Starch is a readily available and inexpensive natural polymer that presents processing difficulties and chemical and mechanical limitations, which hinder its application as a commodity plastic. Therefore, various research studies aim to modify starch structures to expand its range of applications. One of the modification reagents for starch is citric acid, although different publications present varied results regarding the combination of these two materials without delving into the underlying reasons for these interactions.

With the objective of developing new environmentally friendly materials and understanding the activity of citric acid and glycerin in a starch matrix, modified starches were produced using distinct methodologies. The materials were then studied at specific processing stages and final products through structural analyses (amylose:amylopectin ratio, infrared spectroscopy), thermal analyses (thermogravimetry), mechanical analyses (tensile strength), and hydrophilic behavior (contact angle and swelling). Both methodologies resulted in chemical reactions and ester formation due to the addition of citric acid to starch, confirmed by the presence of bands at 1700 cm^-1 in the FTIR spectra.

The change in the order of addition of the modifying agents to starch resulted in different materials concerning their mechanical and hydrophilic properties. It was suggested that Citric Acid, applied via Methodology 1, facilitated starch plasticization, reducing its mechanical strength and increasing hydrophilicity. On the other hand, when applied via Methodology 3, it promoted starch crosslinking, increasing its mechanical strength and reducing hydrophilicity.

The results presented indicate that, using the same reagents, it is possible to produce different environmentally friendly polymers that are cost-effective and possess suitable properties for intended applications.