Effect of dissolved CO₂ on the crystallization behavior of linear and branched PLA

In this study, the crystallization behavior of polylactide (PLA) was investigated in the presence of dissolved CO₂ using high-pressure and regular differential scanning calorimeter. The isothermal and non-isothermal melt crystallization results showed that increasing the CO₂ pressure decreased the crystallization half-time. During isothermal and low-cooling-rate non-isothermal crystallization, a very high crystallinity was achieved at 15 bar CO₂ pressure by facilitating more perfect crystal formation with the plasticization effect of CO₂ while limiting the crystal nucleation rate. At higher CO₂ pressures, a larger number of less close-packed crystals were formed due to chain entanglement, and consequently, the final crystallinity was decreased. The non-isothermal results at high cooling rates showed the total crystallinity decreased for all CO₂ contents, because of less time given for crystallization. Also the effects of the CO ₂ pressure and the cooling rate on T_c and T_g were investigated.