It is of great importance for polymer processing whether and how viscosity influences the wettability of tool surfaces. We demonstrate the existence of a distinct relationship between the contact angle of molten polymers and zero shear viscosity in this paper. The contact angle of molten polypropylene and polymethylmethacrylate on polished steel was studied in a high temperature chamber using the sessile drop method. A high pressure capillary rheometer with a slit die was employed to determine the shear viscosity curves in a low shear rate range. A linear relation between the contact angle and zero shear viscosity was obtained. Furthermore, the contact angle and the zero shear viscosity values of the different polymers were combined to one function. It is revealed that, for the wetting of tool surfaces by molten polymers, a lower viscosity is advantageous. Furthermore, a model based on the temperature shift concept is proposed which allows the calculation of the contact angle of molten polymers on steel for different temperatures directly from shear viscosity data.

The properties of short-fiber-reinforced composites depend on the fiber length of the reinforcing fibers. This fiber length is typically influenced by processing to different extents. In this work, we investigate the influence of processing, i.e., the influence of residence time achieved via different dosing points in compounding, and the fiber content on the fiber length and mechanical properties of short-carbon-fiber-reinforced polypropylene. We found that, with increasing fiber content, the fiber length decreases from 900 to 300 µm after compounding and from 500 to 250 µm after injection molding. Additionally, a decrease in residence time in the compounder leads to an increase in the fiber length of approx. 300 µm compared to the longer residence time. This is later reduced by the injection molding step, but the longer fibers are still longer in the final molded test specimen, thus resulting in a 5–10% increased tensile strength and elastic modulus as well as an some increase in impact strength. As the injection molding step showed considerable fiber length reduction (down to 250 µm), further investigations of injection molding should be undertaken to preserve fiber length better for the increased performance of these composites.

Short-fiber reinforcement is a potent approach to improving the material properties of injection-molded parts. The main consideration in such reinforced materials is to preserve the fiber length, as this is the major influence on the properties of a given composite. The aim of this work was to investigate the different influencing parameters in injection molding processing on the properties of short carbon and glass fiber-reinforced polypropylene. We investigated parameters like melt temperature and back pressure, but also machine size and pre-heating regarding their influence on the tensile properties. We found that adjustments of melt temperature and back pressure only yield small improvements in the fiber length and the tensile properties, also depending on machine size, but a pre-heating step of the granules can significantly improve the properties.

A homogenous melt is the prerequisite to achieve the demanded product quality in single screw plasticising technology. At higher screw speeds and mass flow rates solid particles can occur in the melt. Dispersive mixing elements are often used to improve the melt quality. Calculation models are necessary for designing mixing elements in the right way. A new model for the often used fluted mixing sections like axial and spiral Maddock-elements and Z-elements is presented in this paper. The calculation model is reduced to a single pair of inlet and outlet flute, connected by the shearing gap. Especially in spiral Maddock mixers the longitudinal flow in the flutes is a combined pressure and drag flow but in axial Maddock mixers pure pressure flow occurs. In the shearing gap a combined pressure and drag flow can occur. The leakage flow through the flight clearance is also considered. Geometry functions are introduced for considering the rectangular or circular segment shaped cross section of the flutes. The viscosity is shear rate and temperature dependent, the channel height as well as the channel width can vary along the mixing element. The model allows the calculation of the longitudinal pressure profile in the inlet and outlet flutes, the total pressure drop and the shear stress distribution in the shearing gap. Mixing sections sometimes show a too high pressure consumption and insufficient shearing efficiency. Therefore a geometry optimization method for axial Maddock mixing heads is presented in this paper.