It is because embrittlement isn't caused by heat; it's caused by radiation-induced cross-linking of the polymer. The carbon black keeps the UV from penetrating deep into the polymer and doing the damage. One can help make lighter-colored plastics more UV-stable by adding ZnO as the white pigment, which is often done in higher-value plastic components like garden furniture, but too costly for the really cheapo things like semi-disposable pots. The more high-value things also typically have a lot more plasticizers in the formulation, which is also largely prohibitive in thin plastic pots. As they say, you get what you pay for!
Same reason white plastic labels become brittle after two years (or less) in the sun. Too bad they don't just get wrinkly like we do after years in the sun....
Bob Zone 7, getting some welcome rain and finally cooler temps. A few Lachenalias are waking from their summer siesta.
On Sunday, August 21, 2022 at 06:11:26 PM EDT, Rick Rodich via pbs <pbs@lists.pacificbulbsociety.net> wrote:
I find that white plastic pots seem to turn brittle much faster. Kinda counter-intuitive. Rick Rodich
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