Measurement of crystalline index in nylons by DSC: Complexities and recommendations

Abstract

Differential scanning calorimetry (DSC) is one of the most widely used technique for measuring crystallinity in the polymer industry. The major source of error in the crystalline index (CIDSC) of low crystallinity polymeric articles, is the development of further crystallinity during the DSC scan. Although, this type of cold crystallization is obvious, and thus accounted for in polymers like polyethylene terephthalate, nylons are a difficult class of materials in that respect. The major contributing factors to the failure of DSC in measuring low levels of crystallinity in nylons are identified to be (1) silent crystallization between the glass (Tg) and melting (Tm) 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 with a broad exothermic crystallization), and (3) a sub‐Tm exotherm, especially in low crystallinity nylons, due to relaxation of the processing‐induced stresses. These factors, specific to nylons, mask the observation of cold crystallization and lead to substantially higher than real crystallinities. This manuscript deals with such complications and corrective actions using commercial nylon 6 films of CIDSC = 0−40%. X‐ray diffraction measurements have been included to support the validity of our improved DSC methodology. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35: 2219–2231, 1997

Characterization of Polyamide 66 Obturator Materials by Differential Scanning Calorimetry and Size-Exclusion Chromatography

“…The DSC instrument was calibrated using an Indium standard. The procedure for DSC characterization was adapted from PA66 measurements performed by Khanna and Kuhn (1997). After loading each sample into aluminum autosampler pans and crimping the pans closed, a needle was used to create a small hole in the pan lid.…”

“…After drying, the pan was immediately put into the DSC for a second drying step in which the sample was heated from 25 to ~55 °C at a rate of 20 °C/min, held for 2 min, and then air-cooled to room temperature. The purpose of the second step was to remove additional water and to allow enthalpic relaxations in the amorphous regions of the polyamide that occur as a result of removing moisture during the initial drying step (Khanna and Kuhn, 1997). Khanna and Kuhn found that relaxation of amorphous material causes uncertainty in the baseline above T g which can lead to incorrect interpretations of crystallinity.…”

Compatibility Studies in Binary Blends of PA6 and ULDPE-graft-DEM

“…Some authors like Kim et al, [39] and Khanna et al, [40] have attributed this behavior, named "sub-T m " exotherm, to partial melting and recrystallization during the heating run. Some other explanations have been oriented toward an energy relaxation process, which stored during processing.…”

Obtenção de Membranas Microporosas a partir de Nanocompósitos de Polimida 6/Argila Nacional. Parte 2: Avaliação Microestrutural e de Permeabilidade das Membranas Obtidas

“…Como pode ser observada, a introdução da argila altera o formato desses picos, modificando provavelmente a cristalinidade da PA 6. De acordo com Khanna and Khun [21] , a poliamida 6 pode assumir duas formas cristalográficas, monoclínica α e monoclínica ou pseudo-hexagonal γ.…”