Propylene Copolymer Pelletization Using Nucleating Agents
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Solution Overview
Problem
Soft propylene copolymers with high comonomer content tend to adhere and agglomerate during pelletization, transport, and storage, leading to process disruptions and reduced pellet quality due to their low crystallization speed, which existing methods fail to adequately address.
Innovation Solution
A process involving extruding propylene copolymers with a polymeric nucleating agent through a die plate into an underwater pelletizer, controlling the mass flow rate ratio with cooling water, and using a polymeric nucleating agent to reduce agglomeration and improve pellet handling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If soft propylene copolymers with high comonomer content are used to achieve softness and flexibility, then the desired mechanical properties are improved, but the pellets tend to adhere and agglomerate during processing and storage
Solution Approach 1:
The patent changes the crystallization temperature parameter by adding a nucleating agent, which shifts the crystallization behavior to occur at higher temperatures during cooling. This parameter change allows the polymer to crystallize before reaching temperatures where adhesion occurs, thus maintaining pellet flowability while preserving the softness provided by high comonomer content
Solution Approach 2:
The nucleating agent acts as an intermediary substance that mediates the crystallization process. It provides nucleation sites that accelerate and elevate the crystallization temperature, enabling the polymer to solidify in a controlled manner that prevents pellet-to-pellet adhesion while maintaining the desired mechanical softness
2Strength
If the comonomer content is increased from 7 to 20% by weight to improve softness and impact strength, then the mechanical performance is enhanced, but the crystallization speed is reduced leading to adhesion and aggregation
Solution Approach 1:
The nucleating agent fundamentally changes the crystallization kinetics by providing numerous nucleation sites. This shifts the crystallization curve to occur at higher temperatures and faster rates, counteracting the slowing effect of high comonomer content while maintaining the desired impact strength
Solution Approach 2:
The nucleating agent performs preliminary action by establishing nucleation sites before the polymer begins to cool and crystallize. This preliminary structuring of the polymer matrix enables rapid crystallization upon cooling, preventing the slow crystallization that would otherwise lead to adhesion
3Device complexity
If conventional extrusion and pelletization methods are used, then the production process is simple, but the pellets adhere to apparatus walls and form agglomerates causing process disruptions
Solution Approach 1:
The patent modifies the thermal processing parameters by introducing a nucleating agent that elevates crystallization temperature. This allows the polymer to crystallize during the cooling phase without adhering to apparatus walls, maintaining process simplicity while eliminating disruptions from agglomeration
Solution Approach 2:
The patent converts the potentially harmful slow crystallization caused by high comonomer content into a beneficial controlled crystallization process. By using the nucleating agent to accelerate and elevate crystallization, the slow crystallization tendency is transformed into rapid, controlled solidification that prevents adhesion while maintaining the soft mechanical properties
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 significantly reduces the formation of agglomerated pellets, enhances pellet flowability, and minimizes downtime in subsequent process steps, allowing for efficient handling and storage of the pellets without additional equipment investment.
Implementation Method 1
the propylene copolymer comprises a polymeric nucleating agent
Implementation Method 2
The melt is then pressed through a die plate, usually into a water bath. The molten strands then solidify due to the cooling effect of the water.
Data Source
AI summary
The present invention provides a process for extruding and pelletising a propylene copolymer. The copolymer has a content of comonomer from 5 to 40% by mole, a melt flow rate MFR2 measured at 230° C. under a load of 2.16 kg of from 0.5 to 15 g/10 min and a content of cold xylene soluble material of from 20 to 60% by weight. The process comprises extruding the propylene copolymer through a die plate into an underwater pelletiser and cutting strands of the propylene copolymer into pellets in the underwater pelletiser, wherein the ratio of the mass flow rate of the propylene copolymer to the mass flow rate of the cooling water is from 0.020 to 0.060; and the propylene copolymer comprises a polymeric nucleating agent.