Measurement of Spin Finish on Artificial Fibres Using NMR

By AZoM

Table of Contents

Application
Advantages of NMR
Method
Calibration
Measurement
Results
Instrumentation
Conclusion
About Oxford Instruments Magnetic Resonance

Application

While manufacturing artificial fibers such as polyamide and polyester, the fibers are sprayed with an oil-based coating to reduce static electricity and friction as well as improve certain physical characteristics. This coating is known in different countries as spin finish, oil pick-up (OPU) and finish on yarn (FOY). Measuring the applied spin finish using the MQC analyzer is quick, simple and solvent-free. Similar to the MQA, the MQC supports a non-weighing method, which allows rapid measurements. The rapid, precise results obtainable with the MQC enable tighter control of the manufacturing process, lower production costs and less out-of-specification products.

Advantages of NMR

The traditional method of testing is to dissolve the coating in an organic solvent and then determine the amount of dissolved oil in the solvent either gravimetrically after distillation or by use of infrared spectroscopy. All these methods consume a significant amount of time, use hazardous solvents and require skilled operators. Benchtop nuclear magnetic resonance (NMR) offers an alternative method which is quick and easy to perform, simple to calibrate and capable of determining finish levels below those precisely measurable by solvent extraction. The advantages are:

  • Up to 250 times faster than wet chemistry methods.
  • No hazardous solvents are required, no hazardous waste are produced.
  • Easy and highly reliable, suitable for unskilled personnel.
  • Reliable measurements down to low concentrations.
  • Ideal for high-sample throughput.

Method

Benchtop NMR identifies the hydrogen signal of oil after there is no signal from the solid fibre. Dividing this signal by mass gives the hydrogen density of oil on the fibre which correlates with the spin finish content. For some samples it is possible to substitute mass with the total NMR signal from oil and fiber, eliminating the need to weigh the sample. This is often called the ratio or non-weighing method.

Calibration

The calibration of the instrument requires two well known standards. However, it is first recommended that the instrument is calibrated by 3-6, preferably more, standards with known coating weights evenly spread over the range of interest. NMR is a comparative technique therefore its accuracy is only as good as that of the reference technique against which it is being compared.

Artificial Setting Up Samples (SUSs) are available for re-standardizing calibrations to compensate for small drifts in the instrument, thus enhancing performance and ease of use. Since SUSs are highly stable, they can be used in the long term, avoiding having to recalibrate the instrument on a regular basis using real samples.

Measurement

Samples are first weighed by the weighing method alone, pushed into a sample tube, then compressed to the optimum height using a PTFE stopper. After a suitable conditioning time, either at room temperature or at 40 °C, the sample is inserted into the instrument. Measurement time is approximately one minute per sample. Weights can either be entered manually or transferred automatically from the electronic balance into the application software (weighing method at room temperature only).

Results

Tables 1 and 2 show the results from the same calibration samples measured using weighing and non-weighing methods, respectively. Figures 1 and 2 show the calibration graphs produced.

Both graphs show good correlations between the reference values supplied and the NMR signal, r2 = 0.996 and 0.995 for the weighing and non-weighing methods, respectively. They also show that the spin finish can be measured accurately

Table 1. Comparison of NMR vs. given spin finish contents for a reference sample using the weighing method on the MQC.

Sample Name Given Spin Finish Content Measured Finish Content Difference
1 1.335 1.330 -0.006
1 1.335 1.344 0.009
1 0.877 0.869 -0.008
1 0.877 0.897 0.020
1 0.486 0.506 0.020
1 0.486 0.531 0.045
2 1.565 1.536 -0.029
2 1.565 1.559 -0.006
2 0.537 0.509 -0.028
2 0.537 0.500 -0.037
2 1.039 0.984 -0.055
2 1.039 1.026 -0.013
3 0.450 0.440 -0.010
3 0.450 0.433 -0.017
3 0.864 0.828 -0.036
3 0.864 0.862 -0.002
3 1.110 1.170 0.060
3 1.110 1.117 0.007
4 0.623 0.674 0.051
4 1.005 0.952 -0.053
4 1.364 1.347 -0.017
5 1.575 1.637 0.062
5 0.503 0.528 0.025
5 1.004 1.020 0.016
    Average 0.000%
    Std. Dev. 0.033%

Table 2. Comparison of NMR vs given spin finish content using the non-weighing method on the MQC.

Sample Name Given Spin Finish Content Measured Finish Content Difference
1 1.335 1.326 0.009
1 1.335 1.347 -0.012
1 0.877 0.940 -0.063
1 0.877 0.928 -0.051
1 0.486 0.529 -0.042
1 0.486 0.540 -0.054
2 1.565 1.548 0.017
2 1.565 1.559 0.006
2 0.537 0.497 0.040
2 0.537 0.499 0.038
2 1.039 0.979 0.060
2 1.039 1.063 -0.024
3 0.450 0.424 0.026
3 0.450 0.411 0.039
3 0.864 0.828 0.036
3 0.864 0.853 0.011
3 1.110 1.185 -0.075
3 1.110 1.095 0.015
4 0.623 0.670 -0.047
4 1.005 0.957 0.048
4 1.364 1.373 -0.009
5 1.575 1.575 0.000
5 0.503 0.492 0.011
5 1.004 0.980 0.024
    Average 0.000%
    Std. Dev. 0.038%

Figure 1. Calibration curve for the Weighing method produced by the MQC (SD = 0.0325, r2 = 0.9962).

Figure 2. Calibration curve for the non-weighing method produced by the MQC (SD = 0.0375, r2 = 0.9949).

Out of the two methods, the weighing method offered fractionally better correlation and accuracy than the non-weighing method; however, the non-weighing method has the advantage of reducing the amount of work required to carry out the analysis.

Instrumentation

For accurate determination of low spin finish levels, the MQC-23 with a 0.55 Tesla (23 MHz) magnet, fitted with an 18-mm diameter (8-ml sample) probe is ideal. The Spin Finish on Fibre package comprises the following:

  • MQC-23 which can be controlled using its own built-in computer operating Microsoft Windows or via a stand-alone PC.
  • MultiQuant software including RI Calibration, RI Analysis and the EasyCal ‘Spin Finish’ application.
  • Test/tuning sample.
  • 18-mm glass tubes.
  • PTFE stoppers (to seal the tubes).
  • Stopper insertion/removal rod.
  • Installation manual.
  • Method sheet.
  • A dry block heater and aluminium block with holes for sample conditioning at 40 °C.
  • A precision balance (weighing method only).
  • A set of four Spin Finish Setting-Up-Standards (SUSs).

Conclusion

In conclusion:

  • NMR is very stable over the long term and rarely requires calibration adjustments. If needed, this can be done simply using stable ‘Setting Up Samples’ which recreates the original calibration carried out during installation.
  • NMR penetrates through the whole sample and does not respond to air voids, which means it provides the most precise measurement of the total amount of oil in a given volume of sample.
  • In general, NMR is insensitive to color.
  • The NMR technique is non-destructive so the same sample may be measured several times before being analysed by other techniques.
  • The sample measurement time is fast, around 64 seconds.

About Oxford Instruments Magnetic Resonance

Oxford Instruments Magnetic Resonance are committed to the development and manufacture of information-driven solutions for novel applications in life sciences, research and industrial process control. The company knowledge was founded in the field of Nuclear Magnetic Resonance (NMR) instrumentation, receiving high recognition for its innovation dating over forty years. Today Oxford Instruments Magnetic Resonance are focused on solving complex and often unique technology problems for the understanding of biomolecular structure and function across industrial, life science and drug discovery applications. In the industrial process area, the low field benchtop instruments offer fast, accurate and simple measurement solutions to routine Quality Control problems.

This information has been sourced, reviewed and adapted from materials provided by Oxford Instruments Magnetic Resonance.

For more information on this source, please visit Oxford Instruments Magnetic Resonance.

Date Added: Apr 9, 2012 | Updated: Jun 11, 2013
Ask A Question

Do you have a question you'd like to ask regarding this article?

Leave your feedback
Submit