Search Results (7)

The current work is driven by applying circular principles, and it investigated the potential recyclability of polybutylene succinate (PBS) containing brewer’s spent grain filler (BSGF, 30 wt%) in comparison to the recyclability of pure PBS. PBS is much more stable than the PBS/BSGF composite during processing cycles. Typically, thermomechanical degradation induces radical formation and branching of the macromolecular chain in PBS. Furthermore, PBS becomes less hydrophilic (by 53%, reaching 84°, approaching the 90° threshold), and its surface roughness increases by about 38% after five processing cycles. BSGF increases the viscosity of the melt, especially at low frequencies, and stabilizes the melt in the PBS/BSGF, which has lower torque variations during processing compared to pure PBS. Furthermore, BSGF in r-PBS/BSGF increases both hydrophilicity (by about 15%, from 75° to 64°) and surface roughness (by about 17%) after five processing cycles of the solid bio-composite and limits the formation of carboxylic groups during thermomechanical degradation. PBS is recyclable five times because it maintains its properties unchanged during extrusion cycles. At least two reprocessing steps are required for PBS/BSGF to obtain an optimal dispersion of BSGF, which can be re-extruded approximately three times. PBS/BSGF after four and five extrusion steps shows increased rigidity (E_t PBS/BSGF > E_t PBS) and reduced ductility (ε_b PBS/BSGF < ε_bt PBS), which could limit the recyclability of the PBS-based composite. Full article

The influence of the addition of ground buckwheat hulls on the properties of biocomposite on the basis of 3-hydroxybutyrate-co-3-hydroxyvalerate (PHBV) is presented here. The changes in the material after repeated reprocessing—up to five recycling cycles—are written in the paper. Analysis of the shrinkage, water adsorption, selected mechanical properties, tensile impact strength, hardness and the microstructure of the surface layer was performed. The results show that the application of the buckwheat hulls into the biopolymer decreases the material shrinkage. It improves the material dimensional stability, as well as increases the water adsorption in the wake of the hydrophobic properties of the filler. The addition of the natural filler also leads to an increase in composite stiffness. The decrease in the tensile impact strength and the elongation at break is also noted. The reprocessing of the biocomposite initially led to a decrease in its mechanical properties, but the results stabilized after further processing cycles. This indicates the improvement of the microstructure homogeneity. The microscopic analysis shows that buckwheat hull particles were better embedded in the matrix after recycling. The increase in hardness was also noted. The PHBV–ground buckwheat hull biocomposite is characterized by stable mechanical properties and by recycling resistance, which makes it a promising material in terms of the sustainable development. Full article

An important issue addressed in research on the assessment of the quality of polymer products is the quality of the polymer material itself and, in accordance with the idea of waste-free management, the impact of its repeated processing on its properties and the quality of the products. In this work, a biocomposite, based on poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) with short hemp fibers, was obtained and repeatedly processed, which is a continuation of the research undertaken by the team in the field of this type of biocomposites. After subsequent stages of processing, the selected mechanical, processing and functional properties of the products were assessed. For this purpose, microscopic tests were carried out, mechanical properties were tested in static tensile and impact tests, viscosity curves were determined after subsequent processing cycles and changes in plastic pressure in the mold cavity were determined directly during processing. The results of the presented research confirm only a slight decrease in the mechanical properties of the produced type of biocomposite, even after it has been reprocessed five times, which gives extra weight to arguments for its commercialization as a substitute for petrochemical-based plastics. No significant changes were found in the used parameters and processing properties with the stages of processing, which allows for a predictable and stable manufacturing process using, for example, the injection molding process. Full article

This article is focused on studying the effect of the reprocessing cycles on the mechanical, thermal, and aesthetic properties of a biocomposite. This process is based on starch thermoplastic polymer (TPS) filled with 20 wt% almond shell powder (ASP) and epoxidized linseed oil (ELO) as a compatibilizing additive. To do so, the biocomposite was prepared in a twin-screw extruder, molded by injection, and characterized in terms of its mechanical, thermal, and visual properties (according to CieLab) and the melt flow index (MFI). The analyses carried out were tensile, flexural, Charpy impact tests, differential scanning calorimetry (DSC), thermogravimetric analysis (TGA). The effects of the reprocessing were also studied for the biodegradable unfilled TPS polymer. The results showed that TPS and TPS/ASP biocomposite suffer changes progressively on the properties studied after each reprocessing cycle. Furthermore, it was observed that the addition of ASP intensified these effects regarding TPS. However, in spite of the progressive degradation in both cases, it is technically feasible to reprocess the material at least three times without needing to incorporate virgin material. Full article

Non-isothermal thermogravimetric analysis (TGA) was employed to investigate the degradation of polypropylene (PP) during simulated product manufacturing in a secondary process and wood–plastic composites. Multiple batch mixing cycles were carried out to mimic the actual recycling. Kissinger–Akahira–Sunose (KAS), Ozawa–Flynn–Wall (OFW), Friedman, Kissinger and Augis models were employed to calculate the apparent activation energy (E_a). Experimental investigation using TGA indicated that the thermograms of PP recyclates shifted to lower temperatures, revealing the presence of an accelerated degradation process induced by the formation of radicals during chain scission. Reprocessing for five cycles led to roughly a 35% reduction in ultimate mixing torque, and a more than 400% increase in the melt flow rate of PP. E_a increased with the extent of degradation (α), and the dependency intensified with the reprocessing cycles. In biocomposites, despite the detectable degradation steps of wood and PP in thermal degradation, a partial coincidence of degradation was observed under air. Deconvolution was employed to separate the overlapped cellulose and PP peaks. Under nitrogen, OFW estimations for the deconvoluted PP exposed an upward shift of E_a at the whole range of α due to the high thermal absorbance of the wood chars. Under air, the E_a of deconvoluted PP showed an irregular rise in the initial steps, which could be related to the high volume of evolved volatiles from the wood reducing the oxygen diffusion. Full article

This study explores the reprocessing behavior of polypropylene-sugarcane bagasse biocomposites using neat and chemically treated bagasse fibers (20 wt.%). Biocomposites were reprocessed 5 times using the extrusion process followed by injection molding. The mechanical properties indicate that microfibers bagasse fibers addition and chemical treatments generate improvements in the mechanical properties, reaching the highest performance in the third cycle where the flexural modulus and flexural strength increase 57 and 12% in comparison with neat PP. differential scanning calorimetry (DSC) and TGA characterization show that bagasse fibers addition increases the crystallization temperature and thermal stability of the biocomposites 7 and 39 °C respectively, without disturbing the melting process of the PP phase for all extrusion cycles. The rheological test shows that viscosity values of PP and biocomposites decrease progressively with extrusion cycles; however, Cole–Cole plots, dynamic mechanical analysis (DMA), width at half maximum of tan delta peaks and SEM micrographs show that chemical treatments and reprocessing could improve fiber dispersion and fiber–matrix interaction. Based on these results, it can be concluded that recycling potential of polypropylene-sugarcane bagasse biocomposites is huge due to their mechanical, thermal and rheological performance resulting in advantages in terms of sustainability and life cycle impact of these materials. Full article

The recyclability of polylactide acid (PLA) and poly (3-hydroxybutyrate-co-3-hydroxyvalerate (PHBV)-based biocomposites (10%, 20% and 30% by weight of sisal natural fibre) was evaluated in this work. The mechanical and thermal properties were initially determined and were shown to be similar to commodity plastics, such as polyethylene or polypropylene. Three recycle steps were carried out and the mechanical and thermal properties of recycled samples were evaluated and compared to the reference samples. The tensile modulus increased for recycled PLA biocomposites, whereas it was hardly influenced by recycling the PHBV biocomposites. The tensile strength and deformation at the break decreased notably after the first cycle in all cases. Although all the biocomposites became more brittle with recycling, the properties were conserved along until the third cycle, proving their promising recyclability. From the data obtained from the dynamic mechanical analysis, a slight decrease of the storage modulus of PHBV was observed, whereas PLA showed a significant decay of its properties at the 3rd recyclate. The PLA specimens were filled with sisal fibres until they reached 20%wt, which seemed also less subject to the embrittlement occurring along the recycling phase. The characteristic temperatures (glass transition-T_g, crystallization-T_c, melting-T_m) of all the biocomposites were not highly affected by recycling. Only a slight decrease on the melting point of the recycled PHBV was observed suggesting an overall good reprocessability. Moreover, the processing conditions lied in the same range as the conventional plastics which would facilitate potential joint valorization techniques. Full article