Search

Polymer foams offer high sustainable performance in terms of their lightweight potential, insulation and high specific mechanical properties. The foaming of polymers depends on the properties of gas-laden solids or liquids. For foaming in the solid state, the foaming temperature must be higher than the glass transition temperature of the saturated polymer system. Moreover, the knowledge of sorption conditions and thermal properties is crucial for foam formation. In this study, the correlation between the glass transition temperature and the sorption conditions was investigated. This comparison was made by determining the sorption behavior for different pressure levels and the corresponding glass transition temperature using a high-pressure differential scanning calorimetry. The time, pressure and CO2 content were varied. For the first time, the Chow model could be verified for PLA with a coordination number of 3.

The current work investigates the auxetic tensile deformation behavior of the inversehoneycomb structure with 5 × 5 cells made of biodegradable poly(butylene adipate-coterephthalate) (PBAT). Fused deposition modeling, an additive manufacturing method, produced such specimens. Residual stress (RS) and warpage, more or less, always exist in such specimens due to layer-by-layer fabrication, i.e., repeated heating and cooling. The RS influences the auxetic deformation behavior, but its measurement is challenging due to the very fine structure. Instead, the finite-element(FE)-based process simulation realized by an ABAQUS plug-in numerically predicts the RS and warpage. The predicted warpage shows a negligible slight deviation compared to the design topology. This process simulation also delivers the temperature evolution of a small volume material, revealing the local cyclic heating and cooling. The achieved RS serves as the initial condition for the FE model used to investigate the auxetic tensile behavior. With the outcomes from FE calculation without considering RS at hand, the effect of the RS on the deformation behavior is discussed for the global force-displacement curve, the structural Poisson’s ratio evolution, the deformed structural status, the stress distribution, and evolution, where the first three and the warpage are also compared with experimental results. Furthermore, the FE simulation can easily provide the global stress-strain flow curve with the total stress calculated from the elemental ones.

During processing and bubble growth processes, the melt viscosity changes with temperature, pressure, and blowing agent concentration. Therefore, measurement and prediction methods for viscosity characterization in terms of temperature, pressure, and blowing agent dependency are needed. This study demonstrates the applicability of in-line viscosity measurements during the foam injection molding process and a model for viscosity superposition and prediction. In the present study, polystyrene and a modified polylactide for foaming applications with nitrogen as blowing agent are investigated. By changing the injection speed, temperature, and blowing agent concentration, the process conditions are varied, and thus the resulting pressure drops within the in-line measurement die. The calculated shear rates and viscosities are shifted to a master curve by the application of superposition principles. The viscosity dependency on temperature is described by the Arrhenius equation, the pressure by the Barus equation, and for the blowing agent concentration, a novel Barus-like equation was derived and applied. The prediction of the master curve viscosity function was achieved by the power-law model in combination with the superposition principles and showed good agreement with the shifted in-line data. Finally, the in-line measurements and viscosity predictions are validated by comparing them to rotational and capillary rheometer measurements.

The increasing requirements on plastic parts demand a rising use of combined functional and reinforcing materials. Therefore, often reinforcing particles with different aspect ratios are added to the plastic as additive mixtures. However, the engineering design process of reinforced parts requires an early knowledge of the expected orientation of the reinforcing particles. Numerous models try to predict the orientation of particles in polymer suspensions. However, the interaction coefficient strongly depends on the aspect ratio of the particles and a prediction of the orientation behavior of additive mixtures with differently shaped particles has not been validated using conventional methods. In this work, the orientation of differently shaped particle mixtures in polymer suspensions is investigated for different fluid channel geometries. Finally, the Folgar–Tucker model is applied to filler mixtures and implemented into OpenFOAM®, which enables the comparison of filler orientation in different fluid channel geometries. Regarding the experiments a characteristic increase of the interaction coefficient was observed at a filling level of 5%. Furthermore, it was shown that a balanced mixing ratio yields higher interaction coefficients. With regard to the performed simulations, it was possible to show qualitatively how a considered interaction between fibers and platelets affects the orientations.

Degradation and fragmentation of plastics in the environment are still poorly understood. This is partly caused by the lack of long-term studies and methods that determine weathering duration. We here present a novel study object that preserves information on plastic age: microplastic (MP) resin pellets from the wreck of the SS Hamada, a ship that foundered twenty-nine years ago at the coast of Wadi el Gemal national park, Egypt. Its sinking date enabled us to precisely determine how long MP rested in the wreck and a nearby beach, on which part of the load was washed off. Pellets from both sampling sites were analyzed by microscopy, X-ray tomography, spectroscopy, calorimetry, gel permeation chromatography, and rheology. Most pellets were made of low-density polyethylene, but a minor proportion also consisted of high-density polyethylene. MP from inside the wreck showed no signs of degradation compared to pristine reference samples. Contrary, beached plastics exhibited changes on all structural levels, which sometimes caused fragmentation. These findings provide further evidence that plastic degradation under saltwater conditions is comparatively slow, whereas UV radiation and high temperatures on beaches are major drivers of that process. Future long-term studies should focus on underlying mechanisms and timescales of plastic degradation.

Hygroscopic polymers absorb and bind water. If not dried properly, the residual moisture can cause major problems for converting and affect the product quality significantly. Therefore, an effective drying down to an acceptable moisture level is essential for a successful production. Though data sheets give recommendations for drying parameters, these do not consider the actual current moisture up-take of the plastic pellets or the current ambient conditions. This paper investigates the interdependencies of polymer characteristics, like thermal properties and molecular structure, and the drying kinetics of the respective polymers. Tests are carried out with five different polymers on a State-of-the-Art desiccant dryer. The results show that distinctive drying behaviors can be attributed to the molecular structure of the respective plastic. This is reflected by the activation energy according to Arrhenius, the diffusion coefficient and the Flory-Huggins-Parameter, all showing a positive correlation with drying speed and therefore can be used as indicators to estimate drying times. Also, an industrial scale prototype of a microwave enhanced drying system was used to investigate the effect of microwave application on the drying kinetics. Experimental results show potential for reducing the drying times needed, especially for lower temperatures of the drying air and highly hydrophilic plastics. For higher temperatures, however, the prototype could not compete with the state-of-the-art desiccant dryer, due to heat losses and inefficient tubing of the prototype. Considering this, the benefits of microwave application could be shown representatively for polyamide 6 also at higher temperatures.

It is extremely important to save costs and time while enhancing accuracy in experimentation. However, no study has utilized response surface methodology (RSM) to obtain the effects of independent parameters on properties of PLA/clay/rice husk composites. This study focused on optimization of tensile strength of fiber-reinforced polylactic acid (PLA) composites. RSM using Box-Behnken design (BBD) was used to determine optimum blending parameters of the developed composites. Fiber-reinforced PLA composites were prepared using compression molding. Rice husk fiber and clay filler were used to enhance tensile properties of PLA. Five factors, namely, clay filler loading (1 − 5 wt.%), rice husk fiber loading (10 − 30 wt.%), alkali concentration (0 − 4 wt.%), rice husk variety (K85, K98), and alkali type (NaOH, Mg(OH)2) were varied with 68 individual experiments. Tensile tests were carried out according to ASTM D638 standards. ANOVA results revealed that the quadratic models best fit the tensile strength response, with filler loading and fiber loading factors as the most significant model terms. Interaction effects were more predominant than linear and quadratic effects. The developed models used to determine maximum tensile strengths of PLA/clay/rice husk composites were in close agreement with experimental findings (R2 values of 0.9635, 0.9624, 0.9789, and 0.9731 for NaOH-modified K85 rice husks, Mg(OH)2-modified K85 rice husks, NaOH-modified K98 rice husks, and Mg(OH)2-modified K98 rice husks respectively). Individual optimal conditions were used to predict maximum tensile strengths in each set of developed composites. The predicted tensile strengths were 32.09 MPa, 33.69 MPa, 32.47 MPa, and 32.75 MPa for PLA/clay composites loaded with NaOH-modified K85 rice husks, Mg(OH)2-modified K85 rice husks, NaOH-modified K98 rice husks, and Mg(OH)2-modified K98 rice husks, respectively, which were very close to the obtained experimental values of 31.73 MPa, 33.06 MPa, 32.02 MPa, and 31.86 MPa respectively.

It is well known that polylactide (PLA) is difficult to foam due to its low melt strength. Thus, many ways were described in the literature to enhance the foamability. However, the melt strength was actually determined only in a limited number of publications. In this study, the addition of chemical modifiers was used to change the rheological behavior of PLA and thereby improve its foamability in foam extrusion process. For the first time the use of dicumyl peroxide modified PLA in foam extrusion is described. Both modifications lead to a distinct increase in melt strength. Here, the highest increase was shown for the PLA modified with dicumyl peroxide. Furthermore, strain hardening was observed for PLA modified with the peroxide. Low density foams were achieved for neat and modified PLA in foam extrusion. Neat PLA showed a density of 45 kg/m3, while the peroxide modified PLA showed the highest expansion with a density reduction down to 32 kg/m3. Both modifications result in a more uniform cell structure and an improved compression strength. Here, the foamed, peroxide modified PLA showed outstanding performance compared to neat PLA foam with twice the compression strength (151 Pa) even at a 30% lower density.

In the field of extrusion, a very promising high performance extruder was introduced to the European plastics industry in 1999. This new type of single-screw extruder combines a grooved plasticizing barrel with a barrier screw. Compared to conventional extrusion systems, these extruders have by far a higher output and product quality among other advantages such as lower processing costs and lower energy consumption. In the past, both Newtonian and non-Newtonian models were developed to calculate and predict the melting rate along the flow channel. The aim of this paper is to present experimental investigations on the processes within the melting zone of a single-screw extruder with a grooved plasticizing barrel. To visualize the melting mechanisms, screw extraction experiments as well as dynamic pressure measurements were performed. By means of screw extraction experiments a solid bed was clearly identified only in the solid channel and a melt pool only in the melt channel. Analysis of the dynamic pressure signals also showed the same behavior and therefore allowed in-line characterization of the melting process. Thus, theoretical concepts about the melting mechanisms could be confirmed experimentally.

Incorporation of agricultural wastes as fillers in fiber-reinforced plastics is gaining momentum in plastics engineering research. In this study, fiber-reinforced polypropylene (PP) with rice and coffee husks as filler material were developed. The effect of alkali (sodium hydroxide) pretreatment of the husks on mechanical and thermal properties of developed PP biocomposites was observed. Filler material loading was varied from 0% to 20% for rice husks and 0% to 10% for coffee husks. A twin-screw extruder was used for compounding the PP matrix with rice and coffee husk filler materials. Tensile strengths and percentage elongation results varied from 27.4 to 37.4 MPa and 2.4% to 70.3% (unmodified coffee husks), 31.1 to 37.4 MPa and 5% to 70.3% (unmodified rice husks), 30.7 to 37.4 MPa and 5.3% to 70.3% (modified coffee husks), and 30.7 to 37.4 MPa and 4.8% to 70.3% (modified rice husks). Young’s modulus ranged between 1656 and 2247.8 MPa for biocomposite PP samples with unmodified filler material. Young’s modulus ranged between 1740 and 2160 MPa after alkali treatment of the filler material. Charpy impact strengths ranged from 1.2 to 4 kJ/m2 and 3.1 to 19.6 kJ/m2 for samples containing unmodified and modified filler material, respectively. Thermogravimetric analysis showed that an increase in filler content resulted into delayed weight loss at high degradation temperatures. The results suggest that these developed fiber-reinforced plastics can be used in applications requiring high thermal stability and good mechanical properties.

Single-screw extrusion at high screw speeds is established nowadays since it allows for a high mass throughput at a comparatively small extruder size. Compared to conventional extrusion at low screw speeds, a considerable non-linearity in mass throughput appears by exceeding a certain threshold screw speed. In this study, the solid conveying behavior of different plastic granules with varying geometries was investigated in a smooth, a helically and an axially grooved solid conveying zone for screw speeds up to 1350 rpm. These experimental findings are compared to classical analytical predictions in the literature. It is found for the first time that both the shape and size of the plastic granules play a decisive role in determining the threshold screw speed at which a non-linear mass throughput is observed. It is shown that small and spherical granules exhibit a later onset of non-linear throughput compared to larger lenticular and cylindrical shaped granules. Moreover, it is revealed that the mass throughput equalizes for an axially and a helically grooved solid conveying zone at high screw speeds. This is contrary to the low screw speed range where the axially grooved barrel results in a significantly higher throughput than the helically grooved barrel. Thus, the maximum throughput at high screw speeds is limited by the granule stream provided by the hopper opening and is no longer governed by the groove angle.

This paper presents a CFD simulation of the non-Newtonian and non-isothermal polymer flow through the nozzle of a fused filament fabrication printer. The modeling approach is based on a melt fraction model which allows to cover the entire flow domain from the solid filament entering the nozzle to the melt state at the nozzle exit. The numerical results were compared with a specially developed setup that allows the measurement of the feeding force required to push the filament through the nozzle. The comparison is carried out over a wide range of filament velocities using different nozzle temperatures and nozzle geometries. It is shown that the assumptions used for the simulation are suitable to predict the melting and flow behavior in the relevant processing range. The model represents both the process region where the filament has sufficient time to melt before reaching the nozzle tip and the region of high filament velocities where there is insufficient time for complete melting. In the latter region, the model predicts that the molten region is reduced to a thin melt film at the tip of the filament as it is pushed against the conical transition zone of the nozzle. Furthermore, the simulation results show that the temperature at the nozzle exit decreases with increasing filament velocity. Based on this modeling approach, melting within the additive manufacturing process of material extrusion can be improved. Furthermore, the findings can be used to optimize the strand deposition.

For the preparation of polylactide (PLA)-based foams, it is commonly necessary to increase the melt strength of the polymer. Additives such as chain extenders (CE) or peroxides are often used to build up the molecular weight by branching or even crosslinking during reactive extrusion. Furthermore, a blowing agent with a low molecular weight, such as carbon dioxide (CO2), is introduced in the foaming process, which might affect the reactivity during extrusion. Offline rheological tests can help to measure and better understand the kinetics of the reaction, especially the reaction between the polymer and the chemical modifier. However, rheological measurements are mostly done in an inert nitrogen atmosphere without an equivalent gas loading of the polymer melt, like during the corresponding reactive extrusion process. Therefore, the influence of the blowing agent itself is not considered within these standard rheological measurements. Thus, in this study, a rheometer equipped with a pressure cell is used to conduct rheological measurements of neat and chemical-modified polymers in the presence of CO2 at pressures up to 40 bar. The specific effects of CO2 at elevated pressure on the reactivity between the polymer and the chemical modifiers (an organic peroxide and as second choice, an epoxy-based CE) were investigated and compared. It could be shown in the rheological experiments that the reactivity of the chain extender is reduced in the presence of CO2, while the peroxide is less affected. Finally, it was possible to detect the recrystallization temperature Trc of the unmodified and unbranched sample by the torque maximum in the rheometer, representing the tear off of the stamp from the sample. Trc was about 13 K lower in the CO2-loaded sample. Furthermore, it was possible to detect the influences of branching and gas loading simultaneously. Here the influence of the branching on Trc was much higher in comparison to a gas loading.

The continuous growth of the plastic industry leads to a steady optimization of technical production processes. Supported by the development of the computer technology, modelling and simulation tools provide the possibility to reproduce and analyze complex processes like plastics processing using co-kneaders. A co-kneader is an extruder with the particularity of an axially oscillating screw. Therefore, the rotatory movement of the screw gets superposed by an axial screw movement. In combination with kneading pins within the cylinder, the co-kneader ensures an efficient plastics processing. The present work deals with three-dimensional numerical simulation of a co-kneader in the open source software OpenFOAM. Starting from the real process, the simulation model is successively simplified based on suitable assumptions. Using a simplified steady-state Newtonian simulation model, various geometry and process parameters are finally investigated. The present work thus provides initial insights into the flow processes in the co-kneader.

Comprehensive resource efficiency means far more than the preservation of natural resources. It also includes productivity factors of material, machine and labor. The plastics industry has made a great contribution to resource efficiency, but often finds itself on the defensive. Yet a knowledge of the various relationships involved provides enough material to go on the offensive with arguments illustrating the benefits of plastics and plastics technology.

According to Gibbs, the free mixing energy is decisive for the thermodynamic compatibility of two substances, e. g. polymers. If the free mixing energy is positive, the two mixing partners are separated. For such molecularly immiscible polymers, a finely distributed disperse phase within the matrix can only occur if drop breakage happens during processing. This depends on the strain and shear rates and the capillary number, which must exceed a critical value. If all preconditions are met, coupling agents can be used to improve the phase adhesion of two given polymers and to stabilize the morphology. This is due the reduction of the interfacial tension, thus facilitating drop breakage and simultaneously increasing interfacial tension, which suppresses coalescence. In this work, the effect of three different coupling agents is investigated to evaluate their influences on the property changes in polyamide 6/ethylene-octene-copolymers-blends. It can be shown that the rheological behavior as well as the blend morphology strongly depends to the type and the amount of the used coupling agent. A direct correlation between the rheological behavior and the blend morphology can be assumed but not fully confirmed. For this purpose, the particle size of the soft phase within the matrix is analyzed optically by a scanning electron microscope. Fracture mechanical investigations are carried out to evaluate the blend modifications to the mechanical properties. The results obtained using the method of essential work of fracture shows a significant influence due to the type of coupling agent, but less due to morphology. Therefore, in order to better understand the structural property relationships, the selection of coupling agent is as important as the blend morphology.According to Gibbs, the free mixing energy is decisive for the thermodynamic compatibility of two substances, e. g. polymers. If the free mixing energy is positive, the two mixing partners are separated. For such molecularly immiscible polymers, a finely distributed disperse phase within the matrix can only occur if drop breakage happens during processing. This depends on the strain and shear rates and the capillary number, which must exceed a critical value. If all preconditions are met, coupling agents can be used to improve the phase adhesion of two given polymers and to stabilize the morphology. This is due the reduction of the interfacial tension, thus facilitating drop breakage and simultaneously increasing interfacial tension, which suppresses coalescence. In this work, the effect of three different coupling agents is investigated to evaluate their influences on the property changes in polyamide 6/ethylene-octene-copolymers-blends. It can be shown that the rheological behavior as well as the blend ...

In selective laser sintering (SLS) predominantly polyamide 12 powder (PA12) is used. Often, after the sintering process approximately 70 % of powder, which has not been sintered, remains. The flow properties of this used powder have been affected because of the thermal stress during the sintering process. Due to the high price of new PA12 powder, the used and aged powder must be recycled by refreshing with new powder. This powder mixture can be reused in a next sintering process. However, due to the repeating refreshing process of the used powder, mixtures are produced whose quality is difficult to define. They differ greatly in their flow properties, which in turn has a negative effect on the component quality. In order to generate a good and reproducible powder quality, the thermal aging behavior of PA12 powder has been examined in detail by the authors. Based on these results, a recycling process could be developed step by step, by which the thermal aging can be reversed. A chemical agent is added to the used powder which is able to cleave the long polymer chains of the used powder at its amide bonds. Depending on the kind of chemical agent and its concentration, the flow properties of the used powder can be adjusted selectively, which also makes the quality of these mixtures reproducible. By means of this recycling process, the used powder has better flow and sintering properties and thus, can be reused several times. Thereby, it contributes to material and cost efficiency and thus, leads to an increased cost effectiveness of selective laser sintering.

The description of the specific volume under practical conditions during the processing of plastics still poses a challenge. For the processing of thermoplastic materials, the cooling process is particularly of high relevance. Since integral values for the specific volume are determined with conventional measurements, the local temperatures and cooling rates must already be taken into account during the evaluation of the measurements. The non-isothermal effects are difficult to determine with current analytical devices and yet lack a mathematical model that describes them sufficiently. In this work, the authors present an approach, which considers local temperatures and cooling rates. This is a basic requirement for the optimization of cooling rate dependent material models. The approach is implemented by means of numerical methods using the example of an amorphous thermoplastic material. The results, which are based on a cooling rate independent model, are promising and set the base for further work with cooling rate dependent constitutive models.

Cast polyamides, which are synthesized through anionical polymerization in a forming mold, have a high molecular weight compared to polyamides synthesized through polycondensation. However, high amounts of wastes (e.g. unusable sprues, post-processing wastes) occur with this production method. Because of this and due to the high molecular weight of the cast polyamide, compounding of the wastes and a further processing via methods like thermoforming is a potential approach for the recycling of polyamide wastes. However, when the polyamide wastes are recycled in a twin-screw extruder, the remaining catalyst, which is embedded within the wastes, can lead to a degradation of the polyamide chains. This degradation results in molecular weights respectively melt viscosities, which are suitable for processing via injection molding but not suitable for methods like thermoforming, for which high viscosities are necessary. In this work, cast polyamide wastes were compounded in a twin-screw extruder with additives to obtain maximum viscosities. We considered (mono- and di-)carboxylic acids, which act as catalyst catchers, as well as different additives, which increase the molecular weight, (linear chain extenders and multifunctional polymeric backbones). After the compounding, rheological measurements were conducted to examine the degree of the viscosity increase and thermal measurements to estimate a processing window for thermoforming. The rheological measurements showed that the increase is strongly dependent on the waste batches, which were used for the respective test series. However, the thermal properties were not influenced through the polymer modification. Overall, viscosities could be reached, which were high enough to produce semi-finished parts out of the compounds. Additionally, thermoformed polyamide parts with exact forming shape as well as constant wall thicknesses were realized.

Polylactide (PLA) is one of the most important bioplastics on the market with a permanent growth in production capacity. Due to its good mechanical properties, it is comparable to polystyrene. But in terms of foaming the melt strength and extensibility of commercial polylactide are rather low. Therefore such commercial grades often need to be chemically modified to induce crosslinking, chain extension or grafting by means of reactive extrusion on a twin-screw extruder. In this work different polylactide grades were used, to better understand the influence of the molecular characteristics, such as molecular weight, acid value and D-content, not only on the modification mechanism, but also on the foam properties.Polylactide (PLA) is one of the most important bioplastics on the market with a permanent growth in production capacity. Due to its good mechanical properties, it is comparable to polystyrene. But in terms of foaming the melt strength and extensibility of commercial polylactide are rather low. Therefore such commercial grades often need to be chemically modified to induce crosslinking, chain extension or grafting by means of reactive extrusion on a twin-screw extruder. In this work different polylactide grades were used, to better understand the influence of the molecular characteristics, such as molecular weight, acid value and D-content, not only on the modification mechanism, but also on the foam properties.

Short fiber reinforced thermoplastics are used extensively due to their high mechanical properties and low processing costs. Long fiber reinforced thermoplastics (LFT) show an even more interesting property profile and are used more and more often for structural parts. However, processing is not that simple and their anisotropic properties resulting from the fiber microstructure pose a challenge in terms of engineering design process. To reliably predict the structural mechanical properties of LFT, it is necessary to investigate a method that allows comprehensive consideration of the existing fiber microstructure within the engineering design process. For this purpose, a micromechanical approach developed at IKT has been extended to include the necessary process variables and the associated models.

Particularly in the automotive industry, continuous fiber-reinforced thermoplastics are currently enjoying steadily rising demand. Thermoplastic matrix systems promise shorter cycle times and enhanced joining and recycling characteristics when compared to fiber reinforced thermosets. In order to process continuous fiber reinforced thermoplastics, semi-finished parts are produced first. These are heated and post-processed in a back injection molding process. Design elements such as load transfer elements and ribs are injected onto the flat semi-finished part. To heat the parts, the effect of Joule heating can be utilized. The electrically conductive carbon fibers are heated by an applied voltage. The temperature is distributed through heat conduction into the part's matrix. The use of Joule heating enables high heating rates with low energy consumption. The industrial application of Joule heating of continuous fiber-reinforced thermoplastics requires the specification and investigation of further relationships between the influencing variables. The quality of the heating is significantly influenced by the contacting of the part. Within the scope of this study, heating experiments are compared using a thermographic image system. It is found that higher contact areas yield better heating quality and that rounded corners for the contact pieces additionally improve the temperature distribution.

The influence of injection molding parameters such as melt temperature, mold temperature and holding pressure on the look and feel of structured plastic surfaces are investigated. Therefore, an automated test stand measuring the gloss and color of the surface was developed at Institut fur Kunststofftechnik of the University of Stuttgart. The topography of the surface was analyzed by a digital light microscopy. Test results on structured acrylonitrile butadiene styrene/polycarbonate (ABS/PC) test panels show, that the examined process parameters melt and mold temperature have a higher influence on the color, gloss and topography than the holding pressure. By increasing the melt and mold temperature, the color, gloss and roughness is significantly influenced. The color difference and gloss decreases with increasing melt temperature, mold temperature and holding pressure, whereas the roughness increases. The melt temperature shows the highest influence on the surface properties. Besides the variation of processing parameters, the structure of the mold surface was modified to adapt the molded surface properties of two different plastic types applying standard injection molding process parameters. Furthermore, the screening of the surface made it possible to detect surface defects in terms of color and gloss and the influences of process parameters on the defects.

In order to realize an economical injection molding process, high process speeds and a consistently high quality of the products is necessary. A very effective possibility, which gets more and more famous, is the use of so-called smart machines and processes. If corresponding interactions between machine parameters, process variables and quality characteristics are known, the machine can design the process independently itself – a so-called self-optimizing process. This study presents a concept for optimizing the residual cooling time of the injection molding process. For this purpose, a special mold is used, which allows to detect forces initiated by thermal shrinkages on the mold core. A new evaluation method allows an automated determination of the time of the completed thermal shrinkage, which should also represent the ideal time for ejection. The principle is demonstrated using polypropylene. It is also shown that the measuring principle can be used to characterize material additives and how processing parameters influence the residual cooling time.

Plastics processing machines are often very complex processes in which conventional (body-fitted) simulations reach their limits. The Immersed Boundary Surface Method (IBS) is a novel and promising implementation of the Immersed Boundary Method (IBM) to simulate such complex (moving) processes such as twin-screw extruders, co-kneaders and planetary roller extruders. Generally in IBM, a discretized surface is immersed into a background mesh (computational domain) in whose cells the conservation equations are solved. This work describes the characteristics of IBS and its general approach to use. Furthermore, the results of body-fitted simulations and IBS will be compared to validate the implementation and simulation results of IBS. The data obtained for both methods are perfectly consistent, which validates IBS and forms the basis for further use of this method to simulate complex plastics processing machines.

In order to reduce the potential fire load, polyamides are often compounded with flame-retardant additives like red phosphor or halogenous, nitrogenous or phosphoric molecules. However, to achieve an effective flame retardancy, very high amounts of the additives are necessary, which can negatively affect the mechanical properties of the material or lead to a migration of the additive to the surface of the compound (if the flame retardant is physically bonded to the polyamide). A new attempt to enhance the flame resistance of polyamides is the direct integration of the respective molecules within the polymer chain during the polymer synthesis. By applying this method, the flame-retardant additives function as a chain regulator, which results in low molecular weights and low viscosities. Consequently, these polyamides are difficult to process. Therefore, in this work intrinsically flame-retardant polyamides were compounded with a PC/PA-Blend as a linear chain extender in a twin-screw extruder. The compounds were characterized regarding their rheological and flame-retardant properties. Rheological measurements showed that the viscosity of standard-polyamide was reached and that the chain extension was successful. Thereby, processing through injection molding was possible. Furthermore, a flame test was conducted by measuring the burning duration after two flame treatments. The experiments showed that the polyamide keeps its flame retardancy after the compounding process, which makes the treated polyamide suitable for conventional industry applications.

The reliable prediction of process-induced fiber microstructure, especially for long fiber reinforced thermoplastics (LFRT), is still a considerable challenge. The prediction by means of computational models with standard settings is not effective and current simulation environments do not allow optimizing the resulting fiber orientation quickly. In case of distinctive anisotropy, the consideration of fiber orientation within the scope of structural mechanics in part design can be considered as indispensable. The basis for an improved prediction is a newly developed optimization approach for an automated calibration of the resulting fiber orientation tensor by means of certain experimental tests. This approach allows optimizing the associated model parameters within a few minutes by calculating a single initial flow field.

Adding fillers to polymers allows highly functional materials and thereby properties like electrical conductivity that are not achievable by polymers themselves. But higher amounts of fillers cause an increase in viscosity and thus a change in flow behavior which in turn induces difficulties in plastic processing. Above a certain value (percolation threshold), there is a flow restriction. An important factor is the combination of the polymer and the filler and whether there are any interactions between each other. By differing the amorphous phase of polymers into a rigid amorphous and a mobile amorphous fraction, predictions about interactions are possible. The objective is the generation of such a flow restriction and the combined investigation of a polymer-particle-interaction. Polypropylene (PP) was used as matrix whereas minerals were used as filler materials in different amounts up to 40 vol.-%. SiO2 was chosen because it is available in different spherical sizes. Rheological investigations show that a higher aspect ratio leads to a faster increase in viscosity achieving the rheological threshold. As a result of the caloric investigations, the highly filled plastics show no interaction between polymer chains and filler surface. This leads to the conclusion that the change in flow behavior is mainly caused by direct interaction between the particles.

Smart Structures are able to change their shape under the influence of external stimuli. The shape change takes place without the influence of external forces and is self-induced. In view of the increasing demand for energy efficiency and ecological sustainability, Smart Materials allow for a novel approach to incorporate functionalities into a component without additional energy demand and material costs. Within this project, a structure based on a biobased plastic has been developed that deforms under the influence of moisture in a precalculated manner. The Smart Structure is produced by fused layer modeling. The deformation is achieved by the targeted anisotropic assembly of the structure in the additive manufacturing process by using two filaments with a different sensitivity to moisture, which thus form a hybrid structure in the component.

Cast polyamide 6 is anionically polymerized from e-caprolactam. Its good properties are mainly caused by the higher molecular weights, compared to standard polyamide 6. Because of sprues and post-processing, a larger amount of scrap is produced. This scrap is typically incinerated without sufficient use of its high quality properties. However, cast polyamide 6 also offers great potential for material recycling, particularly if its high molecular weight can be retained. As cast polyamide decomposes during processing as well, it is necessary to add some agents during compounding. By adding a carboxylic acid during compounding, it is possible to adjust the molecular weight and thus the flowing behavior of the polyamide recyclate melt. The highly viscous recyclates are usable for blow molding applications.

The importance of the bioplastic polylactide has increased significantly in the recent years. Due to its quite similar properties to fossil-based polystyrene (PS), it has the potential to substitute foamed PS products and consequently can increase the sustainability and material efficiency of foamed products. However, the low molecular weight of commercial PLA, its sensitivity to hydrolysis during processing and its low rate of crystallization inhibit the production of low density foams and uniform cell morphology. The addition of different modifiers to optimize the melt strength and melt viscosity was performed by means of reactive extrusion. The rheological and thermal properties as well as the foam densities were examined. The melt viscosity and melt strength was increased. Foams with fine and closed-cell structure with relatively thin cell walls were made in batch foaming experiments.

The single-screw extrusion process is often used to produce plastic films. Therefore, the polymer melt is transferred from a round cross-section at the end of the single-screw extruder to a flat shaped rectangular cross-section by a special sheet die. For high product quality, the engineering design of sheet dies is of crucial matter. Today, the design process and the prediction of flow are done by the use of Computational Fluid Dynamics (CFD). The design process itself is in general quite complex. In addition to that, different software is used for geometry creation, meshing and execution of simulations, which increases the necessary process steps and numerous software interfaces. To achieve a higher performance and less risk of errors, a novel method was developed in this study, to optimize the so-called coat-hanger die. The new method eliminates the step of geometry creation and directly generates the CFD mesh by parameterization. For comparing reasons, CFD simulations based on the common and new method were performed and evaluated to optimize a coat-hanger die by means of fluid dynamics. The efficiency of the design process significantly increased compared to nowadays common methods. Even in comparison to a parameterized CAD file, the time for tool design could be substantially reduced.

The drying of hygroscopic polymers is crucial because of their ability to absorb moisture within their molecular structure. If processing takes place at higher residual moisture contents than recommended, processing problems or major quality issues of the product can occur. Therefore, drying by microwaves is a fast way to reach a defined residual moisture content. Microwave drying is based on the stimulation of dipoles within the polymer chain and the dipoles of the absorbed water molecules. This leads to a temperature increase and to an increased speed of migration of moisture within the plastic to its surface. In order to describe and predict the resulting temperature increase caused by the electromagnetic field, the dielectric properties of plastics needs to be analyzed. Five different plastics are examined concerning their temperature and respective moisture content dependence in the electromagnetic field. The measurements of the dielectric loss factor indicates a moisture and temperature dependency for all examined plastic types. It also turns out, that each plastic type reacts differently in an applied electromagnetic field even if they are the same type of plastic. The findings also show that it is possible to calculate the resulting temperature increase through dielectric heating by knowing the dielectric properties obtained from measurements and bilinear interpolations as a function of moisture content and temperature. By knowing the microwave indicated temperature increase, the whole drying process is predicable by using Fick´s second law and the temperature and moisture depended diffusion coefficients.

Kurzfassung Die Methode der Essential Work of Fracture ist ein Konzept der Fließbruchmechanik und eignet sich hervorragend zur Werkstoffoptimierung von duktilen Kunststoffen. Sie zeichnet sich, unter Beachtung gewisser Restriktionen, durch eine relativ einfache experimentelle Durchführbarkeit und Ergebnisinterpretation aus. Speziell die Gewährleistung des ebenen Spannungszustands, eine Grundvoraussetzung zur Anwendung dieser Methode, wird maßgeblich durch den gewählten Ligamentbereich der Prüfkörper beeinflusst. Mit der digitalen 3D-Bildkorrelation wird ein Verfahren vorgestellt, mit dem es möglich ist, sowohl die vollkommene Plastifizierung des Ligamentbereiches zu überprüfen als auch die minimal zulässige Ligamentuntergrenze zu definieren und zu überprüfen. Durch die mit digitaler 3D-Bildkorrelation unterstützte Werkstoffuntersuchung mit der Methode der Essential Work of Fracture ist es möglich, die Genauigkeit und die Verlässlichkeit der Ergebnisse zu steigern.