Poly(citrate glyceride): a hyperbranched polyester for starch plasticization

Effect of branched 1,4-butanediol citrate oligomers with different molecular weights on toughness and aging resistance of glycerol plasticized starch

The thermoplastic starch with glycerol is easy to retrograde and sensitive to hygroscopicity. In this study, branched 1,4-butanediol citrate oligomers with different molecular weights (P1, P2, and P3) are synthesized, and then mixed with glycerol (G) as the co-plasticizers to prepare thermoplastic starch (CS/PG). The results show that the molecular weight and branching degree of the branched 1,4-butanediol citrate oligomers increase as reaction time prolongs. Compared with glycerol plasticized starch, the thermoplastic starch films with branched 1,4-butanediol citrate oligomers/glycerol (10 wt%/20 wt%) have a better toughness, transmittance, and aging resistance, and have a lower crystallinity, hygroscopicity, and thermal stability. The toughness, transmittance, and aging resistance of CS/PG films are positively correlated with the molecular weight of the branched 1,4-butanediol citrate oligomers. These are due to the fact that the branched 1,4-butanediol citrate oligomer with a high molecular weight could form a stronger hydrogen bond and the more stable cross-linked structure with starch chains than that with a lower molecular weight. The elongation at break of CS/P3G film stored for 3 and 30 d are 98.0 % and 88.1 %, respectively. The mixture of branched butanediol citrate oligomers and glycerol, especially P3/G, has a potential application in the preparation of thermoplastic starch.

High-Toughness Poly(Lactic Acid)/Starch Blends Prepared through Reactive Blending Plasticization and Compatibilization

In this study, poly(lactic acid) (PLA)/starch blends were prepared through reactive melt blending by using PLA and starch as raw materials and vegetable oil polyols, polyethylene glycol (PEG), and citric acid (CA) as additives. The effects of CA and PEG on the toughness of PLA/starch blends were analyzed using a mechanical performance test, scanning electron microscope analysis, differential scanning calorimetry, Fourier-transform infrared spectroscopy, X-ray diffraction, rheological analysis, and hydrophilicity test. Results showed that the elongation at break and impact strength of the PLA/premixed starch (PSt)/PEG/CA blend were 140.51% and 3.56 kJ·m-2, which were 13.4 and 1.8 times higher than those of pure PLA, respectively. The essence of the improvement in the toughness of the PLA/PSt/PEG/CA blend was the esterification reaction among CA, PEG, and starch. During the melt-blending process, the CA with abundant carboxyl groups reacted in the amorphous region of the starch. The shape and crystal form of the starch did not change, but the surface activity of the starch improved and consequently increased the adhesion between starch and PLA. As a plasticizer for PLA and starch, PEG effectively enhanced the mobility of the molecular chains. After PEG was dispersed, it participated in the esterification reaction of CA and starch at the interface and formed a branched/crosslinked copolymer that was embedded in the interface of PLA and starch. This copolymer further improved the compatibility of the PLA/starch blends. PEGs with small molecules and CA were used as compatibilizers to reduce the effect on PLA biodegradability. The esterification reaction on the starch surface improved the compatibilization and toughness of the PLA/starch blend materials and broadens their application prospects in the fields of medicine and high-fill packaging.

Effect of hyperbranched poly(trimellitic glyceride) paired with different metal ions on the physicochemical properties of starch

The novel hyperbranched poly(trimellitic glyceride) (PTG) starch plasticizer synthesized in our previous study was neutralized with different alkaline metal hydroxides. Mixed with starch, the effects of different alkaline metal cations, M⁺, on gelatinization of starch suspensions and thermal behaviors of the films were analyzed using RVA and DMA, respectively. The structures of the starch suspensions, films and freeze-dried samples (S/PTG-M) were investigated using DSC, XRD and FTIR spectroscopy, respectively. M⁺ increased the gelatinization temperature of starch suspensions in the order of S/PTG-Li > S/PTG-Na > S/PTG-K. The formation of a complex between M⁺ and starch in the films observed using FTIR spectroscopy improved the stability of the starch paste and gel, and increased the gel temperature of starch dispersions. The corresponding starch gel was relatively thermostable, but not shear-resistant. PTG decreased the T_g of starch films with different paired M⁺. PTG-Li and PTG-K, but not PTG-Na, strengthened the mechanical properties of starch films.