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The aim of this study was the investigation of the use of modified talcum for supporting crosslinking and as novel nucleating agent for physical foaming of polyethylene. For the modification of the talcum, a thermal initiator was linked to the talcum surface. During the extrusion process, the initiator decomposes, and gas and radicals are formed. The gas generates the nucleation of cells and the radicals support the crosslinking process between the polymer chains. The modification of the talcum was performed in three steps: The first step was the grafting of alkoxysilanes onto the talcum surface. The second step was the chlorination of the thermal initiator for an easier linkage, and the last step was the linking between the initiator and the silanes grafted onto the talcum surface. For this study, two investigations were carried out. One investigation was the analysis of the crosslinking effect with the modified talcum. For this purpose, polyethylene plates were compression molded and the viscoelastic properties were measured with a parallel plate rheometer. The use of the modified talcum led to a higher crosslinking density. The second investigation was the physical foaming experiment in an extrusion process with nitrogen as blowing agent using both a pure and the modified talcum as nucleating agents. The foamed samples were characterized in terms of density, cell size and cell density, and compared with each other. The blend with the modified nucleating agent indicated a foam structure with a smaller mean cell size and a lower density compared to the use of the pristine nucleating agent.

The long-term stability of thermally conductive high-density polyethylene (HDPE)-based compounds as phase-change material (PCM) is investigated. For this purpose, the HDPE's thermal conductivity (TC) is first enhanced via compounding two different filler types (expanded graphite and aluminum) into the polymeric matrix. Bulky specimens of these compounds are then stored in air for up to 7289 h in the melt state to investigate the compounds' long-term stability as PCM. Their thermo-oxidative/thermal stability and their ability to maintain the isotropic material character (homogeneous distribution of the incorporated particles) is investigated. The compounds' degradation behavior is monitored via Fourier-transform infrared spectroscopy and the maintenance of the homogeneous filler distribution is examined via a combined differential scanning calorimetry/thermogravimetric analysis mapping of each exposed specimen. The storage capacity decreases minimally after 7289 h of exposure. Furthermore, the incorporated filler particles enhance the thermo-oxidative stability of HDPE as PCM. Consequently, thermally conductive HDPE is a highly interesting PCM.

In injection molding simulation the phase change from melt to solid state is usually simplified by using a so called transition temperature. In the present work, the transition temperatures of several amorphous and semicrystalline polymers were determined using DSCruns at different cooling rates. The transition temperature was described as a function of cooling rate. The obtained transition temperatures of the semicrystalline polymers were used in injection molding simulations with the commercial software package Autodesk Moldflow Insight 2010 to calculate the shrinkage and warpage of box-shaped test parts. The simulation results were compared with the experimental values of optically measured injection-molded boxes. The results showed a strong influence of the transition temperatures on the simulation results of a 3D model and a very low influence for a 2.5D model. Transition temperatures obtained at higher cooling rates improved the 3D simulation results for several dimensions.