Preparation,Characterization And Properties Of Waterborne Polyurethane Containing Liquefied DMPA

Due to their excellent performance,waterborne polyurethanes（WPU）have been widely used in many fields,such as leather,coating,adhesive,and so on.Current technology for producing WPU usually adopts dimethylol propionic acid（DMPA）as hydrophilic chain extender.However,the high melting point of DMPA made it very difficult to be melt at the reaction temperature.It usually requires additional cosolvent,such as N-methyl pyrrolidone（NMP）,etc.However,NMP has been identified as a toxic solvent in the United States and Europe statutes.Thus,use of NMP made WPU have potential risks in environment,health aspects,etc.And due to the use of cosolvent,applications of WPU in food packaging,underwear,clothing and other fields have been restricted.The development of cosolvent-free WPU has become one of the important topics in the polyurethane chemistry.In order to solve the above problem and produce 100%green and environmental friendly waterborne polyurethane emulsion,a new method was proposed to synthesize nontoxic liquefied dimethylol propionic acid（LDMPA）through ring opening reaction ofε-caprolactone（CL）with active hydroxyl of DMPA.A series of waterborne polyurethane emulsions were synthesized by using LDMPA as the hydrophilic soft segment.The structure and properties of the prepared WPU were characterized.The LDMPA type WPU was further modified by introducing sulfonate chain extender,2-[（2-aminoethyl）amino]ethyl sulfonic acid sodium salt（AAS）.The mole ratios of AAS/LDMPA on the stability,particle size,apparent viscosity of the emulsions,as well as the adhesion and mechanical properties of WPU were investigated.Main contents of this paper are as follows:1.LDMPA was synthesized through ring opening reaction of CL with active hydroxyl of DMPA.The optimal reaction conditions were determined as follows:the mole ratio of CL:DMPA was 3:1;content of tetrabutyl titanate for catalyzer was40ppm;reaction temperature at 100℃;reaction duration was 6h.LDMPA was successfully prepared under above conditions.Result of infrared spectrum analysis（FTIR）showed that LDMPA appeared characteristic peak of CL,and its peak was moving towards high wavenumber against characteristic peak of DMPA.This phenomenon indicated that the structure of DMPA had been destroyed,and the corresponding intermolecular force had been greatly weakened.Result of differential scanning calorimetry（DSC）analysis showed that melting point of LDMPA was relatively lower than PCL’s.This was due to the existence of carboxyl,which destroyed the regularity of polycaprolactone molecular chain,hindered chains to crystallize,and resulted in a lower melting point.Result of X ray diffraction（XRD）test showed that LDMPA did not has diffraction peak as DMPA did,and it appeared characteristic peaks of PCL.This phenomenon demonstrated that the original crystal structure of DMPA had been destroyed after the introduction of CL.2.A series of waterborne polyurethane emulsion samples were sythesized by using LDMPA as hydrophilic soft segment part.The properties of the prepared waterborne polyurethane emulsion samples were characterized.With increasing of hard segment content,particle diameter of waterborne polyurethane emulsion samples increased,apparent viscosity reduced,hardness of waterborne polyurethane film increased,and initial peeling strength decreased.Meanwhile,water absorption rate,contact angle,tensile strength,and ultimate peeling strength of waterborne polyurethane film appeared inflation points,while hard segment content rose.When hard segment content of waterborne polyurethane sample increaseed from 16%to 22%,water absorption rate decreased from 12%to 8.9%,contact angle increased from 48°to 56°,tensile strength enhanced from 16 Mpa to21Mpa,as well as ultimate peeling strength raised from 4.2N/mm to 5.5N/mm.When hard segment content of waterborne polyurethane sample increased from 22%to 34%,water absorption rate increased from 8.9%to 10%,contact angle droped from 56°to50°,tensile strength decreased from 21Mpa to 16Mpa,as well as ultimate peeling strength lowered from 5.5N/mm to 4.9N/mm.With increasing of carboxyl content,particle diameter of waterborne polyurethane emulsion sample decreased,apparent viscosity increased,hardness of waterborne polyurethane film sample reduced,water absorption rate increased,contact angle decreased,and initial peeling strength of waterborne polyurethane samples decreased.Meanwhile,tensile strength,and ultimate strength of waterborne polyurethane samples presented inflection points.When content of carboxyl increased from 8mmol/100g to 10mmol/100g,tensile strength of waterborne polyurethane sample rose from 14Mpa to 19Mpa,and ultimate peeling strength increased from5.5N/mm to 6.4N/mm.When carboxyl content increased from 10mmol/100g to14mmol/100g,tensile strength of waterborne polyurethane sample decreased from19Mpa to 8Mpa,and ultimate peeling strength droped from 6.4N/mm to 4.8N/mm.3.LWPU5 and WPU emulsion samples were synthesized by using LDMPA and DMPA as hydrophilic part respectively.Particle diameter of LWPU5 emulsion sample was smaller than WPU’s.Viscosity of LWPU5 emulsion sample was larger than that of WPU.Mechanical properties,hardness,water resistance,and adhesive strength of LWPU5 film sample were smaller than that of WPU film sample.Result of DSC indicated that crystallinity of soft segment of WPU file sample was more complete than that of LWPU5 film sample.Result of dynamic mechanical test（DMA）indicated that micro-phase separation degree and physical cross-linking density of WPU film samples were higher than those of LWPU5 film sample.Result of thermal weight loss test（TG）indicated that thermal decomposition temperature of WPU film samples was higher than that of LWPU5 film samples.4.A series of waterborne polyurethane emulsion samples were sythesized by using AAS and LDMPA as hydrophilic part.The influence of-COOH/-SO₃Na ratio on the structure and properties of WPU samples was characterized.It was found that with decreasing-COOH/-SO₃Na ratio from 10:0 to 3:7,the particle size of the waterborne polyurethane emulsion decreased,while the apparent viscosity of the samples increased.the water absorption of the WPU films decreased,while the contact angle of the films increased.the tensile strength,elongation at break and peeling strength of the samples increased.Furthermore,the results of DMA showed that incorporation of AAS-Na increased the storage modulus of the sample.And the results of DSC showed that with decreasing-COOH/-SO₃Na ratio from 10:0 to 3:7,T_g of soft segment shifted to lower temperature,which indicated that the micro-phase separation degree of the samples increased.The results of TG showed that thermal decomposition temperature of the samples significantly increased with decrease of COOH/SO₃Na molar ratio.When COOH/SO₃Na=3:7 was prepared,the WPU sample showed good comprehensive properties.