Nucleating agents for injection molded biopolymers

The cooling time is an important economical parameter during plastics processing. For biopolymers such as PLA, the cooling rate is low due to a slow crystallization. A focus of this study was to evaluate the effect of different nucleating agents on biopolymers such as PLA and PSM to increase their crystallization rates and thermal diffusivity and to also reduce the half life time in isothermal crystallization and an in-mold thermal diffusivity measurement test. Isothermal crystallization tests of PLA with different nucleating agents (CaCO3, TiO2, BN, Mica, Talc, PSM, aliphatic-aromatic polyester BiomaxRTM 100) were studied. A faster crystallization rate reduces cooling time and increases productivity during a molding process. The maximum crystallinity of 34% was obtained by blending CaCO3 as a nucleating agent. The crystallization rate of PLA is maximum at 105°C and decreases above and below that temperature. PLA with a nucleating agent shows a two dimensional disk shaped crystal growth as predicted from the Avrami experiment.; Thermal properties are also important since they affect the cooling rate. The thermal diffusivities of PLA and PSM were measured using an in-mold method. PSM has a higher thermal diffusivity compared to PLA. PLA with Biomax RTM as a nucleating agent showed an increase in the thermal diffusivity in the amorphous or melt state but it did not affect the thermal diffusivity in the semi-crystalline or solid state.