Today's KNOWLEDGE Share:Mositure Absoption

Today's KNOWLEDGE Share

So, like most of us in Europe, you enjoyed an unusually warm, sunny and dry weather spell this summer.

Now you are back to work and dive again into your plastic part associated with the problems.

The part shown is made of nylon. Nylons are very decent materials for mechanical properties, except they can be very sensitive to some environmental aspects.

In dry weather, PA66 will lose moisture, which acts as a very efficient plasticizer, making the material much more brittle. If such part dries out in the sun, the UV radiation will slowly break down the polymer chains and also contribute to the material becoming more and more brittle over time. Contrary to the moisture effect, UV degradation is irreversible. Moisture absorbed by nylons also translates into some "swell". Look at it as "negative shrinkage". So if nylon dries out around an overmolded insert, the tensile stress becomes much larger until it could trigger part failure, possibly at a weak point like a weld-line.

Because the glass transition temperature is very moisture sensitive, in a dry spell, nylon Yield and Modulus will go up with the increasing Tg, further enhancing the brittle failure risk of this part.

So summertime is great for us to recharge our batteries, but it could kill some of our parts if we are not prepared !

source:Vito leo