A Comparative Study of Raw Rubber Properties of Natural Rubber Manufactured from Latex Coagulated using Pineapple Peel Extract and Formic Acid

Abstract

Ribbed Smoked Sheet (RSS) rubber accounts for over half of the total local Natural Rubber (NR) in the country. Formic acid is the most commonly used acid as a coagulant in the RSS manufacturing process. In light of the scarcity and high cost of formic acid, together with the foreign dependency on the material, it is important to investigate locally available potential sources that could be used as an alternative to formic acid. This study aims to investigate pineapple peel extracts as an alternative to formic acid to assure the continuation of this cottage industry. The extract was used to coagulate the NR latex, in different amounts (20mL, 25mL, and 30mL) per latex volume containing 500g of dry rubber. Raw rubber properties such asWallace Plasticity (P0), Plasticity Retention Index, Mooney viscosity, nitrogen content, volatile matter content, ash content and dirt content were compared against the relevant properties of the rubber prepared using latex coagulated with formic acid. It was found that sheet rubber prepared using 30mL of the extract per 500g of rubber yielded comparable properties to the rubber prepared with latex coagulated with formic acid except for the nitrogen content. It was significantly lower than that of the corresponding standard rubber suggesting pineapple peel extract as a potential candidate coagulant for the manufacture of low protein NR. However, bubble formation occurred probably due to the enzymatic activity that has adversely influenced the visual appearance of RSS. It is concluded that pineapple peel extract has a potential to substitute formic acid and 30mL per 500g dry rubber is the optimum dosage to coagulate NR latex.