Preparation of water-absorbing deep-groove polypropylene fibers through the use of migratory additives and photografting

To change the surface properties of polypropylene (PP) deep-groove fibers, this research applied two different surface modification methods: the use of migratory additives and photografting. To identify effective additives for PP, the molecular weight and architecture of the additives were studied in a film system. Hydrophilic additives under investigation included linear polyethylene glycol (PEG) and four-arm polyethylene oxide (4-PEO) of different molecular weights, and a commercial hydrophilic additive (CHA) Irgasurf HL560. ATR-FTIR detected concentration increases for all additives in the near-surface region, but there was no significant improvement in surface hydrophilicity for the PEGs and 4-arm PEOs by water contact angles measurements. Among the linear additives, low MW PEG (1 kDa) was found to migrate faster than the high MW varieties. The linear PEG and 4-arm PEO with MW higher than 2 kDa did not exhibit significant migration to the surface within 1 month. The CHA was effective in rendering PP surfaces hydrophilic in a relatively short time, and demonstrated an ability to replenish the surface after it had been washed in methanol.; To measure the diffusivity of the CHA in PP, an experiment was designed based on a standard 1-D diffusion model. Experimentally, two cases were compared: (1) washing additive off the film surface with limited contact with the solvent. (2) immersing the film in solvent with continuous stirring. Diffusivity measured by the surface-washing method was 10-14 ∼ 10-12 cm2/s, and 10-12 ∼ 10-10 by the immersion method. It is clear that the continuous immersion method more closely matched the zero boundary condition used in the model and thus gave more accurate diffusivity values than did the surface-washing method. Activation energy for diffusion was in the range of 30-100 kJmol -1.; Deep-groove fibers were spun from the mixture of PP and the CHA migratory additive. A novel dynamic contact angle (DCA) analysis method was designed to measure DCAs on single fibers. Results showed decreased advancing and receding contact angles with longer ageing time. Spontaneous water uptake from these modified fibers was observed.; Upon photografting the deep-groove PP fibers with polyacrylamide (PAAm) and polyacrylic acid (PAA) through a two-step photopolymerization, decreased dynamic water contact angles on single fibers and spontaneous water adsorption into fiber bundles were observed. An increase in monomer concentration was found more effective than longer UV exposure time in creating higher graft density on deep-groove PP fibers. Compared with acrylamide (AAm), acrylic acid (AA) penetrated into the fiber and polymerized below the surface. DCA results showed that advancing water contact angle on single fibers decreased from 100° on plain PP to 55° upon modification with PAAm and PAA, and the wicking amount of vertically placed fiber bundles was a linear function of the square root of time at early wicking times.