Elucidation of the surface chemistry of alkaline-treated poly(ethylene terephthalate)

When a polyester (poly(ethylene terephthalate) or PET) fabric is treated with an aqueous solution of NaOH or CsOH, it becomes more wettable. This improved wettability has beeen attributed to an increase in polar end groups introduced onto the fiber surfaces. We have developed chemical tagging techniques to quantify the number of carboxylic acid end groups found on the surface of alkaline-treated PET.; Neutron Activation Analysis (NAA) was used to measure the amount of cesium-tagged carboxylate groups on CsOH-treated, woven fabric. Absorption spectrophotometry measured the affinity of negatively charged carboxylate groups on the fabric surface for methylene blue, cationic dye. The dye method (1.9-2.4 {dollar}times{dollar} 10{dollar}sp{lcub}14{rcub}{dollar} COO-/cm{dollar}sp2{dollar}) yielded values about twice as high as the cesium method (0.8-1.0 {dollar}times{dollar} 10{dollar}sp{lcub}14{rcub}{dollar} COO-/cm{dollar}sp2{dollar}), but values for alkaline-treated fabric agree well with numbers determined using dye obtained by other researchers for PET film. Untreated PET fabric was observed to have 0.46 {dollar}times{dollar} 10{dollar}sp{lcub}14{rcub}{dollar} COO-/cm{dollar}sp2{dollar} on its surface by cesium tagging. The coefficient of variation for the methods varied from sample to sample, but ranged from 5 to 24%.; Surface chemistry was shown to influence the wettability of CsOH-treated PET film more than surface roughening. Treatment with 0.7 M CsOH lowered the contact angle of the film, measured by the Wilhelmy Balance technique, after only 1 minute of treatment at 60{dollar}spcirc{dollar}C. Longer periods of treatment did not produce surfaces with significantly lower contact angles. Surface roughening of the film was distinguishable by scanning electron microscopy between 30 and 100 minutes of treatment; however, the presence of a rough surface did not significantly lower the contact angle below that measured for films where no roughening was observed.; Chemical modification of the end groups formed by CsOH treatment reversed the gain in wettability detected by contact angle measurement and inhibited dye adsorption, adding further evidence for the involvement of polar end groups in the wettability of alkaline-treated film.