Preparation And Properties Research Of Solvent-free Castor Oil Coatings

Since 2017,severe environmental pressures and economic situation have led to the continuous rise of bulk raw material prices and the upgrading of corporate products.The overall cost of the coatings industry has risen rapidly in the short term.The total loss for the year reached 812 million yuan,a year-on-year increase of 6%.The coating industry is facing a more severe de-capacity situation.The development of low-cost,low-pollution products has become the development road of the coatings industry.Two-component polyurethane coating has occupied 25%of the coating market due to its excellent adhesion,impact resistance,wear resistance and mechanical properties,but more than 52%of the polyurethanes are solvent-based coatings,which is mainly because the viscosity of the hydroxyl component is relatively large,and it needs to be diluted with a large amount of organic solvent.As a low-viscosity,low-cost polyol,castor oil can be directly used in two-component polyurethanes.It can also be used to synthesize bio-based polyols by chemical modification using functional groups such as carbon-carbon double bonds and ester bonds.However,its activity is low.The curing time of the coating is long,and the mechanical properties are poor.In view of the advantages of two-component system coatings and the shortage of castor oil,two modified castor oil polyols were prepared by polycondensation and transesterification and a low-cost,low-pollution solvent-free castor oil coating was successfully developed.The main work summarized as follows:1.Using castor oil,glycerin and adipic acid as raw materials,castor oil modified polyester polyol,with a low viscosity was synthesized by two-step polymerization process.The film is prepared with a curing agent.The synthetic process of castor oil polyester polyol and the effect of alkyd molar on castor oil polyester polyol were studied.The results show that the comprehensive performance of the modified castor oil polyester polyol is obviously improved when the molar ratio of alkyd is 1.32,especially the impact resistance of the coating exceeds 100cm and the scratch resistance reaches 2kg.Compared with unmodified castor oil,it has doubled and the tensile strength has increased by 3 times.2.In order to improve the activity of castor oil,the castor oil alcoholysis was prepared by transesterification.The film was prepared with a curing agent.The effects of different catalysts on the alcoholysis degree of castor oil and the optimization of alcoholysis conditions were studied.The results show that the castor oil alcoholysis has good film forming properties.When the degree of alcoholysis of castor oil is higher,the viscosity of is lower,and the curing time is shorter.Among them,CaO-catalyzed transesterification of castor oil has the highest degree of alcoholysis.When the viscosity is 250 mPa·s,the curing time of the coating film is only 105 min.3.The castor oil polyester polyol and the alcoholysis castor oil are compounded as a hydroxyl component.The solvent-free castor oil resin was prepared with a curing agent.The curing kinetics of solvent-free castor oil resin was also discussed.The apparent activation energy of the reaction is 47.212 kJ/mol.The reaction order was 0.86.And the kinetic equation was:??t?=1-[1-2.65×10⁴exp?-5678.61/T?t]^7.14.Further,a solvent-free castor oil coating was prepared by optimizing titanium white powder,talc powder,fumed silica and auxiliary formulation.The solvent-free coating has good mechanical properties,of which tensile strength is up to 16.8Mpa,water resistance is up to 30 days,alkali resistance is up to 72h.The solvent-free castor oil coating prepared has low cost and excellent overall performance.