Abstract
In order to be recycled, polymers with different molecular masses, designed to be initially processed by different technologies such as thermoforming, injection or blow molding, are collected together. The melt viscosity of this material mixture will depend on the ratio of polymers having different molecular characteristics. The possibility of re-processing implies the use of higher range of temperature or the use of different additives to adjust the melt viscosity. In these conditions, the quality of recycled goods could be affected. This study presents the results obtained by differential scanning calorimetry analysis of some polypropylene-based samples coming from the real waste stream collection (conventional samples) as well as of selected polymers from this stream based on the processing technology and of different brand packages from each of the above-mentioned classified fractions. Based on the thermal data (Tm, Tc, ΔHm, ΔHc and the melting and crystallization curve characteristics), morphological features of the recycled polypropylene, such as crystallinity degree of the initial recycled and re-crystallized polymers (Xm, Xc), melting and crystallization rates (vm, vc), lamellae thickness, and number of tie molecules, were determined, and the prediction of the maximal Young’s modulus was made. This study evidenced that processing technology of the polymers in fresh state or as recycled material strongly influenced the product morphology and, as a consequence, the predicted mechanical properties. By comparing the conventional recycled polymers with the injection-molded mix of virgin polymers, the first one exhibited a lower crystallinity with about 22%, approximately the same lamella thickness, the crystals’ polydispersity higher with about 10% and the Young’s modulus lower with about 22%.
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Acknowledgements
We acknowledge the contribution of Erasmus + master student Alexandra Rusanescu, from Transilvania University of Brasov, Romania, and master student Emma P.A. van Bruggen, from Delft University of Technology, the Netherlands, which prepared the samples used in this study under the kind and competent supervision of Prof. Dr. Peter C. Rem, from Delft University of Technology, Civil Engineering and Geosciences Faculty.
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Baltes, L., Costiuc, L., Patachia, S. et al. Differential scanning calorimetry—a powerful tool for the determination of morphological features of the recycled polypropylene. J Therm Anal Calorim 138, 2399–2408 (2019). https://doi.org/10.1007/s10973-019-08679-7
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DOI: https://doi.org/10.1007/s10973-019-08679-7