Preliminary Studies of Non-Aqueous Volatiles in Lint Cotton Moisture Tests by Thermal Methods

Abstract

The standard test methods for moisture in lint cotton are based on oven drying at 105—110°C. All of the loss in weight is attributable to moisture. The U.S. cotton industry questions the reliability of the oven-drying method due to the concern that non-aqueous volatiles released during drying may be of an amount sufficient to bias the results. Our approach in these initial studies was to conduct a series of probing experiments to help understand the nature of the non-aqueous volatiles. Cottons were assayed for moisture content by standard oven drying and Karl Fischer Titration. The titration results were significantly lower. We oven-dried cottons of varying mass, changed the gaseous atmosphere during heating from air to nitrogen and attempted to “fingerprint” the non-aqueous volatiles by thermogravimetric analysis and thermogravimetric analysis—quadrupole mass spectrometry. The results demonstrate that complicated side reactions occur during oven-drying. However, no specific volatile organics were detected at standard oven-drying conditions.

Preliminary evidence of oxidation in standard oven drying of cotton: attenuated total reflectance/Fourier transform infrared spectroscopy, colorimetry, and particulate matter formation

“…Considering the amount of weight loss of oven-dried cottons is approximately 7.5% for 10 g of cotton, the average weight lost is 0.75 g. The weight loss observed on the taped slides amounts to approximately 0.24% of the 0.75 g of cotton weight loss, or roughly half of the difference seen between KFT and the oven as has previously been reported. 2,3 In addition, NAV components observed in earlier studies 2,3 and cellulose oxidation may also contribute to the observed bias in moisture contents determined by the KFT and SOD methods, although the quantitative amounts of each of these contributors are still unknown.

Figure 6.Particulate and fibrous matter captured on a greased slide placed on top of cotton balls contained in a weighing bottle placed in an airflow oven heated to 105℃.

Figure 7.Particulate and fibrous matter captured on a greased slide placed on top of cotton from crop year 2001 contained in a weighing bottle placed in an airflow oven heated to 105℃.

Figure 8.Particulate and fibrous matter captured on a greased slide placed on top of cotton from crop year 2007 contained in a weighing bottle placed in an airflow oven heated to 105℃.

…”

“…As reported in previous research, differences were noted between moisture measurements determined by KFT and oven drying methods. 2,3 In order to understand these differences, several avenues were explored. One such technique was determining if particulate matter was released during SOD.…”

“…1 However, not all of the water is removed; there is loss of non-aqueous volatiles (NAVs) and indirect evidence suggests sample oxidation. 2,3 The other standard method is based on oven drying in nitrogen combined with Karl Fischer Titration (KFT) of the water vapor removed from the sample. 4 In the latter method there are no known biases; all of the water in the sample is available for titration and sample oxidation does not occur.…”

“…Studies of NAVs by complementary thermal methods at SOD conditions included changing the gaseous atmosphere from air to nitrogen; thermogravimetric analysis; distillation of cotton samples; and colorimetry. 2,3 In collaborative studies performed in Germany, no specific volatile organics were detected at SOD conditions by thermogravimetric analysis–quadrupole mass spectrometry (TGA-QMS). 2 Sample weight loss and weight gain, not attributable to water, was found in the TGA-QMS studies; this was also reported by meticulous SOD studies in our laboratory.…”

“…2,3 In collaborative studies performed in Germany, no specific volatile organics were detected at SOD conditions by thermogravimetric analysis–quadrupole mass spectrometry (TGA-QMS). 2 Sample weight loss and weight gain, not attributable to water, was found in the TGA-QMS studies; this was also reported by meticulous SOD studies in our laboratory. Distillation of cotton in a glass apparatus with air carrier gas confirmed the presence of volatile organics; NAV material of very low volatility and/or particulate matter was visible on the inside walls of the apparatus.…”