A Study of the Rate of Diffusion of Through the

Walls of a Plastic Soda Bottle

Author: Luke BlanchardProfessor: Dr. D. TrethewayClass: ME 447Date: 6/4/2015

Uses of in Soda

• Covers the sweetness of the flavoring• One of the factors that differentiates soda from juice

The Costs of Losing • Once the soda loses its (fizz) it is considered flat• Many consider “flat” soda to be bad soda• The amount of left in soda at the moment of consumption directly relates to the

value of the soda

The Shelf Life of Soda

• The average shelf life of a bottle of soda is between 6 and 9 months

• Soda is considered unmarketable once its concentration drops below 85% of its original concentration

• Many factors account for the losses of over time

Causes of the Loss of Consentration

• Permeation – the diffusion of through the walls of the container• Creep – the expansion of the bottle over time leading to a larger

volume with the same amount of • Water Loss – as water permeates through the walls of the container,

fills in the new vacancies and separates from the beverage• Sorption – the absorption of into the walls of the container• Closure Leakage – the loss of through the imperfect sealing of the cap

or any other defects in the container

A Comparison By Factor of Percentage of Lost From Bottles Made of PET (Polyethylene terephthalate )

Approximate % Loss

Bottle Size 2 L 0.5 LCreep 1.1 0.5

Water loss 0.3 0.5Sorption 0.8 2.0

Closure Leakage 0.1 0.3Subtotal 2.3 3.3

Permeation 12.7 11.7Total 15.0 15.0

The numbers shown in the table above were retrieved from “Kodapak PET Thermoplastic Polyester and Shelf Life of Carbonated Beverages” by Eastman Chemical Products.

Permeation

The process of:

• A substance being absorbed into a membrane

• Diffusing through the membrane

• Desorbing from the membrane into the solution on the opposite side

Factors Affecting Permeation

• Temperature

• The crystal structure of the membrane

• The pressure difference between the sides of the membrane

• Thickness of the membrane

The Setup of a Test Performed By M. Profaizer

• X=point crystallinity• ρ=the point density• 1.335 g/cm^3 = the density of completely amorphous PET• 1.455 g/cm^3 = the density of completely crystalline PET• C = Concentration of • t = time• D = the Diffusion Coefficient

The Setup of a Test Performed By M. Profaizer

• D = the “effective” Fickian Diffusion coefficient• α = a pre-exponential factor• b and c = positive constants• X = point crystallinity• T = temperature

FEA Models of Experiment

Results of Experiment (Temperature)

Results of Experiment (Varying Temperature)

Results of Experiment (Pressure)

Conclusion: How to Keep Your Pop Fresh•Keep it Cold•Keep it in a pressurized atmosphere •Use a thick bottle•Use a low permeability (Glass)•Drink it sooner than later

Reference

Profaizer, M. “Shelf life of pet bottles estimated via a finite elements method simulation of carbon dioxide and oxygen permeability.” Brazilian Journal of Food Technology (2007): Print.

Questions?