RESUMEN
The COVID-19 pandemic resulted in the generation of large quantities of medical waste and highlighted the importance of efficient waste management systems. One good example of this is rapid antigen tests, which contain valuable resources, and which are usually incinerated after their use. The present study aimed to evaluate the potential of waste rapid antigen test cassettes (RATCs) as a resource for the preparation of sustainable flame-retardant plastics. Milled RATCs were compounded with different concentrations (10-30 wt.%) of aluminium diethylphosphinate (ADP) and injection moulded into test specimens. Prepared samples were exposed to ultraviolet (UV) ageing for varying durations and characterised by Fourier-transform infrared spectroscopy (FT-IR), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), dynamic mechanical analysis (DMA), tensile tests, Charpy impact tests, and vertical burning tests. FT-IR analysis revealed that RATCs are composed mainly of high-impact polystyrene (HIPS), which was further confirmed by suitable glass transition temperatures (Tg) determined by DSC and DMA. The addition of ADP resulted in progressive embrittlement of HIPS with increasing concentration, while flammability decreased significantly and reached V-1 classification at loading of 30 wt.%. UV ageing caused photo-oxidative degradation of HIPS, which resulted in decreased strain-at-break, while flammability was not affected.
RESUMEN
The hybridisation of injection moulding (IM) and additive manufacturing (AM) offers the opportunity to combine the high productivity of IM and the high flexibility of AM into a single process. IM parts can be overprinted through fused filament fabrication (FFF) to allow for the customisation of parts or to add new functionalities. However, the right material pair must be chosen, and processing parameters must be optimised to achieve suitable adhesion between the components. The present study dealt with the investigation of the influence of the interfacial area, substrate surface roughness and overprinting processing parameters on the adhesion between the polyamide 6 (PA6) substrate and thermoplastic polyurethane (TPU) rib overprinted via FFF. PA6 substrates were produced through the IM of plates into a mould with different textures to obtain substrates with three different surface roughnesses. The ribs with varied interfacial areas were overprinted onto produced substrates using a desktop FFF 3D printer. To study the effect of overprinting processing parameters, the ribs were overprinted under varying printing and substrate temperatures and printing speeds according to the Box-Behnken design of experiments (DoE). The chemical composition and thermal properties of used materials were determined via attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA). The surface properties of prepared substrates were studied via digital optical microscopy (OM), through surface roughness measurements using a confocal microscope, through contact angle (CA) measurements and through the determination of free surface energy (SFE). The adhesion between the components was determined by evaluating the tear-off strength using a universal testing machine (UTM). With an increasing interfacial area, the tear-off strength decreased, while substrate surface roughness had no statistically significant effect. Overprinting parameters influenced the tear-off strength in the order of printing speed > printing temperature > substrate temperature. High values of tear-off strength were found for the lowest printing speed, while there were no important differences found between the middle and upper values. With increasing printing and substrate temperatures, the tear-off strength increased linearly. The highest value of tear-off strength (0.84 MPa) was observed at a printing temperature, substrate temperature and printing speed of 250 °C, 80 °C and 2 mm/s, respectively.
RESUMEN
This study investigated the influence of viscose fibre (VF) geometry on the microstructures and resulting properties of high-density polyethylene (HDPE) composites. Seven types of viscose fibres varying in cross-section shape, linear density, and length were pelletised, compounded into HDPE with a twin-screw extruder, and injection moulded. The microstructures of the composites were characterised by investigating their cross-sections and by extracting the fibres and measuring their lengths using optical microscopy (OM). The mechanical and thermal properties of the composites were characterised using differential scanning calorimetry (DSC), tensile tests, Charpy impact tests, and dynamic mechanical analysis (DMA). The composites prepared using cylindrical fibres with a linear density of 1.7 dtex exhibited the best fibre dispersion, highest orientation, and lowest fibre-fibre contact area. The decrease in the linear density of the cylindrical fibres resulted in increasingly worse dispersion and orientation, while composites containing non-cylindrical fibres exhibited a comparably larger fibre-fibre contact area. The initial fibre length of about 3 to 10 mm decreased to the mean values of 0.29 mm to 0.41 mm during processing, depending on the initial geometry. In general, cylindrical fibres exhibited a superior reinforcing effect in comparison to non-cylindrical fibres. The composites containing cylindrical fibres with a linear density of 1.7 dtex and a length of 5 mm exhibited the best reinforcing effect with an increase in tensile modulus and strength of 323% and 141%, respectively.
RESUMEN
This study reports on the development of a novel polymer processing approach that combines low-temperature (LT) processing and fibre direct compounding (FDC) to reduce the thermal stress on thermosensitive components that occurs during compounding and subsequent injection moulding (IM). Composites based on polyamide 6 (PA6) and cellulose fibres (CeF) were prepared using an LT-FDC process and in parallel with a conventional approach using a twin-screw extruder and IM. The morphological, optical, thermal, and mechanical properties of the prepared samples were investigated using optical microscopy (OM), differential scanning calorimetry (DSC), colorimetry, dynamic mechanical analysis (DMA) and tensile tests. Composites prepared using LT-FDC exhibited worse fibre dispersion but lower fibre degradation. In comparison to neat PA6, the LT-FDC composites had increased tensile modulus (Et) and storage modulus (E') at 120 °C by up to 32% and 50%, respectively, while the tensile strength (σm) decreased by 20%.
RESUMEN
A stone chest found in 1971 near one of the largest early Christian basilicas in Northern Dalmatia (Croatia) contained brass tiles decorated with various biblical scenes. An archaeological study confirmed the thesis that the fragments of brass tiles are most likely the remains of a wooden chest made in the 4th century AD, and that this is one of the best preserved archaeological finds of its kind in the world as one of the biblical scenes shows Mary, together with a record of her name (Maria). Based on the preserved brass tiles, a reconstruction of the wooden chest was made in 1973 with tiles glued onto a plastic frame. Subsequent studies have shown that such a reconstruction was not adequate, as some of the brass tiles were destroyed (disintegrated), and they were not connected properly into a whole that could represent the original. For the new reconstruction of this archaeological object it was necessary to carry out a material analysis, including the chemical composition of the brass tiles, as well as to find a solvent for the glue which could be used to remove the brass tiles from the plastic framework without any additional destruction. Based on extensive investigations and material analyses including the following techniques (SEM, EDX, FTIR, DSC), the starting points for the restoration process of the wooden chest with brass tiles were set, as well as the proposal for the appearance of the new chest.
RESUMEN
Engineering polymers reinforced with renewable fibres (RF) are an attractive class of materials, due to their excellent mechanical performance and low environmental impact. However, the successful preparation of such composites has proven to be challenging due to the low thermal stability of RF. The aim of the present study was to investigate how different RF behaves under increased processing temperatures and correlate the thermal properties of the fibres to the mechanical properties of composites. For this purpose, hemp, flax and Lyocell fibres were compounded into polypropylene (PP) using a co-rotating twin screw extruder and test specimens were injection moulded at temperatures ranging from 180 °C to 260 °C, with 20 K steps. The decomposition behaviour of fibres was characterised using non-isothermal and isothermal simultaneous thermogravimetric analysis/differential scanning calorimetry (TGA/DSC). The prepared composites were investigated using optical microscopy (OM), colorimetry, tensile test, Charpy impact test, dynamic mechanical analysis (DMA) and melt flow rate (MFR). Composites exhibited a decrease in mechanical performance at processing temperatures above 200 °C, with a steep decrease observed at 240 °C. Lyocell fibres exhibited the best reinforcement effect, especially at elevated processing temperatures, followed by flax and hemp fibres. It was found that the retention of the fibre reinforcement effect at elevated temperatures can be well predicted using isothermal TGA measurements.