Study On The Waterborne Polyurethane Modified By Organosilicon

Waterborne polyurethane(WPU)is a dispersible polymer in water medium.WPU possess characteristic such as good mechanical capability, high adhesion strength,good flexibility,noncombustible,non-pollution, easy processing,so it is regarded as a kind of green and environment-friendly materials and widely used in many industries nowadays.However,WPU has poor the water resistance and solvent resistance,so it has to be chemically modified for its application. Polysiloxanes,with good low-temperature flexibility,thermal stability, weather resistance and excellent water resistance and good performance, could be used to modify WPU.Hydroxyalkyl terminated polysiloxanes were generally used to modify WPU.However,due to the formation of the Si-O-C bond in modification of WPU with these polysiloxanes,the material has poor hydrolysis resistance performance.When hydroxyalkyl terminated polysiloxanes are used to modify WPU,hydrolysis resistance performance can be reached because of the Si-C-O bond formation. Therefore,in the thesis,dihydroxyalkyl-terminated polysiloxanes are used to modify the WPU,and anionic acid type WPU was synthesized.At the same time,the properties of WPU were also explored.Tetramethyltetraethylcyclotetrasiloxane was prepared through reactions between bromoethane and methyltriethoxysilane.Meanwhile,a series of dihydroxypropyl-terminated polysiloxanes(PEMS-OH),with molecular weight below 8000,are prepared using allyl alcohol, tetramethyldisiloxane and tetramethyltetraethylcyclotetrasiloxane.The final and intermediate products in each process of PEMS-OH preparations were fully characterized by the FT-IR and NMR spectra.The molecular weights of PEMS-OH were estimated by end-group analysis and ~1HNMR respectively.Good agreements between the theoretical molecular weights and those obtained from end-group analysis and ~1HNMR are obtained.The anionic WPU modified with PEMS-OH were prepared from toluene diisocyanate,polypropylene glycol,PEMS-OH, dimethylolpropionic acid,ethylene glycol,glycerol,and triethylamine through acetone method.Experiment was implemented by the gradual addition method.First PEMS-OH and TDI were added to the flask to react. After a period of time,the PPG and other components were put into the flask in form.The target product was investigated by transmission electron microscope(TEM).When the molecular weight of PEMS-OH was higher than 4000 and the content is above 8%,rod shaped aggregates were observed.In the rest of the experiments,spherical or spheroid aggregates were found.The results of the size and the size distribution of particles show that the mean particle diameter of WPU and PSU is about between 400 nm and 500 nm.The distribution of most of particle size is relatively concentrated,however,micron sized large particles were also detected. The morphologies of fractured section of PSU films are observed using scanning electron microscope(SEM).The results show that phase separation in PSU films increases with the increase in PEMS-OH content and its molecular weight,and polysiloxane enriches in PSU film surface. Mechanical property tests show that better performance can be obtained when the molecular weight of PEMS-OH is between 2000 and 4000 and its content at 4%.Water and solvent resistant properties test show that the material has better water-resistant performance when the molecular weight of PEMS-OH is 4000 and its content at 8%,while the better solvent-resistant performance appears when the molecular weight of PEMS-OH is 2000 and its content at 8%.Thermal gravimetric analyses (TG)indicate that the material has better heat-resistant performance when the molecular weight of PEMS-OH is about 2000 and its content at 4%. Polysiloxane and PU have the poor compatibility.When the phase separation reaches a certain level,its water-resistance,and mechanical properties are in an optimum value.As the phase separation continues to increase,the performance deteriorated.The PSU belongs to monocomponent WPU emulsion.Compared with WPU film,PSU film has the better water resistance,solvent resistance and mechanical properties.Own to these high-performances,PSU emulsion can be widely applied in painting,coating,leather finishing agent,fabric finishing agent,etc.