Polyacrylonitrile (PAN) fiber is one of the most important synthetic fibers in the world because it is a precursor to carbon fiber. Compared to the traditional solution spinning process, the melting spinning process of PAN is less costly and can further reduce the price of PAN fiber. This dissertation is concerned with the objective of establishment of conditions (temperature, plasticizer type, and plasticizer composition) that a PAN copolymer is able to be stable melt spun with water based plasticizers. More specifically, PAN/water/acetonitrile (70/15/15) mixture is considered as reference sample in this study because it was proposed in a BASF patent in which it was claimed it could be stably melt spun. We are looking for a more benign plasticizer so that the use of acetonitrile can be avoided and PAN can still be stably melt spun. To achieve this objective, the first step is to measure the melting point (Tm) of PAN copolymer with various plasticizers and compositions by using differential scanning calorimetry (DSC). The results indicate the Tm of PAN copolymer can be reduced to around 160 oC with water only as a plasticizer, which is lower than the degradation temperature of PAN (180 oC). Moreover, using a water/ethanol mixture and water/acetonitrile as plasticizers can further reduce the melting point of PAN to 150 oC and 135 oC, respectively. The second step is conducting rheological measurements on the PAN/plasticizers mixture. A pressure chamber was designed and attached to the capillary rheometer in order to prevent the foaming and evaporation of plasticizers during the viscosity experiments. Both steady-shear and time-dependent viscosity measurements were conducted. The rheological measurement results indicate that PAN can keep stable for more than 120 minutes with all plasticizers under 170 oC, and it starts to degrade in 60 minutes at 180 oC, except samples plasticized with 30 wt% of water (which keep stable for 120 minutes as well). The steady-shear viscosity results indicate the shear-thinning behavior is observed for the PAN/plasticizer mixtures at a temperature ranging from 170 oC to 190 oC and provide the fundamental viscosity data which can be applied to the extrusion process. In conclusion, the rheological measurements show PAN/Water (70/30 wt%) at 180 oC and PAN/EtOH/Water (70/15/15) at 170 oC are two potential systems for carrying out the PAN melt spinning process. Scanning electron microscopy (SEM) images were taken for the reference state and potential conditions. These images show that the copolymer strands have more and larger voids when plasticized with water only compared to those plasticized with water/acetonitrile and water/ethanol mixture. In this case, PAN/EtOH/Water (70/15/15) at 170 oC is considered to be the most benign system for that PAN melt spinning. / Doctor of Philosophy / The melt spinning process of polyacrylonitrile (PAN) has been studied in the past few decades. Compared to the traditional solution spinning process, it does not require toxic organic solvents. The major problem of the PAN melt spinning process is the melting point (Tm) of PAN is much higher than its degradation temperature. However, by adding plasticizers the Tm of PAN can be significantly reduced, which makes PAN melt spinning feasible. In this work we discuss the feasibility of the melt spinning process of polyacrylonitrile (PAN) copolymer plasticized with water based plasticizers by using differential scanning calorimetry (DSC) and rheological methods. The objective is to use water only as a plasticizer to melt spin PAN under specific conditions (composition, temperature etc). The melting point and rheological measurements have been conducted by DSC and a modified capillary rheometer, respectively, for this plasticized system. The DSC results show that the melting point of the PAN copolymer can be reduced below the degradation temperature of PAN, and the rheological results show that the PAN copolymer can be extruded with a reasonable viscosity at 15-20 o v above its melting point, and also the stability and viscosity are strongly dependent on temperature and the plasticizer type and content. Furthermore, the Scanning electron microscopy (SEM) images show the copolymer strands extruded from PAN/H2O mixture have many more and larger voids than PAN/H2O/EtOH mixture. In conclusion, the results indicate that the most appropriate condition for PAN melt spinning is PAN/H2O/EtOH mixture of 70/15/15 wt% ratio at a temperature of 170 oC

Wall slip in the die of a capillary rheometer was investigated. Corn meal and water were mixed to a moisture content of 35% wet basis. Oil was then added at 0%, 2.5%, and 5% of the total mass. A capillary rheometer was used to extrude the mixture at 100C. Three die diameters were studied: 2mm, 4mm, and 8mm. Two length to diameter ratios were studied: L/D=4 and L/D=8. Pressure and flow rate in grams per 30 seconds were collected from the capillary rheometer to perform the Bagley correction, determine the flow behavior index, and correct for slip using the Mooney slip analysis method. Several slip analysis methods were considered prior to the selection of the Mooney method. Overall, the Bagley correction was successful for all die diameters except 2mm. The Mooney method was successful for the 5% added oil content samples. An increase slip velocity was observed as shear stress increased. Mooney plots for 0% and 2.5% resulted in negative shear rate values. An empirical model was developed to predict apparent viscosity of the mixture as a function of total oil content.

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