Environmental Engineering Reference
In-Depth Information
LOD, limit of detection; NR, not recovered (OP, NP, and BPA not recovered in
acetic acid 3%).
Ratesofdiffusionofmoleculesinapolymerwillgenerallybefasterathigher
temperatures. The Arrhenius equation gives the dependence of the change
in magnitude of the diffusion coefficient
D
P
with temperature:
where Δ
E
is the activation energy and
A
is the preexponential factor. Log
(
D
P
) is inversely proportional to the temperature
T
(K). Diffusion
coefficients at two temperatures,
T
1
and
T
2
, can be used to calculate the
value of Δ
E
:
Thiseffectoftemperatureisalsothebasisfortheprecautionagainstheating
food contained or wrapped in plastic materials that contain additives or
residual monomer. Several studies (Galotto and Guarda, 2004; Rijk and
Kruijf, 1993) suggest that lower migration rates are obtained with
microwave heating compared to oven (thermal) heating of fatty foods in
contact with plastics, possibly because of the shorter durations of contact.
8.2.3 Residual Monomer in Packaging Resin
PE and PP being based on gaseous monomers do not result in any trapped
residual monomers. Generally, only traces of residual Ziegler-Natta
catalysts used in low-pressure polymerization of polyolefins are usually
present in the resin and that too at low (<100 ppm) concentrations. Other
plastics such as polystyrene (PS), acrylics (PMMA), poly(ethylene
terephthalate) (PET), poly(vinyl chloride) (PVC), and polycarbonate (PC) as
well as thermoset polymers such as epoxy and polyurethane generally carry
traces of residual monomer as well as by-products of the polymerization
reaction (Araújo et al., 2002). Efforts are continually being made to reduce
residual monomer levels, and therefore, only those reported in the recent
literature are reliable. Also, the reported residual monomer levels depend
primarily on the specific type of polymerization used (e.g., bulk, solution,
emulsion) in manufacture as well as on the sensitivity of analytical methods
used to estimate them. The values reported varied by as much as 100%
depending on the analytical method used to estimate styrene in PS resin
