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In the literature it is well known that foaming is a highly complex process which is influenced by e.g. the process parameters, the choice of polymer and its structure as well as by the blowing agent type and concentration. Due to the dependency of both, shear and elongational viscosity on such influencing factors, the melt viscosity is highly influenced during the foaming process. Thus, the viscosity is a crucial parameter for the foaming process. A collapse of single bubbles or even of the whole foam structure is often a result of a too low elongational viscosity and the associated melt strength. Therefore, polylactide (PLA) is difficult to foam. In this study the melt viscosity in shear and extensional flow, and the melt strength was increased by modifying PLA with dicumyl peroxide on a twin-screw extruder. Thus, the polymer chain structure was changed from linear to branched and strain hardening was observed during uniaxial viscosity measurements with a Sentmanat extension rheometer at different temperatures and Hencky strain rates. The uniaxial elongational viscosity of the modified PLA including the observed strain hardening was predicted at different temperatures and different Hencky strain rates with the molecular stress function model (MSF). Because of the good accuracy of the MSF model predictions in comparison to the uniaxial viscosity measurements, the equibiaxial viscosity was modeled as well since equibiaxial deformations mainly occur during the foaming process. Therefore, the elongational viscosity of modified polymers for foaming applications can be characterized and predicted. [ABSTRACT FROM AUTHOR]

When considering material models describing pressure, specific volume and temperature (pvT) behavior, that are used in engineering practice, one can still find that the used methods comprise sufficient potentials for improvement. In scientific literature the KAHR model is a well-established approach, in order to model time dependent specific volume of amorphous thermoplastics. The KAHR model uses a generalized Kelvin-Voigt retardation time spectrum, along with empirically fitted shift factors for temperature and free volume. The determination of material-specific model parameters is costly, since time consuming temperature-jump experiments, that allow volume retardation at temperatures below glass transition at different pressures, would have to be performed. In previous work, it could be shown, that the underlying rheological information could also be gained using a combination of dynamic mechanical analysis, temperature and pressure dependent viscosity measurements as well as pvt measurements. This work discusses how the sample preparation influences the determination of material parameters using dynamic mechanical analysis. It was shown that the conformation of the polymer molecules frozen during sample preparation has a significant influence on the parameter determination. As expected, the best results can be obtained with samples whose conformation corresponds most closely to the theoretical equilibrium state. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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 fiberreinforced 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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Generally, Thermoforming is used for the production of simple shaped packaging or housing parts, which do not feature any additional functions. However, by the use of heat conductive plastic materials, a heat loss function can be implemented to the thermoformed parts. Increased filler contents are correlated with higher heat conductivity. Unfortunately, higher filler content also leads to a degraded thermoformability of plastic sheets. As a result, simulation becomes more and more important, when operating the thermoforming process at its limits. To obtain high predictive accuracy in thermoforming simulation, material models as well as data fitting methods are needed, which match with the real thermoforming material and process. In this investigation the use of the K-BKZ model for thermoforming simulation of heat conductive plastics is evaluated. Two different kinds of parameter fitting algorithms are examined. On the one hand, the K-BKZ model is fitted by a reverse-engineering procedure using the IKT Thermoforming-Material-Characterization-test (TMC-test) as reference test. On the other hand, classic rheological measurements by means of rotational rheometry and Rheotens-test are used for the data fitting of material parameters. As reference material a polystyrene is combined with two graphite fillers (spherical and platelet). The predictive accuracy of the material model and the two parameter fitting procedures are quantified by a comparison of the simulation with real thermoforming experiments. [ABSTRACT FROM AUTHOR]

Hygroscopic polymers absorb water and bind it within; therefore an effective drying down to an acceptable moisture level is essential for a successful production. If not dried properly, the residual moisture can cause major problems for converting and also significantly affect the product quality. Usually, data sheets give standard recommendations for drying temperatures and times; however, these do neither take into account the actual current moisture up-take of the plastic pellets, nor the current conditions. In this work, a simulation model is presented, calculating the heat and mass transfer within the polymer pellet in order to predict the drying progression. In addition to approaches from the literature describing the diffusion coefficient of water in plastic with a complex function and a high number of material parameters, a linear function was used to model the dependence of diffusion from moisture and temperature. Moreover, the effect of microwave application for an accelerated drying was included by calculating the resulting temperature rise from dielectric heating. The simulation of the drying process shows a very good conformity with experimental results. The linear approach used in this work leads to good results and allows to reduce the complexity of the whole model compared to approaches from the literature. The calculation of a temperature rise through dielectric heating also shows satisfying agreement with that measured in the real process from a prototype for microwave drying on an industrial scale. Therefore, the model is a reliable tool to predict required drying times for different polymers and under variation of drying conditions. [ABSTRACT FROM AUTHOR]

Thermoforming generally describes the shaping of a thermoplastic semifinished part above its softening temperature to a three dimensional part. The sub-step of heating the sheet can be seen as the very crucial process step. In most thermoforming machines, the sheet is heated by means of infrared radiation inside a radiation furnace. Depending on the thickness and the absorption characteristics of the sheet material as well as the working temperature of the radiators, different temperature profiles along the sheet thickness will occur. The knowledge of this temperature distribution is important to control the heating step since the sheet temperature directly influences process stability and part quality like sagging, burnings, orientations and wall thickness distribution of the part or accurate reproduction of surface details. In this paper a new approach by combining three different infrared sensors for determining the temperature distribution along the sheet thickness at any time of the heating phase will be presented. At first, the different amounts of radiation will be calculated in order to separate reflected and transmitted radiation from the actual measuring signals. At second the sheet will be divided into a certain number of layers and the amount of emitted radiation of each layer will be calculated and compared to measured signals in order to finally determine the real temperature distribution along sheet thickness. Calculated and measured results will be shown using polypropylene as sheet material. [ABSTRACT FROM AUTHOR]

The shrinkage and warpage behavior of injection molded parts is very complex. By using a new measuring method it was shown for the first time that the warpage can be classified as warping and distortion. In general, warpage can only be reduced substantially by a sufficiently high volumetric compensation in the holding pressure phase. The shrinkage and warpage behavior of injection molded parts is very complex. By using a new measuring method it was shown for the first time that the warpage can be classified as warping and distortion. In general, warpage can only be reduced substantially by a sufficiently high volumetric compensation in the holding pressure phase. [ABSTRACT FROM AUTHOR]

Bioplastics, which will see rising demand in the next years, have to be compounded by using a twin screw extruder like conventional plastics. By using a twin-screw extruder, the molecular weight of the bioplastic polyhydroxybutyrate (PHB) can be degraded under control. In a second step, the short-chain PHB and a soft phase can be compounded to a larger block copolymer by means of reactive extrusion. The processing step takes place in a process- and material-efficient manner without catalysts, solvents and purification processes. The development of the block copolymer improves the ductile properties of the material without changing the thermal or chemical characteristics. [ABSTRACT FROM AUTHOR]

Cast polyamide 6 is a high-quality material due to its long polymer chains. Because of sprues and post-processing, a comparably large amount of the produced material, up to 30 %, becomes waste. Until today, this high-quality waste is burned or added into standard virgin polyamide 6 raising its molecular weight. Instead of using cast polyamide waste as an additive or combustion material, it would be beneficial to process high-molecular weight recyclates made of this cast polyamide 6. To enhance its processability, using a lubricant as a processing additive is a reasonable approach. Our previous findings within this field revealed an unusual behavior of a lubricant consisting of a polyester modified wax, which is already used for standard polyamide 6 without known problems. In this work, milled cast polyamide 6 chips obtained from machining are washed and dried and then used for producing high-molecular weight recyclates. In literature the deposition of such waste is recommended because of pollution and contaminations. It is hence possible to get clean material for recycling. The recycling step itself is performed on a twin-screw extruder type ZSK 26MC of Coperion, Stuttgart, by processing a dry-blend of cast polyamide and said lubricant. Rheological measurements show increasing complex viscosities of recyclates depending on the lubricant’s content. It is possible to achieve viscosities higher than those of the solely processed polyamide recyclate. Even the viscosity of unprocessed cast polyamide 6 can be reached. Compared to virgin extrusion polyamide 6, the processed recyclates achieve higher tensile strengths, while an increasing amount of lubricant does neither affect Young’s modulus nor tensile strength. It is also shown that the lubricant raises impact strength significantly. [ABSTRACT FROM AUTHOR]

Polyamide 6 can be produced by anionic ring-opening polymerization of ε-caprolactam using e. g. sodium-caprolactamate as a catalyst. One of the best known anionically polymerized polyamide 6 is so called cast polyamide 6, used for particularly stressed parts. The reason for its good mechanical properties is the comparably high molecular weight. When using cast polyamide 6 for extrusion or injection molding, its high molecular weight can be a disadvantage due to its very high viscosity. To enhance processability, the flow behavior of these materials has to be adjusted. Besides the use of a lubricant, shorter chains would be another way to achieve better processability. In this work, the latter is performed by compounding anionically polymerized cast polyamide 6 using a chain scissorer, e. g. terephthalic acid. Compounding of dry-blends made of cast polyamide 6 and said terephthalic acid is done on a twin-screw extruder type ZSK 26MC of Coperion, Stuttgart. Mechanical properties and flow behavior were investigated afterwards. Surprisingly, it could be shown, that adding very small amounts of terephthalic acid did not reduce but raise viscosity significantly. However, higher amounts of terephthalic acid reduce these viscosities, as expected. Additionally, a reduction of viscosity can be seen over time, because remaining ingredients seem to still be active. Mechanical properties such as Young’s modulus or tensile strength are not affected by adding terephthalic acid and are comparable to those of injection molding polyamide 6. Solely impact strength was slightly reduced, when a larger amount of terephthalic acid was added. [ABSTRACT FROM AUTHOR]

Polyhydroxybutyrate (PHB) belongs to the family of polyhydroxyalkanoates and is both, biobased and biodegradable. Due to its linear chain structure, PHB is highly crystalline and has a melting temperature close to its decomposition temperature. Pure PHB crystallizes very slowly, so that the use for some technical applications is not commercially viable. This paper describes the crystallization kinetics of pure and nucleated PHB by means of differential scanning calorimetry (DSC). The cooling curve and the metabolic rate as a function of temperature are elaborated. [ABSTRACT FROM AUTHOR]

Plastics are made of polymers and additives. For good processability special additives are necessary. Some additives were used for a better ejection and flow behavior. To get a proper classification of additives, new in-line measurements were developed. The flow behavior of plastics can be determined with an in-line viscosity measurement in an injection mold. To classify the ejection behavior during the injection molding process, the demolding force and the normal force were used. The new in-line measurement allows a detailed classification of processing aids in plastics. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Cast polyamide 6 is anionically polymerized from ε-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. [ABSTRACT FROM AUTHOR]

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 twinscrew 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. [ABSTRACT FROM AUTHOR]

Shear- and mixing elements in single-screw extruders have to meet high requirements in order to achieve good melt homogeneity even at high rotational speeds. A model for the description of the fluid element deformation has been implemented in the CFD-Code Open FOAM® for the characterization of dispersive mixing. The calculation approach has been implemented in an Eulerian frame (stationary observer) as well as in a Lagrangian approach (calculation along streamlines) to examine the influence of numerical dissipation on the calculation results. Using two analytically calculable test cases, the correct implementation of the calculation approach in OpenFOAM® has been verified. In case of the Couette flow a greater variance due to numerical dissipation has been observed for the Eulerian frame calculations, while the Langrangian calculations still provided correct results. Finally the calculation model has been successfully applied to a three-dimensional Saxton mixer geometry. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Fiber reinforced plastics (FRP) hold considerable potential for the construction and design of light-weight parts. FRP are rapidly gaining in importance in various industrial sectors. Although this group of materials combines high strength and stiffness while simultaneously being lightweight, major difficulties still arise when it comes to high volume production and the return of manufactured parts back into the cycle of materials at the end of their lifecycle. A new approach follows the idea of producing structural parts through the forming and back-injection molding of preforms with a large portion of recycled fibers and recycled matrix, without drastically compromising the mechanical properties. To achieve this, carbon fibers retrieved out of a recycling process are blended with recycled polyamide fibers and spun into a hybrid yarn. Subsequently these yarns are processed into preforms by means of Tailored Fiber Placement. This process allows for a precise fiber positioning in accordance with the load path. Additionally, back-injection molding allows functional integration into the parts, aiming for weight reduction and lowering installation effort. Recycled carbon fibers and recycled matrix granules are also utilized for the back-injection molding process using an Injection Moulding Compounder to investigate their influence on mechanical properties of the parts. [ABSTRACT FROM AUTHOR]

Polylactide (PLA) is the most important bioplastic on the market due to its good mechanical properties and a permanent growth of the production capacity. But in terms of extrusion foaming the melt strength and extensibility of commercial polylactide is too low. Therefore such commercial grades need to be modified to induce crosslinking, chain extension or branching by means of reactive extrusion on a twin-screw extruder. In this work different modifiers (chemical as well as physical modifiers) were used. The most effective results were achieved with organic peroxide. With this modifier the molecular weight, the melt viscosity, the melt strength and the crystallization rate were improved leading to foams with a closed-cell structure and improved compression behavior. Furthermore, the modifier was found to be more effective than a commercial modifier. [ABSTRACT FROM AUTHOR]