Thermal and Morphological Analysis of Linear Low-Density Polyethylene Composites Containing d-limonene/β-cyclodextrin for Active Food Packaging

Abstract

Composites made of linear low-density polyethylene (LLDPE) and β-cyclodextrin/<font style="font-variant: small-caps">d</font>-limonene inclusion complex (CD-lim) were prepared by melt extrusion to develop a novel food packaging material. Scanning electron microscopy evidenced a fairly good dispersion of the filler within the polymeric matrix. Infrared spectroscopy coupled with thermogravimetric analysis confirmed the presence of CD-lim in the composites, proving that the applied technology of including the essential oil within β-CD cages allows for preventing a sizable loss of <font style="font-variant: small-caps">d</font>-limonene despite a high temperature and shear applied upon extrusion processing. Moreover, the influence of the filler on the thermal properties of PE was assessed. It was found that the cyclodextrin-based inclusion complex significantly fastens the crystallization path of the polyethylene matrix with an improved crystallization rate of the PE/CD-lim composites compared to the neat polymer.

Linear low‐density polyethylene modified with d‐limonene/β‐cyclodextrin inclusion complex: Antimicrobial composite for active food packaging

“…48,49 Upon cooling from the melt, these compounds crystallize at higher temperatures than the polyolefin, creating a dense fibrillar mesh that favors growth of polyolefin crystals [50][51][52] and results in a peculiar crystal morphology, with much smaller crystals that leads to a reduction of light scattering. 53 Based on results detailed in Dobrzy nska-Mizera et al, 32 it is also likely that CD-lim favors nucleation of polyethylene crystals, resulting in smaller spherulites, and in turn higher transparency, that is, less hazed material. The latter is a key issue for development of food packaging materials, because a transparent film attracts the customers' attention better than opaque counterparts.…”

“…An enhancement in the stiffness compared to the plain polymer is expected and typically observed for composites reinforced both with organic and inorganic fillers, including cyclodextrins. 10,55,56 Moreover, the slight plasticization of the PE matrix due to the small leakage of D-limonene occurred during processing, 32 which also affects optical properties, is counterbalanced by the presence of the solid β-CD filler that results in an overall increase of Young's modulus, higher for larger filler content. The latter is also affected by the increased crystal fraction of the formulations containing CD-lim, 31 which also contributes to a higher modulus.…”

“…Encapsulation of D-limonene within β-CD cages to obtain CD-lim inclusion complex was conducted via precipitation method, as specified in our previous articles. [29][30][31][32] Polyethylene granules were combined with the inclusion complex in a circulating blender Retsch GM 200 (2000 rpm; 3 min). The ingredients were further mixed in a molten state using a Zamak extruder equipped with two screws which ran at 160 C and 60 rpm.…”

“…28 To improve thermal stability of D-limonene, an inclusion complex, where D-limonene molecules are trapped within β-cyclodextrin molecules (CD-lim) has been developed. [29][30][31][32] This procedure greatly limits the terpene evaporation during preparation of polymerbased composites via melt processing, as detailed in Dobrzy nska-Mizera et al, 32 also ensuring excellent germicidal properties retained upon inclusion with the efficiency against pathogen growth, as proven for CD-lim added as filler to poly(L-lactic acid). 30 The aim of this research is to investigate suitability of this polyethylene-based composite for active food packaging.…”

“…Only minor amounts of D-limonene are released from the β-CD cages upon melt processing, improving the interaction and interfacial adhesion between the polymer and filler particles, which appear homogeneously distributed within polyolefin matrix, as detailed in our previous article. 32 These preliminary data constitute the starting point for further assessment of the CD-lim effect on mechanical properties, optical features, namely UV-vis and haze, as well as water absorption and gloss of linear lowdensity polyethylene. These issues, together with evaluation of antibacterial and antifungal efficiency against the most common food-related microbial species, are presented and discussed herein.…”