عنوان پایان‌نامه
گفتمان جهان سوم گرایی و تاثیر آن بر روند مدرنسیم در ایران
- رشته تحصیلی
- علوم سیاسی
- مقطع تحصیلی
- کارشناسی ارشد
- محل دفاع
- کتابخانه دانشکده حقوق و علوم سیاسی شماره ثبت: LP2744;کتابخانه مرکزی -تالار اطلاع رسانی شماره ثبت: 48170
- تاریخ دفاع
- ۲۵ آبان ۱۳۸۹
- دانشجو
- هادی باوندپور
- استاد راهنما
- الهه کولائی
- چکیده
- ندارد
- Abstract
- The application of electrically conductive polymer composites is increasingly growing in various areas due to their excellent chemical and corrosion resistance, low weight, smart functional performances and ease of shaping into small and complex geometries. It has been previously observed that foam injection molding of conductive polymeric composites containing nano-size carbon black particles, surprisingly increases their electrical conductivity while lowers the part weight. These advantages of foaming lead to higher interest and capability for using conductive polymer composites. In this work to investigate the effect of processing method, injection and compression molding were used to make and characterize the samples of carbon black nanocomposites. Furthermore, composites of graphite and expanded graphite, prepared by compression molding, were compared from the aspect of morphology and electrical conductivity. The electrical percolation threshold was much lower for expanded graphite composites compared to that of graphite composites. The electrical conductivity of graphite and expanded graphite composites was studied to see whether foaming has similar effect to that for carbon black composites. Results showed that electrical conductivity of injection molded carbon black composites increased in both in-plane and through-plane directions due to foaming; while no significant change was observed for the compression molded carbon black composites. This difference can be related to the difference in melt flow for these processes i.e. the existence of melt flow at the time of cell growth in injection molding and the absence of such melt flow in compression molding. In the case of expanded graphite compression molded composites, increase in electrical conductivity in both directions was obtained as a result of foaming. However, the cells could not be considered as a factor to be able to displace the huge expanded graphite assemblies. The change in the relative vertical or horizontal position of graphite nano sheets as a result of cell growth can be the cause. The method in which expanded graphite was added to melt during compound preparation had a great influence on the electrical conductivity of expanded graphite composites. Flexural strength measurements showed a reduction for all composites as compared to pure polymer. This reduction bacame more significant as the filler content increased. The reduction in flexural strength with increase in filler content was less steep for the foam composites compared to that for the solid ones.
