What is difference between Epoxy & Polyester Resins

Whith Epoxy.

And the Spectra, Dyneema stuff is a good choice in some cases. (but not easy to work)

Regards
Richard

 

Jimbo, the data sheets for the locally available resins shows that a good number of the epoxy resins have a lower elongation, tensile strength, flexural strength and much lower HDT than VE even at 40'C cure. And these are premium and not cheap epoxies, 2 to 3 times dearer than premium grade VE. There are also toughened VE resins available that have elongations of 8 - 10%, dont know how these compare on price.

This is why I recommend that you get full data sheets when selecting a resin. For epoxy this includes data for each individual hardener, do not assume that the fast and slow will give you the same properties.

 

That is all well known and does´nt change the general statement!
And of course it is NOT the resin which makes the properties of Epoxy, it always is the hardener mainly! And comparing apples and apples you will not change the fact, that Epoxy IS the far superior material. And what means a 40°C curing temperature? Go over 70°C to talk about post curing.

Regards
Richard

 

My previous post on the subject of http://www.boatdesign.net/forums/wo...ion/epoxy-comparisons-21105-2.html#post182681.

Jimbo

 

Hi Richard,
Like you I also think epoxy resin systems are superior and that is why I am using it for my current boat.
And yes it is mostly the hardener and cure temperature that governs the final mechanical properties.
Various posters have made general statements like epoxy is tougher, stronger etc without specifying the system or cure conditions.
I was trying to compare apples with apples, and stated that my observations are that locally most boats are not post cured. In this case the fair comparison is for resin properties at long term ambient cure. And the data sheets for local epoxy systems used for boat building show that they are not always stronger or tougher at these cure conditions.
"And what means a 40'C curing temperature?" this was a response to Jimbos statement that even if boat builders do not post cure their boats, that they will see temperatures of over 38'C for hours on end. Once again my data shows that the referred epoxies at a 40'C cure will not necessarily have a higher strength or elongation than a VE resin at long term ambient cure.

So my message is once one has decided on the cure conditions that are going to be achieved is to go and get data for these conditions. Then make a choice comparing apples with apples.

Cheers
Andrew

 

Right............

 

Good grief Richard, are you blokes still on this thread

It is true that epoxy resin offers a little better characteristics ie flex etc than polyester resin.

I would again like to point out that wether you work with either the calculated strength is done on the glass allone - and not on the binder resin.

No one could so far offer a comparasson between the same layups regarding strengths and pro's or cons on either.

 

It´s all known Fanie, no need to make a comparison.

The glass is the same, no matter which one of the thousands of formulations of resin we use. The resin makes the difference.

 

This thread has run its course and thanks to a few mechanics with some respectable hands-on time, polyester came out of it with better representation than it normally gets in these discussions.
Having read seven pages of this discussion, I suspect that many readers are going to come away more confused than they were when they started.
For the benefit of the layman, I'm going to try to elaborate ( while trying not to get too technical) on some of the differences and hopefully, install some confidence in polyester repairs.
Epoxy obviously has some structural benefits but to suggest that all repairs should be done with it isn't very realistic. Not only has polyester proven itself in millions of successful boats but also in millions of well executed repairs.
For little understanding of the relationship between the fiberglass reinforcing and the resin, fiberglass will elongated approximately 4.8% before rupture with 100% elastic return up to rupture. An iso-resin (a good polyester) will elongate just over 2% before failure at 9400 pounds per square inch (which is better than an ortho or a DCPD resin), a vinyl ester resin will elongate over 4% and provide a tensile strength of 11,800 pounds, and most laminating epoxies had elongation's in the 5 to 6% range and a tensile strength near 12,500 pounds per square inch. With those values in mind you can understand how a resin can become overloaded before the fiber was fully loaded and how that might affected ultimate strength and damage tolerance a laminate. Admittedly, all of that is not very complimentary to the polyesters but keep in mind the outstanding success rates and the fact that recreational boats are not designed with a very sharp pencil ( the safety factors are supposed to be huge).
Most repairs are pretty straightforward and with good bonding techniques, an understanding of structure, and a good iso-resin, satisfactory results are very predictable. Occasionally it's difficult to determine which resin system was used ( Polyester will not stick to epoxy) or for some other reason, the reliability of secondary bonding is a concern and in those situations a peel test should be conducted.
The purpose of a peel test is to prove repair-ability of an existing panel ( damaged or in need of modification, boat, airplane, pipe, whatever). The test is conducted by preparing the panel being tested in the manner recommended by the resin manufacturer and then laminate 3 x 6" test panels half on the panel and half on mylar tape. After curing the test laminates are levered off the panel with a wonder-bar and the delamination is evaluated. It is generally accepted that less than 10% failure on the bond line is acceptable but much better results are typical with good procedure.
I recently did a presentation and in interest of showing the repair ability of fiberglass products with several resins, I prepared two test panels. The first a scrap piece of fiberglass that previously served as a baffle in a diesel fuel tank for over 25 years. I chose that piece of scrap in the interest of illustrating the reliability of repairs to integral fuel tanks and expected less-than-perfect performance. The second panel was a nice, clean iso laminate cut off. The test laminates were of iso-resin, vinyl ester resin, and West system epoxy.
Of the first three that I delaminated, the iso-coupon failed within the coupon ( test laminate), the vinyl ester and epoxy coupons both tore fibers from the test panel. On the second panel, all three failed within the test laminates. These would be referred to as “ peel failures” ( a repair laminates weakest loading) and the epoxy was handicapped by being the thinnest of the laminates but in all cases the bond was 100%.

 

The idea of any repair job is to restore the original part as close to what it was previously or better.

Delamination is a reality but depends where the repair was done and how much endurance the patch have to withstand. I have delaminated both epoxy as well as polyester.

In all cases it is always better to add mechanical strenth to prevent delamination. One such method I have used that was very successfull is the use of rivits. These cannot always be used but it depends where the repairs are to be done. Another layer or two hide the presence of these rivits, but they defenately contribute huge strength to the repair. I have once stripped such a part from the boat I had, and it was a nighmare. I couldn;t believe how well it kept the glassed parts together and how strong it was.

Another method is to add new material from both sides, say inside and outside but so the new (and still wet) repair at least makes a good bond with each other.

And yet another would be to extend the repair to where other parts of the structure whould force the new material to stay in place.

One should keep in mind that a repair, and even a bad repair will work in calm weather. If you end up in a storm and waves, you don't want to lose the patch and make water, or have structures getting torn loose, or have decks become soggy under your feet. Most guys just want the thing fixed up, but it makes a difference in the long run if you do it well.

Preperation is probably the most important factor that will improve the repair. So will experience and a knowledge of the material you use.

Personally I don't like the use of wood, but if you do then epoxy is the binder material to use.

I have made structures on a few occasions using a pre-made former that I have used polyester for. The former removed left a pure glass structure which I then glassed into place. Worked awesome and never had problems with these. No wood that will rot over time and saved a bit on weight.