mechanical properties; we note a progressive decrease of micro-hardness up to 30% in 216 h of aging; in addition, The superposition of the spectra shows us the chemical modification of the groups after thermal ageing.