Diffusion of Erucamide (13-cis-Docosenamide) in Isotactic Polypropylene

Abstract

Diffusion coefficients of erucamide (13-cis-docosenamide, H3C(CH2)11HCCH(CH2)7CONH2, eru) into isotactic polypropylene (i-PP) were determined under different isothermal conditions, viz., 323, 333, and 353 K in times of 15 days. Some other experiments were performed for several predetermined time intervals (5, 10, and 15 days) at a constant temperature (343 K). The diffusion cell which has been used to establish eru concentration profiles of diffusant within the polymer matrix is similar to that described and used by Roe et al. The concentration profiles of additive in film stacks have been analyzed after soxhlet extraction by capillary gas−liquid chromatography (CGLC). On one hand, these profiles were compared with theoretical curves based on solutions of Fick's diffusion equation for the best fitting, with the appropriate boundary conditions. However, the measured concentration profiles do not show a good agreement with the Fickian law as will be desirable. Values of the diffusion coefficient D in the range from 10-9 to 10-11 cm2 s-1 have been obtained. On the other hand, probably due to a dual mechanism and/or some other characteristic effects of the diffusion of erucamide through i-PP it is to be expected that the diffusion process itself may be more complex than that predicted by a simple Fickian model. In this paper we present the diffusion or migration of erucamide through i-PP by means of a semiempirical dual mechanism, in which two simultaneous Fickian processes, perhaps with two types of diffusant molecules, with diffusion coefficients D 1 and D 2 are involved. Some plausible explanations are given at this respect. Similarly, we have estimated by means of the method of Matano an overall diffusion coefficient which is related to the erucamide concentration. Furthermore, this overall diffusion coefficient has also been related to the concentration of erucamide and temperature by using an empirical model. The dependence of diffusion coefficients D, D 1, and D 2 on temperature followed Arrhenius-type relationships over the temperature range investigated. The activation energies were calculated as E d(D) = 117, E d(D 1) = 100 and E d(D 2)= 130 kJ mol-1, respectively. The values of diffusion coefficients and activation energies are in the range found for some other additives. The solubility of erucamide in i-PP as a function of temperature has been determined directly by extrapolation of diffusion data to penetration depth equal to zero. From the plot of these solubility parameters as a function of temperature, it is very easy understood that erucamide is insoluble (incompatible) within i-PP for temperatures below 313 K. By using Fujita's equation a good correlation between diffusion coefficient and free volume fraction estimated by means of Williams−Landel−Ferry' equation has been found.

Spectroscopic characterization of molecular interdiffusion at a poly(vinyl pyrrolidone)/vinyl ester interface

“…The activation energy of various solvents in PMMA ranged from 19 to 35 kcal/mol [145], and that of bis(2-ethylhexyl)phthalate in PVC was measured as 29 kcal/mol [146]. One example of activation energy for the molecular transport of middle-size molecules on the order of 337 g/mol was for instance 100 kJ/mol, determined for the diffusion of erucamide in isotactic polypropylene [147]. As far as the diffusion of polymers within polymers is concerned, an activation energy of 11.7 kcal/mol was found for the (PVC/poly(A-caprolactone))/system [148].…”

“…Consequently, a two stage-diffusion process may be better in modelling this data. For example, two simultaneous Fickian processes, assuming a constant diffusion coefficient, were employed for the (erucamide/isotactic polypropylene) system above T g by Quijada-Garrido et al [147]. Furthremore, Dr. Hideko Oyama [144] showed using electron microprobe analysis (EMP), that for the (PVP/VER) bilayer films, the concentration profile could be divided into two parts.…”

Fickian diffusion of erucamide (13-cis-docosenamide) in poly(laurolactam) (Nylon 12) (PA-12)

“…The diffusion of small molecules in semicrystalline polymers occurs almost exclusively through the amorphous phase; for this reason the process has been considered classical Fickian as in a rubbery matrix [14][15][16][17][18][19] . However, there are some evidences suggesting the opposite in some special cases [20][21][22] . Diffusion is a function of structure of both the polymer and the diffusant.…”

“…For example, some diffusant molecules may be too large to enter the available amorphous interlayer separating two crystallites. The diffusion of eru in a semicrystalline matrix of i-PP was studied in 1996 by Quijada-Garrido et al 20) They showed that the diffusion of erucamide does not obey a classical Fickian model 23) and therefore it could not be accordingly explained by a simple diffusion mechanism. The nonFickian behaviour was justified by the complex morphology and texture of i-PP, the nature of the incompatible long-chain additive (eru), and its thermodynamic and hydrodynamic interactions [24][25][26] .…”

Ionic and excited intermediates in pulse-irradiated polypropylene doped with aromatics

“…erucamide, diffusion in isotactic PP were found in the range emission detected during the 17 ns pulse at 105 K was probably generated as a result of photoexci-100-130 kJ mol 01 . 24 The very low activation energy found for T tation by Č erenkov radiation. 25 In PP film, contrary to the polyethylene system 4,6 no Py excimer õ T g in the case of PP is very similar to those estimated for polyethylene [5][6][7][8] ; hence, at temperaemission was detected for pulse irradiated samples.…”