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Rapid rotational foam molding of polyethylene integral-skin foamed core moldingsChristian, Kimberly Anne 01 June 2009 (has links)
This thesis focuses on the design, development, and evolution of a novel patent-pending
plastic processing technology entitled “Rapid Rotational Foam Molding” with special
emphasis on the processing of polyethylene (PE) integral-skin foamed core moldings.
Rapid Rotational Foam Molding is a technology deliberately designed to address the
intrinsic disadvantage of conventional rotational foam molding, i.e., its very long cycle
times. In this context, a physical system that exploits the positive synergistic effects of
innovatively combining extrusion melt compounding and rotational foam molding was
designed and built. The fundamental processing steps of this system comprise (i)
rotationally molding a non-foamable PE powder in a lab-scale oven while, (ii)
simultaneously melt compounding and foaming a pre-dry blended foamable PE and
chemical blowing agent (CBA) formulation in an on-line lab-scale extruder, and then (iii)
filling the newly created foaming material into the non-chilled hollow article thereby
created in the mold through a special interface.
Two varieties of PE resins ranging from linear low density PE (LLDPE) to high
density PE (HDPE) were selected for experimentation with melt flow rates (MFR)
ranging from 2.0 to 3.6 g/10min. The implemented CBA was Celogen OT. The
materials were characterized using thermal analysis techniques such as differential
scanning calorimetery (DSC) and thermogravimetric analysis (TGA) to ensure their
correct operating temperatures ranges. Scanning electron microscopy (SEM) was utilized
for characterizing the quality of the foam samples and achieved skin-foam interface for
the final moldings. Improvements to the achieved molding quality were accomplished
through various system and process modifications described throughout this research
work.
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Rapid rotational foam molding of integral skin polypropylene cellular compositesAbdalla, Emad 01 May 2009 (has links)
Rapid Rotational Foam Molding (RRFM) is a novel patent-pending process that was
designed and developed to maximize the synergistic effects resulting from the deliberate
combination of extrusion and rotational foam molding and thereby serve as a time-andenergy
efficient technology for the manufacture of integral-skin rotationally molded
foams of high quality. This thesis presents a thorough study of the scientific and
engineering aspects related to the evolution of the RRFM process and its feasibility. This
innovative processing technology was assessed and verified through a battery of planned
experimental trials conducted utilizing an in-house custom-built industrial-grade lab-scale
experimental setup. The experimental trials involved a variety of polypropylene (PP)-
based foamable formulations with a chemical blowing agent (CBA) that were
compounded and processed by utilizing an extruder and then foamed and injected as a
foamed core, instantly, into the cavity of a suitable non-chilled rotationally molded
hollow shell made of non-foamed pulverized PP grades. The investigated mold shapes
included a cylindrical shaped mold and a rectangular flat shaped mold. The obtained
moldings were examined for the quality of the skin surface, the skin-foam interface, and
the achieved foam morphologies that were characterized in terms of foam density,
average cell size, and average cell density. Optimal processing parameters were
successfully determined for three different PP skin-foam formulation combinations. The
accomplished reduction in processing time and energy consumption by implementing
RRFM were substantial. A variety of processing impediments that hindered the efficiency
of the single-charge conventional rotational foam molding practice were resolved by
implementing RRFM; these include: the foam/skin invasion into the skin/foam layer of
the manufactured article and the premature decomposition of CBA during compounding
or subsequent rotational foam molding processing steps. / UOIT
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