Piperidine-conjugated polyfunctional star-shaped PLLA as a novel bio-based antioxidant additive for bioplastics

Antioxidant-conjugated star-shaped PLLA (star-PLLA-PPD) were originally proposed as a novel polyfunctional free radical stabilizing additive for bioplastics. By a simple ring opening polymerization of l-lactide (L-LA) on a poly-functional core molecule (i.e., pentaerylthritol) using tin (II)-2-ethylhexanoate (SnOct2) as a catalyst, the 4-arms star-shaped PLLA was successfully prepared and confirmed by FT-IR and 1H-NMR. Percent conversion of L-LA to 4-arms star-PLLA was 78.50% and the weight and number average molecular weights determined by GPC were 34726 Da and 27286 Da, respectively (PDI = 1.27). Piperidine (PPD) was then conjugated onto 4-arms star-PLLA to obtain star-PLLA-PPD. As observed by SEM and DSC, the star-PLLA-PPD exhibited excellent compatibilizer as well as nucleating agent for PLA. A model study on free radical scavenging ability of the star-PLLA-PPD in PLA blends was carried out under radiation-induced free radical process. Irradiation doses of 10 kGy and 25 kGy were used because they are generally used for food and medical device sterilization, respectively. Free radical scavenging ability was demonstrated using EPR spectroscopy. The star-PLLA-PPD efficiently scavenges the free radicals in PLA matrix upon irradiation. The star-PLLA-PPD additive could retard the degradation of PLA under irradiation as observed by protecting molecular weight reduction when compared with the neat PLA. The migration of star-PLLA-PPD is significant lower than PPD. A novel star-PLLA-PPD additive would be a good model of polyfunctional bio-based antioxidant additive for bioplastics especially for food packaging and biomedical materials.