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Reaction Monitoring of in-Situ Formation of Poly(sodium acrylate) Based Nanocomposites Using ATR-FTIR Spectroscopy Samaneh Khanlari, and Marc Arnold Dubé Ind. Eng. Chem. Res., Just Accepted Manuscript • Publication Date (Web): 12 May 2015 Downloaded from http://pubs.acs.org on May 12, 2015
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Industrial & Engineering Chemistry Research
Reaction Monitoring of in-Situ Formation of Poly(sodium acrylate) Based Nanocomposites Using ATR-FTIR Spectroscopy
Samaneh Khanlari, Marc A. Dubé* Department of Chemical and Biological Engineering Centre for Catalysis Research and Innovation University of Ottawa, 161 Louis Pasteur Pvt., Ottawa, Ontario, Canada K1N 6N5 E-mail:
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ABSTRACT: The in situ formation of poly(sodium acrylate)-based nanocomposites was monitored in-line using an attenuated total reflectance/Fourier transform infrared (ATR-FTIR) spectroscopic probe. Results were compared with conversion measurements using an off-line gravimetric method. A multivariate statistical data treatment based on the on-line data for the nanocomposite containing 0.5 wt.% of nanosilver was used to calibrate the ATR-FTIR spectroscopic probe. The ATR-FTIR method was shown to be reliable based on 95% confidence intervals for monitoring the production of polymers synthesized in the presence of different amounts of nanosilver over the full range of monomer conversion.
Keywords: ATR-FTIR spectroscopy, Reaction monitoring, Poly(sodium acrylate), Redox solution polymerization
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1. INTRODUCTION Sensor technologies for polymerization reaction monitoring have seen significant growth during the past years. Online monitoring of polymerization reactions is crucial to the production of polymers with pre-determined properties because it provides information on the state and evolution of the on-going reaction1. Sensor-based online monitoring has some advantages over traditional off-line monitoring; for example, online monitoring is typically much faster than offline methods, thus enabling more frequent measurements with less effort. Moreover, effective online measurement methods do not involve complicated sample workup and allow for a quick response to rapidly changing reaction conditions for the purposes of process control1, 2. Attenuated total reflectance Fourier Transform infrared (ATR-FTIR) spectroscopy is a method for which robust, reliable sensors are commercially available (e.g., ReactIR™ from Mettler-Toledo). ATR-FTIR probes can be used as immersion probes to provide continuous data transmission in real-time. This permits one to implement closed-loop control strategies on various reaction conditions and polymer properties. This eventually leads to more consistent product quality. In the case of process investigations, in-line sensors such as ATR-FTIR spectroscopy probes permit an enhanced understanding of the underlying phenomena in polymerization reactions that might be overlooked with off-line analysis1. A number of polymerizations have been successfully monitored using the ReactIR 1000™ probe (Mettler-Toledo) and later models3, 4. These examples provide continuous conversion and polymer composition data under a wide range of reaction conditions. For some systems, a noncalibrated univariate method was sufficient to calculate individual monomer conversions by monitoring the peak height of characteristic IR absorbances for each monomer2. An alternative, calibrated method using multivariate partial least squares (PLS) regression to relate the IR spectral 3 ACS Paragon Plus Environment
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changes to monomer concentration was necessary in other cases 4. One challenge often faced by users of infrared spectroscopy as a quantitative tool, is the presence of water. This has been overcome using spectral subtraction of the water absorbance with good success3-5. In any case, ATR-FTIR real-time monitoring has been used in many fields other than polymer reaction engineering6-10. To our knowledge, there are no reports of online ATR-FTIR monitoring in the production of nanocomposite materials, which is the focus of the current work. The addition of nanoparticles to polymers serves as a convenient means towards property modification, most notably, the modification of mechanical properties. Remarkably, significant property modification results from very low nanofiller concentrations (e.g., 1-3 wt.%) and this is due to their high surface to volume ratio11. Nanosilver is one nanomaterial receiving significant attention as a polymer nanofiller. Nanosilver particles comprise 20 to 15,000 silver atoms and have a characteristic dimension below 100 nm12. Nanosilver products are used in a broad range of applications, but our particular interest is due to its anti-bacterial properties13-17. Polymer-based nanocomposites are produced via solution blending, melt mixing or, as in our case, in situ polymerization. In situ polymerization consists of dispersing the nanoparticles into a polymerization reaction mixture during reaction. This method yields a particularly good nanoparticle dispersion and thus, this technique is considered ideal for polymer nanocomposite production18. Poly(sodium acrylate) (PNaA) is a material finding increased use as a bioadhesive19 and superabsorbent20. It is produced through the polymerization of acrylic acid monomer neutralized by sodium hydroxide (see Figure 1). PNaA bioadhesives can be modified to enhance their antiseptic properties by combining them with nanosilver15, 21-23.
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Figure 1. Poly(sodium acrylate) synthesis.
In a previous study, we reported the properties of PNaA based polymers synthesized in the presence of different amounts of NS; the monomer conversion was calculated using an off-line water removal gravimetric method16. In this work, the free radical aqueous solution in-situ polymerization of sodium acrylate in the presence of nanosilver (NS) using a redox initiation system was monitored via ATR-FTIR spectroscopy. Monomer conversion from the ATR-FTIR spectroscopy was compared to the off-line gravimetric method.
2.
EXPERIMENTAL 1.1
Materials
High purity (+99.5%) acrylic acid (Acros Organics), sodium hydroxide pellets, ammonium persulfate (APS) and potassium disulfite (KDS) were used without further purification. The solvent used was distilled deionized water (DDW) and hydroquinone (JT Baker Chemicals) was 5 ACS Paragon Plus Environment
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used to short-stop the reaction. Nanosilver powder with an average particle size of
