How optical microscopy can be used to determine cotton fiber strength

Cotton plants have been cross-bred to form a wide variety of genera, and only recently has it been modified genetically to reduce heavy reliance on pesticides. Genetically modified cotton now accounts for a third of all cotton fiber sales worldwide.

Cotton’s value is determined by taking samples from the dense bales resulting from the ginning of the cotton fiber. Each sample is classified according to fiber length (also called a staple), strength, micronaire, color, and cleanness. Intrinsic fiber strength is though to be influenced by the structure of the primary and secondary cell walls of the fibers. As for a micronaire,it is the weight in micrograms per inch of fiber length.

Optical microscopy can obviously be used to grade cotton color and cleanness, but it can also measure its staple and classify the structure of the fiber’s cell walls to determine the cotton’s strength.

Cotton fibers seen under a microscope at 400X

Specific requirements

A sample of cross section of cotton fibers on a glass slide was analyzed at 400X. The purpose of this analysis is to discriminate cross section of cotton fibers (without lumens), and make measurements based on surface and shape with the image analysis system Clemex Vision PE.

One requirement was to discriminate objects at the midpoint of the fibers' black outlines. This specification is arbitrary and could be easily adjusted. 




The main difficulty of the analysis was to fill the small holes and scratches without removing the lumens. In fact, a large part of the analysis is dedicated to this task. Image processing algorithms were then required to maintain the original size of the objects.

Some objects overlapped each other. Most of them were separated or discarded but despite all precautions some still overlapped. These remaining objects are negligible considering total number of objects (1,915). The size-based Transfer also removes objects that are too small to be cotton fibers.

Cotton fibers detected and ready to be measured with a Clemex Vision PE image analysis system

Advantages of automation

A zone of interest was chosen so that all incomplete objects could be eliminated on the edges of each field. Objects that are eliminated are necessarily analyzed in a subsequent field since the stage moves in guard frame size steps. That is the reason why fields are 26 400 μm2 rather than 33 460 μm2 (full image size).

The same analysis was repeated several times and the results are highly reproducible. The results can also be exported in MS Excel to offer many valuable statistical tools and substantial graphical versatility.


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