A Temperature Sensing Face Mask Using Thermochromic Dye Chaudhary Khan1 John Eisenbrey2 Brian George1 1School of Design & Engineering 2Department of Radiology Thomas Jefferson University Thermochromism • An adaptive technology that causes a change in optical properties as a function of temperature • This is usually manifested as a change in color • Color change can be reversible or irreversible, depending on the type of thermochromic system (1‐3) • Heat can be a direct stimulus as the sole cause of color change or an indirect stimulus, by causing a change in pH or chemical properties (1,2,4) • Has been used in asphalt to improve its properties, building coatings to improve energy efficiency, and NDT of engineered and electronic products (1‐3,5‐11) Thermochromic Colorants • Thermochromic pigments were invented in 1970 by Suzuki (12) • Thermochromic fabrics entered the marketplace in 1980 (13, 14) • Fabric would change color between cold and warm • Fabric was initially treated with a regular dye to provide a base color • Afterwards a microencapsulated leuco dye system containing a lactone, a weak acid, and a solvent was applied to the fabric • Color transition occurred 75.6°F (13‐16) • Have been used for thermometers, food quality indicators, toys, process control (2, 16) • Have the potential to be used in camouflage or fashion (13‐14, 17) • Generally are difficult to apply and can be expensive (18) Developments in Thermochromic Dye Systems • Limburg and Ridgeway created thermometers on films and magnets, but found limited application due to requiring different ink types for each substrate (19) • Joshi et al produced a color changing polyester umbrella by dyeing with thermochromic dyes and then screen printing photochromic dyes on the fabric (20) • Thermochromic dye changes color according to temperature, photochromic dye changes color according to UV light levels • This system was also used on different fibers for use in wall hangings, curtains, and t‐shirts (21) • Others have examined screen printing thermochromic ink onto fabric and using an external heating element (i.e. integrated heater or stainless steel yarns to conduct heat) (22‐24) Leuco Dyes • A colorant that transitions between two chemical forms due to heat, light, or pH (1‐3) • This gives two different states of color, but one state is colorless • Thermochromic leuco dyes are often blended with non heat sensitive pigment or dye to change from one color to another (2, 25‐27) • For example, an azo group can be added to s spirolactone molecule, and when heat is added the ring opens up, causing a change in color (28) • When heat is removed the ring closes again, reverting to its original color • Commercial leuco dyes that are activated by heat are classified according to the temperature at which they transition Color Transition of a Leuco Dye by Adding Heat (2) Formation of a Thermochromic System • Thermochromic systems need a color former, a color developer, and a solvent (4, 17‐18) • Color former acts as an electron donor and is pH sensitive (29) • Color developer acts as an electron acceptor, they are generally weak acids (30‐31) • Solvent is a hydrophobic, non‐polar material with a large molecular weight that allows the phase transition to occur (3, 32) • The color former, color developer, and solvent are combined and encapsulated before being applied to the product Face Masks • FDA has approved disposal face masks as a medical device (33) • They are designed to prevent spread of infectious viral or microbes to surrounding areas • A face mask that changes color based on the temperature of the wearer could alert medical professionals whether or not someone has a fever • This knowledge could be beneficial in triage or emergency rooms where temperatures may not be immediately taken, and could allow for the separation of people with greater than normal temperatures from other patients as a means to reduce spread of viruses or microbes Methodology • To test the validity of the color changing face mask a three component dye system based on a premade leuco dye was created by combining it with non‐heat sensitive dyes from different dye classes • The dye systems were applied to spunbond fabric • Fabric was evaluated for color change properties Creation of Thermochromic Systems • A commercial microencapsulated leuco dye thermochromic system, Black‐ Pink, with an activation temperature 35°C Thermochromic Screen Print Ink supplied by Atlanta Chemical Engineering was used • Non heat sensitive dyes were incorporated within the encapsulated thermochromic system • This allowed for the creation of systems with different colors • Classes of dyes incorporated (obtained from Huntsman Textile Effects): • Direct dye (Solophenyl red 4GE) • Reactive dye (Novacron Brilliant Red FN‐3GL) • Cationic dye (Maxilon Red GRL 200%) • Acid dye (Erionyl Yellow A‐3G) • A disperse dye (Permasil Red FB 200%) was obtained from Standard Colors Production of Samples • Dyes were added at a 0.5% by weight volume ratio to a solution of water and thermochromic system • Incorporation was accomplished by manually stirring the mixture for 10 minutes at room temperature • DuPont polyester spunbond was used to simulate a mask • This was scoured by immersing in a bath of water and 1.5% owf Orcoterge 35‐C anionic biodegradable detergent (donated by Huntingdon Yarn Mill) at 82.2°C for 30 minutes with an Ahiba Texomat • Fabrics were rinsed with cold water twice and then allowed to air dry for 24 hours at room temperature • The thermochromic mix paste was applied to the fabric through a hand screen printing process using 110 mesh monofilament screen (Speedball Screen Printing Fabric),, and a squeegee • Thermochromic screen printing ink apparently contains a water activated binder, no binder was required • Craft brushes were used to further spread the dye onto the fabric to give a uniform coating • Fabrics were allowed to air dry at room temperature for 24 hours • Four specimens of each thermochromic system and dye type were produced • Fabrics were then evaluated for activation temperature, crockfastness and resistance to perspiration Color Changes of Different Thermochromic System and Dye Combinations Leuco LRed RedFN 4 euco RedLeuco FN Red Red RedFN GRL FN Red FB Fudge Yellow Evaluation of Activation Temperature • Each specimen was heated with a Wagner Furno 750 heat gun while being observed with a Flir i5 series thermal imaging camera at 0.90 emm (supplied by Coats North America) • Activation temperature was measured when the color began to change Results of Activation Temperature Analysis Leuco Activation Temperature Results • The red direct dye had the lowest activation temperature, this is attributed to the sodium carbonate in the dye acting to alter the sensitivity of the color former • Reactive and cationic dyes had little effect on the activation temperature, it is believed that this is due to either charges on the dye molecules or small dye molecules not being able to strongly influence the color developer or color former, thereby not dominating the mechanism of the change in ring structure that leads to color change Evaluation of Crocking Due to Perspiration • Four specimens of each dye system were evaluated • 60x60 mm swatches of fabric were weighed with a Mettler PM100 scale • A one liter perspiration solution of 0.25g/L‐ histidine monohydrochloride monohydrate, 10g sodium chloride, 1g sodium dihydrogen orthophosphate anhydrous, and 1g lactic acid (85%) was created from materials supplied by Fisher Scientific • Specimens were immersed in the solution in a 2cm deep petri dish for 30 minutes and stirred to obtain a mass 2.25 times the original mass • Specimens were then attached to a standard 5 fiber multifiber strip obtained from Testfabric Inc and then placed between perspiratory plates of an AATCC PR‐1 perspiration tester by Atlas Electronic Devices Co. under a 5Kg load at 38°C for 6 hours in a Carbolite Gero oven • Specimens were removed from the oven and compared to an AATCC Grey Scale for Staining under an SDL Atlas color cabinet with D65 light source Results of Resistance of Color Transfer Due to Perspiration Leuco Results of Resistance of Color Transfer Due to Perspiration • The original leuco system had the best results –no color transfer • This is attributed to the dyes being tightly bound in the microcapsules that contain it • The anionic reactive and acid dyes offered good performance also • The cationic and direct dyes had the worst performance, perhaps due to the small size of the dye molecules affecting their ability to effectively bond to the thermochromic microcapsules Evaluation of Dry and Wet Crocking • 4 specimens of each dye system were evaluated • Specimens were mounted to a Crockmeter with a 50x50mm white cotton fabric (Testfabric Inc) mounted to the finger • Crocking was performed under a 920 gram downward force, following ASTM TM8‐2016, using 10 cycles in 10 seconds • Crocking was done under dry and wet conditions • Wet conditions were obtained by blotting the dyed fabrics in distilled water to obtain a 65% wet pick up, crocking, and then drying at room temperature before evaluating • Specimens were evaluated for staining be being compared to an AATCC Grey Scale for Staining under an SDL Atlas color cabinet with D65 light source Evaluation of Dry and Wet Crocking Leuco Evaluation of Dry and Wet Crocking • Acid and leuco dyes offered the best performance in dry crocking • Direct, reactive, cationic, and disperse all gave low dry crocking performances • Acid dye had the best wet