Here's an old article I just found from a NZ fishing web page on knotting Spectra/Dyneema line, retaining 90% of strength with sleeving of polyester / Dacron, which I recommended above, but have not noticed prior reference to at HF.
They're serious amateurs, and I like their serious testing, which doesn't require lots of gear. Just method. Of course, the knots they are putting in are not meant to be untied. Sorry, OP.:
At Paul's Fishing Kites we rigorously test every brand of fishing line we use on our kitefishing gear and, while testing some spectra recently, we discovered a new knot which we feel is about as good as it gets (knot tying instructions and diagram below).
First we applied the standard nylon fishing line strength test used by fishing line manufacturers around the world.
A granny knot is tied into the middle of the line being tested and increasing weight is applied incrementally until the line snaps.
The same test is applied ten times and the lowest figure is taken as the knotted tensile strength of fishing line tested.
Just about everyone knows that a granny knot is about the worst knot you can tie as it forces the line around a very small diameter and causes it to cut into itself.
Usually monofilament lines that break above 50% are considered good quality and lines that break above 60% in this brutal test are exceptional.
During tests on the strongest nylon fishing line we have had up to 68%.
We were amazed to find the 37kg spectra samples broke at 21.5 kg in the granny knot test. This is 57% of the rated breaking strain and much higher than we thought possible.
We then went on to try a series of other popular knots and, as expected, a bimini twist (a complex fishing line twist knot) was found to be one of the best breaking at 27kg or 73% of the rated breaking strain.
Other popular mono knots, like a uni knot and clinch knot were little better than the granny knot when tied into the spectra line and we do not recommend using them.
After looking at the various knots under strain with a powerful magnifying glass it was obvious that spectra cuts into spectra just as easily as mono will cut into mono.
Also, because spectra is so slippery, the knots pull up incredibly tightly, further compounding the issue.
We then decided to put the spectra line inside a short piece of 80lb dacron fishing line (dacron is hollow) and retest to see what would happen if the spectra was insulated from cutting into itself by the dacron.
A granny knot was re-tested with a 10cm long 80lb dacron casing over the spectra and this consistently broke at 33kg, an astounding 90% of the rated breaking strain of the spectra.
Our testing of fishing line strength is done with a set of lifting weights.
Slight bounce in the weights during testing leads to the line and knot strengths being UNDER estimated with this method.
Fishing line testing this way is not such a problem with nylon fishing line tests.
EUREKA! The simplest knot in the world, the humble granny, when protected by dacron is probably among the strongest fishing line knots you can tie in spectra.
For maximum strength all that is required to make the knot is a metre or two of dacon fishing line of bigger breaking strain than the spectra you are using.
For example, use 80lb dacron for 50lb spectra and 130lb dacron for 80lb spectra.
The spectra is threaded through a needle and the needle is fed backwards completely through the inside of the dacron.
For bigger lines feed one piece of dacron inside another to double the breaking strain before putting the spectra inside.
A granny knot is then tied into the dacron near the end where the spectra was inserted.
This results in a 10% reduction in strength at the granny knot and a vastly increased breaking strain in the last couple of metres of line where both the dacron and spectra continue to the end of the line.
Any secure knot can then be tied to whatever terminal tackle, clip or swivel you wish with real confidence that the final attachment will be 90% of the breaking strain of the spectra.
Fishers who use this method of knotting spectra will be able to tie consistent 90% knots in spectra that vary less than 2% regardless of how poorly they are tied. Absolutely no knowledge of how to tie fishing knots is required.