Lignin Blended Polyacrylonitrile (PAN) Terpolymer Based Carbon Fiber and Manufacturing Process Thereof

Lignin is a biobased alternative for low cost carbon fiber production as compared to Polyacrylonitrile which is a petroleum based.

The present invention provides a process for producing PAN-Lignin (PL) carbon fiber of good homogeneity and superior tensile properties by a stable wet spinning operation which does not involve troubles ascribable to filament breakage which where encountered in the prior art.

Another objective of this invention is the effect of lignin properties on producing the PL carbon fiber with better mechanical properties.

That is, the present invention relates to a process for producing PL carbon fiber comprising the following claims:

(i) process for making PL blend concentrated solution by two step method in which first step comprises of dissolution of lignin with suitable solvent say dimethyl sulphoxide at 40-50  ^oC for say 15-20 h. In the second step, PAN copolymer having weight average molecular weight of at least 1.5 x 10⁵ and containing at least 95 wt % acrylonitrile is added to the solution formed in first step so as to have a total solid content of 15-25 wt % to provide a spinning solution of having viscosity 80 to 200 poise at 50 ^oC.

(ii) Extrusion of solution into a coagulation bath comprising of water and dimethyl sulphoxide at 23-28 ^oC.

(iii) wet stretching the coagulated filaments to a draw ratio of at least 7 to 10 times and subsequently hot stretched 1.3 to 2 times to get the required precursor fiber.

 (iv) the precursor fibers are stabilized by oxidation by heating at 200-300 ^oC for 60 to 180 min in the presence of air.

(v) the stabilised fiber is precarbonized and carbonized under nitrogen atmosphere from 400 to 1300 ^oC to get the PL carbon fiber.

Industrial Application Sector:  

Non-strategic sectors, Automobile industries, Insulating materials, thermal/firefighting suits, energy storage, etc.

1. Homogenous preparation of Lignin/PAN terpolymer blend in dimethylsulfoxide solvent
2. Use of wet spinning technology to get minimal leaching out of lignin during coagulation.
3. Provide a complete and continuous process technology from Lignin/PAN terpolymer blending to carbon fiber.
4. Cost effective way for the production of carbon fiber since lignin is a renewable bioresources.