Big Indiana Bass

Two material scientists walk into a bar (LOL)...This is the resulting discussion on the subject of monofilament and copolymer fishing lines. This goes back to a forum post from March 2002 on the BFHP, but the science remains the same. Only the fishing lines are different these days.

TIM:  There are really two considerations here...the composition of the line and the process by which the line is manufactured.

Traditional monofilament fishing line is a single layer of extruded nylon resin. One material in the composition and one layer in the extrusion process. One of the inherent properties of all nylon resins is that they are hygroscopic. That is they will aggressively absorb moisture. As they do absorb moisture the physical properties of the material change. Specifically the tensile strength goes down, stiffness goes down and ductility, or "stretchiness" goes up as the moisture content of the material goes up. This is a dynamic process which reverses itself continuously as the line is exposed to varying conditions ( ie submerged at the lake vs stored in your garage or where ever). The rate at which the resin will absorb maoisture and how much it's properties will change as a result of moisture depends on the particular type of nylon resin used.

In the case of the lines being described as "copolymer" lines, and I'm not speaking specifically to the brand you mention as I'm not familiar with their product, they typically are manufactured using two or more resins rather than one. However, the materials are not blended or alloyed to create a third "species" but rather are co-extruded in discrete phases where one material encapsulates the other. The benefits of this approach can vary depending upon the materials used, the relative thicknesses of each resin and other variables. In the case of a flourocarbon resin coating, or copolymer as commonly used in this context, the objectives are primarily two fold: First flourocarbon resins are hygrophobic, meaning that they do not absorb moisture and second, the refractive index ( an optical characteristic) of the resin is essentially equivalent to that of water. The benefit of having a hygroscopic resin encapsulating the nylon core material in a fishing line is that the tendency of the line to absorb moisture and lose strength while becoming more "stretchy" is significantly reduced. The benefit in this application of having a refractive index closer to that of water is that the line is more difficult to see underwater.

Note too that there are true "copolymers," where two different resin have been combined chemically to create a third material.

 

MARK G:  I'll try to leave out the hype since I'm not selling anything. (Doyle) is correct in that either a copolymer or a single polymer (homopolymer) can be extruded in to monofilament fiber. This is as opposed to a braided line or even something like a core sheath construction. I think there was a line once made by Dupont (Prime?) that employed a core sheath construction.

So the mono v braid is specific to the line construction whereas the question of homopolymer, copolymer, blend or alloy are just few examples of polymer types, again all of which could be made into a mono or a braid. Nylon is a common polymer for monos and ultra high molecular weight polyethylene (UHMWPE) is the homopolymer used in most, if not all of today’s braided lines.

Co-polymers are made by polymerizing two different starting units (monomers) together to form a new so-called "co-polymer" resulting in a combination of new properties. It gets a little bit technical, but there are sub types of co-polymers. A random co-polymer is a case were the monomers are essentially randomly mixed together. A block co-polymer is where you have one long co-polymer chain, but there are blocks of polymer A and B along the chain. A good example of a block co-polymer is Kraton rubber which has rubbery blocks that are combined with polystyrene (glassy polymer used in Jewel cases) to significantly improve it's mechanical properties such as strength and hardness.

You may have also heard a little bit about polymer alloys lately since I believe that Berkley might be using that term to describe its new Sensation line. A polymer alloy is typically used to describe a blend, or mix of two polymers that are immisible...meaning they are blended together but they don't mix and dissolve into each other.

Sorry for that list of definitions, but I think you might be asking about the advantages of monos made from copolymers/alloys over those made from a single polymer like nylon.

The typical answer is that ideally when you start to co-polymerize or blend materials, you can achieve a combination and as a result you have more control over your properties. So then you can adjust the balance to tailor the line to a specific application. You could engineer in more or less stretch, stiffness...you pick the property and it gives you some latitude to go either way with it in the hope that you can get the performance that you're after.

Just a side note but I have noticed that the lines that are more limp like Berkley XL tend to have more stretch and the low stretch lines like Sensi-Thin tend to be stiffer. I'm sure what they're working on are new formulas to tweak the systems. Like Sensation as an improvement over Sensi-Thin. Maybe to engineer a line tough and abrasion resistant that's low stretch, but not obnoxiously stiff and wiry for example.

 

MARK G:  I was a little hesitant to jump back in here but I didn't refresh and see (Tim's) post when I posted mine. Otherwise, I might have added a little more to clarify what I said since we're not consistent in our answers. (Tim) gave some good info there on the moisture issue but I have to disagree, respectfully of course, on the co-extrusion of two polymers resulting in a co-polymer.

There’s a lot you can do when you co-extrude polymers but if you mix two polymers in the hopper or in the extrusion screw you'll come out with a blend, which is different than a copolymer. You can also bring the homopolymers together at the die which can give you a layered system such as a multilayer film or co-fiber/co-filament, which may well have unique properties, but both again not the same as either a co-polymer or a blend.

 

TIM:  Interesting and informative comments Mark. I've always wanted to discuss this with a fellow fisherman that also works in the plastics field.

Mark, I absolutely agree that co-extrusion does not produce a co-polymer and that co-polymerization does/can. Much like a mechanical blend of polymers, even with a compatibilizing agent such as maleic anhydride, does not necessarily produce an alloy. Also, you are correct of course that spinning results in a yet different product (braided lines) and that it can employ either one or multilpe resins in almost any combination of homopolymers and copolymers ( eg a monofilament core with a braided sheath). However it is a matter of process type and design rather than chemistry and I didn't intend to suggest otherwise. I think we are basically on the same page but approaching it from different perspectives.

My intention was to describe a coextrusion process wherein one polymer is extruded over the top of another one in a profile extrusion process ( eg a cross-section of concentric rings of different resins in the case of a "c0-filament line). Not a compounding or polymerization process. Two completely different types of extrusion processes with completely different objectives. One is aimed at achieving homogeneity in the end product ( a resin) while the other is designed to maintain discrete phases of resin in specific locations of the finished product (a part). I think if you go back and look at my original post you'll see that I referred to the end-product of the coextrusion process as one with two discrete phases wherein one polymer encapsulates/is bonded to another. This is done on a regular basis in a variety of profiles/processes including blow molding and sheet extrusion as well as profile extrusion. The objective of course is to do basically the same thing as you describe but through process rather than through chemistry. For example, in the packaging world you might have a sheet that is a co-extrusion of 5 different layers & 4 types of resins. Perhaps one for structural integrity, one as a tie layer ( read: compatibilizer), one for an oxygen barrier ( your coke would go flat pretty quick in those plastic bottles w/o it), another tie layer, and a contact surface, Or whatever.

In essence what I was describing, or at least trying to, LOL, is a composite structure made from different materials combined in such a way as to realize some combination of application desirable attributes that could not be achieved with either resin by itself. I think this is the same thing that you called a "Co-filament" in your post. Not a copolymer resin, blend of multiple resins nor an alloy created by combining two or more resins to create a true third species.

P.S. I have been using one of the so-called Copolymer lines, which is not a copolymer at all but a co-extrusion/co-filament, on all my reels for several years now and can't see going back to a monofilament at this point.

 

TIM: I just re-read your posts Mark and I really think we are saying the same thing. Sorry about being so long winded.

 

MARK G: Hey Tim, Thanks for not taking my disagreement the wrong way! And I agree completely with what you said in point 7. Well said too. A couple of other interesting caveats..... There is a method of extrusion called reactive extrusion whereby the monomers are fed in and the polymerization takes place in the screw simultaneous with the extrusion process. It is possible to react and extrude a co-polymer in this fashion.

After reading your comments about the fluorocarbon lines I took a look at the P*Line ads to see what some of the claims were. Since I don't use that type of line I found them interesting and there is one small source of confusion there as well.

Take the P-Line Fluroclear as a good example. They speak both about a fluorocarbon coating and a copolymer construction, but my guess is that the copolymer is extruded first and the fluorocarbon is put on in a second step, rather than co-extruded with the base fiber. The reason being that these fluorocarbons are extremely low surface energy materials and it'd be dang tricky to co-extrude some of them without some kind of surface treatment to the co-polymer base first. Once done though it wouldn't be all too tough to dip or spray coat the line in a continuous process.