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Identification of polymers by IR spectroscopy.



While infrared spectroscopy is considered an established technique, it is also a relatively under-utilized technique in most analytical laboratories. This is primarily due to current interest in identification of trace materials in products. However, other factors which contribute to this under-utilization are the difficulty of obtaining sufficient reference spectra in certain fields and the experience needed to provide thorough analytical solutions from infrared spectroscopy alone.

As an aid to vibrational spectroscopists and polymer scientists, this article discusses some of the most important commercial polymers and their infrared spectra. Identification of polymers is ideally suited to infrared analysis, but has become more difficult with the many blends of polymers that now exist. Spectra can be obtained as either a pressed or cast film, or by attenuated total reflectance Attenuated total reflectance (ATR) is a sampling technique used in conjunction with infrared spectroscopy which enables samples to be examined directly in the solid or liquid state without further preparation. . Other instrumental techniques would require the decomposition of the polymer and identification of its fragments.

Two dozen of the most important commercial polymers and their infrared spectra are discussed. This is followed by a flowchart which should prove useful in determination of the polymer type or identification of the source of an extra peak. The latter is usually the strongest peak in the spectrum of a minor component. The discussion that follows assumes that there are either no plasticizers or fillers present or that they have been removed from the polymer by extraction, dissolution and filtering.

Commercial polymers

Polyethylene

The simplest polymer structure would be a chain of methylene units terminated on each end by methyl groups. This is the structure of polyethylene, or PE. Since the polymer is composed almost completely of methylene groups, its infrared spectrum would be expected to consist solely of methylene stretches and bends. Four sharp peaks dominate the spectrum: The methylene stretches at 2,920 and 2,850 [cm.sup.-1] and the methylene deformations at 1,464 and 719 [cm.sup.-1]. Due to the crystallinity of polyethylene, the 1,464 and 719 [cm.sup.-1] peaks are split, and additional peaks are seen at 1,473 and 731 [cm.sup.-1]. High density polyethylene High-density polyethylene (HDPE) is a polyethylene thermoplastic made from petroleum. It takes 1.75 kilograms of petroleum (in terms of energy and raw materials) to make one kilogram of HDPE.  (HDPE HDPE
abbr.
high-density polyethylene
) is very regular and is about 70% crystalline. Low density polyethylene Low-density polyethylene (LDPE) is a thermoplastic made from oil. It was the first grade of polyethylene, produced in 1933 by Imperial Chemical Industries (ICI) using a high pressure process via free radical polymerisation [1].  (LDPE LDPE
abbr.
low-density polyethylene
), on the other hand, is more branched and is only about 50% crystalline. The crystallinity of a polyethylene sample can be determined from the ratio of the 731 to 719 [cm.sup.-1] peaks (ASTM ASTM
abbr.
American Society for Testing and Materials
 D5576).

Polytetrafluoroethylene polytetrafluoroethylene

a synthetic material commonly used as a nonstick lining in domestic cooking utensils (frypans); abbreviated PTFE; called also Teflon. Overheating produces toxic fumes that cause an acute hemorrhagic pneumonitis and death in small caged birds, which are
 

If all the hydrogens in polyethylene were replaced with fluorine fluorine (fl`ərēn, –rĭn), gaseous chemical element; symbol F; at. no. 9; at. wt. 18.998403; m.p. −219.6°C;; b.p. −188.14°C;; density 1.  atoms, we would have another important plastic called polytetrafluoroethylene. This is better known by its tradename, Teflon. Because fluorine atoms are more massive than hydrogen atoms, the C[F.sub.2] stretches are much lower in frequency than the C[H.sub.2] stretches. These peaks appear at 1,200 and 1,146 [cm.sup.-1]. The C[F.sub.2] deformation peaks are also lower in frequency and do not appear on the spectrum shown here. Fluorine atoms are highly electronegative electronegative /elec·tro·neg·a·tive/ (e-lek?tro-neg´it-iv) bearing a negative electric charge.

e·lec·tro·neg·a·tive
adj.
1. Having a negative electric charge.

2.
, which gives the CF bond a large dipole moment. The result is an extremely strong infrared absorption. The spectrum here was collected by ATR ATR Achilles tendon reflex, see Ankle reflex  to provide a sufficiently short pathlength of polytetrafluoroethylene so that the asymmetric and symmetric stretches could be distinguished.

Polypropylene

The addition of a methyl side group on every other carbon atom in polyethylene gives us polypropylene and quickly complicates the infrared spectrum. In addition to the methylene, we now have methyl and methine groups present. The methyl peaks appear at 2,962/2,952 (split peak), 2,868 and 1,377 [cm.sup.-1]. A methyl deformation is also overlapped with the methylene deformation, and this peak has shifted slightly to 1,458 [cm.sup.-1]. The methine peaks are weak and of no analytical value.

Ethylene-propylene rubber

An elastomer can be made from the copolymerization copolymerization (kōpäl´imrizā´sh  of ethylene and propylene. The ethylene content of EP rubber usually ranges from 50 to 75%. A diene is regularly added to provide sites for crosslinking. The diene content in EPDM EPDM Ethylene-Propylene-Diene-Monomer
EPDM Enterprise Product Data Management
EPDM Ethylene Propylene Dimonomer (industrial/commercial piping/plumbing components)
EPDM Engineering Product Data Management
 is customarily less than 10%, and infrared peaks due to this component are thus very weak. The spectrum is dominated by the methylene peaks at 2,925, 2,854, 1,464 and 721 [cm.sup.-1]. The methyl peak at 1,377 [cm.sup.-1] is also significant. The methyl stretches can be seen as shoulders at 2,952 and 2,871 [cm.sup.-1].

Polyvinylchloride

If the group on polypropylene were a chlorine atom rather than a methyl group, the polymer would be polyvinylchloride. With one chlorine atom attached to every other carbon atom, the degree of chlorination chlorination Public health Addition of chlorinated compounds to drinking water as disinfectants. Cf Ozonation.  will be 56.7%. The methyl stretches and bends have disappeared and are replaced by CCL 1. CCL - Coral Common LISP.
2. CCL - Computer Control Language. English-like query language based on COLINGO, for IBM 1401 and IBM 1410.
 stretches at 688 and 615 [cm.sup.-1]. Also prominent in the infrared spectrum is a strong band with a maximum at 1,255 [cm.sup.-1]. This is due to C[H.sub.2] wagging when the adjacent C atom has a chlorine atom attached. A methine wag can be seen at 1,200 [cm.sup.-1]. The methylene asymmetric stretch peaks at 2,912 [cm.sup.-1] with a methine C-H stretch peaking at 2,970 [cm.sup.-1]. The methylene scissors scissors

Cutting instrument or tool consisting of a pair of opposed metal blades that meet and cut when the handles at their ends are brought together. Modern scissors are of two types: the more usual pivoted blades have a rivet or screw connection between the cutting ends
 deformation is split at 1,435 and 1,427 [cm.sup.-1]. PVC PVC: see polyvinyl chloride.
PVC
 in full polyvinyl chloride

Synthetic resin, an organic polymer made by treating vinyl chloride monomers with a peroxide.
 is sometimes heavily plasticized with phthalates or phosphates, and its infrared spectrum can be obscured until the plasticizer has been extracted.

Chlorinated chlorinated /chlo·ri·nat·ed/ (klor´i-nat?ed) treated or charged with chlorine.

chlorinated

charged with chlorine.


chlorinated acids
some, e.g.
 polyethylene elastomer

When polyethylene is chlorinated, there will not be a chlorine atom on every other carbon atom. This chlorinated polyethylene elastomer, CPE (Customer Premises Equipment) Communications equipment that resides on the customer's premises.

CPE - Customer Premises Equipment
, has a degree of chlorination between 25 and 47%. We would expect the infrared spectrum of CPE to be similar to that of PVC, with perhaps stronger C-H stretches and bends and weaker C-Cl stretches. The C-Cl stretches appear at 660 and 609 [cm.sup.-1]. The methylene wag appears as a broad band at 1,263 [cm.sup.-1]. The methylene stretches at 2,929 and 2,856 [cm.sup.-1] are present, and the methylene bend at 1,460 [cm.sup.-1] is also present, but shows some splitting due to the variety of geometrical structures within the polymer.

Chlorosulfonated polyethylene

Closely related to chlorinated polyethylene is chlorosulfonated polyethylene. The latter usually contains between 24% and 43% chlorine and 1% to 1.5% sulfur. The sulfonyl sul·fo·nyl
n.
The bivalent radical SO2. Also called sulfuryl.
 chloride group gives rise to an asymmetric S[O.sub.2] stretch at 1,369 [cm.sup.-1] and a symmetric S[O.sub.2] stretch at 1,160 [cm.sup.-1].

Polystyrene

When the side group on the methylene chain is an aromatic ring, the infrared spectrum becomes a combination of methylene and mono-substituted aromatic ring peaks. The polystyrene spectrum has dominant peaks at 2,926 and 2,851 [cm.sup.-1] from the methylene stretches. The out-of-plane C-H bends of the aromatic ring are intense at 698 and 756 [cm.sup.-1]. The aromatic ring breathing modes appear at 1,601, 1,493 and 1,452 [cm.sup.-1]. The peaks at 3,082, 3,061 and 3,027 [cm.sup.-1] are absorptions from the aromatic C-H stretches.

Polyvinylacetate

Polyvinylacetate has the infrared spectrum of a typical acetate ester. The dominant peaks are the carbonyl carbonyl /car·bon·yl/ (kahr´bah-nil) the bivalent organic radical, C:O, characteristic of aldehydes, ketones, carboxylic acid, and esters.

car·bon·yl
n.
The bivalent radical CO.
 stretch at 1,739 [cm.sup.-1] and the C-O C-O Coherent Orthogonal  single bond stretch of the acetate group at 1,242 [cm.sup.-1]. Also significant are the methyl deformation at 1,373 [cm.sup.-1] and the C-O single bond stretch of the polymer backbone carbons at 1,022 [cm.sup.-1].

Polyvinylalcohol

Polyvinylalcohol is produced by the reaction of polyvinylacetate with methanol. The extent of hydrolysis in commercial plastic is between 79 and 100%. The spectrum should be a fairly simple combination of methylene and hydroxyl vibrational peaks. It is, however, complicated by the electronegativity electronegativity (ĭlĕk'trōnĕgətĭv`ətē), in chemistry, tendency for an atom to attract a pair of electrons that it shares with another atom (see chemical bond).  of oxygen. The resulting hydrogen bonding between hydroxyl groups produces a wide hydroxyl stretch at 3,410 [cm.sup.-1] and wide hydroxyl deformations at 1,334 and 592 [cm.sup.-1]. The methylene stretch is split at 2,910 and 2,943 [cm.sup.-1]. The methylene scissors deformation can be seen at 1,450 [cm.sup.-1]. The C-O stretch appears at 1,095 [cm.sup.-1], as is typical of secondary alcohols. Sometimes polyvinylacetate peaks are seen at 1,739 and 1,239 [cm.sup.-1] when hydrolysis is not complete. Peaks at 1,568 and 1,412 [cm.sup.-1] due to sodium acetate and/or peaks at 1,746 and 1,246 [cm.sup.-1] due to methyl acetate by-products are sometimes discernable.

Poly(ethylene-vinylacetate) EVA Eva

to marry winner of singing contest. [Ger. Opera: Wagner, Meistersinger, Westerman, 225–228]

See : Prize



1. Eva - A toy ALGOL-like language used in "Formal Specification of Programming Languages: A Panoramic Primer", F.G.
 

EVA plastic is a combination of polyethylene and polyvinylacetate, with the latter usually contributing 7.5% to 33% of the weight of the polymer. The infrared spectrum is a combination of the peaks of the two components as listed above.

Polyisoprene

When diene monomers add to each other, the resulting polymer contains unsaturation in its backbone. Natural rubber is composed almost entirely of cis-polyisoprene, while gutta percha and balata balata (băl`ətə), nonelastic natural rubber obtained as a latex from the South American tree Manikara bidentata and from related trees.  are primarily trans-polyisoprene. Besides 1,4-addition, 1,2- and 3,4-addition structures can be introduced into synthetic polyisoprene. The methylene stretches at 2,925 and 2,854 [cm.sup.-1], the methyl stretch at 2,962 [cm.sup.-1] and the deformations at 1,450 and 1,377 [cm.sup.-1] dominate the infrared spectrum. Also prominent is the =C-H out-of-plane wag at 837 [cm.sup.-1]. Smaller but distinctive peaks exist at 3,035 [cm.sup.-1] for the =C-H stretch, 2,727 [cm.sup.-1] for the overtone overtone

In acoustics, a faint higher tone contained within almost any musical tone. A body producing a musical pitch—such as a taut string or a column of air within the tubular body of a wind instrument—vibrates not only as a unit but simultaneously also in
 of the methyl deformation and 1,664 [cm.sup.-1] for the C=C stretch.

Polychloroprene

When the methyl group of polyisoprene is replaced with a chlorine atom, the polymer is known as polychloropene. Between 85 and 92% of the polymer is formed from trans 1,4-addition of the monomer. Around 2.5% of the polymer contains vinyl groups with the chlorine atom on either the or [gamma] carbon. The remainder consists of cis 1,4-addition product. Total chlorine content is about 40% by weight. Dominant peaks include the 2,920 [cm.sup.-1] methylene stretch, the C=C stretch which is split between 1,695 and 1,660 [cm.sup.-1], and the methylene deformation which is split between 1,444. and 1,431 [cm.sup.-1]. The 1,119 [cm.sup.-1] peak, which is probably related to the methylene wag deformation, and the 825 [cm.sup.-1] peak, which is probably due to the =C-H bend, are also strong. The C-C C-C Carbon-Carbon
C-C Carotid-Cavernous (relating to the carotid artery and the sinuses) 
1 stretches occur at 658 and 602 [cm.sup.-1]. Also noticeable are the 3,309 [cm.sup.-1] overtone of the C=C stretch, the 3,024 [cm.sup.-1] =C-H stretch and another methylene deformation band at 1,304 [cm.sup.-1].

Butyl rubber

Butyl rubber is produced from the polymerization polymerization

Any process in which monomers combine chemically to produce a polymer. The monomer molecules—which in the polymer usually number from at least 100 to many thousands—may or may not all be the same.
 of isobutylene Noun 1. isobutylene - used also in making gasoline components
butene, butylene - any of three isomeric hydrocarbons C4H8; all used in making synthetic rubbers

butyl - a hydrocarbon radical (C4H9)
 with a small amount of isoprene isoprene or 2-methyl-1,3-butadiene (ī`səprēn, by'tədī`ēn), colorless liquid organic compound. . The dominant peaks are due to the methyl stretches at 2,954 and 2,897 [cm.sup.-1], the methyl/methylene deformation at 1473 [cm.sup.-1], the gem-dimethyl deformation at 1,390 and 1,367 [cm.sup.-1], and the mostly methyl rock vibration at 1,230 [cm.sup.-1]. Weaker methyl rock vibrations are also visible at 924 and 951 [cm.sup.-1]. Halogenated halogenated

pertaining to a substance to which a halogen is added.


halogenated salicylanilides
see rafoxanide, clioxanide.
 butyl rubber contains only 1 to 2% of chlorine or bromine bromine (brō`mēn, –mĭn) [Gr.,=stench], volatile, liquid chemical element; symbol Br; at. no. 35; at. wt. 79.904; m.p. –7.2°C;; b.p. 58.78°C;; sp. gr. of liquid 3.12 at 20°C;; density of vapor 7.  by weight. Due to this very low level, it is difficult to distinguish halogenated from non-halogenated rubber by infrared spectroscopy.

Polybutadiene

1,3-butadiene can be polymerized to polybutadiene. Various proportions of different microstructures have found commercial use. This varies from almost pure cis-substitution to almost pure trans-substitution. The most significant infrared peaks are due to the methylene stretches at 2,945 and 2,854 [cm.sup.-1] for cis- and 2,918 and 2,846 [cm.sup.-1] for trans-, the =C-H stretch at 3,008 [cm.sup.-1], and the partially split methylene bend at 1,436 and 1,450 [cm.sup.-1]. Peaks due to out-of-plane bending of hydrogens on the double bonded carbons are strong when there is a high percentage of a given microstructure present. The upper spectrum has a strong and broad peak at 741 [cm.sup.-1] for the cis C-H bends, while the lower spectrum has strong peaks at 912 and 993 [cm.sup.-1] for the vinyl component and at 966 [cm.sup.-1] for the trans component.

Nitrile rubber

Nitrile rubber (NBR NBR Number
NBR Nightly Business Report (PBS show)
NBR National Business Review (New Zealand weekly business newspaper)
NBR National Bureau of Asian Research
NBR National Board of Review
) is produced from the copolymerization of butadiene and acrylonitrile. As such, its infrared spectrum is essentially that of trans-polybutadiene with a sharp peak at 2,238 [cm.sup.-1] from the nitrile triple bond stretch. Carboxylation carboxylation /car·box·y·la·tion/ (kahr-bok?si-la´shun) the addition of carbon dioxide or bicarbonate to form a carboxyl group, as to pyruvate to form oxaloacetate.

car·box·yl·a·tion
n.
 of NBR with acrylic or methacrylic acid provides additional sites for crosslinks. The carbonyl band appears as a split peak at 1,699 and 1,732 [cm.sup.-1]. The C-O single bond produces a peak at 1,222 [cm.sup.-1]. Although hydrogenation hydrogenation (hīdrôj`ənā'shən, hī'drəjənā`shən), chemical reaction of a substance with molecular hydrogen, usually in the presence of a catalyst.  is never 100% complete, HNBR HNBR Hydrogenated Acrylonitrile-Butadiene Rubber  can be readily distinguished by the significant reduction in the 966 [cm.sup.-1] peak upon removal of the unsaturation.

Styrene butadiene rubber

A typical emulsion SBR SBR - Spectral Band Replication  contains about 23% styrene and a butadiene microstructure of 18% cis, 65% trans and 17% vinyl. The microstructure of solution SBR is usually higher in cis content than emulsion SBR. The dominant infrared peaks are due to the methylene stretches at 2,925 and 2,854 [cm.sup.-1] and to the out-of-plane aromatic C-H deformation at 700 [cm.sup.-1]. Other significant peaks are related to the aromatic ring breathing mode at 1,603, 1,495 and 1,452 [cm.sup.-1], the aromatic C-H deformation at 760 [cm.sup.-1] and the trans and vinyl double bond out-of-plane C-H bending at 968 [cm.sup.-1] and 995 and 912 [cm.sup.-1], respectively.

Epichlorohydrin ep·i·chlo·ro·hy·drin  
n.
A colorless liquid, C3H5OCl, used as a solvent in making resins.
 

Epichlorohydrin homopolymer contains 38% chlorine by weight, while the 1:1 copolymer of epichlorohydrin and ethylene oxide contains 26%. The additional chlorine content gives EC a better fuel resistance, while the ethylene oxide provides ECO E·co   , Umberto Born 1932.

Italian writer best known for his novels, including The Name of the Rose (1981). He has also written extensively on semiotics and British and American popular culture.
 with better low temperature flexibility. The C-O stretch produces a broad band centered at 1,110 [cm.sup.-1]. The C-Cl stretches appear at 706 and 746 [cm.sup.-1]. The intensity of the symmetric methylene stretch is enhanced relative to the asymmetric stretch. This produces a broad multi-peaked absorption in the 2,850 to 2,975 [cm.sup.-1] region. A number of methylene deformations appear as medium intensity peaks in the 1,250 to 1,475 [cm.sup.-1] region.

Polycarbonate

Despite the presence of a carbonyl group, at 1,774 [cm.sup.-1], the strongest infrared absorptions in polycarbonate are due to the C-O single bond stretches. An intense triplet triplet /trip·let/ (trip´let)
1. one of three offspring produced at one birth.

2. a combination of three objects or entities acting together, as three lenses or three nucleotides.

3.
 appears at 1,165, 1,194 and 1,228 [cm.sup.-1]. Additional C-O related peaks continue down to 1,000 [cm.sup.-1], with the strongest of these at 1,016 [cm.sup.-1]. Among the aromatic ring breathing modes, only the 1,506 [cm.sup.-1] peak is relatively intense. While the methyl stretch at 2,970 [cm.sup.-1] is weak, it is noticeable due to the absence of other peaks in this region.

Bisphenol epoxy resin

Since both bisphenol epoxy and polycarbonate are based on Bisphenol A, there are a number of similarities in their infrared spectra. There is no carbonyl band in the bisphenol epoxy spectrum, but the aromatic ring-breathing mode at 1,510 [cm.sup.-1] is very strong. Here the 1,610 [cm.sup.-1] ring-breathing mode is also relatively strong. The C-O stretch is strong and appears as two bands, a broad band with a maximum near 1,247 [cm.sup.-1] and a narrower and slightly weaker band with a maximum near 1,182 [cm.sup.-1]. Significant intensity is also seen in the out-of-plane aromatic C-H wag at 830 [cm.sup.-1].

Polyethylene terephthalate

Polyethylene terephthalate, and to a lesser extent polybutylene terephthalate, have become synonymous with the term polyester. The carbonyl stretch is lowered to 1,717 [cm.sup.-1] by conjugation conjugation, in genetics
conjugation, in genetics: see recombination.
conjugation, in grammar
conjugation: see inflection.
 with the aromatic ring. The second strongest peak at 1,261 [cm.sup.-1] is generally described as the asymmetric C-C-O stretch that involves the carbon in the aromatic ring. The O-C[H.sub.2]-C[H.sub.2]- asymmetric stretch is split at 1,128 and 1,099 [cm.sup.-1]. The aromatic C-H wag is also affected by the carbonyl group and shifted down to 723 [cm.sup.-1].

Poly(acrylates and methacrylates)

Polymers with esters as ligand groups are usually named for the monomeric repeating unit that includes the ester group. In addition to polyvinylacetate above, two of the more important polymers of this type include the acrylates and methacrylates. These are useful where hard, clear coatings are needed.

The most intense peak is the carbonyl between 1,730 and 1,737 [cm.sup.-1]. The C-O stretch forms a broad split band between 1,150 and 1,200 [cm.sup.-1] with an additional weaker broad band with a maximum between 1,240 and 1,265 [cm.sup.-1]. This additional band has two distinct maxima in polymeth-acrylates near 1,240 and 1,270 [cm.sup.-1].

Polyamides

Polyamides, better known as nylons, are made from the polymerization of lactams or the condensation of diamines with dicarboxylic acids. The number following the name, e.g., nylon 6 or nylon 6,6, indicates the number of carbon atoms in the starting material(s). The strongest peaks are those of the Amide I and Amide II bands found near 1,640 and 1,545 [cm.sup.-1], respectively. Also, the N-H stretch near 3,300 [cm.sup.-1] is very intense. Different nylons can be distinguished by subtle differences in frequencies and intensities in the Amide III band between 1,260 and 1,280 cm-1, and in the symmetric methylene stretch and the methylene deformation bands.

Silicone rubber

Polydimethylsiloxane is the most common of the silicone rubbers. The Si-O-Si backbone produces a broad band with two maxima at 1,092 and 1,018 [cm.sup.-1]. The methyl deformation band at 1,261 cm-1 is strong and sharp, and the methyl rock with contribution from the Si-C stretch at 798 [cm.sup.-1] is also strong. The asymmetric C[H.sub.3] stretch at 2,964 [cm.sup.-1] is also sharp and relatively strong.

Conclusion

Infrared spectroscopy is the most direct means of identification of polymers. Through the use of the accompanying flowchart and reference to the spectral descriptions above, an unknown polymer can be quickly identified. When additional peaks are present in the infrared spectrum, they may be the strongest peaks from an additional polymer which has been blended with the main polymer. They may also be due to unremoved plasticizer or fillers or to residual solvent used to dissolve the polymer.
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peyyeti.veeru
P Veerabhadra Rao (Member): Identification of polymers by IR 4/4/2008 5:51 AM
Its nice topic to read.
Please let me know the what is the acceptance critera for PVC film Identification by IR
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Author:O'Keefe, Jerome F.
Publication:Rubber World
Date:Jun 1, 2004
Words:3118
Previous Article:New technology to produce silicone sponge without chemical blowing agents or VOCs.
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