In case the factory failed to place a recycling symbol on plastic bottle or container, it can be identified by following the simple tests.
1) Water test. Force a piece of polymer under water. Wait and see if it is a floater or a sinker.
2) Water floater test 1 – alcohol test. Force several pieces in 45.5%(by volume) alcohol solution. HDPE(2, High Density Polyethylene) if sinker, continue to floater test 2 otherwise.
3) Water floater test 2 – oil test. Force several pellets in corn oil. LDPE(4, Low Density Polyethylene) if sinker, PP (5, Polypropylene) if floater.
4) Water sinker test 1 – copper wire or burn test. Place a piece of copper wire against flame to make it red hot. Then punch it immediately to polymer to grab a small portion. Bring back the copper wire on flame and observe flame color. Green flame means PVC(3, Polyvinyl Chloride). Continue to next test if flame is orange .
5) Water sinker test 2 – acetone test. Submerge a pellet in acetone for 20 seconds. Softened and sticky surface is a positive reaction. PS(6, Polystyrene) if positive, continue to next test otherwise.
6) Water sinker test 3 – heat or water boiling test. Place piece of polymer in water and boil for 30 seconds. PET(1, Polyethylene Terepthalate) if softened. Might not give accurate results due to popularity of heat resistant PET bottles.
Note: All above test were courtesy of David A. Katz, 1998. Advancement in polymer manufacture might give inaccurate results.
The test procedure for code 7 plastic was not included. No simple test are available cause this group is a mix or collection of all others. Mostly made of polycarbonates or abs.
I found useful information on boedeker.com. Place a piece of polymer against flame source for 10 seconds and observe. If polycarbonates – burn test results to faint sweet aromatic ester odor, orange flame color, with drippings. It produces black smoke with soot in air.
On the contrary forum from eng-tips.com said that polycarbonate produces oily or acrid odor on burn test (thread712-184534: how can I tell what type of plastic?)
If acrylonitrile butadiene styrene, ABS. Produces acrid odor, yellow flame with blue edges, no drippings. Able to continue burning after removal from flame source. It also produces black smoke with soot in air.
I gonna collect code 7 bottles to conduct tests.
Baby feeding bottles made of group 7 are often rigid that it cannot be pressed in between fingers. PP bottles or group 5 are more flexible.