Thermal and Thermo-Mechanical Properties of Poly(L-lactic Acid) Biocomposites Containing β-Cyclodextrin/d-Limonene Inclusion Complex

Abstract

Bio-based composites made of poly(L-lactic acid) (PLLA) and β-cyclodextrin/d-limonene inclusion complex (CD-Lim) were prepared by melt extrusion. Encapsulation of volatile d-limonene molecules within β-cyclodextrin cages was proven to be a successful strategy to prevent evaporation during high-temperature processing. However, small amounts of limonene were released upon processing, resulting in the plasticization of the polymeric matrix. Morphological analysis revealed good dispersion of the filler, which acted as a nucleating agent, favoring the growth of PLLA crystals. The composites′ lowered glass transition temperature upon the addition of CD-Lim was also proved by thermomechanical analysis (DMA). Moreover, DMA revealed constant stiffness of modified materials at room temperature, which is crucial in PLLA-based formulations.

Optical, mechanical, and antimicrobial properties of bio‐based composites of poly(L‐lactic acid) and D‐limonene/β‐cyclodextrin inclusion complex

“…Incorporation of D-limonene within β-cyclodextrin cages was conducted through the precipitation method, as detailed in our previous manuscript. 22,23 First, PLLA was blended with inclusion complex in a rotary mixer Retsch GM 200 (3 min at a speed of 2000 rpm). Secondly, the premixed components with different modifier contents (0-30 wt%) were homogenized via co-rotating extrusion with a Zamak extruder at 190 C and 60 rpm.…”

“…. 23 ΔE values are the observer's visual impressions, that is, the observer cannot notice any color change when the ΔE value is within the range 0 and 1; for the value ranging between 1 and 2, merely a knowledgeable observer may perceive a variation; between 2 and 3.5 everyone can notice the color difference; for the ΔE values above 5 the observer see two different colors. 2 The yellowness index (YI) was estimated, as per the ASTM E313 norm, 28 to describe the change in color upon CD-Lim addition from clear to yellow.…”

“…In our previous manuscript, we detailed the encapsulation of D-limonene within cyclodextrin cavities and introduction of CD-Lim inclusion complex into PLLA via melt extrusion to prepare composites with various filler content. 23 We proved with careful design of processing parameters, that the encapsulation within cyclodextrin is a successful way to raise thermal stability of the essential oil. Despite small amount of D-limonene (~1.5 wt%) was released from CD-Lim upon melt processing, resulting in Lim dissolved within PLLA amorphous chain portions, still sizable fraction of D-limonene remained trapped within β-CD cavities.…”

“…Despite small amount of D-limonene (~1.5 wt%) was released from CD-Lim upon melt processing, resulting in Lim dissolved within PLLA amorphous chain portions, still sizable fraction of D-limonene remained trapped within β-CD cavities. 23 A slight plasticization of the polymer was noted, resulting in anticipated onset of cold crystallization in the composites, compared to plain PLLA. Nevertheless, the plasticizing effect was overwhelmed, in terms of mechanical properties, by a presence of high content of β-cyclodextrin particles inside the polymeric matrix since microscopic images evidenced quite homogeneous filler dispersion, with some particle agglomeration noted at the highest CD-Lim content (30 wt%).…”

“…The initial material characterization detailed in ref. [23] is completed by analyzing the films' tensile behavior and determining the barrier and optical properties of PLLA/CD-Lim, as presented in this manuscript. Most importantly, antibacterial properties against the rise of a wide variety of different bacteria, both gram-positive and -negative, as well as fungi, are also discussed to evaluate the relevance of these materials for active nourishment packages.…”