Preparation Of Waterborne Polyurethane And Its Application In Playground Coatings

Compared with solvent-based polyurethane,waterborne polyurethane (WPU) dispersion is a binary colloidal system in which polyurethane (PU) particles are dispersed in a continuous aqueous phase due to the presence of ionic and nonionic hydrophilic segments in their structure.currently,a great interest in the development of a queous polyurethane dispersions (PUD) has come out in industry because of their lackof flammability and toxicity that comply with the restricted environmental legislation with respect to the emission of organic solvents to the atmosphere. waterborne polyurethane dispersions offer an efficient alternative to solvent-based polyurethane products.WPU are segmented copolymers that consist of alternating soft and hard segmentunits, with a minorityof repeat units carying ionic groups which neutralized or quatanized to form salts,or of nonionic hydrophilic segments.The flexible soft segment generally consists of polyether or polyester polyol,whereas rigid hard segments are usually formed by the extension of a diisocyanate with a chain extender of a low molecular weight polyolor amine.It is now generally accepted that the properties of WPU are primarily due to the phase behaviour of soft and hard segments as wel as ion character. This behaviour also depends on the content of crystallizability, length and polarity of soft and hard segment, intra and intersegment interactions such as hydrogen bonding,overall composition, and molecular weight.In this paper we choose especial structure,non-pollution and cheap of castor oil as polyol component of polyurethane.Waterborne polyurethane was prepared by the reaction of castor oil, dimethoxyPionic(DMPA) and diisocyanate.Based on the waterborne polyurethane we carried out the modification by cross chain reagent. Prepolymerization reactions were carried out in substantial amount of methyl edtyl ketone (MEK) to lower the viscosity and to aid the coalescing action for film formation.Several synthetic technologies were studied. The influence factors on the performance of a coationgs such as the mole radio of NCO and OH, DMPA%, neutralizing agent and neutralizing ratio and castor oil were discussed in detail. Furthetmore, neutralizing degree and the using amount of castor oil were also discussed.The test showed that the hardness and mechanical robustness of film of PU emulsion have been heightened when the initial mole rate of NCO/OH increases, but the appearance turns bad. Proper mole rate of NCO/ OH can endow PU emulsion with high hardness,good appearance and performances. the dispersions had excellent storage stability while the content of DMPA was more than 4.08%. However, the water resistance was harmed if the content of DMPA was too high. The viscosity of aqueous PU was affected by the content of DMPA, neutralization degree, and temperature. Average particle size became smaller while the content of DMPA increased. The appearance of emulsion and mechanical properties of film can be improved with increasing the content of DMPA properly, while excessive content of DMPA makes the emulsion bad water resistance and high water absorption. The appearance, stability and tensile shearing strength enhanced with the increase of neutralization degree, but water resistance and break extensibility decreased.IR spectrum of the cast film showed that carbon-carbon double bond and carbon-oxygen double bond existed between the hard segments and the soft segments, and crosslinking Structure was formed,which played a very important role on the mechanical properties.The mechanical properties and water resistance of WPU coating film were increased with addition of castor oil.Artificial the optimal method and technology of waterborne polyurethanecompounded exterior sports coating.The relationship between composition and performance of waterborne polyurethane compounded exterior sports coating are presented.It was found that at 1:1 molar ratio of castor oil to N 220,1. 4 molar ratio of NCO / OH ,5. 5 % DMPA content, the castor oil waterborne polyurethane had excellent filmforming property ,high hardness ,good resistances to water and petrol and excellent adhesion to base materials.And the waterborne polyurethane compounded exterior sports coating have excellent performance.