Environmental Engineering Reference
In-Depth Information
2
Egypt's pyramids, the largest and the oldest stone structures, were built
about 4500 years ago.
3
Lifetimes of plastics outdoors or in the ocean, sometimes published in the
popular literature, are speculative and not reliable.
4
This is an axiomatic principle of photochemical phenomena and is
referred to as the Grotthus-Draper law.
the thickness of peripheral layer (and therefore the diameter of daughter
particle) and
d
is the diameter of the parent particle.
6
A host of such blends including starch + cellulose acetate, PCL, starch +
PP; and starch + copolymers are commercially available.
7
The temperature of the plastic heated by sunlight will not be high enough
to cause thermolysis or pyrolysis of the plastic. But it can be high enough
to very noticeably accelerate the photooxidation process.
8
Data from “Paint it Cool” Brochure” BASF Chemical Company.
9
Shorter wavelength (<290 nm) called UV-C is far more damaging than
UV-B, but this radiation is filtered out by the stratospheric ozone layer
and does not reach the Earth's surface.
10
A good review of the technique is found in the study of Torikai (2000).
11
Someoftheavailablestandardaccelerationtechniquesexposethesample
to as much as 6 suns of radiation but at a controlled temperature.
12
Minsker et al. (1982) have suggested that the intensity not be increased
beyond three times the standard solar intensity in the geographic region.
But this arbitrary value is likely to be excessive. It is safer to use the
highest natural sunlight intensity (1 Sun) and lengthen the light-time as
opposed to dark-time in the accelerated weathering exposure.
13
The term “photodegradable plastics” is in quotes to recall that it is a
misnomer. All plastics are photodegradable; these are designed to
photodegrade at a faster rate in sunlight.