Mechanical recycling of polylactide, upgrading trends and combination of valorization techniques

The upcoming introduction of polylactides in the fractions of polymer waste encourages technologists to ascertain its valorization at the best quality conditions. Mechanical recycling of PLA represents one of the most cost-effective methodologies, but the recycled materials are usually directed to downgraded applications, due to the inherent thermomechanical degradation affecting its mechanical, thermal and rheological performance. In this review, the current state of mechanical recycling of PLA is reported, with special emphasis on a multi-scale comparison among different studies. Additionally, the applications of physical and chemical upgrading strategies, as well as the chances to blend and/ or composite recycled PLA are considered. Moreover, the different valorization techniques that can be combined to optimize the value of PLA goods along its life cycle are discussed. Finally, a list of different opportunities to nurture the background of the mechanical recycling of PLA is proposed, in order to contribute to the correct waste management of PLA wastes

Thermal stability enhancement of poly(hydroxybutyrate-co-hydroxyvalerate) through in situ reaction

Poly(hydroxybutyrate-co-hydroxyvalerate) (PHBV) has recently caught more and more attention due to its renewability, good mechanical and barrier properties, as well as marine biodegradability. However, the severe thermal degradation during processing is a major drawback and limits its application. In this work, the thermal stability of PHBV during melt-processing was investigated by incorporating reactive agents. Various contents of Di(tert-butylperoxyisopropyl)benzene (DB), Triallyl isocyanurate (TAIC) and multi-functional epoxy chain extender (ECE) were used. The mixing torque, mechanical and thermal properties were studied. The results revealed that the mixing torque of PHBV gradually decreased during 10 min of melting time and eventually dropped to 2 N.m. Upon adding ECE, the mixing torque slightly increased but still decreased during 10 min period. For the system consisting of DB/TAIC or DB/TAIC/ECE, the mixing torque reached the equilibrium and their values were roughly twofold higher than PHBV alone. The possible crosslinking reaction and torque reversion were predominantly observed when adding high contents of DB and TAIC. 1 H NMR spectra suggested the reaction of DB/TAIC and PHBV. Young’s modulus and tensile strength of system consisting of DB at 0.3 phr, TAIC at 0.1 phr and ECE at 0.5 phr increased from 1440 and 40.4 MPa to 1803 and 55.5 MPa, respectively. TGA thermograms showed that the onset temperature and inflection point were improved when adding DB/TAIC and ECE. From the findings, it indicated that the combination of DB/TAIC and ECE was one of the simplest and effective ways to improve the melt viscosity without sacrificing the mechanical properties

Biosourced blends based on poly (lactic acid) and polyamide 11: Structure-properties relationships and enhancement of film blowing processability

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