Preparation Of Temperature Sensitive Textile By Plasma-induced Grafting And Its Mechanism Study

Poly (N-isopropylacrylamide)(PNIPAAm) hydrogel can sense a very minute change in theexternal environment temperature and generates a volume phase transition, which was widelyused in the field of biological tissues. The mechanical strength of PNIPAAm itself is poor, so itsapplication has great restrictions. In order to overcome this drawback, many methods, such aschemical grafting, gamma ray radiation grafting, photo-induced grafting, low temperatureplasma grafting and so on, can be applied to graft PNIPAAm on the substrate of fiber. In thesemethods, low temperature plasma grafting is an environmentally friendly, efficient, and dryprocessing technology, which was concerned by researchers. However, some of the basic issuesrelated to the grafting by plasma-induced are yet need to be further investigated or confirmed.In this paper, the low-pressure RF glow discharge plasma and atmospheric pressure glowdischarge plasma were used to activate cotton and PET fiber surface. Thetemperature-responsive cotton fabric and polyester fabric were successfully prepared bydifferent plasma induced grafting methods. The effects of reaction conditions, such as plasmatreatment parameters, grafting reaction parameters on the grafting were investigated.Meanwhile, the temperature-responsive property of the graft fabrics and its influence factorswere investigated. The relationship between the graft ratio and switching effect of fabrics wererevealed. To reveal the grafting mechanism, the morphological changes and structure of graftedfabric were characterized through analysis methods, such as field emission scanning electronmicroscopy (FESEM), Fourier transform infrared spectroscopy (FTIR), EDS, X-rayphotoelectron spectroscopy (XPS),1HNMR and EPR. And the active species in atmosphericpressure discharge plasma were determined by plasma emission spectroscopy.The effects of plasma treatment parameters on the graft ratio of fabrics were investigated,such as discharge time, discharge power and flow pressure. The results showed that there existsa close relationship between plasma parameters and the graft ratio. The plasma activation andetching occur simultaneously at the plasma treatment process. Strong plasma etching willweaken the activation effect of fabrics. A higher graft ratio can be obtained by controlling theplasma parameters. To obtain a higher grate ratio, a longer plasma treatment time and higher discharge power should be selected, when polyester fabrics are grafted by argon plasmainduced in one step method (plasma treatment on fabrics pre-impregnated), compared withoxygen plasma induced in two step method (plasma activation of fabric followed by soakinginto monomer solution).When APGD plasma activated cotton fibers, energizing voltage shouldbe controlled at90-120V, a certain amount of argon gas will be helpful to obtain good glowdischarge effect. Meanwhile, a higher graft ratio can be obtained by controlling the atmosphericpressure plasma treatment conditions.The effects of monomer solution concentration, reaction temperature and time on thecotton and PET fabrics grafting using NIPAAm monomers were discussed and optimumgrafting reaction conditions were obtained. The increase in the monomer concentration leads tothe increase in the graft ratio. Increasing reaction temperature is not helpful to get a higher graftratio. At a higher temperature, the grafted polymers shrink on the surfaces of fabrics andmonomer diffusivity is restricted significantly. The reaction temperature should be controlled at15-20℃. In order to ensure the complete reaction, grafting reaction time of cotton fabricsshould be selected for16hours, and8h is an appropriate reaction time for polyester fabrics.After grafting, a significant difference on the water flux was observed at differenttemperatures as compared to the control fabrics. Grafted cotton fabric show obvious phasetransition endotherm at34℃, and grafted polyester fabric show obvious phase transitionendotherm at32~34℃. In a certain range, the switch effect of cotton and polyester fabric isgetting stronger as the graft ration increases, after reaching a certain threshold, increasing graftration will weaken switch effect of polyester fabrics. According to wetting experiments andwater contact angle tests results，the surface of grafted cotton fabric by APGD plasma inducedis hydrophilic with a water contact angle of0°below LCST at room temperature, andhydrophobic with a water contact angle of128.3°above LCST at40℃. Methylene blue dyeingresults revealed yet the temperature-responsive property of the grafted polyester fabrics.The increasing of BIS concentration benefits to getting a higher graft ratio and improvingthe grafting uniformity, but further increase will weaken the switch effect of the graftedpolyester fabrics. The reaction temperature which is too high will weakentemperature-responsive coefficient of the grafted polyester fabrics. In a certain range, the morethe amounts of AAm are added in the grafting reaction, the higher the LCST increases. And with the concentration of NaCl solution increasing, the LCST decreases.FTIR and XPS spectra of grafted fabrics by plasma-induced indicated that the NIPAAmmonomers were grafted from cotton and PET fabrics surfaces, which was further confirmed bythe EDS test and SEM results. EPR spectra of plasma-treated fabrics showed that the freeradicals have been generated on cotton and polyester fabric surfaces after plasma treatment.Plasma diagnostic results show that there exists Ar positive ion, O positive ion and N positiveions in the APGD plasma. When the oxygen plasma or APGD plasma activated cotton fabrics,free radicals are generated in the hydroxyl groups of the C (2) and C (6) atom of the cotton fibermacromolecules. And the grafting polymerization take place at this position. When the oxygenplasma and argon plasma activated polyester fabrics, the free radicals were generated only onthe EG chain segments of the polyester macromolecules, and then chain propagation grew atthat points.