In this study, the effect of various parameters of a single screw extruder on the rheology and mechanical properties of a polylactic acid (PLA) filament with a 1.75 mm diameter was investigated. The barrel temperature, nozzle and cooling bath temperature, screw speed, nozzle diameter, water bath length, and distance to the nozzle were the process variables. A Taguchi experimental design was implemented using an L8 orthogonal matrix with seven factors and two levels, and their influence on roundness and diameter were evaluated. Among the various processing parameters, the temperature of the cooling bath affected the roundness the most. The mechanical properties and surface roughness of the PLA filament were examined using a tensile test and nanofocus optical system, respectively. Moreover, to assess the filament’s reliability and investigate its behavior further, the filament was used to print 0° plates, and then dog-bone samples were cut from them to evaluate the mechanical properties of the printed specimens. Finally, the results indicate that improved-roundness filaments of 0.004 mm can lead to enhanced mechanical properties in 3D-printed samples with 3.54 MPa.

In this work, self-lubricating and electrically conductive polymers on a polypropylene (PP) matrix were prepared and investigated. These properties were obtained by additivating PP with carbon black (CB) and multi-walled carbon nanotubes (MWCNTs), in combination with a surface active ionic liquid (IL, trihexyltetradecylphosphonium docusate [P66614][DOC]). These polymeric composites are expected to achieve coefficients of friction (COFs) comparable to lubricated systems. Combined with electrical conductivity, these materials could be applied in electrically loaded tribosystems. The COF was reduced by up to 25% compared to that of plain PP, and high electrical conductivity and self-lubrication were achieved. Fundamental differences between the carbon-based fillers in their interaction with IL were investigated with high-resolution surface analysis (TEM, AFM) and Raman and ATR-FTIR spectroscopy. By varying the tribological test parameters, the application limits of self-lubrication were identified. It was demonstrated that the contact pressure has a strong influence on the COF. Therefore, this work points to potential applications in (e.g. 3D-printed) bearings and electrically loaded bearings where electrical conductivity and relatively low COFs are required.

An alternative approach for the production of Molded Interconnect Devices (MID), using additive manufacturing of thermoplastics, is presented. Two-component 3D printing enables the processing of a pristine polymer together with a second phase composed out of conductive nanocomposite. For the validation of this concept, two different demonstrators were developed and produced using anArburg Freeformer printer: a USB insert with an integrated LED (“Lightstick”) and a capacitive touch sensor system. The conductive paths were printed in PC/ABS made conductive with carbon nanotubes (CNTs). Measured resistivity of each conductive layer, of 200$\mu$m thickness, was of 1 $\Omega$textbf{{cm. The whole circuit resistance together with the contacts has proved to be low enough to successfully light up the LEDs. Furthermore, printed capacitive electrodes demonstrated that the functions of touch pad, proximity sensor and slider can be integrated in a thermoplastic without additional metallic components. This technique presents promising results for the integration of electrical functionality into thermoplastic parts and their processing chain.

Nanocomposites with polypropylene as matrix material and nanoclay as filler were produced in a double twin screw extruder. The extrusion was monitored with a spectrometer in the visible and near-infrared spectral region with a diode array spectrometer. Two probes were installed at the end at the extruder die and the transmission spectra were measured during the extrusion. After measuring the transmission spectra and converting into turbidity units, the particle distribution density was calculated via numerical linear equation system. The distribution density function shows either a bimodal or mono modal shape in dependence of the processing parameters like screw speed, dosage, and concentration of the nanoclays. The method was verified with SEM measurements which yield comparable results. The method is suitable for industrial in-line processing monitoring of particle radii and dispersion process, respectively.

Nanocomposite materials represent a success story of nanotechnology. However, development of nanomaterial fabrication still suffers from the lack of adequate analysis tools. In particular, achieving and maintaining well-dispersed particle distributions is a key challenge, both in material development and industrial production. Conventional methods like optical or electron microscopy need laborious, costly sample preparation and do not permit fast extraction of nanoscale structural information from statistically relevant sample volumes. Here we show that optical coherence tomography (OCT) represents a versatile tool for nanomaterial characterization, both in a laboratory and in a production environment. The technique does not require sample preparation and is applicable to a wide range of solid and liquid material systems. Large particle agglomerates can be directly found by OCT imaging, whereas dispersed nanoparticles are detected by model-based analysis of depth-dependent backscattering. Using a model system of polystyrene nanoparticles, we demonstrate nanoparticle sizing with high accuracy. We further prove the viability of the approach by characterizing highly relevant material systems based on nanoclays or carbon nanotubes. The technique is perfectly suited for in-line metrology in a production environment, which is demonstrated using a state-of-the-art compounding extruder. These experiments represent the first demonstration of multiscale nanomaterial characterization using OCT.

PS was compounded with MWCNT loadings of 1,2,3,5 and 7.5 wt.% at varying speeds, throughputs and extruder barrel temperatures. High SME inputs at enhanced processing speeds seem to have had the single largest effect in enhancing dispersion. Relative evaluations of PS-MWCNT interaction indicate an interphasial layer growth of 24% for 2 wt.% MWCNT additions at 1100 rpm compared to 18% growth at 500 rpm. Raman analysis does not show MWCNT peak shift when incorporated into PS but a constant increase in FWHM is observed irrespective of the MWCNT content. Significant enhancement in thermal stability occurs up to 2 wt.% MWCNT loading while 1-2 wt.% shows the rheological threshold. A drop in 10 orders of magnitude of volume resistivity is achieved on a 2 wt.% sample processed at 1100 rpm compared to those processed at 500 rpm and these do not differ by much to those achieved with higher MWCNT contents.

1, 2, 3, 5, and 7.5?wt% MWCNTs are incorporated into PS in a twin-screw extruder at varying speeds, throughputs and extruder barrel temperatures. Increased SME at enhanced processing speeds seems to have the single largest effect in enhancing dispersion. A relative evaluation of PS/MWCNT interactions indicate an interfacial layer growth of 24% for 2?wt% MWCNT at 1100?rpm compared to 18% growth at 500?rpm. Raman analysis does not show an MWCNT peak shift but a constant increase in FWHM is observed irrespective of the MWCNT content. A significant enhancement of thermal stability occurs up to 2?wt% MWCNT loading while 12?wt% shows the rheological threshold. The volume resistivity decreases dramatically in a 2?wt% sample processed at 1100?rpm compared to those processed at 500?rpm.