Wettable Polymer Fiber Separator Sheet With Sustained Porosity
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Solution Overview
Problem
Current lead-acid battery separators face challenges in achieving high porosity, mechanical robustness, acid resistance, and sustained wettability, particularly in 'start-stop' applications, and they often rely on hazardous solvents in their manufacturing processes.
Innovation Solution
A polymer fiber sheet is developed with a fiber modifying agent that acts as both a plasticizer and a surface modifying agent, ensuring high porosity, mechanical strength, and sustained wettability, and can be processed without hazardous solvents, using materials like di-n-butyl phthalate and sodium dodecylbenzene sulfonate, which are incorporated during the extrusion and fiber formation process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If traditional solvents like trichloroethylene and hexane are used for extracting process oil, then extraction efficiency is improved, but health and safety risks increase due to hazardous and flammable properties
Solution Approach 1:
The patent replaces hazardous solvents (trichloroethylene, hexane) with water as the extraction medium. Water is non-hazardous and non-flammable, eliminating health and safety risks while maintaining extraction efficiency through the hydrophilic nature of the fiber-modified polymer structure that facilitates oil removal without requiring dangerous chemicals.
2Reliability
If silica-filled polyethylene separators are used in flooded lead-acid batteries, then acid resistance is improved, but wettability is insufficient requiring additional processing steps
Solution Approach 1:
The patent combines the acid-resistant polyethylene base material with hydrophilic fiber-modifying agents (surfactants) during the extrusion process. This integration creates a composite separator that simultaneously provides both acid resistance from the polyethylene matrix and excellent wettability from the incorporated fiber-modifying agents, eliminating the need for separate wettability treatment steps.
Solution Approach 2:
The patent modifies the surface properties of the polyethylene separator by incorporating fiber-modifying agents that change the surface energy and wettability parameters. This allows the separator to maintain its chemical resistance while achieving the required hydrophilic characteristics for electrolyte absorption without additional processing.
3Productivity
If the extraction and drying steps are performed quickly to increase production output, then productivity is improved, but the quality and uniformity of porosity deteriorate
Solution Approach 1:
The patent incorporates fiber-modifying agents during the extrusion process before extraction and drying. This preliminary modification of the polymer structure during extrusion creates a pre-conditioned matrix that facilitates uniform solvent removal and consistent porosity development during subsequent extraction and drying steps, allowing faster processing without sacrificing quality.
4Reliability
If polyethylene and polypropylene are used as separator materials, then acid resistance is improved, but hydrophilicity is insufficient requiring secondary processing
Solution Approach 1:
The patent creates a composite separator material by combining polyethylene or polypropylene base polymers with hydrophilic fiber-modifying agents (surfactants) during extrusion. This composite structure maintains the excellent acid resistance of the polyolefin matrix while incorporating hydrophilic components that provide the necessary wettability for electrolyte absorption, eliminating the need for secondary hydrophilization processing.
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 resulting polymer fiber sheet exhibits excellent tensile properties, sustained wettability after multiple washing and drying cycles, and can be densified and embossed for specific thickness and porosity, addressing the limitations of existing separators while avoiding hazardous solvents.
Implementation Method 1
The fiber modifying agent functions as either one or both (1) a plasticizer that reduces the polymer extrudate melt viscosity and allows the formation of fine fibers during processing
Implementation Method 2
a surface modifying agent that promotes the instantaneous and sustained wettability of individual polymer fibers and a porous fiber sheet formed from them
Implementation Method 3
sufficiently porous to permit the electrolyte to reside in the pores of the separator material, thereby permitting ionic current flow between adjacent positive and negative plates
Data Source
AI summary
A polymer fiber sheet exhibits high porosity and good tensile properties in both “wet” and “dry” states. A fiber modifying agent is incorporated into a polymer extrusion and fiber formation process to produce a highly porous polymer fiber sheet that is instantaneously wettable by an aqueous medium. The fiber modifying agent functions as either one or both (1) a plasticizer that reduces the polymer extrudate melt viscosity and allows the formation of fine fibers during processing and (2) a surface modifying agent that promotes the instantaneous and sustainable wettability of individual polymer fibers and a porous fiber sheet formed from them. The polymer fiber sheet maintains its wettability even after repeated washing and drying cycles. The resultant fiber sheet can be densified and embossed to provide a desired thickness and porosity, while at the same time longitudinal ribs with desired pattern can also be formed on the fiber sheet.