Günter R. Langecker

Strategies to improve the mechanical properties of high-density polylactic acid foams

In this study, different strategies to improve the mechanical properties of physically foamed high-density polylactic acid sheets were examined to produce polylactic acid foam sheets with tailor-made mechanical properties. The first part was the determination of the effect of different blowing agents (CO2 and N2) on the foam morphology. The second part of the study was the modification of the formulation. For this purpose, both a linear and a branching chain extender and a thermoplastic elastomer were used to improve the elongational properties (tensile modulus and strain at break) of the polylactic acid foam sheets. Additionally, the effect of the addition of cellulose fibers on the foam morphology and the mechanical properties was investigated. All experiments were carried out on a laboratory flat-film line. This extrusion line consists of a 30-mm single-screw extruder attached with a 250-mm flat sheet die. The results show a strong influence of the material formulation on the mechanical properties of the high-density foam sheets. Both the mechanical properties and foam morphology could be improved by the right material formulation. The addition of the thermoplastic elastomer leads to a better foam morphology and also to a reduced brittleness of the foam sheets. Furthermore, it could be demonstrated that cellulose fiber can be used as a nucleating agent for polylactic acid but causes a further decrease in the strain at break.

Rheological properties of wood polymer composites and their role in extrusion

The influence of the rheological behaviour of PP based wood plastic composites (WPC) has been investigated in this research by means of a high pressure capillary rheometer incorporating dies having different geometries. The rheological experiments were performed using slit and round dies. The influence of moisture content on the flow properties of the WPC has been investigated as well. It was observed that higher moisture contents lead to wall slippage effect. Furthermore, measured viscosity data have been used in flow simulation of an extrusion profile die. Also, the influence of different rheological models on the simulation results is demonstrated. This research work presents a theoretical and experimental study on the measurement and prediction of the die pressure in the extrusion process of wood-plastic composite (WPC).

Hochglanzoberflächen beim Spritzgießen

Kurzfassung Hochglänzende Spritzgussteiloberflächen werden aus Design- und aus funktionellen Gründen eingesetzt. Eine hervorragende Oberflächenqualität des korrespondierenden (Stahl-)Formeinsatzes ist eine Grundvoraussetzung, welche neben der Auswahl des Kunststoffes und der Prozessführung des Spritzgießens das gewünschte Erscheinungsbild der Formteiloberfläche beeinflusst. Im Rahmen eines multilateralen Forschungsprojektes am Polymer Competence Center (PCCL), Leoben wurden 12 unterschiedliche metallische Hochglanzpoliturgüten erstellt und über Topografiemessungen mittels Weißlichtinterferometrie, dreidimensionaler Rauigkeitsauswertung und 3 daraus abgeleiteten topografischen Qualitätsparametern eindeutig beschrieben. Letztere berücksichtigen die in unterschiedlicher lateraler Ausprägung auftretenden Oberflächendefekte Orangenhaut sowie Mattigkeit (Rauheit sowie Feinstrauheit). Weiters wurde die Abformung in die Kunststoffe Polypropylen und Polycarbonat untersucht.

Tailor-made high density PLA foam sheets – strategies to improve the mechanical properties

In this study, different strategies to improve the mechanical properties of physically foamed high density polylactic acid (PLA) sheets were examined to produce PLA foam sheets with tailor-made mechanical properties. The first part was the determination of the influence of the blending of PLA with polybutylene succinate (PBS) on the properties of the high density foam sheets. Additionally, the influence of the PBS on the rheological properties was investigated with a cone plate rheometer. The second part was to manufacture multilayer films with a physically foamed middle layer and highly filled skin layers. The foamed sheets were characterized in terms of mean cell size, cell density, density and surface roughness. The experiments were carried out on lab scale multi-layer extrusion line.