Publication: Preparation and characterization of kenaf fiber filled starch grafted polypropylene composites
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Date
2022-07-01
Authors
Eszer, Nur Hayati
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Abstract
Starch-g-PP is an advantageous polymeric material due to environmental friendliness but its mechanical properties limit its potential in material selection. Therefore, thermoplastic starch and natural fibers were produced to solve this problem. In this research, kenaf fiber was incorporated into starch-g-PP to form composites in order to improve the properties of starch-g-PP. The composites were prepared by melt-mixing process by using an internal mixer and then compression molded to produce the sample. Effects of KF loading and compatibilizer on starch-g-PP were investigated. The tensile strength of the composites increased with increasing KF loading up to 30wt.% and decreased thereafter. The tensile modulus of the composites increased with increasing KF loading from 10-40 wt.%. Moreover, the flexural strength increased with increasing KF loading with 40 wt.% was highest about 34.47 MPa and the flexural modulus of the composites increased about 52.48-326.73% with increasing KF loading from 10-40 wt.%. This was attributed to the incorporation of KF which was used as reinforcements to thermoplastic starch. Besides, the tensile strength of KF was relatively higher than starch-g-PP. The increment was due to chemical similarity between starch and fiber which consist mainly of cellulose, improve the interfacial adhesion and leads to bring stress transfer from matrix to fibers. Then, maleic anhydride polypropylene (MAPP) was incorporated into composites as a compatibilizer to improve the mechanical properties. The optimum enhancements in tensile and flexural strength were served with addition of 3 wt.% compatibilizer. The higher mechanical properties of compatibilizes composites than uncompatibilized composites probably due to chemical reaction between anhydride group of MAPP and hydroxyl (-OH) group of KF which could improve the interfacial interaction between matrix-fiber. This was revealed in SEM by surface morphology. From SEM, there have no gaps between matrix and fiber. In addition, thermal behavior of starch-g-PP composites was studied from the differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). Lastly, water absorption and soil burial test were carried out to evaluate the performance of the composites. The incorporation of KF and compatibilizer resulted in decreased water uptake. This was believed due to less hydrophilic behavior of KF than starch and the formation of strong fiber-matrix interfacial adhesion with the presence of compatibilizer. The composites experience deteriorated after 7 days of water immersion, ascertained from the water uptake, reduction in flexural properties, morphological properties and composites’ structure change. Exposure of uncompatibilized and compatibilized of starch-g-PP compositesto soil burial test for a period of 60 days resulted in decrease of tensile properties due to penetration of water molecules and microorganism attack. The addition of KF into composites decreases the biodegradation rate due to less hydrophilic nature of KF than starch. However, the reduction in tensile properties upon soil burial observed for uncompatibilized composites was higher than compatibilized composites due to poor interfacial interaction between matrix-fiber. The biodegradation of the composites is also revealed by percentage weight loss, SEM examination and structural changes. The biodegradability of starch-g-PP was also compared with polypropylene. For all cases, there are insignificant changes in weight loss, tensile properties, morphology and structural changes even after 60 days of soil burial. This was attributed to more hydrophobic characteristics of polypropylene than starch.