Nucleating and clarifying agents for semicrystalline thermoplastics based on certain supramolecular additives improve dramatically the optical characteristics such as haze and clarity while maintaining the mechanical properties. This is achieved by an in situ formation of finely dispersed nanosized supramolecular objects, which initiate heterogeneous nucleation reducing the crystallite size and inducing a suitable crystal modification. So far, this concept has been successfully implemented mainly for isotactic polypropylene. Here we report for the first time on supramolecular additives capable of efficiently nucleating and clarifying the engineering plastic polyamide 6 (PA6). This class of supramolecular additives consists of a trans-1,4-disubstituted cyclohexane core to which two urea units with aliphatic side groups are attached. We show that these bisurea derivatives enable significant nucleation of PA6 at a concentration as low as 0.02?wt.%. A remarkable characteristic is that the supramolecular additives induce the α-phase of PA6 in rapidly processed injection molded samples. Together with the resulting small crystallite size, this leads to significantly improved optical properties. Compared to the neat PA6, the addition of 0.8?wt.% of a distinct additive improves in 1.1-mm thick specimens the clarity from 68% to 97% and reduces the haze from 98% to 19%, resulting in highly transparent samples.
Kremer et al. (Wed,) studied this question.