Study On Synthesis And Performance Of Stearic Acid Type Polyurethane Coatings

As an important component of polyurethane coatings,curing agent had great influence on the mechanical properties,thermal resistance,water resistance and corrosion resistance of coatings.So it had important research significance.In the present society,the pursuit of sustainable development of green and environmental protection had become the research direction by the petroleum scarcity and the increasing environmental concerns.Based on the research direction,using biomass itaconic acid?IA?and natural vegetable oil-linoleic acid?LA?as the raw material which could substituted for some petroleum based polymers.Stearic acid type polyurethane curing agent and unsaturated polyester were prepared by hydroxylation and esterification polycondensation reaction,which applied to two component polyurethane coatings.Finally,coatings performance was further studied.9,10,12,13-four hydroxy stearic acid?THSA?was prepared with LA and formic acid by oxidative hydrolysis of H₂O₂,which further reacted with isocyanate.Stearic acid type curing agents?THSA-TDI curing agents and THSA-HDI curing agents?were successfully synthesized by this reaction.The effects of reaction time and temperature,mole ratio of raw materials and isocyanate type on the NCO content,viscosity and thermal properties of the curing agent were investigated.And the structures of two kinds of curing agents were characterized by FT-IR.Suitable reaction conditions of THSA-TDI curing agents:under N₂ atmosphere,n_TDI:n _THSA=2.5:1,TDI was slowly added at 50°C for 1 h,and then heated to 70°C for 2 h,and sealed and preserved after cooling.Similarly,suitable reaction conditions of THSA-HDI curing agents:under N₂ atmosphere,n_HDI:n _THSA=2:1,HDI was slowly added at 50°C for 1 h,and then heated to 70°C for 2 h,and sealed and preserved after cooling.Comparing the performance of THSA-TDI curing agents with THSA-HDI curing agents that included the NCO content,viscosity,solid content,storage time,color and stateand and thermal properties.The results showed that THSA-TDI curing agents had low NCO content,high viscosity,yellowing,limited heat resistance,short storage time.And THSA-HDI curing agent had relatively higher NCO content,low viscosity,not yellowing,strong heat resistance,longer storage time.Through esterification and polycondensation reaction of mixed dibasic acid and dihydric alcohol,hydroxyl terminated poly?ethanediol itaconate succinate??PEIS?was synthesized by IA,succinic acid?SA?and ethylene glycol?EG?.And PEIS crude product was purified by methanol-water solvent extraction.By studying esterification temperature and time,polycondensation temperature,catalyst and the mole ratio of diacid,the most suitable synthetic conditions were obtained:n _IA:n_SA:n_EG=2:1:3.75,P-toluene sulfonic acid was catalyst and hydroquinone was inhibitor,esterification temperature was 140°C for 7h with N₂,polycondensation temperature was 170°C for 4 h under the vacuum degree of0.1 MPa.The structure of product was assessed by FT-IR and ¹H-NMR,and the molecular weight of product was determined by GPC,and the thermal properties of product was analyzed by TG.Under this synthetic condition,the acid value and hydroxyl value of PEIS were 21.5 mgKOH·g^-1 and 87.68 mgKOH·g^-1,and dense distribution of number-average molecular weight was 2067,and the heat resistance was also obviously improved.Stearic acid type polyurethane curing agents were applied to the preparation of coatings.The coating mixed curing agents with homemade PEIS and industrial DL2000D to form film at room temperature.The effects of the NCO/OH molar ratio of two components on the mechanical and thermal properties of the film were investigated,and the apparent morphology was observed by SEM analysis.The conclusions were as follow:mixing PEIS with THSA-TDI curing agents existed deficiencies of shrinkage,and mixing DL2000D with THSA-HDI curing agents were not appropriate for application because of slow drying.Mixing PEIS and THSA-HDI curing agents?PEIS-PU?and mixing DL2000D and THSA-TDI curing agents?DL2000D-PU?exhibited excellent performances.PEIS-PU and DL2000D-PU had better mechanical properties.The results showed that:with the decrease of NCO/OH mole ratio of the two coatings,the drying time gradually prolonged,the hardness decreased,the impact strength first increased and then remained stable,the tensile strength decreased and the elongation at break increased.SEM analysis showed that the two components had good miscibility and compacted with the structure.The thermal properties showed that the heat resistance of PEIS-PU was better than DL2000D-PU,however DL2000D-PU had better cold resistance.