Mature cotton field, Cherokee County
The touch, the feel! Cotton is one of the most used fibers in the world, from your BVDs to your Egyptian 3,000 thread count sheets and your stonewashed whiskered bootcut low rise jeans.
The journey from field to garment is quite an amazing one, but I want to get a bit closer, if you know what I mean. I posted a while back about about the molecular structure of cellulose, this is called the micro-structure, today I want to talk about the macro-structure.
The figure above is cotton strands magnified 630 times by an electron microscope. On average cotton fibers are 1/8 – 2.5 inches long (0.32-6.35 cm) and the diameter of the fibers is generally between 16-20 micrometers, making is one of the finest natural fibers. When they are growing on the bole cotton fibers are round, but processing causes them to collapse into flat twisted ribbons. This twisted structure is part of what helps such short fibers grab onto each other as they are spun into threads and yarns.
There is much more to cotton however then can be seen by the naked eye under a microscope. Cotton is made of many layers which are primarily cellulose.
Layer 1- The cuticle is a waxy protective layer that provides water resistance to the fibers as they are growing. This layer is removed by scouring during processing before spinning.
Layer 2- The primary wall is made up of chains of cellulose called fibrils. These fibrals spiral around the fiber at 20-30 degree angles. Mature cotton fibers have thick primary walls, immature fibers do not and often collapse and tangle, causing neps (aka those little tangely bits) when the fibers are being carded and spun.
Layer 3- The winding layer is really the first part of the Secondary wall. It is made up of fibrils that run at 40-70 degress and spiral around the fiber. This layer helps support the rest of the secondary wall.
Layer 4- The secondary wall is the last layer and ts is actually made up of many layers of fibrils, each layer grows over a day and forms rings, kind of like a tree. The fibrils in the secondary wall are different in the way they grow, they do not really spirl, they change direction somewhat at random, making for a zig zag kind of formation. Weak sports can occur in the spots where the fibrils change direction and the winding layer helps compensate for this.
Layer 5- The lumen is not really a layer per say but rather the hallow tube that runs through the center of the fiber. When the fibers are growing this tube is filled with fluid but during processing it is emtpy and collapses, which results in the flat appearance of the fibers and the kidney bean appearance of cross sections of the fibers. The lumen is also part of what makes cotton so very absorbent.
All these layers of fibrils make for a densely packed fibers, ever notice how much heavier a cotton sweater is then a wool one? Also, as the fibrils layer around each other they make tons of microscopic capillaries, which also ups cottons absorbency. Cotton is a very hydrophilic (water loving) fiber and the cool thing about cotton fiber is when it is gets wet it swells and unlike a lot of other fibers (like silk or rayon) instead of getting weaker, it gets stronger. Any boater can tell you, cotton makes great sailing rope because it takes a soaking and then just works even better.
For more technical information on cotton then you would ever need to wear a t-shirt and be comfortable check out the info page at Cotton Inc. (The Touch The Feel, you know the guys that made the commericals). There you can find out more about cotton’s absorbency powers, tencile strength, thermal properties, and more that would make for a very long blog post.
