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Irreversible-Upon-Activation Thermochromic Pigments for the Time-Temperature Indicator Barcodes for Food Safety


The research and development of thermochromic pigments has been ongoing at URI for six years. During this time, we discovered and patented a new type of visually retrievable thermal sensor based on poly(thiophene)s. We also uncovered a property of these materials that provides an irreversible-upon-activation (IUA) thermochromic response. <P>The University of Rhode Island is working collaboratively with SIRA Technologies (Pasadena, CA) to develop IUA thermochromic inks for use in time-temperature indicator barcodes. The collaboration is supported by a sub-contract from SIRA Technologies from a U.S. Army Natick Soldier Systems Center research contract to develop irreversible thermochromic inks with irreversible transition temperatures of 40 and 80 oF. <P>In this project, we will fine tune the transition temperature of the IUA thermochromic pigments for commercial food safety applications. In particular, we will develop a method to allow small changes (+/- 2-5 oC) in the transition temperature. This will allow the IUA transition temperature to satisfy small differences in requirements for the food safety of different types of packaged food products. Recent estimates on the market size for TTI barcodes approach $100 Million per year.

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Non-Technical Summary: One of the most important aspects of food safety is maintaining the proper handling and storage temperature of food products. At a recent symposium sponsored by the Food Safety and Inspection Service (FSIS) of the U.S. Department of Agriculture it was disclosed that 76 million Americans reported having a food borne illness each year. In addition, 1 in 1000 people are hospitalized each year with food borne illnesses. These health problems result in over $6.5 Billon in medical expenses. Of the over 2,700 cases reported to the Centers for Disease Control (CDC) between 1993 and 1997, 73 % were the result of improper holding conditions of the food products. The development of an easily integrated, computer monitored, low-cost, track and trace temperature monitoring system for food products could eliminate three-quarters of all food borne illness. Development of pigments which can be used in TTI barcodes will allow for the creation of an inexpensive, computer verified, track and trace system that continuously monitors the temperature of food products. At any point during storage, transport, or distribution of food products the barcode can be scanned to determine that proper holding temperatures have been maintained. Improper storage temperatures will be indicated by a change in the barcode allowing the product to be removed from the food chain to protect the consumer. <P> Approach: The investigation of novel thermochromic pigments for use in food packaging materials can be broken down into four primary topics. First, the synthesis of new poly(thiophene)s will be investigated. Second, the effect of small molecule additives with structural similarity to the polymer on the thermochromic behavior will be probed. Third, the color changes will be analyzed using optical absorption and reflection spectroscopy. Fourth, the phase transitions of the polymers will be investigated with Differential Scanning Calorimetry (DSC). This integrated research effort will provide a thorough understanding of the interrelationship of structure and thermochromic transition in polythiophenes. A thorough understanding of the mechanism of thermochromic transition will allow the development of a series of thermochromic pigments for TTI barcode applications. While most of our preliminary investigations have focused on long sidechain poly(3-alkylthiophene)s (> C22H45), owing to the lower temperature IUA thermochromic transition required for the food product applications, we will focus our efforts in this proposal an the synthesis and investigation of poly(3-methyl-4-oligoethylene oxide thiophene)s.

Lucht, Brett
University of Rhode Island
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