Polylactic Acid (PLA) Nucleating Agents
Polylactic acid decomposes as a result of the action of microbes and enzymes; that is, it is biodegradable. It is converted into lactic acid or carbon dioxide and water that are harmless to the human body. Thus, polylactic acid has attracted attention as an alternative to medical materials and general-purpose resins. Although polylactic acid is a crystalline resin, it is crystallized at a low rate, and it exhibits features practically similar to those of noncrystalline resins. Namely, polylactic acid is softened rapidly and extremely at about the glass transition temperature (typically, less than 1/100 in terms of elastic modulus), and thus, it has been difficult to attain sufficient properties in terms of heat resistance, moldability, mold releasability, and the like. Accelerated crystallization would greatly expand the usefulness of polylactic acid polymers. Nucleating agent may help attain that goal. (Ouchi et al. US Patent 7,825,212; 11/2/2010)
Recent US Patents
11/2/2010
7,825,212
Polylactic acid resin and composition and molded article of the same
Ouchi et al of Toyota, Japan developed a a polylactic acid resin composition in which stereocomplex crystals of poly-L-lactic acid and poly-D-lactic acid can be selectively crystallized to obtain polylactic acid having a sufficiently high speed of crystallization and a sufficiently high ratio of stereocomplex crystal so that a crystalline polylactic acid article can be molded. This is made possible by adding an aromatic urea complex as a crystallization accelerator. (RDC 3/2/2011)
Recent Journal Articles
Effect of Nucleating Agents on Physical Properties of Poly(lactic acid) and Its Blend with Natural Rubber
(288-296) Journal of Polymers and the Environment 19 #1 (2011)
Sukut and Deeprasertkul, Thailand, usedcyclodextrin (CD), calcium carbonate (CaCO3) and talc as nucleating agents. Adding talc and CD decreased cold crystallization temperature (Tcc) of the PLA. All nucleating agents increased the degree of crystallinity (ΧC) of PLA, whereas only talc and CaCO3 increased ΧC of PLA in PLA/NR blends. (RDC 4/22/2011)
The synergetic effect of phenylphosphonic acid zinc and microfibrillated cellulose on the injection molding cycle time of PLA composites
(689-698) Cellulose 18 #3 (2011)
Suryanegara et al, Japan, evaluated the effects of nucleants phenylphosphonic acid zinc (PPA-Zn) and talc, mold temperature, and microfibrillated cellulose (MFC) reinforcement in the acceleration of injection molding cycle of polylactic acid (PLA). PLA was dissolved in an organic solvent, mixed with nucleant and MFC, and dried compounds were injection molded into molds at temperatures ranging from 40 °C to 95 °C and holding times from 10 s to 120 s. PPA-Zn is more effective nucleating agent compared to talc. The addition of 1 wt% PPA-Zn and the mold temperature of 95 °C exhibited the fastest crystallization rates for the molded PLA, however, at this temperature the parts could not be quickly ejected without distortion. Addition of 10 wt% MFC increased the stiffness of PLA at high temperatures and allowed ejection of parts without distortion at a holding time of just 10 s. At this holding time, the crystallinity of the PLA composite was 15.3% but the storage modulus above T gwas superior to that of fully crystallized neat PLA due to MFC reinforcement, retaining the shape of the molded part during demolding. The mechanical properties of the composite at room temperature were also higher than those of fully crystallized neat PLA. (RDC 5/5/2011)