Study On Synthesis Technology Of Castor Oil-based Waterborne Polyurethane And Its UV Curing And Hybrid Modification

Castor oil-based waterborne polyurethane(CWPU)is an eco-friendly polymeric material with many advantages such as wide source of raw materials,renewability,biodegradability,good biocompatibility and low VOCs emission.Recently,as the environmental protection policies are increasingly strict,CWPU has rapidly turn into the focus of the coatings.However,the introductions of long fatty acid moieties of castor oil and hydrophilic emulsifiers result in unsatisfactory mechanical properties and water resistance,limiting their wider applications.Therefore,it makes great sense to develop a method for preparation of CWPU with high castor oil content,excellent water resistance and mechanical properties.In this paper,CWPU was prepared by taking castor oil as polyol.The synthetic process improved by researching the effects of feeding modes,dimethylol propionic acid(DMPA)content,n(-OH)/n(-NCO)value and castor oil content on the properties of material.Furthermore,in order to prepare CWPU with high castor oil content,excellent water resistance and mechanical properties,the UV curable SiO2/CWPU shell-core hybrid system was fabricated.The effects of UV curing and ratios of y-MPS/TEOS on properties of conventional CWPU and UV curable CWPU were researched,respectively,and the best preparation method was obtained.Through data analysis,several conclusions were obtained and shown as follows:(1)For preparation of stable emulsions,fractional step method is better than one-pot method.Taking fractional step method,the reasonable formula for preparation of CWPU was as follows:the content of DMPA,n(-OH)/n(-NCO)value and the content of castor oil were 5～7 wt%,0.91 and 42.5～50 wt%,respectively.(2)After CWPU was modified by UV curing,the water absorption and elongation at break decreased from 436.7%and 324.1%to 21.1%and 276.4%,respectively,while pencil hardness and young’s modulus increased from B and 49.2 MPa to HB and 211.4 MPa.In addition,for UV curable CWPU,when the DMPA content increased from 5 to 7 wt%,the flexibility of resin significantly decreased.Therefore,the UV curable CWPU with 5 wt%DMPA content had the best comprehensive performance.(3)The fabrication of UV curable SiO2/CWPU shell-core hybrid structure improved the water resistance and mechanical properties of UV curable CWPU with high castor oil.As the ratio of γ-MPS:TEOS increased from 0:1 to 1:0,the water absorption and elongation at break decreased from 11.7%and 227.4%to 7.9%and 83.9%,respectively,while the tensile strength,young’s modulus and pencil hardness increased from 12.5 MPa,178.6 MPa and HB to 18.9 MPa,487.8 MPa and 3H,respectively.Therefore,the F-S2 sample with 1:0 of ratio of y-MPS:TEOS has the best comprehensive performance and the corresponding formula is the best suitable synthetic formula.To sum up,the UV curable SiO2/CWPU shell-core hybrid coatings were successfully prepared in this paper.These coatings have many advantages such as high castor oil content,good emulsion stability as well as outstanding water resistance and mechanical properties and can act as excellent wood coatings.It is also expected that the coatings prepared by the method of this paper can be applied to high-added products in the future.