Synthesis And Property Of Polymeric Dyes Based On Waterborne Polyurethane

Traditional monomolecular dyes or pigments present such drawbacks as poor thermal migration resistance, limited universality, complex process and wastewater treatment. which cannot meet the environmental requirements. Thus, polymeric dyes are developed to satisfy the market requirement in safety, efficiency and environmental protection. Polymeric dyes are termed as colored polymers which are synthesized by bonding dye chromophore into the main or side chains of polymers via chemical reaction. Polymeric dyes integrate both characters of dyes and polymers, such as chromaticity, tinting strength, photoabsorption, transparency, processibility, etc. They also provide excellent film-forming ability, solvent resistance, thermal stability and migration resistance. Additionally, polymeric dyes cannot be absorbed by the skin on account of the large molecules and their chemical stability, presenting outstanding safety. Consequently, polymeric dyes are able to be developed as promising candidates for textile dyeing, coating industry, printing ink and other aspects.Here, anthraquinone and azobenzene dye chromophores are covalently introduced into polyurethane chain to prepare waterborne polyurethane based polymeric dyes via the reaction of isocyanate group and active hydrogen. The common, blocked and UV curing waterborne polyurethane based polymeric dyes were designed from molecular level and successfully synthesized. The molecular structure, essential performances, application properties of textile coating or printing of each synthesized polymeric dye were investigated in detail. It is aimed at solving the problems of traditional dyes in safety, thermal migration, solvent resistance and other aspects, and meanwhile realizing synchronously coloring and functional finishing of textiles. The main research are as follows:Waterborne polyurethane covalently bonded anthraquinone dye chromophore was successfully synthesized via incorporating micromolecule red anthraquinone dye chromophore into the polyurethane skeleton. The number- and weight-average molecular weights of the waterborne polyurethane based polymeric dye were about 6567 and 10295, respectively. The maximum absorption wavelengths are 260 nm, 520 nm and 555 nm, which show hypsochromic effect compared with corresponding micromolecule dye. Thermal stability and centrifugal stability can be distinctly enhanced after the micromolecule dyes are covalently bonded into polyurethane skeleton. The solubility of waterborne polyurethane based polymeric dye also offers reversibility and good color stability at different p H values. Thermal migration property of this polymeric dye is improved by 82.4 %, compared to that of the simple mixture of the chromophore and polyurethane. The polymeric dye with enhanced color stability in centrifugation, acid, alkaline and thermal conditions can upgrade the product quality as it is employed in dyeing, coating or printing ink.In order to enhance the bonding strength between waterborne polyurethane based polymeric dye and fabric substrate, dye-bonded blocked waterborne polyurethanes were developed with anthraquinone chromophore and methyl ethyl ketoxime blocking agent. The number-average molecular weight of the dye-bonded blocked polyurethane is 2303 g/mol and the polydispersity is 1.06, indicating a narrow molecular weight distribution. The maximum absorption wavelengths do not shift after the monomolecular anthraquinone chromophore bonded into polyurethane. The dye-bonded polyurethanes provide better centrifugal stability and water solubility than the dye-mixed blocked polyurethane. Additionally, the dye-bonded blocked polyurethane offers good thermal stability below 100 °C and undertakes de-blocking at about 150 °C. The covalent bonding of anthraquinone moiety with polyurethane chain and temporary blocking of the terminal isocyanate groups are conducive to enhancing the tinting strength and color fastness of the treated cotton fabrics. The self-colored blocked polyurethane with good elasticity and toughness can improve the recovery angle of the treated cotton up to 120°, endowing the fabric with wrinkle resistance which synchronously realizes coloring and finishing of textiles.To further investigate the relationship between printing performance and molecular weight of polymeric dye, a series of polymeric dyes based on blocked waterborne polyurethanes(BWPUs) with varied molecular weights have been synthesized successfully. The molecular weight of the polymeric dyes was tailored via selecting different chain length polyethylene glycol as soft segments. The influence of molecular weights on structure-property relationship is discussed. The rheological, thermal, and printing properties of these polymeric dyes are mainly investigated. Results show that Tg of the BWPUs decreased from 5.1 °C to-52.6 °C with increasing molecular weight of PEG soft segment. And BWPUs with higher molecular masses exhibit better thermal stability. The viscosity of BWPUs decreases as the shear rate increases, showing shear thinning behavior(especially BWPU-PEG2000). The higher molecular weight of BWPUs also leads to higher storage modulus and loss modulus. The synthesized BWPUs are applied in cotton fabric printing as both colorant and adhesive. PVI values of all BWPUs pastes are below 0.3, demonstrating that they show very high structural viscosity. The color fastness of the printed cotton fabrics can be improved as molecular weight and baking temperature increase.An azobenzene-polyurethane based polymeric dye with environmental responsive performances and anti-wrinkle property was prepared via covalently bonding N, N-di(2-hydroxyethyl) azobenzene with polyurethane chain in order to synchronously realize coloring and functional finishing and enhance the thermal migration. FTIR and 1H NMR results showed that the azobenzene chromphore has been successfully introduced into waterborne polyurethane chain. And reaction rate of the azobenzene and its content in polyurethane chain were 87.81% and 3.53%, respectively. The maximum absorbance wavelength remained unchanged after the azobenzene chrowas introduced into the polyurethane. Furthermore, the azobenzene chromphore and its polymeric dye would translate into hydrazone type under acidic condition with the color changing from luminous yellow to amaranth, and they also showed excellent reversibility. Meanwhile, the K/S value of the polymeric dye coated fabric was improved from 4.31 to 12.26 and the color also changed from yellow to amaranth under acidic condition, indicating that the azobenzene-polyurethane based polymeric dye also presented outstanding acidichromism effect. The coated cotton fabric with the azobenzene-polyurethane polymeric dye showed more vivid and richer shade than that with azobenzene physically mixed polyurethane, and the K/S value increased from 1.50 to 4.61. The immediate-elastic and delay-elastic recovery angles of the coated fabric were improved from 110° to 183° and 136° to 227°, respectively. The thermal migration rate was dramatically reduced to 5%. Consequently, the azobenzene-polyurethane polymeric dye exhibited outstanding anti-wrinkle property and thermal migration property, which provided a novel route for shortening the textile technological process.Three novel UV curable polymeric dyes(UVPDs) based on multifunctional waterborne polyurethane have been successfully developed to overcome the drawbacks of thermo-curing. The functionality of UVPDs is tailored by end-capping with 2-Hydroxyethyl acrylate(HEA), pentaerythritol triacrylate(PETA) and dipentaerythritol pentaacrylate(DPEPA), respectively. The chemical structure, molecular weight and carbon-carbon double bond(C=C) contents of the UVPDs were investigated. The C=C contents of UVPD2, UVPD6 and UVPD10 are 0.586 %, 1.641 % and 2.753 %, respectively. The thermal property, curing behavior and color property of the UVPDs were discussed. It is found that the thermal stability of the UVPDs is improved with the functionality increasing from 2 to 10. Compared with the transparent UVPU6, UVPD6 with the same functionality shows slower curing rate which may be due to the presence of the dye chromophores. Additionally, the UVPDs show higher initial double bond conversion rate. The curing behavior demonstrates that the UVPDs can cure rapidly under UV radiation, especially the ones with higher functionality. The cured UVPD films also exhibit higher cross-linking degree and better water resistance with 5% photoinitiator. Furthermore, the maximum absorption wavelength and curve trend of the cotton fabrics coated with the UVPDs keep unchanged while the color of the coated cotton fabrics turns slightly dim with prolonging the UV curing time. The color fastness to rubbing and washing of coated cotton fabrics with UVPD10 cured for 60 s can be enhanced up to 4-5 grade.