Tapioca starch-poly (lactic acid)-based nanocomposite foams as affected by type of nanoclay

Tapioca starch (TS), poly (lactic acid) (PLA), and clay nanocomposite foams, with three clays (Cloisite 30B, Na+, and 20A), were prepared by melt-intercalation method. The structural, thermal, physical and mechanical properties were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), differential scanning calorimetry (DSC), and Instron universal testing machine, respectively. XRD results indicated that the intercalation of TS/PLA into the nanoclay layers occurred for all three clays. The extents of intercalation depended on the types of clay and were exhibited in the sequence of Cloisite 30B > Na+ > 20A. At the same time, a mixture of intercalation and tactoid phenomena was observed for the TS/PLA/Cloisite Na+ nanocomposite. SEM results indicated a decrease in cell size of the TS/PLA foam matrix with the addition of nanoclay and cells had hexagonal and pentagonal shapes. Melting temperature (T.) decreased with the addition of clays into TS/PLA matrix. Expansion ratios of the nanocomposites were significantly different (p < 0.05) from each other TS/PLA/Cloisite Na+ nanocomposite had the highest expansion ratio of 20.9 compared to its TS/PLA/Cloisite 20A (9.65) and TS/PLA/Cloisite 30B counterparts (8.23). Addition of Cloisite Na+ resulted in the lowest unit density of 0.046 kg/m(3), while no significant differences in unit density were observed for the foams with addition of Cloisite 30B and Cloisite 20A. Bulk spring index (BSI) was influenced significantly (p < 0.05) with the addition of nanoclays into the TS/PLA matrix. TS/PLA/Cloisite Na+ nanocomposite had the lowest BSI of 0.936 The bulk compressibility was decreased from 14.1 MPa for pure tapioca starch foam to 4.45 MPa with the addition of PLA. The nanocomposite with Cloisite 30B showed the highest value of 17.4 MPa, followed by those with Cloisite 20A (10.4 MPa), and Cloisite Na+ (647 MPa).