I've found that if you polish the wooden handle on a buffing machine, the buffing compound helps seal the knife, but water still gets absorbed, especially if sent through a cycle in a dishwasher
I learnt a good trick recently from an old, experienced knife maker. Pre-cut a selection of rough knife scales, then soak then for several days, even weeks in floor sealant (the white, milky type) a big jar or sealable bucket. The sealant permeates the wood completely and stabilises it once dry. It works like a charm and is cheap. A 5 litre container of floor sealant will probably last a lifetime.
I've heard of other guys putting the scales in a thin resin and then vacuum-packing it in those heavy duty vacuum pack bags that butchers use. This process "sucks" the resin into the wood.
Another alternative is to give it a layer of good quality sealant, sand it off when dry with steel wool, repeat, repeat again, and repeat a few more times. I guess this could also work if you have a vacuum packing machine at you disposal.