Comparison of Aging Resistance and Antimicrobial Properties of Ethylene–Norbornene Copolymer and Poly(Lactic Acid) Impregnated with Phytochemicals Embodied in Thyme (Thymus vulgaris) and Clove (Syzygium aromaticum)

Abstract

The effects of plant-based extracts on the solar aging and antimicrobial properties of impregnated ethylene–norbornene (EN) copolymer and poly(lactic acid) (PLA) were investigated. In this study, the impregnation yield of polyolefin, lacking in active centers capable of phytochemical bonding, and polyester, abundant in active sides, was measured. Moreover, two different extracts plentiful in phytochemicals—thyme (TE) and clove (CE)—were employed in the solvent-based impregnation process. The effect of thymol and eugenol, the two main compounds embodied in the extracts, was studied as well. Interestingly, oxidation induction times (OIT) for the impregnation of EN with thyme and clove extracts were established to be, respectively, 27.7 and 39.02 min, which are higher than for thymol (18.4 min) and eugenol (21.1 min). Therefore, an aging experiment, mimicking the full spectrum of sunlight, was carried out to investigate the resistance to common radiation of materials impregnated with antioxidative substances. As expected, the experiment revealed that the natural extracts increased the shelf-life of the polymer matrix by inhibiting the degradation processes. The aging resistance was assessed based on detected changes in the materials’ behavior and structure that were examined with Fourier-transform infrared spectroscopy, contact angle measurements, color quantification, tensile tests, and hardness investigation. Such broad results of solar aging regarding materials impregnated with thyme and clove extracts have not been reported to date. Moreover, CE was found to be the most effective modifying agent for enabling material with antimicrobial activity against Escherichia coli to be obtained.

Natural Active Ingredients for Poly (Lactic Acid)-Based Materials: State of the Art and Perspectives

“…Compounds such as eugenol, carvacrol, thymol, limonene, geranial and linalool ( Figure 9 ) were used to prepare active food packaging materials based on PLA with antioxidant and antimicrobial properties to extend the shelf-life of products [ 142 , 143 , 144 , 145 , 146 , 147 , 148 , 149 , 150 ]. The versatility of SFE to obtain EOs and terpenes offered a chance to design productive processes of active PLA materials activated with individual terpenes or their mixtures that are up-scalable to obtain green and sustainable industrial processes.…”

“…The antimicrobial properties of terpenes are mainly due to their lipophilic character, resulting in an effect on the structure and functionality of microbial cell membranes [ 215 ]. The activation of PLA-based matrices with thymol revealed antimicrobial effects on the most important bacterial related to food-borne illness, such as Gram-negative Escherichia coli [ 17 , 139 , 145 , 148 , 151 ], Pseudomonas spp. [ 142 ], and Gram-positive Bacillus subtilis [ 151 ], Staphylococcus aureus [ 17 , 139 , 145 ], and Micrococcus lysodeiktus [ 142 ].…”

“…Masek et al used the ASTM E2180 method to evaluate the antimicrobial activity of a PLA matrix activated through an impregnation process with commercial thymol, eugenol, and Thymus vulgaris L. extracts. All formulations showed a reduction of E. coli colonies, but the composite PLA/thymus extract achieved the best performance [ 148 ].…”

Thymol, a Monoterpenoid within Polymeric Iodophor Formulations and Their Antimicrobial Activities

“…Thyme is a globally well-known medicinal plant utilized historically against microbial infections [42,[57][58][59][60][61][62][63][64][65][66][67][68][69][70]. Thyme extracts contain the antimicrobial secondary metabolites Thymol and carvacrol [3,5,[9][10][11][12][13][14]42,[60][61][62][63][64][65][66][67][69][70][71].…”

“…Thyme is a globally well-known medicinal plant utilized historically against microbial infections [42,[57][58][59][60][61][62][63][64][65][66][67][68][69][70]. Thyme extracts contain the antimicrobial secondary metabolites Thymol and carvacrol [3,5,[9][10][11][12][13][14]42,[60][61][62][63][64][65][66][67][69][70][71]. Thymol, a monoterpenoid with outstanding antimicrobial properties, appears in an increasing number of investigations in combination with other essential oils, plant extracts, nanoparticles, and chitosan [70][71][72][73][74][75][76][77][78][79][80][81][82]…”