Does anyone find synthetic knots get worse over time? I've now had a couple go from super soft to quite soft but slightly scratchy like the very tips of the fibres break off leaving a subtly harsh contact surface. They still lather fine, just less pleasant to use.
I've only been wetshaving for 3 years, so my oldest synth is 3 years old and doesn't get used all the time. Still, with all my synthetic brushes I haven't noticed any change over time.
I have just a simple Maggard synthetic brush and I don't think it's even the slightest bit scratchy. But I don't have a newer synthetic brush to compare it to so it's possible that if what you say is true then I just haven't realized changing slightly over the years.
I mostly just rinse them out but now and then use something stronger (sal suds, roughly equivalent to a concentrated dish soap but I prefer the scent).
The fibres aren't breaking in a way I can visually see, I'm just speculating that my perception of synths getting scratchier over time is perhaps due to the very tip breaking off. I prefer smaller brushes, my 22mm Yaqi Tuxedo with a short loft was my first synth but at some point (3ish years?) became unpleasant so I upgraded to a 23mm Muhle STF which, after two years, is starting to feel a bit scratchier. I have a larger Yaqi Tuxedo that I use very rarely and it's noticeably softer so I was wondering if this is maybe just how synths are?
...or maybe I'm just imagining it on the STF, the larger brush is just a bit softer and I must have scrubbed the poor little Tuxedo to an early death by not being sufficiently gentle with it?
I clean mine from time to time with a diluted vinegar solution. Afterwards, I have the impression that the brushes become considerably softer. Especially if you have hard water, you may want to try this.