Microplastic Photooxidative Fragmentation

UV Exposure Conditions

UV intensity (sun exposure) 70%

Ambient temperature 32°C

Dissolved O₂ availability 80%

Particle State

Fragments

Chain scissions

Relative Mw

100%

Exposure time

0 d

How it works

Sunlight-driven degradation of plastic in the environment is photooxidation, not simple erosion. UV photons (mainly UV-B, 280–315 nm) are absorbed by chromophores in the polymer backbone, homolytically cleaving a C–C or C–H bond and producing a carbon radical. In the presence of O₂ that radical propagates a chain reaction (Norrish I/II photolysis) that ends in chain scission — the backbone snaps — steadily lowering the polymer's molecular weight until the material embrittles and fragments into smaller pieces, one route by which primary microplastics generate secondary micro- and nanoplastics.

This sim models the particle as a network of bonded monomer units. Each incoming photon that strikes the surface has a probability of breaking a nearby bond, set by an Arrhenius-type scission rate:

k = Φ · I_UV · exp(−Ea / RT) · f(O₂)

Φ    = quantum yield of chain scission per absorbed photon
I_UV = UV irradiance (intensity slider)
Ea   = 42 kJ/mol, activation energy of the radical propagation step
R,T  = gas constant, absolute temperature (temperature slider)
f(O₂)= 0 in anoxic conditions, rising to 1 as O₂ availability increases
       (photo-oxidation stalls without dissolved oxygen to trap the radical)

UV intensity — sets how often photons strike the particle (shaded water vs. full midday sun).
Temperature — accelerates the radical propagation step through the Arrhenius exponential; warm, sunlit sand degrades plastic far faster than cold, deep water.
O₂ availability — without dissolved oxygen the radical can't propagate to a full scission; buried or anoxic sediment plastics persist far longer than surface-floating ones.
When enough bonds around a region break, that cluster mechanically detaches and drifts free as its own particle — a new, smaller piece of secondary microplastic that can itself keep fragmenting.

UV photon Intact polymer network Detached fragment

⚠ Couldn't load the 3D engineThree.js failed to load from the CDN. Check your connection and reload.