PDS Pellet Extrusion With Devolatization for Uniform Resin Yield
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Solution Overview
Problem
The production of absorbable poly(p-dioxanone) (PDS) polymer faces challenges due to non-uniformity in molecular weight, viscosity, and polymerization level, leading to issues during extrusion, with fines often discarded, causing yield loss and degradation, and the slow crystallization rate complicating pelletization.
Innovation Solution
A twin-screw extrusion process with an inverted temperature profile and devolatization steps is used to produce uniform PDS pellets from ground resin and fines, removing unreacted monomer and reducing drying time, ensuring consistent polymer properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of substance
If ground resin and fines are pelletized using conventional extrusion, then polymer yield is improved by utilizing fines, but the slow crystallization rate of PDS resin makes the pelletization process extremely difficult and results in non-uniform pellets
Solution Approach 1:
The patent applies parameter changes by implementing a specific temperature profile along the extruder zones, controlling residence time, and adjusting screw rotation speed to optimize the pelletization process. These parameter modifications enable successful pelletization of PDS resin despite its slow crystallization rate, transforming the manufacturing difficulty into a controllable process.
Solution Approach 2:
The patent employs preliminary action by adding a devolatization step before the main extrusion and pelletization process. This preliminary step removes unreacted monomer and volatile components from the ground resin and fines, preventing degradation during subsequent processing and enabling successful pelletization that would otherwise be impossible due to the resin's slow crystallization.
2Loss of time
If ground resin is pelletized without devolatization, then processing time is reduced, but unreacted monomer causes polymer degradation during drying and reduces pellet uniformity
Solution Approach 1:
The devolatization step performed before main extrusion serves as a preliminary action that removes unreacted monomer and volatile components. This prevents polymer degradation during subsequent drying operations and ensures pellet uniformity, addressing the reliability issue without significantly extending overall processing time.
Solution Approach 2:
The patent applies the extraction principle by specifically removing unreacted monomer and volatile components through the devolatization step. This separation of harmful volatiles from the polymer matrix prevents degradation and improves pellet quality, resolving the contradiction between processing efficiency and polymer stability.
3Loss of substance
If high monomer content resin is used for pelletization, then polymer yield is maximized, but moisture sensitivity causes significant degradation prior and during drying
Solution Approach 1:
The devolatization step serves as a preliminary protective action that removes unreacted monomer before the drying process. By eliminating the source of moisture sensitivity (unreacted monomer) in advance, the patent enables high-yield processing without the degradation problems that would otherwise occur during drying.
Solution Approach 2:
The patent applies preliminary anti-action by removing unreacted monomer through devolatization before drying. This preemptive removal counteracts the potential harmful effect of moisture sensitivity, allowing the polymer to be processed at high yield without suffering degradation from moisture exposure during subsequent drying operations.
4Reliability
If monomer is removed during pelletization, then polymer degradation stability is improved and drying time is reduced, but additional devolatization equipment and process steps are required
Solution Approach 1:
The patent merges the devolatization function with the extrusion and pelletization process by integrating a devolatization zone within the extruder apparatus. This combination allows monomer removal to occur during the existing pelletization operation, improving polymer stability without requiring completely separate equipment or significantly increasing overall process complexity.
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
The process results in chemically and physically uniform PDS pellets with reduced monomer content, improving yield and extrusion efficiency, and maintaining fiber properties.
Implementation Method 1
heating the PDS powder within the extruder to form a flowable PDS mass
Implementation Method 2
heating the PDS powder within the extruder to form a flowable PDS mass
Implementation Method 3
The pelletization step may include additional devolatization features removing unreacted p-dioxanone monomer
Implementation Method 4
conveying said PDS mass along the length of said cylindrical barrel by action of the screw
Implementation Method 5
quenching the PDS extrudate after extrusion from the outlet
Data Source
AI summary
The present invention is directed to methods for processing absorbable, slow-to-crystallize poly(p-dioxanone) ground resin and its fines utilizing a twin-screw extruder apparatus to produce uniform pellets. Advantageously, the ground resin materials resulting from solid-state polymerization do not undergo processing, such as sieving, to remove fines from the feedstock for an extrusion and pelletizing system that has been configured with an inverted temperature profile along the extrusion barrel. The resulting PDS pellets have improved resin uniformity and greater polymer yield for improved operational efficiencies and production of extruded filaments.