Solvent-free/self-catalyst Synthesis Bio-based Internal Emulsifier And Its Application In Waterborne Polyurethane

Polyurethanes(PUs) are among the most versatile polymers and have been widely used in various applications.However,conventional PU products usually contain large amounts of organic solvents,which is hazardous to human health and the environment.Increasing concern with the emission of volatile organic compounds(VOCs)and hazardous air pollutants(HAPs)has led to strong interest in the development of waterborne PU products.Waterborne PUs are environmentally friendly and exhibit exceptional performance.Generally,polyurethanes,formed by step-growth polymerization of di-isocyanates with polyols,are hydrophobic.Therefore,the use of emulsifiers is necessary in order to disperse the polymers in water.Dimethylolpropionic acid(DMPA)and dimethylolbutanoic acid(DMBA)are two internal emulsifiers that have been widely used as hydrophilic chain extenders in the synthesis of anionic PUDs.However,the use of these two internal emulsifiers leads to some drawbacks.For instance,the high melting point and their low solubility leads to the heavy use of toxic solvents during the synthesis of PUDs;the different reactivates of hydroxyl groups from these two reactants,in comparison with other polyols,toward isocyanates lead to an uneven distribution of carboxylic acid groups throughout the PU backbone,resulting in poor stability and performance.Therefore,the development of liquefiable emulsifiers with compatible reactivity with polyols has attracted much attention.It is said that some liquefiable emulsifiers have been.However,the syntheses of the above emulsifiers involve the use of large amounts of organic solvents,which increases both process cost and environmental burden.In addition,most starting materials utilized are derived from petroleum feedstock,so the bio-content of the waterborne PUD system is limited.With increasing environmental concerns and rapid depletion of petroleum feedstock,the utilization of renewable resources for the synthesis of chemicals to replace their petroleum-based counterparts has attracted much attention from industry and academia.This paper mainly studies from the following three aspects:(1)A novel,fully bio-based emulsifier has been successfully prepared from epoxidized soybean oil and glutaric acid through a solvent-free and self-catalysis method.The effects of reaction time and carboxyl: epoxy molar ratios on the structures of the emulsifier were systematically investigated.It is found that the reaction time of 90 min and the molar ratio of epoxy groups to glutaric acid of 4: 1 are optimized reaction conditions.This novel emulsifier exhibits similar properties to those of DMPA and DMBA,in which hydroxyl groups serve as cross-linking agents and the carboxylic acid group acts as an ionic segment.In addition,a similar method was used to synthesize two other emulsifiers from epoxidized soybean oil and adipic acid,epoxidized soybean oil and pimelic acid.The results showed that as the length of carbon chain of the natural dicarboxylic acid increases,the acid number and hydroxyl number of the corresponding emulsifiers reduced.(2)In order to validate the robustness of this emulsifier,a series of anionic,waterborne polyurethane dispersions were prepared from typical polyols(vegetable oil-and petroleum-based).The structure of this emulsifier and its good compatibility with bio-based polyols confer the resulting dispersions excellent storage stability and high solid content(up to 45%).The prepared waterborne polyurethane films exhibited higher toughness and thermal stability than traditional solvent-based polyurethane films and waterborne polyurethane films prepared from DMPA and DMBA.Moreover,a high biobased content of up to 74% was achieved for the prepared polyurethanes.This new environmentally friendly,liquid emulsifier,prepared using a solvent-free and self-catalysis synthetic route,can potentially replace typical petroleum-based emulsifiers for the production of waterborne polyurethanes.(3)In this study,emulsifier from adipic acid and emulsifier from pimelic acid were employed to synthesize a series of the castor oil-based PUDs.The effects of these two emulsifier and their contents on the properties of the PUDs as well as their films were investigated systematically.The results show that as the emulsifiers contents increase,the particle size decrease;the absolute value of zeta potential of the PUDs,thermal stability and hydrophilic increase.The PUDs from emulsifier based on adipic acid exhibit smaller particle size than those from emulsifier based on pimelic acid,while the films from theformer show higher thermal stability and hydrophilic.In addition,the bio-based content of anionic PUD in this work was up to 77.7%,and the pressure-sensitive adhesive of PU was tested,which shear resistance is more 100 h,which provided a new idea for its use as a waterborne polyurethane pressure-sensitive adhesive.