Validation of a Comprehensive VOC Analysis Method for Architectural Coatings

Transcription

1 Validation of a Comprehensive VOC Analysis Method for Architectural Coatings Dane Jones and Max Wills California Polytechnic State University, San Luis Obispo, CA polymerscoatings.calpoly.edu

2 Overview Background of the VOC problem ASTM 6886: Low VOC waterborne coatings Other 1K coatings possible use of headspace analysis for certain coatings 2K coatings UV curable coatings

3 VOC Definitions VOLATILE ORGANIC COMPOUND (VOC) is any volatile compound of carbon, excluding methane, carbon monoxide, carbon dioxide, carbonic acid, metallic carbides or carbonates, ammonium carbonate, and exempt compounds which participates in atmospheric photochemical reactions. VOCs are solvents which evaporate from the coating during and after application, excluding exempt compounds U.S. VOCs are what you measure by ASTM D-3960 (EPA Method 24) ISO (Europe) VOCs are compounds with boiling points lower than diethyladipate (shorter GC retention times) Problems: Method 24 fails for low VOC waterborne coatings Method 24 provides no determination of exempt solvents Method 24 provides no determination of HAPs Method 24 provides no speciation information cannot apply reactivity-based VOC analysis Method 24 cannot be used for radiation-cured coatings

4 Traditional VOC Measurement EPA Method 24 Determine density of coating Weight-per-gallon cup Determine solids of coating Heat at 110 C for 1 hour ASTM 2369 Determine water in coating GC or Karl-Fisher titration VOC water solids

5 Equations for VOC Analysis f VOC = 1 f W f ex f S = f V f W f ex VOC Material = f VOC( DP) VOC Coating = 1 [( f V f f VOC VOC ( DP) )( D P / D W )] = ( fv 1 [( f W f + W f fex)( DP) ( DP / D ex) W )] Where f W = Water weight fraction f VOC = VOC weight fraction f S = Solids weight fraction f ex = Exempts weight fraction f V = Total volatile weight fraction

6 ASTM D Standard Test Method for Speciation of the Volatile Organic Compounds (VOCs) in Low VOC Content Waterborne Air-Dry Coatings by Gas Chromatograpy

7 Assumptions For air-dry waterborne architectural coatings with a material VOC level below 5%, the number of different individual solvents will be a small, and The probable solvents are likely to be ethylene glycol(eg), propylene glycol(pg), ethylene glycol butyl ether(eb), diethylene glycol butyl ether(db), and/or Texanol(TX).

8 Sample Preparation A) Stock solution: 1-2 g of each suspected analyte + internal standard (EGDE), transfer 100 µl to 10 ml vol. flask, dilute with IPA to give approx. 2 mg/ml. B) Internal standard solution: 1g/mL EGDE (or other suitable internal standard) in IPA, dilute to approximately 1 mg/ml C) Paint sample solution: Pipette 10 ml standard solution into ml vial containing 3-5 g ceramic beads, seal with septum cap and weigh, add g paint using disposable syringe, reweigh. Mix well, sonicate, let settle.

9 Analysis Chromatograph diluted stock solution, measure areas, and determine response factors for each possible analyte RF = AA* MI AI * MA Chromatograph paint solution by direct injection, use areas to determine mass fraction of each analyte in sample. AA* MI W A = AI * RF * MC

10 Results for 20 flat coatings sold in Southern California Sample A B C D E F G H I J K L M N O P Q R S T density (lbs/gal) density (g/l) Solids fraction, average VOC fraction, average Water fraction (calcd) Material VOC, ALL (g/l) Coating VOC, ALL (g/l) Coating VOC, to TX (g/l) Material VOC(MSDS) Coating VOC (MSDS) How should we define VOC -- include all volatiles measured or only those volatiles up to some agreed upon marker? Does it make a difference for these flat coatings?

11 Flat C Note small amounts of Aromatic 100 and peaks after Texanol Response_ Signal: MW396.D\FID1A.CH Flat C Time

12 Applying the direct ASTM 6886 method to non-traditional 1-K architectural coatings Low VOC, low solids coatings Low solids, high exempts, solventborne coatings Coatings with unusual VOCs

13 Response_ Low solids, waterborne, low VOC concrete curing coating Signal: MW716.D\FID1A.CH ARB Sample 81-2 Direct Analysis internal standard wax components Cpd fraction HC HC HC HC HC HC HC Total Time Is this a zero VOC coating or???

14 Response_ Low solids, solventborne, high exempts lacquer in diethyladipate EtOH MeOH MEK Signal: MW593.D\FID1A.CH ARB Sample 57-2 Direct Injection acetone + IPA co-elute EGDE (int. std.) BuOAc m,p-xy o-xy EtBz MAKEBz Time Acetone co-elutes with IPA. A second analysis must be performed, either with a different column, or using a different temperature program. Notice the analysis also shows the presence of several HAPs: methanol, ethyl benzene, xylenes

15 Response_ Solventborne, low solids, clear coating in diethyladipate Signal: MW570.D\FID1A.CH EtOH ARB Sample 84 direct injection EGDE (int. std.) IPA MEK MIBK 5-methyl-3-heptanone Time Sum of solids + VOCs 1 Karl-Fisher analysis shows ~5% water

16 GC analysis - direct and static headspace

17 Coating Analysis by Headspace Injection Place 5 µl of 20% aqueous coating solution in a 20mL headspace vial and seal with a crimp cap. Place vial in headspace autosampler and start run. Equilibration temperature = 110 o C for 20 minutes. Loop and transfer line temperature = 160 o C. Can run analysis at higher equilibration temperature

18 Sample Preparation Add g wb coating to 20mL vial containing ceramic media Add 10.0mL 0.2% standard in water and mix contents by shaking (analyze by direct injection) Transfer 5uL of above solution to 20mL headspace vial (analyze by headspace injection)

19 Low VOC waterborne driveway sealer Response_ ARB Sample 41 headspace analysis 150 C Signal: MTW019.D\FID1A.CH Analysis requires extraction of dried film to determine fraction VOC. Alternate method uses headspace analysis polynuclear aromatic hydrocarbons Time

20 Analysis of 2K Coatings Want to approximate actual mixing and application conditions Components are mixed, sample weighed into a 20mL headspace vial, vial sealed with crimp cap, mixture allowed to cure for 24 to 36 hours at room temperature. After the initial RT cure, sample heated for 30 minutes at 110 o C. After cooling, a known quantity of acetone containing an internal standard is added to the sealed vial and the contents are mixed. This solution analyzed by gas chromatography.

21 Preparation of 2K samples Determine density of the individual components Prepare approximately 100 to 200g of the mixture and mix well. Transfer 100 mg mixture to 20 ml headspace vial and weigh. Add a paper clip, seal with crimp cap. Using magnet, spread mixture evenly over bottom surface of vial. Transfer 0.5 g of mixture to each of three aluminum foil dishes (58 mm in diameter by 18 mm high) containing a paperclip stirrer and weigh to 0.1 mg. Spread the coating mixture evenly over the bottom of pans. DO NOT ADD ANY SOLVENTS TO THE PANS. Let vials and foil pans stand at room temperature for 24 to 36 hour cure. After the RT cure, place the sealed vials and aluminum foil pans in an oven at 110 o C. The vials should remain in the oven for 30 minutes and the aluminum foil pans should remain in the oven for 60 minutes. Determine the total volatile content of the coating mixture by reweighing the cooled aluminum foil pans. Add 3-4 ml of acetone containing internal standard to vial, mix and sonicate. analyze using direct injection GC.

22 WB 2K Epoxy Wood Coating Run 1 Run 2 Run 3 Reported by manufacturer Reported by 3d Party Testing Lab using Method 24 Compound fraction fraction fraction Average UK Methoxy-2-propanol UK UK UK UK UK Benzyl alcohol Total VOC fraction Total VOC fraction by Method Total volatile fraction by ASTM D Density Water fraction (Calcd) Water fraction (ASTM D3960) Material VOC by GC Coating VOC by GC

23 WB 2K Epoxy Pool Coating Run 1 Run 2 Run 3 Compound fraction fraction fraction Average Reported by manufacturer 1-Propoxyethanol Aromatic Total VOC fraction Total volatile fraction by ASTM D Density 1217 Water fraction (Calcd) Material VOC by GC Coating VOC by GC

24 SB 2K Epoxy Pool Coating Run 1 Run 2 Run 3 Compound fraction fraction fraction Average Reported by manufacture MEK Butanol PM Acetate Ethylbenzene Total Xylene Benzyl alcohol Total VOC fraction Total volatile fraction by ASTM D Density 1571 Coating VOC by GC 319 Coating VOC by Method

25 SB 2K High Solids Epoxy Run 1 Run 2 Average Reported by manufacturer Compound fraction fraction Furfuryl alcohol None Ethylbenzene Total Xylene Aromatic Total VOC fraction Total volatile fraction by ASTM D Density 1465 Coating VOC by GC 184 Coating VOC by Method

26 Validation studies Selected samples sent to other labs for analysis Provide suggested methods Compare interlab results, make modifications where necessary

27 Results comparing EPA 24 with ASTM Rule 1113 Assessment Sample Description Formulation Value SCAQMD Method 24 SCAQMD D-6886 Cal Poly D-6886 Nonflat, medium gloss Nonflat, low gloss Nonflat, low gloss Primer Clear wood coating Rust preventative Masonry sealer <

28 VOC analysis of UV-curable coatings Currently only gravimetric method: ASTM 5403, not for waterborne Film thickness - small sample size Small mass change Don t directly measure VOCs (analogy to Method 24 for low VOC waterborne coatings) Challenges Insure proper film thickness Insure complete cure, not under or over cure Decide what is a VOC

29 Joint SCAQMD-Cal Poly project Goal obtain more reasonable and verifiable limits for VOCs Analysis of 16 waterborne and 100% solids UV-curable coatings Consultations with RadTech Developed direct and headspace UV methods

30 UV-VOC methods Waterborne: mg coating weighed into glass vial, sealed with septum cap correct film thickness Sample cured using appropriate UV lamp Known amount of solvent (acetone) containing internal standard (ethylene glycol diethyl ether - EGDE) added to vial After thorough mixing, sample of resulting solution containing VOCs analyzed using GC/MS (identification) and GC/FID (quantification) Percent of each VOC calculated using areas of peaks and previously determined response factors for each analyte

31 UV-VOC Methods Solventborne ( 100% solids ) Sample weighed into vial and small amount acetone added to aid in obtaining thin film Acetone allowed to evaporate at room temperature Sample cured Solvent containing internal standards added Sample analyzed using headspace GC at 110, 130, 150 o C Uncured sample also analyzed by direct injection

32 Vial undergoing curing in Visions curing system Cured UV inks

33 Waterborne wood topcoat 119 mg 164 mg Cpd fraction fraction PG toluene cylohexanone benzaldehyde DPM NMP acetophenone benzophenone Response_ Time PG toluene cyclohexanone Signal: MTW016.D\FID1A.CH DPM waterborne wood topcoat 110C n-mepy Density Volatile fraction Water fraction (calcd) Material VOC Mat VOC reptd Coating VOC Coating VOC reptd BP

34 Waterborne UV clear 105 mg 224 mg Cpd fraction fraction triethyl amine PnP benzaldehyde acetophenone tributyl amine UK Total Density Volatile fraction Water fraction (calcd) Material VOC Mat VOC reptd Not reptd Not reptd Coating VOC Coating VOC reptd Not reptd Not reptd

35 UV Cure Gloss Ink Topcoat Direct Analysis of Uncured Material Response_ Signal: MTW059.D\FID1A.CH toluene EGDE gloss ink topcoat before cure acetone acrylic acid Time Response_ toluene o C Headspace Analysis EGDE cyclohexanone Signal: MW011.D\FID1A.CH gloss ink topcoat after cure benzaldehyde DEGDE 110C fraction uncured cured total cured fraction 110C C C Time

36 UV Cure Gloss Ink Varnish 110 o C Headspace Analysis Response_ EGDE Signal: MW009.D\FID1A.CH DEGDE Gloss UV topcoat, cured BPO fraction uncured cured total cured fraction BPO 110C C C Time

37 Summary The direct analysis of VOCs is possible for virtually all architectural coatings Methods applicable to 1K, 2K, waterborne, solventborne, at all levels of VOCs Methods also provide information on exempt solvents and HAPs Methods for UV-curable coatings look highly promising

38 Acknowledgments Students: Eric Appel, Christina Blattner, Megan Lydon California Air Resources Board Coatings Manufacturers SCAQMD, Sherwin Williams, Rohm and Haas

39 Western Coatings Technology Center Cal Poly Center for Science and Mathematics