| Polyurethane(PU)is called “the fifth largest plastic”,which has the advantages of high strength,corrosion resistance,etc.,but it has some disadvantages such as poor water resistance and poor mechanical properties.In view of poor water resistance,a strong hydrophobic group is generally introduced.Organic silicon-containing groups in the low surface energy silicon polymers have the property of being concentrated toward the surface during film forming process,therefore,the polymer films can have good chemical resistance and high mechanical properties by introducing hydrophobic Organic silicon.At the same time,it can reduce or even eliminate the use of acetone during the synthesis of polyurethane,so that it can reduce the pollution to the environment.Acrylic acid(PA)is also a kind of polymer material,which has the advantages of high gloss,weather resistance,and high flexibility,but it generally has disadvantages such as poor solvent resistance and “heat stickiness and cold brittleness”.PA can be introduced into Si-PUA by polymerization,which can achieve the complementary advantages of them and improve the overall performance of emulsions and their films.First,about 30% solid content WPU emulsion was prepared.The effects of initial R value,carboxyl group content,degree of neutralization and other effects on the properties of emulsion and coating films were discussed.The study found that the optimal preparation conditions were as follows: the initial R value was 2.0,the dosage of DMPA was 4.0-4.5%,the neutralization degree was 90-100%,the poly-rotating speed was 250-300r/min,the shear dispersion speed was 1400-1600r/min,the water addition speed was 100-150ml/min,the prepolymerization temperature was 75-80 ℃,the chain extending temperature was 75-80°C,the sealing temperature was 70°C and the neutralization temperature and dispersion temperature were 30-35°C.The the viscosity of WPU was 25-65 mPa·s and a particle size distribution was 40-160 nm.The water resistance of flim was 17.2%-47.5%,the tensile strength was 6.072-10.028 MPa,and the elongation was 307.2-421.4%,which was suitable to be further modified.Secondly,about 30% solid content SiPU was prepared through bulk polymerization by using hydroxypropyl Organic silicon(PDMS-1000)as a modifier,The effects of the sequence of PDMS,prepolymerization temperature and the dosage of PDMS on the properties of the emulsion and films were discussed.The optimal conditions were as follows: the initial R value was 2.0,the R total was 1.2,the dosageof DMPA was 4%,the prepolymerization temperature was 80-85°C,the prepolymerization time was about 120 minutes,the dosage of PDMS was about 5%,and PDMS was added after PCDL.The viscosity of the emulsion was 8-23 mPa·s,the particle size was 23-94 nm,the water resistance was 9.0%.-14.2%,the tensile strength was up to 15.072 MPa,the elongation was up to 740.7%.Finally,the Si-PUA emulsion was synthesized by semi-continuous pre-emulsification seed emulsion polymerization with SiPU as the shell and acrylic ester as the core layer.The effects of temperature,stirring speed,and ratio of core-shell on performance of emulsion and films were studied.The optimal conditions were as follows: the polymerization temperature was about 80°C,the drying temperature was about 35°C,the stirring speed was 100-105 r/min,the nucleo-cytoplasm ratio was 2:1,the emulsifier ratio was 2:1,and the emulsifier dosage was 3.0-3.5%,the dosage of initiator was 0.5-0.7%,the solid content was about 35%,and the humidity was about40%.The emulsion and the films have good overall performance.The tensile strength reaches 5.5473 MPa and the elongation was up to 408.3%,the water resistance was6.6%,the hardness of the film was 1H,and the gloss of of the film was 80.2. |
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