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Controlled Release of Antimicrobial ClO2 Gas from a Two-layer Polymeric Film System Zhifeng Bai, Diego Edison Cristancho, Aaron A. Rachford, Amy L Reder, Alexander Williamson, and Adam L Grzesiak J. Agric. Food Chem., Just Accepted Manuscript • DOI: 10.1021/acs.jafc.6b03875 • Publication Date (Web): 13 Oct 2016 Downloaded from http://pubs.acs.org on October 25, 2016
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Journal of Agricultural and Food Chemistry
Controlled Release of Antimicrobial ClO2 Gas from a Two-layer Polymeric Film System
Zhifeng Baia, *, Diego E. Cristanchob, Aaron A. Rachforda, Amy L. Redera, Alexander Williamsonb, Adam L. Grzesiaka,*
a
The Dow Chemical Company, Core Research and Development, 1702 Building, Midland, MI
48674 b
The Dow Chemical Company, Core Research and Development, 2301 N. Brazosport Blvd.,
Freeport, TX 77541
* Author for correspondence:
Zhifeng Bai, Ph.D.
Adam L. Grzesiak, Ph.D.
Core R&D - Formulation Science
Core R&D - Formulation Science
Dow Chemical Company
Dow Chemical Company
Building 1702, 103B
Building 1702, 107B
Midland, MI 48674
Midland, MI 48674
Phone: (989) 636-3156
Phone: (989) 636-7749
[email protected] [email protected] ACS Paragon Plus Environment
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Journal of Agricultural and Food Chemistry
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ABSTRACT
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We report a two-component label system comprising a chlorite-containing polymer film and an
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acid-containing polymer film that can release antimicrobial ClO2 gas upon adhering the two
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films together to enable a reaction of the chlorite and acid under moisture exposure. The chlorite-
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containing film comprises a commercial acrylate-based pressure sensitive adhesive polymer
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impregnated with sodium chlorite. The acid-containing film comprises a commercial polyvinyl
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alcohol polymer loaded with tartaric acid. Both of the films were prepared on low ClO2-
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absorbing substrate films from stable aqueous systems of the polymers with high reagent
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loading. Rapid and sustained releases of significant amounts of ClO2 gas from the label system
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were observed in an in-situ quantification system using UV-vis spectrometry. It was found that
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the ClO2 release is slower at a lower temperature and can be accelerated by moisture in the
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atmosphere and the films. Controlled release of ClO2 gas from the label system was
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demonstrated by tailoring film composition and thickness. A model was developed to extract
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release kinetics and revealed good conversions of the label system. This two-component system
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can potentially be applied as a two-part label without premature release for applications in food
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packaging.
17 18
KEYWORDS: chlorine dioxide, antimicrobial polymer, food packaging, controlled release
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Journal of Agricultural and Food Chemistry
Introduction
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Antimicrobial polymers have received much interest due to the significant concern of
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microbial infection from food, drugs, and other perishable.1−3 In general, antimicrobial polymers
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are antimicrobially active themselves, which comprise bioactive functional groups4,5 or are
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impregnated with antimicrobial agents in polymer matrix.6−8 In comparison with conventional
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low molecular weight antimicrobial agents, antimicrobial polymers hold promise for mitigating
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potential toxicity of residuals to the environment, controlling release rate, promoting efficiency
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and synergy, etc. arising from widely tunable chemical and physical attributes of polymers.9
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Chlorine dioxide (ClO2) is an antimicrobial and oxidative agent that can be used in food
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industry such as for food disinfection10−15 and pesticide oxidation.16,17 It possesses broad
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spectrum kill, facile diffusion, i.e., as a gas, to crevices and uneven surfaces where microbes may
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be dwelling, rapid acting, non-chlorinating and selective oxidation, regulatory compliance, etc.
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ClO2 is often released from aqueous solutions18 or sachets19 through reaction, e.g., between
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chlorite and acid in liquid20 or powder,21,22 or physical encapsulation and release.23 Examples of
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controlled release of ClO2 gas from polymer films however are limited. For instance, Ray et al.
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reported ClO2 gas-releasing polylactic acid polymer films that contained sodium chlorite and
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citric acid and were prepared by casting a methylene chloride solution of the polymer and
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reagents.24 Wellinghoff patented composition of single-layer films that comprise a blend of a
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hydrophobic polymer containing an acid-releasing agent and a hydrophilic chlorite-containing
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polymer.25 The films were prepared by hot-melt mixing and released ClO2 gas upon exposure to
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moisture, where the moisture accelerates diffusion of the reagents in the polymer films.
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Wellinghoff and Kampa also developed moisture-triggered ClO2 gas-releasing multi-layer film
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compositions that comprise a hydrophobic polymer layer containing an acid-releasing agent
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adjacent to a hydrophilic chlorite-containing polymer layer.26 One drawback of these ClO2 gas
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generating systems is premature release of ClO2 under exposure to moisture that may occur even
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without moisture exposure due to direct contact of the reagents.
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Herein, we report a two-component label system that releases ClO2 gas upon adhering the two
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layers together and exposure to moisture when the release is needed, which thus minimizes
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premature release. The label system comprises a commercial acrylate-based pressure sensitive
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adhesive (PSA) polymer impregnated with sodium chlorite and a commercial polyvinyl alcohol
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polymer loaded with tartaric acid. The two polymer layers were prepared from stable aqueous
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systems of the polymers with high reagent loading. Releases of ClO2 gas from the label system
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were determined in an in-situ quantification system using UV-vis spectrometry. Effects of
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temperature, humidity, film composition, and film thickness on the release were examined.
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Release kinetics and yield were extracted by modeling.
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Experimental Procedures
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Materials
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All chemicals were used as received from their respective manufacturers unless noted
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otherwise and include NaClO2 (80%), L-(+)-tartaric acid (TA), and acetic acid from Aldrich;
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RHOPLEX™ PS-7850 adhesive from The Dow Chemical Company; K2SO4 from Alfa Aesar;
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K2CO3 from Acros; H2SO4 from Fischer Scientific; and 88% hydrolyzed poly(vinyl alcohol)
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from Kuraray.
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ClO2 Generation and Detection
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ClO2 gas generation was conducted in a glass reactor in dark conditions and monitored by UV-
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vis spectroscopy27 with a Shimadzu UV1800. The reactor was connected to a 10 cm pathlength
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Journal of Agricultural and Food Chemistry
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gas cell (Starna) via polytetrafluoroethylene tubings and unions (total volume = 791 mL) that
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were equipped with a Cole-Parmer MasterFlex (Model 77390-00) peristaltic pump (typical
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setting = 40) to facilitate ClO2 mass transport from the reactor to the gas cell in the
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spectrophotometer. The UV-vis absorbance was acquired from 200 to 500 nm with a step size of
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0.1 nm and acquisition frequency of 15 or 60 min (see supporting information). The wavelength
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at maximum absorption (λmax), typically at 351.7 nm, was typically monitored to produce
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absorbance versus time plots. The quantity of ClO2 gas generated was calculated using known
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absorption cross section values of ClO2 gas,28,29 absorbance, reactor volume, and UV cell length.
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Evaluation of the signal-to-noise at low concentrations of gas combined with the known
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absorption cross-sections of 1.275 x 10-17 cm2 at 296 K at 351.30 nm,28 which translates to a
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molar absorptivity of 3338 M-1cm-1, indicates a detection limit of
