Liquid Crystal Polyester Fiber for Balanced Tensile and Compressive Strength
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Solution Overview
Problem
Liquid crystal polyester fibers exhibit weakness in compressive direction stress and require improvements in mechanical properties, particularly tensile and compressive strength, as well as fatigue resistance, especially for applications involving both tensile and compressive forces.
Innovation Solution
The production process involves using a liquid crystal polyester with specific weight-average molecular weight and melting point, adjusting extruder and spinning conditions to apply shear stress, and heat-treating the as-spun fiber to minimize unmelted particles and voids, resulting in a fiber with enhanced tensile and compressive strength and fatigue resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If liquid crystal polyester fiber is heat-treated at high temperature for long time to improve tensile strength, then molecular weight and melting point increase, but compressive strength and fatigue resistance remain insufficient
Solution Approach 1:
The patent applies parameter changes by precisely controlling the molecular weight of the liquid crystal polyester within 40,000-160,000 and the ratio of specific structural units (2,6-naphthalenediyl groups at 30-70 mol%, 2,7-naphthalenediyl groups at 5-30 mol%, and other aromatic diol structural units at 10-40 mol%). These parameter optimizations simultaneously improve tensile strength through molecular orientation and enhance compressive strength and fatigue resistance through controlled crystallinity and molecular structure, resolving the contradiction between tensile and compressive performance.
2Strength
If the molecular weight of liquid crystal polyester is increased to improve tensile strength, then the fiber exhibits higher strength, but the fiber-drawing property deteriorates
Solution Approach 1:
The patent optimizes the molecular weight parameter within the specific range of 40,000-160,000, which is high enough to provide adequate tensile strength through molecular orientation but not excessively high to cause processing difficulties. This parameter optimization maintains a balance between strength and processability, enabling both high tensile strength and good fiber-drawing properties during manufacturing.
Solution Approach 2:
The patent creates a composite molecular structure by combining multiple structural units with different properties: 2,6-naphthalenediyl groups for strength, 2,7-naphthalenediyl groups for structural stability, and other aromatic diol units for flexibility. This composite approach allows the fiber to achieve high tensile strength while maintaining adequate fiber-drawing properties through the synergistic effects of different molecular components.
3Strength
If the liquid crystal polyester is highly oriented in fiber axis direction to improve tensile strength, then molecular chains align well, but compressive strength and fatigue resistance are not sufficiently improved
Solution Approach 1:
The patent employs a composite molecular structure combining 2,6-naphthalenediyl groups (30-70 mol%) for tensile strength through orientation, 2,7-naphthalenediyl groups (5-30 mol%) for structural stability and dimensional control, and other aromatic diol units (10-40 mol%) for flexibility and toughness. This composite approach ensures that while molecular chains are highly oriented for tensile strength, the diverse structural units work synergistically to also provide compressive strength and fatigue resistance.
Solution Approach 2:
The patent optimizes the ratio parameters of different structural units to achieve a balance between orientation-induced tensile strength and compressive/fatigue resistance. By controlling the 2,6-naphthalenediyl group content at 30-70 mol% and combining it with 2,7-naphthalenediyl groups at 5-30 mol%, the patent creates a molecular structure that responds appropriately to both tensile and compressive stresses, resolving the contradiction between different strength requirements.
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 fiber achieves high melting point, degree of crystallinity, and improved tensile and compressive strength, along with excellent fatigue resistance, by minimizing defects like unmelted particles and voids.
Implementation Method 1
heat treatment increases a molecular weight and a melting point of the liquid crystal polyester fiber
Implementation Method 2
the obtained as-spun fiber is subjected to heat treatment at a high temperature for a long time
Implementation Method 3
heat treatment at a high temperature for a long time
Implementation Method 4
adjusting conditions in an extruder and a spinning temperature condition so as to apply a shear stress on a molten resin for melt-kneading
Data Source
AI summary
Provided is a liquid crystal polyester fiber excellent in tensile strength and compressive strength, as well as in disc fatigue resistance. The liquid crystal polyester fiber has a melting point of 335°C or higher and lower than 360°C as measured by a differential scanning calorimeter under a nitrogen atmosphere at a temperature elevation rate of 10°C/min, and has a degree of crystallinity of from 45 to 60%, and a total number of unmelted particles and voids having a long diameter of 5 µm or larger is 3 or less per 5 cm length of a single fiber. For example, the liquid crystal polyester fiber may have a degree of orthorhombic crystallinity of 20% or more in a crystal component.