What DB posted is what I call a “double” uni-knot when attaching two lines, but that's neither here nor there. That’s like calling the Improved Clinch knot a Fisherman’s knot! Many use different names for different knots.
I know breaking at 45 pounds sounds low, but that is actually about right. The general rule has been a knot reduces strength approximately 50%. That is pretty much true with any material. How do I know, do as mlaag - get your scales out! I also have two friends who for some reason just can’t tie uni-knot? I have been using the uni-knot almost exclusively for many years and have found it just as strong as or stronger than any other knot, if done right! When “not” done right… it will break well below the “normal” 50% ratio! I have gotten as high as 80% using monofilament and when “tested”, but I would have to believe, out fishing “my” knots would also fall into and be closer to the 50% ratio rule?
If you do want to try to increase the breaking strength that gets back to comments of wetting the line and don't twist the line and tighten up slow and hard... and don't let any of the line crossover or overlap any more than necessary; but, in reality – don’t expect to see much over that 50% ratio?