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[zerotofifty]

What I wrote to the sunglass company...

I want to alert you to a problem with sun glasses you manufacture. I had bought two pairs of your Completion sun glasses, SRO 119 at Rite Aid. The first pair seemed fine upon purchase, I wore it the day of purchase while Kayaking over a couple hours. I also applied sun screen to my face, hands, and arms. I was careful not to damage the glasses, never dropped them, nor set anything on them. When I got home I set the glasses on my kitchen counter, the next morning the frames near the nose bridge had cracked. I returned the broken glasses to Rite Aid for a replacement. When I selected the replacement, I was very careful to examine them for any defects, cracks and such, they looked fine. I then used the replacement that day, again wearing sun screen. Again, the next day, same thing, the frame came apart, cracked in several spots. The glasses just fell apart while sitting on my table. (image 1.) What's happening here?

I then got to thinking that maybe the problem is related to the sun screen. Plastics can be suseptable to Enviromental Stress Cracking, (ESC). Certain chemicals can cause the enviromental conditions that cause ESC, which happens when a plastic part is under stress, even molded in stress, and is exposed to the chemical. Under ESC conditions, the bonds between the plastic molecules can be broken, resulting in part failure.

I took the second pair of broken glasses and did an experiment overnight. I placed a dab of sun screen on the side ear piece and put a small amount of stress on it using a weight. I also put the same stress on the new unused pair of glasses, with no sun screen as a control sample. (see image 2.) The next morning, the sun screen exposed side frame part was cracked under the sun screen, (see image 5.). The control sample with no sunscreen was not cracked, even though it was exposed to the same bending stress. This is pretty conclusive, the failures are do to ESC from the sunscreen!

I then noticed that on the control sample glasses I accidently got a finger print of sun screen on the frame near the left side of the nose bridge while setting up the test, and it had cracked, despite it not be stressed by the wieghts. I then did a second experiment by placing a dab of sunscreen on the unused control sample glasses on the unbroken right side of the nose bridge, and left it over night on my kitchen counter, completely unstressed. (see image 3). The next morning it too had failed. (see image 4). Evidently there is residual stress in the frame from the moulding process, allowing ESC to occur with exposure to sun screen.

The sun screen used is made by Day Logic, a Rite Aid house brand and contains commonly used sun screen chemicals, including...

Avobenzone, Homosalate, Octisalate, Octocrylene, Oxybenzone (see image 6 for the label)

Among chemicals know to cause ESC in plastics are Esters, Ketones, Aldehydes, Aromatic Hydrocarbons, and Chlorinated Hydrocarbons. (see the attached pdf file below, Environmental Stress Cracking, The Plastic Killer, by Jeffery A. Jansen, Advanced Materials and Processes, June 2004)

Of course it is reasonable to conclude that sun screen will he used with sun glasses. Thus the glasses are really not fit to be merchantable, as failure occured in as little as 12 hours, even from incidental exposure to a finger print of sun screen.


I have included a Wikipedia link to ESC for your reference, a very brief description of molded in stress issues, and the short paper by Jansen on ESC that includes a list of chemicals I referenced that can cause ESC failures.

[Cusser]

[Xevin]

[Shonandb]

[KTPhil]

[busdaddy]

Link

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