Bionanocomposite Films Containing Halloysite Nanotubes and Natural Antioxidants with Enhanced Performance and Durability as Promising Materials for Cultural Heritage Protection

Abstract

In the last decade, the interest toward the formulation of polymer films for cultural heritage protection continuously grew, and these films must be imperatively transparent, removable, and should not react/interact with surface of the artworks. In this research, bionanocomposite films, based on chitosan (Ch) and pectin (P) and containing naturally occurring fillers and antioxidants, were formulated by solvent casting methods and were accurately characterized. The natural halloysite nanotubes (HNT) have a two-fold role, specifically, physical compatibilizer and antioxidant carrier. Therefore, the theoretical solubility between Ch and P was estimated considering Hoy’s method for solubility of polymers, while the optimum ratio between biopolymer constituents was assessed by ζ-potential measurements. The transparency, wettability, and mechanical behavior of Ch:P films, also in presence of HNT without and with antioxidants, were investigated. The beneficial effects of natural antioxidants, such as vanillic acid (VA) and quercetin (Q), on Ch:P/HNT durability were found.

Understanding the Effects of Crosslinking and Reinforcement Agents on the Performance and Durability of Biopolymer Films for Cultural Heritage Protection

“…The photo-oxidative degradation of CS:PC blend can be profitably followed monitoring the changes in the spectra in range 1700–1480 cm −1 in time, which contains two different peaks: first peak at around 1630 cm −1 due to the C=O presence of COO (ester) ion stretching of secondary amide group (amide I) for CS (~1626 cm −1 ) and -O(-)-C=O, for PC (~1634 cm −1 ), and expectedly, the peaks due to C=O stretching for both CS and PC appear a single peak and second peak at around 1530 cm −1 attributed to N-H bending, according to literature [ 19 ]. In Figure 5 a–c, the FTIR spectra of CS:PC, CS:PC/CA and CS:PC/HNT, obtained at different exposure time, are plotted.…”

“…However, according to our previous work [ 19 ], the adding of HNT to biopolymer matrices leads to the formulation of suitable bionanofilms as coverage for cultural heritage protection, although the film transparence is slightly penalized. As known, the HNT protect efficiently the polymer matrices against ultraviolet exposure, because the alumino-silicates structure can absorb UV irradiation, and polymer-based systems containing HNT have improved photo-oxidation resistance [ 19 , 37 , 38 , 39 ]. Therefore, the HNT marked absorption ability, especially if the HNT are added at high concentrations, could induce the decrease of the transparence in the visible range, and this could be taken into account for some specific film applications, where high transparency in the visible range is required.…”

“…Our previously published paper [ 19 ] was focused on the preparation of bio-nanocomposite films based on a chitosan and pectin blend, the investigation of theoretical solubility of pectin into chitosan, and the definition of the effective ratio between the two constituents. Based on the theoretical calculation using Hoy’s method, pectin is very soluble into chitosan.…”

“…Interestingly, the effective ratio between the two constituents is 1:1 for the film formulation through solvent casting, based on the z-potential measurements, considering the different charges of both polysaccharides, and the resultant handling of the final film. Further, to introduce naturally occurring stabilizers, aiming to improve the stability of the bio-nanocomposite films, the halloysite clay were considered as carrier for vanillic acid and quercetin molecules [ 19 , 20 ]. Therefore, by adding natural compounds, such as halloysite clay and antioxidants, some performance and properties of polysaccharide films [ 21 , 22 , 23 ] can be improved and makeable for numerous challenging applications [ 24 , 25 , 26 ].…”

Determination of the Tensile Properties and Biodegradability of Cornstarch-Based Biopolymers Plasticized with Sorbitol and Glycerol

“…The biomaterial analysis will also continue to take account of local raw materials, including cornstarch in research projects for the replication of technological growth of biodegradable plastics via solution casting method. According to previous studies, the solution casting approach is suitable for the preparation of biocomposite films using a solvent with variable polarities, such as water [22,23] and 1,2-dichloroethane [24].…”