Influences of Sequential Biaxial Stretching Parameters on the Interior Structure of Polypropylene Membrane Liang-Yu Chen, Chung-Cheng Su and Ren-Haw Chen Department of Mechanical Engineering National Chiao Tung University

Introduction

Application of polymer membrane Packaging Water filter Battery ion exchange membranes Barrier Filter

Membrane Sequential Biaxial Stretching Extruder Cutting Cooling Roller Transverse Direction (TD) Stretching Machine Direction (MD) Stretching Melt extrusion die Drawing Stretching Interlamellar region Lamellar Bridging structure Micropores Direction of uniaxial stretching 1μm

Advantage of polypropylene(PP) Resistant to many chemical solvents Fine mechanical strength Low glass transition temperature Semi-crystalline

Experimental

Heat Deflection Temperature Materials Polypropylene ( Sumitomo Chemical Asia, AV161) Mold temperature 130°C 70 x 70 x 0.5 mm Properties Method Unit Value Density ASTM D792 g/cm3 0.9 Tensile Strength ASTM D638 MPa 24 Rockwell Hardness ASTM D785 HRC 88 Melt temperature ISO 3146 °C 170 Heat Deflection Temperature ASTM D648 114 Melt Flow Rate ASTM D1238 g/10min 5

Stretching device With Controllable: Temperature Stretching Speed Controller Servo Motor Heater Plate Grippers Roller With Controllable: Temperature Stretching Speed Drawing Ratio

Stretching procedure PP Sheets Injection Molding Injection Cooling Ejection Heating MD Stretching Thermal Setting TD Pre-stretching TD Stretching Dimensional Measurement Membrane Analysis Optical Microscopic Observation Polarized Optical Microscopic Observation Plastification

Optical microscopic observation

Results and Discussion

Effects of mold temperature on interior structure of membrane Polarized optical microscopy micrograph cross-section of PP sheets formed at various mold temperatures. (a)90°C, (b)120°C, (c)130°C.

Interior structures of the membrane formed by stretching The interior structure of membrane. (a)after MD stretching, (b)after TD stretching. The micrographs of structure of PP sheet before stretching. The net-like interior structure of membrane

Effects of MD stretching temperature on membrane’s interior structures MD Drawing Ratio TD Pre-stretching Temperature Ratios of TD Pre-stretching to Total TD Stretching TD Stretching Temperature TD Drawing Ratio ↓ 300% 90°C 60% 120°C 200% (a)110°C, (b)120°C, (c)130°C, (d)140°C, (e)150°C MD TD

Effects of MD stretching temperature on membrane’s interior structures percentage of the net-like structure mean size of the net-like Structures (µm^2) MD stretching temperature MD stretching temperature standard deviation of sizes of the net-like structures (µm^2) thickness of the membrane (µm) MD stretching temperature MD stretching temperature

Effects of MD drawing ratio on membrane’s interior structures 260% 280% 300% 320% 340% (a) (b) (c) (d) (e) MD Stretching Temperature MD Drawing Ratio TD Pre-stretching Temperature Ratios of TD Pre-stretching to Total TD Stretching TD Stretching Temperature TD Drawing Ratio 120°C ↓ 90°C 60% 200% (a)260%, (b)280%, (c)300%, (d)320%, (e)340% MD TD

Effects of MD drawing ratio on membrane’s interior structures percentage of the net-like structure mean size of the net-like Structures (µm^2) MD drawing ratio MD drawing ratio standard deviation of sizes of the net-like structures (µm^2) thickness of the membrane (µm) MD drawing ratio MD drawing ratio

Effects of TD pre-stretching temperature on membrane’s interior structures MD Stretching Temperature MD Drawing Ratio TD Pre-stretching Temperature Ratios of TD Pre-stretching to Total TD Stretching TD Stretching Temperature TD Drawing Ratio 120°C 300% ↓ 60% 200% (a)80°C, (b)90°C, (c)100°C, (d)110°C, (e)120°C MD TD

Effects of TD pre-stretching temperature on membrane’s interior structures percentage of the net-like structure mean size of the net-like Structures (µm^2) TD pre-stretching temperature TD pre-stretching temperature standard deviation of sizes of the net-like structures (µm^2) thickness of the membrane (µm) TD pre-stretching temperature TD pre-stretching temperature

Effects of ratio of TD pre-stretching to total TD stretching on membrane’s interior structures 20% 40% 60% 80% 100% (a) (b) (c) (d) (e) MD Stretching Temperature MD Drawing Ratio TD Pre-stretching Temperature Ratios of TD Pre-stretching to Total TD Stretching TD Stretching Temperature TD Drawing Ratio 120°C 300% 90°C ↓ 200% (a)20%, (b)40%, (c)60%, (d)80%, (e)100% MD TD

Effects of ratio of TD pre-stretching to total TD stretching on membrane’s interior structures percentage of the net-like structure mean size of the net-like Structures (µm^2) 10% 60% 110% 10% 60% 110% ratios of TD pre-stretching to total TD stretching ratios of TD pre-stretching to total TD stretching thickness of the membrane (µm) standard deviation of sizes of the net-like structures (µm^2) 10% 60% 110% 10% 60% 110% ratios of TD pre-stretching to total TD stretching ratios of TD pre-stretching to total TD stretching

Effects of TD stretching temperature on membrane’s interior structures MD Stretching Temperature MD Drawing Ratio TD Pre-stretching Temperature Ratios of TD Pre-stretching to Total TD Stretching TD Stretching Temperature TD Drawing Ratio 120°C 300% 90°C 60% ↓ 200% (a)110°C, (b)120°C, (c)130°C, (d)140°C, (e)150°C MD TD

Effects of TD stretching temperature on membrane’s interior structures percentage of the net-like structure mean size of the net-like Structures (µm^2) TD stretching temperature TD stretching temperature standard deviation of sizes of the net-like structures (µm^2) thickness of the membrane (µm) TD stretching temperature TD stretching temperature

Effects of TD drawing ratio on membrane’s interior structures 180% 200% 220% 240% 260% (a) (b) (c) (d) (e) MD Stretching Temperature MD Drawing Ratio TD Pre-stretching Temperature Ratios of TD Pre-stretching to Total TD Stretching TD Stretching Temperature TD Drawing Ratio 120°C 300% 90°C 60% ↓ (a)180%, (b)200%, (c)220%, (d)240%, (e)260% MD TD

Effects of TD drawing ratio on membrane’s interior structures percentage of the net-like structure mean size of the net-like Structures (µm^2) TD drawing ratio TD drawing ratio standard deviation of sizes of the net-like structures (µm^2) thickness of the membrane (µm) TD drawing ratio TD drawing ratio

Conclusions

For sequential biaxial stretching process MD stretching Increasing the orientation of the structure of the membrane TD pre-stretching (with low temperature) Separating the interior structure of the membrane TD stretching Leads to a net-like interior structure

During MD stretching Increasing MD stretching temperature The uniformity of the structure of the membrane would increased Improves the generation of fibers in the net- like interior structure Increasing MD drawing ratio

During TD pre-stretching Increasing TD per-stretching temperature Significantly reduces the number of net-like structures Increasing the ratio of TD pre-stretching to total TD stretching Increases the number of net-like structures and improves the consistency of their sizes

During TD stretching Increasing the stretching temperature Reduces the amount of net-like structures formed Increasing TD drawing ratio Increases the size of the formed net-like structures

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