What is difference between Epoxy & Polyester Resins

The strength depends on the conditions.
Epoxy is more flexible and streches more before fracturing. That means it will be better for shock loads. Compression is mainly a factor of the fiberglass and won't have a significant difference. In high temperature conditions, epoxy will get soft and polyester will be superior. If there are free solvents, epoxy is more resistant. Etc,

 

Because mainly the glass (or better fiber) content provides strength, to a lesser extend the resin.

But there is no general layup comparison (as far as I know). Too many different Poly and many more different Epoxy mixtures are available. Even high temp EP is on the market, to prevent failures as Gonzo described.

If there was´nt the substantial price difference, I would never produce our larger designs in Vinylester, but in EP!
But at 100 tonnes per boat you feel the difference, really. And the market does´nt pay for the better resin.

Regards
Richard

 

In all the time buggering around with boats I still have to see a boat getting bent through 90 degrees, never mind 180

Are we talking anything practical here or is it minute's again. How much further than a same polyester resin will an epoxy layup bend ? How is this practical

If two boats are built identical, same everything, the one polyester and the other epoxy, if at exactly the same conditions they hit at the same speed a rock, how much bigger will the polyester's hole be ? 1mm ?

While there are many differences between the two under various conditions, if one say the one is superior then surely there must be a practical reason. If one dissolved in sea water for instance then it would be fair to say use the other one because this one has that drawback.


In the high temperature conditions Gonzo, I suspect one will be well cooked long before the difference in the two materials become aparent Again, is this a practical indication of the one is better than the other ?

 

Military boats specify high temperature fire resistant resin. As far as I know, that is only acomplished with palyester.
90 degree bends, or close, happen when sharp objects hit a laminate, like in puncture damage.

 

Fanie

Depends on layup design of course, so no one line answer.

Poly resin cannot withstand water ingress. That IS a drawback. And it is the main problem behind the so called osmosis. In fact there is no osmosis in the first moment when water ingress happens.
Osmotic and micro molecular chemical processes start within the glass poly matrix and make the blister and delam problems.
The main issue is the gelcoat that has to protect the poly glass matrix. It is hard (good) and brittle (bad), and tends to get haircracks. Through these cracks you get water ingress and sometimes severe issues inside the laminate. You might not notice for a long time, that the boat you are sailing is already shot!
Epoxy does´nt know such issues.

To the temp. question: yes Poly can stand a bit higher temp.s than EP, but 125°C should be sufficient for non military use.

If you´re interested in a deeper insight have a look here:http://www.yachtsurvey.com/BlisterBlues.htm
and here:http://www.yachtsurvey.com/HiTech.htm
and go to the other related articles on his website too.
Though I do´nt see Pascoes elaborations as the last and only true word spoken, it tells the truth in all cases. His opinions sometimes seem to be a bit biased. But we all have more or less biased opinions.

Hope that could help a bit.
And when we come back to the original question:

the answer is clear, and doubts are not possible, in the hands of a novice, only Epoxy will make a good repair job!

Regards
Richard

 

Now you're talking about gell coat That is something totally different from polyester resin.

No kiddin I still stick with my opinion that one uses what is suitable for your application method. It just makes sense.

The polyester resin I'm using for my boat is specifically for prolonged exposure to sea water, I won't use gellcoat (yuk !). But I will probably paint it.



Eh Par, I actually got my almond cake. If I stay alive then the arsenic levels was a bit low The wife like baking and cooking so at 03h00 when I went to bed and whispered 'almond cake' I got the 'ihmm' reply (as to the usual 'uhh uhhhh' )

 

Gelcoat is resin with a load, pigment and usually UV protection.

 

Have fun..............

 

This stuff is all well covered in several references, but some high lights.

Ortho polyester tends to be brittle, because it's elongation is quite low, before fracture. This makes it unsuitable for modern fabric weaves or high modulus materials. The resin system will fail, long before the reinforcement. Ortho's have a less then stellar chemical attack properties as well. In spite of these short comings, it's the plane Jane of the industry and heavily used for it's cost and because shops are geared for it's use.

Next up the polyester ladder is isophthalic. Is has a little better elongation and a little better chemical resistance. It's about 20% less brittle then ortho. As a result you can vacuum bag a mat/roving laminate with fairly strong results and only a modest change in resin system cost.

Moving further up the polyester scale is vinylester. This stuff is about as good as you can get with a two dimensional molecule. It's elongation is twice that of iso's and can have a tensile strength near 11,500 psi when used with modern fabrics in a well controlled laminate. It's interlaminate bonds are much better then the other polyesters and it's peel strength is also much higher. Vinylester is also even more resistant to chemical attack.

This stuff was developed partly to address production shops around the world in a polyester environment, as this resin is compatible with all the polyester products. Used with biax, stitch mat, E-'glass or other high modulus material, a strong laminate and still cheaper then epoxy, though not by much, plus a production shop doesn't have to retool and retrain for the different resin system.

By every way you measure epoxy (at least the stuff we use) it's better then vinylester, except cost. Because of it's 3 dimensional cross linking, it doesn't need to be "bulked" up with mat products. Using mat with epoxy is just wasting resin (lots of it). Epoxy's peel strength and interlaminate bonds are so strong, mat will actually weaken the final product. How strong? Let's take a 1/4" thick, biax S-'glass, bagged laminate. It's flexural strength will be in the 80,000+ psi range. This is stronger then stainless steel of the same weight and makes all the polyesters quiver and hide by comparison.

 

Well engineered items that need to hold up to extreme stress, need to be light, use fibers other than, or in combination with glass, are less effected by cost, or are being used over a wooden structure are good candidates for epoxy.

Mass produced items that need to hold up well, but can tolerate slightly more weight, are using only glass fiber (with some exceptions) and are affected a great deal by cost are good candidates for the “correct” polyester.

There are many horror stories out there about how a polyester failed and how it was the resin’s fault. Little research is actually done to find the real cause though.

Blisters can be caused by many things, but even if all the best methods are used, a low cost polyester that was never designed to be used in a hull can, or will, blister. If the “correct” recommended products are used then the chance of blisters are drastically reduced, even to the point of them not being much of a concern, especially when barrier coats are used.

There was a time during the boom in polyester boat building that almost any resin that got hard was used in production, cost was the deciding factor. This along with poor methods of production and shoddy workmanship created a huge fleet of boats that didn’t fair well a few years after they were put into use. This is where most of the bad rep for polyesters was born, that, and that if you had a 1 gallon bucket and 4” brush, you were in the boat building business.

While there are still some (very few) boats built this way, many have upgraded the products and methods used to avoid most of these issues, price still becomes an issue at times, so the “best” products may not always be used.

Skill of the worker and the equipment used (spray type for the most part) can still be a factor though, so while the polyester resin used may be fine for this application, there can still be issues with other parts of production that may cause problems. This is where many of the differences in the survival of final products made from either epoxy or polyester come from.

Almost everything made from epoxy is less price concuss than items made with polyester, this means good experienced engineers are involved, these items tend to be custom built and in lower volumes, more actual craftsman are employed and shop conditions tend to be better. This results in fewer items on the market and more care taken to produce the products. As price comes into play, each of these factors is compromised.

The other issue has to due with cost of production, while the cost of using epoxy compared to polyester seems clear at first by just looking at the price of each product, that’s only the beginning of the difference. Epoxy isn’t as user friendly in production and the same type of equipment can’t be used and when equipment is available, the cost will be much higher. There are also the health problems associated with epoxy, while I don’t recommend being exposed to polyester for good health, exposure hasn’t been a big problem in the industry, where epoxy can have some real issues when the correct handling procedures aren’t used. These all add up to a much higher final cost of an epoxy product when compared to the same type of item made from polyester.

If non engineered epoxy products were made with the same poorly trained employees, in shops with shabby working conditions there would be horror stories about them also. Then factor in the epoxy being sold on price alone, not physical properties or suitability for the application and you would have resins that were junk being used to build to a price point. How do you think these hulls would hold up?

 

The mentioning of methods is going to keep on surfacing.

Anything poorly designed an build is going to be problematic. If a boat or parts are properly designed you won't have problems. It does not matter if you use polyester or epoxy.

The differences between polyester and epoxy have been mentioned numerous times by now, still, the strength of a layup is determined by the glass and not whether epoxy or polyester is used.

If it was so that epoxy makes such a big difference in strength then surely one can get away using less glass and hence possibly make up some of the difference in price to make epoxy more attractive. Doesn't work that way.

Even if the molecule structure of epoxy leans itself to glue more dense to the glass strands, the end product doesn't make such a big difference. It is the glass that produces the strength, the binding epoxy or polyester adds very little to the strength of the structure.

That is why only the glass is considered in design strength.

The method used to create the structure is the factor that determine which will be used, epoxy or polyester. And off late it seems personal preference as well

If anyone wants to buy a boat he chooses between fiberglass, wood, iron, aluminum as the basis for the construction. I have never heard of someone looking at a boat to buy, asking if it is an epoxy or a polyester boat. It does not matter.

Sure, if a shape is casted, one in polyester and one in epoxy, both without glass, then the epoxy may bend more than polyester or prove the epoxy is stronger.

But you have to remember when the glass is used then the epoxy or polyester required is limited only to wetting out the glass properly. More just adds weight. Less compromises the strength. Now only the strength of the glass matters.

 

ondarvr mentioned a "barrier coat" in his post above. Do you know what that is? EPOXY
So, when poly has to be coated by Epoxy, which one is the better product? (and if it was only in this case, what it is´nt)

Quite obvious you did not take the time to read some of Pascoes articles I linked to!
And you do´nt believe us people using the goo daily?

You should!

Regards
Richard

 

This isn't correct, 'glass is used with most of the polyesters because the resin needs the mechanical help of the reinforcement. With a better resin system you can work to the limits of each material, which is the ideal engineered structure, when everything fails all at once.

Actually, several production shops are advertising all epoxy laminates, specifically because they know what their clients want. Or, in the case of a polyester boat, asking if it's been barrier coated with epoxy.

You are under the false impression that it's the 'glass that makes the product. The matrix (resin/reinforcement combination) makes the product. The 'glass alone is useless, polyester resin alone is brittle and epoxy alone is as well, though less so.

Epoxy and carbon, epoxy and Spectra, epoxy and Kevlar, epoxy and polyester, epoxy and modified acrylic, combinations of each - these are all fairly common laminates now and they have none, zero, no 'glass in them. Apparently 'glass isn't as useful as believed. In fact, there will soon come a day when we will look fondly back at the days when there was only 'glass to use as a reinforcement fabric. I'm personally looking forward to the day they can build a machine to weave Spectra and treat it with a sizing.

And yes, you can use thinner laminates and less materials for the same strength with epoxy, compared to polyester, which is the whole point (and done all the time). Lighter is faster, given the same strength, which just leads to more capacity, higher ballast ratios, stiffer boats and bigger sail plans, etc.

 

PAR

You left out a whole class of polyester resin, DCPD's, these are the lowest cost and most used resins with many of the poorest physical properties. The main reasons DCPD's are used is because of their low cost and low shrink characteristics, the other reason is they require less styrene to thin them to a usable viscosity.

The down side is they tend to be brittle, weak, have poor water and UV resistance and secondary bonding over them needs to be done with more care.
The secondary bonding problem was where a great deal of the bad rep came from with polyesters, not all of it though. DCPD’s will cure on the surface much more like a waxed resin, so the window of bonding over it is very short. If they cure for very long, the surface needs to be sanded very well before the next layup.

DCPD’s took the industry by storm when they were first released because of their low price, it wasn’t until later that these limitations were understood and how they were used changed. Now DCPD’s are blended with other resins (Ortho, ISO, VE) to lower the cost and make them conform to MACT compliant regulations (FRP industry limits on hazardous air pollutants). Ortho is considered a big upgrade from a DCPD.

 

Ondarvr
you think DCPD´s are still the most used resins? I thought even my dumbest competitor would have given up on that crap!?