| Poly(N-isopropyl acrylamide)(PNIPAAm) as a thermo-responsive polymer owns hydrophilic group and hydrophobic group and transforms its own molecular conformation reversibly near its lower critical solution temperature(LCST) about 33 ℃ in water. PNIPAAm is hydrophilic and dissolved in water below the LCST, but is hydrophobic and precipitated from the aqueous solution above the LCST. However, the fragile PNIPAAm greatly limits its own application. So, some researchers have been trying to improve its mechanical performance by nano-composite technology, grafted polymerization method and so on. In this work, ammonium persulfate(APS) and hydrogen peroxide and ascorbic acid(H2O2-H2A) was chosen to graft PNIPAAm onto cotton fiber, to improve the mechanical performance of PNIPAAm and endow cotton fiber with the thermo- responsive hydrophilicity/ hydrophobicity of PNIPAAm.APS was chosen to initiate N-isopropyl acrylamide to polymerize and obtain PNIPAAm. The molecular structure and weight of PNIPAAm were respectively characterized by FTIR, XRD, Ubbelohde viscometer and GPC. The glass transition temperature(Tg) and LCST of PNIPAAm were measured by DSC, MDSC and UV/VIS spectrometer. Then, PNIPAAm was coated on the surface of cotton fiber. The contact angle measurement of the cotton fiber coated with PNIPAAm on the surface shows thermo-responsive hydrophilicity/ hydrophobicity: hydrophilic below the LCST and hydrophobic above the LCST.By the analysis of FTIR and SEM, APS and the initiator system of H2O2-H2 A respectively by the free-radical precipitating grafting polymerization and the free radical solution grafting polymerization, have successfully initiated the cotton fiber to be grated PNIPAAm in the aqueous solution under the Nitrigen atmosphere, obtaining cotton fiber grafted PNIPAAm(CF-g-PNIPAAm). Under the two initiator systems respectively, the effect of monomer concentration, initiator concentration and monomer concentration with constant ratio between the monomer and initiator concentration on the grafting ratio of CF-g-PNIPAAm have been studied. The CF-g-PNIPAAm obtained by H2O2-H2 A has the maximum grafting ratio 21.1wt% at the H2O2 concentration of 0.06mol/L, H2 A concentration of 0.036mol/L and monomer concentration of 0.6mol/L. Also, the CF-g-PNIPAAm obtained by APS showed the maximum grafting ratio 23.9wt% at the APS concentration of 0.24mol/L and monomer concentration of 1.2mol/L.CF-g-PNIPAAm showed thermo-response at LCST(near 33 ℃) by directly measuring the reversible heat capacity by using the MDSC technology. Water contact angle test also showed the thermo-responsive hydrophilicity/hydrophobicity of CF-g-PNIPAAm, which was barely influenced by their grafting ratio. CF-g-PNIPAAm was hydrophilic below the LCST but hydrophobic above the LCST. The water wetting time of CF-g-PNIPAAm can characterize their thermo-responsive absorbency, which has been tested by water absorbency test(AATCC 79-2000) below and above the LCST respectively. For CF-g-PNIPAAms obtained by H2O2-H2 A, their thermo-responsive absorbency enhanced with the increase of their grafting ratio. However, that of CF-g-PNIPAAms obtained by APS owned the optimum value at the scope of grafting ratio 1.5wt%-3.5wt%, which was caused by the distribution non-uniformity of the grafted PNIPAAm with high grafting ratio. As a whole, the thermo-responsive absorbency of CF-g-PNIPAAms obtained by APS was better than that of CF-g-PNIPAAms obtained by H2O2-H2 A. Keywords: cotton fabric, Poly(N-isopropyl acrylamide), ammonium persulfate, hydrogen... |
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