Mechanical and Thermal Characterizations of Polypropylene Composite Reinforced with Alkali-Treated Sisal Fiber

Background: Owing to the promising characteristics— high strength-to-weight ratio, acoustic and thermal insulation, renewable and biodegradable, sisal fiber-based composites have been explored. Including patents, interesting literature is available on sisal fiber-based composites. Methods: The materials under investigation were sisal fiber (SF), polypropylene (PP), and sisal- fiber-reinforced polypropylene composite (SFR-PC). Three different samples of SFR-PC were fabricated via injection molding. Their morphological-, mechanical-, thermal-, and water absorption- properties were analyzed. Results: The untreated sisal fiber (USF) sample showed a network microstructure with micro-void; however, the alkali (NaOH)-treated sisal fiber (TSF) sample envisages surface roughness morphology. The C-O stretching vibration of the acetyl groups of lignin in the USF vanished after the alkali treatment of SF. The degree of crystallinity index, thermal stability, weight loss, and water resistance improved with the alkali (NaOH) treatment of SF. The tensile modulus (E) for SFR- PC showed an increasing trend with the addition of TSF at all weights % envisaging a better interaction between polymer matrix and reinforcement; however, the 90PP-10TSF sample exhibited the highest storage modulus (Eˈ) at all temperatures due to the TSF distribution and agglomeration in the polymer matrix. The addition of TSF improved the loss modulus (E˝) for the SFR-PC sample as compared to the PP sample. Conclusion: The 90PP-10TSF sample showed the optimum distribution of TSF in the PP matrix. DSC secondary heating thermograph depicted that the addition of TSF did not affect the melting temperature of SFR-PC samples, and the cooling thermograph showed that the addition of TSF in the polymer matrix gradually increased the crystallization temperature, suggesting a better packing of the cellulose chain. The 70PP-30TSF sample showed the highest absorption, followed by 80PP-20TSF and 90PP-10TSF samples, whereas the PP sample showed the lowest absorption.