Insight into the role of bound water of a nucleating agent in polymer nucleation: a comparative study of anhydrous and monohydrated orotic acid on crystallization of poly(L-lactic acid)

To gain an insight into the role of bound water of a nucleating agent in polymer nucleation, a biobased nucleating agent, orotic acid (OA), was selected as a model to investigate the effects on crystallization of poly(L-lactic acid) (PLLA). In such a context, two commercially available types of OA in anhydrous (OA-a) and monohydrated (OA-m) forms were melt mixed with PLLA, and their nucleation effectiveness on nonisothermal and isothermal melt crystallization of PLLA was comparatively studied. Results indicate that both forms of OA can significantly improve nonisothermal crystallization temperature and degree of crystallinity, overall isothermal crystallization rate, as well as nucleation density of PLLA. Interestingly, OA-a shows more prominent nucleation efficiency than OA-m. That is, the bound water of OA-m and its dehydration transition play a negative role in nucleation effects on PLLA crystallization. It is attributed to the deteriorated dispersion and the reduced active concentration of dehydration-transformed OA-a in PLLA/OA-m blends, as compared with pristine OA-a in PLLA/OA-a blends. Furthermore, an epitaxial mechanism is proposed to explain the nucleation phenomenon of PLLA/OA blends.