OBJECTIVE

The aim of this work is to study the surface properties of PLA films when they are subjected to plasma treatments, both of a reactive gas (oxygen) and of an inert gas (argon), and to determine which chemical and physical changes are responsible for the modification in each case, and to establish the duration of the effects of the two treatments.

MATERIAL AND METHODS

The effects of both argon and oxygen plasma on polylactic acid (PLA) films deposited on titanium.

RESULTS

Regarding physical surface changes, there were scarcely any differences between both plasmas: roughness was very similar after treatments, root mean square height being 10 times higher than the control, without plasma. Water contact angle showed that the surface became more hydrophilic after application of the plasma, although hydrophilization was longer lasting in the case of argon treatment. With regard to chemical changes, it was observed that the argon plasma treatment caused greater fragmentation of the polymer chains, and increased crosslinking between them. ToF-SIMS analysis made it possible to propose mechanisms to explain the formation of the fragments observed.

CONCLUSION

Argon plasma favours the crosslinking of polymer chains, as well as the fragmentation into low molecular weight moieties, as can be deduced from data obtained by ToF-SIMS. However, oxygen plasma reacts with the free radicals generated in the treatment, leading to new oxygen-rich, higher molecular weight species. The analysis of the fragments obtained in the ToF-SIMS has also allowed us to propose possible reaction paths to explain the formation of these species, and to confirm the presence of traces of O2 in the argon plasma. Although the nature of the chemical modifications is different, similar physical changes are observed for both plasmas: increase in surface roughness and decrease in hydrophobicity. However, the latter is more durable in the case of argon plasma, due to the lower mobility of the chains.