Mechanical, Diffusion and Degradation Behaviour oF Sausage Fruit Tree Fiber (Kigelia Africana) Reinforced Polypropylene Composites

Abstract

Polypropylene is a thermoplastic polymer used in cement mortars, concrete, packaging plastics, and in re-usable containers. It is made from monomer propylene. It is economical and has a good resistance to fatigue in comparison to other polymers. Polypropylene is however non-biodegradable and liable to chain degradation especially in external applications evidenced by cracks and crazing. Previously use of U-V absorbing additives to curb external exposure degradation was increasing on cost and also unfavorable to the environment. The only solution to this is blending polypropylene with natural fiber (cellulose) to modify its structure. PP/Starch blends have poor rigidity, very low thermal stability and high diffusivity. Cellulose is rigid, has high diffusivity and thermal stability hence suitable in reinforcement of polypropylene. Research work is still going on how to improve the mechanical properties and lowering the density of the composites, as well as have biodegradable high performance engineering materials at low cost. This research investigated the mechanical properties, creep, thermal degradation, diffusion and biodegradation measurements of sausage fruit tree fiber reinforced polypropylene composites. Injection molded samples were used, where the fiber was first grinded in to fine powder. Dynamic mechanical analysis was carried out using torsion pendulum at temperature range 300 C to 100ºC. Creep measurements were performed at 30, 40, 50 and 600C .The time for deformation and recovery of sample was 12 minutes. Diffusion measurements were done at room temperature and mass difference monitored after 7, 30,60, and 90 days. Thermal degradation was done within temperature range 25 to 5500C at a heating rate 5 oC/min. Biodegrability was monitored by burying the samples 20 cm under soil. Mass difference monitored after 7, 30,60 ,and 90 days. Cellulose addition in small amounts increased the storage modulus (stiffness) and loss modulus of the polypropylene. Models of analysis for creep data were Burger model and Weibull model. Increase in cellulose loading decreased resistance to creep hence increased deformation. Water intake increased with cellulose loading. Fickian diffusion behavior was noted and diffusion coefficients increased from approximately 1.481×10-12 cm2/s to 1.646×10-10 cm2/s with cellulose loading. Thermal stability of the blends increased with cellulose loading (activation energy increased from approximately 69.22 to approximately 210.01kJ/mol). Biodegradability improved. Lifespan decreased from approximately 199 years for pure polypropylene to approximately 15 years for 20% fiber loading. When polypropylene is reinforced with cellulose the structural rigidity is improved, thermal stability, hydrophilicity and biodegradation increases. Use of SFTF particles in polypropylene matrix should be adopted since these PP blends are promising non-environmental pollutants.