Thermal-and PH-sensitive Polyurethane Hydrogel Materials:Preparation And Adsorption Property

Intelligent hydrogels that can induce the external environment and make intelligent response,have attracted growing attentions for their broader range of applications in separation,material purification,medical material and drug sustained release,etc.The polyurethane hydrogel has received extensive attention and research because the polymer possesses the excellent properties of polyurethane and hydrogel.In this study,the thermaland pH-sensitive hydrogels were synthesized and prepared from polyethylene glycol(PEG),dimethylol propionic acid(DMPA),N-Methyldiethanola Mine(MDEA),4,4`-diphenylmethane diisocyanate(MDI)and Trimethylolpropane(TMP).The chemical structure,micro morphology,Critical transition temperature and crystallization property for the PU hydrogels were characterized.The temperature-and pH-sensitive properties for the PU hydrogels were detected.At the same time,the adsorption properties for the PU hydrogel toward Pb2+ and brilliant crocein were studied.The main results obtained are as followes:Using DMPA,PEG(with different molecular weight),MDI and TMP as main raw materials,a series of thermal-and pH-sensitive PU hydrogel materials were prepared and the thermal-sensitive property characteristic was discussed.Fourier transform infrared(FTIR)spectroscopy,scanning electron microscope(SEM),differential scanning calorimetry(DSC)and X-ray diffraction(XRD)were employed to characterize the basic properties for the PU hydrogels.The swelling tests were simultaneously used to measure the thermal-and pH-sensitive properties for the PU hydrogels.FTIR analysis demonstrated that the PEG(the temperature-sensitive component)and –COOH groups(the pH-sensitive component)were successfully introduced into the PU molecule chains.SEM study indicated that the PU hydrogels possessed a honeycomb structure.According to the analysis of DSC,the Critical transition temperature of the PU hydrogels increased with the increase of PEG molecular weight.XRD and POM showed that the PU hydrogels have obvious crystallization properties and change from crystalline state to rubbery state at a certain temperature.In addition,the ESR showed an obvious decrease when temperature was exceed the the starting point of Critical transition temperature,exhibiting the thermal-sensitive property.Moreover,the ESR increased sharply when the pH value was increased from 4.0 to 7.0,exhibiting the pH-sensitive property.Using MDEA,PEG(Mn=6000),MDI and TMP as main raw materials,a series of thermal-and pH-sensitive polyurethane hydrogel materials were prepared and the pH-sensitive property characteristic was discussed.The effects of –N(CH3)-addition on chemical structure,microstructure,phase transition temperature and crystallization properties for PU hydrogels were systematically studied.The results indicate that the prepared PU hydrogels showed a similar chemical strectrue and irregular porous structure.The crystallinity and Critical transition temperature for all PU hydrogels were negatively correlated with the increase of inventory of –N(CH3)-and the phase transition temperature appeared at 60.2 oC,59.4 oC,57.6 oC and 54.8 oC,respectively.The ESR for PU hydrogels showed an obviously decrease when temperature was exceeded Critical transition temperature,exhibiting thermal-sensitive property.Moreover,the ESR increased sharply in the pH value range from 8.5 to 10.0,exhibiting the pH-sensitive property.The prepared hyrdogel 3 and hydeogel(a)to hydrogel(d)were chose as adsorption material to remove the heavy metal(Pb2+)and dyestuff(brilliant crocein)from water.The effects of temperature and initial pH value on the adsorption properties of polyurethane hydrogels were also stdied.The effect toward Pb2+ reaced optimum(qe=0.91mg/g,R=91.28%)when the temperature was 25 oC and initial pH value was 4.5 to 5.0.And the effect was decreased with the increase of themperature or the decrease of initial pH value,exhibiting the thermal-and pH-sensitive property.The effcet toward brilliant crocein reaced optimum(qe=29.66mg/g,R=99.4%)when the temperature was 25 oC and initial pH value was 2.5.And the effect was decreased with the increase of themperature and initial pH value,exhibiting the thermal-and pH-sensitive property.Thus,the qe and R of PU hydrogels towards water pollutants can be changed by the variation of temperature and pH value.It can be used to control the adsorption and desorption properties of PU hydrogel toward water pollutants,which is beneficial to the controllable separation of pollutants in the water.In this paper,the thermal-and pH-sensitive PU hydrogels were successfully prepared and the themal-sentive regulation,pH-sensitive regulation and adsorption property were also studied.It can provide reference value and reference function for the research and development of new polyurethane hydrogel materials.