Thermal Properties of Banana Starch Nanocrystals Prepared by Acid Hydrolysis as Reinforcing Filler

Abstract

Banana is one of the most important tropical fruits in Thailand. It is available throughout the year, i.e., no specific growing season, resulting to the low cost. All parts of banana plant can be used, particularly its fruit has several adaptable in term of how to eat it. However, banana is ripe and perishable easily. Therefore, it is a potential resource that can be utilized and developed in order to add more value to this raw material. In this work, green banana fruits were used as a raw material for preparing a starch nanocrystal reinforcing filler in bio-nanocomposites. The green banana was extracted into banana starch by using 0.05 N sodium hydroxide solution. The composition of the obtained banana starch contained 90.61% of starch, 18.82% of amylose, 0.19% of protein, 0.11% of ash, and 0.03% of lipid. The banana starch composition exhibited low content of protein, ash, and lipid (<0.5%) indicating that the obtained banana starch was pure enough to be used. After that, starch nanocrystal (SNC) was prepared from banana starch by acid hydrolysis with 3.5 M sulfuric acid and 3.0 M hydrochloric acid at 40°C for 7 and 5 hours, repectively. The obtained banana SNC showed an increase in the degree of crystallinity from 28.03% for native banana starch to 47.13% and 40.15% for banana SNC prepared from sulfuric and hydrochloric acid hydrolysis, respectively. Furthermore, the thermal properties of banana SNC were investigated by differential scanning calorimeter (DSC) and thermogravimetric analyzer (TGA) in order to assess thermal stability of banana SNC for using as reinforcing filler in bio-nanocomposite. The decomposition temperature of native banana starch and SNC was in the range of 260-315°C. The gelatinization temperature of banana SNC increased as a result of the increment of its degree of crystallinity when comparing with native starch.