- Wednesday, August 10, 1988
- Effects of annealing on the crystallinity and microparacrystallite size of Kevlar 49 fibres
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The effects of annealing in the range (20-500)°C on the crystallinity and microparacrystallite (mPC) size of Kevlar 49 fibres were studied by X-ray diffraction techniques. The crystallinity (75.5%) remained constant until (350°C) ,at (400°C) it reached its maximum value (81%), and at (500°C) it decreased to (51%). The mPC size (D110 = 4.23nm and D200 = 3.85nm) remained constant until (250°C), then reached the maximum values(D110 = 4.89nm and D200 = 4.22nm) at (400°C), after which they decreased. The netplane spacings were not affected until (400°C) , but the relative peak intensities of the (200) and (110) reflections increased by (10%) at (400°C). The TGA thermogram indicated a weight loss <1% below (350°C), (3.9%) at (450°C) , (5.5%) at (500°C) and (20.4%) at (657°C). The DTA curve showed a peak melting point at (536.7°C) and six transition temperatures. The shrinkage of Kevlar 49 fibres is about (1%), in effect the constant – length annealing and the free-length annealing produced similar results for crystallinity. Thermal ageing in static air at (150°C) for periods ranging between (1- 150)days showed no change in the crystallinity within the first (7days), but an increase in the lateral mPC sizes occurred.