Study on thermoplastic cassava starch modifications via chemical, photo and irradiation induced crosslinking

Abstract

The characterization of modified thermoplastic starch (TPS) was investigated by means of mechanical properties, thermal properties, scanning electron microscope (SEM), Fourier transform infrared spectroscopy, high performance liquid chromatography and biodegradability test. Before performing the modification, the TPS was prepared by plasticized 65 % of native cassava starch with 35 % of glycerol. The TPS was prepared by using heated two roll mill at the 150 oC for 10 minutes. Different type of modification, which photo radiation, electron beam radiation crosslinking, and carboxylic acid modification was prepared on TPS sheets. In photo crosslinking, TPS were irradiated under lamps at different irradiation time, from 30 minutes to 480 minutes. Meanwhile, dosage ranging from 25 kGy to 100 kGy were introduced in electron beam radiation crosslinking process. Crosslinking of TPS using photo radiation and electron beam radiation showed improved thermal properties and mechanical properties, which 2.70 MPa and 3.18 MPa respectively. The gel mass (NGM) value increases up to 22.98 mg/cm2 and 19.28 mg/cm2, respected to the photo irradiation time and electron dose range proved the formation of crosslinking in the TPS. However, excessive irradiation caused further degradation of the TPS, thus reduce the crosslinking formation. Citric acid and ascorbic acid were introduced into the chemical modification process of TPS. Addition of carboxylic acid were varied from 1% - 4%, and 10% - 50%. Based on SEM analysis, the addition of carboxylic acid gives a smoother fracture surface. Further increment in carboxylic acid content led to the crosslinking formation. The NGM value was increase until 49.00 mg/cm2 and 57.43 mg/cm2, respected to increases of citric acid and ascorbic acid content. As a resulted, the tensile value at 40% was increased up to 6.25 MPa compared to unmodified TPS. Moisture absorption analysis also showed improved moisture resistivity as compared to unmodified TPS. Biodegradability test performed resulted acid modification TPS give low degradation rate compared to unmodified TPS. These was due to their improved moisture resistivity, resulted reduce in the water permeability into the TPS structure