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NSF Industry/University Cooperative Research Center (I/UCRC) for

Advanced Composites in Transportation Vehicles

Ecofriendly Nano-Composites for Automotive and Aerospace Applications Darshi Dissanayake1, Hossein Toghiani1 and Ratneshwar Jha2

1Dave C. Swalm School of Chemical Engineering, 2Raspet Flight Research Laboratory, Mississippi State University

Background

Approach

Few commercial lignins were fractionated in a precipitation-redissolution process to extract the high molecular weight

fraction suitable for highly ordered graphene nano platelets (GnPs) production. The effects of sequential washing and

solvation were studied using 3 solvents acetone, methanol and tetrahydrofuran (THF). Change in glass transition

temperature was studied using differential scanning calorimetry (DSC) according to the standard ASTM E 1356-08. Fourier

transform infrared spectroscopy (FTIR) was used for chemical structural analysis .

Lignins samples were washed with aqueous HCl at a controlled pH to determine the possibility of sulfur removal. The

treated samples were compared with as received samples in FTIR to find any change in distinct peaks.

Results

Fractionation

Acid washing for sulfur removal

The original samples contained sulfur as S-H, sulfoxides and sulfones as it could be identified by the FTIR peaks at wave-

numbers 2570, 1050, and 1350 cm-1, respectively.

Acid washing could remove at least part of the sulfur in lignin bonded with hydrogen.

Fig: FTIR spectra for lignin PB 1000 (blue– as received, red-treated)

The path towards high strength graphene composites

Studies have shown that the increase in molecular weight would increase many desired properties like tensile strength and

toughness. Removing impurities will increase the rate of production such as increasing melt spin ability which is a key issue

in carbon fiber production; moreover, sulfur removal reduces the brittleness.

References

Saito, T., Perkins, J. H., Vautard, F., Meyer, H. M., Messman, J. M., Tolnai, B., & Naskar, A. K. (2014). Methanol Fractionation of Softwood Kraft Lignin: Impact on the Lig-

nin Properties. ChemSusChem, 7(1), 221–228.

Landel, R. F., & Nielsen, L. E. (1993). Mechanical Properties of Polymers and Composites, Second Edition. CRC Press.

Fractionated samples were analyzed in GPC for their molecular weight

distribution.

Solvent fractionation can be used to extract the high molecular

weight fraction of lignin effectively.

Solvents acetone, methanol and THF are suitable for removing low

molecular fraction of lignin.

The fractionation capability of solvents vary with type of lignin. For

the samples tested, fractionation of lignin PB 1000 using acetone

and lignin PB 2400 using methanol gave the best results.

Sequential dissolution in solvents acetone and methanol followed by

precipitation will increase the average molecular weight. However in

THF, the average molecular weight in second precipitate decreases.

2000

2500

3000

3500

4000

4500

ASR Acetone Methanol THF

Mo

lecu

lar

we

igh

t (D

a)

Effect of solvent in fractionationanalysis of first precipitate

PB 1000

PB 2400

PB 4000

2500

3000

3500

4000

Acetone Methanol THF

Mo

lecu

lar

we

igh

t (D

a)

Effect of sequential washing For Protobind 1000

First precipitation

Second precipitation

Lignin structure and AFM images of Graphene

Lignin is an amorphous polymer present in vegetal cell wall with complex 3D randomized

network. The annual lignin production in pulp and paper industry alone exceeds 50 million

tons which is currently underutilized. Oak Ridge National Laboratory (ORNL) has demonstrated

the use of lignin as a low-cost precursor for carbon fiber production. We are evaluating the

potential use of lignin as a starting material for graphene production, so that it can be used as

nano-reinforcements for applications in automotive and aerospace industries.

Why graphene?

Mass reduction (low density and concentration)

Increased stiffness (high aspect ratio)

Increased toughness (engineered adhesion)

Electrical conductivity (electrostatic painting and dissipation, EMI shielding)

Thermal conductivity, lower coefficient of thermal expansion

Reduced flammability (less combustible material)

Barrier to permeants (platelet morphology)

Challenges

Unreliable precursor to polymer production : Complex 3D structure and structural

variability depends on biomass species, the botanical origin and isolation process;

unknown reactivates and kinetics due to the presence of multiple functional groups.

Polydispersity of lignin (~200-200000 g/mol): low molecular weight lignin is unsuitable for

high-end applications such as thermoplastics

High level of impurities such as sulfur 1-3% (w/w) in Kraft lignin and ash 4-8% in

lignosulfonates

Thermal instability

Obtain uniform dispersion and optimize volume fraction for desired mechanical, thermal

and electrical properties