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. 2021 May 21;13(11):1677.
doi: 10.3390/polym13111677.

Biocomposites of Epoxidized Natural Rubber/Poly(Lactic Acid) Modified with Natural Substances: Influence of Biomolecules on the Aging Properties (Part II)

Anna Masek  1 , Stefan Cichosz  1
Affiliations

Biocomposites of Epoxidized Natural Rubber/Poly(Lactic Acid) Modified with Natural Substances: Influence of Biomolecules on the Aging Properties (Part II)

Anna Masek et al. Polymers (Basel). .

Abstract

The aim of this study is to present the possible influence of natural substances on the aging properties of epoxidized natural rubber (ENR) and poly(lactic acid) (PLA) eco-friendly elastic blends. Therefore, the ENR/PLA blends were filled with natural pro-health substances of potentially antioxidative behavior, namely, δ-tocopherol (vitamin E), curcumin, β-carotene and quercetin. In this way, the material biodeterioration potential was maintained and the material's lifespan was prolonged while subjected to increased temperatures or high-energy UVA irradiation (340 nm). The investigation of the samples' properties indicated that curcumin and quercetin are the most promising natural additives that may contribute to the delay of ENR/PLA degradation under the above-mentioned conditions. The efficiency of the proposed new natural anti-aging additives was proven with static mechanical analysis, color change investigation, as well as mass loss during a certain aging. The aging coefficient, which compares the mechanical properties before and after the aging process, indicated that the ENR/PLA performance after 200 h of accelerated aging might decrease only by approximately 30% with the blend loaded with quercetin. This finding paves new opportunities for bio-based and green anti-aging systems employed in polymer technology.

Keywords: antioxidant; epoxidized natural rubber; natural additives; poly(lactic acid); polymer blend.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
Structures of natural additives employed in this research: (a) δ-tocopherol (δ-TF), (b) curcumin (CM), (c) β-carotene (β-CT), (d) quercetin (QU).
Figure 2
Figure 2
ENR/PLA blend properties before the accelerated aging processes: (a) analysis of the swelling experiment, (b) tensile strength of analyzed specimens, (c) elongation at break of investigated samples, (d) surface free energy and its components analysis.
Figure 3
Figure 3
SEM images for: reference sample of ENR/PLA blend (a,b), ENR/PLA + δ-tocopherol (c,d), ENR/PLA + curcumin (e,f), ENR/PLA + β-carotene (g,h), ENR/PLA + quercetin (i,j) with magnifications, respectively, 250 and 1000.
Figure 4
Figure 4
Investigation of the ENR/PLA blends’ properties before and after the accelerated aging processes: (a) mass loss during the thermo-oxidative and UV aging, (b) color change during the thermo-oxidative and UV aging, (c) tensile strength changes and (d) elongation at break variations during the thermo-oxidative aging, (e) tensile strength changes and (f) elongation at break variations during the UV aging. *—sample too brittle to be examined with the selected method; the measurement was impossible.
Figure 5
Figure 5
Additional parameters, namely, whiteness index, chroma, hue angle, contributing to color change of ENR/PLA blends and their variations during the thermo-oxidative (respectively: (a,c,e)) and UV (respectively: (b,d,f)) accelerated aging processes. *—sample too brittle to be examined with the selected method; the measurement was impossible.
Figure 6
Figure 6
Color change representation for the prepared ENR/PLA blends before and after the accelerated thermo-oxidative (T), as well as UV-initiated (UV) aging processes. *—sample destroyed significantly.
Figure 7
Figure 7
Aging coefficients attributed to the filled and unfilled ENR/PLA specimens at a certain aging time during thermo-oxidative (a) and UV (b) aging.
Figure 8
Figure 8
Possible mechanisms of free radical scavenging and oxidation behavior according to the available literature data: (a) δ-tocopherol (δ-TF), (b) curcumin (CM), (c) β-carotene (β-CT), (d) quercetin (QU).
See this image and copyright information in PMC

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