Structure, properties, and photodegradation of polymer biocomposites based on polylactide filled with A-Len® thermoplastic compound

Objectives. The work set out to investigate the influence of the compounding and technological parameters of polymer biocomposite materials based on polylactide (PLA) filled with the A-Len^® thermoplastic compound (Alen) on their structural, thermophysical, and mechanical properties, as well as to determine the mechanism of their destruction under the impact of ultraviolet radiation.

Methods. Films of PLA and Alen, as well as polymer composites based on them (PLA/Alen), were obtained using a flat die extruder (MashPlast, Russia). The structural and morphological properties of the films were determined with a JCM-6000 PLUS scanning electron microscope (JEOL, Akishima, Tokyo, Japan); their thermal properties were obtained using a DSC 204 F1 calorimeter (NETZSCH, Germany). The chemical composition and degradation mechanism were analyzed by infrared spectroscopy with an FSM-1201 spectrometer (Russia) fitted with an attenuated total internal reflection attachment. The mechanical properties were examined using a Z010 ZwickRoell tensile testing machine (Zwick Roell Group, Germany). The effect of ultraviolet radiation was assessed using an ultraviolet chamber.

Results. It was shown that the presence of Alen in mixtures with PLA affects the formation of a heterogeneous structure due to the presence of polyethylene in the Alen composition. This mediated a reduction in Young’s modulus by 34% (to 1050 MPa) in comparison with the initial value for PLA (1600 MPa). In the polymer composites, the PLA phase recrystallizes to yield a denser-ordered supramolecular structure, while in the polyethylene phase, the segmental mobility of macromolecules decreases and crystallization process is hindered by their different polarities to form an interface between the components under study.

Conclusions. The photodegradation mechanism in PLA/Alen polymer composites is shown to be primarily due to the presence of a prooxidant additive in Alen, which initiates the oxidation process to degrade and subsequently fragment the low-molecular fraction of polyethylene. In addition, the PLA matrix photodegrades through the Norrish Type II mechanism, which describes the oxidation of polymer chains by a radical mechanism to produce C=C bonds. The developed polymer composites are promising for the fabrication of certain polymer products due to their optimal performance characteristics and accelerated photochemical degradation kinetics.

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