Soft Polypropylene Nonwovens via Copolymer Molecular Weight Control
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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 50-99 wt% reactor grade propylene-α-olefin copolymer with 5-35 wt% units from ethylene and/or C4-C12 α-olefins, and a second polypropylene with a melting point greater than 110°C, both having specific molecular weight and melt flow rate ranges, to achieve a CD Elongation value of greater than 50%, allowing for adjustable softness and elasticity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If semicrystalline polymers are made at high molecular weight for fiber and fabric manufacture, then the polymer structural integrity and fabric strength are improved, but the meltblown processability deteriorates due to insufficient chain mobility
Solution Approach 1:
The patent applies parameter changes by precisely controlling the molecular weight to fall within the range of 50,000 to 250,000 g/mol and the comonomer content within specific ranges. This optimization allows the polymer to achieve both adequate structural integrity for fabric strength and sufficient chain mobility for meltblown processability, resolving the contradiction between these two requirements
Solution Approach 2:
The patent uses composite materials by incorporating copolymers with specific comonomer contents into the polypropylene matrix. This creates a composite structure where the base polymer provides structural integrity while the copolymer segments enhance chain mobility and processability during meltblowing, simultaneously achieving both fabric strength and manufacturability
2Ease of manufacture
If free radical assisted thermal processes are used to reduce molecular weight for meltblown processing, then the processability is improved, but the polymer undergoes degradation and loss of desired properties
Solution Approach 1:
The patent applies preliminary action by pre-adjusting the molecular weight and comonomer content during polymer synthesis before the meltblown process. This preliminary optimization eliminates the need for aggressive post-synthesis degradation processes like free radical treatment, allowing direct meltblown processing while maintaining polymer property stability and avoiding degradation
Solution Approach 2:
The patent replaces the chemical/mechanical degradation process (free radical assisted thermal processes) with a controlled polymerization approach. Instead of using harsh chemical methods to reduce molecular weight, the invention uses controlled polymer synthesis to achieve the desired molecular weight range, substituting a destructive process with a controlled constructive process that maintains polymer reliability
3Ease of manufacture
If isotactic polypropylene is produced at low molecular weight for meltblown applications, then the processability is improved, but the fabric softness and extensibility deteriorate
Solution Approach 1:
The patent applies parameter changes by optimizing both molecular weight (50,000 to 250,000 g/mol) and comonomer content within specific ranges. This dual parameter optimization allows the polymer to achieve low enough molecular weight for meltblown processability while maintaining sufficient chain flexibility and crystallinity for fabric softness and extensibility, resolving the contradiction between processability and final fabric properties
Data Source
AI summary
Disclosed herein is a nonwoven fabric comprising within the range of from 50 to 99 wt %, by weight of the composition, 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 500 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 CD Elongation value of greater than 50% (measuring the fabric of 35 g/m2 basis weight). The fabric described herein 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.