Epoxy vs TTitebond

[sunderll]

At the last launch, I was talking to another gentleman, and he told me he only uses Titebond for assembling his rockets. He was launching larger rockets, with J-350s and up, weighing 6-15 pounds. He said his entire motor mount, fin mounting everything was constructed using Titebond . Obviously he was having success, but does it stand up to repeated stresses and the heat Ok. Just curious if anyone else does this. Thanks!

 

[danielsadjadi]

Titebond wood glue? I've never used it but I have only heard good things about it. To be honest, all the wood glues work just as good. People say one preforms better than the other but I disagree.

 

[G_T]

You'd have to specify the materials being bonded.

Cured epoxy systems are polycrystalline. If they are heated some, they undergo a phase transition where the crystal structure is lost and the structure becomes glass-like. This is called the glass transition temperature, or Tg. Different systems have different glass transition temperatures. The temperature of the cure and the post cure cycle have an influence on Tg. For most systems, the greater the post-cure temperature (if cycled correctly and NOT exceeding the max for that epoxy system) the higher the Tg. Tg is typically roughly 10 degrees C or so above the peak post-cure temperature.

Different systems have different Tg. West System, which is commonly used, has pretty much the lowest Tg of any epoxy system you'll get your hands on. Outdoors on a summer sunny day the surface can exceed Tg. Unlike nearly all other systems, Tg is not improved by post-cure elevated temperatures.

Real aerospace epoxy systems and structural epoxy systems come with data specifying Tg, and the effect of cure treatment on Tg. That lets one pick an epoxy system based on expected temerature service as well as the usual data on structural properties of the reinforced and un-reinforced epoxy.

While Tg is exceeded, epoxy systems become rubbery and weak. As the temperature drops back down, they recrystallize. At even higher temperatures, they decompose. One can heat cured epoxy above its Tg, bend it, then cool it. It will keep the as-bent shape. I do not know offhand if this sort of heat cycling reduces the strength of the epoxy. I would expect it to have some negative effect.

Tite-Bond II is an aliphatic resin. I don't recall offhand about 1 and 3 but likely they are as well. These have an interesting property that if it is heated post-cure the adhesive will soften, and then re-polymerize when cooled. This can be used for veneer. Apply glue to each surface and let the coat dry. Apply veneer with hot iron.

So, in both cases, if the temperature is elevated beyond the design service temperature range, the adhesive becomes weak and flexible.

Both adhesives are quite good within their design range of uses. Both are capable of at least quite good bonds to most materials with proper preparation. Both can tolerate some degree of external exposure. But, many epoxy systems degrade under UV exposure. Some contain UV blockers to eliminate this issue. Aliphatic resins get weaker and probably eventually fail if kept wet. Epoxy doesn't do all that great for the most part with continuous water exposure either.

Each has its place. Which is better depends on the application.

For low power rockets it likely doesn't matter at all.

Sorry for the bit of random brain dump.

Gerald

 

[rharshberger]

Also remember that TBII is and TBI and TBIII are all stronger than the materials they are bonding, so the glue is not what fails, its the cardboard (usually) or the wood. Epoxy really isn't necessary on cardboard and wood rockets. Epoxy is easier to make pretty fillets with, but it also weighs more than the Titebond glues. While all wood glues are basically the same formula, each company has additives that modify it slightly, but for our purposes Elmers wood glue is just as effective as Titebond. FYI Titebond No Run No Drip (Titebond Trim and Molding Glue) is a thicker Titebond formula that works well for fillets, its a thicker glue that doesn't run, I have heard of people doing all their fillets at once then setting it aside to dry, after it is fully cured another layer can be added, unlike epoxies if you add TB in layers too fast the outer ones will dry creating a seal not allowing the underlayers to cure via solvent evaporation (water is the main solvent in wood glue iirc).

TBIII mainly has additives to give it better water resistance, its not waterproof but it takes a long time to degrade in moist conditions.

Also certified motors have a max temperature they can reach and still be certified, which is below the combustion temperature of cardboard.

 

[sunderll]

Thanks Gerald, some good info!!