Wholly Aromatic Polyester Stirring and Solid State Polymerization
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Solution Overview
Problem
The challenge lies in effectively reducing the amount of byproduct gases, such as acetic acid, during the production of wholly aromatic polyester, which can lead to erosion, poor insulation, and discoloration, while maintaining excellent thermal and mechanical stability and fluidity.
Innovation Solution
A two-stage polymerization process using a rectangular or trapezoidal plate type stirring impeller with a specific L/D ratio and power per unit volume, ensuring uniform shear stress and efficient removal of byproducts, combined with controlled temperature and heating rates in solid state polymerization to prevent adhesion and foaming.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If conventional stirring methods are used in melt condensation polymerization, then the reaction mixture can be stirred, but the Carvan phenomenon occurs preventing effective stirring and byproduct removal
Solution Approach 1:
The stirring speed is dynamically adjusted during the polymerization process. High stirring speed (e.g., 600-1200 rpm) is applied in the early stage when viscosity is low to prevent Carvan phenomenon and ensure effective byproduct removal. As polymerization progresses and viscosity increases, the stirring speed is reduced to maintain mixing while avoiding excessive shear stress that could cause adhesion. This dynamic adjustment resolves the contradiction between maintaining stirring effectiveness and preventing harmful byproduct accumulation.
Solution Approach 2:
The stirring process employs periodic variation in speed and intensity rather than constant stirring. Cyclic patterns of high-speed stirring followed by lower-speed mixing are implemented to periodically disrupt the Carvan phenomenon and enhance byproduct removal efficiency while preventing continuous shear stress that leads to adhesion. This periodic action maintains stirring effectiveness without generating harmful effects.
2Productivity
If high temperature is used to accelerate polymerization, then reaction rate increases, but byproduct gases increase causing erosion and discoloration
Solution Approach 1:
The polymerization process is segmented into multiple stages with different temperature profiles. The first stage uses higher temperature (e.g., 260-280°C) to accelerate initial polymerization and achieve high productivity. The second stage reduces temperature (e.g., 220-240°C) to minimize byproduct gas generation and prevent erosion and discoloration. This temporal segmentation of temperature conditions resolves the contradiction between reaction rate and harmful byproduct formation.
Solution Approach 2:
Byproducts are removed more effectively in the preliminary stages of polymerization when the reaction mixture is less viscous and stirring is more effective. This preliminary byproduct removal prevents accumulation that would later cause erosion and discoloration at higher temperatures. The process proactively addresses byproduct removal before harmful effects can manifest.
3Ease of operation
If stirring speed is increased to improve byproduct removal, then mixing efficiency increases, but adhesion and foaming occur
Solution Approach 1:
Stirring speed is dynamically controlled based on polymerization progress and viscosity changes. High stirring speed is applied only in early stages when viscosity is low and byproduct removal is critical. As polymerization advances and viscosity increases, stirring speed is reduced to prevent adhesion and foaming. This dynamic control maintains byproduct removal efficiency while avoiding harmful adhesion and foaming effects.
Solution Approach 2:
The stirring parameters (speed, intensity, duration) are changed according to the polymerization stage and mixture viscosity. Specific stirring speed ranges are assigned to different viscosity levels and reaction phases. This parameter adjustment ensures effective byproduct removal at low viscosity while preventing adhesion and foaming at high viscosity, resolving the contradiction between removal efficiency and harmful effects.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This method results in wholly aromatic polyester with reduced byproduct gases, maintaining high thermal and mechanical stability, preventing discoloration and foaming, and ensuring uniform properties, thus enhancing the quality and processability of the polymer.
Implementation Method 1
a rectangular or trapezoidal plate type stirring impeller, a length (L) to diameter (D) ratio of the stirring impeller is 1 ∼ 3 : 1, and a distance between a bottom of the reactor and a lower portion of the stirring impeller is 1/100 - 1/15 times of the diameter (D) are used. In a reactor in which a turbulent stress is applied
Implementation Method 2
Such condensation polymerization includes heating and stirring the reaction mixture under atmospheric or reduced pressure conditions, and removing excessive monomers and byproducts
Implementation Method 3
The wholly aromatic polyester forms liquid crystal without entanglement between its molecular chains in melt state due to its rigid molecular structure
Implementation Method 4
removing byproducts, pulverizing products, and solid state polymerizing the pulverized polymer
Data Source
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AI summary
Provided is a method of preparing a polyester resin suitable for electronic parts having its inherent mechanical strength and heat resistance, in which the amount of byproduct gas generated form molded articles is reduced. That is, provided is a method of preparing wholly aromatic polyester including: mixing monomers, introducing the mixed monomers into a reactor having a rectangular or trapezoidal plate type stirring impeller, and polymerizing the introduced monomers through esterification with a power per unit volume of 10 ~ 60 kW/m3, wherein a length (L) to diameter (D) ratio of the stirring impeller is 1 ~ 3 : 1, and a distance between the bottom of the reactor and a lower portion of the stirring impeller is 1/100 ~ 1/15 times of the diameter (D); b) pulverizing the obtained polymer; and c) solid state polymerizing the pulverized polymer. Provided is also a method of preparing wholly aromatic polyester having excellent heat resistant properties in which byproduct is effectively discharged by controlling a heating rate and reaction holding time between the weight loss initiating temperature and the melting point of a low molecular weight polymer generated in a melt polymerization in a solid state polymerization, adhesion does not occur, and discoloration due to heating does not occur. Provided is also a method of preparing a high heat resistant liquid crystal polyester resin composition having improved fluidity and used to form optical pick up parts, etc. by mixing a resin mixture including liquid crystal polyester resin A and liquid crystal polyester resin B, with a fiber and/or flake inorganic filler, wherein the difference of the melting points between liquid crystal polyester resin A and liquid crystal polyester resin B is in a certain range.