Page 335 - Handbook of Plastics Technologies

PLASTICS ADDITIVES

PLASTICS ADDITIVES 5.15

These techniques do not destroy the polymer, but they embrittle it enough to crumble, and
oxidize it enough to promote biodegradation later (Table 5.17).

TABLE 5.16 Accelerated UV Embrittlement of Polypropylene

Time to embrittlement
Ferrous laurate, % Unstabilized, hr Heat-stabilized, hr

0 118 384
0.01 0 167
0.1 0 167
1.0 0 95
2.0 0 47

*
TABLE 5.17 Fungus Growth on Molded Plastics: Effect of UV Degradation
UV degradation before fungus test None 4 months
High-density polyethylene Trace Heavy
Polystyrene Trace Trace

90 percent PS + 10 percent styrene/vinyl ether copolymer Trace Slight
50 percent PS + 50 percent styrene/vinyl ether copolymer Trace Moderate
*.Trace = barely noticeable, slight = 10–30% of surface, moderate = 30–60% of surface, heavy =
60–90% of surface.

5.1.5 Biostabilizers
Microorganisms such as bacteria, actinomycetes, and fungus can attack plastics, produc-
ing discoloration and degradation of mechanical and electrical properties. They thrive pri-
marily at 20 to 30°C and high humidity, whenever they can find a source of food. Natural
polymers such as cellulose and protein are a good source of food. Animal fats and vegeta-
ble oils are a good source of food; when they are used in paints, alkyds, and urethanes,
these polymers are biodegradable. Synthetic polymers that contain aliphatic hydroxyl and
ester groups may be a good source of food; these include polycaprolactone, polyester ure-
thanes, and the new purposely biodegradable polylactic acid, polyhydoxybutyrate, and
polyhydroxyvalerate. Fairly sensitive polymers include polyvinyl acetate, polyvinyl alco-
hol, and ethylene/vinyl acetate. Most other polymers are not inherently biodegradable.
However, monomeric additives are often an excellent source of food and primary focus of
biological attack: ester plasticizers, epoxy ester stabilizers, and natural esters used in poly-
urethanes and fatty ester lubricants are the most common problems. (Starch fillers have ac-
tually been used to incorporate biodegradability in plastics.) A variety of chemicals can be
used to stabilize plastics against biological attack.

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