MEASUREMENT OF CRYSTALLINE INDEX IN NYLONS BY DSC - COMPLEXITIES AND RECOMMENDATIONS

Differential scanning calorimetry (DSC) is one of the most widely used technique for measuring crystallinity in the polymer industry. The ma jor source of error in the crystalline index (CIDSC) of low crystallin ity polymeric articles, is the development of further crystallinity du ring the DSC scan. Although, this type of cold crystallization is obvi ous, and thus accounted for in polymers like polyethylene terephthalat e, nylons are a difficult class of materials in that respect. The majo r contributing factors to the failure of DSC in measuring low levels o f crystallinity in nylons are identified to be (1) silent crystallizat ion between the glass (T-g) and melting (T-m) transitions, (2) extreme difficulties in packing a moisture-free nylon in the sample pan (the response due to traces of moisture being a broad endotherm competing w ith a broad exothermic crystallization), and (3) a sub-T-m exotherm, e specially in low crystallinity nylons, due to relaxation of the proces sing-induced stresses. These factors, specific to nylons, mask the obs ervation of cold crystallization and lead to substantially higher than real crystallinities. This manuscript deals with such complications a nd corrective actions using commercial nylon 6 films of CIDSC = 0-40%. X-ray diffraction measurements have been included to support the vali dity of our improved DSC methodology. (C) 1997 John Wiley & Sons, Inc.