Q1. You are designing a package for 200 g of snack food that is sensitive to oxy

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Q1. You are designing a package for 200 g of snack food that is sensitive to oxygen, and fails when it absorbs 40 ppm of oxygen (by weight). Marketing tells you it wants the snack to be in a plastic pouch measuring 4 inches by 6 inches (ignore seems), so it will have a total surface area available for permeation of 48 in, (4” x 6” x 2 sides). You need to recommend an appropriate plastic material for this product, to provide a minimum of 60 days shelf life when stored at 70°F. Follow these steps a. Calculate the allowable oxygen gain, in cm3 at STP. (5 pts) b. At this point, you do not know the material you will use, so you do not know the permeability coefficient or the thickness. The better the barrier the plastic you choose, the thinner the material can be to provide the appropriate barrier. Rather than simple trial and error, a sensible approach is to solve for the ratio of P/L that is required. We can solve the basic permeability equation for this ratio Use the information you have to determine the required value for P/L, expressing your answer in cm/(100 in2 d atm). (5 pts) c. Use the information in the textbook (chapters 4 and 14) or in another reliable source on oxygen permeability coefficients for various polymers to select a polymer that would be suitable, and calculate the required thickness. (Be sure this is reasonable; for example, if the required thickness polymer!) Note that chapter 4 presents these values in the units you used in (b) while chapter 14 presents values with different units, so unit conversion would be required In your answer, state the material you have chosen, its oxygen permeability coefficient, and the minimum thickness you recommend. (Be sure to express the thickness with no more than one decimal place.) Obviously, there is more than one solution to this problem, but you only need one. (10 pts) ore than 20 mils, you need to choose a different Extra Credit: (5 points) Q2. Assume that the carbon dioxide permeability P of amorphous PP at 30°C is 75 cc cm/d m2 atm. What is the value of P at 40°C? Other information: Ep (activation energy) 38,000 J/mol, and R (gas constant) 8.314 J/mol K.

Explanation / Answer

In the given question your ends of diameter will become (-59.28,40) and (79.28,-40) and the center of the circle is (20,0).

By taking the above points u can easily draw a circle.

For more details u can watch this:

http://www.youtube.com/watch?v=SQ7UYPN1Yrg

In the above video in the place of 80 Mpa we are taking 59.28 Mpa. and in the place of 40 Mpa we are taking 79.28 Mpa and 30Mpa is replaced by 40 Mpa.

and the signs are differed because of the direction of the stress arrows.

For elaborated explanation you can see the following pdf,

http://www.iit.edu/arc/workshops/pdfs/Mohr_Circle.pdf

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