Yash P. Khanna

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 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.

The glass transition and molecular motions of poly(chlorotrifluoroethylene)

Abstract Molecular motions in poly(chlorotrifluoroethylene) have been studied over the range −150 to +200°C by thermal/mechanical techniques with the specific intent of clarifying the glass transition (Tg) of this polymer. An extremely broad Γ relaxation, centred at ≈ −15°C and associated with an activation energy of 17 kcal mol−1, is proposed to be a predominantly amorphous phenomenon involving small scale motions. A β relaxation peak at ≈ 95°C with an activation energy of 64 kcal mol−1 represents the amorphous segmental mobility and its onset at 75 ± 2°C is assigned as the Tg. This value for the Tg of poly(chlorotrifluoroethylene) is supported by dynamic mechanical, thermomechanical and differential scanning calorimetric techniques. We are unable to support the existence of an α relaxation at 140–150°C, i.e. Tg

The glass transition of Cu78Ni6P7Sn9 amorphous alloy ribbon

Etude experimentale par calorimetrie differentielle a balayage et par mesures des proprietes mecaniques