Back to Basics Fundamentals of Polymer Analysis Using Infrared & Raman Spectroscopy
Molecular Spectroscopy in the Polymer Manufacturing Process Process NIR NIR Production Receiving Shipping QC R&D Routine FT-IR Advanced FT-IR FT-IR Microscopy Raman Microscopy 2
Molecular Spectroscopy Helps the Entire Supply Chain FT-IR, Raman, NIR, Infrared & Raman microscopy Adds Value for: FT-IR, NIR Material Characterization Control & Monitoring Incoming Material ID & Verification Material Deformulation Root Cause Analysis Reverse Engineering FT-IR, Raman, NIR, IR & Raman microscopy, TGA-IR FT-IR, Raman, NIR, IR & Raman microscopy, TGA-IR 3
The Electromagnetic Spectrum visible Range x-rays ultraviolet near-ir mid - IR far-ir radio Wavenumbers (cm -1 ) 10 7 10 6 10 5 10 4 10 3 10 2 Technique XRF UV-Vis Infrared Wavelength (µm) 10-3 0.01 0.1 1 10 100 4
Molecular Vibrations Produce Spectral Fingerprints Bending Twisting + - C C C C C Stretching Deformation 100 90 80 70 %T 60 50 40 30 20 4000 3500 3000 2500 2000 Wavenumbers (cm -1 ) 1500 1000 5
Sample Handling I o =0 o Transmission Solids, Liquids, Gases Attenuated total reflectance (ATR) Solids, Liquids, Gels, Pastes and more D D S D D Diffuse reflectance (DRIFTs) Powdered solids in a KBr matrix I o =R o Specular reflectance Films and coatings on reflective surfaces Aris Associates Ltd 2010 6
Transmission Sampling Most often used for quantitative measurements Co-polymer ratios Polymer additive levels Provides results more representative of bulk sample Hot-melt films often prepared from 25 500 microns I o =0 o Bulk Polymer - saturated absorbance Additive - on-scale absorbance 50 micron thick film 7
ATR Sampling - Attenuated Total Reflectance Most popular, easy to use FT-IR sampling technique Mainly for qualitative material identification/verification Diamond crystal often used (Germanium for carbon-filled materials) Surface analysis technique IR light penetrates about 2 4 micrometers into the sample May require sample surface cleaning or excision 8
FT-IR Identifies Various Polymers Aromatic (PS, SAN, ABS, PET etc.) vs. aliphatic (PE, PP, PVC etc.), and more Infrared clearly differentiate aliphatic and aromatic polymers Low and high density Amorphous vs. crystalline chains 9
FT-IR Detects Differences Within Similar Polymers Similar polymers, with different structure Infrared can reveal structural differences within the same class of compound Example: Nylon 6,6 and Nylon 6,12 spectral differences 10
FT-IR can Detect Differences Within Similar Polymers 0.85 0.80 0.75 0.70 HDPE High Density Polyethylene (low methyl CH3 groups shows none or little absorption at 1375) LLDPE Linear LDPE (1375 peak of CH3 groups shifted depending on copolymer C4, C6 or C8); butene shows a 770 peak. LDPE Low Density Polyethylene (high CH3 methyl groups shows intense 1375 peak) 0.85 0.80 0.75 0.70 0.65 0.60 0.55 HDPE High Density Polyethylene (low methyl CH3 groups show none or little absorption at 1375) LLDPE Linear LDPE (1375 peak of CH3 groups shifted depending on copolymer C4, C6 or C8); butene (C6) shows a 770 peak. LDPE Low Density Polyethylene (high CH3 methyl groups show intense 1375 peak) 0.65 Absorbance 0.50 0.45 0.40 Absorbance 0.60 0.55 0.50 0.35 0.30 0.25 0.20 0.15 0.10 3500 3000 2500 Wavenumbers (cm-1) 2000 1500 1000 0.45 0.40 0.35 0.30 0.25 1390 1380 1370 1360 1350 Wavenumbers (cm-1) 1340 1330 1320 11
Infrared Quantitative Analysis Polymer manufacturers develop hundreds of methods for Co-polymers monomer ratio Additives concentration 0.36 0.34 0.32 0.30 0.28 0.26 Std EVA 32.6% b Std EVA 5.3% b Std EVA 28% Std EVA 24.6% b Std EVA 18.2% Std EVA 9.1% Std EVA 15.2% b Examples: Absorbance 0.24 0.22 0.20 0.18 0.16 Vinyl acetate in EVA Ethylene, butene in terpolymer olefins Acrylonitrile in styrene acrylonitrile Tinuvin, Chimassorb UV stabilizers Plasticizers in PVC 0.14 0.12 0.10 0.08 0.06 0.04 0.02 1200 1100 1000 Wavenumbers (cm-1) 900 800 12
Common Additives Characteristic IR Spectra Additive: Irganox 1010 Irganox 1076 Irganox 3114 Irgafos 168 BHT Chimasorb 944 Erucamide Tinuvin 622 IR Frequency: 1746 cm-1 1741 cm-1 1697 cm-1 1215 cm-1 3648 cm-1 1560 cm-1 3365 cm-1 1738 cm-1 Polyethylene film with Erucamide 13
Irganox 1076 Quantitative Analysis in Polyethylene Polyethylene 2020 cm-1 thickness correction band Irganox peak Calibration curve Built-in quant analysis report 14
Multi Component Quantitative Analysis in Polyethylene 15
NIR Spectroscopy
NIR Near-infrared Spectroscopy Measures weak harmonics of the mid-infrared region Many sampling benefits over Mid-IR: Deeper penetration for more representative sampling Light transmits through glass Allows use of fiber optics Good for : Co-polymer ratios Correlation to other physical/chemical methods, such as density Some additive levels Main disadvantage of NIR: Requires extensive modeling of material to obtain working method Most common sampling techniques Diffuse reflectance Transmission/Transflection 17
Density of Polyethylene by NIR Calibrate the instrument for density Classify new PE batches by density No sample preparation Load the spinning sample cup Qualify sample Catalyzed Polymerization 18
Density of Polyethylene by NIR 19
Ethylene/Polypropylene Copolymer Ratio by NIR 9000 cm -1 5000 cm -1 Ethylene in PP: 2% to 16% 20
21 At Line Cross-Linked Polyethylene (PEX) by NIR
Process Control by Multi-Channel NIR Antaris MX 22
Raman Spectroscopy
Raman Spectroscopy Laser-based technique, visible and near-ir lasers Laser light interacts with vibrations of molecules and scatters at a shifted wavelength Analysis of the shifted, scattered light provides a vibrational spectrum reveals molecular structure Excellent microscopy technique Downside Many samples have significant fluorescence interferences Sampling is not representative due to focused laser beam 24
Raman vs. Infrared Spectroscopy A technique similar to infrared spectroscopy Both molecular vibrational techniques Used to characterize covalently bonded materials Both useful for Micro and macro sampling Solids and liquids Organic and inorganic materials Both give definitive identification of unknown material R H H R 1000 900 800 700 600 500 400 300 Raman shift (cm-1) 25 For a more in-depth introduction we also have a recorded webinar and other material.
Raman Compared with Infrared Complementary information End functional groups dominant in infrared spectrum Molecular backbone dominant in Raman spectrum Raman often useful for characterizing morphology Weak IR absorbers often strong Raman emitters and vice versa Aqueous solutions pose fewer challenges with Raman FT-IR Transmission Spectrum %Transmittance 80 60 40 20 4 Raman Spectrum Raman Intensity 3 2 1 4000 3000 2000 Wavenumbers (cm -1 ) 1000 26
Raman can Detect Differences Within Similar Polymers Nylon 6 Nylon 6,6 Nylon 6 Nylon 6,6 27
Raman is the Ideal Choice for Crystallinity Studies Raman spectra of crystalline and amorphous polyethylene tere-phthalate (PET) films 28
Analysis of Inorganics in Polymers by Raman 400 *Subtraction Result:*White PVC 780nm Int 200 0 60000 Anatase Int 40000 20000 40000 0 Rutile Int 20000 0 800 600 Raman shift (cm-1) 400 200 Two polymorphs of TiO 2 Two peaks are characteristic of Rutile Third peak is characteristic of Anatase Infrared spectrum of TiO 2 is not as much informative Its spectrum does not show sharp well-isolated peaks 29
Summary Molecular spectroscopy is a good tool for polymer analysis Mid-infrared is an excellent all-around tool Near-infrared s sampling advantages help get it out of the lab Raman s unique capabilities to supplement infrared analysis 30
Today s Spectroscopic Analysis of Polymers Simplified by Thousands of spectra in Search libraries Knowledge base allowing the understanding of polymers in infrared spectroscopy 31
Please Contact Us for More Information View our website: www.thermoscientific.com/polymers or Please feel free to email me: mike.garry@thermofisher.com 32