Study On The Preparation And Property Of Waterborne Polyurethane Resin Applied In Wood Paint Materials

Several types of isocyanates and polyols are selected to prepare series of polyurethane (PU) resin by using the chain-extender dimethyl propionic acid (DMPA) with hydrophilicity and external crosslinking agent as modifier according to the internal emulsion method. The isocyanates used in the process include toluene diisocyanate (TDI), 1,6-hexamethylene diisocyanate (HDI) and IPDI. The polyols used include polyethers as polytetrahydrofuran (PTMG), water-resistant polyesters as polyhexamethylene adipate glycol (PHA), polyneopentylene adipate glycol (PNA) and polycaprolactone glycol (PCL). The chain-extender and crosslinking agent used include 1,4-butanediol, hexanol and TMP. The structure of waterborne PU emulsion is analyzed by IR; relationship between the particle size of emulsion and stability was studied by transmission electron microscopy (TEM); the low-temperature properties of emulsion cast film was studied by the differential scanning calorimetry (DSC); the heat-resistant properties of emulsion cast film also studied by TG; the crystallinity of the emulsion cast film is analyzed by X-ray diffraction; the relationship between the mechanical property, solvent resistance, adhesion, abrasion resistance and impact resistance of the emulsion cast film and the structure of molecular chain are investigated as well. The waterborne PU resin with best property is prepared as the film former applied in wood paint.The results shown that the stability of the PU emulsion, besides increasing with the content of DMPA, is also related to the mole ratio of NCO/OH, therefore the stabile PU emulsion can be prepared with optimal ratio of NCO/OH . The PU emulsion cast film prepared from PHA(Mn =2000) shown obvious crystallinity and tensile strength. Water-resistance, solvent-resistance, adhesion, abrasion and impact-resistance of this kind of film are better than its counterpart prepared from PNA and PTMG. The comprehensive properties of PU emulsion cast film can be obviously increased by combination of appropriate internal crosslinking (e.g. TMP) and external crosslinking (e.g. polyaziridine). The hardness and tensile strength of this kind of film can reach 95 (Shao A) and 45.90 MPa, respectively. Also it showed a excellent water resistance (water, ethanol absorption ratio is nearly 0% and 2%) and adhesion, abrasion-resistance and impact resistance.