Synthesis Of Polyurethane Ionomers By Reactive Extrusion And Preparaton & Characterization Of Its Anionic/Nonionic Aqueous Dispersions

Polyurethane ionomers(PUI)have unique chemical properties due to containing ionic groups and can be dispersed in water to form stable aqueous dispersions.As an environmentally-friendly polymer material,polyurethane dispersions(PUD)are widely used in coatings,printing inks,adhesives and other fields due to its excellent physical and chemical properties.However,the main processes at present for preparing PUD are acetone method and prepolymer method,which are batch synthesis methods and have many disadvantages,such as low synthesis efficiency,high energy consumption,low solid content and high viscosity of PUD,difficulty to control performance and needing large amount of acetone.In this paper,a synthesis method for polyurethane ionomers(PUI)and anionic/nonionic polyurethane dispersions(PUD)was introduced.PUI were synthesized in twin-screw extruder without organic solvent.PUI were then dissolved in acetone and dispersed in water.The PUDs were obtained after distilling off acetone and the solid content of PUDs was about 55%and had excellent stability.Polyurethane ionomers(PUI)were synthesized from poly(1,4-butylene adipate glycol)(PBA)as soft segments,1,4-butanediol(BDO)and diphenylmethane diisocyanate-50(MDI-50)as hard segments,poly(ethylene glycol)methyl ether(MPEG)as nonionic hydrophilic monomers,polyether diol-containing sulfonate(SPPG)as anionic hydrophilic monomers and dibutyltin dilaurate(DBTDL)as catalyst.The continuous production of PUI can be completed in twin-screw extruder,and the production process is easy to control due to no solvent is involved in the production process,and have high production efficiency and low energy consumption.The synthesized PUI can be stored in solid form and has low storage and transportation costs.The structure and molecular weight of PUI were tested by Fourier transform infrared spectroscopy(FTIR)and gel permeation chromatography(GPC).The results of FTIR indicated that the synthesized PUI was the target product of this study.The GPC results showed that the molecular weight of the PUI increased with the increment of R value within the R value ranged from 0.98 to 1.04.The average particle size test results of PUD showed that the average particle size of dispersions was below 220 nm,which had good stability.With the increasing of R value,particle size decreased initially and followed by an increase when R value was greater than 1.02.The average particle size decreased with the increase of anionic hydrophilic monomer content(AHGC)and nonionic hydrophilic monomer content(NHGC),and increased with the increase of hard segment content(HSC).Viscosity test results show that the trend of viscosity changed just the opposite with the trend of the average particle size.The results of TEM test showed that PUD particles were irregularly spherical and the size distribution was not uniform,the small particles were distributed between the large particles.The adhesive properties of the PUDs were measured and the results indicated that PUDs obtained have excellent adhesive properties,such as the maximum initial peel strength and T-peel strength were 2.38 and 11.82 N/mm,respectively.The initial peel strength and T-peel strength both gradually increased with the increment of R value and NHGC,and decreased with the increasing of HSC,and with the increasing of AHGC,initial peel strength and T-peel strength increased initially and followed by a slight decrease when AHGC was greater than 8mmol/100 g PUI.The heat resistance test results showed that the heat resistance of the adhesive increases with the increase of R value and hard segment content(HSC).The thermal properties of PUD films were tested by differential scanning calorimetry(DSC)and thermo gravimetric analysis(TG).The DSC results showed that with the increase of hard segment content(HSC),the melting temperature(T_m)of PUD films increased and the enthalpy(△H_m)of PUI decreased;the TG results showed that the PUD films had good thermal stability below 282℃.The water resistance results showed that the water absorption of PUD films was 2%-5%,and PUD films had good water resistance.The mechanical properties of PUD films were also tested and the results show that the tensile strength and elongation at break of PUD films increased with the increase of R value.With the increase of hard segment content and anionic hydrophilic monomer content,the tensile strength of the films increased and the elongation at break decreased;and there was a yield point,which is a characteristic point of the crystalline polymer in tensile curves.