ABSTRACT This study systematically investigates the influence of annealing temperature () on the thermomechanical behavior and dimensional stability of carbon fiber‐reinforced polyethylene terephthalate (PET‐CF) components manufactured via fused filament fabrication (FFF). Test specimens were subjected to thermal post‐processing at temperatures ranging from 145°C to 225°C. Differential scanning calorimetry (DSC) was used to analyze the melting behavior and degree of crystallinity. To evaluate thermal softening behavior, Vicat softening temperature (VST) measurements were performed. The DSC analysis revealed the formation of a secondary endothermic melting peak at the lower melting temperature that exhibits a linear correlation with the annealing temperature. While the total crystallinity remained largely unaffected, annealing significantly shifted the onset of softening to higher temperatures compared to untreated samples. Furthermore, the thermal post‐processing significantly improved the repeatability of the VST measurements. However, the improvements in thermal resistance were accompanied by increased longitudinal and transverse shrinkage, with the most pronounced dimensional shrinkage occurring in the build direction ( Z ‐axis). The results demonstrate that while annealing is an effective strategy for enhancing the heat resistance and reliability of FFF‐printed PET‐CF components, industrial applications must balance the gains in thermal stability against the corresponding loss in dimensional precision.

Antibacterial properties of components are increasingly becoming an important challenge in material development especially in polymer technology. A well-known additive with which an antibacterial effect can be achieved is the metal oxide titanium dioxide. The aim of this research work was to investigate possible influences on the flexural properties of additively manufactured components resulting from the addition of titanium dioxide as an antimicrobial additive. Compounds with 5 %, 10 % and 15 % titanium dioxide and polyamide 12 as matrix material were produced. Three-point bending test specimens were fabricated out of these compounds, anaylsed and the results were compared with specimens made of virgin polyamide 12. The investigations show a general loss in ductility compared to the virgin polyamide 12. A comparison of the different titanium dioxide contents shows no clear change in the flexural stress at conventional bending. The flexural strain at break seems to decrease for higher titanium dioxide contents. Antibakterielle Eigenschaften von Bauteilen werden zunehmend zu einem wichtigen Bestandteil in der Werkstoffentwicklung, insbesondere in der Polymertechnologie. Ein bekannter Zusatzstoff, mit dem eine antibakterielle Wirkung erzielt werden kann, ist das Metalloxid Titandioxid. Ziel der vorliegenden Forschungsarbeit war die Untersuchung m & ouml;glicher Einfl & uuml;sse auf die Biegeeigenschaften von additiv gefertigten Bauteilen durch die Zugabe von Titandioxid als antimikrobielles Additiv. Hierf & uuml;r wurden Compounds mit 5 %, 10 % und 15 % Titandioxid und Polyamid 12 als Matrixmaterial hergestellt. Aus diesen Compounds wurden Biegeproben gefertigt, untersucht und die Ergebnisse mit Proben aus reinem Polyamid 12 verglichen. Die Untersuchungen zeigen einen Verlust an Duktilit & auml;t durch Zugabe des Titandioxids gegen & uuml;ber den Proben aus reinem Polyamid 12. Werden die verschiedenen Titandioxidgehalte miteinander verglichen, so konnte keine deutliche Ver & auml;nderung der maximalen Biegespannung bei konventioneller Biegung festgestellt werden. Die Bruchdehnung scheint bei h & ouml;heren Titandioxidgehalten erneut abzunehmen. Decrease of the ductility when using titanium dioxide compounds in selective laser sintering. This paper determines the effects on the flexural properties when using titanium dioxide as an antimicrobial additive with polyamide 12 powder as matrix material. image

Effects of global warming can now be seen and felt more than ever, especially in the Alps. The Alps and other mountains are massively affected by glacier retreat and permafrost degradation. Sustainable production, widespread recycling and a closed-loop product life cycle to reduce greenhouse gas emissions are becoming a major concern. This study serves as a preliminary identification of the material and the thermal properties of old climbing ropes with the aid of further developing a recycling process. Old climbing ropes were collected and investigated using dynamic differential scanning calorimetry and thermogravimetric analysis. The rope core and sheath were investigated separately. The research confirmed the purity of the material, i.e. that core and sheath are made of the same material for most of the ropes. Polyamide 6 and polyamide 66 were identified as the manufacturing materials. The determined characteristic thermal properties like the melting temperature could be used for the development of the thermo-mechanical recycling process.

Liquid silicone rubber (LSR) is characterized by a wide range of advantageous properties and is therefore used in many branches and industries. However, the material is difficult to recycle due to the non-reversible cross-linking reaction. A promising approach to recycle the already cross-linked (post-industrial) waste is the mechanical recycling of LSR via grinding and addition of the powder as filler in virgin material. This research focused on the processing of such LSR-powder-compounds via injection molding and the influence of the powder content on mechanical properties. Compounds of virgin LSR and ambient ground powder were prepared and injection molded. Both the processability and the mechanical properties were analyzed. Compounds of up to 40 wt% powder content could be processed with standard injection molding machine equipment without any noticeable issues. The results show a similar compression set for the virgin as for the recycled compounds. Hardness decreases slightly but constantly. Tensile strength and elongation at break are at similar levels for all powder added compounds and drop only by 16.6% and 12.6% compared with the virgin LSR. The results are promising and should be the basis for further and more detailed investigations to industrialize the mechanical recycling of LSR.Highlights Processing on standard injection molding machine with standard parameters. Up to 40 wt% recycled silicone powder content. Using recycled silicone particles has no effect on compression set. Tensile strength and elongation at break decrease only by 16.6% and 12.6%. Schematic representation of the processing of mechanical recycled liquid silicone rubber powder via injection molding. image

With the help of computational fluid dynamics (CFD) simulations a nozzle system (top nozzle system) for hot gas welding, which encloses the weld seam during heating, was developed. The significantly more controlled flow behavior of the hot gas improves the processing window, increases the reproducibility and achieves a more efficient heating of the polymer weld seam with inclination angles up to 60°. The heating behavior and weld strength are investigated on three types of plate specimens with varying inclination angles. The investigations are carried out on a series-production hot gas welding system with PA6-GF30 and a PA66-GF35. Stainless steel additive manufactured top nozzle systems for 0°, 15°, 30°, 45° and 60° inclination angles are tested. With the optimized top nozzle system, weld seams with inclination angles of up to 60° can be reproducibly joined thanks to the wide processing window without a significant reduction of the component strength.

The processing of optical liquid siliconerubber (LSR) formulations is associatedwith significant quality issues and high rejection rates. Often, the quality issuescan be attributed to deviations in LSR dosing. To address these issues, specificmixing ratios of components A and B that deviate from the standard 1:1 ratiowere intentionally created. These mixtures were characterized via differentialscanning calorimetry, rheometer, and Fourier-transform infrared spectroscopy.The mixtures were then processed via injection molding and mechanical proper-ties such as shrinkage, density, hardness, and tensile properties were determinedand analyzed. The results show that deviating mixing ratios for optical LSR have asignificant influence on processing in terms of shifts in cross-linking temperatureand exothermic energy released, viscosity, and cavity pressure, as well as on thefinal component properties in terms of varying shrinkage, density, hardness, ten-sile strength, and elongation at break. This study shows that even small deviationshave a major influence and should therefore be avoided. The requirements for theaccuracy of the dosing system with regard to the mixing ratio must therefore bevery high. In practice, such deviationsin the mixing ratios are most likely tobe detected in geometry via shrinkage, hardness, or tensile properties.

Climate change is one of the significant challenges of the 21st century. To achieve climate goals a change in plastic waste management needs to be implemented. This research examines the potential of thermo-mechanical recycling of plastic waste, focusing on agricultural binding twines made from polypropylene. Old binding twines from agriculture were collected and recycled with a twin screw extruder. The ageing behaviour of the recyclate in terms of multiple recycling is examined in detail with tensile tests and melt volume rate measurements. The findings indicate a general degradation in mechanical properties and a decrease in viscosity due to molecular chain scission. Despite these degradations, the material remains processable, indicating the potential for continued recycling loops.

Antimicrobial properties of plastic components are an important part of polymer engineering. One commonly used additive with an antibacterial effect is titanium dioxide. The aim of this study is to investigate the influences on the mechanical properties resulting from the addition of titanium dioxide as an antimicrobial additive and the processing of the compounds with selective laser sintering. Compounds with 5 %, 10 % and 15 % titanium dioxide and polyamide 12 as matrix material are fabricated. Tensile test specimen are produced from the compounds, examined and the results compared with virgin polyamide 12. The investigations show a general loss in the ultimate tensile strength compared to the virgin polyamide 12. Comparing the different titanium dioxide contents with each other, an increasing tensile strength with increasing titanium dioxide content of the compound can be examined. A decreasing elongation at break and thus a decreasing ductility can also be observed. Furthermore, the results of the tensile test show a stiffening effect, i. e. an increase in the elastic modulus due to the addition of titanium dioxide.

Global warming has increasingly drastic consequences, especially in the Alps but also in the rest of the world. To reduce greenhouse gases, widespread recycling of plastic waste is becoming an essential necessity. This research investigates a possible recycling process for old climbing ropes made out of polyamide 6. Old climbing ropes were collected and processed with a twin screw extruder to fabricate recycled granulate. Investigating different shredding techniques showed that pretreatment with liquid nitrogen or water and liquid nitrogen are proven to be insufficient. A good shredding was achieved using a shredding-granulator. Tensile test specimens had been fabricated out of the recycled granulate using an injection moulding process. The tensile tests showed a sufficient material quality and higher tensile strength than the virgin polyamide 6 used for the comparison. Tensile strength and Young's modulus increased, whereas the elongation at break decreased. A previous cleaning of the old ropes showed slightly better material properties of the recycled granulate.

The processing of liquid silicone rubber (LSR) in the injection molding process to molded parts offers high economic potential due to its great scalability. Unlike the well-researched and understood injection molding process of thermoplastics, LSR still lacks basic process knowledge. The cavity pressure curve shows a completely different pattern, as the cold LSR expands strongly once placed in the hot mold due to volume dilation. During processing of LSR exothermic and irreversible cross-linking, occurs. In this work, a method is introduced to display the cross-linking reaction in the cavity pressure curve. Using a self-developed testing device and conventional differential scanning calorimetry measurements, a correlation between cross-linking and the pressure signal can be demonstrated. A typical deflection is evaluated in the pressure curve by differentiating, which is attributed to the cross-linking. The relationships established are confirmed by pressure measurements in the mold during the processing of LSR in the injection molding process. The knowledge gained contributes to a better understanding of the process, helps to optimize existing processes and save resources. Existing cavity-pressure-measuring-systems are to be supplemented by an evaluation logic and thus, in addition to cycle time optimization, process variations are to be detected, energy consumption optimized and quality ensured and verified.

AbstractAntimicrobial properties of plastic components are an important part of polymer engineering. One commonly used additive with an antibacterial effect is titanium dioxide. The aim of this study is to investigate the influences on the mechanical properties resulting from the addition of titanium dioxide as an antimicrobial additive and the processing of the compounds with selective laser sintering. Compounds with 5 %, 10 % and 15 % titanium dioxide and polyamide 12 as matrix material are fabricated. Tensile test specimen are produced from the compounds, examined and the results compared with virgin polyamide 12. The investigations show a general loss in the ultimate tensile strength compared to the virgin polyamide 12. Comparing the different titanium dioxide contents with each other, an increasing tensile strength with increasing titanium dioxide content of the compound can be examined. A decreasing elongation at break and thus a decreasing ductility can also be observed. Furthermore, the results of the tensile test show a stiffening effect, i. e. an increase in the elastic modulus due to the addition of titanium dioxide.

Liquid silicone rubber (LSR) is becoming increasingly popular due to its chemical, UV, and heat resistance as well as its excellent optical properties. However, there is currently a lack of research and understanding of the rheological properties of the material. During the processing of liquid silicone rubber, the material can assume different rheological states. In the present work, both the physical and the chemical gel behavior are investigated rheologically. For this purpose, measurements are carried out with a rotational rheometer and a high-pressure capillary rheometer. Depending on the temperature and pre-shear rate, times are given for the physical gel point, after which a significantly destroyed physical network is recovered. Investigations at higher temperatures, which lead to chemical crosslinking and, therefore, to a chemical gel point, resulted in a representation of the temperature-dependent chemical gel point. The presented results serve as a material database for reliable simulations.

Additive manufacturing is one of the key technologies for the future production of complex and individualised components. One of the most challenging questions to minimize the production cost is the reuse of the powder leftover after the building process. This study investigates the influence on the mechanical properties when reusing the leftover powder out of the process chamber up to four times. Tensile test specimens are produced and investigated. The results show a decreasing in the ultimate tensile strength with repeated reuse of the leftover powder. After four times of reuse the strength increases again. This cannot be explained by the literature and has to be verified in further investigations. The investigations reveal a high mechanical anisotropy as the strength highly depends on the component orientation in the process chamber. The particle shape does not show any differences between virgin and aged powder under the scanning electron microscope.

The standard hot gas welding process uses a nozzle system consisting of multiple round tubes. With the top nozzle system, the weld seam is encapsulated to minimize heat loss and allow better control of the hot gas flow. This significantly reduces the required heating time of the polymer. Temperature measurements and welding tests with plates of various thicknesses and burst pressure specimens are performed to verify the improvements of the top nozzle. For polyamides with different base polymers and different glass fiber contents, an average reduction in heating time of up to 50 % is possible on average. The achieved weld strengths or burst pressures for the tested materials are comparable or higher with the top nozzle system. The top nozzle makes the process more economical due to a short cycle time and lower gas consumption. It can be added to existing hot gas tools. In addition, a larger process window, shorter heating time and higher achievable temperatures with the top nozzle lead to a higher acceptance of hot gas welding in industries. New weld able materials in turn open up new application areas and markets.

Additive manufacturing is one of the key technologies for the future production of complex and individualised components. One of the most challenging questions to minimize the production cost is the reuse of the powder leftover after the building process. This study investigates the influence on the mechanical properties when reusing the leftover powder out of the process chamber up to four times. Tensile test specimens are produced and investigated. The results show a decreasing in the ultimate tensile strength with repeated reuse of the leftover powder. After four times of reuse the strength increases again. This cannot be explained by the literature and has to be verified in further investigations. The investigations reveal a high mechanical anisotropy as the strength highly depends on the component orientation in the process chamber. The particle shape does not show any differences between virgin and aged powder under the scanning electron microscope.