Modified Lignin Linking for High-Yield Carbon Fiber Precursors
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Solution Overview
Problem
Current methods for producing carbon fibers from lignin result in highly branched products with low molecular weight, leading to weak mechanical strength and brittleness, making them unsuitable as marketable products due to low carbon yield and high material loss during thermal conversion.
Innovation Solution
A modified lignin is produced by linking lignin molecules with aromatic linking units via a methylene group, using an aromatic linking compound with two hydroxymethyl groups, resulting in a linear structure with controlled molecular weight and reduced porosity, suitable for carbon fiber production.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If lignin is used as a precursor for carbon fibers, then carbon yield is improved, but mechanical strength is worsened due to low molecular weight and highly branched structure
Solution Approach 1:
The invention segments the lignin processing approach by first fractionating lignin to isolate specific molecular weight ranges (2,000-20,000 g/mol) before polymerization, thereby selecting molecules suitable for both high carbon yield and improved mechanical properties
Solution Approach 2:
The invention creates a composite polymer structure by covalently bonding lignin molecules to synthetic polymer chains through coupling agents, combining the high carbon yield of lignin with the mechanical strength of synthetic polymers to produce hybrid precursor fibers
2Quantity of substance
If lignin molecules are fragmented during pulping to obtain cellulose, then cellulose purity is improved, but lignin molecular weight is worsened resulting in low molecular weight oligomers
Solution Approach 1:
The invention performs preliminary fractionation of lignin to isolate and concentrate molecules within the desired molecular weight range (2,000-20,000 g/mol) before the polymerization step, ensuring that only suitable lignin molecules are used as precursors
Solution Approach 2:
The invention changes the molecular weight parameter of lignin through controlled polymerization reactions, transforming low molecular weight oligomers into high molecular weight polymers with target ranges of 50,000-500,000 g/mol
3Strength
If flexible auxiliary polymers are added to improve mechanical strength, then precursor fiber flexibility is improved, but carbon yield is worsened due to reduced aromatic content
Solution Approach 1:
The invention creates a controlled composite where lignin is covalently bonded to synthetic polymers in specific ratios (30-70 wt% lignin), maintaining sufficient aromatic content for high carbon yield while incorporating flexible polymer chains for improved mechanical properties
Solution Approach 2:
The invention optimizes the composition parameters by controlling the weight ratio of lignin to synthetic polymer (30-70 wt% lignin) and adjusting molecular weight parameters to achieve the balance between flexibility and carbon yield
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 modified lignin achieves high carbon yield and improved mechanical properties, enabling the production of carbon fibers with enhanced tensile strength and modulus of elasticity.
Implementation Method 1
linking lignin molecules with aromatic linking units via a methylene group, using an aromatic linking compound with two hydroxymethyl groups
Data Source
Figure 1
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AI summary
The invention relates to modified lignin based on substituted and/or unsubstituted lignin, the lignin molecules of the substituted and unsubstituted lignin (A) being linked by means of linking units (B) in order to increase the molecular weight. Said modified lignin is characterized in that the linking units (B) are aromatic and are bonded to the lignin molecules (A) by means of a methylene group. The invention further relates to a method for producing a modified lignin of this type, wherein the lignin (A) is dissolved in a solvent and is reacted in the solution with an aromatic linking compound (C), which has at least two hydroxymethyl groups, in particular two terminal hydroxymethyl groups, in the presence of an organic acid (D) at elevated temperature to form modified lignin. The invention further relates to the use of the modified lignin to produce precursor fibers, which can be converted into carbon fibers by carbonization.