Preparation And Performances Of Reactive Branched Polyurethane Dispersants

Polymer dispersant has attracted extensive attention over the past few decades for its prominent dispersing property and stability,which helps to balance pigment aggregation forces,including electrostatic attraction,van der Waals forces,hydrogen bonding and hydrophobic interaction.It equips with numerous anchoring groups that enhance the adsorption between particles and dispersant to form durable adsorption layers on the pigment particles.Furthermore,Long hydrophilic chains in the dispersant structure are wrapped around the surface of the pigment particles to provide effective steric hindrance.Polyurethane molecular chain segments are flexible,easy to prepare and stable in performance,which can be used as an excellent pigment dispersant.It displays great dispersion stability for organic and inorganic pigments.The polyurethane dispersant is designed into a hyperbranched polymer structure,which can take advantage of its many end groups and high activity to introduce more targeting groups at the molecular end.So the dispersant with better stability can be prepared.In addition,the design of polyurethane into a hyperbranched structure can be modified by the highly active isocyanate group at its end to give the dispersant self-adhesive properties,so as to solve the stiffness of the fabric's hand feeling caused by the adhesive in the application of pigments.Polyurethane prepolymers with branched and linear structures were synthesized by reacting isophorone diisocyanate with trimethylolpropane and 1,4-butanediol,respectively.Polyethylene glycol monomethyl ether was incorporated into polyurethane as a water-soluble segment.And hydroxyimidazole was added at the end of the polyurethane as the anchor group of the pigment to synthesize branched and linear dispersants.The FT-IR spectroscopy proved the complete reaction of the-NCO group,the molecular weight difference of the branched/linear polyurethane dispersant was characterized by gel chromatography,and the thermal stability of the two structures was further characterized by thermogravimetric analysis and DSC testing.Two dispersants were applied to the preparation of pigment pastes.The particle sizes of the prepared pastes were about 161 nm and 172 nm,and the viscosities were8.9 m Pa·s and 19.7 m Pa·s,respectively.In addition,the surface tension of the color paste prepared by the branched structure dispersant was slightly higher than that of straight chain.The centrifugal stability test showed that the centrifugal stability of branched and linear polyurethane dispersant under the condition of 3000 r/min were 90.7% and 87.0%,respectively.According to the test results of storage stability and electrolyte stability,it was found that the performance of branched polyurethane dispersant was better than linear structure.In order to solve the hand feeling problem of pigment printing fabrics,a branched polyurethane dispersant with self-adhesive properties was designed.The content of PEG400 and DMPA was changed to synthesize polyurethane prepolymers with different hydrophilic and hydrophobic properties.Polyurethane prepolymer and trimethylolpropane were reacted to synthesize branched polyurethane.The epoxy groups were used as reactive groups,and nitrogen-containing heterocycles were used as anchoring groups to synthesize a series of branched polyurethane dispersants(BPUs).The structure,molecular weight and thermodynamic properties of BPU were characterized by FT-IR,Tg,DSC and GPC.The pigment dispersions were prepare with BPUs by ball milling,and then evaluated its characteristic parameters,such as particle size,viscosity,stability,color performance and color fastness.The experimental results found that the particle size of the five dispersions were all below 200 nm,and the viscosity was as low as 6-9 m Pa·s.It is worth noting that the centrifugal stability of all pigment dispersions remained above 90% at 3000 r/min.As the storage time increases,the particle size and viscosity of the dispersant change within a relatively narrow range.The best hydrophilicity and hydrophobicity of the dispersant were studied through dispersion stability,which showed that the BPU3 color paste had the best stability.The prepared color paste is printed on cotton fabrics,and its washing fastness was about grade 4 without adding a binder.The polyurethane dispersant was designed into a hyperbranched structure,and a photosensitive self-adhesive branched polyurethane dispersant(UV-BPUs)was synthesized by introducing anchor group and acrylic group respectively at the end of the polyurethane.In the experiment,the number of branching units was changed to synthesize polyurethane dispersants with different branching degrees and different molecular weights.The branching degree and molecular weight of the dispersant were tested by nuclear magnetic carbon spectroscopy and gel chromatography.It was found that the branching degree and molecular weight increased with the increase of the number of branching units.The 25% pigment pastes prepared with UVBPUs displayed great dispersion properties.The particle sizes were 167 nm,163 nm,168 nm,163 nm,and 189 nm.The viscosity are 12.9 m Pa·s except for UV-BPU1.The viscosity of other color pastes was below 10 m Pa·s;the color paste(UV-BPU2)with the smallest change in particle size after high temperature storage for 5 days was within 20 nm,the color difference was 0.20,and the centrifugal stability at 3000 r/min was above 92%.Using this color paste for direct printing,its washing fastness was maintained at 3?4 level.