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

Abstract

In the last two decades, the naturally occurring polysaccharides, such as chitosan and pectin, have gained great attention having potential applications in different sectors, from biomedical to new generation packaging. Currently, the chitosan and pectic have been proposed as suitable materials also for the formulation of films and coatings for cultural heritage protection, as well as packaging films. Therefore, the formulation of biopolymer films, considering only naturally occurring polymers and additives, is a current challenging trend. This work reports on the formulation of chitosan (CS), pectin (PC), and chitosan:pectin (CS:PC) films, also containing natural crosslinking and reinforcement agents, such as citric acid (CA) and halloysite nanotubes (HNT), through the solvent casting technique. The produced films are characterized through water contact angle measurements, infrared and UV–visible spectroscopy and tensile test, while the durability of the CS:PC films is evaluated subjecting the film to accelerated UVB exposure and monitoring the photo-oxidation degradation in time though infrared spectroscopy. All obtained results suggest that both crosslinking and reinforcement agents have beneficial effects on the wettability, rigidity, and photo-oxidation resistance of biopolymer films. Therefore, these biopolymer films, also containing naturally occurring additives, have good properties and performance and they are suitable as coverage films for cultural heritage protection.

Control of end‐of‐life oxygen‐containing groups accumulation in biopolyesters through introduction of crosslinked polysaccharide particles

“…Additionally, to evaluate the film transparency, the linear attenuation coefficient ( K ) values were calculated considering the measured absorption values ( A ) at λ = 750 nm, samples thickness ( D ) and using the formula: K = A /(2.3 D ). [ 44 ] The corresponding data are reported in Figure 5(B). Although the differences are small, the transparency of the PLA‐based films is slightly lower due to the presence of both Ch and cCh.…”

Effect of different processing techniques and presence of antioxidant on the chitosan film performance

“…According to literature, the CA molecules could interact with the functional groups of chitosan chains through physical and/or chemical interactions/reactions. [29,35] To evaluate the durability of sc_Ch, sc_Ch/CA, cm_Ch and cm_Ch/CA films, thin films have been subjected to accelerated UVB exposure and the photooxidative degradation in time of all investigated films has been monitored through FTIR analysis at regular intervals at about 8 h. According to literature, chitosan degradation mechanism occurs mainly by depolymerization, followed by deacetylation, oxidation and interchain crosslinking, [36,37] see Figure 6A, [37] and as documented elsewhere, the photo-oxidation behavior of Ch and Chbased systems can be profitably investigated monitoring the changes in time of the FTIR spectra in range 1750-1480 cm À1 , which contains three different peaks: first peak at around 1730 cm À1 due to >C=O stretching, second peak at around 1626 cm À1 due to the C=O stretching of secondary amide group (amide I) and third peak at around 1530 cm À1 attributed to N-H bending. [36][37][38] Interestingly, as currently documented by Bussiere et al, [38] if the weathering is carried out without humidity, the chitosan film shows a remarkable photoxidation resistance, and particularly, the formation of oxygencontaining groups, that leads to arising of a peak at ca.…”

“…Besides, the weight losses are overall about 50% than the initial ones in the temperatures between 250 and 350 C. According to literature, this could be related to random split of glycosidic bonds, releasing low molecular weight compounds and decomposing the pyranose rings through dehydration and ring-opening reactions. [35] In Table 1, the temperature values at overall weight losses at about 50% of the all investigated samples are reported and it can be noticed that sc-Ch and sc-Ch/ CA samples show higher values, than the cm-Ch and cm-Ch/CA, suggesting a better thermal stability for the sc samples in this temperature range. Besides, although less pronounced, the CA presence has a beneficial effect on the Ch thermal resistance in the range 30-350 C. This could be understand considering that the CA is a polycarboxylic compound, and the CA molecules exert antioxidant action through hydrogen atoms donation at low temperature.…”

“…For example, the chitosan can be crosslinked by acid treatments, [5,7] ultrasound treatment [26] and/or introduction of appropriate crosslinking agents that can interact and/or react with chitosan functionalities during film formulation. [28][29][30][31][32][33][34][35] Interestingly, some naturally occurring acids, such as ascorbic, ferulic and citric acids, are recently gained attention as good additive for chitosan, also thanks to their ability to react and stabilize polysaccharide materials.…”

Special Issue “Investigation of Polymer Nanocomposites’ Performance”

“…In the last decades, bioderived polysaccharides, such as chitosan (CS) and pectin (PC), have attracted the attention of researchers and industries, as they can be applied in the biomedical and packaging field [7]. Moreover, they can be promising candidates for the development of sustainable films and coatings for cultural heritage protection, as highlighted in the paper of Infurna et al, entitled "Understanding the Effects of Crosslinking and Reinforcement Agents on the Performance and Durability of Biopolymer Films for Cultural Heritage Protection" [8]. In order to improve the physical behavior of these chitosan, pectin, and chitosan/pectin films, the authors proposed the addition of natural crosslinking and reinforcement agents, such as citric acid (CA) and halloysite nanotubes (HNTs).…”