PREPARATION OF PNIPAAm GRAFTED COTTON AND ITS THERMAL SENSITIVITY

Abstract

The thermal sensitive cotton-g-PNIPAAm was prepared through free radical grafting reaction initiated by different initiators including ammonium ceric nitrate(CAN),potassium persulfate(KPS) and hydrogen peroxide/ascorbic acid(H_2O_2/H_2A system).The degrees of grafting(G) achieved by different initiators could be sorted into descent order as following: G(H_2O_2/H_2A)G(KPS)G(CAN).The other factors affecting the degree of grafting,such as the concentration of initiator,reaction time,temperature and the concentration of monomer,were studied.The results showed that the optimal conditions for grafting reaction using H_2O_2/H_2A initiating system were: initiator dosage 7.5 mmol/L(mole ration of H_2O_2to H_2A=1∶0.6),reaction time 1.5 h,monomer concentration 5%～15% and the reaction temperature 25℃.FTIR spectrogram of grafted cotton fiber showed characteristic absorptions of(—CH_3,)(CO,)(—N—H,)(—C—N) and(—CH(CH_3)_2) groups at 2967.5,2857.4,1623.9,1540.3,1457.4 cm~(-1),1385.6 and 1365.4 cm~(-1) giving the evidence for the successful grafting of PNIPAAm onto cotton fiber surface.The extraneous polymer attached to fiber surface can be observed in SEM images of grafted cotton samples.DSC analysis revealed that all grafted cotton fibers had the LCST around 32～33℃ which was very close to the LCST of pure PNIPAAm gel(32.48℃).The raising of grafting degree has little impact on LCST but increases the reversible enthalpy change(ΔH) of the cotton-g-PNIPAAm.In the falling-drop test(AATCC 79) and capillary rise test(FZ/T 01071), the fabric samples of cotton-g-PNIPAAm demonstrated different water absorbing abilities at different temperatures which meant that the cotton fiber had been endowed with thermo sensibility by PNIPAAm grafting.A grafting degree between 25%～45% is suitable for creating high thermo sensitivity.Other grafting degrees out of above range were not suggested.The analysis and discussion about the relationship between ΔH and swelling/shrinking time of cotton-g-PNIPAAm indicated that cotton-g-PNIPAAm reacted to temperature much quickly than pure PNIPAAm gel.