High-Strength PLA Filament via Sub-Zero Cooling
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Solution Overview
Problem
Current processes for producing high-strength polylactic acid (PLA) elongated objects face challenges in achieving high tensile strength on an industrial scale due to difficulties in spinning and drawing high molecular weight PLA, leading to commercially unattractive product properties and low throughput.
Innovation Solution
A process involving the formation of a PLA solution with an intrinsic viscosity of at least 4 dL/g, spinning through a spinplate, cooling with a medium at less than 0°C, and applying draw ratios to achieve high tenacity PLA elongated objects, allowing for higher PLA concentrations and scalable production.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If high molecular weight PLA (intrinsic viscosity ≥ 4 dL/g) is used to achieve high tensile strength, then the tenacity of the filament increases, but the spinning and drawing process becomes increasingly difficult
Solution Approach 1:
The patent changes the temperature parameter of the cooling medium to below 0°C, which fundamentally alters the freezing behavior of the solvent and enables effective gelation of high molecular weight PLA filaments that would otherwise be too difficult to handle and draw
Solution Approach 2:
The patent introduces a cooling medium as an intermediary substance that facilitates the gelation process. This medium acts as a bridge between the spun filament and the final solid product, enabling the transformation from difficult-to-handle high IV PLA to drawable gel filaments through controlled freezing
2Strength
If ultra-high molecular weight PLLA is used to achieve high tenacity (1.70 N/tex), then the tensile strength increases, but the process requires high dilution (4 mass%) which negatively affects upscaling and economic feasibility
Solution Approach 1:
The patent changes the concentration parameter from 4 mass% to 5-50 mass%, which increases the solids content and enables higher throughput. This parameter change, combined with low temperature cooling, allows processing of concentrated PLA solutions that would normally be too viscous to spin
Solution Approach 2:
The patent applies local quality by creating different zones in the spinning process: the spinplate region where solution is extruded, the air-gap region where initial formation occurs, and the cooling medium region where gelation happens. Each zone has optimized conditions that collectively enable high concentration 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 process results in PLA elongated objects with unmatched tensile properties and higher tenacities than known gel-spun objects, enabling production of high-strength PLA filaments and yarns at an attractive rate for commercial scale.
Implementation Method 1
contacting the fluid elongated object with a cooling medium to form a solvent-containing gel elongated object
Data Source
Figure 1~2
AI summary
The present invention relates to a process for making high-strength polylactic acid elongated object comprising the steps of making a solution of polylactic acid in a solvent at a concentration of 5 to 50 mass%; spinning the solution through a spinplate comprising at least 1 spinhole to form a fluid elongated object; cooling the fluid elongated object with a cooling medium to form a solvent-containing gel elongated object; removing at least partly the solvent from the gel elongated object to form a solid elongated object; and drawing the elongated object while applying a draw ratio of at least 2, to form a high strength PLA elongated object, characterized in that the cooling medium has a temperature Tq of less than 0°C. The present invention also relates to gel-spun elongated objects comprising PLA with an IV in the range of 4-40 dl/g, and having a tenacity in N/tex such that Ten ≥ 0.146 * IV, as well as gel-spun elongated object having a tenacity and a filament titer in tex (t) such that Ten ≥ 1.40 * t-0.3. The invention also relates to articles containing said gel-spun elongated objects.