Bimodal Poly(hydroxyalkanoate) Composition for Lower Melt Viscosity
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Solution Overview
Problem
Existing poly(hydroxyalkanoate) polymers face challenges in achieving high molecular weights for desirable physical properties while maintaining a manageable melt viscosity for efficient thermal processing.
Innovation Solution
A bimodal molecular weight distribution is achieved by combining a first portion with a high weight average molecular weight and a second portion with a significantly lower weight average molecular weight, typically at least 50% less, resulting in a polydispersity of at least 1.9, through a method involving the polymerization and blending of substituted lactones, particularly beta-propiolactone, to form a poly(hydroxyalkanoate) composition.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If molecular weight is increased to improve physical properties, then strength and durability are improved, but melt viscosity increases making thermal processing difficult
Solution Approach 1:
The patent segments the molecular weight distribution into two distinct modes: a high molecular weight portion (first mode) providing strength and durability, and a low molecular weight portion (second mode) providing low melt viscosity for easy thermal processing. This segmentation allows each mode to fulfill its specific function without compromising the other.
Solution Approach 2:
The patent creates a composite polymer system by combining polymers with different molecular weights in a single composition. The composite nature of the material allows simultaneous achievement of high strength (from high MW component) and low melt viscosity (from low MW component), resolving the contradiction between these properties.
2Strength
If molecular weight is increased to achieve desirable physical properties, then polymer strength improves, but melt viscosity becomes too high for typical conversion equipment
Solution Approach 1:
The patent divides the molecular weight distribution into discrete segments or modes. The first mode represents high molecular weight chains providing strength, while the second mode represents low molecular weight chains providing processability. This segmentation enables independent optimization of each function.
Solution Approach 2:
The patent changes the molecular weight parameter by introducing a bimodal distribution rather than a unimodal distribution. This parameter change allows the material to exhibit both high strength (from high MW portion) and low melt viscosity (from low MW portion), making it suitable for both performance and processing 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 bimodal poly(hydroxyalkanoate) composition maintains good physical properties associated with higher molecular weights while reducing melt viscosity, enabling easier thermal processing and broader application in films and fibers.
Implementation Method 1
Poly(hydroxyalkanoates) may be prepared by a ring opening polymerization process
Implementation Method 2
the physical properties of the polymer are often a function of molecular weight. In order to obtain desirable physical properties, it is often desirable to produce polymers with molecular weights that are as high as can be achieved
Data Source
AI summary
A poly(hydroxyalkanoate) composition having a bimodal molecular weight distribution. The composition includes of a first portion and a second portion of a poly (hydroxy alkanoate). The first portion has a first weight average molecular weight and the second portion has a second weight average molecular weight which is at least 50 percent less than the first weight average molecular weight. The poly(hydroxyalkanoate) is made up of at least 10 mole percent monomer repeat units of 3 -hydroxypropionate. A method for making the composition is also disclosed.