Technology of crystallization of polyamide 6 via a mesophase for generation of a semicrystalline structure with specific properties. Part II: Kinetics of homogeneous nucleation

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The supermolecular structure and properties of crystallizable polymers are strongly controlled by the pathway of crystallization. This project focuses on crystallization of polyamide 6 from the glassy state which has not been investigated in detail yet. Rapid cooling of the melt of this important polymer to ambient temperature is connected with complete vitrification of the amorphous phase, with the opportunity to generate ordered domains of variable perfection and morphology by subsequent annealing at elevated temperature. This includes the generation of non-spherulitic semicrystalline structures composed of non-lamellar crystals and amorphous phase with specific properties which cannot be obtained by melt-crystallization. In the first part of the project, the technological pre-requisites for generation of non-spherulitic semicrystalline polyamide 6 with nodular crystals were determined. In particular, the conditions of cooling the melt to obtain fully amorphous glassy samples, necessary for realization this special pathway of crystallization, were evaluated, and the effect of the conditions of annealing on cold-ordering/-crystallization was analyzed. In the second part of this project, the kinetics of homogeneous nucleation, dominating structure formation at high supercooling and being the key to obtain non-lamellar ordered domains/crystals, will quantitatively be analyzed for the first time. The analysis will be performed using the novel technique of fast scanning chip calorimetry which permits generation of amorphous states of different stability and therefore different cold-crystallization behavior/kinetics of homogeneous nucleation. Of particular importance in this project is the consideration of relaxation and ordering processes of the amorphous phase at temperature below the glass transition. The investigation of the kinetics of homogeneous nucleation, effective at high supercooling of the melt, allows gaining fundamental insights about polymer crystallization such that local ordering also occurs in the glassy state, ultimately affecting the stability of the amorphous phase and structure formation at elevated temperature. The prove of local ordering at temperatures close to the glass transition is of high application-related relevance for polyamide 6 since it is connected to physical aging and since it allows generation of materials with special properties due to the possibility for controlled structuring at the nanometer scale.