PLA Resin Blend for Non-Woven Fabric Shrinkage Reduction
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Solution Overview
Problem
Polylactide (PLA) non-woven fabrics face challenges in melt rheology and high shrinkage due to degradation at elevated temperatures and low crystallinity, leading to increased energy costs and reduced tensile strength.
Innovation Solution
A spun-melt process using a PLA resin blend with at least 75% PLA having a high number average molecular weight and a combination of aliphatic or aliphatic-aromatic polyester, which reduces shrinkage and operating pressures, allowing for lower energy consumption and improved tensile strength.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If PLA is processed at higher temperatures to reduce melt viscosity, then the melt viscosity decreases and throughput increases, but the polymer degrades more rapidly and molecular weight is lost
Solution Approach 1:
The patent changes the chemical composition parameter of the polymer blend, incorporating 5-20 weight percent of a different aliphatic polyester to fundamentally alter the melt rheology. This allows processing at lower temperatures while maintaining acceptable viscosity, thus preventing thermal degradation and molecular weight loss while still achieving adequate throughput.
Solution Approach 2:
The patent creates a composite material system by blending PLA with another aliphatic polyester. This composite approach combines the beneficial properties of both polymers: PLA provides the base structure and the second polymer modifies the melt flow characteristics, enabling lower temperature processing that preserves molecular weight while maintaining productivity.
2Ease of operation
If PLA non-woven fabrics are exposed to elevated temperatures for drying or application, then the fabric can be processed or used, but the fabric exhibits significant shrinkage
Solution Approach 1:
The patent changes the thermal and structural parameters of the fabric by using the polyester blend, which has different thermal expansion and crystallization characteristics than pure PLA. This modification reduces the fabric's tendency to shrink when exposed to elevated temperatures during drying or application, while still allowing the fabric to be processed and used at these temperatures.
3Productivity
If higher operating pressures are used to process PLA, then the throughput is maintained, but the energy costs and equipment costs increase
Solution Approach 1:
The patent changes the rheological parameters of the polymer through blending with another aliphatic polyester. This composition modification reduces the melt viscosity and improves flow characteristics, allowing the same throughput to be achieved at lower operating pressures, thereby reducing energy consumption and equipment 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 process results in non-woven fabrics with significantly reduced shrinkage, lower energy costs, and enhanced tensile strength, while maintaining comparable elongation, making them suitable for various applications.
Implementation Method 1
The selection of the PLA resin blend provides important benefits. Very surprisingly, the non-woven fabric exhibits significantly reduced shrinkage, compared to otherwise like fabrics made using neat PLA resin. Operating pressures are reduced very significantly at equivalent operating rates, compared to when a neat PLA resin is used.
Implementation Method 2
In spun-melt processes, the orientation occurs almost exclusively during the drawing step. The available time window is very short and the extent to which the filaments can be attenuated is often small, compared to other fiber-spinning processes. Orientation helps to induce crystallinity in crystallizable polymers such as PLA.
Implementation Method 3
It is common to strengthen the fabric by calendering or heat bonding it. Calendaring and heat bonding processes involve the application of heat and pressure to the fabric or (more commonly) localized portions of the fabric, to melt individual filaments so that they adhere to each other.
Implementation Method 4
Another problem with PLA non-woven fabrics is their tendency to shrink when exposed to moderately elevated temperatures. This is an important consideration for any fabric that is to be laundered and then machine dried, or when the fabric is to be used in an application in which it is exposed to moderately elevated (for example, up to about 100°C) temperatures. Shrinkage is strongly affected by the orientation of the polymer and (in crystallizable polymers such as PLA) the development of crystallinity.
Data Source
AI summary
Non-woven fabrics are made in a spun-melt process, in which a PLA resin blend is melt-spun into filaments, which are pneumatically drawn and then deposited onto a surface to produce the fabric. The PLA resin includes 1-25% of certain aliphatic or aliphatic-aromatic polyesters that have a number average molecular weight from 4,000 to 70,000 g/mol.