Today's KNOWLEDGE Share
It is fairly common knowledge that a loss of molecular weight, as possibly induced by degradation, will produce parts with lower mechanical performances.
Some people however believe that a simple test like a stiffness/modulus check can confirm the absence of degradation. Wrong !
If you take, say, PP, a loss of molecular weight will actually speed-up crystallization kinetics typically resulting in slightly stiffer parts.
However, should you focus on strength, impact, creep performance, fatigue, crack growth, fracture toughness or similar long term properties, you would see a clear loss of performance.
Also, remember that chain scission in Injection Molding typically does not produce any smoke, discoloration or other easily spotted defects. This is why one should cautiously check molecular weight, one way or another, when chain scission is suspected.
Failing to do so creates a huge risk of part failure in the field with serious financial consequences and liabilities.
source:Vito leo
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