Autoxidation of Spin Finishes
By Fok, Wing Y; Hild, Debra N; Petrick, Lauren M; Obendorf, S Kay
Abstract Spin finishes, including lubricants, emulsifiers, antistatic agents, and wetting agents are used to facilitate the manufacturing and processing of textiles. Autoxidation of ten spin finish components was studied by subjecting them to air and heat over time. Chemical changes were observed visually and evaluated using UV/Vis spectroscopy, viscosity measurements, and Fourier Transform infrared (FTIR) spectroscopy. Yellowing occurred for HCO- 16, TMP, wetting agent, coconut oil ethoxylate, and coconut oil. Changes in solubility were observed for wetting agent. Significant changes in viscosity were measured for CO-16, HCO-25, anti-static agent, and wetting agent. Finally, changes in FTIR spectral ratios were observed for CO-25, HCO-16, CO-16, and anti-static agent. Chemical changes observed were consistent with autoxidation of spin finish components.
Key words fiber nylon, spin finish, polyamide, textile, spinning, autoxidation
Spin finishes have been developed and formulated to facilitate successful processing of synthetic fibers during manufacturing. They must meet many requirements including lubrication and static dissipation. Spin finishes are complex, formulated mixtures of ingredients such as lubricants, emulsifiers, antistatic agents, wetting agents, and antimicrobial compounds. Many, if not all, components of spin finishes are susceptible to oxidation. When exposed to heat and in situations where oxygen is present, autoxidation can occur. If unsaturated double bonds are present in the component, the reaction starts by addition to the double bond and the formation of free radicals and can proceed to cross-links that result in formation of oligomers and polymers with increased viscosity. Ozone, present in the atmosphere, is an especially strong oxidizing agent that may trigger the oxidation process.
This research investigated the oxidation of individual spin- finish oil components found in formulations used on nylon fibers. Nylon fabrics are known to be easily discolored by excessive exposure to sunlight [I]. In the presence of atmospheric oxygen, moisture and air pollutants, excessive heat energy and UV radiation degrade the fiber-forming polymers, producing chromophores. Fabrics finished with aminofunctional silicone in order to enhance the softness of the fabric also tend to yellow when subjected to excessive heating and curing. The primary cause of this yellowing is the chromophoric groups with conjugated double bonds formed by oxidative decomposition of the aminofunctional group . It is also known that soiling and most lipids in the soiling oxidize to cause yellowing [3, 4]. Some of these lipid compounds, such as oleic acid, are naturally found in the spin-finish components (castor oil and coconut oil.) According to a previous study of the distribution of spin-finish within nylon fibers, aged fibers contain spin-finish deep within the core of the fiber . Therefore, it is possible for the yellowing of nylon to be caused both by the yellowing of the aging fiber and by the yellowing of the spin-finish surrounding and within the fiber. We studied the autoxidation of each spin-finish component.
The spin-finish components chosen for this study were: castor oil ethoxylate (16 moles ethylene oxide) (CO-16); castor oil ethoxylate (25 moles ethylene oxide) (CO-25); hydrogenated castor oil ethoxylate (16 moles ethylene oxide) (HCO16); hydrogenated castor oil ethoxylate (25 moles ethylene oxide) (HCO-25); pure castor oil; trimethylolpropane tripelargonate (TMP); polyoxethylene tridecyl phosphate K+ salt (anti-static agent); polyoxyethylene decyl ether (wetting agent); coconut oil ethoxylate (14 moles ethylene oxide); and pure coconut oil. Both pure castor oil and pure coconut oil are composed of fatty acid mixtures; the former being predominately (90%) ricinoleic acid , and the latter being predominately (47- 50%) lauric acid . A summary of the spin finish components is given in Table 1. These components were obtained from Ethox Chemicals, LLC (Greenville, SC). The other chemicals used in this study were highperformance liquid chromatography (HPLC) grade methylene chloride from Mallinckrodt Chemicals (Hazelwood, MO), and 95% ethanol (5% methanol) from Aldrich Chemicals Inc. (Milwaukee, WI).
Oxidation of Samples
Individual spin-finish components (6 g) were measured into 8 drams (29.6 mL) screw caps vials. These vials were sealed and immersed half-way into an oil bath at 33-35C. Samples were oxidized by bubbling air using a pressure of approximately 2 p.s.i. passing through rubber tubes and into the samples for 2, 3 and 7 days (Figure 1). Control specimens were neither air-treated nor exposed to heat, i.e. 0 days. After preparation and treatment, samples were sealed in argon (industrial grade) and stored in the dark at 4C in their original screw cap containers.
A Perkin-Elmer Lambda 2 UV/VIS spectrometer was used to scan from 200 to 500 nm. With the exception of the control wetting agent, samples were diluted (v/v) with methylene chloride at a ratio of 2: 1 CH^sub 2^Cl^sub 2^: sample. The blank used was methylene chloride. The wetting agent was analyzed neat due to its reaction with methylene chloride. The blank used with this sample was air.
Solubility of Wetting Agent
The solubility of the wetting agent in organic and watersoluble solvents was tested before and after treatment. The solvents used were methylene chloride and denatured alcohol (95% ethanol, 5% methanol). Untreated wetting agent was mixed with CH^sub 2^Cl^sub 2^ at an approximately 1: 5 v/v ratio and with denatured alcohol at a 1: 3 ratio. The solubility of the treated wetting agent (3 days) was evaluated with methylene chloride and denatured alcohol at the same v/v ratios.
Kinetic viscosity measurements of TMP and coconut oil ethoxylate were taken with a Cannon-Ubberlohde semimicro viscometer (size 200); measurements of all other spin finish components were taken with a Cannon-Ubberlohde semi-micro viscometer (size 400). The viscometers and the holder were purchased from Cannon Instrument Co. (State College, PA). Measurements were taken using methods from ASTM D445 and ASTM D446 at 35C. Methylene chloride was the solvent, whereas acetone was the drying agent. High grade gaseous N^sub 2^ was used as the filtered air.
Kinetic viscosity (v) was calculated using the relationship, v = C . t, where t is flow time (s), and C is viscometer constant (cSt/ s). Viscometer constants were provided by Cannon Instruments Co. Kinetic viscosity was calculated for the control and 7-day air treatment, based upon four replicates.
Fourier Transform Infrared Spectroscopy
Fourier Transform infrared (FTIR) measurements were taken using Mattson Polaroid(TM). Results were analyzed using WinFirst v. 3.60 (Mattson Instruments.) Samples from each treatment were taken neat on KBr plates from 4000 to 400cm-1.
Results and Discussion
Yellowing of Oxidized Components
Yellowing was observed visually for the following components: TMP, coconut oil, coconut oil ethoxylate, wetting agent, and HCO- 16. To quantify the observed yellowing due to oxidation, we used ultraviolet/visible absorption spectroscopy. The appearances of peaks or shifts near the violet region of the visible spectrum would be consistent with yellowing of the sample after oxidation.
There were no shifts or new peaks observed in UV/Vis spectra of CO-16, CO-25, HCO-25, castor oil, or anti-static agent. Changes in UV/Vis spectra occurred over time for those compounds that were observed to yellow. These changes can be seen in Figure 2. The UV/ Vis spectra of HCO-16 exhibited an increase in the range of absorption from 247 to 304 nm to a band from 247 to 310 nm. TMP showed the appearance of a new peak at 320 nm and a new band from 327 to 386 nm. Treatment of wetting agent resulted in a shift of absorption peak from 214 to 248 nm, and the formation of two additional peaks from 310 to 321 and at 345 nm. Spectra of coconut oil ethoxylate showed a similar peak shift from 286 to 321 nm along with appearances of three new peaks at 344, 353 and 363 nm. Finally, treatment of coconut oil exhibited a peak shift from 287 to 315 nm, along with an additional peak at 341 nm, after 7 days of treatment. These results are consistent with autoxidation forming yellow chromophores.
Changes in Solubility
Untreated, wetting agent was soluble in denatured alcohol and was insoluble in methylene chloride. Upon mixing with methylene chloride, the untreated sample immediately became cloudy; after 1 day of standing, a phase separation occurred. After treatment (3 days), wetting agent was soluble in both methylene chloride and denatured alcohol. The chemical change in wetting agent was supported by the shift in the UV/Vis spectrum (Figure 2).
Visual observation of the physical condition indicated a change in viscosity of wetting agent and anti-static agent. These findings were tested by measuring the viscosity of both components before and after treatment. Viscosities of other components were also measured for change (Table 2). It was observed that changes (with 95% confidence interval) in viscosity occurred for CO-16, HCO-16,anti- static agent, and wetting agent.
FTIR did not show changes in the types of functional groups present in samples, but did show changes in ratios of peaks for several functional groups. Evaluation of ratios was performed using a reference peak as well as the apex of peaks corresponding to functionalities consistent with the oxidation process, such as C=C (1680-1640 cm^sup -1^), C=O (1820 and 1680 cm^sup -1^), and C-O-C (1150-1060 cm^sup -1^) groups. The peak of 2925 cm^sup -1^ corresponding to the C-H stretch of a -CH^sub 2^ group was selected as the reference because it has been shown to remain stable in the presence of heat and oxygen . For each compound, the maxima with the wavenumber range for a specific functionality, was used for comparison. For example, the C=O apex for CO-16 was selected at 1734 cm^sup -1^, whereas the CO-25 peak was selected at 1733 cm^sup -1^. This allowed comparisons to be made between FTIR spectra of different samples that may have slight shifts in wavenumber.
There was no consistent change in FTIR spectra before and after treatment for the following samples: HCO-25, castor oil, TMP, wetting agent, coconut oil ethoxylate, and pure coconut oil. For some of the other components, changes over time in the ratios of functional groups of C=C, C=O, and C-O-C were observed. There were increasing ratios of the C=O absorbance found for CO-25 and HCO-16 as well as of the C-O-C absorbance for CO-16. In addition, there was a decreasing ratio of C=C bond found for anti-static agent. Changes in these ratios are consistent with observations made on the thermo- oxidative degradation of similar oils .
Autoxidation of spin finish components was observed through yellowing, a change in solubility, and changes in viscosity. These changes were confirmed through UV/Vis spectroscopy, viscosity measurements, and FTIR. Yellowing was observed for HCO-16, TMP, wetting agent, coconut oil ethoxylate, and pure coconut oil. This was confirmed through shifts and the appearance of new peaks in the UV/Vis spectrum near the violet region. A change in solubility occurred for wetting agent. This sample went from being soluble in methylene chloride and insoluble in denatured alcohol, to being soluble in both after oxidation. This chemical change was also supported by shifts in the UV/Vis spectral data. Autoxidation resulted in an increase in viscosity for wetting agent, anti-static agent, CO-16 and HCO-25. These observations indicate that chemical changes are occurring in spin finish components in the presence of heat and air. Finally, FTIR spectra supported chemical changes in CO- 25, HCO-16, and anti-static agent. There were changes in C=C, C=O, and C-O-C peak ratios, consistent with changes that may occur during oxidation. To determine the overall effect of oxidation, future work may include studying the oxidation of mixtures of spin finish components.
We wish to thank Ethox Chemicals, LLC (Greenville, SC), for supplying the spin finish components. We wish to thank Nylon Textile Technology of Solutia, Inc. (Pensacola, FL) for providing the yarn used in the study, particularly Rusty Carter. We thank Kuitian Tan, Cornell University, for the statistical analysis, Emil Delgado, Ethox Chemicals, LLC (Greenville, SC.), and Tatyana Dokuchayeva, Cornell University, for analytical assistance. This research was supported in part by the Cornell University Agricultural Experiment Station federal formula funds, Projects No. NYC329407 received from Cooperative State Research, Education, and Extension Service, U.S. Department of Agriculture and by Nylon Textile Technology of Solutia, Inc. (Pensacola, FL).
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Wing Y. Fok, Debra N. Hild, Lauren M. Petrick, and S. Kay Obendorf1
Department of Textiles and Apparel, Cornell University,
Ithaca, New York 14853-4401, U.S.A.
1 Corresponding author: Textiles and Apparel, Martha Van Rensselaer Hall, Cornell University, Ithaca, NY 14853, U.S.A. Tel.: +1607351 1155; e-mail: email@example.com
Copyright Textile Research Institute Aug 2006
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