Effect of silicon dots into coconut fibers on the nucleating capacity of β-crystals of polypropylene

Abstract

Three concentrations of sodium hydroxide (3, 5, and 7% based on a composition by weight) and 2 reaction times (1 and 4 h) were used to treat coconut fiber. According to the results, the inclusion of treated fiber in polymer influenced the melting temperature of the composite incremented it to 165°C, which is attributable to the a-crystal melting; however, the introduction of the untreated fiber interrupts the crystallinity sequence for a-crystallinity and favors the formation of the b-crystals. The X-ray diffraction analysis confirmed that pristine coconut fiber can be an efficient β-nucleating agent when it is used with no alkaline treatment, indicating that its b-nucleating capability is related to the presence of silicon dots on the fiber surface. In terms of mechanical behavior, the untreated fiber composites presented the highest value in storage modulus (4260 MPa) compared to pure polypropylene; and the presence of a higher content of β-crystals in the polymer matrix gave an improvement of 82%. The results suggest that a high formation of β-crystals in polypropylene matrices reinforced with coconut fiber occurs when a previous alkaline treatment is not used.