Film casting is one of the important processes for obtaining the plastic film products. Molten polymer casting is conducted by cooling the extruded melts at the surface of chill roller laid below the extrusion dies. Flow instabilities in the film casting are divided into two categories. One is the shear flow instability and the other is the extensional flow instability. These instabilities are similar to those appearing in the melt spinning process. Among many parameters governing shear flow instability, shear rate and Deborah number defined as the ratio of polymer relaxation time to retention time in the land of dies or spinneret orifice are likely to be most important. The small value of Deborah number is found to be effective for depressing the shear flow instability. Regarding the extensional flow instability, draw resonance phenomena were summarized and discussed. Polymer parameters such as power low index in the power low fluid model and relaxation time in Maxwell fluid model were found to be important for onset of draw resonance instability. As process parameters, cooling effect of extruded melts, draft ratio defined as elongation ratio of melts and air gap length corresponding the distance from dies exit to chill roller were also important. Further study on transient response of disturbances having various frequencies was done. It was found that film thickness uniformity changed depending on disturbance frequency.
We have investigated structural rearrangement of an aqueous solution of hydroxypropylecellose (HPC) caused in a transient Couette flow between two parallel plates. After a pre-shear flow, a subsequent flow starts with a different direction. The flow induced structural changes were examined with the SALS (Small Angle Light Scattering) method and measurements of the dichroism and orientation angle. We have tested 9 patterns of flow direction change from acute to obtuse angle. After several strains in the subsequent flow, a streak obtained in the SALS method became clear and sharp, and then its direction was gradually turned to the final one. A corresponding peak and gradual change of the dichroism was obtained. A periodic isotropic scattering light was simultaneously observed in the SALS experiment and the damping oscillation in orientation angle was also measured. It is considered that the former shows the rearrangement of the flow structure includes a collapse and reconstruction of a macro structure and the latter means the synchronized tumbling motion was generated in this procedure.
The effect of hydrophilic head of drag reducing cationic surfactants on the micellar structures has been studied by using fluorescence probe technique. Sodium 3-hydroxy-2-naphthoate, NaHN, has been used as a fluorescence probe in these experiments. Four types of surfactants having the same alkyl chain but different in number of hydroxyethyl, HE, group changed from 0 to 3 have been tested. A method of calculating the molar ratio of free counter-ions is suggested with the fluorescence decay behavior of counter-ion. From the results, it is found that the lifetime of fluorescence decay in micellar interior phase decreases while the molar fraction of free counter-ion increases when the HE group number increases. It is also found from the results on the molar ratio of free counter-ions and the comparison of Stokes diameters that the decrease of the critical Reynolds number is related to the number density of micellar structures and its strength.
The nanosized magnetite particles were synthesized by means of a coprecipitation method and used to prepare the aqueous ferrofluids with various volume fractions. The magnetorheological properties of the aqueous ferrofluids have been investigated as a function of magnetic field. Under steady-state shear, the apparent viscosity for all of the ferrofluids exhibited a shear thinning behavior. But the Bingham model was invalid since the ferrofluids did not show a yield stress before they began to flow. However, the shear stress increased linearly with shear rate after a critical shear rate, showing a Bingham-like behavior. A Bingham-like yield stress, which was obtained by extrapolating the shear stress to the zero shear rate, increased with both the volume fraction of magnetic particles and the strength of magnetic field. The Bingham-like viscosity was approximately independent of the magnetic field at a given volume fraction of magnetic particles, but increased with the volume fraction under a given magnetic field. In the strain sweep experiment at an angular frequency of 10 rad/s, a transition from a gel-like state to a sol-like state was observed and a chain model has been proposed to qualitatively explain the mechanism of the transition. From the frequency sweep tests, it was found that there existed a plateau of storage modulus G′, which was independent of frequency but dependent on the volume fraction. A scaling law has been proposed to correlate the G′ plateau with the volume fraction.
Mesoporous silica(MPS) particles are synthesized in the presence of templates of surfactant micelles and the doping treatments are carried out to form copper phthalocyanine(CuPh)-doped MPS. The rheological properties of suspensions of CuPh-doped MPS particles dispersed in a silicone oil are studied on the application of DC electric fields. The electrorheological(ER) effect of CuPh suspensions is very weak, although the CuPh compounds are well known as semiconducting materials and widely used in industries. However, the doping of CuPh into MPS causes a drastic increase in ER effect and conductivity of suspensions. It is generally accepted that the interparticle forces generated in electric fields are polarization forces due to the dielectric mismatch between the particles and continuous liquid phases. In some cases, the surface conduction of thin layers on the particles can play an important role in promoting the ER effect. The increase in surface conduction by doped CuPh on the MPS may be responsible for enhancement of ER effect. The doping of semiconducting materials into mesoporous particles provides a new formulation method of excellent ER particles.
Velocity profiles of polymer solutions were directly measured in a microchannel with rectangular cross sections. The test fluids are 0.2 wt% aqueous solutions of polyacrylamide whose molecular weights are 6 × 106 (fluid A) and 1.5 × 107 (fluid B). The microchannel was made of PDMS and it was mounted on the glass plate. The velocity profile in the depth direction is discussed as a function of the flow rate and shear stress on the wall. Consequently, for the flows of fluid A, a symmetric profile is observed in the region between the PDMS wall and the glass wall in a low flow rate, but the velocity profile slightly becomes asymmetric with increasing flow rate: the velocity near the PDMS wall is larger than that near the glass wall. For the flows of fluid B, a slightly asymmetric profile is observed even in the low flow rate and a largely asymmetric one in the large flow rate. The PDMS wall significantly affects the velocity profile in the flow of polymer solution through a PDMS microchannel.
Effects of cell destruction on thermal resistance in foamed plastics were studied by time dependence of dynamic compression modulus of four closed-cell polyethylene based foams at temperatures under load. Logarithm of time t50%, at which the dynamic compression modulus came to be 50% of its initial value has been found to be a linear function of reciprocal of the absolute temperature, T−1, in all foams before destruction of cell and in two PE foams after destruction of cell. Because of decrease of the resistance against the internal pressure of the cells by cell destruction, the amount of initial decrease of dynamic compression modulus increases. However, the temperature at which dynamic compression modulus starts to decrease rose with cell destruction, and thermal resistance was improved.