Effect Of Nucleating Agent And Annealing On Crystalline And Heat Resistance Properties Of Poly(Lactic Acid)

Poly(lactic acid)(PLA) is a kind of biodegradable thermoplastic polyester. Compared with traditional polymer materials, there are some advantages, such as wide range of sources and fully biodegradable, etc.. PLA not only reduces the people’s excessive dependence on oil resources, but also has high strength and good transparency, so it is widely used in biomedical, pharmaceutical and disposable supplies. However, the limits in extending the fields of application for PLA are the low crystallization rate, crystallinity and heat resistance properties. Currently, methods to improve these shortcomings are mainly the following two ways: adding nucleating agents and annealing. Adding nucleating agents is a inexpensive and effective method to improve heat resistance properties, however, so far, we have not found one kind of nucleating agent that can accelerate the crystallization rate of PLA greatly to meet the requirements of industrial production scale. Annealing treatment is the effective method to increase the crystallinity of PLA and to improve its heat resistance. But annealing treatment not only prolongs the molding cycle of products, but also increases the cost. We combined addition of nucleating agents with annealed in order to improve the heat resistance of PLA.In this paper, firstly, we used diisocyanate activated sepiolite(ADI-S) as nucleating agent of PLA, and chose the best quality content. Then at the same time, we did annealed controlled annealing temperature, annealing time, annealing medium separately. The effects of nucleating agent and annealing conditions(annealing temperature, time and medium) for the crystalline and heat resistance of PLA were analyzed by differential scanning calorimetry(DSC), polarized optical microscopy(POM), wide-angle X-ray diffraction(WAXD), scanning electron microscopy(SEM), fourier transform infrared spectroscopy(FTIR) and VEKA softening point tester, etc.The results showed that ADI-S was effective heterogeneous nucleation agents of PLA. It can accelerate the crystallization rate of PLA, and increase the crystallinity. when the ADI-S content was 1.0%, the crystallinity of PLA materials appeared maximum value. Adding activation sepiolite as nucleating agent can significantly reduce the annealing temperature, annealing time and increase the crystallinity and heat resistance. Annealing increases the crystallinity of PLA materials, enhanced heat resistance. The annealing temperature can be reduced when water was used as the annealing medium, and the degree of crystallinity and heat resistance can be enhanced simultaneously.The data of WAXD diffractogram indicated that no characteristic band of PLA β-form was found. Hence, all these PLA samples were still formed the most common crystal modification(α-form).The micrographs of POM revealed that the PLA crystals were the most common spherulites. The POM images showed the Maltese Cross of the samples. SEM presented the three-dimensional spherical crystal after etched by potassium hydroxide(0.1mol/L) at 50℃ for 13 hour.