Preparation And High-Pressure Vessel Foaming Of Poly(Lactic Acid)/Acetylated Starch Blends And Their Nanocomposites

In this paper, the twin-screw extruder was used to prepare poly(lactic acid)/acetylatedstarch (PLA/AS) blends (60/40,50/50, and40/60). Results showed that AS contentsignificantly influenced the phase morphology, rheological properties, and thermal propertiesof the blends. With increasing the AS content, the size of dispersed phase (AS) was increasedand the phase morphology was changed from “sea-island” to co-continuous structure. Storagemodulus and complex viscosity of the blends were reduced when AS content was increased.Glass translation temperature (Tg) of PLA phase was slightly decreased when AS content wasincreased, which showed poor compatibility between PLA and AS phases. The existence ofAS had a significant effect on PLA crystallization, but the influence of AS content on PLAcrystallization was not significant.PLA/AS (70/3030/70w/w) blends and PLA/AS/organic modified montmorillonite(OMMT)(70/30/330/70/3w/w/w) nanocomposites were prepared using the twin-screwextruder connected with HP single-screw extruder with chaotic mixing. The influence ofOMMT on the phase morphology, rheological behaviors, and thermal properties of blends wasstudied. The results showed that smaller size and narrower size distribution of the dispersedAS phase were found in PLA/AS/OMMT nanocomposite upon the addition of OMMT. Thestorage modulus of the nanocomposite was slightly lower than that of the blend at the highfrequency area. Moreover, the OMMT reduced the Tgand crystallization degree of PLA phase.High-pressure vessel foaming were used to foam PLA/AS (70/30) blend and theinfluence of saturation pressure (12～20MPa) and foaming temperature (145～160°C) on cellstructure was studied. The results showed that cell density was the highest and mean celldiameter was the smallest under the saturation pressure of16MPa; Mean cell diameterdecreased and cell density increased with further increasing saturation pressure. Mean celldiameter was the smallest and cell density was the highest when foaming temperature was150°C; Mean cell diameter increased and cell density decreased with further increasingfoaming temperature. High-pressure vessel foaming was also used to foam PLA/AS blends(70/30,60/40,50/50,40/60, and30/70) at saturation pressure of20MPa and foamingtemperature of150°C. The results showed that AS can lead to the cell rupture during cellgrowth and the formation of the open-cell structure when AS content was30wt%. Meltelasticity of PLA/AS blends was reduced when AS content was too much in the blend(60wt%), resulting in smaller mean cell diameter and higher cell density. The addition ofOMMT caused the decrease of melt visvosity of the PLA/AS/OMMT nanocomposites, which results in the formation of the open-cell structure.