Preparation Of Castor Oil-based Waterborne Polyurethane And Its Application In Paper Surface Enhancing

Nowadays, with the fast development of printing industry, paper should have better surfaceproperties, especially surface bonding strength. It prompts the study and application of newpaper surface enhancing agent. Waterborne polyurethane has excellent performance and it isenvironmental friendly. Used for paper surface sizing agent, it can greatly improve papersurface property in low consumption, especially improve printing surface strength and makepaper to meet the needs of modern high-speed development of printing and so on. In order tomake the preparation of polyurethane to wean itself off dependence on oil resources, naturalrenewable castor oil is used as raw materials to replace the traditional oil type polyols toproduce polyurethane, and to provide crosslinking structure for polymer at the same time.In this research, a castor oil-based waterborne polyurethane was synthesized by a “inneremulsification” method using toluene diisocyanate (TDI), castor oil (C.O.), dimethylolpropionic acid (DMPA), triethyl amine (TEA) and distilled water. The polymer had a certaincrosslinking degree. The emulsion performance and the film performance were investigatedby the Fourier infrared spectrometer (FT-IR), MaErWen particle analyzer and universal tensiletest machine. The influence of dosage of acetone on reaction system in reaction process wasdiscussed. The effect of mole ratio of TDI to C.O., prepolymerization temperature and dosageof close water extender chain agent on emulsion properties was mainly investigated, includingpreploymer appearance, emulsion appearance, emulsion storage ability, emulsion particle size,water absorption of film, mechanical property of film, such as tensile strength and elongationat break. When mole ratio of TDI to C.O. was3.0, prepolymerization temperature was75℃,dosage of DMPA was11.4%-12.1%, the reaction took place smoothly and the preparedpolyurethane emulsion had good properties.The prepared polyurethane emulsion was applied in surface sizing electrostatic copy paper.It was found that product had excellent film forming property on paper surface through theobservation of SEM. By measuring picking speed, prinking ink absorption value, PPS value,Cobb value and other physical strength, the influence of mole ratio of TDI to C.O.,prepolymerization temperature and dosage of close water extender chain agent on surface enhancing results of electrostatic copy paper was investigated. Picking speed of paper surfacesized by this emulsion was increased from0.81m/s to2.86m/s, compared to base paper. Itshowed a good surface enhancing effect. Compared to base paper, printing ink absorptionvalue had fallen to a certain extent, but in the reasonable scope. PPS value had also fallen to acertain extent. When dosage of DMPA was10.7%-12.8%,60sCobb value was below30g/m2.Tensile strength, bursting strength, tear strength and folding strength of paper surface sized bythis emulsion were improved to varying degrees compared to base paper. Through theapplication, it was further verified that paper surface sized by product had better surfaceenhancing effect when mole ratio of TDI to C.O. was3.0, prepolymerization temperature was75℃, dosage of DMPA was12.1%.