Water and Solute Permeability of Plant Cuticles: Measurement and ...

7.3 Effects of Plasticisers on Diffusion of Lipophilic Solutes in Wax 219
Effect (D/D control)
28
24
20
16
12
8
4
0
C 16E 8
C 12E 8
C 14E 7
C 12E 6
C 4 E 2
C 10E 5
C 8E 4
5 6 7 8 9 10 11
Alcohol ethoxylate concentration in wax (g/kg)
Fig. 7.9 The effect of different alcohol ethoxylates on diffusion coefficients (D/Dcontrol) of PCP
(pentachlorophenol) in reconstituted barley wax as a function of the internal equilibrium concentration
of the alcohol ethoxylates in barely wax. Effects are calculated by dividing the D of PCP
measured in the presence of the corresponding alcohol ethoxylate by D measured in the absence of
an alcohol ethoxylate. Error bars represent 95% confidence intervals. Data redrawn from Schreiber
et al. (1996b)
Table 7.2 Wax/receiver partition coefficients Kwrec of n-alkyl esters for reconstituted wax of
Hordeum vulgare and Stephanotis floribunda
n-alkyl ester Kwrec H. vulgare Kwrec S. floribunda
DMSU (dimethyl suberate) 3.1 15.5
DESU (diethyl suberate) 5.9 55.7
DES (diethyl sebacate) 31.2 447
DBSU (dibutyl suberate) 503 5,319
DBS (dibutyl sebacate) 1,821 28,590
Data from Simanova et al. (2005)
Intrinsic effects of n-alkyl esters linearly increased with increasing concentrations
of n-alkyl esters in the wax (Fig. 7.10). This shows again that there is no specificity
in the plasticising effect between the different n-alkyl esters tested. However, effects
with barley and Stephanotis wax differed greatly. For the same plasticising effect,
about ten times higher n-alkyl ester concentrations are needed with Stephanotis wax
than with barley wax (Fig. 7.10). Sorption capacity in Stephanotis wax is ten times
higher than that of highly crystalline barley wax (Table 7.2).
Desorption of 14 C-labelled 2,4-dichlorophenoxybutyric acid (2,4-DB) from
Stephanotis was also studied with alcohol ethoxylates (Fig. 7.10). At identical plasticiser
concentrations in Stephanotis wax, intrinsic effects were about five-fold higher
C 6E 3