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"Heat compaction of glass fibers"?

"Heat compaction of glass fibers"?

(OP)
I few years ago I made the following note in a file I made on glass properties:
'Note that there is a "heat treatment" called "heat compaction" which can increase the moduli by 18% (E-glass) and 9% (S-glass).'

I didn't note where I read this and can't remember (sloppy; slap wrist), but I do remember that there were no other details given in the original source, and in spite of a quick hunt about I couldn't find any more on the treatment.

I recently looked again for any information on this and the internet was fairly unhelpful. "Compaction Effects in Glass Fibers" by William H. Otto is about the only possible that came up and will take money to further assess it (the preview looked interesting and implies that thermal treatment of the glass may increase modulus, saying that fiber properties tend to change towards bulk glass—it says that the modulus is reduced when the fiber is spun compared with the "massive annealed form of glass", so thermal treatment would also decrease strength). (The preview is at http://onlinelibrary.wiley.com/doi/10.1111/j.1151-... ).

Can anyone tell me more about "heat compaction"?

RE: "Heat compaction of glass fibers"?

I have never heard of such a process being useful. Obviously as heat compacts the fibers they will fuse and approach the properties of bulk glass, which is strong but very brittle and flaw sensitive, and thus appears to be weak. Modulus of the fibers is reduced due imperfect alignment with the load. Also, bulk glass has strength and stiffness in all directions, while fibers only in one. There is probably a modulus effect due to Poison's ratio.

RE: "Heat compaction of glass fibers"?

(OP)
Ta. I will look for where I first read this info (may take me a few days). https://pure.strath.ac.uk/portal/files/40240792/Je... has some bumf on the thermal effects, though no mention is made of an increase (or decrease) in modulus. As the title implies they only looked at strength reduction, which looks quite severe and seems so after quite modest exposures. I have to worry a little about the effects of an autoclave cure at 180°C for an hour or two... I had thought that the increase in modulus might be an asset but tensile strength looks to be reduced by maybe 10% after cool-down from 200°C and there's no data on fiber compression strength.

RE: "Heat compaction of glass fibers"?

J.P. Stevens glass used to use a thermal method of removing sizing from glass fabric after weaving, you might check with them to see if there is any documented reduction in strength after de- sizing.
B.E.

You are judged not by what you know, but by what you can do.

RE: "Heat compaction of glass fibers"?

Heat scouring is used to remove the "sizing" that is used to protect glass fibers from abrasion during weaving. This sizing is usually starch based. Coupling agents are then applied to the fabric to improve bonding with resins. Due to tradition, these coupling agents are also called sizing.

RE: "Heat compaction of glass fibers"?

(OP)
Looks like J.P. Stevens has gone out of business? http://www.businesswire.com/news/home/200306050054...

The same bunch at Strathclyde have done some work which does show an increase in modulus, but the reduction in strength is also still apparent. http://strathprints.strath.ac.uk/47130/ , "The properties of glass fibres after conditioning at composite recycling temperatures."

CompositePro: what sort of temperature is reached in heat scouring?

RE: "Heat compaction of glass fibers"?

RP Stress.
Here is a heat schedule for scouring: I did not realize J P Stevens had folded, I thought they had just been absorbed into some other company.
A batch process recommended by Owens-Corning Fiberglass Corporation, Toledo, Ohio to remove the sizing on the glass filaments results in a heat-set fabric and consists of the following steps:

1. Start at 220° F. for 1.5 hours;

2. Raise to 480° F. over a period of 5 hours and hold for 12 hours;

3. Raise to 700° F. over a period of 3 hours and hold for 33 hours;

4. Cool to room temperature.

See if that answers your question , or if Composite Pro has more.
B.E.

You are judged not by what you know, but by what you can do.

RE: "Heat compaction of glass fibers"?

(OP)
Owens Corning should know...they seem to be saying that a treatment at 700°F for 30+ hours should be used to remove the size. That may be necessary to clean the fibers effectively but does it also reduce fiber strength a lot (and increase modulus a bit)?

According to the data in those papers it will. That probably has implications for people wanting to recycle glass fiber. I was more curious about potential benefits of "heat compaction," and apart from the modest modulus increase (at the expense of strength) there doesn't seem to be any (it also seems to increases fiber density a bit; not quite sure if we should consider changing fiber volume fraction for any of this but it might have a tiny effect on that—not much info on the density change as far as I noticed). Some of that data seems to be saying that the modulus will drop with time without any further thermal processing. Although a ~20% increase in modulus would be very welcome in many applications it looks like it cannot be produced reliably or guaranteed for a long service life. If higher modulus would be a benefit it looks like it would be better to use S-3 fiber (E apparently 99 GPa, the highest glass (and basalt) goes).

There's still no good explanation of what the effect of heat compaction is. It apparently 'affects the microstructure somehow' is the best summary I can see from the info given. I'm also not sure why the rapid cooling fiber gets makes it differ from bulk glass.

Far from being potentially useful it seems as if thermal processing may be detrimental and should be avoided.

In that last paper ("The properties of glass fibres after conditioning at composite recycling") the reduction in modulus over five years and the extrapolation of that reduction to ten and twenty-five years is quite scary.

We only make limited use of glass on this site and if we ever start using more I think we ought to talk to our fiber producer (as opposed to supplier) quite earnestly. There only appear to be about a dozen fiber producers worldwide.

Any affects of 'heat compaction' due to processing should be accounted for in allowables so there shouldn't be any nasty surprises hiding.

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