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Synergistic Effect of Talc and Titanium Dioxide on Poly(lactic acid) Crystallization: An Investigation on the Injection Molding Cycle Time Reduction

Petchwattana, Nawadon, Narupai, Borwon
Journal of polymers and the environment 2019 v.27 no.4 pp. 837-846
crystal structure, crystallization, differential scanning calorimetry, polylactic acid, synergism, talc, titanium dioxide
Injection molding cycle time is one of very important parameters relating to the plastic production rate. In neat poly(lactic acid) (PLA), it requires more than 25 min to obtain its half crystallinity (t₁/₂). This indicates that the injection molding of neat PLA with high degree of crystallinity (Xc) and high production rate is impossible. This research aims to increase the crystallization rate of PLA by combining two inorganic fillers namely; titanium dioxide (TiO₂) and talc. Differential scanning calorimetry (DSC) study indicated that the t₁/₂ of PLA decreased from 27 min to < 81 s, while the Xc increased by around 16% with the adition of TiO₂. Modifying PLA with talc was found to reduce t₁/₂ down to 36 s and the Xc increased from 0.92 to 20% only at a heating rate of 1 °C/min. The combination of talc and TiO₂ was significantly increased the Xc for all cooling rates applied. Synergistic crystallization behavior was clearly observed when TiO₂ was added to PLA/talc for all TiO₂ concentrations. Minimum t₁/₂ of 18 s was observed together with the increased Xc by around 26% when TiO₂ was added to PLA/talc at 3 wt%. This reduced the injection cycle time from around 28 min, in neat PLA, down to 68 s at this TiO₂ content. With the presence of talc and TiO₂, the flexural modulus of the composites was improved significantly.