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
22
Embed
NIR FT Raman spectroscopy and micro spectroscopy · 2012. 5. 16. · Martin Luther University Halle-Wittenberg . Institute of Agriculture and Nutritional Science. NIR FT Raman spectroscopy
This document is posted to help you gain knowledge. Please leave a comment to let me know what you think about it! Share it to your friends and learn new things together.
Transcript
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
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
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)