Extrusion technology is one of the most prominent methods for processing polymers. The shape of polymer pellets plays an important role in conveying solid material through the extruder and thus directly influences the mass flow rate. In the course of this article, the influence of the pellet shape of a polypropylene homopolymer on the processing conditions using a smooth barrel single‐screw extruder is evaluated. Especially the mass flow rate, the melt temperature, and the pressure build up in the barrel are investigated. It can be shown that processing long cylindrical pellets leads to a higher mass flow rate than comparable experiments with virgin pellets or short cylinders. Additionally, screw cool and pull‐out tests, measurements of the external coefficient of friction as well as the bulk density of the different pellet geometries are performed. The interaction of the screw geometry and the pellet shape is found to have the biggest influence. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 41716.

Short glass fiber reinforced polymers are used in many different applications due to their good property profiles. These properties are directly correlated with the fiber length present in the final composite, which can be influenced through the process. Therefore, the aim of this work was to investigate the influence of processing temperature and screw configuration in compounding on the properties of glass fiber reinforced polypropylene. On the one hand, the barrel temperature was varied between 180°C and 260°C and, on the other hand, four different screw configurations were applied using a standard temperature profile. Specimens were produced by injection molding, which were tested via mechanical characterization, density, and fiber length measurements as well as morphology through microscopical analysis. We found, that with higher barrel temperatures and screw configurations bringing lower shear into the melt the glass fiber length is preserved better, thus resulting in improved composite properties. Also the interfacial interaction is not influenced within the investigated parameters, as was checked via the application of a micromechanical model in composite strength. POLYM. ENG. SCI., 59:1552–1559 2019. © 2019 Society of Plastics Engineers

In this work, the relation of injection molding parameters to the mechanical properties of various polypropylene grades is investigated to find the optimal processing parameters to minimize weld‐line effects like reduced mechanical and/or optical performance. Injection molded test specimens of five polypropylene grades with different melt flow rates were characterized for their mechanical behavior and compared with equal‐shaped specimens with a colliding weld line in the middle of the specimen. For the production of these weld‐line specimens, a special mold was used and injection molding parameters were systematically varied, tensile (ISO 527‐2) and impact (ISO 179‐1/1eU) properties were measured, and statistical analyses were performed to gain insight on the correlation between melt flow rate and weld‐line behavior. It showed that mechanical properties of specimens with weld lines can be influenced by the processing parameters, but the effect is limited. Positive correlations were found between tool temperature and tensile modulus and strength. Polypropylene grades with low melt flow indexes seem to be more susceptible to weld‐line‐induced property reductions. In a second test series similar to the pure PP investigations, glass‐fiber‐ and talc‐filled PP were used to gain insight into the weld‐line behavior of PP composites. In addition to mechanical characterization, optical and scanning electron micrographs were taken of the weld‐line areas. It was found that the reinforcing particles align along the melt flow front in the weld‐line area. As a result, the mechanical performance of weld‐line specimens is poor. Injection molding parameters were found to have only a small effect.

Interfacial adhesion of basalt and glass fibre reinforced polypropylene composites was studied using microdebond testing technique. A focus was put on a simple approach of applying extruded thermoplastic films as a matrix material for microdroplet formation. The ability of different viscosity and thickness polypropylene films to form symmetrical droplets under a temperature range of 200–240℃ was evaluated. Emphasis was put on polypropylene matrix chemistry, silane fibre surface treatment and testing loading rate impact on interfacial performance change in polypropylene-basalt fibre and polypropylene-glass fibre microcomposites. It was found that it was possible to obtain high symmetrical droplet yield out of polypropylene films of melt flow rate 50 and 125 g/10 min and 55–85 µm thickness at 240℃. The presence of maleic anhydride grafted polypropylene coupling agent increased the interfacial shear strength significantly. Microcomposites with glass fibre had higher interfacial shear strength in comparison with the used basalt fibre, mainly due to the difference in their sizing. Various silane-based fibre surface coatings did not result in significant interfacial adhesion changes. Polypropylene-glass fibre microcomposite interfacial shear strength at 0.5, 3.0 and 10.0 mm min–1 loading rates had similar values with high maximum pull-out force scatter at 0.5 and 3.0 mm min–1 loading rates and low scatter at 10.0 mm min–1.