Testing peel strength of 10D orange silnylon

I have made a tarp/tent by mostly glueing instead of sewing, and it has been a success story.  Search this blog for earlier reports -- suggest click on "light" category link at bottom of this post to quickly find them.

The fabric used is silnylon, which is nylon ripstop weave impregnated with silicone -- so there is silicone on both sides. When two pieces are overlaid and glued together, the join has been found to be very strong. However, there are two forces to be tested -- "longitudinal" strength, and "peel" strength.

There is a chap (Samuel) who made a video testing glued strength of silnylon, linked from an earlier blog post:

https://bkhome.org/news/202105/glueing-silnylon-fabric-versus-sewing.html

...the blue 10 denier silnylon purchased from Adventure Expert is what I used in the TreeHugger 1P Mark-1 tarp/tent. Here is a direct link to the video:

https://www.youtube.com/watch?v=_5yGxdJveZk

...Samuel uses the term "lateral" the same as my "longitudinal", and the term "perpendicular" same as my "peel" strength.

The longitudinal strength is fantastic, photo taken from the video:

What is not so good is the peel strength, that is, when try to pull the two pieces apart. In the above photo, the two pieces are glued together, but if you were able to lift up one edge and pull on it, that would be testing the peel strength.

If there is glue right to the edge, then there is no opportunity for peel strength to be a concern. However, with a tent flapping in the wind, there could be a weak spot, maybe at the end of a join, that might start to peel apart.

I did subjective tests on the blue 10D silnylon from Adventure Expert, and found peel strength to be far less than longitudinal strength.

Planning for Mark-2 tent, I ordered 20D olive silnylon from Extrem Textil:

https://www.extremtextil.de/en/ripstop-nylon-tentfabric-silicone-coated-20den-36g-sqm.html

...I found peel strength to be very poor.

I also purchased 10D light-green silnylon from Rex Outdoors:

https://www.aliexpress.com/item/32625219053.html

...found peel strength to be very good.

These tests are only subjective, me just pulling on the fabric with my hands. I used neutral-cure silicone sealant, this stuff:

https://www.bunnings.com.au/monarch-150g-mini-translucent-silicone_p1662110

I don't have enough of that light-green silnylon to construct the planned Mark-3. Unfortunately, Rex Outdoors have sold out of that color, so purchased their pantone-orange color -- I would describe it as "burnt-orange".

It arrived a week ago, and I cut off two pieces to perform peel tests. One piece, used the Monarch neutral-cure, and the other piece used Selleys RTV Engineering Grade acetic-cure, this one:

https://www.bunnings.com.au/selleys-310g-401-rtv-engineering-grade-silicone_p1231042

Left them for a week, so today is the big day, the peel tests. Here are the two pieces, propped up with clips for the photo-shoot:

I wanted to find out if there is any difference in peel strength on each side, hence you can see in the above photo, glued both sides.

Result: just like the green fabric, very strong. Takes considerable strength to peel them. Not quite sure, as this is very subjective, but the acetic cure might be a tad stronger. Both sides seem to be equally strong.

I wonder why the 20D silnylon from Extrem Textil has such poor peel strength? This is wild speculation, but it could be due to the manufacturing process, how the silicone is applied. With the 10D silnylon from Rex Outdoors, the silicone seems to be impregnated right through. However, what if the the 20D silnylon has separate coating of silicone on each side, not impregnated right through?  -- that would account for the poor peel strength. Or, it could be that the silicone on the silnylon is a different chemical composition, that does not bond well with silicone sealant.

Lesson here, for anyone thinking of constructing a tarp/tent by glueing: test the peel strength first.

EDIT 2021-08-15:
I have discovered a possible reason why some silnylon has poor peal strength. I was browsing through the offerings at RipstopByTheRoll, and saw that their 1.1oz 20D silnylon is described as:

Sil/PU (silicone/polyurethane) double coated 1.1 oz ripstop nylon (silnylon). This fabric is coated with a sil/PU layer on each side and is non-breathable.

I contacted them, and they explained that actually the coating is a blend of silicone and PU, to achieve higher waterproofness.

As far as I can see, only their 7D silnylon has pure silicone. It seems that this is a trend, to coat the nylon fabric with a silicone/PU blend. I am wondering if some vendors don't bother to inform of that fact.

This is interesting, a sil/PU coated silnylon becoming sticky:

https://www.trek-lite.com/index.php?threads/sticky-sil.2343/

Something else that has puzzled me: I have read, again and again, that silnylon will stretch when wet, and this is given as a big disadvantage. However, I asked myself, the silicone is permeating the nylon fibres, so how can they get wet?

What people are actually referring to is fabric that has silicone coating on the outside and PU on the inside. Probably most tents have this fabric. Yes, moisture will get into the fibres and it will stretch. Really, the only good thing about this fabric is that the manufacturer is able to seam seal it by applying tape on the inside. Sealing of silicone coated silnylon has to be painted on manually, not something that most tent makers want to do.

To obtain an appreciation of why silnylon, with pure silicone coating both sides, is superior, read this:

https://www.slingfin.com/blogs/the-beta/fabric-coatings-101-pu-vs-pe-vs-silicone

...his reference to Sil/PU coating is silicone on the outside and PU on the inside. We now have a new trend, a mix, or, blend, of silicone and PU, coated on both sides.

I have a suspicion that this sil/PU blend is the cause of the poor peel strength.       

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