Semi-crystalline Polymer Cooling via Evaporative Devolatilization
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Solution Overview
Problem
Existing methods for pelletizing low viscosity semi-crystalline polymers are inefficient, particularly in large-scale industrial processes, as they require prolonged cooling times or multiple extruders due to the limitations of surface-cooled extruders in effectively removing heat from high volumes of polymer.
Innovation Solution
A method involving the use of a devolatilizing device where a molten polymer composition is subjected to vacuum conditions to evaporate solvent, facilitating both heat removal and crystallization, allowing for the production of pellets with controlled viscosity and crystallization levels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If surface-cooled extruders are used to cool polymer melt, then cooling can be achieved through the extruder housing, but the cooling efficiency is insufficient for large volume industrial processes because heat removal capacity is proportional to surface area while heat to be removed is proportional to volume
Solution Approach 1:
The invention extracts the cooling function from the extruder housing and implements it as a separate, dedicated cooling device. The polymer melt is withdrawn from the extruder and passed through a cooling device where heat is removed more efficiently, then the cooled melt is returned to the extruder for pelletization. This separation allows the cooling capacity to be independently scaled and optimized.
Solution Approach 2:
The invention introduces a cooling device as an intermediary component between the extruder and the pelletizer. This intermediate cooling step allows the polymer melt to be cooled below its melting point before pelletization, enabling efficient heat removal through a dedicated cooling mechanism rather than relying solely on the extruder housing surface area.
2Manufacturing precision
If low temperature processing is used to form acceptable pellets from low viscosity polymers, then pellet quality improves, but processing time increases due to the need for prolonged cooling
Solution Approach 1:
The invention implements continuous cooling of the polymer melt through the cooling device as it circulates between the extruder and pelletizer. This continuous cooling action maintains the polymer at the optimal temperature range for pelletization, ensuring consistent pellet quality without requiring prolonged cooling periods. The process operates in a steady state where cooling, extrusion, and pelletization occur simultaneously and continuously.
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 approach enables efficient pelletization of low viscosity semi-crystalline polymers by effectively managing heat removal and crystallization, allowing for scalable production without the need for prolonged cooling times or multiple extruders, thereby improving processing efficiency.
Implementation Method 1
the solvent is at least partially evaporated under vacuum conditions, resulting in both removal of heat from the polymer by evaporative cooling and crystallization of the polymer
Implementation Method 2
supplying a molten polymer composition comprising the semi-crystalline polymer and a solvent to a devolatilizing device. In the devolatilizer, the solvent is at least partially evaporated under vacuum conditions
Implementation Method 3
removal of heat from the polymer by evaporative cooling
Implementation Method 4
crystallization of the polymer
Data Source
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Figure 3A
AI summary
Methods and systems for pelletizing low molecular weight semi-crystalline polymers are provided herein. Polymer compositions comprising the semi-crystalline polymer and a solvent are provided to a devolatilizing device, where the solvent is at least partially evaporated under vacuum conditions, resulting in removal of heat from the polymer by evaporative cooling and crystallization of the polymer. Once the polymer has reached the desired temperature, the polymer exits the devolatilizer and is pelletized. Semi-crystalline polymers that may be used in the present invention include propylene-based copolymers, such as propylene-ethylene and propylene-hexene copolymers having a heat of fusion, Hf, from about 5 to about 75 J/g and a weight average molecular weight, Mw, from about 10,000 to about 200,000 g/mol.