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It is well known that the processing conditions in polymer processing have a high impact on the resulting material morphology and consequently the component’s mechanical behavior. However, especially for semicrystalline polymers, the tools available for predicting the final morphology of injection molding parts still have significant limitations. In order to investigate the potential of injection molding simulation for the prediction of the morphology, POM homopolymer specimens were injection molded. The crystallization kinetics data were measured, and simulations in 3D and 2.5D with and without crystallization analysis were conducted in Autodesk Moldflow. The simulations are found to be good accordance with the experiments. Predicted spherulite size and crystalline orientation factor reveal a good qualitative correlation with optical micrographs. Also, the evolution of these parameters along the flow path is plausible. The simulation is found to be a powerful tool for morphology prediction in polymeric parts. Its applicability, however, is still limited to 2.5D models in Autodesk Moldflow, which, of course, is insufficient for complex, thick-walled 3-dimensional parts.

Specific nano- and micro-scale morphologies of composites can affect the resulting optical and UV reflectivity of the materials. One example is “Vantablack®” made from aligned carbon nanotubes (CNTs) with 99.96% absorption. A similar material with CNTs grown on surface-activated aluminum (CNTs/sa-Al) even yielded 99.995% absorption, one order of magnitude higher than Vantablack®. On the other hand, fresh snow reflects 90% or more of the incident electromagnetic radiation with wavelengths between 400 and 1,000 nm. The reflectivity of snow originates from multiple scattering in the porous morphology made of snow grains. Taking these complex morphologies as inspiration, CFRP epoxy composites with different types, sizes, shapes, and amount of nanoparticles are prepared and compared regarding their optical and ultraviolet (UV) reflectivity. Increasing the reflectivity in the near and far UV may be beneficial for the durability of the epoxy composites, but selective higher or lower reflectivity in certain wavelength ranges may also yield tailored visual effects. Results from different processing approaches with selected nanoparticles are presented and discussed.

An experimental study on the impact response of foam core sandwich panels subjected to low velocity impact is performed. Panels with glass fiber laminated facesheets and polystyrene and polyurethane foam core with density of 32 kg/m3, respectively 100 kg/m3, were tested in impact on an INSTRON Ceast 9340 drop tower at different impact energies. The composite facesheets were made of epoxy resin, glass fiber roving of 500 g/m2 and short glass fibers of 3 mm in 5 different combinations. The effect of foam core and facesheet type on the resulting impact damage and contact force is analyzed. It was noted that higher impact energies introduce matrix damages and the partial fracture of the fibers which significantly change the force-displacement histories, particularly after the maximum impact force is reached. Also, the use of polyurethane foam core increased the impact damage indentation in size and depth compared to the panels with polystyrene core. Panels having facesheets only with short glass fibers show a very poor resistance compared to the ones with roving and are completely perforated even for the smallest impact energy.

Surface Mounted Devices (SMDs) are widely spread throughout microelectronics and power electronics. They mostly employ epoxy molding compound (EMC) based encapsulations. Thus, enhanced lifetime assessment methods are necessary. To understand the stress situation in SMDs at the end of the production cycle, an improved model approach for the curing of EMC is implemented within Finite Element Analysis (FEA) simulations. During production in e.g a RTM process, material properties are spatially varying due to different curing degrees. Hence, a mismatch of mechanical properties is present, which in return leads to internal stresses. The introduced model approach is an extension to the work of Gschwandl. et al [1] and includes a stress-free deformation before vitrification, changing material properties during curing as well as plastic deformations and visco-elastic effects. The implementation in numerical FEA simulations allows for a better understanding of arising residual stresses and help optimizing the production cycle of SMDs.

Different polyolefin matrix materials were melt-blended with high-molecular weight paraffin waxes as phase change materials (PCM) on a lab-scale extruder. Afterwards, the compounds were converted into latent heat storage plates via compression molding. Detailed morphological investigations of the functional materials with Differential Scanning Calorimetry and Small Angle X-ray Scattering revealed various types of interaction between the applied components. Distinct correlations between the material formulation, the resulting overall compound morphology and the mechanical characteristics of the compounds were established. Moreover, a high long-term stability in terms of latent heat storage capacity, morphology and mechanical properties was ascertained, which emphasizes a high application potential of the functional materials. However, since the mechanical characteristics of the compounds deteriorated significantly upon the melting of the PCM (i.e. beginning storage of latent heat), latent heat storages in the form of polymeric compounds are not applicable as load-bearing component.

Functionalization of silica nanoparticles is needed as to improve the mechanical performance of epoxy nanocomposites. Previous experience showed that direct dispersion of commercially available silica nanofillers does not improve significantly the mechanical properties of resulting nanocomposites. Different methods of fabrication are presented along with comments on the possibilities to improve the quality of obtained specimens. Both functionalized and unfunctionalized silica nanoparticles were added in three epoxy resins. The considered filling fraction was in most cases 0.1, 0.3 and 0.5 wt%. The obtained nanocomposites were subjected to monotonic uniaxial loading at room temperature. The static mechanical properties were not significantly changed regardless the filler type or percentage and type of epoxy resin.

The mechanical recyclability of the technical biopolymers polytrimethylene terephthalate (PTT), cellulose acetate butyrate (CAB), polybutylene succinate (PBS) and polyhydroxy alkanoate blend (PHBV/PBAT) was evaluated by assessing the effect of repeated polymer processing (extrusion without further compounding with virgin material or additives) on the material structure and mechanical properties. Reprocessing-induced hydrolytic degradation was found to be the prevalent aging mechanism of the investigated biopolymer grades. However, susceptibility to hydrolysis, and thus maintenance of the performance characteristics, differed strongly between the biopolymer types. To that effect, PTT and CAB especially exhibit a high potential for mechanical recycling. By taking advantage of appropriate additivation, the mechanical recyclability of PBS and PHBV/PBAT is also assumed to be high.

Poly(ethylene terephthalate) films with oriented lamellar structure were deformed in tensile experiments and investigated in situ using small angle X-ray scattering. The tensile direction was set parallel, normal and in an angle of 45° relative to the surface normal of the lamellae. Data were interpreted in terms of two-dimensional autocorrelation functions. The deformation of lattice spacing and lamellar orientation can largely be explained by affine transformations. The sample, where the lamellar surface normal was normal to tensile direction, developed a chequerboard type arrangement of crystalline parts. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017

The rapid expansion of the Internet of Things (IoT) and consumer electronics is driving the demand for microelectromechanical systems (MEMS) in the area of wearables, smartphones, and home and building applications. MEMS sensor packages feature a variety of polymeric materials which can significantly affect their behavior under environmental loads as humidity or temperature. A broad range of different polymeric materials can be applied in the packages, but to get a good MEMS sensor performance, an optimized application tailored material combination should be applied. To analyze the effect of the applied material types an advanced simulation approach has to be considered. A hygro-thermo-mechanical simulation based on measured temperature and moisture dependent material properties is presented. As MEMS sensor packages are complex multimaterial systems, the main challenge is the modeling of the moisture discontinuities in the interfaces. The discontinuity of moisture concentration has been solved by using the solubility approach.

To achieve future recycling targets and CO2 and waste reduction, the transfer of plastic contained in mixed waste from thermal recovery to mechanical recycling is a promising option. This requires extensive knowledge of the necessary processing depth of mixed wastes to enrich plastics and their processability in polymer processing machines. Also, the selection of a suitable processing method and product application area requires appropriate material behaviour. This paper investigates these aspects for a commercial processed, mixed waste, and two different mixed polyolefin fractions. The wastes are processed at different depths (e.g., washed/not washed, sorted into polyethylene, polypropylene, polyethylene terephthalate, polystyrene/unsorted) and then either homogenised in the extruder in advance or processed heterogeneously in the compression moulding process into plates. The produced recyclates in plate form are then subjected to mechanical, thermal, and rheological characterisation. Most investigated materials could be processed with simple compression moulding. The results show that an upstream washing process improves the achievable material properties, but homogenisation does not necessarily lead to an improvement. It was also found that a higher treatment depth (recovery of plastic types) is not necessary. The investigations show that plastic waste recovery with simple treatment from mixed, contaminated wastes into at least downcycling products is possible.

Fused filament fabrication is a material extrusion-based additive manufacturing technique that has been strongly growing in popularity, for it is accessible, versatile, and affordable. The 3D-printing of semi-crystalline polymers still faces major challenges, though. Apart from common issues such as shrinkage and warpage phenomena, a variety of process-related morphological and crystallographic changes can occur. Since these changes strongly influence the resulting material properties, it is crucial to understand the complex relationships between the material, its processing and final properties on a fundamental level. In this context, the present work examines the impact of different nozzle temperatures and printing speeds on 3D-printed polypropylene (PP) samples. One extreme parameter set (high nozzle temperature, low printing speed) reveals a homogeneous morphology, weak flow-induced orientations, isotropic thermal conductivities and a strong inter-layer diffusion. In contrast, the other extreme parameter set (low nozzle temperature, high printing speed) forms an inhomogeneous morphology with a complex growth of shish-kebab structures, a pronounced weld line morphology and a highly anisotropic behaviour. By in-depth analyses of four parameter sets, this paper offers novel insights into the complex formation of crystalline structures in 3D-printed semi-crystalline polymers and suggests how to purposefully design the property portfolio of these materials.

Microelectromechanical systems (MEMS) and MEMS packaging solutions are gaining increased interests for electronic applications. These packages feature a variety of polymeric materials and composites e.g. fiber reinforced polymer laminates, insulating and conductive adhesives. Due to the sensitivity of MEMS devices to mechanical stress and environmental factors such as temperature and humidity, the influence of these factors on the device’s performance needs to be accounted for. In this contribution, a fabric woven glass fiber reinforced epoxy resin (BT epoxy resin) and two chosen adhesives commonly used in semiconductor and MEMS packaging have been considered and their dependency on environmental parameters have been studied with different testing methods. Based on the measured material properties a simulation process predicting the package under defined environmental loads is presented.

The present study was inspired by different industry projects in which a strong dependence of the fatigue fracture performance of POM on the processing conditions was observed. To examine the relationships under more reproducible conditions, plates of two different POM homopolymer resins (one significantly nucleated) were produced by compression molding and by injection molding under moderate conditions. For the injection molding, three different mold temperatures were used. At specific locations, the plates were analyzed concerning their hierarchical structure on the micro- and nanolevel and concerning their fatigue fracture performance. For the fatigue fracture performance, the dependence on the processing conditions was rather small for the nucleated resin but much more significant for the other resins. This dependence could not be related to morphological effects only, and thus, a combined effect of morphology and residual stresses was assumed.

In this study, different strategies to improve the mechanical properties of physically foamed high-density polylactic acid sheets were examined to produce polylactic acid foam sheets with tailor-made mechanical properties. The first part was the determination of the effect of different blowing agents (CO2 and N2) on the foam morphology. The second part of the study was the modification of the formulation. For this purpose, both a linear and a branching chain extender and a thermoplastic elastomer were used to improve the elongational properties (tensile modulus and strain at break) of the polylactic acid foam sheets. Additionally, the effect of the addition of cellulose fibers on the foam morphology and the mechanical properties was investigated. All experiments were carried out on a laboratory flat-film line. This extrusion line consists of a 30-mm single-screw extruder attached with a 250-mm flat sheet die. The results show a strong influence of the material formulation on the mechanical properties of the high-density foam sheets. Both the mechanical properties and foam morphology could be improved by the right material formulation. The addition of the thermoplastic elastomer leads to a better foam morphology and also to a reduced brittleness of the foam sheets. Furthermore, it could be demonstrated that cellulose fiber can be used as a nucleating agent for polylactic acid but causes a further decrease in the strain at break.

The fracturing behavior of polymers and polymeric composites is of great interest in the scientific and application community. Especially in the case of silicate-layered nanocomposites the influence of fillers on the fracturing behavior is still fairly unclear. Fractures of semicrystalline polymers are accompanied by various processes of which shearing and cavitations are the most common ones. Nanocomposite deformation due to the delamination of fillers seems to be the most practical way leading to fractures with relatively low strains. With the method of scanning small angle X-ray scattering (SAXS) and wide angle X-ray diffraction (WAXD) it is possible to combine information on the structural details with the position on the sample, with the actual position resolution of the investigation being defined by the size of the X-ray beam used to scan the sample. By means of the application of synchrotron radiation it is nowadays possible to adjust the actual beam size to the dimensions of the region of interest, which is why it is an adequate tool for studying the deformation region near a crack tip. In a native polypropylene sample, the fracturing process was accompanied by shear yielding as well as lamellae fragmentation and reorienting. In the highly deformed material near the crack tip fibrillated material could be found. However, in the polymeric nanocomposites (PNC) shearing, lamellae fragmentation, and fibrillation were hindered by the filler due to which the material did not have so much freedom to dissipate energy and fractures occurred much earlier. In this paper the comparison of a PNC and its native polymer is to provide an overview of the different deformation mechanism and the structural details around the crack tip.

Structural characterization in polymer nanocomposites is usually performed using X-ray scattering and microscopic techniques, whereas the improvements in processing and mechanical properties are commonly investigated by rotational rheometry and tensile testing. However, all of these techniques are time consuming and require quite expensive scientific equipment. It has been shown that a fast and efficient way of estimating the level of reinforcement in polymer nanocomposites can be performed by melt extensional rheology, because it is possible to correlate the level of melt strength with mechanical properties, which reflect both the 3D network formed by the clay platelets/polymer chains as well as final molecular structure in the filled system. The physical network made of silicate filler and polymer matrix has been evaluated by X-ray diffraction and transmission electron microscopy. Extensional rheometry and tensile testing have been used to measure efficiency of the compatibilizer amount in a polypropylene-nanoclay system. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009

This research addresses the fracture mechanical analysis of two commercially available polyoxymethylene homopolymer resins. Two types of experiments are used: monotonic fracture toughness tests and cyclic fatigue crack growth tests. The resulting total lifetimes in the fatigue crack growth tests are split up into the appropriate parts of crack growth initiation and fatigue crack propagation. Fracture surfaces of monotonic and cyclic tests are analyzed using light microscopy and scanning electron microscopy. Besides the mechanical tests, the morphology within the used compact tension specimens is examined in detail by using differential scanning calorimetry, small- and wide-angle X-ray scattering, and polarized light microscopy. The results are analyzed and discussed, considering observations in the previous studies published in the literature. It is shown that both materials can be well analyzed using linear elastic fracture mechanics and their fracture mechanical properties are presented in conjunction with a detailed documentation of the microstructure. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 40831.

The morphology of polymer nanocomposites is usually characterized by various methods like X-ray diffraction (XRD) or transmission electron microscopy (TEM). In this work, a new approach for characterizing nanocomposites is developed: the results of small angle x-ray scattering, on-line extensional rheometry (level of melt strength) and Young's modulus out of tensile test are correlated with those of near infrared (NIR) spectroscopy. The disadvantages of the common characterization methods are high costs and very time consuming sample preparation and testing. In contrast, NIR spectroscopy has the advantage to be measured in-line and in real time directly in the melt. The results were obtained for different aggregate states (NIR spectroscopy and on-line rheotens test in melt state, tensile test, and XRD in solid state). Therefore, important factors like crystallization could not be considered. Nevertheless, this work demonstrates that the NIR-technology is perfectly suitable for quantitative in-line characterization. The results show that, by the installation of a NIR spectrometer on a nanocomposite-processing compounder, a powerful instrument for quality control and optimization of compounding process, in terms of increased and constant quality, is available. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

In this study, different strategies to improve the mechanical properties of physically foamed high density polylactic acid (PLA) sheets were examined to produce PLA foam sheets with tailor-made mechanical properties. The first part was the determination of the influence of the blending of PLA with polybutylene succinate (PBS) on the properties of the high density foam sheets. Additionally, the influence of the PBS on the rheological properties was investigated with a cone plate rheometer. The second part was to manufacture multilayer films with a physically foamed middle layer and highly filled skin layers. The foamed sheets were characterized in terms of mean cell size, cell density, density and surface roughness. The experiments were carried out on lab scale multi-layer extrusion line.