Characterization of Methylcellulose Based Hydrogels by Using Citric Acid as a Crosslinking Agent

摘要

This research work aims at studying citric acid crosslinking capacity, evaluating structural modifications produced on hydrogels based on methylcellulose and sorbitol, along with the effect on the barrier properties of the obtained hydrogels. This additive, besides its preservative capacity in foods, can act as a crosslinking agent in some polymers matrix. Methylcellulose (A4M) solutions were prepared at 1.5%/v at 80°C. Sorbitol analyzed concentration was 0.25%. Citric acid was added to 5 and 10 (p/pMC) concentrations as a cross-linker agent in hydrogels forming solutions. Hydrogels were obtained by casting and drying method. Moisture content, swelling capacity and films' solubility in water at different temperatures were evaluated. Hydrogels' microstructural and mechanical properties were determined through DMTA and FTIR. Water vapor permeability was determined according to the ASTM E96 standard, and oxygen permeability through an Oxtran 2/20 permeability meter by following the method described in ASTM standard. All experiments were performed on triplicate samples. ANOVA was used to analyze results by using the statistical program INFOSTAT. Formulation with better properties: low permeability to water vapor and oxygen, lower swelling capacity and greater mechanical strength was the result of combining MC with 0.25% sorbitol and 5% AC additive (w/w MC). Studies carried out on microstructural Fourier-transform infrared spectroscopy (FTIR) and barrier properties (permeability to water vapor and gases), and tensile strength tests (Dynamic Mechanical Analysis, DMA) of hydrogels obtained from cellulose derivatives (MC) confirmed that polymer's crosslinking capacity is enhanced in the presence of citric acid. Hydrogels could have applications as a controlled release agent of nutrients and/or antioxidants in food and fertilizers in soils for agriculture by using electro-stimulation techniques and/or taking advantage of their swelling capacity. They can also be used as a support for biopreservatives or as a model system for edible coatings.