Know-How - Materials

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Published: 9/23/2013

Melt Flow Rate Testing—Part 3
There is a well-established relationship between something called the weight-average molecular weight of a polymer and a parameter known as the zero-shear viscosity.

Published: 8/26/2013

Melt Flow Rate Testing – Part 2
To fully appreciate the strengths and weaknesses of the melt-flow-rate (MFR) test it is important to know something about the way the test is performed.

Published: 6/24/2013

Melt Flow Rate Testing–Part 1
Though often criticized, MFR is a very good gauge of the relative average molecular weight of the polymer. Since molecular weight (MW) is the driving force behind performance in polymers, it turns out to be a very useful number.

Published: 4/29/2013

Dimensional Stability after Molding—Part 5
All materials possess a property called the coefficient of thermal expansion (CTE). The vast majority of materials increase in size as their temperature increases and decrease in size as their temperature declines.

Published: 3/25/2013

Dimensional Stability After Molding: Part 4
In the first three parts of this series we focused on those influences that cause molded parts to get smaller. But there are environmental factors that also cause parts to increase in size over time.

Published: 2/26/2013

Dimensional Stability after Molding—Part 3
Any process that involves melting and re-solidifying a polymer involves a compromise between achieving the perfect structure and producing a part that can be sold at a price that the market is willing to pay.

Published: 1/28/2013

Dimensional Stability After Molding—Part 2
After molding, acetal parts can continue to shrink at room temperature and even in the cold.

Published: 12/28/2012

Dimensional Stability After Molding: Part 1
The degree to which molded parts shrink as they cool is largely dependent upon the composition of the material being processed.

Published: 11/28/2012

Is It Glass Filled or Glass Reinforced?
Here is how to tell the difference.

Published: 10/26/2012

PBT & PET Polyester: Part 2 The Performance Factor
All things being equal, PET will outperform PBT mechanically and thermally. But the processor must dry the material properly and must understand the importance of mold temperature in achieving a degree of crystallinity that allows the natural advant...