Preparation Of Waterborne Polyurethane From Waste PET And Its Modification By Epoxy

PET polyester material has been widely used as packaging material because of its excellent properties such as light weight, easy processing, high transparency, dimensional stability etc. However, waste PET not only causes pollution, but also waste resources. In this paper, ethylene glycol was choosed as the solvent to degrade the PET widely used in mineral water bottles. Then, the degradation products were used to prepare environment-friendly polymer materials-waterborne polyurethane(WPU). Not only reducing the pressure on the environment, this method can be applied to help cyclic economy as well. Epoxy resin E-44 was employed to modified waterborne polyurethane to improve the overall performance, and the epoxy-modified waterborne polyurethane material was prepared successfully with good stability and excellent performance.Waste PET was depolymerized by ethylene glycol(EG) with zinc acetate as catalyst. The optimum conditions for the degradation process were studied. When the reaction temperature is about 196 ?, the mass ratio of EG and PET is 3, the reaction time is 3 hours, and the mass ratio of zinc acetate to PET is 0.2%, PET is substantially completely degraded and the yield reachs the maximum,97%. The glycolyzed product was characterized by hydroxyl value determination, Fourier transforms infrared spectroscopy, Nuclear magnetic resonance and Thermogravimetric analysis. The results show that bis-2-hydroxyethyl terephthalate(BHET) monomer and its oligomers are predominant glycolysis products.A series of aqueous polyurethane emulsion were prepared through prepolymer dispersion method using isophorone diisocyanate(IPDI) and PET degradation products as the main raw material, dimethylol propionic acid(DMPA) as the hydrophilic chain extender, 1,4-butanediol(BDO) as the small molecule chain extender, trimethylol propane(TMP)as the internal-crosslinking agent, triethylamine(TEA)as the neutralizing agent.The effects of initial n(NCO)/n(OH) value, isocyanato Index(R), the content of DMPA and TMP, the neutralization degree on the performance of waterborne polyurethane emulsion and film were studied. The results show that the waterborne polyurethane exhibited the best performance when the initial n(NCO)/n(OH) was 4.0, isocyanato index of 1.3-1.4, the content of DMPA was 5 wt% and the TMP content was 3 wt%(with respect to the prepolymer weight), the neutralization degree was 90%-100%. Under the condition, the average particle size of WPU emulsion was 36 nm, and the viscosity was 65 mPa.s. The tensile strength of WPU film was 3.2 MPa, pencil hardness was H, and adhesion was 0 grade. The structure and thermal stability of the product was characterized by Fourier transforms infrared spectroscopy, thermogravimetric and differential scanning calorimetry analysis.In order to improve the performance of waterborne polyurethane, epoxy resin E-44 was used to prepare the epoxy-modified waterborne polyurethane(PUE). The influence of adding modality and adding dosage of E-44 on the performance of modified waterborne polyurethane were discussed.The results show that water resistance, hardness and tensile strength of the film were significantly improved after it was modified by E-44. Epoxy resin was added at the chain extension stage, with the appropriate amount of 6% to 8%. Under the optimum condition, the average particle size of PUE emulsion was 50 nm, the viscosity was 44 mPa.s; the tensile strength of PUE film was 6.4 MPa, water absorption(24 h) decreased to 7%, the pencil hardness was 3H and adhesion was 1 grade. Epoxy-modified polyurethane emulsion show good appearance, storage stability and moderate viscosity, the mechanical strength and thermal stability of the film were improved significantly.