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.

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