Dynamic Rheological Properties Of The Pvb Film Material

Dynamic rheological properties of the membrane materials have important effect on the processability and final properties of the products for the preparation of poly (vinyl butyral) (PVB) hollow fiber membranes via thermally induced phase separation (TIPS). The influence of composition, temperature and shear frequency on the rheological properties of PVB/ Polyethylene glycol (PEG) and PVB/Pluonic F127/ PEG blend systems were investigated by a rotational rheometer.Shear thinning behavior is observed in the two blend systems. The complex viscosities increase with mass fraction of PVB or Pluronic F127 enhanced and decrease with temperature increased at low-frequency region, however, the mass fraction of PVB or Pluronic F127 and temperature have little influence on the complex viscosity at high-frequency region. These results show that viscosities of the blend systems are becoming less sensitive to temperature as the frequency increases. The complex viscosity can be fitted by Power-low model and Cross model, and the later fits better. It can be observed via non-Newtonian exponent that the non-Newtonian behavior enhances with the increase mass fraction of PVB Pluronic F127 and weakens with the increase of temperature, while effect of PEG molecular weight on complex viscosities and non-Newtonian behavior is not obvious.Dynamic storage modulus and loss modulus of the two blend systems cross at a certain frequency. And both of them increase with the increase of PVB or Pluronic F127 mass fraction and frequency, increase with the decrease of temperature. Viscous component dominates while frequency is below crossing point and elasticity component becomes a dominating factor while frequency is above it. The crossing point moves to the higher frequency as the temperature increases. The tan delta (G" /G'), which quantifies the balance of the loss and elastic properties, decreases as the fraction of PVB or Pluronic F127 increases. This tends to suggest that the flow recovery of the blend systems increase with the increase of PVB or Pluronic F127. The two blend systems show upper critical solution temperature (UCST) behavior. The blend systems show a typical terminal behavior in homogeneous region, on the other hand, the storage modulus deviate from classical terminal behavior at low frequencies in phase-separated region. In contrast to the storage modulus, the loss modulus show insensitive to phase separation. Dynamic temperature test shows that the phase separation temperature of the PVB/PEG200 blend system is about 144.5℃, while the time-temperature superposition (tTS) principle and Han plots detect the phase separation temperature of the PVB/F127/ PEG200 blend system is smaller than 140℃.