- 學位論文
鐵氟龍高分子押出過程流變特性之研究
Study on the Rheology of the PTFE Paste Extrusion Process
摘要
隨著高分子科技的進步，新的聚合物不斷推陳出新，微孔洞薄膜技術也不斷創新。本研究乃係針對薄膜材料高分子聚四氟化乙烯PTFE (Polytetrafluoroethylene)在押出過程中，流變特性量測系統的建立，並藉由此系統探討PTFE原料在押出過程中之流變行為。 由於PTFE材料性質特殊且混合潤滑油作加工，使PTFE材料在模頭內流動的實際情況比一般高分子的情形複雜。研究中之流變量測儀器是以電腦下達速度命令給DV/P卡，藉由數位式PID控制放大器控制油壓缸伺服閥，以壓力感測器與電阻尺來做訊號回饋。本研究與以往文獻最大不同點是利用低速押出速度控制，而非押出壓力控制。低速押出PTFE塑料可以得到較均一的密度，由誤差5.8%下降至0.48%，以減少密度變化對流變量測的影響。 實驗上針對不同低速押出速度V=0.5mm/s、1mm/s、2mm/s做探討，同時也針對不同的毛細管直徑D=2.3mm、3mm、4mm，也就是模頭有不同L/D和RR比(Reduction Ratio)設計做實驗比較，其中L/D比分別為11.74、9、7.5，RR比分別為80.06、47.06、26.47。在含油量上針對18wt％、20wt％、22wt％等不同重量比例來作變化。利用實驗過程中擷取之速度訊號及壓力降，作毛細管流變公式推算出非牛頓流體行為下之黏度値，其黏度值介於0.1~1kPa.s，同時利用模流分析軟體MOLDFLOW來驗證實驗量測之壓力值正確性。另一方面，也利用流體計算軟體COMET來探討邊界滑動效應。在邊界滑動行為下，PTFE之黏度值介於0.1~1MPa.s。
並列摘要
Polymeric porous membranes play an important role in separation engineering and a variety of techniques have been adopted for the production of membranes. However, Polytetrafluoroethylene (PTFE) is a remarkable material having high melting temperature, high chemical resistance, low frictional and dielectric coefficients, etc. Due to its high melting point, PTFE fin powder cannot be processed using the conventional techniques such as the injection molding, extrusion and blow molding, etc. Instead, techniques involving cold pressing, such as paste extrusion, and sintering have to be employed. The purpose of this study is to establish a PTFE capillary rheometer system, which controls the extrusion speed and extrusion pressure in an accurate way, to explore the rheology of PTFE paste in the paste extrusion process. In the capillary rheometer system, the PID control technology is used to keep the extrusion speed in constant. Due to the lower constant speed, the variation of PTFE extrusion density can decrease from 1.75g/cm3 (±5.8%) to 1.68g/cm3 (±0.48%). In addition, different lubricant content with 18wt%, 20wt%, and 22wt%, respectively was used to monitor the pressure drop under different extrusion speeds (0.5mm/s, 1mm/s, 2mm/s) and reduction ratios(RR=26.47, 47.06, 80.06). It was founded the viscosity of PTFE paste basically follows the power law with shear thinning behavior analog to thermoplastics melt. To verify the magnitude of pressure drop obtained from experiments, commercial code MOLDFLOW was employed. In addition to explore the effect of wall slip, commercial CFD code COMET was also employed. In the backward analysis of PTFE viscosity, it was found that the magnitude of viscosity is about 0.1~1MPa.s under wall slip effect.