Soft Polypropylene Nonwovens via Polymer Blending
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Solution Overview
Problem
Existing methods for producing soft and extensible nonwoven fabrics from polypropylene and its copolymers face challenges in achieving the right balance of properties, particularly in using semicrystalline polymers made at high molecular weights for meltblown fibers and fabrics, which require lower molecular weight polymers without post-reactor degradation.
Innovation Solution
A nonwoven fabric comprising 1-49 wt% reactor grade propylene-α-olefin copolymer with 5-35 wt% units from ethylene and/or C4-C12 α-olefins, a melt flow rate of 600-7500 g/10 min, and a weight average molecular weight less than 200,000, blended with a second polypropylene having a melting point greater than 110°C and a melt flow rate of 20-7500 g/10 min, to achieve a Handle value of less than 60%.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If semicrystalline polymers are made at high molecular weight (above 250,000 daltons), then the polymer has improved strength and structural properties, but the polymer cannot be used for meltblown fiber fabrication which requires lower molecular weight (less than 250,000 daltons)
Solution Approach 1:
The patent divides the polymer system into two distinct components: a high molecular weight semicrystalline polymer (providing strength) and a low molecular weight amorphous polymer (enabling meltblown processing). This segmentation allows each component to fulfill its specific function without compromise - the semicrystalline polymer provides structural integrity while the amorphous polymer ensures processability at lower molecular weights.
Solution Approach 2:
The invention creates a composite material system combining semicrystalline and amorphous polymers in a blended composition. The semicrystalline polymer (5-50 wt%) contributes strength and thermal properties, while the amorphous polymer (50-95 wt%) provides low-temperature processing capability. This composite approach resolves the contradiction by allowing the final product to exhibit both high strength and ease of meltblown fabrication.
2Ease of manufacture
If post-reactor degradation processes are used to achieve lower molecular weight, then the polymer becomes suitable for meltblown processing, but the polymer loses structural integrity and crystallinity
Solution Approach 1:
Instead of degrading the polymer after reactor production, the invention uses preliminary action by selecting appropriate polymers from the outset - a semicrystalline polymer already at suitable molecular weight and an amorphous polymer designed for low-temperature processing. This eliminates the need for post-reactor degradation while maintaining crystallinity, as the amorphous polymer inherently provides the required processability without compromising the semicrystalline component's structural integrity.
3Adaptability or versatility
If copolymers with limited crystallinity are produced, then the polymer has improved flexibility and elongation, but the polymer lacks the crystallinity needed for fiber and fabric fabrication
Solution Approach 1:
The patent segments the crystallinity function from the flexibility function by assigning them to different polymer components. The semicrystalline polymer (5-50 wt%) provides the necessary crystallinity for fiber fabrication and structural stability, while the amorphous polymer (50-95 wt%) provides flexibility and elongation. This segmentation allows the final nonwoven fabric to achieve both high elongation (50-200%) and manufacturability without relying on limited-crystallinity copolymers.
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 solution enables the production of soft and elastic nonwoven fabrics with improved elongation and tensile strength, maintaining desired elasticity and softness while eliminating stickiness issues, and can be used in various structures including multilayer laminates for hygiene and medical products.
Implementation Method 1
a first polymer component which is a propylene-α-olefin copolymer... and a second polypropylene... wherein the fabric has a Handle value of less than 60%
Implementation Method 2
a first polymer component which is a propylene-α-olefin copolymer possessing... a weight average molecular weight of less than 200,000; and a second polypropylene having a melting point, Tm, of greater than 110° C.
Implementation Method 3
a melt flow rate (230° C./2.16 kg) within the range of from 600 to 7500 g/10 min; and a second polypropylene having a melting point, Tm, of greater than 110° C.
Data Source
AI summary
Disclosed herein is a nonwoven fabric comprising within the range of from 1 to 49 wt %, by weight of the fabric, of a reactor grade propylene-α-olefin copolymer possessing; within the range of from 5 to 35 wt %, by weight of the copolymer, of units derived from one or more of ethylene and/or C4 to C12 α-olefins; a melt flow rate (230° C./2.16 kg) within the range of from 600 to 7500 g/10 min; and a weight average molecular weight of less than 200,000; and a second polypropylene having a melting point, Tm, of greater than 110° C. and a melt flow rate (230° C./2.16 kg) within the range of from 20 to 7500 g/10 min; wherein the fabric has a Handle value of less than 60% (measuring the fabric of 35 g/m2 basis weight). The fabric can be used in structures comprising one or more layers of the fabric described herein, and can include any number of other fabric layers made from other materials.