Sometimes pitch builds up on the blade. It is like tar and sticks to the material. In my experience more heat seems to make this worse. Feeding too fast can cause more heat. High tooth count carbide blades make a difference. Freud makes a really good blades but there are less expensive blades that do a good job. Cheap blades are not worth bothering with unless you know you are going to have to cut nails or something hard like staples, at least that is what I save them for. Low tooth count bigger teeth are supposed to be better for rough cuts or rips cuts, but in my experience high tooth count carbide toothed blades give the best cuts and last longer, and could even be argued to be safer because they are smoother, but technique trumps blade style.