toward high value thermoplastic lignin polymers · departments of chemistry and forest biomaterials...

Toward High Value Thermoplastic Lignin Polymers

H. Sadeghifar, C. Cui,

S. Sen Dimitris S. Argyropoulos*

Departments of Chemistry and Forest Biomaterials North Carolina State University , Raleigh , NC USA

& *Advanced Materials Research Center of Excellence,

King Abdulaziz University, Jeddah, Saudi Arabia.

Lignin is the second most abundant biopolymer on the planet

Together with cellulose they can be considered as the batteries of the planet

Lignin structure is highly irregular but extremely challenging

Lignin presents opportunities for our chemical industry since it represents the reduced part of the lignocellulosic substrate compared to sugars

Objective

To describe our philosophy and approach aimed at creating heat stable technical lignin melts

& Aimed at Thermoplastics, Precursor to carbon Fibers & Engineering Heat Stable Polymers

Fundamental Science aimed at Creating Thermoplastic Lignin Melts

Heat Stable Polyarylene Ether Sulfone -Kraft Lignin Co-Polymers

Defining the Science & a Novel Approach aimed at Creating Carbon Fibers from Lignin Melts

Fundamental Science aimed at Creating Thermoplastic Lignin Melts

Softwood kraft lignin is highly susceptible to thermally induced

reactions that cause its molecular characteristics to be severely

altered. These events seriously interfere and prevent such materials

from being considered as candidates for thermoplastic applications.

MeO

OH

CHCH

CH

MeO

OH

SCH2OH

COOH

CHCH2OH

HC

OHOMe

OH

O O

HOOC

OMeO

O

MeO

CHOHCHCH2OH

HO

MeO

OH

OH

CH

CH

OHOMe

C

CH2

O

CH CH

OMe

O

CHC OCH2

OH

CH2

HOH2C

OHOMe

CHCHO

CH2OH

CH2

MeO

OH

OMe

COOH

Kraft Lignin Structure

Marton, J. 1971.

Effect of Heating on the Molecular Weight Distribution

of Underivatized Kraft Lignin

Cui, C., et al. “Toward Thermoplastic Lignin Polymers; Part II: " BioResources 8(1), 864-886, (2013).

Starting Softwood Kraft Lignin “Indulin” Molecular Weight : Mw = 8000 (g/mol) Mn = 2000 ( g/mol) ( Mw/Mn = 4 ) Total phenolic-OH = 3.85 mmol/ g Total Aliphatic-OH = 2.4 mmol/g Tg : 150-160°C .

MeO

OH

CHCH

CH

MeO

OH

SCH2OH

COOH

CHCH2OH

HC

OHOMe

OH

O O

HOOC

OMeO

O

MeO

CHOHCHCH2OH

HO

MeO

OH

OH

CH

CH

OHOMe

C

CH2

O

CH CH

OMe

O

CHC OCH2

OH

CH2

HOH2C

OHOMe

CHCHO

CH2OH

CH2

MeO

OH

OMe

COOH

Effect of Heating Between 120-140 °C on MWD of Underivatized Kraft Lignin

Annealing Temperature, °C --- 120 130 140

Mw (g/mol) 8000 13000 128000 340000

Mn ( g/mol) 2000 2030 2200 2100

Mw/Mn 4 6.4 58.2 162 H. Sadeghifar , Toward Thermoplastic Lignin Polymer Part I , Ind. Eng. Chem. Res., 2012, 51 (51), pp 16713–16720 DOI: 10.1021/ie301848j

OOCH3

R

OOCH3

OOCH3

OOCH3

H�

�

�

OOCH3

�H

OOCH3

OOCH3O

H3CO�H

OOCH3OH

H3CO

Rearomatization

Radical Coupling

4-O-5 Ether Linkage Formation

OOCH3HO OCH3

OH3CO

H

H

Rearomatization

OHOCH3

OHH3CO

Radical Coupling

5-5' Linkage Formation

Kawamoto, et al. J. Wood Sci. 2007, 53(2) &53(3)&27(2); J. Anal. Appl. Pyrolysis 2008, 81 (1), 88-94. Holzforschung 2008, 62 (1), 50. Ohashi, et al.. Org. Biomol.. Chem. 2011, 9 (7), 2481-2491

O

O

H

L

OOCH3

OCH3

O

L

OHOCH3

OCH3

-HCOH

Quinone Methide

O

O

H

L

OOCH3

OCH3

Formaldehyde Generation

O

OH

L

OOCH3

OCH3

Quinone Methide

O

OH

L

OOCH3

OCH3

�

�

Phenoxy Radicals

Kawamoto,et al, J. Wood Chem. Technol. 2007, 27 (2), 113-120.; Holzforschung 2008, 62 (1), 50

Working Hypothesis & Statement of Purpose

• Since the phenolic OH is implicated as being pivotal in

thermal events operating within lignin we aim to devise

technically feasible methods to selectively protect

these groups in kraft lignin and examine their effects

on their thermal properties

• Methylation with Methyl Iodide in ( DMF ) • Methylation with Dimethyl Sulfate in NaOH

Lignin Methylation

A L

OH

L

OMeOMe OMe

CH3I , DMF, K2CO3

(CH3)2SO3, NaOH(aq)

H. Sadeghifar , Toward Thermoplastic Lignin Polymer Part I , Ind. Eng. Chem. Res., 2012, 51 (51), pp 16713–16720 DOI: 10.1021/ie301848j

Comparison of Methylation Effectiveness as a Function of Reagent Concentration

Phenolic-OH Methylation with Dimethyl Sulfate is a lot more effective & Selective than Methyl Iodide.

0 0.25 0.5 1 1.5 2 2.5

3.85

3.1

2.31

1.73

1.24

0.5

0.03

3.66 3.52

2.9

2.4

1.8 1.6

mmol/g

Lignin

Molar ratio of methylation reagent/phenolic-OH

Methylation with dimethyl sulfate Methylation with methyl iodide

Kraft lignin methylation with (CH3)2SO4

Ratio of (CH3)2SO4 to total phenolic-OH in lignin

The progressive and selective elimination of phenolic-OH’s is apparent CONFIDENTIAL

Kraft Lignin Oxypropylation with Propylene Oxide in Aqueous Base


Kraft Lignin Oxypropylation

• Procedure • Kraft lignin was reacted with propylene oxide in 0.5M NaOH solution

at 40°C for 12hrs with stirring • Degree of oxypropylation was measured by phosphorus NMR

L

OH

L

O-CH2CH-O-CH2CHO-HOMe OMe

NaOH (aq)O

CH3 CH3 n


How does the Phenolic OH & its Derivatives Define the Thermal

Reactivity of Kraft Lignin ?

Effect of Heating Kraft Lignin & Derivatives 20 0C above Tg on Molecular Weight


Effect of Heating on the Molecular Weight Distribution

of Fully Oxypropylated Kraft Lignin


Effect of Heating at 150 °C on Fully Oxypropylated Kraft Lignin Molecular Weight Distribution as a Function of Time

Heating Time ( min) 0 1 5 20 40 60

Mw , g/mol 9000 44000 58000 150000 210000 210000

H

OO

HH

H

HL

OR

HO

H

L H+

LH

HH

OH HO

OxoniumIon

Deprotected Phenolic OH

Hydride Transfer

- H2O

H2O

Why Oxypropylated Lignin Shows Thermal Lability ?

•Facile dehydration of 20 OH of the oxypropyl substituent •Dehydration facilitated by an immediate α-hydride transfer forming an oxonium intermediate •New phenolic OH group generated from the deprotection

Olah G.& Prakash, G. K. S., Carbocation Chemistry. J. Wiley & Sons,.: New Jersey, 2004. Vollhardt, K. P. C.& Schore, N. E., Organic Chemistry: Structure & Function. NY. 2007.

Since methylation of the Phenolic OH with Dimethyl Sulfate showed promising thermal stability…

• Is this stability permanent ? • Can the material withstand heating &

Cooling cycles ? • How does the Molecular Weight

Distribution of the material is affected by repeated Heated & Cooling Cycles? Polymer Processing Simulating Conditions.

2nd Heating

3rd Heating

Minute Changes in the Mol. Wt Distributions are Indicative of the Sought Chemically Stable Melt Characteristics


MeO

OH

CHCH

MeOOH

SCH2OH

COOH

CHCH2OH

HC

OH

OH

O O

HOOC

OMeO

O

MeO

CHOHCHCH2OH

HO

MeO

OHOH

CHCH OH

OMe

CH2C

O

CHCH

OMe

O

CHC OCH2

OH

CH2

HOH2C

OHOMe

CHCH

OCH2OH

CH2

MeO

OH

OMe

COOH

OH

OHOMeMeO

OOMe

OHHO

OH

OH

(B)

MeO

(A)

(A)

(A)

(A)

HO

HO

OH

OH

HO

HO

A+A

4-O-5

Ether

Linka ge

Form

ation

A +A

5 -5 Li nk ag e

F ormati on

A+BA-A, B-B and

A-B Linkag es

Formation

HO

HO

OH

OH

A multitude of inter & intra molecular thermal events in Kraft lignin may be avoided by the selective and complete methylation of its phenolic OH groups. Thus preventing the phenoxy radicals & QM’s from forming and reacting .

Toward Carbon Fibers from Technical Lignin

Defining the Science & a Novel Approach aimed at Creating Carbon Fibers from Lignin Melts

S. Sen, et al. “Toward Thermoplastic Lignin Polymers; Part III: " Biomacromolecules (2013).

Since derivatization of the Phenolic OH allowed the modulation of the thermal stability…

Eventual aim: Carbon Fibers from Lignin

• Can one modulate thermal crosslinking? • Can one regulate the rate of Mol.

Weight Increase? • By introducing activated (thermally

labile) centers how does the Molecular Weight Distribution of the material is affected ?

KL 20% methylated 80% activated 150 °C, 10 min

KL 20% methylated

80% activated 150 °C, 60 min



KL 20% methylated

80% activated 150 °C, 60 min


The molecular weight distribution gradually increases with increasing temperature and time of heating

Toward Heat Stable Poly (Arylene Ether)

Sulfone-Lignin Heat Stable Copolymers

Why Poly (Arylene Ether Sulfones) • Ease of preparation, • Ease of functionalization, • Thermal & chemical stability • Relatively low cost • Excellent mechanical performance.

Copolymerization of Kraft Lignin with DifluoroDiphenyl Sulfone (DFDPS)

SF FO

O

Ar OHL DMSO/toluene-H2O

Ar O-Na+L

Ar O-L

SF

FO

OOAr L

-SF

FO

OOArL

-

SF

FO

OAr L

O-

SF

FO

OOAr L

-

S FO

OOArL

-X-

Ar OHL = Lignin molecule with phenolic -OH end group

NaOH

0

0.2

0.4

0.6

0.8

1

1.E+001.E+011.E+021.E+031.E+041.E+051.E+06

22% Methylated KL-DFDPS Co-Polymer

Starting Kraft Lignin

71% Methylated KL-DFDPS C0-Polymer

63% Methylated KL-DFDPS C0-Polymer


Size Exclusion Chromatographic Analyses of Methylated Kraft Lignin DFDPS Co-Polymers .

Typical Step growth polymerization Mol wt. distribution shapes are observed, progressively moving to higher molecular weights

13C NMR Spectra of Starting Kraft Lignin & Its Co Polymer with DFDPS

Initial Kraft Lignin

Copolymer of Kraft Lignin with DFDPS

13C NMR Spectra of Starting Kraft Lignin & Its Co Polymer with DFDPS

Thermal Degradation Analyses of Methylated Kraft Lignin DFDPS Co-Polymers

DFDPS



35.0

45.0

55.0

65.0

75.0

85.0

95.0

100 150 200 250 300 350 400 450 500 550

KL-DFDPS Co-Polymer

Kraft lignin

Heat stabilities up to 270 0C are observed for these Kraft Lignin DFDPS Copolymers with Tg values at least 100 0C lower

Differential Thermal Scans of Methylated Kraft Lignin DFDPS Co-Polymers .

Tg,172 °C

Tg,170 °C

Tg,166 °C Tg,147 °C

Glass Transitions Temperature (Tg) as Function of Molecular Weight for a Series of Kraft Lignin –DFDPS Co-Polymers

90

147

166 170

60

80

100

120

140

160

180

1200 3900 5900 6800

Tg ,

°C

Molecular Weight , g/mol

100 % Lignin

74 % Lignin

69 % Lignin

86% Lignin

Conclusions

• The selective methylation of the phenolic OH is pivotal in

controlling the thermal stability of technical Lignin

• Molecular Weight Distribution measurements offer a

detailed way of understanding such thermal events

• 100% Kraft Lignin Thermoplastic Polymers & Specialty

Copolymers are possible

Conclusions

• Thermoplastic Co-polymers of Polyarylene ether Sulfones

with Kraft Lignin have been synthesized displaying :

- Typical Step Growth Mol. Weight Distributions

- Excellent Thermal Stability

- Predictable Mol. vs Wt. Tg Relations

Strategic Decisions

• Treating Lignin with respect will pay off • Focus & capitalize on current limitations • Expand into Hardwood & Biorefinery

Lignins • Work with Specific Lignin for specific

high value applications • Work with Industry to bring these to

further development

toward high value thermoplastic lignin polymers · departments of chemistry and forest biomaterials...

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