Bi-axial nano oriented crystals (NOCs) of Polyamide 66

M. Hikosaka1, K. Okada1, K. Yasui2, M. Ishikawa3 and H. Masunaga4

1Graduate school of integrated arts and sciences, Hiroshima University, Japan.
2Bridgestone corp., Japan, 3ASAHI KASEI corp. , Japan.
4Japan synchrotron radiation research institute (JASRI), SPring-8, Japan.

We found that polyamide 66 (PA66) crystallizes into novel “bi-axial nano-oriented crystals (bi-NOCs)”, when the supercooled melt was elongated above a critical elongational strain rate.
We used PA66 (Mw=87×103, Mw/Mn=2.31). We used roll system to generate strain rate. We observed the structure and morphology of NOCs by means of polarizing optical microscope and small/wide angle X-ray scattering from three directions, through, edge and end. Polarizing optical micrographs suggested the formation of NOCs. SAXS patterns showed typical two-point pattern, which indicates the formation of NOCs. The two-point pattern showed orientation along machine direction (MD) for through and edge view, while along normal direction (ND) for end view. Size of a nano crystal (NC) was 11nm along MD and ND. WAXS patterns showed chain orientation along MD for through and edge views, while along ND for end view. From these observed facts, we concluded that the arrangement of NCs and chains showed bi-orientation along MD and ND.
The bi-orientation of NCs and chains suggests the important role of hydrogen bond planes (HBPs) in formation of NOCs. As the crystals of PA66 includes “rigid” HBPs[1], the HBPs should change into hydrogen bond clusters (HBCs) after melting. The HBCs should become nuclei. Under large strain rate, the HBCs would be parallelly oriented to the roll surface due to hydrodynamic effect, which should be the reason of the formation of bi-NOCs.

[1] Bunn, C. W. & Garner, E. V. Proc. Royal Soc. London, A(189), 39 (1947).  (link)