Application of Polymer Rheology in Melt Blowing Process and Online Rheological Sensor

Polymer rheology plays a significant role in many polymer-processing operations such as polymer extrusion, fiber spinning, and nonwovens processing. To develop real time, online process and quality control system in these operations, knowledge of polymer rheology and how the rheological properties can be determined is crucial. In this work, rheological properties of two melt blowing grades polypropylene (PP) under different processing conditions were determined by various off line methods, which includes dynamic rheological properties, shear and elongational viscosities. The elongational viscosity was measured at different Hencky strain by using semi-hyperbolic dies developed in this research group. Good master curves were generated for the temperature and Hencky strain shifting, and simultaneous shifting with respect to both temperature and Hencky strain. Carreau and Cross-rheological models were used to fit the rheological properties to generate different functions that were used to calculate the viscosity at different processing during typical melt blowing process conditions. The correlation between the melt blowing processing condition and the properties of final nonwoven products were achieved by introducing dimensionless numbers, such as air Reynolds number, polymer Reynolds number and Hencky strain. A high resolution IR camera was used to capture thermographs during the melt blowing process. From these thermographs, a plateau or shoulder was evident in thermographs taken during fiber drawn down by high velocity air. This represented the crystallization of polypropylene during the melt blowing process, assuming that fiber attenuation cease at the point of crystallization, which is a fundamental problem during the melt blowing process. It was found that the polymer degraded to a small extent during the melt blowing process, the degree being dependent on the processing variables such as melt temperatures, airflow rate and throughput. The rheological properties of PPs were used to determine the molecular weight and molecular weight distribution based on Mead’s approach. The technique for measuring shear and elongational viscosities in the laboratory was used as the basis for an online rheological sensor to measure the shear and elongational viscosities simultaneously online in a twin-screw extruder by drawing a small amount of polymer melt from the main processing stream. A laptop with software based on Labview and instruments bridged by an OPC server for MODBUS communication protocol through RS485 serial interface were configured for the control and measurement

Exploring the College EFL Self-access Writing Mode Based on Automated Feedback

The present study is intended to construct a college EFL self-access writing mode based on automated feedback under the guidance of Formative Assessment Theory and Autonomous Learning Theory and attempts to apply it into college EFL teaching practice. Findings of this empirical-based study suggest that this self-access writing mode contributes to the enhancement of students’ English writing competence, English writing motivation as well as their autonomy in self-revision

Novel ensemble algorithms for random two-domain parabolic problems

In this paper, three efficient ensemble algorithms are proposed for fast-solving the random fluid-fluid interaction model. Such a model can be simplified as coupling two heat equations with random diffusion coefficients and a friction parameter due to its complexity and uncertainty. We utilize the Monte Carlo method for the coupled model with random inputs to derive some deterministic fluid-fluid numerical models and use the ensemble idea to realize the fast computation of multiple problems. Our remarkable feature of these algorithms is employing the same coefficient matrix for multiple linear systems, significantly reducing the computational cost. By data-passing partitioned techniques, we can decouple the numerical models into two smaller sub-domain problems and achieve parallel computation. Theoretically, we derive that both algorithms are unconditionally stable and convergent. Finally, numerical experiments are conducted not only to support the theoretical results but also to validate the exclusive feature of the proposed algorithms

Passive Wireless Surface Acoustic Wave CO2 Sensor with Carbon Nanotube Polymer Nanocomposite

Geological sequestration, where the CO2 generated from power plants was collected and dumped into the mines and oil fields deep under ground, has attracted lots of attention. There is urgent need for developing a sophisticated system that can monitor the ground leakage in those remote sequestration sites. Surface acoustic wave sensor equipped with on-chip sensitive layer is the best choice for low cost wireless monitoring of sequestration sites leakage monitoring with minimum power consumption. A passive wireless CO2 sensing system based on surface acoustic wave technology and carbon nanotube nanocomposite was developed. Surface acoustic wave device was studied to determine the optimum sensor operation parameters. Delay line structure was adopted. A surface acoustic wave flow sensor was developed and showed linear relationship between the applied pressure and the change of the acoustic wave transmission time. Percolation studied showed that the CNT began to form a network at concentration over 1wt%. CNT polymer nanocomposite was then fabricated and tested under different temperature and strain condition for natural environment impact evaluation. Nanocomposite resistance increased for 5 times under pure strain with the thermal coefficient of nanocomposite at 75ppm/℃, while the temperature dependence of resistance for CNT solely was -0.1375%/℃. The overall effect of temperature on nanocomposite resistance was -0.1%/℃. Test of polyimide based nanocomposite showed less than 0.4% resistance increase over pure CO2, which corresponded to about 0.001% frequency change. Polyethyleneimine instead of polyimide was used to construct the nanocomposite. The gas response for the alternative nanocomposite was about 10% resistance increase under pure CO2, which gave an estimated 0.1% frequency change. The fabricated sensor frequency change was around 0.03% for pure CO2. The lowest detection limit of the sensor is 1% gas concentration, with 0.0036% frequency change. The sensor was tested at various humidity environments and showed over 0.1% frequency change under saturated humidity. With paralyne packaging, the sensor frequency change on humidity reduced to less than 0.01% while maintaining the same gas sensing performance. Wireless module was tested and showed over one foot transmission distance at preferred parallel orientation

CHARACTERIZATION OF A PLANT-SPECIFIC PRC1 (POLYCOMB REPRESSIVE COMPLEX 1)- LIKE COMPLEX AND ITS ROLE IN FLOWERING-TIME REGULATION

Ph.DDOCTOR OF PHILOSOPH