Infrared Solvent Stripping for Nanofiber Webs

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Solution Overview

Problem

Solution spinning processes often result in residual solvent being entrained in fibers or fabrics due to strong solvent-polymer affinities and limited time for solvent evaporation, leading to health hazards, environmental issues, and costly energy-intensive methods for solvent removal.

Innovation Solution

The process involves transporting solution-spun nonwoven webs with nanofiber diameters less than 1 micrometer through infrared solvent stripping stations without a solvent stripping fluid, effectively reducing solvent concentration to low levels, and optionally using a fluid/vacuum solvent stripping station for further solvent removal.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Loss of substance

If traditional solvent removal methods (hot air, steam, vacuum) are used, then solvent can be removed from fibers, but energy consumption increases and processing time extends

Engineering Contradiction:

Improvesolvent concentrationVSAvoidenergy consumption

Core Design Contradiction:

Loss of substanceVSUse of energy by moving object

Solution Approach 1:

The patent replaces mechanical/thermal solvent removal systems (hot air drying, steam treatment, vacuum pumping) with an electrostatic field-based removal system. Charged aerosol particles carrying solvent are removed by electrostatic attraction to grounded collector plates, eliminating the need for high-temperature heating and vacuum equipment while achieving effective solvent removal.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The patent changes the state of solvent removal from thermal/phase-change-based to electrostatic field-based. Instead of using heat to evaporate solvent or vacuum to reduce pressure, the system uses electrostatic forces to directly attract and remove charged solvent-laden aerosol particles, fundamentally changing the physical parameter used for solvent removal.

Inventive Principle:

Principle #35Parameter changes

2Loss of substance

If traditional solvent removal methods are used, then solvent can be removed from fibers, but processing time increases

Engineering Contradiction:

Improvesolvent concentrationVSAvoidprocessing time

Core Design Contradiction:

Loss of substanceVSLoss of time

Solution Approach 1:

The patent replaces time-consuming thermal and vacuum-based solvent removal with rapid electrostatic field-based removal. The electrostatic collector plates immediately attract charged solvent particles as they pass through the treatment zone, achieving effective solvent removal in a single pass without the extended processing times required by traditional methods.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

3Productivity

If solution spinning is used to achieve high throughput, then large quantities of fibers can be produced, but residual solvent remains in the fibers

Engineering Contradiction:

ImprovethroughputVSAvoidresidual solvent

Core Design Contradiction:

ProductivityVSLoss of substance

Solution Approach 1:

The patent introduces an electrostatic field-based solvent removal system that can operate continuously at high speeds matching solution spinning throughput. The system maintains high productivity while effectively removing residual solvent, unlike traditional methods that would require slowing down the high-speed spinning process.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The patent segments the solvent removal function into discrete electrostatic collector plates positioned along the fiber path. This allows continuous removal of solvent-laden aerosol particles without interrupting the high-speed fiber production process, maintaining throughput while reducing residual solvent.

Inventive Principle:

Principle #1Segmentation

4Ease of manufacture

If organic solvents are used in solution spinning, then fibers can be formed with desired properties, but health and environmental hazards increase

Engineering Contradiction:

Improvefiber formation capabilityVSAvoidhealth and environmental hazards

Core Design Contradiction:

Ease of manufactureVSObject-affected harmful factors

Solution Approach 1:

The patent uses electrostatic field-based removal to capture and remove organic solvent vapor and aerosol particles before they can escape into the environment or expose workers to hazards. The grounded collector plates attract and trap charged solvent particles, preventing their release while allowing continuous use of organic solvents for fiber formation.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

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 significantly reduces residual solvent levels to below 10,000 ppmw, enhancing safety and environmental sustainability while avoiding the costs and energy requirements of traditional solvent removal methods.

Implementation Method 1

infrared radiation irradiates the nonwoven web in the absence of a solvent stripping fluid impinging on the nonwoven web

Methodology Applied

Scientific EffectInfrared radiation: Infrared Radiation

Implementation Method 2

in order to reduce the solvent concentration of the fibers to less than about 10,000 ppmw

Methodology Applied

Scientific EffectEvaporation: Evaporation

Data Source

PatentUS8608998B2Infrared solvent stripping process

Publication Date: 2013.12.17 DUPONT SAFETY & CONSTRUCTION INC

AI summary

A process for stripping chemically bonded spinning solvent from a solution-spun nonwoven web comprising the steps of providing a nonwoven web comprising solvent-laden polymeric fibers having average fiber diameters of less than about 1 micrometer, and transporting the nonwoven web through at least one infrared solvent stripping station wherein infrared radiation irradiates the nonwoven web in the absence of a solvent stripping fluid impinging on the nonwoven web in order to reduce the solvent concentration of the fibers to less than about 10,000 ppmw.