Martin Luther University Halle-Wittenberg

Institute of Agriculture and Nutritional Science

NIR FT Raman spectroscopy and

micro spectroscopy

efficient methods for determining objective parameters of cellulose – based plant fibres

Karla Schenzel, A. Jähn, P. Peetla, S. Kovur

Kumar, D. Hong

1. Origin of our work

2. Aim of analytical projects

3. FT Raman spectroscopy/micro spectroscopyon cellulosic plant fibre materials

3.1 spectroscopic

method

and spectrometer3.2 plant fibre

material

3.3 special

FT Raman

investigations3.3 results

4. Summary

Martin Luther University Halle-Wittenberg

Institute of Agriculture and Nutritional Science

Topics

Martin Luther University Halle-Wittenberg

Institute of Agriculture and Nutritional Science

1. Origin of work

• agricultural institute →

cultivation of fibre plants

• fibre plants (1) and (2) →

so-called bast fibres

• main constituent →

cellulose

• very important properties (low density, high tensile strength)• attractive alternatives to glass fibres in composite materials

(1) hempCannabis sativa, L.

(2) flaxLinum usitatissimum, L.

Martin Luther University Halle-Wittenberg

Institute of Agriculture and Nutritional Science

Assessment of the quality of cellulosic plant fibres

2. Aim of analytical projects

• with respect to high variability of fibre material

variability

caused

by: special

growing

conditions

different harvest

times

different retting

conditions

chemical

fibre

treatments

Y development of objective fibre parameters

Y rapid determination of fibre quality

• Why is FT Raman spectroscopy used here?

Intensity

of Raman

signals

→

Characterization of skeletal structures of hydrocarbons

Y Characterization of cellulose backbone structures

• Advantages of NIR FT Raman spectroscopy:quick method, without

material destructionlow

fluorescence

excitationspectra

of good resolutioneasy

sample

preparationlow

amounts

of sample

materialbiological materials →

H2 O doesn´t disturb

3. FT Raman spectroscopy/microscopy on fibres

Martin Luther University Halle-Wittenberg

Institute of Agriculture and Nutritional Science

Martin Luther University Halle-Wittenberg

Institute of Agriculture and Nutritional Science

3. FT Raman spectroscopy/microscopy on the fibres

N2 cooled detectordirectly coupled microscop,polarisation devices,mapping table

λ0 =1064 nm und λ0 =785 nm Laser Power: 20 - 1500 mW frequency range: 3500-80 cm-1spectral resolution: 4 cm-1

3.1 FT Raman spectroscopy on fibre bundles

Fibre

bundle

in a metal ring

Martin Luther University Halle-Wittenberg

Institute of Agriculture and Nutritional Science

3.1 FT Raman micro spectroscopy on single fibres

Measuring experiments on single fibres:

• Standard arrangement of sample and optics:single

fibre

parallel to x-axsis

of mapping

table

• orientation dependend measurements

• fibre straining measurements

y

x

Single fibre

in theRaman

microscope

10-30μm

3.2 cellulose - based fibre material

• hemp and flax fibres = composite materials• cellulosic single fibre cells included into matrix material• matrix material of hemicelluloses, pectins and lignin

Fibre bundle: 20-40 single fibres

Single fibre:

15-30 mm long, φ

15-25 μm

Chemical composition of fibre bundles:

70%-78% (w/w) Cellulose

matrix substances: 16% (w/w) hemicelluloses

3% (w/w) pectine

3% -5% (w/w) lignin

low amounts of fats and waxes

→

vibrational spectra of fibre bundles

= superpositions of the molecular components

single fibre cell

ESEM picture

of retted

hemp

fibre

bundle

bundle ∅

80 μm

typical FT Raman spectrum of hemp fibres with assignements of the vibrational modes of characteristic cell wall constituents of the fibres

lignin partcellulose component

3500 3000 2500 2000 1500 1000 500

ν(OH)δ(COC) *

δ(COC) *

νas(CH/CH 2)

δ(COH) (CCH) (OCH)

δ(CH/CH 2) and δ(OH)

ν(C=C)

νas(COC)νs(COC)

νs(CH/CH 2)R

aman

Inte

nsity

(Arb

itrar

yun

its)

Wavenumber

(cm -1)

3.3 Results of special FT Raman investigations(1) Changes in molecular fibre composition, e.g. lignin content

3000 2500 2000 1500 1000 500

ν (CH)aromat.

ν (CH)aliph.

ν (C=C) arom. rings**ν (C=C) conjugated with (C=O)

νs (C-O-C) νas (C-O-C)

region of matrix and conformational sensitive vibrational modes of cellulose

ν (C=O) modes of acetyleted hemicellulosic polysaccharides

vibrational modes of lignin parts

(10)

(7)(3)

(1)

Ram

an in

tens

ity

Wavenumber/ cm-1

after mechanical fibre treatments

3000 1500 1000 500

0,000

0,005

0,010

0,015

0,020

0,025

0,030 ν (C=C)

Var. 9, später Ernteterm in Var. 10, später Ernteterm in Var. 9, m ittlerer Ernteterm in Var. 10, m ittlerer Ernteterm in Var. 9, früher Ernteterm in Var. 10, früher Ernteterm in

Inte

nsity

W avenum ber / cm -1

Different lignin contents depending on the fibre harvest times

early harvest

middle

late harvest

-1

1175 1150 1125 1100 1075 1050 1025

16%

5%0%

Inte

nsty

Wavenumber

/ cm

↓

↓νas (C-O-C)

νs (C-O-C)Peak fitting on marker bands

Quantification of the lignin contents

•R1 = I ν

(C=C) / I νs (C-O-C)

relative lignin content

•R2 = I νs (C-O-C) / I ν

(CH)

relation cellulosic/ non-cellulosic aliph. carbohydrogens

•R3 = I νas (C-O-C) / I νs (C-O-C)

matrix effect of non-cellulosiccomponents

R1- R3 = Raman intensity ratios→spectral fibre parameter

marker bands

(2) Characterization of secondary structures of the cellulose withrespect to alkaline pretreatments of the fibres

1 5 0 0 1 2 5 0 1 0 0 0 7 5 0 5 0 0 2 5 0

1 1 5 2

1 1 2 0

1 0 9 8

* *1 4 5 5

1 4 7 6

3 5 1 +

3 7 8 *

1 4 6 0 +

2 2 %

2 0 %

1 5 %

1 3 %

1 0 %

7 %

5 %

c N a O H / %

Ram

an in

tens

ity

W a v e n u m b e r/c m -1

typical changes in conformational sensitive frequency range of the spectra

cell I

cell II

typical changes in cellulose sub-structure in CH frequency range depending on alkaline concentration of the fibre treatments

2950 2900 2850 2800

untreated

20 %13 %5 %

cNaOH

2887+2895*

Ram

an in

tens

ity

Wavenumber/ cm-1

FT Raman

spectra

second derivatives

of the

spectra

cell

I cell

II

(3) Characterization of plant fibre surfaces after silylation

3000 1500 1000 500

ν(C-O-C)Cellulose

ν(CH2)vinyl

ν(SiC)

ν(C=C)vinyl

Ram

an in

tens

ity

Wavenumber / cm-1

VES 25%

VES 10%

VES 1%

pure VES

alkali treated

untreated fibre

vinyl-triethoxysilane

Si

OC2H5

C2H5O

OC2H5

CH

CH2

3 5 0 0 3 0 0 0 1 8 0 0 1 6 0 0 1 4 0 0 1 2 0 0 1 0 0 0 8 0 0 6 0 0

ν ( C = C )v in y l

Inte

nsity

W a v e n u m b e r ( c m -1 )

R a m a n IR

Proof of changes in fibre surfaces by FT IR spectroscopy (1), light microscopy (2), ESEM (3) and EDX (4)

(1)(2)

(3) (4)

(4) Determination of micro mechanical fibre properties

E: Young`s Modulus/ GPaσ: Stress /MPaε: Strain /%F: Force /mNA: cross sectional area /μm2

L0

:initial length /μm∆L:difference between initial and final length/μm

Fibre straining experiments on micro fibres:→ frequency shifts, changes in signal intensity and band shape of typical

Raman lines of cellulose

• characterisation of molecular deformation of cellulose skeletons• distribution of stress and straining over the cellulose chains

Raman shift sensitivity (dΔν) for polymeric materials with respect to strain (dε) ~ (E) to modulus of elasticity of the materials (R.J.Young, S.J.Eichorn)

LALFEΔ×

×==

0

εσ

1140 1120 1100 1080 1060

10

90

10

94

10

96

F=0-baseline F=123mN-baseline F=177mN-baseline F=0-derivative F=123mN-derivative F=177mN-derivative

Ram

an In

tens

ity

Raman wavenumber (cm-1)

d dEd d

σε εΔν

∝ =

1140 1120 1100 1080 1060

1096,02918

1092,17207

1096

1092

Hanf HB7, ohne Zug Hanf HB7, mit Zug

Inte

nsity

Wavenumber / cm-1

νs (C-O-C)

→ (E) modulus of elasticity is a measure of the stiffness of the material

0 1 2 30

1

2

3

Retting level 3

Retting level 2

Retting level 1

Stre

ss /

108 Pa

Strain / %

(a)

Fibre Retting level

Fibre Diameter

[μm]

E-Modulus[GPa]

Failure Stressσ

f [MPa]

Failure Strainεf [%]

Hemp1 35 ±

10 11.1 ±

0.04 132 ±

0.05 1.7 ±

0.06

Hemp2 35 ±

10 12.8 ±

0.05 250 ±

0.08 2.5 ±

0.07

Hemp3 35 ±

10 7.8 ±

0.08 130 ±

0.05 2.5 ±

0.04

Hemp 1 + 2: high tensile

strengthlinear stress-strain

curves→ nearly

elastical

behaviour

Hemp 3: low

tensile

strengthnonlinear

stress-strain

curvewith

strain

hardening→ plastical

behaviour

Stress-strain behaviour of hemp fibres of different retting levels

Results:•Hemp 1+ 2: high mechanical

properties

and elastical

fibre

behaviour

•Hemp 3: lower

mechanical

properties

and plastical

fibre

behaviour

4. Summary

Martin Luther University Halle-Wittenberg

Institute of Agriculture and Nutritional Science

FT Raman spectroscopy and microscopy cause objective fibreparameters at different structural levels:

(1) Raman intensity ratios R1-R3 are spectral fibre parameters: -molecular composition of fibre bundles

(2) Differentiation between secondary cellulose structures:- polymorphic forms- amorphous/crystalline phase

(3) Characterization of modified (silylated) plant fibre surfaces

(4) Determination of micro mechanical parameters and deformation behaviour of the fibres

Martin-Luther-Universität Halle-Wittenberg

Institut für Acker- und Pflanzenbau

• Bestimmung der Orientierung charakteristischer Gruppen zur Faserachse FT Raman Mikroskopie an orientierten Einzelfasern

Ergebnis: Y

C-H Gruppen Y

senkrecht zur

Faserachse Y

CH2

-Gruppen

und glycosidische

Brücken (C-O-C) Y

parallel zur Faserachse

3 0 0 0 1 8 0 0 1 6 0 0 1 4 0 0 1 2 0 0 1 0 0 0 8 0 0 6 0 0 4 0 0 2 0 0

ν (C H 2)ν (C H )

ν s(C -O -C )

9 0 0

8 0 0

6 0 0

4 0 0

2 0 0

0 0

Ram

an in

tens

ity

W a v e n u m b e r /c m -1

A=Industriefaserlein

B=Öllein

C=Hanf

Cluster-Analyse an den Datensätzen des Kulturarten und Sortenspektrums

YDifferenzierung hinsichtlich der Kulturarten und Sorten

0

1

2

3

4

5

6

7

8

Het

erog

enitä

t

A A A A A A A B B B B B B B B B CC C C C C C C C C

Spektrenauswertung mit multivariaten Methoden