Anal. Chem. 1983, 55,1R-18R
Coatings D. G. Anderson* and ,J. T. Vandeberg DeSoto, Inc., 1700 South Mt. Prospect Road, DesPlaines, Illinois 600 18
This review covers the analysis of coatings and related raw materials, byproducts, etc. since the last review in 19181 (8). The compiled references, nearly 1000, or a 20% increase over 1981, were extracted after searching Chemical Abstracts, Analytical Abstracts, World Surface Coatings Abstracts, and the Journal of Coatings Technology. The contents are divided into 19 categories for ready access by the reader. New categories are enviironmental amd industrial hygiene and physical testing-miscellaneous techniques, Readers are highly advised to survey the entire review, for the analyses of specific paints, coatings, or related materials may be found in each section. The five highest referenced categories are: (1) chemical and electrochemical, (2) gas chromatography, (3) thermal methods, (4)gel permeation chromatography, and (5) surface analysis. Surface analysis, miscellaneous measurements (including physical tests), environmental and industrial hygiene, and spectroscopymiscellaneous contain several new techniques and ideas for the examination of coatings and related materials. Many general publications appeared covering the analysis of paints and coatings (18,23,31). Other publications mentioned methods applied to archaeologicad paintings (15, 33, 39,44), forensic examinations (43), and paint media (34,35). The uses of instrumental techniques in paint analysis and testing were presented (9, 10, 42). The analysis of high polymers was reviewed by Cobller and Chow (19). Developmenb in 15 popular analytical techniques from late 1978 to late 1980 were reviewed. Three hundred twenty references were cited. Reviews of analytical methods for surfactant analysis1 in the period 1975-1980 were presented with 186 references (32). The International Standards Organization published standard methods for testing flash points (30), heat stability of pigments (29), and flow time using flow cups (28). The American Society for Testing and Materials published several standard methods for application to paint imd related coatings materials. Methods which appeared were: sampling and testing volatile solvents and chemical intermediates (1I, flash point by Tag closed testeir (2), flash point by Pensky-NIarings closed tester (3), purity of hydrocarbons from freezing points (4),closed cup flash points of liquids by the equilibrium method (5), flash point of liquids by Tag open-cup applaratus (6), and wet film thickness of organic coatings (7). Standard setting organizations in various foreign countries published test methods for the evaluation of paint and paint coinstituents. Those countries include: Standards Associal ion of Australia (45-62), British Standards Institution (16,17), Inst. Nac. di Racionalizaciony Normalizacion (24-27), Association Francoise de Normalisation (11-14), Lleutschen hrormenausschuss (20), Deutsches Institut Fuer Normung (21,22), Norges Standardisenings-Forbund (36), Polski Komitel Normalizacyjny (40,41), and Office Hondrois de Normalization (37, 38).
CHEMICAL AND ELECTROCHEMICAL Gravimetric techniques continue as a vital tool in coatings characterization. A recent report noted the use of a centrifuge to remove entrained air during density measurements (56). Separation and quantitataon of carbon containing species can be quite difficult and an automated analyzer was developed which allows differentiation of organic and elemental carbon in suspended particulates (24). The removal of coatings from paper also received special attention (37) as did a comparison of three methods for measuring suspended particulate concentrations (62) and the characterization alf paints containing calcium aluminum sulfate hydrate (43). Extraction techniques to remove plasticizers from polymer films (30) were adiopted as a standard method. Gravimetry allownd the ready determination of the lead content in mixed lead oxides (55) and 0003-2700/83/0355-1 R$06.50/0
the measurement of sulfur, as sulfates, from dilute aqueous solution (83). Wet ashing remains popular for the solubilization of volatile metals. Reports appeared for the determination of antimonv and for metallic elements in sov" (20) . bean oil (44). The LeRosen test (69) was used to qualitatively identify mint tmes in forensic analvsis. Chemical analvsis techniaues bere al% reported for the iualitative identificition of ant:que pigments (78). Articles dealing with the determination of emulsion stability via turbidometric measurements (90) and the measurement of the effective HLB value for nonionic surfactants by a phenol titration (72) also appeared. Standards organizations continue to develop and update analytical procedures useful in coatings analysis. Methods have appeared for the determination of nonvolatile content in titanium dioxide slurries ( I I ) , the preparation of extracts for the measurement of soluble metals (14) and the quantitation of antimony (16), barium (17), total chromium (19), hexavalent chrome ( I @ , and lead (15) in these extracts. Procedures for the determination of functional group concentrations were written for: acid value (63, 82), hydroxyl content in fats and oils (96), and isocyanate content (7,23, 29). Standard methods for alkyd characterization were published (10) as well as for the quantification of phthalic anhydride (1,2,35), isophthalic acid (9), and unsaponifiable matter (3). Numerous methods were proposed for the determination of functional groups in polymer systems (38,101). Hydroxyl content waa measured by using N-methylimidazole catalysis (39, 65), N-bromosuccinimide (50,87) and triphenylchloromethane (64). Of special interest are techniques useful for measuring the hydroxyl content in epoxy resins (34, 60). Procedures for amine value (28),epoxide content (32),olefinic unsaturation (84), and allophonate or biuret functionality (57) are also of interest. With the growing concern over the volatile organic content of coatings, an extensive comparison of methods to determine the water content of paints was reported (21, 47). The concern over formaldehyde in amino type cross-linking agents prompted studies for the total characterization of these systems (36, 71,93) as well as methods for the measurement of free formaldehyde (31, 33, 48, 80). Complexometric techniques were used to quantitate the total lead content in green lead chromate pigment (79) as well as EDTA methods for cobalt (4), lead (5), manganese (6), and zinc (8) in driers. Certain pigments can be determined with N-bromosuccinimide, including chlorinatedp-nitroaniline red, toluidine red, and red oxide (85, 95). Water-soluble polyelectrolytes in polyurethane dispersions were measured by conductometric titration (70). Colorimetric titration was reportedly useful in studying poly(viny1amine) and poly(irninoethylene) (68). Hydrolysis followed by titrimetric measurements was the subject of two studies (52,53) as was the detection of active oxygen in polyester polymers (40, 67). Polarographic techniques have been reviewed in general (22) as well as for the determination of trace inorganic species in paints (94). Organic polarographic studies were reported for the characterization of amino-formaldehyde condensates (76, 77) and the measurement of styrene in epoxy resins (42, 75). Coulometry was used to measure the olefinic double bond content in natural oils (51) and turpentine (86). Sulfur in aromatic hydrocarbon solvents was also reported by using oxidative microcoulometry (12). Poteniometrictitrations were useful in the measurement of the critical micelle concentration of nonionic surfactants (59). Specific polymer types were also studied potentiometrically, including maleic anhydride copolymers (74,88) and carboxymethylcellulose (98,99). The determination of soluble cyanide in ferric ammonium ferrocyanide pigments wa13 reported (97) as were the colorimetric measurements of ethylene oxide in polyesters (100) and cobalt I
0 1983 American Chemical Society
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in paints and environmental paint samples (46). Electrochemical techniques are frequently used to measure the corrosion protection provided by coatings systems. A quantitative test for zinc phosphate coating quality was published (102). Many general articles have appeared which document corrosion studies relative to coated substrates (45, 49,61,81,91,92). Zinc rich (13) and paints containing corrosion inhibiting pigments (73) were the subject of special studies. Ellipsometric measurements were also used to evaluate corrosion under organic coatings (66) as were the more accepted resistance and impedance measurement techniques (25-27, 41, 54, 58, 89).
GAS CHROMATOGRAPHY Gas chromatography remains an extremely valuable tool to the coatings analyst. Several series of review articles have appeared which deal with the use of gas chromatography in the examination of paints and inks (82,831. Another series of papers by the same author deals with the analysis of raw materials (84,85),binder resins (86,87),and whole paint (88). Other articles have dealt specifically with the analysis of solvent mixtures in general (43) and the specific problems encountered with electrodeposition paint systems (28). Solvent residues in flexible packaging laminates have received special attention (34). Unique detector systems continue to be developed; for instance, a hydrogen atmosphere flame ionization detector sensitive to organometallic compounds has found utility for the analysis of organotin compounds (39). New or updated as chromatographic methods have been published by the AITM for the determination of water content of water reducible paints ( 3 ) ,purity of methyl ethyl ketone ( 2 ) ,styrene monomer ( 5 ) ,and purity of several higher boiling aliphatic ketones (4). Techniques and procedures for the preparation of fatty acid methyl esters have been reported by several groups (I6,24, 79) as well as a new procedure for the gas chromatographic separation of these derivatives (80). The determination of trace concentrations of volatile species remains one of the largest uses for gas chromatography in the coatin s industry. New preconcentration techniques have been feveloped and reported (45, 72) as has a general procedure for the analysis of additives in plastics (75). Equally important is the detection of odor causing species in finished products and raw materials. One study appeared (52) dealing with latex coated paper. The presence of potentially harmful or unwanted species in coatings raw materials was determined for benzene in petroleum thinners (25) and acrylic acid in methacrylates (12)and durin the synthesis of pentaerythritol tetramethacrylate (77). Resitial monomer determination was reported via the use of capillary columns (651, in styrene/ acrylonitrile polymers (9,19)and in vinyl chloride containing resins (30,59,64). Unreacted phenolic compounds were also detected in novolac (38)and epoxy (74)resins following derivative formation. The utility of gas chromatography for analyzing polymeric systems is greatly hampered by the low volatility of polymers. Chemical degradation methods (35, 37, 55) continue to be used; however, the use of elevated temperature or pyrolysis remains the most popular degrative technique (8,13,46,47, 51, 66,89). Among the specific polymer types studied pyrolytically were acrylates and methacrylates (41,61,70, 71,81), styrenated polymers and oligomers (18,48, BO, 58, 73),and rubber materials and vinyls ( I , 7,22,40,44,53,62).Materials other than addition type polymers have also been reported including amino-formaldehyde condensates (67,681,phenolics ( I B ) , and cellulose ethers (11). Compositional data on natural oils remain of interest to coatings analysts and several new studies have appeared (6, 14,29,31,42). Several examinations of volatile amine species have been reported (20,23,63)as well as alkyl poly(ethy1ene glycol) ethers ( l o , % ) . Unique problems have been encountered with the nonvolatile content of melamine resins. Among the approaches used toward the resolution of this difficulty involves gas chromatographic techniques (21, 78). Studies of curing mechanisms also have been reported, including those dealing with epoxy polymers (32). Thermodynamic properties remain important to coatings chemists, many of which can be obtained and measured by using gas chromatography. Among the studies reported include measurement of reactivity ratios ( I 7,57,g o ) , migration of species through polymer films (60,69),the determination 2R
ANALYTICAL CHEMISTRY, VOL. 55, NO. 5, APRIL 1983
of solubility parameters (33, 49, 54, 56), and the use of reversed-phase chromatography for emulsifier characterization (36). Gas chromatography has also been reported for the examination of the surface properties of inorganic species such as pigments (27) and ferric oxide (76).
GEL PERMEATION CHROMATOGRAPHY Gel permeation or size exclusion chromatography was the subject of two new books (26, 78) dealing with the general operating principles of this technique. Related papers in the literature dealt with phase distribution chromatography (40) and orthogonal chromatography (8). Coupling of gel permeation chromatography and high-performance liquid chromatography was beneficial in cross-fractionation of styrenebutyl methacrylate copolymers prior to ultraviolet detection (10). Theoretical studies were also performed on the mechanism of (13) and the presence of nonexclusion effects operative during gel permeation chromatographic separations (7). Separation of mixtures (38),resin blends (31),and copolymer systems (70) have also received special attention. Long chain branching measurements for polymer systems (6, 15, 21) were also attempted by using gel permeation chromatographic data. The reproducibility of a low-temperature chromatographic system vs. a system operated a t elevated temperature was compared over a several-year period (67). Special applications reported include high polymerization conversion kinetic modeling (9)and the study of some reversed micellar systems (30). Universal calibration remains a fertile area for gel permeation chromatographic studies. Several general papers have appeared (44,53,54)as well as theoretical models for concentration effects related to elution behavior ( I 7 , 57) and the simultaneous determination of calibration and dispersion parameters (3). Peak broadening effects during analysis (34,411were related to molecular weights calculated from chromatographic data. General works on the molecular weight of polymer systems appeared (11,63) along with the measurement of molecular dimensions with a low angle laser light scattering detector (46). Relating osmometric data to elution behavior in gel permeation chromatography continues as an active area of general study (29,33,57,64,79). Specific applications in this field include the calculation of MarkHouwink constants in several homopolymer systems (28,56). Aqueous size exclusion chromatography was also reviewed in several articles (12, 59, 61, 66). One paper dealing with the characterization of oligomeric materials useful to the coatings industry (50) was presented. Other oligomeric systems studied were vinyl chloride polymers (37)and the gel fraction in polymeric materials (23, 32, 43). Additives in polymer systems were also studied by using size exclusion chromatography (49, 72). Partial argentation resin chromatography was reported for the separation of fatty acid esters (1, 2). Separation of polyelectrolytes in emulsion polymers (22),free amines in polyamide curing agents ( 1 4 , and monomeric species in phenol-formaldehyde condensates (19) were also achieved. Polymer systems continue to be the main use of gel permeation chromatography. Specific studies of varnishes (24) and anodic electrodeposition paints (58)have been published. Among the specific addition type polymers reported were styrene containing systems (35,36,42,52,55,73),vinyl monomer grafts on cellulose nitrate (74),poly(viny1acetates) (27), polyacrylates (18, 60, 68) and polymerized petroleum pitch (39). Condensation polymers that were examined via gel permeation chromatographic techniques include alkyd resins (16, 76), urea-formaldehyde condensates (20, 47, 71, 75), melamine oligomers (65), epoxy systems ( 4 , 69),silicones (5, 77),polyamides (45,48),nitrocellulose (25),and photochemi c d y cross linked allyl ether modified fumaric acid esters (62).
HIGH-PERFORMANCE LIQUID CHROMATOGRAPHY The nonvolatile nature of many coatings components dramatically increases the utility of high-performance liquid chromatography in solving coatings related problems. Among the general papers which indicate newer developments in this field are multidimensional chromatography where sample fractions are transferred from one column to another for greater separation (22) and the use of moderate pressure with supports of high specific surface area (13). Column technology continues to advance (8,21) with the introduction of reversible
COATINGS
(3,18) were reported. Finally, reversed-phase high-performance liquid chromatography was used to separate high molecular weight polynuclear aromatic hydrocarbons in carhon hlack (28)and ion-pair techniques were employed to study a sulfonated copper phthalocyanine pigment (25).
THIN-LAYER CHROMATOGRAPHY Thin-layer chromatography continues as a viable analytical tool for coatings research. The separation of polyricinoleic acids from castor oil fatty acids (7,8) and the qualitative characterization of amber (5) have been reported. Reactive species have also been studied by using thin-layer chromatographic analysia techniques. For example, hydroxymethyl melamines were separated (2,3) and organotin compounds isolated and characterized with infrared (6) and flameless atomic absorption (4) spectroscopy. Residual monomer analyses have also been reported for monomeric isocyanates ( I ) and for the determination of formaldehyde in can lining paints (9).
Jokl T. vandwbw ia Dcecta of Pdyrlw DeMlopmsot. AdminkIralive and Research Center. DeSom. Inc. His responsblinies include pc%mwdevelapment. radiation cwaMe matings. and new vemwe research. He has m e then 18 years of expedence with DesOto. having held several technical and managerial p k b n s . He obtained his 0.A. degree in chemlsIry bom Carroll Collegs. Helene. MT. He receivBd the M.S. and Ph.0. degrees in chemlslry from Loyola Unbersny. Chicago. IL, In 1966 and 1969. respemeiy. He has s W e d 17 publications in inhared and nmiear magnetic reso.
name
spectroscopy.
tetraaryiborate
ATOMIC SPECTROSCOPY
:
chemistry. polymer Characterization. chebting polymers. and coatings analy$15. He Is coauMa of two b w k s in me field 01 infrared s ~ e c t ~ o s c o the ~v. latest. published in 1980. entkied. "An Inhared Spectroscbpy Atlas i& the Coatings Indusw. He has been a reclpbnt of awards for distinguished end OutStanding sewim to the coatings industry. He is a member of the FederaHon of SDCieties f a Coatlngs Technology. Chicago Society tor Coatings Technology, Sigma XI. American Chemical Swlety: Coatings Division and PolyDivision. American Assmiation f a the Advancement of Science. Society tor Applied Spctroscopy. and the Chicaw Gas Chramatcgraphy DisCuSsbn Group. He has been Included in "Who's Who in Technalagy T&y" and "Who's Who in the Mldwesr.
high-performance liquid chromatography columns (6)and capillary (24)or open small bore columns (17). Hydrodynamic chromatography has been treated theoretically (23) particularly with respect to column behavior and modeling. Stopflow ultraviolet sranning and variable wavelength detection continues as a viable technique for the qualitative identification of column eluants (30). Applications of high-performance liquid chromatography to coatings continue to appear (32), with specific studies relative to oligomeric species (19) and cathodic electrodeposition paint polymen via ion-pair techniques ( 1 1 ) . Epoxy resin systems have heen thoroughly studied (31) with sperial investigations of the byproducts formed during synthesis (34) and the mechanisms of cure in two model resin systems (7). Addition type polymers, including acrylates (35), methacrylates ( 4 J ,and nitrile resins (37) were also studied chromatographically. Curing studies for condensation products continue, with specific work reported for melamine (36). phenol ( 1 5 ) .and urea (33)formaldehyde oligomer systems. Condensation polymer systems were also reported, inrluding and polyurethanes (2). Natural products polyesters (25,27) used in roatings have received special attention, panicularly triglycerides and fatty acids ( 5 . 29). In one report, partial argentation resin chromatography ( 1 ) was used to enhance the separation of fatty acids, fatty esters. and triglycerides. rhe determination of unreacted or modifying speries in polymeric systems remains an important application of high-performance liquid chromatographic techniques. The measurement of unreacted 2,4-~olueoediisncyanaw (12) and diphenylmethane diisocyanate (MDI) ( 1 0 ) in urethane prepolymers was reported. Curing agents. such as dicvandiamide ( / 4 1 , hnve also been quantitnted Rli have rhlorinated phenols in surface treated lumher (91and polymerization inhibitors in acrylic monomers 12OJ. Nonionic surfactant nnnlysis and chararterization normally requires complex analysis techniques to achieve adequate separation. Studies related to the chromatography of alkyl phenols
