COOKSEY SHELF LIFE
PERMEATION EXAM 2024
UPDATED QUESTIONS
If you take a random sample from a retail environment, what kind of shelf life test is it? -
CORRECT ANSWER>>>>Endpoint study
Zero order reactions change in concentration of component is ___ over time while first
order is ____ over time - CORRECT ANSWER>>>>Linear, non-linear
For 0 order reactions, n=?
For 1st order reactions, n=? - CORRECT ANSWER>>>>n=0
n=1
Ln in equation - CORRECT ANSWER>>>>natural log
Why do we use ln for 1st order equation? - CORRECT ANSWER>>>>Taking the ln of
the data helps make it linear so that we can measure the slope aka the reaction rate
What material is the best water barrier and why? - CORRECT ANSWER>>>>HDPE is
the best because it is very nonpolar so it repels polar h2o molecules. HDPE also has
tighter chain packing so it has less free volume for molecules to permeate through
Using the permeation diagram, explain how permeation occurs assuming you have a
dry product on one side and a humid environment on the outside surface. Define the
components P=DxS. Indicate which is a kinetic term and which is a dynamic term.
define X=l. - CORRECT ANSWER>>>>1. Diffusion coefficient: measure of how rapidly
penetrant molecules are moving through barrier in the direction of lower conc/pp
2. Solubility coefficient: the amount of transferring molecules retained or dissolved in the
film at equilibrium conditions
3. Diffusion is kinetic, solubility is dynamic
4. l represents the thickness of the package
Partial pressure and concentration difference create a net flux from high to low humidity
Moisture has to sorb through the exterior surface, make its way through the material,
and desorb into the internal environment
Explain why Nylon and EVOH exhibit nonsteady state conditions permeation -
CORRECT ANSWER>>>>These are hydrophilic polymers. Because of their -OH polar
groups, they partake in hydrogen bonding with water.
Which format should you ask for film barrier data to be provided: Permeation rate or
transmission rate? Why? - CORRECT ANSWER>>>>Permeation rate because the
thickness is included in the calculation so the films are compared on an equal basis
Units: permeation: cc*mil/(m^2*day) vs transmission cc/(m^2*day)
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