Formation of Double Melting Peak of Poly(propylene-co-ethylene-co-1-butene) during the Preexpansion Process for Production of Expanded Polypropylene

Abstract

A new additional melting peak is formed on the DSC thermogram as a result of preexpansion of poly(propylene-co-ethylene-co-1-butene) (terpolymer). The new melting peak appears at ∼152 °C, which is ∼12 °C higher than the tail end temperature (offset temperature) of the pristine terpolymer to exhibit a double melting peak. The origin of the new melting peak is traced to melting and recrystallization of less perfect crystals of the terpolymer at the preexpansion temperature, which situates usually between the onset and the offset temperature of the melting peak, contrary to the common presumption that the less perfect crystals are melted leaving the more perfect crystals intact during the preexpansion step and that the peak at ∼152 °C comes from melting of the more perfect crystals. The higher the temperature to which the terpolymer was heated above the offset temperature, the longer time of annealing was required at the preexpansion temperature for the new peak to appear. Once the terpolymer was completely melted by heating to 175 °C, at least 24 h of annealing was needed to show up the new melting peak, indicating that crystallization with homogeneous nucleation takes place much more slowly than that with self-nucleation.

Development of polylactide bead foams with double crystal melting peaks

“…However, after annealing, the melting peak of these crystals started to shift to higher temperatures (above T m ) due to the crystal perfection that occurred during annealing [28,29].…”

“…This concept has been used for the existing expanded polypropylene (EPP) bead foaming technology [24e27] but has not been used for other materials, especially for the EPLA bead foams. Specifically, crystals with a high melting temperature form during the isothermal saturation step in the batch-based bead foaming process [24e26], through crystal perfection [28,29]. In the steam-chest molding process (that is, the process used to produce three-dimensional foam products), sintering among the beads occurs when the steam temperature is between the high and low melting peaks.…”

Evolution of double crystal melting peak in polypropylene foam assisted by β‐nucleating agent and supercritical CO2

“…[6][7][8][9][10] In this method, the rearrangement and perfection of PP crystal during the isothermal treatments could be employed to form another new crystal melting peak with higher temperature. [6][7][8][9][10] In this method, the rearrangement and perfection of PP crystal during the isothermal treatments could be employed to form another new crystal melting peak with higher temperature.…”

A novel technology to manufacture biodegradable polylactide bead foam products

“…Bead foaming has been introduced as a continuous foam manufacturing technology to produce low-density foam products with three dimensional complex geometries [25][26][27][28][29][30][31][32][33][34][35][36][37][38]. In this technology, numerous low-density foam beads are molded into the desired final product shape.…”

“…This will provide bead foam products with superior mechanical properties while a short/less expensive processing route is applied. We should also mention that this manufacturing technique has been used to produce expanded polyolefins, specifically expanded polypropylene (EPP) bead foams [25][26][27][28][29][30][31][32] but has not been utilized for other materials, especially for PLA with low melt strength and slow crystallization kinetics.…”