This topic contains a solution. Click here to go to the answer

Author Question: How does changing the molecular weight distribution (MWD) alter the processability of the plastic? ... (Read 67 times)

MGLQZ

  • Hero Member
  • *****
  • Posts: 579
How does changing the molecular weight distribution (MWD) alter the processability of the plastic?
 
  What will be an ideal response?

Question 2

Explain why isotactic polypropylene can crystallize and the other polypropylene stereoisomers cannot crystallize.
 
  What will be an ideal response?



Related Topics

Need homework help now?

Ask unlimited questions for free

Ask a Question
Marked as best answer by a Subject Expert

Zebsrer

  • Sr. Member
  • ****
  • Posts: 284
Answer to Question 1

If the MWD is broad, the short molecules will melt before the long molecules and serve as lubricants for the entire plastic mass, even before complete melting occurs. This results in some residual entanglement among the long molecules which gives tensile strength to the melt. Processes that require melt strength, such as extrusion and blow molding, are thus improved in processability by broad MWD. On the other hand, narrow MWD will result in a sharper melting point and a lower viscosity melt conditions that are favored in injection molding. The cooling of the polymer is also faster with a narrow MWD to further improve injection molding processability.

Answer to Question 2

In isotactic polypropylene all of the methyl groups are on the same side of the tertiary carbon. This reduces the intermolecular interference between these groups and allows the molecules to pack tightly together, thus forming crystals.





 

Did you know?

Multiple experimental evidences have confirmed that at the molecular level, cancer is caused by lesions in cellular DNA.

Did you know?

Stroke kills people from all ethnic backgrounds, but the people at highest risk for fatal strokes are: black men, black women, Asian men, white men, and white women.

Did you know?

It is widely believed that giving a daily oral dose of aspirin to heart attack patients improves their chances of survival because the aspirin blocks the formation of new blood clots.

Did you know?

Hypertension is a silent killer because it is deadly and has no significant early symptoms. The danger from hypertension is the extra load on the heart, which can lead to hypertensive heart disease and kidney damage. This occurs without any major symptoms until the high blood pressure becomes extreme. Regular blood pressure checks are an important method of catching hypertension before it can kill you.

Did you know?

In the United States, congenital cytomegalovirus causes one child to become disabled almost every hour. CMV is the leading preventable viral cause of development disability in newborns. These disabilities include hearing or vision loss, and cerebral palsy.

For a complete list of videos, visit our video library