Polymer processing and characterization of LLDPE films loaded with α‐tocopherol, quercetin, and their cyclodextrin inclusion complexes

Abstract

Natural antioxidant additives were compounded into linear low-density polyethylene (LLDPE) using a twin-screw counter-rotating mixer and compression molded into films. Manufactured LLDPE films contained 2715 mg kg À1 a-tocopherol in its free and b-cyclodextrin complexed form and 1950 mg kg À1 quercetin in its free and c-cyclodextrin complexed form. Both cyclodextrin complexes were loaded into films at 1.5% by weight. These natural antioxidants were incorporated into LLDPE resins with two different catalyst types, Ziegler-Natta and metallocene. Films were characterized by optical microscopy, oxidation induction time (OIT), oxygen transmission rate, contact angle analysis, and atomic force microscopy (AFM). All antioxidant additives increased the oxidative stability of LLDPE as measured by increased OIT, particularly quercetin. Natural antioxidants and their cyclodextrin inclusion complexes may provide a dual function in packaging to protect the polymer from oxidative degradation during melt processing and to delay the onset of oxidation of the packaged food during storage.

Efficient melt stabilization of polyethylene with quercetin, a flavonoid type natural antioxidant

“…One way packaging must be protected only during processing and 50 ppm quercetin is sufficient, while pipes must usually have an OIT of at least 20 min, thus 200-250 ppm is needed in this case. However, the composition dependence of all properties indicates unambiguously that already much smaller amounts of quercetin stabilize PE efficiently than those reported before [12,13].…”

“…As mentioned in the introductory part, the stabilizing effect of quercetin was always studied at quite large additive contents at around and above 2000 ppm [12,13]. Figs.…”

“…The compound is a flavonol type flavonoid, which has proven antioxidant, antiviral and anti-inflammatory effect in the human body. Some research groups have attempted already to use quercetin as an antioxidant in polyolefins [12,13], while others tried to apply it as a component of active packaging material [14][15][16][17]. In the latter case mostly the migration and dissolution of the antioxidant was studied in various solvents modeling food.…”

“…In the latter case mostly the migration and dissolution of the antioxidant was studied in various solvents modeling food. Koontz et al [12], for example, homogenized quercetin and its complex with cyclodextrin with PE in a twin-screw extruder and investigated homogeneity as well as stability. The authors did not find any aggregates in the polymer, stability increased considerably, while oxygen permeation decreased simultaneously.…”

“…In most studies quercetin was added at concentrations of 2-3000 ppm [12,13] or in even larger quantities, which raises again the question of solubility, but also price, since the compound is rather expensive. As a consequence, the goal of our work was to study the stabilization effect of quercetin in a wide concentration range not investigated before.…”