Effect of wood fiber loading on the chemical and thermo-rheological properties of unrecycled and recycled wood-polymer composites

Novel wood fiber (WF)-polypropylene composites were developed using the extrusion process with a twin-screw extruder. The influence of different mass addition of WF to unrecycled polypropylene (PP) and recycled PP (R-PP) on the chemical, thermal and rheological properties of the processed WF-PP and WF-R-PP composites was investigated. For this purpose, the chemical surface structure of the composites was followed with ATR-FTIR (attenuated total reflection Fourier transform infra red spectroscopy), while the thermal properties of the WF-PP composites were investigated with differential scanning calorimetry (DSC). Furthermore, the crystalline structure of the composites was determined by X-ray diffraction (XRD) analysis. Finally, the rheology of the materials was also studied. It was observed that a stronger particle formation at high additional concentrations was observed in the case of recycled PP material. The addition of WF over 20% by weight increased the crystallinity as a result of the incorporation and reorganization of the WF and also their reinforcing effect. The addition of WF to pure PP had an influence on the crystallization process, which due to the new β phase and γ phase PP formation showed an increased degree of crystallinity of the composites and led to a polymorphic structure of the composites WF-PP. From the rheological test, we can conclude that the addition of WF changed the rheological behavior of the material, as WF hindered the movement of the polymeric material. At lower concentrations, the change was less pronounced, although we observed more drastic changes in the material behavior at concentrations high enough that WF could form a 3D network (percolation point about 20%)

Rheological behavior of spectrally selective coatings for polymeric solar absorbers

Since the world’s energy demands are growing rapidly, there is a constant need for new energy systems. One of the cleanest, most abundant, and renewable natural resources available is solar energytherefore, the development of surfaces with high absorption of solar radiation is increasing. To achieve the best efficiency, such surfaces are coated with spectrally selective coatings, which are strongly influenced by the pigments and resin binders. Spectrally selective paints have a very specific formulation, and since the applied dry coatings should exhibit high spectral selectivity, i.e., high solar absorptivity and low thermal emissivity, the rheological properties of liquid paints are of great importance. In the present work, we studied the effect of the rheological properties of liquid thickness-insensitive spectrally selective (TISS) paints on the spectral selectivity and adhesion of dry coatings on a polymeric substrate. The results showed that the functional and adhesion properties of dry coating on polymeric substrates is strongly dependent on the rheological properties of the binder and catalyst used for the preparation of the liquid paints. It was shown that the paints with good spectral selective properties (thermal emissivity e$_T$ 0.92) and good adhesion (5B) can be prepared for polymer substrates

Influence of stabilization additive on rheological, thermal and mechanical properties of recycled polypropylene

To decrease the amount of plastic waste, the use of recycling techniques become a necessity. However, numerous recycling cycles result in the mechanical, thermal, and chemical degradation of the polymer, which leads to an inefficient use of recycled polymers for the production of plastic products. In this study, the effects of recycling and the improvement of polymer performance with the incorporation of an additive into recycled polypropylene was studied by spectroscopic, rheological, optical, and mechanical characterization techniques. The results showed that after 20 recycling steps of mechanical processing of polypropylene, the main degradation processes of polypropylene are chain scission of polymer chains and oxidation, which can be improved by the addition of a stabilizing additive. It was shown that a small amount of an additive significantly improves the properties of the recycled polypropylene up to the 20th reprocessing cycle. The use of an additive improves the rheological properties of the recycled melt, surface properties, and time-dependent mechanical properties of solid polypropylene since it was shown that the additive acts as a hardener and additionally crosslinks the recycled polymer chains

Viscoelastic properties of bread dough kneaded with a kitchen machine

Linear viscoelastic range (LVR) of bread dough with various composites was determined with oscillatory amplitude tests, while frequecy test (performed in LVR) enabled determination of viscoelastic behaviour at small deformation. In order to determine flow characteristics of the dough and to evaluate the toreque, which was generated during the kneading on the impeller shaft, rotational flow tests were performed. As the dough is highly viscoelastic material, normal forces stimulate the dough to climb up the impeller shaft. Thus, shear stress dependence of first normal stress coefficient and firts normal stress difference was determined for all compositions of the dough

The Influence of HDPE recycling on rheological properties and processing conditions

According to the latest analysis of European plastics production performed by Plastics Europe, High Density Polythylene (HDPE) together with Medium Density Polythylene were on the third place among the most demanded plastics in Europe in 2016. Mostly used for manufacturing of packaging HDPE gained its demand due to superior mechanical properties, resistance to external impacts and ease of processing

Advancements in metal additive manufacturing

Additive manufacturing (AM) has attracted huge attention for manufacturing metals, ceramics, highly filled composites, or virgin polymers. Of all the AM methods, material extrusion (MEX) stands out as one of the most widely employed AM methods on a global scale, specifically when dealing with thermoplastic polymers and composites, as this technique requires a very low initial investment and usage simplicity. This review extensively addresses the latest advancements in the field of MEX of feedstock made of polymers highly filled with metal particles. After developing a 3D model, the polymeric binder is removed from the 3D-printed component in a process called debinding. Furthermore, sintering is conducted at a temperature below the melting temperature of the metallic powder to obtain the fully densified solid component. The stages of MEX-based processing, which comprise the choice of powder, development of binder system, compounding, 3D printing, and post-treatment, i.e., debinding and sintering, are discussed. It is shown that both 3D printing and post-processing parameters are interconnected and interdependent factors, concurring in determining the resulting mechanical properties of the sintered metal. In particular, the polymeric binder, along with its removal, results to be one of the most critical factors in the success of the entire process. The mechanical properties of sintered components produced through MEX are generally inferior, compared with traditional techniques, as final MEX products are more porous

In-depth rheological characterization of tungsten sol-gel inks for inkjet printing

The inkjet printing of the functional materials prepared by the sol-gel route is gaining the attention for the production of the variety of the applications not limited to the printed boards, displays, smart labels, smart packaging, sensors and solar cells. However, due to the gelation process associated with the changes from Newtonian to non-Newtonian fluid the inkjet printing of the sol-gel inks is extremely complex. In this study we reveal in-depth rheological characterization of the WO$_3$ sols in which we simulate the conditions of the inkjet printing process at different temperature of the cartridge (20–60 °C) by analyzing the structural and rheological changes taking place during the gelation of the tungsten oxide (WO$_3$) ink. The results provide the information on the stability of the sol and a better insight on the effects of the temperature on the gelation time. Moreover, the information on the temperature and the time window at which the inkjet printing of the sol-gel inks could be performed without clogging were obtained. The WO$_3$ ink was stable in a beaker and exhibited Newtonian flow behavior at room temperature over 3 weeks, while the gelation time decreased exponentially with increasing temperature down to 0.55 h at 60 °C

Tribological behaviour of green wood-based unrecycled and recycled polypropylene composites

In this study we evaluated the tribological performance of polypropylene composites with wood-flour fillers obtained as a by-product from the wood-processing industry, which were based on unrecycled and recycled polypropylene polymer matrices. The mechanical properties of polypropylene-wood composites with wood-filler loadings of 0–40\ua0wt % were determined with tensile tests and their friction and wear behaviours were studied with dry reciprocating ball-on-disc sliding tests against 100Cr6 steel balls at room temperature. The addition of the wood fillers resulted in a significant improvement in the tribological performance compared to the neat, unrecycled, and recycled polypropylene materials: the friction coefficient decreased by up to 30%, while the wear resistance was improved by up to two orders of magnitude. While neat unrecycled polymers have better properties than recycled, addition of 40\ua0wt % wood-filler content in both, recycled and unrecycled composites, resulted in almost the same level of coefficient of friction (∼0.25) and wear coefficient (2\ua0 7\ua010−6 mm3/(Nm) to 3\ua0 7\ua010−6 mm3/(Nm)). Even with the addition of as low as 5\ua0wt % of wood fibres the wear resistance was improved for 63% and 43% for unrecycled and recycled composites, respectively, which indicates that the use of wood fillers could be a sustainable and cost-effective way to improve the polymer tribological performance, and could compensate for the normally poorer properties of recycled materials, making the recycled polypropylene-wood composites a suitable sustainable choice for tribological applications

Tensile properties of mineral fibers determined with Sentmanat extensional rheometer

Within the presented research, we utilized a non-standard technique, i.e. Sentmanat Extensional Rheometer (shorter SER-tool), which can potentially provide tensile measurements (i.e. tensile strength and Young\u27s modulus) on relatively short and brittle fibrous materials such as slag mineral fibers. For easier transportation and fastening of the fibers, physical model of SER-tool was slightly modified. Consequently, modified technique was theoretically (through parametric error analysis) and experimentally (through mechanical characterization) evaluated on four different types of mineral fibers. Despite a fair, yet distinguishable scatter of tensile strength which cannot be theoretically evaluated due to size effect (related to thermo-mechanical histories), fiber\u27s weakest link (related to fiber defects), etc., mechanical response, which is universally presented by Young\u27s modulus, was reproducible. Parametrical error analysis, which determines the accuracy of modified SER-tool showed that the large part of the error arises from the combination of fiber diameter and error in fiber diameter, however by careful selection of fibers (related to the magnitude of the diameter and its error) the result remains within the predicted ranges. From the results different types of mechanical responses can be observed, which is related to ceramic content, i.e. SiO2+Al2O3, within the slag fiber. Utilized technique demonstrates the high performance and the capability of modified SER-tool to perform various studies, investigating the effects of thermo-mechanical histories, chemical composition and other parameters on mechanical properties of single fiber filaments