Effects of consolidation parameters on mechanical properties and thermal degradation of self reinforced high density polyethylene composite
Mwangi, Wachira Anthony
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The numerous applications of high density polyethylene (HDPE) in industries for production of domestic and commercial commodities have made it necessary to find ways of improving its mechanical properties. The most common way of doing this is to add reinforcement such as glass fibers. However these composites suffer limitations due to reduced recyclability, great weight and difficult to thermo-form. In order to improve properties such as specific strength, stiffness and thermo-formability of the composite and maintain recyclability, self reinforced HDPE composites are being focused on as an alternative to glass fiber reinforced HDPE. In this study, self-reinforced high density polyethylene composite was fabricated by film stacking HDPE films and HDPE fibers under carefully controlled temperatures (128- 142°C), pressure (2MPa) and time (100 seconds to 3S0 seconds). While holding all other factors constant, the optimum consolidation temperature of 133°C was obtained by carrying out creep tests and dynamic mechanical analysis. Consolidation time was then optimized in the same manner using the optimum temperature and was found to be 300 seconds. Then, using the optimum conditions, the effect of fiber draw ratio and fiber weight fraction on creep, dynamic mechanical behavior, fatigue and thermal degradation were studied. The creep was measured by application of force for 12 minutes and allowed to recover for another 12 minutes at a temperature of 30, 40, SO, and 60°C. Creep strain percentage and creep compliance were observed to decrease as draw ratio and fiber weight fraction increased. Long term creep behavior up to 107 seconds was studied using time temperature superposition. William-Landel-Ferry model revealed that constants Cl and C2 increase with draw ratio and fiber weight fraction. Dynamic mechanical analysis was carried out in the frequency range of 0.3 to 30 Hz and temperature range of 27°C to 110°C at a heating rate of 3°C/minute. Storage modulus was found to increase with draw ratio and fiber weight fraction while tan delta peak was found to decrease with increase in draw ratio and fiber weight fraction. Fatigue test consisted of a frequency sweep of SHz at a constant force applied on the specimen. It was observed that draw ratio and fiber weight increase fatigue endurance limit. Thermogravimetric analysis was carried out using Lindberg Blue furnace (TFSS03SC-l) within a temperature range of 2S to 610°C at a heating interval of SOC per minute. Increase in draw ratio and fiber weight was found to increase peak degradation temperature and lower degradation rate. Using the Broido equation, activation energy of neat HDPE was found to be 100.9KJmol and this increased with draw ratio and fib er weight fraction.