Antimicrobial biodegradable films based on thermoplastic corn starch (TPS) and chitosan oligomers (CO) were obtained in order to develop a package prototype for perishable food products. Active films were fabricated thermo-compressing a sandwiched structure constituted by a thin layer of an oligomers enriched solution between two TPS films, previously made by melt-mixing and hot-pressing. Regarding enriched solution, it was obtained by dissolving oligomers in diluted acetic acid. Final material was characterized, determining its physical and optical properties, as well as, studying its microstructure. By diffusion assays it was demonstrated the capability of CO to migrate from the active film towards the aqueous simulant media. Moreover, oligomers were able to diffuse from the matrix, regardless the aqueous medium acidity. Experimental data of diffusion assays were fitted using a mathematical model, estimating diffusion coefficients at three studied pH values (3, 5, and 7). Active film was used to obtain sachets to package perishable foods such as strawberries, ricotta, and flavored breads, which were stored for 7 days under controlled conditions. Antimicrobial capacity of active sachets was corroborated through molds and yeast counts in the stored food products. Additionally, it was demonstrated that CO incorporation to the packaging material resulted in a more efficient way to inhibit microbial development than the spraying technique. This gradual release allows maintaining an effective concentration of

A kinetic Monte Carlo model of a reversible addition− fragmentation chain transfer (RAFT) process is presented. The algorithm has been developed and implemented in Julia for the three main RAFT theories under current discussion (slow fragmentation, intermediate radical termination, and intermediate radical termination with oligomers). Julia is a modern programming language designed to achieve high performance in numerical and scientific computing. Thanks to a careful optimization of the code, it is possible to simulate a RAFT reaction scheme in short computing times for any of the three theories. The code is benchmarked against other programming languages (MATLAB, Python, FORTRAN, and C), showing that Julia presents advantages for this particular system. The model offers an efficient method for predicting average properties and molecular weight distributions of the polymer species, including the bivariate molecular weight distribution of the intermediate two-arm adduct. The proposed model can also be employed to obtain additional detailed information regarding the polymer microstructure at any reaction time.

RESUMEN Una de las líneas para el desarrollo de envases activos contempla la incorporación de agentes antimicrobianos como el quitosano, polisacárido derivado del exoesqueleto de crustáceos. No obstante, su elevada masa molar restringe su difusión desde el envase hacia el alimento por lo que el empleo de oligómeros de características diferenciales es una alternativa interesante, aún poco investigada. El objetivo de este trabajo fue obtener películas activas a base de almidón de maíz termoplástico (TPS) mediante la incorporación de oligoquitosanos (OQ, masa molar = 290 g mol-1 y grado de polimerización = 2). Estos materiales fueron obtenidos mediante termo-compresión en una prensa hidráulica. Se realizaron ensayos de difusión de los OQ desde la matriz de TPS hacia un medio líquido con diferentes grados de acidez (pH = 3, 5 y 7). Las condiciones del medio líquido fueron seleccionadas según la acidez de una amplia variedad de alimentos. A partir de estos ensayos, se demostró la capacidad de difusión de los oligómeros y su dependencia con el pH del medio. La eficiencia de la incorporación de los OQ en el material de envase se comparó con la correspondiente al método convencional de spray del alimento con una solución del agente activo. La capacidad antimicrobiana de las películas y de las soluciones de OQ se evaluó a partir del recuento de hongos y levaduras, empleando frutillas frescas como alimento de estudio. Los resultados derivados de estos ensayos evidenciaron el carácter activo de la película desarrollada, demostrándose además la mayor eficacia del uso de envases activos antimicrobianos, respecto de los métodos convencionales.

A mathematical model of the activators regenerated by electron transfer atom transfer radical polymerization copolymerization of styrene-acrylonitrile (SAN) is developed for the first time that calculates the bivariate molecular weight distribution (MWD)-copolymer composition distribution (CCD) of the copolymer. In addition, the model calculates the overall MWD, the overall CCD, average molecular weights and composition, and conversion. The model is implemented in the open-source programming language Julia, a high-level language designed for scientific computing, which is easy to use and that performs very fast calculations. The probability generating function technique is used to process the infinite population balances of the system. The mathematical model, composed of a very large system of equations, is solved by applying parallel computing to speed up its execution. In this way, the distributions of polymer properties are calculated in a very efficient manner. The evolution of the joint MWD−CCD and other molecular properties along the reaction path is analyzed under different operating conditions. The model allows obtaining very detailed insights into the copolymer microstructure during the polymerization reaction.