Your fishing line is possibly

your most important item of

tackle, but what is it and

how is it made.

Origins

Nylon monofilament (a monofilament is a single thread composed of a single strand rather than twisted fibres) is a fully synthetic product made from nylon 6 or 66 polymers.

Nylon was invented in the USA by Wallace Corruthers in the 1930's while working for Dupont. first used commercially in a nylon toothbrush in 1938, followed more famously by women's stockings in1940.

There is no truth in the common myth that the name 'Nylon' was thought of because it was invented in New York and London at the same time. Various other names like Nulon and Nilon were considered and discarded before Nylon was decided on.

Nylon was the first commercially successful polymer and the first synthetic fibre to be made entirely from coal, water and air. These are formed into monomer of intermediate molecular weight, which are then reacted to form long polymer chains. It is made of repeating units linked by peptide bonds (another name for amide bonds) and is frequently referred to as polyamide (PA).

Nylon was intended to be a synthetic replacement for silk and substituted for it in many different products after silk became scarce during World War II. It replaced silk in military applications such as parachutes, flak vests, and was used in many types of vehicle tires.

Nylon fibers are now used in a great many applications, including fabrics, bridal veils, carpets, musical strings and rope.

Solid nylon is used for mechanical parts such as gears and other low- to medium-stress components previously cast in metal. Engineering grade nylon is processed by extrusion, casting, and injection molding. Type 6/6 Nylon 101 is the most common commercial grade of nylon, and Nylon 6 is the most common commercial grade of cast nylon. Nylon is available in glass-filled and molybdenum sulfide-filled variants which increase structural and impact strength and rigidity or lubricity.

Chemistry

Nylons are condensation copolymers formed by reacting equal parts of a diamine and a dicarboxylic acid, so that peptide bonds form at both ends of each monomer in a process analogous to polypeptide biopolymers. The numerical suffix specifies the numbers of carbons donated by the monomers; the diamine first and the diacid second. The most common variant is nylon 6-6 which refers to the fact that the diamine (hexamethylene diamine) and the diacid (adipic acid) each donate 6 carbons to the polymer chain. As with other regular copolymers like polyesters and polyurethanes, the "repeating unit" consists of one of each monomer, so that they alternate in the chain. Since each monomer in this copolymer has the same reactive group on both ends, the direction of the aramide bond reverses between each monomer, unlike natural polyamide proteins which have overall directionality: Cterminal > N terminal. In the laboratory, nylon 6,6 can also be made using adipoyl chloride instead of adipic It is difficult to get the proportions exactly correct, and deviations can lead to chain termination at molecular weights less than a desirable 10,000 daltons(u). To overcome this problem, a crystaline, solid "nylon salt " can be formed at room temperature, using an exact 1:1 ratio of the acid and the base to neutralize each other. Heated to 285 °C, the salt reacts to form nylon polymer. Above 20,000 daltons, it is impossible to spin the chains into yarn, so to combat this, some acetic acid is added to react with a free amine end group during polymer elongation to limit the molecular weight. In practice, and especially for 6,6, the monomers are often combined in a water solution. The water used to make the solution is evaporated under controlled conditions, and the increasing concentration of "salt" is polymerized to the final molecular weight.

DuPont patented nylon 6,6, so in order to compete, other companies (particularly the German BASF developed the homo polymer nylon 6, or polycaprolactam — not a condensation polymer, but formed by a ring-opening polymerisation (alternatively made by polymerizing aminocaproic acid). The peptide bond within the caprolactam is broken with the exposed active groups on each side being incorporated into two new bonds as the monomer becomes part of the polymer backbone. In this case, all amide bonds lie in the same direction, but the properties of nylon 6 are sometimes indistinguishable from those of nylon 6,6 — except for melt temperature (N6 is lower) and some fiber properties in products like carpets and textiles. There is also nylon 9.

Nylon 5,10, made from pentamethylene diamine and sebacic acid, was studied by Carothers even before nylon 6,6 and has superior properties, but is more expensive to make. In keeping with this naming convention, "nylon 6,12" (N-6,12) or "PA-6,12" is a copolymer of a 6C diamine and a 12C diacid. Similarly for N-5,10 N-6,11; N-10,12, etc. Other nylons include copolymerized dicarboxylic acid/diamine products that are not based upon the monomers listed above. For example, some aromatic nylons are polymerized with the addition of diacids like terephthalic acid (>Kevlar) or isophthalic acid (>Nomex), more commonly associated with polyesters. There are copolymers of N-6,6/N6; copolymers of N-6,6/N-6/N-12; and others. Because of the way polyamides are formed, nylon would seem to be limited to un branched, straight chains. But "star" branched nylon can be produced by the condensation of dicarboxylic acids with polyamines having three or more amino groups.

The general reaction is:

A molecule of water is given off and the nylon is formed. Its properties are determined by the R and R' groups in the monomers. In nylon 6,6, R' = 6C and R = 4C alkanes, but one also has to include the two carboxyl carbons in the diacid to get the number it donates to the chain. In Kevlar, both R and R' are benzene rings.

Raw Materials

Today there are many different types of polymer and co-polymers that can form the basic make up of any nylon line. The quality and blending of different polymers are what gives a line its characteristics and it here where experience counts because there can be chemical incompatibility between even the best materials. This is particularly the case with the dye element because different colours from different sources can be made from completely different chemical substances and these can react with the polymer to weaken or breakdown the line even over quite a long period after manufacture. Other elements are also sometimes added, for example silicone to improve abrasion resistance or titanium dioxide to make a line opaque.

Manufacture

Nylon Monofilament begins life in granular form (or chips) to which the dye is added and this normally comes in the form of a powder. The components are then mixed mechanically for some time to ensure consistency. The mixture is then fed into the extrusion machine which heats the granules so they become molten and then this liquid it is extruded at great pressure through very small holes in a device called an extrusion head or spinneret. There can be up to 50 lines being extruded at one time from one extrusion head. The nylon filaments solidify once they come in contact with air and immediately pass through a fixing water bath to further solidify them. At this point the nylon fibre is formed but is weak and extremely elastic and would be unsuitable for use as fishing line.

The line must now be drawn. The diameter of the extruded line is thicker that its final diameter will be as the drawing process permanently stretches the line thus makes it thinner.

The effects of drawing in fishing line production

Fig 1

The important effect of the drawing process makes the molecules in each filament fall into parallel lines, giving the nylon monofilament strength and making it less elastic. Figure 1 above shows the effect on the line that drawing has. It make a line stronger but reduces stretch. This is why high tech / high strength lines usually have less stretch. The more a line is drawn to increase strength also has an effect on its softness so high strength lines often tend to be more springy. Ultima always adds an extra stage softening process to any high tech product and Fluorocarbon coating further helps soften the product.

Some lines are referred to as 'pre stretched'. There is no such thing. All lines are stretched, you couldn't use then otherwise. It's just a question of how much. The more you stretch a line the higher the breaking strain becomes but past an optimum point the knot strength begins to fall. As the most important factor for any line is the knot strength, hitting this point is critical.

The optimal point in fishing line production

Fig. 2

As with many things, fishing line production is a question of compromise. There is an optimum point in the drawing process where knot strength reaches its maximum and after this begins to fall even though the linear strength continues to increase. Every line needs a knot so to produce a line with higher linear strength but lower knot strength is pointless. With our lines the goal is to hit the maximum knot strength at this optimum point as we call it as shown in (Fig.2)

So the drawing sequence commences as part of the continuous production process. First they are softened again by air heaters before they pass through rollers that stretch the line. This process is repeated twice and then a third set of rollers allow the line to contract or 'relax' before the finished line is wound onto a large bulk spools.

The whole production process occurs on a production line of some 70 - 80 metres in length, and is a continuous production process. Extruders run 24hours a day and our only usually shut down very rarely for cleaning and maintenance.

Copyright Ultima International 2008