Abstract
Bionanocomposite films processed by twin screw extrusion followed by thermo molding were prepared from corn starch (Zea mays) and pH-sensitive nano-clays packaged with Jamaica flower (Hibiscus sabdariffa) extract (JFE). The hydrogen (H)-bonding interactions of the materials obtained were evaluated by ATR/FTIR spectroscopy, and their influence on the physicochemical and surface properties of the materials was analyzed. The degree of biodegradability and compostability of the films was also recorded. This latter was analyzed in terms of the ecotoxicity of the films using the variations in the growth of the primary root of lettuce (Lactuca sativa) seedlings exposed to three concentrations (1, 10 and 100 μg/mL) of the powdered films as a biomarker. The addition of the JFE-containing nano-fillers strengthened the H-bonding interactions with the thermoplastic starch (TPS) matrix, and these interactions were more efficient when there were fewer steric impediments between the JFE and the TPS. Additionally, stronger H-bonding interactions produced more hydrophilic surfaces, with greater surface energy and rougher surface morphology. All the films tested were biodegradable. Our research group had previously encountered high cytotoxicity in one of the evaluated nano-clay systems, and in this study, we confirmed that this same nano-clay system produced a non-compostable material at high concentrations (100 μg/mL), as measured by its effect on lettuce seedlings. This confirms that biodegradable materials are not necessarily compostable.
Highlights
The growing global concern about environmental pollution caused by the accumulation of petroleum-derived plastics has led to the search for novel, natural and biodegradable polymers to replace them (Gao et al, 2014; Zhang, Wang, Zhao, & Wang, 2013)
Six nano-filler – Jamaica flower (Hibiscus sabdariffa) extract (JFE) combinations were used and labeled as follows: natural Mnt (NMnt), natural Mnt containing JFE (NMnt + JFE), Mnt modified with dimethyl benzylhydrogenated tallow ammonium (MntMB), Mnt modified with dimethyl benzylhydrogenated tallow ammonium containing JFE (MntMB + JFE), Mnt modified with dimethyl dihydrogenated tallow ammonium (MntMD) and Mnt modified with dimethyl dihydrogenated tallow ammonium containing JFE (MntMD + JFE)
The bands mentioned above occurred at the same frequencies in all the samples tested, differences were observed in the absorbance of the peaks appearing at 3280 and 1365 cm−1, both of which can be attributed to the O-H stretching vibrations
Summary
The growing global concern about environmental pollution caused by the accumulation of petroleum-derived plastics has led to the search for novel, natural and biodegradable polymers to replace them (Gao et al, 2014; Zhang, Wang, Zhao, & Wang, 2013). One of the nano-clay systems (Mnt modified with dimethyl benzylhydrogenated tallow ammonium, MntMB) showed high cytotoxicity at two different doses (0.25% w/v and 0.5% w/v) using the normal human lung fibroblast (MRC-5, ATCC CCL-171)-cell line as a test material (see Appendix A and B) (Gutiérrez, León, et al, 2018) These results led us to ask further important, and as yet unanswered, questions: 1) Could this high cytotoxicity put at risk the compostability of the material? The novelty of this study lies in: 1) the use of pH-sensitive nanoclays as natural fillers of food hydrocolloid matrix used (corn starch), 2) the processing methodology used: extrusion followed by thermo compression (large-industrial scale) which has been little studied as compared to the casting methodology (small-laboratory scale) that has been well studied over many years, 3) the examination of the H-bonding interactions that occur on the surfaces of these types of materials, which has been little studied, and 4) the determination of the compostability (ecotoxicity) of these materials using a novel bioassay
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