Short CommunicationsDiffusion of liquids into semicrystalline polyethylene
Introduction
An understanding of the diffusion of small molecular penetrants through a polymer matrix is required for a variety of technological applications, including the design of materials for separation processes, controlled pharmaceutical and agrochemical release devices, and packaging materials. This paper summarises the results of a study of the transport characteristics of a number of alkane penetrants within nine different semicrystalline polyethylene (PE) samples. In a semicrystalline polymer, liquid penetration is believed to occur within the amorphous material;1 a semicrystalline polymer can therefore be considered a porous material, with the amorphous material representing the pore space and the solid matrix represented by the crystallites.
Section snippets
Materials and methods
PE plaques (15 cm2 and 2.8 mm thick) were prepared from commercially available PE pellets by moulding in a hot press held at 150°C for 10 min. Four high density polyethylene (HDPE) and five linear low density polyethylene (LLDPE) samples were studied in this work. The PE samples were characterised in terms of crystallinity and lamellar thickness using Raman spectroscopy, nuclear magnetic resonance (NMR) spectroscopy and relaxation time analysis, differential scanning calorimetry, and x-ray
Results and discussion
Typical profiles for hexane diffusion into a HDPE and a LLDPE sample are shown in Fig. 1. The liquid concentration profiles are in excellent agreement with gravimetric mass uptake experiments. There is very little swelling in the samples; the total density of the system must therefore be increasing on absorption of the penetrant. The maximum liquid concentration at the surface was found to increase with time, a result of the viscoelastic response of the polymer to the penetrating liquid.
Figure
Conclusions
The results described above indicate the importance of polymer crystallinity in determining the diffusivity of simple organic penetrants in semicrystalline PE. The effects of annealing of the polymer on the liquid diffusivity have been investigated.
Acknowledgements
S.H. thanks the Ministry of Agriculture, Fisheries, and Food (MAFF) for financial support.
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Diffusion of small-molecule penetrants in semicrystalline polymers
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