Steam-Chest Molding of Expanded Polypropylene Foams. 1. DSC Simulation of Bead Foam Processing

Abstract

To investigate the evolution of melting behavior during the steam-chest molding process of expanded polypropylene (EPP) bead, a differential scanning calorimetry (DSC) test involving fast heating, isothermal treatment, and fast cooling was used to simulate the bead foam processing. The EPP bead foam had two original melting peaks: a low melting peak, T mlow , and a high melting peak, T mhigh . A new melting peak, T mi , was induced in the DSC curves, resulting from the heating process, when the treatment temperature was 80-150 °C. The T mi was about 7 °C higher than the treatment temperature and tended to increase linearly with the increased treatment temperature. A new melting area and further a melting peak, T mc , were observed in DSC curves, resulting from the cooling process, when the treatment temperatures were higher than 135 °C. The high sensitivity of the T mi and T mc to treatment temperature provided a clue to the actual temperature inside the mold during the steam-chest molding process. Different steam pressures were applied during EPP bead processing, and the melting behavior of molded EPP samples was measured to check the processing thermal history. A comparison study was done between the DSC simulations and the actual results to understand the melting behavior evolution of EPP bead foam during processing. Some fundamental issues in the steamchest molding processing, such as the actual steam temperature, the temperature gradient across the mold cavity, and the accurate pressure parameter used to describe the actual processing temperature were also studied based on the DSC simulation.

Improved cell morphology and thermal properties of expanded polypropylene beads by the addition of PP with a high melting point

“…The melting properties of the bead foams with different HPP content at different T f are shown in Figure ; Table shows the corresponding parameters. As seen, all samples exhibit double melting behaviors, important for the steam‐chest molding . During the soaking and foaming, the polymer crystals partially melted and while a portion remained crystalline.…”

“…In the steam‐chest molding of EPP, the molding temperature is usually chosen to be between T mlow and T mhigh . In this range, the low temperature crystals melt to form the interbead bonds and the high temperature crystals maintain the mechanical properties of final materials, especially the stiffness, which are very important in applications . A high X clow / X chigh would favor the formation of interbead bonds while a low X clow / X chigh would endow final materials with high stiffness.…”

“…The enthalpy and temperature of the first melting peak directly relate to the processing conditions for interbead bonding and the characteristics of the second melting peak relate to the mechanical properties of the final material. The dual peaks often occur in the autoclave foaming process, during which a new peak is created . The present main focus is to adjust the ratio of high and low melting peaks and to increase the difference of the two melting peaks which would improve the properties of EPP and widen the steam‐chest molding temperature .…”

Effect of stereocomplex crystal on foaming behavior and sintering of poly(lactic acid) bead foams

“…The PLA blends and their bead foams were heated to 200 ∘ C at a rate of 10 ∘ C min −1 to study the effect of PDLA content, branching structure and foaming condition on the Sc and crystallization of PLA. The and Sc crystallinity of PLA, , can be calculated using Eqns (1) and (2):…”

“…Bead foaming manufacturing is a subtle technology characterized by producing low-density foam and complex product shape, simultaneously. [1][2][3] Due to its continuous manufacturing process and excellent properties of final product, the development of bead foam has been continually attracting attention. Especially, expanded poly(lactic acid) (EPLA) has become a hot spot in both research and industry.…”