| Polyurethane (PU) is one class of polymers which contains repeating urethane groups in the structure. The macromolecular chains of PU contain a lot of polar bonds, so it is apt to form the hydrogen bonding between the PU chains which endows PU with the outstanding strength, abrasion resistance, water repellency, solvent resistance, low-temperature resistance and adhesive.With the inevitable trend of "low-carbon & environmental protection", the regulations and consumer demands are forcing polyurethane industries to develop environmentally friendly products, thus waterborne polyurethane (WPU) comes into being. WPU is a novel PU system dispersed into water instead of organic solvents, so it is a kind of environmentally friendly materials which combines the high performance of solvent-type PU with little or no volatile organic compounds (VOCs). Due to the existence of hydrophilic groups and their inherent defects in the structure, the application range of WPUs is limited. Consequently, many researchers have been devoting their work to modifing the WPUs. Usually, WPUs can be modified by acrylate, epoxy, organosilicone, fluorined compounds, vegetable oils and nano-particles.We had prepared the WPU modified by epoxy resins (E-51) and the non-ionic WPU modified by acrylate, respectively, based on the extensive literature research. The detailed research of this dissertation is composed of the following two parts:1. Preparation and properties of the WPU modified by epoxy resins (E-51) The anionic WPU was synthesized by the phase inversion method, using isophorone diisocyanate (IPDI), polytetramethylene glycol (PTMG), dimethyopropionic acid (DMPA) and diethylene glycol (DEG) as the main raw materials. The epoxy resins (E-51) modified by excess amine were added into the above WPU and stirred for the chain extension (30 min). Then the WPU emulsions modified by epoxy resins (E-51) were obtained. Compared with the unmodified WPU, the influence of the epoxy resins (E-51) content on the particle size, the viscosity, and the storage stability of the emulsions was studied. Meanwhile, the effect of the epoxy resins (E-51) content on the strength, the contact angle, the water absorption, the hardness and the thermal resistance of the WPU coatings was also investigated. The results indicated that:(1) It can be observed from TEM that the particles of the WPU and the epoxy modified WPU (EPU) presented a spherical structure. The particle size tests indicated that the average particle size was lower than 100 nm. Moreover, the average particle size of EPU became larger and the distribution of the particle size became broaden, with the increase of the epoxy resins (E-51) content.(2) The viscosity of the epoxy modified WPU emulsions was improved with the increase of the epoxy resins (E-51) content. However, the storage stability of the emulsions was deteriorative when the epoxy content was 8%.(3) The FTIR spectra suggested that the reaction between ethylenediamine and epoxy resins (E-51) was successfully performed and the FTIR spectra of the EPU displayed the characteristic absorption bands of the epoxy resins (E-51).(4) The tensile tests showed that the tensile strength of the EPU coatings was improved gradually while the elongation at break was reduced gradually as the epoxy resins (E-51) content increased.(5) The water absorption tests indicated that the incorporation of epoxy resins can decrease the water absorption of the EPU coatings obviously. Meanwhile, the contact angle of the EPU coatings became larger with the increase of the epoxy resins (E-51) content.(6) The TGA results showed that the addition of epoxy resins can enhance the thermal stability of the EPU coatings and the MCC results showed that the heat release rate of the EPU coatings was lowered with the increase of the epoxy resins (E-51) content, suggesting the improvement of the flame resistance.2. Preparation and properties of the WPU modified by acrylateThe procedure for fabricating the acrylate modified WPU was illustrated as follows:firstly, the NCO-terminated PU prepolymer was synthesized by isophorone diisocyanate (IPDI), polypropylene glycol (PPG, N-210) and polyethylene glycol (PEG); secondly, the 2-hydroxyethyl acrylate (HEA) was added into the NCO-terminated PU prepolymer as the end capping agent and then the non-ionic WPU modified by HEA (HPU) were prepared via phase inversion method; lastly, the methyl methacrylate (MMA) and the butyl acrylate (BA) monomers were incorporated into HPU by the thermally-initiated free radical polymerization. Thus, the non-ionic acrylate modified WPU emulsions (PUA) were obtained and characterized by the water resistance test, the particle size analyzer, the hardness test, the electron microscope, the thermogravimetric analyse (TGA) and the differential scanning calorimetry (DSC). The detailed research results of this part are listed as follows:(1) It can be observed from TEM that the particles in the HPU emulsions presented a spherical structure, while their counterparts in the PUA and PA emulsions displayed a core-shell structure. The particle size tests indicated that the average particle size was lower than 100 nm. Moreover, the average particle size of PUA became larger and the distribution of the particle size became broaden, with the increase of the HPU content.(2) The viscosity of the PUA emulsions was improved with the increase of the HPU content. However, the water resistance and the hardness exhibited the opposite trend.(3) The FTIR spectra indicated that the end capping reactions between PU prepolymer and HEA were performed thoroughly at 70℃for 3 h when the HEA addition was 120% of the theoretical value. The FTIR spectra of the PUA displayed the characteristic absorption bands of the HPU and PA.(4) The TGA results showed that the thermal stability of the PUA coatings was improved compared with the HPU, and inceased gradually with the increase of the acrylate monomer content. The DSC data indicated that the glass transition temperature (Tg) of the PUA coatings was increased with the increase of the acrylate monomer content. |
PDF Full Text Request