  Citation: Chia, M.-R.; Ahmad, I.; Phang, S.-W. Starch/Polyaniline Biopolymer Film as Potential Intelligent Food Packaging with Colourimetric Ammonia Sensor. Polymers 2022, 14, 1122. https:// doi.org/10.3390/polym14061122 Academic Editors: Nadia Lotti, Michelina Soccio, Alexey Iordanskii and Valentina Siracusa Received: 27 February 2022 Accepted: 9 March 2022 Published: 11 March 2022 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. Copyright: © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). polymers Article Starch/Polyaniline Biopolymer Film as Potential Intelligent Food Packaging with Colourimetric Ammonia Sensor Min-Rui Chia 1 , Ishak Ahmad 1, * and Sook-Wai Phang 2, * 1 Polymer Research Centre (PORCE), Department of Chemical Sciences, Faculty of Science and Technology, Universiti Kebangsaan Malaysia, Bangi 43600, Selangor, Malaysia; minruichia98@gmail.com 2 Department of Physical Science, Faculty of Applied Sciences, Tunku Abdul Rahman University College, Setapak, Kuala Lumpur 53300, Malaysia * Correspondence: gading@ukm.edu.my (I.A.); pinkyphang@gmail.com (S.-W.P.) Abstract: The use of petroleum-based plastics in food packaging leads to various environmental im- pacts, while spoilage of food and misinterpretation of food-date labelling account for food insecurity; therefore, a biopolymer capable of indicating food edibility is prepared to resolve these issues. In this research, starch/polyaniline (starch/PANI) biopolymer film was synthesised and investigated as an ammonia sensor for potential application as intelligent food packaging. FT-IR and XRD were used to confirm the composition of the biopolymer films, while UV-Vis spectrometry was applied to identify the oxidation state of PANI in emeraldine form. PANI was successfully incorporated into the starch matrix, leading to better thermal stability (TGA) but decreasing the crystallinity of the matrix (DSC). The performance of the polymer-film sensor was determined through ammonia- vapour sensitivity analysis. An obvious colour change from green to blue of starch/PANI films was observed upon exposure to the ammonia vapour. Starch/PANI 0.4% is the optimum composition, having the best sensor performance with good linearity (R 2 = 0.9459) and precision (RSD = 8.72%), and exhibiting excellent LOD (245 ppm). Furthermore, the starch/PANI films are only selective to ammonia. Therefore, the starch/PANI films can be potentially applied as colourimetric ammonia sensors for intelligent food packaging. Keywords: starch; polyaniline; biopolymer film; ammonia sensor; intelligent food packaging 1. Introduction There are countless adverse environmental impacts resulting from the large-scale production of petroleum-based plastics, including the risk of global warming [1]. These highly durable polymers in the environment are regarded as hazardous waste, and there are more than 250 thousand tons of plastic pieces accumulated in the ocean, posing a detrimental effect on marine culture [2,3]. The development of biopolymers is crucial for the conservation of fossil resources, reduction of greenhouse-gas emissions, and to curb polymer pollution [4]. Starch and cellulose are biopolymers that have attracted the most attention due to their abundance, biocompatibility, nontoxicity, and simplicity of manipulation [5–7]. On the other hand, food-safety issues have gained much public concern and attention. The contamination of foodstuffs due to microbial or chemical reactions compromises the quality and sensorial properties of the food, which may be harmful to human health [8]. Moreover, consumers may be confused on how long the food can be stored or the exact time for uneaten food items to be disposed of due to confusing food-date labelling, leading to unnecessary food wastage [9,10]. According to the Food and Agriculture Organization (FAO), approximately one-third (1.3 billion tons) of the world’s edible food is wasted annually [11]. On the other hand, the expiry date is just a vague indication of the food condition, since the condition of the food may vary with different storage environments [12]. Polymers 2022, 14, 1122. https://doi.org/10.3390/polym14061122 https://www.mdpi.com/journal/polymers