For anyone interested in a technical read on epoxy crosslinking here is a link:
[
www.masterbond.com]
"The origin of this crosslinking process occurs when linear polymer chains link to form a three dimensional network (See Figure 1)1. The resultant crosslinked polymer network is defined by the crosslink density, which is essentially the number of effective crosslinks per unit volume. Polymers with a high crosslink density typically cure fairly rigid, and offer good structural strength, while polymers with a low crosslink density, tend to be more flexible. This might be useful in applications requiring lower stress."
One issue I see in the industry is that epoxy brands or manufacturers don't always make it clear where their epoxy product stands in the scale of hardness or softness, or rigidity or flexibility.
I try and steer clear of hard, brittle epoxies because they tend to crack and develop spaces between the epoxy and rod blank where dirt can get in as well as water.
Until this thread I was not familiar with this term crosslinking in epoxy. I assumed it had something to do with the layering of epoxies coatings and how well or not they "crosslink" into the lower coating. If an epoxy is allowed to fully cure before the next coat, then crosslinking adhesion is minimal. But if the lower coating is still tacky when the top coat is put on, there is a lot more crosslinked adhesion going on between coatings, and this is another situation I aim for if using more than one coat together and I can see why a full cure before use is requested.
Something I was not aware of until reading the technical details is this one:
"if one were to cure a one component heat curing epoxy at 175° C for 1 hour, versus 125° C for 1.5 hours, the Tg and physical strength properties will most likely be higher with the higher temperature cure."
I am not sure how large of a temperature swing it takes for a noticeable difference, but let's consider the possibilities... men who build rods up north in the dead of winter may have cooler temps in rod building rooms, while down in Florida if I make a rod in say the garage in middle of the summer, and we all use the same epoxy, according to the technical report, the curing strength of the epoxy will be stronger in Florida in summer than those made in cooler temps in the winter. Now, the amount of strength deviation may not even be noticeable as far as fishing rods go, but it is interesting to consider this.
And I wished the technical report had elaborated more on this:
"Not only is curing at the right temperature important, it is also critical to follow the right sequence in terms of temperatures."
I'll be honest and say that I never really cared to bother with temperature adjustments for rod building. I did use thermal changes for aluminum boats though as old tin boat experts have shared with me a nifty detail for how they epoxy up old riveted aluminum boat hulls. A really cool process on how to use temps to actually draw in the epoxy into places it would not normally flow into, but by using a temperature variation at the right time causes an "inhalation" of the liquid epoxy drawing and pulling it deeper into the seams and rivets. It blew me away when I learned that trick and started using it on all my aluminum boats. On my third one now. A freebie brought down from Minnesota to Florida and abandoned in a backyard until it was given to me and I still use the now 50 year old alumacraft boat and there are no leaks. So temperature is more important than I gave it credit for, but a sequence of temperature variations to improve results? I will have to look into this more...
Good post and great thread!
Edited 3 time(s). Last edit at 01/17/2022 09:18AM by Kent Griffith.
