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Epoxy resins - strength and suitability 11 Dec 2013 00:25 #605

One of the reasons I'm looking for suitable vacuum infusion resin is that the process limits your exposure to the raw epoxy compounds to just the act of mixing them - there's no messing around with brushes, rollers and wet gloves. The infusion process also allows you as much time as you need to set up the part / stack and check the vacuum bag's integrity before you mix and introduce the resin - it's much more controllable. The only down-side is that the plastic mesh used to assist the resin flow / transfer uses considerably more resin than a hand lay-up. The excess resin doesn't end up in the part (you end up with the optimum resin to fiber ratio) but gets trapped in the mesh which is placed between the bleeder film and the vacuum bag layer.

Ozzie Haynes (a UK CD builder) wrote an article describing his project in Skywings mag (UK hang gliding club mag) where he related his rather extreme reaction to exposure to wet epoxy resins... it landed him in hospital with large parts of his skin falling off and severe breathing problems. He's ok now! I rather like my skin where it is and would like to avoid becoming sensitised to it - hence my interest in the vacuum infusion process! As Charlie Johnson mentioned, different people react differently. I keep around 15 hives of bees and get many stings each week but it doesn't affect me (apart from the pain!!) My mother (who used to keep them) goes into anaphylactic shock if she gets stung.

For post-curing the smaller parts I believe a standard domestic electric fan-oven will do the job nicely. The temperature can be controlled reasonably closely using an external temperature gauge with a thermocouple wire placed inside the oven. The duty-cycle of the oven's heating element means the temperature varies by around +/-5deg C but this is acceptable. For the larger parts (like the main 22 foot long wing spars) I have been experementing with using electric blankets for beds placed directly on the composite part and covered by a thick quilt / duvet or loft insulation and blankets. Again, the thermostatic controllers that come with the electric blankets allows the temperature to be controlled very nicely. I wasn't aware of the importance of the heat ramp-up rate and will have to do some more tests to see if it stays on the correct side of the curve - thanks for that Charlie!

Kenny - I'm ordering some 10mm closed cell PVC foam board today and will knock up another test rib next week hopefully - I'll post the results. I've also asked them to check the tensile strength figure for their infusion resin or to let me know how the figure is derived. I'll keep you posted.

Phil.



From: This email address is being protected from spambots. You need JavaScript enabled to view it. [This email address is being protected from spambots. You need JavaScript enabled to view it.] On Behalf Of russell wilson
Sent: 03 January 2012 04:51
To: This email address is being protected from spambots. You need JavaScript enabled to view it.
Subject: Re: [Carbondragonbuildersandpilots] Epoxy resins - strength and suitability




good point kenny on how the resin holds the layers together under tension in a de lamination situation.
i got the impresion that epoxy was carcenogenic from a of bert ranton/rutan? book...a chapter on safety....think the book was called moldless composites?
if the epoxy is not carsonogenic.....was it the hardener?pehaps a quick google search will tell......any way in this surcumstance considering other resins,i think would be a smart move?it does not hurt to open our minds to all options...seems to me although an epoxy can be the best it terms of strenth...the rest are very very closein ...there are some old wood gliders here still flying glued together with glue made from milk....if a particular epoxy is not carceonogenic...... there is still a problems with supply/postage/cost........and id also like to add that a sensitization to epoxy is not something that should be taken lightly,its a serious emun reaction and i do remember reading some were that the epoxy's interfear with your hormones.but i cant tell you were i read that.......any way phill id be interested to hear your comparisons on other resins and if they are toxic as well if you feel like comparing?
i personaly would like to move away from epoxy.actually if i ever get back to this fuselage,i will move away from epoxy,unless i see a good reason that is.
russ.



On Tue, Jan 3, 2012 at 1:00 PM, <This email address is being protected from spambots. You need JavaScript enabled to view it.> wrote:



Phil,

Yes the Aeropoxy reported tensile strength is dominated by the glass, epoxy is not that strong 8,000 to 12,000 is a common range for neet epoxy. You should never trust a manufacturers data sheet to use as design numbers. The Tg reported is most likely a post cured number as well I think Aeropoxy is around 155 F before post cure but I would not post cure them as it takes a large oven. The sun method is too uncontrolled to get an even temperature and post curing is ramp rate sensitive. The ramp rate has to be slower than the Tg curve or it will soften and distort.

Epoxy components are not carcinogenic but they are sensitizers with repeated exposure you can become allergic to them. So gloves, good ventilation, and if you get the components on you wipe all you can off with a paper towel then wash with soap and water or a citrus hand cleaner. Never use a solvent to clean epoxy off of skin it will remove the oil barrier and dissolve the epoxy allowing it to be carried into the body. If you become allergic to epoxy, it is for life your reaction severity depends on your body chemistry. It is like a bee sting some people are not affected and some have violent reactions. Most common reactions are skin dermatitis and swelling of the mucus membranes i.e. airways.

Aeropoxy is not a good infusion resin.


Regards,

Charlie Johnson
Composites Materials Engineer
Ogden Utah

In a message dated 1/2/2012 9:47:25 A.M. Mountain Standard Time, This email address is being protected from spambots. You need JavaScript enabled to view it. writes:
Hi Folks,

I'd like to pick your brains on the subject of epoxy resins...

In planning this project I came across a recommendation by Jim Marske for a resin called Aeropoxy - excellent strength and workability, and a high Tg temperature following post curing. The only problem is that importing Aeropoxy from the States to Ireland (it can't be got here in Europe) is prohibitively expensive as it is classed as a haz-mat substance by the airlines. It is also not well suited for using in Vacuum Assisted Resin Infusion - it's too thick / viscous.

I have come across another resin supplier, in the UK, and much closer to home, who is able to supply Infusion Resin in volume at a reasonable price. Easy Composites IN2-Infusion-Resin is a possible alternative, and I'd welcome any comments or observations on the suitability of this product for use in building a Carbon Dragon.

There is one significant difference in the post-cured properties of the two resins - the IN2 Inusion resin appears to have a much lower Tensile Strength. Given that the carbon fiber is carrying the lion's share of the load, is the tensile strength of the epoxy actually that important?

Aeropoxy Easy Composites
PR2032/PH3665 IN2-Infusion Resin


Viscosity (cps=mPa.s.) 925 - 975cps @ 25C 225mPa.s. @ 25C
Pot Life 120mins 80-100mins
Glass Transition Tg 194F / 90C 201-212F / 94-100C
Cured Hardness 87 Shore D 84.5 - 88.5 Shore D
Tensile Strength 45,870psi (=316MN/m2) 65.5 - 73.5 MN/m2


The data sheet states that the tensile strength of the Aeropoxy was derived from a 10-ply laminate hand lay-up using style 181 fiberglass fabric, 55% glass content. No similar information is given for how the data for the Easy Composites IN-2 Infusion Resin is derived. Given the huge disparity in the tensile strengths of the two resins, could the Easy Composites data be referring to the tensile strength of the un-reinforced resin alone (no CF involved)?

You can find the data sheets for both products here:

Easy Composites IN2 - www.easycomposites.co.uk/downloads/TDS/E...2-Infusion-Resin.pdf
Aeropoxy - www.ptm-w.com/dynamicdata/data/docs/PTM_...neCatalog30Jun06.pdf - pg.32-33

Happy New Year all,

Phil.

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