toward thermoplastic lignin polymers; synthesis &...

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.  Cost Action FP 0901, “Biorfinery Analytics”,

Turku, Finland, September 17-18, 2013.

Toward Thermoplastic Lignin Polymers; Synthesis & Analysis  

Objective

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

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

The concerted use of a variety of analytical tools

is indispensable in such endeavors

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.

Kraft Lignin Structure In Bad Need for A New Model

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 .

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

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

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

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

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 (Measure Melt Torque, f(time) with a Lab Mini-extruder).

2nd Heating

3rd Heating

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

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

3500  

3700  

3900  

4100  

4300  

4500  

4700  

4900  

5100  

1   2   3   4   5   6   7   8   9   10  

Exrtrude

r  force,  N

Time,  min.  

Comparison of Torque ( N ) as a function of melt mixing time for Blends of PP with Non Derivatized (Un-Methylated) and Fully

Methylated Kraft Lignin 25% lignin

Methylated

Un-methylated

The melt stability of methylated Kraft Lignin has been verified using melt torque measurements

There is no melt stability for non-derivatized Kraft Lignin due to the onset of crosslinking reactions

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 ?

Towards Reactive Extrusion Lignins

Kraft Lignin Chain Extension Chemistry via Propargylation, Oxidative Coupling & Claisen

Rearrangement

Biomacromolecules : http://dx.doi.org/10.1021/bm4010172,

Propargylation of lignin

Biomacromolecules : http://dx.doi.org/10.1021/bm4010172,

Initial Characterizations of Propargylated Lignin

60  

80  

100  

120  

140  

1,000  2,000  3,000  4,000  

98%

89%

68%

42%

22%

0% Cm-­‐1  

Intensity  

Alkyne C-H stretching

Terminal alkyne CC stretching

NMR Spectroscopy

Alkyne proton

Alkyne  carbon  

1H  

13C  

FT-IR Spectroscopy

% of propargylation

20  

Non-Condensed Phenolic -OH

Condensed Phenolic -OH

Aliphatic -OH

Reactivity of Lignin Hydroxyl Groups Towards Propargylation

•  Initial reaction rate of the condensed phenolic –OHs are same as non-condensed phenolic –OHs

•  However the rate of substitution slows down in non-condensed phenolic -OHs in the latter part

•  Aliphatic –OHs remain unaffected during propargylation reaction

0.00

20.00

40.00

60.00

80.00

100.00

120.00

0.00 0.50 1.00 1.50 2.00 2.50

%  of  -­‐OH  remaining

Molar  ratio  of  propargyl  bromide  to  total  phenolic  -­‐OH

0.00

20.00

40.00

60.00

80.00

100.00

120.00

0.00 0.50 1.00 1.50 2.00 2.50

%  of  -­‐OH  remaining

Molar  ratio  of  propargyl  bromide  to  total  phenolic  -­‐OH

0.00

20.00

40.00

60.00

80.00

100.00

120.00

0.00 0.50 1.00 1.50 2.00 2.50

%  of  -­‐OH  remaining

Molar  ratio  of  propargyl  bromide  to  total  phenolic  -­‐OH

Biomacromolecules : http://dx.doi.org/10.1021/bm4010172,

ASKL Starting Material

25% Propargylated

48% Propargylated

72% Propargylated

92% Propargylated

98% Propargylated

Exo  

Thermal Properties of the Propargylated Lignin

•  The thermal stability increases significantly after propargylation

•  The thermal stability keeps on improving marginally with the increase of degree of propargylation

•  DSC traces show an exotherm with an onset and a maximum around 150 °C and 215 °C respectively

22  

40

50

60

70

80

90

100

100 200 300 400 500 600

Wt %

Temperature ( C)

40

50

60

70

80

90

100

100 200 300 400 500 600

Wt %

Temperature ( C)

40

50

60

70

80

90

100

100 200 300 400 500 600

Wt %

Temperature (°C)

98%89%

68%43%22%

0

1

2

3

4

5

0 100 200 300

Heat  flow  

Temperature  °C)

0%

Degree of Propargylation

DSC Traces

TGA Traces

The Versatility of the Installed Propargyl Groups Toward Chain Extension Chemistry

Biomacromolecules : http://dx.doi.org/10.1021/bm4010172,

Hydride  shi,   Benzopyran  

Claisen  Rearrangement    

Thermal  PolymerizaMon  

Thermally Induced Polymerization of the Propargylated Lignin

Biomacromolecules : http://dx.doi.org/10.1021/bm4010172,

Bulk Thermal Polymerization of the Propargylated Lignin

•  About 40 mg of the propargylated softwood kraft lignin samples were heated within the chamber of a thermogravimatric analysis apparatus (TGA) for predetermined times at predetermined (to optimize the molecular weight) temperatures under a nitrogen atmosphere

  Temperature (°C)

Time (min)

Mn (g/mol)

Mw (g/mol)

PDI

Before thermal polymerization

0 0 1,500 2,160 1.44

Sample 1 150 10 2,100 5,200 2.53

Sample2 150 60 2,300 10,400 4.49

Sample 3 170 10 2,330 11,400 4.88

Sample 4 170 20 Gelation Confiden5al  NCSU  Informa5on  to  Solvay    

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, 10 min

KL 20% methylated 80% activated 170 °C, 10 min

KL 20% methylated

80% activated 150 °C, 60 min

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

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

1, 2 3, 4 O

OOCH3

OCH3 L

L

1  

2  

3  4  

Before  bulk  thermal    PolymerizaMon  reacMon  

AOer  bulk  thermal    PolymerizaMon  reacMon  

Biomacromolecules : http://dx.doi.org/10.1021/bm4010172,

Aliphatic –OH (mmol/g)

Total phenolic –OH (mmol/g)

Carboxylic –OH (mmol/g)

25% methylated 75% propargylated lignin 1.44 0.36 0.43

25% methylated 75% propargylated lignin after heating at 150 oC for 60 min

1.22 0.40 0.32

Stability of Aliphatic and Phenolic –OHs of Lignin after Thermal Polymerization

25% methylated 75% propargylated lignin

25% methylated 75% propargylated lignin

after heating at 150 0C

for 60 min

Confiden5al  NCSU  Informa5on  to  Solvay    

Diacetylene

Terminal alkyne

13C  NMR  Spectrum  

•  13C NMR spectrum of the polymer after the oxidative coupling reaction. The peaks of dialkyne carbons can be clearly seen between 68 to 72 ppm.

•  Peaks between 85 to 91 ppm are due to unreacted terminal alkynes

Characterizations of the Coupled Propargylated Lignin

  Lignin sample used for coupling reaction

Temperature (°C)

Time (h)

Mn g/mol

Mw g/mol

PDI

 Coupling 0  98% propargylated  25  1  Gelation Before coupling 25% methylation 75%

propargylation 0 0 1,500 2,140 1.42

Coupling 1 25% methylation 75% propargylation

25 24 2,100 3,600 1.71

Coupling 2 25% methylation 75% propargylation

60 24 2,300 10,000 4.68

Coupling 3 25% methylation 75% propargylation

80 6 2,000 11,000 5.77

Coupling 4 25% methylation 75% propargylation

80 24 Gelation

Oxidative Coupling of the Propargylated Lignin

Oxidative coupling reaction was conducted at different temperature and for different time period (as shown in the following table)to optimize the molecular weight distribution

Biomacromolecules : http://dx.doi.org/10.1021/bm4010172,

Before Coupling

Coupling  1  

Coupling 2

Coupling 3

Molecular Weight Distributions

•  With the increase in time and temperatur of the reaction medium the molecular weight distribution curves shifts towards the higher molecular weight direction showing progression in the polymerization reaction

0

0.2

0.4

0.6

0.8

1

1.00E+001.00E+031.00E+06

Absorption (a.u.)

Weight average molecular weight distribution (Mw) g/mol

0

0.2

0.4

0.6

0.8

1

1.00E+001.00E+031.00E+06

Absorption (a.u.)

Weight average molecular weight distribution (Mw) g/mol

0

0.2

0.4

0.6

0.8

1

1.00E+001.00E+031.00E+06

Absorption (a.u.)

Weight average molecular weight distribution (Mw) g/mol

0

0.2

0.4

0.6

0.8

1

1.00E+001.00E+031.00E+06

Absorption (a.u.)

Weight average molecular weight distribution (Mw) g/mol

Biomacromolecules : http://dx.doi.org/10.1021/bm4010172,

Thermal Properties after Oxidative Coupling Reaction

40

50

60

70

80

90

100

100 200 300 400 500 600

Wt %

Temperature (°C)

0% Propargylated

25% Propargylated

48% Propargylated

92% Propargylated

72% Propargylated

98% Propargylated

(A)

Biomacromolecules : http://dx.doi.org/10.1021/bm4010172,

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.

ACS Sustainable Chemistry , Argyropoulos et al December 2013

Copolymerization of Kraft Lignin with DifluoroDiphenyl Sulfone (DFDPS)

0  

0.2  

0.4  

0.6  

0.8  

1  

1.E+00  1.E+01  1.E+02  1.E+03  1.E+04  1.E+05  1.E+06  

22% Methylated KL-DFDPS Co-Polymer

Starting Kraft Lignin

71% Methylated KL-DFDPS C0-Polymer

63% Methylated KL-DFDPS C0-Polymer

38% Methylated KL-DFDPS Co-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

Thermal Degradation Analyses of Methylated Kraft Lignin DFDPS Co-Polymers

DFDPS  

71%  Methylated  KL-­‐DFDPS  Co-­‐Polymer  

38% Methylated KL-DFDPS Co-Polymer

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

ACS Sustainable Chemistry , Argyropoulos et al December 2013

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    

ACS Sustainable Chemistry , Argyropoulos et al December 2013

Conclusions

•  The selective methylation of the phenolic OH is pivotal in

controlling the thermal stability of technical Lignin

•  Molecular Weight Distribution & Melt Extrusion Torque

measurements offer a detailed way of understanding

such thermal events

•  Lignin propargylation/methylation offers a versatile new

avenue towards lignin chain extension, reactive extruding

and carbon fiber precursors.

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

Acknowledgments •  Solvay Specialty Polymers •  Domtar Inc. Plymouth NC •  King Abdul Aziz University, Centre for

Advanced Materials Research, Jeddah, Saudi Arabia.