One of my favourite hobbies has become the craft of crocheting, and I am in good company with my mum, gramma, close friends, and even Queen Victoria. I find this craft to be incredibly relaxing, giving me something to do while I try to relax my mind after working. I can take it anywhere, it is super portable, as evidenced by the picture on the left, which is me crocheting in the Zurich train station while traveling in the summer. I will crochet while teaching in a help room and I found this very beneficial in keeping me calm when dealing with even the most difficult of students (which is NOT the majority of the students I teach) and also keeping me from getting bored when students didn't have a lot of questions without making me difficult to approach. You can hold a conversation, watch a movie, listen to a presentation all while crocheting. I do also know how to knit; however, I have yet to ever finish a knitting project. I find crochet to be faster, simpler, and easier to pick and put down-but that is my preference. A good many ladies in my department also crochet/knit, and like many things in life, this craft is filled with chemistry.
When you start a craft like crocheting or knitting there are a few important things that you need, namely the hooks (if you are crocheting) or needles (if you are knitting) and yarn. Yarn is the general term for fibers that have been spun together. With the yarn comes a number of options and this can be daunting for a newbie. What is the difference? What does it all mean? What yarn is best for what project? What is the difference between wool and yarn? Well there are three main categories for yarn types: protein fibers, cellulosic (or plant) fibers, and synthetic fibers. Each type has pros and cons and is best for different types of projects. Because there are three different types, I have decided to break the entry into three different parts. Today's part is brought to you by protein fibers.
Protein fibers are animal in origin and are, as the name suggests, comprised of proteins, so before we can discuss protein fibers we need to discuss proteins in general. What is a protein? Proteins are large, 3-dimensional structures that are made up of amino acids (pictured on the right). There are 20 natural amino acids and they differ only at the position I have labelled "R". This R group gives each amino acid unique properties which, when many amino acids are strung together, will result in the protein properties. A string of amino acids makes a polypeptide. There are four levels of protein structure. The first level (called primary) is the specific sequence of amino acids strung together to make the polypeptide. This is determined by DNA code. The second level (called secondary) is localised conformations, which is created by the was that neighbouring amino acids interact with each other. The third level (called tertiary) is the over three-dimensional structure of the entire polypeptide. The fourth level (called quaternary) happens in proteins that are made of many different polypeptides. Now I find all of this very cool because muscles and hair are two very different types of proteins, but each are made up of the same 20 amino acids and simply differ by how those 20 amino acids are put together, which is what creates the overall shape, and thus the function. What I find even more awesome is that those 20 amino acids are dictated by the four base pairs in DNA. So depending on how those four base pairs are oriented in your DNA will determine what sequence the 20 amino acids in your proteins are put together, which will ultimately determine the protein function and that results in this amazing thing called life! But to carry on with my Ode to DNA I digress from the point of this entry, which is protein fibers.
The first, and major, type of protein fiber is wool. Wool comes from sheep (and sheep-like animals). But not all wool is created equal. Different sheep give different wool. There is huge variation in the structure of wool (just like the variation in the animals themselves) and the overall structure is pretty complex. For the interest of crocheters and knitters I am going to focus on pure, fine wool. Raw wool can contain 30%-70% impurities. Pure wool is almost entirely protein. Wool is characterised by its diameter, length, and crimp (how curly it is). Smaller diameters, shorter lengths, and more crimp result in finer, warmer wools and super soft wools, really really soft wools (I can't stress that enough).
The basics of the fiber can be boiled down to the outside, which is called the cuticle, and the inside which is called the cortex. The cuticle is about 10% of the fiber and results in the surface properties of wool. What is most interesting about the cuticle is that the cells are put together like scales, i.e. they overlap, and this creates directional friction which means that the fiber is smoother (less friction) in one direction compared with the other direction. This is what makes wool so easy to spin into yarn, but also what causes it to felt and shrink because the scales cause the fibers to get entangled and thus felted. The cortex results in the overall structure of the yarn. Depending on how the cortex proteins are put together will influence the amount of crimp in the yarn.
The protein that makes up wool is called keratin. Wool is over 80% keratin. What makes keratin interesting is that it is high in the amino acid cysteine. The R group in cysteine is CH2SH. The remaining amino acids cause the protein to adopt a helical structure and then the cysteine amino acids in two protein strands bond together. The result is two protein fibers that are coiled together and then cross-linked through sulfur bonds, making them pretty strong. (Side note: sulfur-sulfur linkages are also what give vulcanised rubber its strength.)
Let's compare types of wool: 1) merino wool is soft, not terribly expensive, but does pill. Its fibers are 17-25 micrometers in diameter. 2) Mohair-this is wool that comes from the angora goat (not to be confused with angora wool, which is made of bunny fur). Mohair is a little coarser at 25-45 micrometers in diameter, but is quite fuzzy. I have used it in a blend for a sweater, super nice. 3) Alpaca-oh how I love thee alpaca. Alpaca wool is from, shockingly, alpacas. On the left I have a picture of my Queen Victoria scarf that I made using alpaca. It happens to be the second softest yarn I have EVER put my hands on. Alpaca is 18-25 micrometers in diameter (remember smaller is softer and warmer) and I can tell you that this little number is very VERY warm, which is helpful up here on the prairies. Actually, this particular pattern is nice with a yarn like this because the space between double crochet clusters keeps you from over heating. I have another alpaca scarf that is much more densely crocheted. It is also super soft, but I won't wear it if it is warmer than -10 C because it is just too hot.
4) Cashmere-and on the right we see a picture of the softest yarn I have ever felt. Cashmere is combed from the bellies of cashmere goats and is very fine, at no more than 19 micrometers in diameter. Naturally this makes it more expensive (those little 50g balls are $26 CND each), so I have a very special plan for those two little balls. Now both alpaca and cashmere are less durable than merino wool, something to consider when planning your projects.
The other type of protein fiber is silk, which is produced by some very specific moth larvae (a.k.a. silk worms.) Basically when it is time for those larvae to morph into moths, they excrete a thread of the protein fibroin out of its head and glues it together with a protein gum, wraps about 2 Km of it into a cocoon, under goes its metamorphosis and leaves the shell of its cocoon behind to be unraveled and degummed and sold as silk. Since it is already a thread, silk doesn't need to be spun to form yarn, the silkworm already took care of that. So instead of keratin (the protein in wool), silk is fibroin. This protein has very little cysteine in it, and therefore doesn't have sulfur bonds holding the fibers together. The main amino acids in fibroin are alanine and glycine, which are the smallest of the amino acids. This means that the silk fiber is more crystalline, and less stretchy. It has more tensile strength than wool, but tends to be more brittle. These fibers are 15-25 micrometers in diameter. This makes silk quite soft. It is also quite light. But it is also quite expensive. It is shiny though. It makes a good choice for a shawl or wrap.
Coming up in part 2-cellulosic fibers: cotton, linen, bamboo.
References:
Stoller, D. Stitch'N'Bitch: The Knitter's Handbook 2003, Workman Publishing Company, Inc. New York, NY.
Crowfoot, J. Ultimate Crochet Bible 2010, Sterling Publishing Co. New York, NY.
Pratt, C. W.; Cornely, K. Essential Biochemistry 2004, John Wiley & Sons, Inc. Hoboken, NJ.
Mather, R. R.; Wardman, R. H. Chemistry of Textile Fibers 2011 Royal Society of Chemistry.
