Exam 1 Flashcards
Name two possible morphologies of a solid homo-polymer. Draw schematic diagrams for each one
Amorphous and semicrystalline
In one or two sentences, define viscoelasticity
It is property of a material when the material exhibits both elastic and viscous behavior
depending on the rate of deformation.
Define Deborah number. Write the meaning of each term used in your definition.
De= (lambda)/(tp)
Lamda= relaxation time tp= characteristic process time
Deborah number of 0 means __ and Deborah number of infinity means ____
Viscous; elastic
Use a schematic and describe the heat distortion temperature (HDT; sometimes known as the
deformation under load at elevated temperature). What is the value of this “relative” test to a part
designer?
The deflection temperature under load is the temperature at which a test bar loaded to a specific bending stress deflects by 0.010 in. The test is generally run at 66 psi or 264 psi. It is useful as a relative measure of the ability of various materials to perform at elated temperatures while supporting loads
Write the Power Law model for viscosity. Define each term used in your equation.
(nu)= K* (lowercase gamma)^n-1
(nu)= viscosity
(lowercase gamma)= shear rate
What does the Power Law index, n, represent when its value is 1, less than 1, and
greater than 1?
n=1; newtonian
n<1 ; shear thinning
n>1 ; shear thickening
Does the Power Law describe the viscosity behavior of all kinds of thermoplastic melt? Explain your
answer. Use schematic if needed.
NO. Sometimes we need a model with more parameters to fit the data
Write the 3 suggested material selection steps. (Maki presentation)
a. Use resin morphology
b. Use thermal and cost requirements
c. Fine tune and special features
Is it possible to make polypropylene, a semi-crystalline opaque material, transparent? How? 3
points change
Yes. We can add nucleating agent to reduce the size of the crystalline phase to below the
wavelength of natural light therefore making a semi-crystalline material transparent.
Name the 4 environmental factors that change the appearance of color of a thermoplastic material? 6
points (kreofsky presentation)
- observer
- light source
- background
- viewing angle
Based on case studies presented, which mechanical property is mostly affected when coloring
thermoplastics
Impact strength (tested by notched izod)
Define melt flow index. Your answer must be complete and detailed.
Melt flow index or MFI is a measure of the ease of flow of the melt of a thermoplastic polymer. It is
defined as the mass of polymer, in grams, flowing in ten minutes through a capillary of a specific
diameter and length by a pressure applied via prescribed alternative gravimetric weights for alternative
prescribed temperatures.[1] The method is described in the similar standards ASTM D1238 [2] and ISO
1133.[3]
High MFI means
Low viscosity
Low MFI means
High viscosity
