Improvement of the interfacial compatibility between cellulose and poly(L-lactide) films by plasma-induced grafting of L-lactide: the evaluation of the adhesive properties using a peel test.

Hypothesis: The interfacial compatibility between hydrophilic cellulose and hydrophobic poly(L-lactide) film surfaces is dependent on the interactions and interlocking of the macromolecular chains of the uppermost layers of both polymers. Grafting or coating the cellulose surface with molecular structures similar to the lactide monomer or oligomer is expected to improve the compatibility. Therefore, it should be possible to enhance the adhesive properties.

Experiments: Cellulose films were oxygen plasma treated and immersed in a L-lactide solution. The grafting was performed under various conditions (power, pressure, time). The treated cellulose and poly(L-lactide) films were hot-pressed, and the resulting bi-layer laminates were subjected to a peel test. Comparative experiments were performed with the bi-layer laminates prepared from the cellulose films coated with poly(L-lactide-graft-vinyl alcohol) copolymers.

Findings: X-ray photoelectron spectroscopy, infra-red analyses and wettability measurements revealed that chains bearing ester groups similar to that of lactide were covalently grafted onto the cellulose. The possible grafting mechanism that was initiated by the ionic species from the surface is discussed. As a result, the peel strength to separate the cellulose and the poly(L-lactide) films increased significantly. A comparison with data in the literature highlights the formation of entanglements inside the interfacial zone showing the efficiency of the plasma treatment.