PLA Fiber Melt Strength via Polyepoxide Branching
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Solution Overview
Problem
Polylactic acid (PLA) nonwoven webs exhibit low bond flexibility, high roughness, and low elongations due to high glass transition temperature and slow crystallization rate, which are not suitable for certain applications, and the use of plasticizers like polyethylene glycol leads to mechanical property deterioration over time.
Innovation Solution
Melt blending polylactic acid with a polyepoxide modifier to form a thermoplastic composition, where the polyepoxide modifier reacts with polylactic acid to improve melt strength and stability during fiber spinning, reducing glass transition temperature and enhancing elongation properties without using plasticizers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If plasticizers like polyethylene glycol are added to reduce glass transition temperature and improve bonding, then bond flexibility and softness are improved, but mechanical properties deteriorate over time due to phase separation
Solution Approach 1:
A compatibilizer comprising a copolymer of a C3-C20 alpha-olefin and an epoxy-functional (meth)acrylic monomer is introduced as an intermediary substance between the polyolefin and polylactic acid. This compatibilizer has a glass transition temperature of -50° C. to -100° C. and reduces the glass transition temperature of the polyolefin by 10° C. to 50° C. The compatibilizer improves bond flexibility and softness without causing phase separation, thereby maintaining mechanical properties stability over time.
2Stability of the object's composition
If high draw ratios are applied to achieve desired crystallization and overcome heat shrinkage, then crystallization is improved, but high levels of draw energy are required
Solution Approach 1:
The glass transition temperature of the polyolefin is reduced by 10° C. to 50° C. through the addition of compatibilizer, which enables the fiber to achieve desired crystallization at lower draw ratios. This parameter change reduces the energy required for drawing while maintaining or improving crystallization quality and reducing heat shrinkage.
3Ease of operation
If polyethylene glycol is used as plasticizer to improve bonding, then bond flexibility is improved, but degradation in melt spinning and reduction in melt strength occur
Solution Approach 1:
The compatibilizer serves as an intermediary that improves bonding between polyolefin and polylactic acid without the harmful effects of polyethylene glycol. The compatibilizer has appropriate molecular weight and glass transition temperature that enable effective interfacial adhesion while maintaining melt strength and drawability during the melt spinning process.
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 polylactic acid fibers exhibit improved mechanical properties, including peak elongation of 50% or more and tenacity of 0.75 to 6 grams-force per denier, maintaining strength and ductility, while avoiding the degradation issues associated with plasticizers.
Implementation Method 1
the polyepoxide modifier reacts with polylactic acid to improve melt strength and stability during fiber spinning
Implementation Method 2
the thermoplastic composition is extruded at a temperature above about 230° C. to facilitate reaction of the polyepoxide modifier with the polylactic acid
Data Source
AI summary
A method for forming biodegradable fibers is provided. The method includes blending polylactic acid with a polyepoxide modifier to form a thermoplastic composition, extruding the thermoplastic composition through a die, and thereafter passing the extruded composition through a die to form a fiber. Without intending to be limited by theory, it is believed that the polyepoxide modifier reacts with the polylactic acid and results in branching of its polymer backbone, thereby improving its melt strength and stability during fiber spinning without significantly reducing glass transition temperature. The reaction-induced branching can also increase molecular weight, which may lead to improved fiber ductility and the ability to better dissipate energy when subjected to an elongation force. Through selective control over this method, the present inventors have discovered that the resulting fibers may exhibit good mechanical properties, both during and after melt spinning.