Surface chemical derivatization of plasma‐treated PET and PTFE

Abstract

Surfaces of two widely used biomaterials -poly(tetrafluoroethylene) (PTFE) and poly(ethylene terephthalate) (PET) -have been modified using gas plasmas. The concentrations of hydroxyl, carboxyl, carbonyl and amine groups were analysed with chemical derivatization (CD), using different aldehyde, acetic anhydride, alcohol and hydrazine reagents, and SIMS. Quantification was done by comparing the CD/SIMS results with XPS atomic ratios. Ammonia helical resonator plasma (HRP) treatment was found to incorporate mainly amine and hydroxyl groups on both materials. Argon HRP treatment of PTFE and nitrogen capacitor plate plasma (CPP) treatment of PET were found to increase carboxylic functionalities. The double-bonded oxygen of the ester group of the unmodified PET was attacked and transformed to other groups in the order ammonia plasma > nitrogen HRP > nitrogen CPP, with carbonyl content being reduced to 2.6, 4.1, and 7.6 respectively from 13.5 groups per 100 carbon atoms of the untreated PET. Chemical derivatization greatly helped to distinguish between the functional groups on the plasma-treated surfaces. The difference between the surface specificity of SIMS and XPS has been discussed in the light of these results.

Effects of oxygen and carbon dioxide plasmas on the surface of poly(ethylene terephthalate)

“…The plasma also removes the low-molecular-weight materials or converts them to highmolecular-weight materials [40]. In particular, the DRIFT spectrum of PET-O 2 (15 min) also indicates the introduction of oxygen functionalities, which can be take place during the treatment [10,[41][42][43][44][45][46][47][48], and/or when the surface is exposed to the ambient atmosphere [46,49,50]. The fastest degradation of PET under O 2 plasma compared to CO 2 plasma can be attributed to the fact that the plasma-generated UV radiation is more intense in the former case [44,47], which should accelerate the degradation process of PET through enhanced absorption of UV light by chromophore functionalities and subsequent ring opening [50].…”

Surface characterisation of plasma-modified poly(ethylene terephthalate)

“…Moreover, oxygen functionalities can also be attributed to post-plasma reactions (i.e., to ageing effect): When the polymer surface is exposed to air after plasma treatment the active sites (radical species) generated on the surface will react with the oxygen present in the ambient. Thus, nitrogen and oxygen functionalities are expected to develop on polymer surfaces following He, Ar, N 2 , or NH 3 plasma treatment [45,[53][54][55][56][57][58][59][60] and/or when the surface is exposed to the ambient [45,[53][54][55][56][57][58][59][60]. The fastest degradation of PET under He plasma compared to N 2 plasma can be attributed to the fact that the plasma-generated UV radiation is more intense in the former case [56,59,61], which should accelerate the degradation process of PET through enhanced absorption of UV light by chromophore functionalities and subsequent ring opening [62].…”

Chemical analysis of functionalized polymer surfaces

“…If poly(tetrafluoro ethylene) (PTFE, Teflon) is used as a substrate, other labels have to be used, which do not rely on fluorine but bromine, [13] or XPS and SIMS are combined in the determination of functional groups. [14] Although with the labelling techniques more information can be gathered about a surface we must be aware of the limitations and the possibility of artefacts (see 'Discussion' in Ref. [15]).…”