Abstract
We explore the foam extrusion of expanded polypropylene with a long chain branched random co-polypropylene to make its production process simpler and cheaper. The results show that the presence of long chain branches infer high melt strength and, hence, a wide foamability window. We explored the entire window of foaming conditions (namely, temperature and pressure) by means of an ad-hoc extrusion pilot line design. It is shown that the density of the beads can be varied from 20 to 100 kg/m3 using CO2 and isobutane as a blowing agent. The foamed beads were molded by steam-chest molding using moderate steam pressures of 0.3 to 0.35 MPa independently of the closed cell content. A characterization of the mechanical properties was performed on the molded parts. The steam molding pressure for sintering expanded polypropylene beads with a long chain branched random co-polypropylene is lower than the one usually needed for standard polypropylene beads by extrusion. The energy saving for the sintering makes the entire manufacturing processes cost efficient and can trigger new applications.
Highlights
Polymer bead foams are produced by a sintering process of foamed polymer beads
We explore the foam extrusion of expanded polypropylene with a long chain branched random co-polypropylene to make its production process simpler and cheaper
We present insights into the process and the characterization of the foamed PP beads produced by extrusion using isobutane and CO2 as blowing agent
Summary
Polymer bead foams are produced by a sintering process (usually, steam chest molding) of foamed polymer beads. The sintering process allows us to obtain complex shapes with low density, a unique feature among all the technologies to produce polymer foams [1]. For this reason, polymer bead foams have attracted enormous attention from various foam industries, and they are used in automotive, leisure, sport, and long-life packaging. In the early 1980s, expanded beads of polypropylene (ePP) were introduced into the market and, since their applications have been constantly growing [2]. EPP applications in the automotive sector have been spreading rapidly (i.e., bumpers, exterior and interior energy absorbers, door panels, knee protection, tool kits, trunk liners, console components, seat backs, bolsters etc.) with the goal to minimize car weight and increase safety. The current green revolution asks for more sustainable polymers, and polypropylene (PP) could be a good candidate to replace polystyrene (PS) because it has a more advantageous Life Cycle Assessment for many categories (e.g., Ozone depletion, Climate change, Water resource depletion etc.) [2]
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