Preparation and characterization of sugar palm (Arenga pinnata) starch grafted with oligo(lactic acid) via ex situ oligomerization

Sugar palm (Arenga pinnata) starch was grafted with oligo(lactic acid) (OLA) prepared via ex situ oligomerization. Two types of OLA with distinct characteristics were used: OLAA, which contains lactide and has an average molecular weight (Mw) of 349 Da, and OLAB, which does not contain lactide and has an average Mw of 680 Da. The grafting reaction was carried out using stannous octoate as a catalyst in dimethyl sulfoxide (DMSO) at 90 °C for 6 h. The resulting products were characterized by Fourier-transform infrared spectroscopy (FTIR), proton and carbon nuclear magnetic resonance (¹H NMR, ¹³C NMR), heteronuclear single quantum coherence (HSQC), differential scanning calorimetry (DSC), and thermogravimetric analysis (TGA). The formation of grafted products was confirmed by the appearance of new absorption bands corresponding to carbonyl (-C=O) groups in the FTIR spectra and new chemical shifts in the NMR spectra. The degree of substitution, determined by ¹H NMR, was 0.059 for OLAA-grafted starch and 0.077 for OLAB-grafted starch.