Making Fibers Stronger

To read more about fibers, click here.

The ordered part, that is, the crystalline part, of the fiber makes it strong. So, what would happen if we make some of the jumbled-up parts line up? That would make the fiber be more like a crystal, and stronger, right?

You know what? That works! Yay!
To make nylon fibers stronger, they're stretched (or drawn) when they're cool. This is called -you guessed it - "cold drawing." As the fiber stretches, more of the chains line up next to each other.

insert picture or video of cold drawing model with cord

What else could make fibers strong?
What if the chains were kind of sticky? That way, when the fibers are pulled, the chains wouldn't slide past each other very well.

We can show this by taking a closer look at the way nylon 6,6 packs to form a crystalline fiber.

three nylon chains have many hydrogen bond bridges between them

The dotted lines between the H's and the O's are called hydrogen bonds. Pretend the H's and O's are little magnets that stick to each other, not holding hands, just kind of close and cozy and not wanting to be apart. When you pull on the fiber, those magnets won't want to let go. The fiber won't stretch very much, if at all. That's why fibers are good for rope and thread.

By the way, cellulose chains are stretched out and packed together with a whole bunch of hydrogen bonds between them - just like nylon! Even though the repeat units for cellulose and nylon are really different, they're alike in how the chains act. That's why cellulose is so strong too!

Fibers do have a down side. They're strong when you pull or stretch them, but they're weak when you try to squish or press them. Also, fibers are usually only strong in one direction, lengthwise. If you pull on them the other way, width-wise, they tend to be weak.

fibers pulled in each direction

Working Together to Make Stronger Stuff

Because of this weird combination of weak and strong, it's often a good idea to mix fibers with another material, such as a thermoset. (A "thermo-set" is a polymer that sets, or gets hard, when it gets hot - that's the "thermo-" part.)

The fiber helps make the thermoset stronger, and the thermoset helps make the fiber stronger. Any mix of two or more materials is called a composite. When fibers are mixed in, it's called a "fiber-reinforced composite." They work together to be stronger!

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