A study on multiple melting of isotactic polypropylene

Abstract

Multiple melting characteristics of a highly isotactic polypropylene (iPP) were studied by means of differential scanning calorimetry (DSC). Double melting characteristics were observed on melting iPP crystallized isothermally at temperatures ranging from 110 to 140°C. iPP crystallized below and above 125°C exhibited different double melting characteristics from each other. For iPP crystallized below 125°C, the single melting peak split into two peaks during slow DSC heating scans without changing the total crystallinity in the polymer. On the other hand, the double melting endotherm of iPP crystallized above 125°C seemed to come from two preexisting crystal fractions having different Tm. There existed an optimum annealing temperature range where the five‐minute annealing of iPP raised Tm of the polymer significantly. The treatment also increased the crystallinity of iPP crystallized isothermally at 110°C by 12%.

The dynamic crystallization and multiple melting behavior of polypropylene in the in‐reactor alloy: A differential scanning calorimetry study

“…18 Later on, the effect of lamellar thickening mechanism has been confirmed experimentally by Mezghani et al 20 Kim et al studied the multiple melting behavior of iPP by annealing the sample at different temperatures, and attributed the double peaks to the melting of two different preexisting crystals originating from molecules with different molecular weights. 21 Despite the controversy in the past, a general consensus has been achieved among most of the authors in the recent couple of years. The multiple melting behavior of iPP can be explained from two aspects.…”

Effects of the addition of small amounts of a thermotropic liquid crystalline polymer on the processing characteristics of polyphenylene oxide–polyamide alloys

“…The lower temperature endotherms correspond to the melting of original "imperfect" crystals initially formed during cooling, whereas the higher temperature is associated with the melting of crystals obtained during recrystallization. 24 This so-called multiple melting behavior has been reported for many other polymers, including PP, 25 nylons, 24−26 PET, 27 and PEEK. 28 For the system examined, the maximum of the lower melting peak T m 1 tends to decrease with the increase in the LCP content in the blends, indicating a reduction in the perfection of crystals formed during the cooling cycle (Table I).…”

Crystallization and dynamic mechanical properties of polypropylene/polystyrene blends modified with maleic anhydride and styrene

“…It is much easier for SMA than MAH to graft with PP; therefore, the degree of grafting of MAH increases, and more MA-g-PP is formed in situ. 41,43,44 The addition of St and MAH had a significant effect on the crystallization behavior of PP in the blends because of the formation of MA-g-PP and the heterogeneous nucleation of MA-g-PP on PP. 45,46 When the comonomer concentration in the PP/PS blends was lower, the variability of the crystallization behavior of PP was low.…”

“…As a result, there was no MA-g-PP in the blends, or its concentration was low because of the low grafting rate between MAH and PP. 41 The main grafting product was MA-g-PS, which hardly changed the crystallization and melting behavior of PP.…”