Estabilidade de quitosana em ácido pirolenhoso destilado e desenvolvimento de filmes com adição de mucilagem de ora-pro-nóbis

Abstract

Pyroligneous acid (APD) and chitosan (Q) are biodegradable products obtained from renewable sources. They present antimicrobial and antioxidant activities and induce resistance in plants, characteristics that enable them to be used in the formulation of agricultural inputs. In combination, they form colloidal systems and films with high absorption of ultraviolet radiation. On the other hand, mucilage of ora-pro-nóbis (MOPN) is composed of protein, carbohydrates and metals, which can be applied as nutrients for plants; arabinogalactan, the main component, is a polysaccharide capable of forming polymeric blends. We evaluated the stability of colloidal systems containing 10 and 30 g·L-1 of Q in APD for up to 30 months of storage at room temperature (20 ± 5 °C), which showed Newtonian behavior. Posteriorly, those systems were destabilized and the precipitates showed phenolic compounds from APD linked to chitosan; the amount of total phenols bonded to the polymeric chains increased with storage time. The colloidal system containing 30 g·L-1 chitosan was submitted to accelerated aging, at 60 °C for up to 41 days, which, according to the rheological analyses, was equivalent to 14 months-aging at room temperature. The photoprotective and mechanical properties of the films, obtained obtained from those systems, were influenced by storage time. We investigated the interaction of MOPN with systems containing 10 g·L-1 chitosan in APD and in a model APD solvent containing 0.1% (m/v) hydroquinone and 2% (v/v) acetic acid in water. Mucilage was extracted from dry leaves of Pereskia aculeata e contained 41.16 ± 9.20% of carbohydrates and 5.87 ± 0.22% of proteins, in addition to K, Mg, and Ca. The systems showed a Newtonian behavior and the mucilage decreased viscosity to values close to pure mucilage. The films obtained with the incorporation of mucilage in the Q/APD system showed a reduction in absorption in the UV region, decrease in surface energy dissipation and solubility in water. Mucilage interacts with the chitosan, preventing the crosslinking of chains promoted by phenols. The film containing only Q/APD released 6.28% of phenols, and the burst effect was observed, that is, a rapid release of the compound from the polymeric matrix. The addition of MOPN to the Q/APD system decreases the film photoprotection and potentiates relevant properties for use in agriculture, such as the addition of nutrients and viscosity reduction in the systems.