Aliphatic Polyester Molecular Weight Control via Diisocyanate Mixing
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional methods for producing high molecular weight aliphatic polyesters face challenges such as reduced accuracy in controlling molecular weight, gelation, and fish eyes formation due to evaporation of diisocyanate at high temperatures, leading to incomplete reaction and poor film formation.
Innovation Solution
A method involving quantitative injection and continuous stirring of diisocyanate into an aliphatic polyester prepolymer at a temperature above its melting point, followed by a coupling reaction in a specially designed mixing tank with partitioning plates and multistage stirring blades, prevents evaporation and ensures uniform mixing, thereby increasing molecular weight and reducing gelation and fish eyes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If diisocyanate is added to a polymerization tank at high temperature not lower than the melting point of the aliphatic polyester prepolymer to increase molecular weight, then the molecular weight increases, but the diisocyanate evaporates due to high temperature and adheres to the inner wall of the reaction tank, reducing accuracy in controlling molecular weight and causing gelation and fish eyes
Solution Approach 1:
A mixing tank equipped with partitioning plates and multistage stirring blades is introduced as an intermediary device between the polymerization tank and the coupling reaction tank. This mixing tank ensures complete mixing of diisocyanate with the prepolymer before the coupling reaction, preventing diisocyanate evaporation and adhesion to the polymerization tank walls, thereby maintaining accuracy in controlling molecular weight while achieving the desired molecular weight increase.
Solution Approach 2:
The diisocyanate is completely mixed with the aliphatic polyester prepolymer in the mixing tank before the coupling reaction is initiated in the reaction tank. This preliminary mixing action ensures that the diisocyanate is uniformly distributed and prevents evaporation and adhesion issues during the subsequent heating and reaction process, enabling accurate control of molecular weight.
2Quantity of substance
If diisocyanate is added at high temperature to increase molecular weight, then the molecular weight increases, but gelation and fish eyes formation occur
Solution Approach 1:
The mixing tank with partitioning plates and multistage stirring blades acts as an intermediary that ensures complete and uniform mixing of diisocyanate with the prepolymer before the coupling reaction. This preliminary uniform mixing prevents localized concentration variations that would otherwise cause gelation and fish eyes formation during the high-temperature coupling reaction, thereby improving reliability of the product quality.
3Device complexity
If conventional stirring blades are used in the polymerization apparatus, then the apparatus structure is simple, but the surface area of reactants cannot be sufficiently enlarged and effectively renewed, preventing sufficient reaction progress
Solution Approach 1:
The stirring function is segmented into two stages: conventional stirring in the polymerization tank for initial mixing, and intensive stirring in the mixing tank with partitioning plates and multistage stirring blades for complete mixing before coupling reaction. This segmentation allows each stage to perform its specific function optimally, ensuring sufficient reaction progress while maintaining overall system efficiency.
Solution Approach 2:
The mixing process is extended from a single-tank system to a two-tank system (polymerization tank + mixing tank), adding a spatial dimension to the mixing process. The mixing tank with partitioning plates creates multiple mixing zones, effectively increasing the surface area and renewal rate of reactants through multistage stirring, thereby ensuring sufficient reaction progress.
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 enables the continuous production of high-quality aliphatic polyesters with increased molecular weight and improved melt-flow rate, minimizing gelation and fish eyes, and maintaining high accuracy in controlling molecular weight.
Implementation Method 1
reacting the aliphatic polyester prepolymer with the diisocyanate in the coupling reaction tank
Implementation Method 2
quantitatively and continuously introducing the diisocyanate-containing aliphatic polyester prepolymer obtained at step (i) into a mixing tank, discharging same from the mixing tank under stirring
Data Source
Figure 1
Figure 2
Figure 3
AI summary
The present invention addresses the problem of providing a method for continuously and effectively producing an aliphatic polyester having an increased molecular weight by preventing evaporation of a diisocyanate when blending the diisocyanate with an aliphatic polyester prepolymer in a molten state at a temperature not lower than the melting point thereof so that the diisocyanate and the aliphatic polyester prepolymer are uniformly blended. In order to solve the above-mentioned problem, the present invention provides a method for producing an aliphatic polyester having an increased molecular weight comprising the steps of (i) quantitatively injecting a diisocyanate into an aliphatic polyester prepolymer which has a number average molecular weight of 5,000 or higher and has terminal hydroxyl groups and in which at least one acid component is a succinic acid compound, in a melting state at a temperature not lower than the melting point thereof wherein the amount of the diisocyanate is equivalent to between one tenth and two times the amount of hydroxyl groups in the aliphatic polyester prepolymer, (ii) quantitatively and continuously introducing the diisocyanate-containing aliphatic polyester prepolymer obtained at the step (i) into a mixing tank, discharging same from the mixing tank under stirring and supplying it to a coupling reaction tank, and (iii) reacting the aliphatic polyester prepolymer with the diisocyanate in the coupling reaction tank.