The work described in this paper was not funded by the U.S. Environmental Protection Agency. The contents do not necessarily r d l e c t the views of the Agency and no official endorsement should be inferred.

ACRYLATED LESQVERELLA OIL IN ULTRAVIOLET CURED COATINGS

Shelby F. Thames 'Department of Polymer Science University of Southern Mississippi Box 10037, Hattiesburg, MS 39406-0037

Min D. Wang Chemcraft Sadolin, Inc. 3750 New Walkertown Road Winston-Salem, NC 27105

Haibin Yu Department of Polymer Science University of Southern Mississippi Box 10076, Hattiesburg, MS 39406-0076

Thomas P. Schuman Department of Polymer Science University of Southern Mississippi Box 10076, Hattiesburg, MS 39406-0076

INTRODUCTION

Environmental concerns focusing on the emission of volatile organic compounds (VOCs) can be ameliorated via the development and use of very low- to no-VOC coatings. Ultraviolet (W) radiation curing is an effective means of incorporating low molecular weight reactive species into high performance, non- volatile polymers. The advantages of W curing include rapid polymer network formation on heat sensitive substrates, reduced energy consumption, low emissions, and minimal space requirements.' When cost is a consideration, W curing offers additional advantages by eliminating the need for high volume air movement, expensive to operate ventilation systems, solvent recovery units, or sir scrubbers. However, more often than not, W curing is accompanied by appreciable volume shrinkage which can cause loss of adhesion, poor edge coverage, and other film defects .

Lesquerella oil (LO) is a vegetable oil of significant commercial potential and, we believe, can be a valuable raw material for the design and formulation of W cured coatings. Lesquerella oil is obtained from a promising new oilseed crop, Lesquerella f end le r i . This domestic renewable resource offers a reduction in America's dependence on imported oils of similar structural features.. For instance, LO contains 55-60% 14-hydroxy-cis-11-eicosenoic or lesquerolic acid, a 20-carbon fatty acid homolog of castor oil's ricinoleic acid.' The hydroxy functional fatty acid offers a reactive site for

' derivative synthesis. such as acrylated LO ( A L O ) . Acrylated lesquerella oil's synthesis, characterization, formulation into, and evaluation of W cured coatings, are the focus of this work.

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EXPERIMENTAL

Materials

Lesquerella oil was purchased from International Flora Technology, Ltd. Methacryloyl chloride (MAC) , 2-hydroxyethyl methacrylate ( H E M A ) , sodium hydride (95%), toluene diisocyanate (80% 2,4-TDI and 20% 2,6-TDI), triethylamine, tetrahydrofuran (THF), hydroquinone, dibutyltin dilaurate, sodium hydride, and dichloromethane were purchased from Aldrich Chemical Company. All chemicals were used as received except THF, and it was refluxed over sodium hydride for 1 h and freshly distilled before use.

Oligomeric reactive diluent photomers 3016, 4061, 4094, 4149, 4770, and 6008 were supplied by Henkel Chemical Company. Byk 065 and Byk 325 were supplied by BYK Chemie. Silwet 7604 was obtained from Union Carbide, Irgacure 651 from Ciba-Geigy, and Benzophenone from Aldrich Chemical Company.

Synthesis of Methacrylated Lesquerella Oil

A solution of 50 g (0.092 eq hydroxyl) of LO and 9 g triethylamine in 100 mL of dichloromethane was added to a three- neck, 250 mL round bottom flask, equipped with nitrogen inlet, magnetic stir bar, thermometer, and addition funnel. The flask was purged with a'slow flow of nitrogen while the contents were stirred at 30oC. Methacryloyl chloride was added dropwise (10.4 g, 0.1 eq) to the reaction flask over 1 h. After addition was complete, the reaction was continued for 2 h while maintaining a temperature of 25oC with an ice bath. A 4-4.5 pm glass frit Buchner funnel was dried at llOoC for 3 h, cooled to room temperature, and used for salt removal by filtration. The solvents were rotary evaporated. in vacuo.

Synthesis of Acrylated Lesquerella Oil from Hydroxyethyl Methacrylate

A solution of 16.9 g ('0.097 moles) TDI and 0.05 g hydroquinone in 50 mL THF was added to a three-neck, 250 mL round bottom .flask equipped with magnetic stir bar, heating mantle, thermometer, condenser, addition funnel, and nitrogen purge through a vacuum adaptor. The stirred flask contents were heated to reflux (70oC). 2-hydroxyethyl methacrylate (12 g, 0.092 eq) dissolved in 100 mL THF was added into the addition funnel and transferred into the flask dropwise over 1 h. The stirred flask contents were maintalned at 50oC for 0.5 h. A solution of 0.1 g dibutyltin dilaurate in 10 mL THF was added in one portion to the flask and maintained at 50oC for an additional 0.5 h. Lesquerella oil (50 g, 0.092 eq) was added to the addition funnel and transferred dropwise into the reaction mixture over 2 h. The contents were then maintained at 50oC for 1 h. Finally, 0.65 g (0.005 eq) REMA was introduced in one portion to the reaction

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a

mixture to end cap any remaining isocyanate. THF was removed from the final product by rotary evaporation in vacuo.

Characterization Methods

A Bruker AC-200 (200 MHz, 'H/13C dual probe) spectrometer. and a Nicolet IR/42 FTIR spectrophotometer were used for nuclear magnetic resonance (NMR) and Fourier transform infrared (FTIR) spectroscopic analysis, respectively. Nuclear magnetic resonance samples were dissolved in deutero-chloroform spiked with tetramethylsilane for reference.: Fourier transform infrared samples were analyzed as a film smear on polished NaCl.

Coating Formulations

The raw materials used in the filler and finish coatings are contained in Table I.

A 100% solids wood sealer formulation containing pigment, additives, photoinitiators, ALO, and acrylic monomers and oligomers, was dispersed for 0.5 h to a Hegman 7 grind using a 3.5 in cowles high speed mixer at 1500 rpm. The UV wood filler *formulations are included in Table 11. The sealer was applied on sanded poplar with a draw bar at 2 mils wet thickness, and subsequently cured via W radiation for 7 sec at 11 cm from a 300 W medium pre'ssure mercury W lamp.

The 100% solids wood and metal finish coatings were formulated with the materials of Table 111 and prepared in a .manner identical to the filler coatings. The finish coatings were applied at 2 mils wet film thickness with a draw bar onto a lightly sanded sealer coating (wood), chromate treated aluminum (American Society of Testing and Materials Method (ASTM) D-1750, Type B, Method 21, or cold rolled steel panels. The applied finishes were irradiated under a 300 W medium pressure mercury W lamp for 7 sec at 11 cm distance.

Coating Characterizations

Pencil hardness and cross-hatch adhesion tests were performed according to ASTMD-3362 and ASTM D-3359, respectively. Impact resistance was measured with a BYK-Gardner heavy duty impact tester, Model IG-1120 with 1.8 kg (4 lb) mass and 1.59 cm (0.5 in) diameter round peen. Yellowness indexes were measured by the Applied Color System CS-5 Chroma-Sensor. Specular gloss was taken with a Gardco Statistical Novogloss as speci-fied by ASTM D-523. Dry film thicknesses were determined by a Gardco Minitest 4000 Microprocessor coating thickness gauge. Chemical resistance was analyzed through a 2 h spot exposure test according to ASTM D-1308. The tensile strength and percent elongation were determined by an MTS Model 810. Thermal analysis was performed with a Mettler TA4000 system equipped with a DSC 30 measuring cell under a nitrogen purge (25 cc/min) and at a heating rate of lOoC/min.

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a

Table I. Raw Material Descriptions Materials Molecular Acrylate Function

Weight Functionality

HEMAL0 1996 1.6 Monomer

MACLO 1084 1.8 Monomer

Photomer 3016 452

Photomer 4061 300

Photomer 4094 428

Photomer 4149 428

Photomer 4770 ”

Photomer 6008 ”

Byk 065

Disperbyk 163 OmeyaCarb F

Byk 325

Irgacure 651

Benzophenone

Silwet 7604

2 Monomer

2 Monomer

3 Monomer

3 Monomer ” Oligomer

” Oligomer

Defoamer

Dispersant

Pigment

Mar-slip

Photoinitiator

Photoinitiator

Surfactant

Table XI. Ultraviolet Cured Wood Filler Formulation

Materials Amount (g 1

Photomer 4061 26

Photomer 4094 2 0 . 5

Photomer 4149

Photomer 4770

Photomer 6010

Disperbyk 163

OmeyaCarb F

12

5

5

1

30

Benzophenone 1.5

” Irgacure 651 1

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Polymer Swelling Experiments

The extent of crosslinking was determined from swelling experiments of free films. Fil-ms were obtained by draw downs

Free films were removed from polyethylene and fashioned to approximately 2 X 0.1 mm dimensions, placed on a microscope slide, covered with a flat glass cover slip, and viewed microscopically at 18X magnification. The microscope was equipped with an ocular scale for millimeter measurements. After the film dimensions were measured, several drops of methylene chloride were placed at the slide/cover interface. Swelling occurred immediately and was complete in less than 1 min after which 5 individual measurements of the swollen film were taken and used for determination of the swelling ratio (see Table IV). The swelling ratio was calculated as the ratio of the length of the swollen film (L,) to that of the initial and unswollen (Lo) film.

I I onto polyethylene, and subsequent curing with W as described. I

Table III. Ultraviolet Cured Lesquerella Oil Acrylate High Gloss Wood Finish Formulation

Materials 1 2 3 Amount Amount Amount

(9) (g) (53)

HEMAL0

MACLO

Photomer 3016

Photomer 4061

Photomer 4094

Photomer 4149

Photomer 4770

Photomer 6008

-Byk 065

Byk 325

Irgacure 651

Benzophenone

Silwet 7604

"

16.1

20.0

17 .'O

4.1

5.0

10.0

0.4

0 . 5

2.1

1.1

0.3

15.1

16.4

20.1

17.2

4.3

5.1

10.2

0 .,4

0.5

2.5

1.3

0.4

"

15.0

16.0

20.1

17.1

4.2

5 . 0

10.2

0.4

0.5

2.5

1.3

0.3

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RESULTS AND DISCUSSION

Synthesis

of MAC with LO (Scheme 1). Structural characterization was performed via FTIR and I3C-NMR spectroscopy.

hydroxyl (-OH) absorption centered at 3454 cm-I and carbon-carbon double bond (-C=C-) absorption at 1598 cm-'. Ester formation gives rise to a new absorption in the 1598 cm-' region accompanied by the disappearance of the 3454 cm'l hydroxyl absorption.

Lesquerella oil methacrylate was synthesized by the reaction

The FTIR spectrum of LO (Figure 1) offers characteristic

Table IV. Mechanical Properties and Solvent and Chemical Resistance of Lesquerella Oil Acrylate Coatings

Formulation # 1 2

. Tensile 2928 2220

3

1894 Strength (psi)

Percent 5.5 6.1 Elongation ( % I

5.4

A ? (3C)

Linear Swelling 45

1.111

5 1 . 4

1.108 Ratio

h%' per X-link 115 106

42.3

1.150

138

KEK Double Rubs 350 310 ion steel (2 mil) ( 2 mil) panel 1

2 h Spot Test

220 ( 2 mil)

(ASTM 0-1308)

20'6 H,S04 5 5 4

Soap Solution 5 5 5

D. I. Water 5 5 5

Vinegar 4 4 4

Additional structural confirmation was obtained from I3C-NMR analysis (Figure 2). The C,, hydroxyl bearing carbon of LO

absorb at 35.32 ppm and 36.81 pprn, respectively.' Ester formation shifts the absorption of the oxygen bearing carbon

\ absorbs at 71.453 ppm, while the adjacent C,, and C,, carbons

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downfield to 74.0 ppm, while' the C13 and C,, absorptions move upfield to 31.50 and 3 3 . 3 3 ppm, respectively.5

' Coatings prepared exclusively with MACLO were soft, and adhered poorly to metal surfaces. In an effort to improve film properties, aromaticity was introduced via reacting TDI with HEMA and LO to give HEMALO according to Scheme 1.

TDI was initially combined with HEMA in a 1:l molar ratio to produce the acrylic-isocyanate intermediate, which was subsequently reacted with LO to give the desired product, HEMALO. The synthesis of HEMALO was confirmed by FTIR (Figure 1) and 13c- NMR (Figure 2) analyses. The FTIR spectrum of HEMALO experienced a shift of the free hydroxyl absorption from 3454 cm-I to 3341 cm-l with derivative formation, and the 1600 cm-I absorption

Scheme 1: Synthesis of MACLO and HEMALO from LO

broadened and intensified signaling the presence of the acrylate double bond and benzene's aromaticity. The 13C-NMR spectrum of HEMALO showed decreased absorptions at 71.45, 36.81 and 35.32 ppm, and the appearance of absorption frequencies at 76.00, 33.69, and 31.66 ppm, signaling acrylic ester formation.

The amount of acrylic functionality added to LO was calculated from 'H-NMR spectral integration (Figure 3). The

determined via the ratio of the absorption area corresponding to -. fraction of the acrylic moiety compared to fatty acid was

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WCLO

Figure 1: FTIR Spectra of LO, HPIALO, and MACLO

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LO

8

HEMALO

I I 1 I I I 60 50 40 30 20 70

Parts Per Million

Figure 2: Carbon-13 NMR Spectra of LO, MACLO, and HEMALO

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LO 1

HEMALO

1 7

I

6 I 5

I 4

I 3

I

2 I 1

, Parts Per Million

. Figure 3: Proton NMR Spectra of Lo, MACLO, and HEMALO

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the trans alkene proton (ma) to the area corresponding to the C20 methyl protons (A201 according to Equation 1:

r = F a p20

The calculated values of acrylation are enumerated in Table V. Based on lH-NMR spectrum of LO, the mole fraction of hydroxy fatty acids of LO is 0.55,6 and if one makes the assumption that no s.ide reactions occur, the theoretical acrylic/fatty acid ratio is equal to the hydroxy fatty acid fraction, 0 . 5 5 . In practice, MACLO derivation was determined to be 0.54, or a 98% theoretical conversion. For HEMALO, additional HEMA was added to end-cap unreacted TDI after reaction of the HEMA/TDI intermediate with LO. Therefore, the acrylate/fatty acid ratio was larger than theoretical although there remained some unreacted hydroxyls in HEMALO.

Table V. Fraction of Acrylate Group Relative to Fatty Acid

Derivative Theoretical ’H-NMR Calculated Acrylate/Fatty Acid Ratio Acrylate/Fatty Acid Ratio

MACLO 0.55 0.54

0.55 0.61 HEMALO

Swelling Experiments

Swelling of the W cured films was performed with methylene chloride. The Flory-Rehner equation (Equation 2 ) was employed to calculate the molecular weight between cross-links and the cross- link density of the

(Equation 2 )

where v 2 is the volume fraction of polymer in the swollen mass, x1 is the Flory-Huggins polymer-solvent dimensionless interaction term, V, is the molar volume of the swelling solvent, and n is the number of active chain segments per unit volume. The number of active chain segments per unit.volume (n) equals p/M,, where p is the polymer density and M, is the molecular weight between crosslinks. The published interaction parameter in chlorinated

’ solvents indicates a value in the range of 0.4-0.5,” while our efforts determined an interaction parameter of 0.5. The molar volume of methylene chloride is 64.2 mL/mol. ?he swelling ratio and the calculated M, experimental values are given in Table IV.

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Swelling data provides overall crosslink density and polymer segment molecular weight between crosslinks. Coating #3 was the least crosslinked (138 g/crosslink) followed by coatings ‘#1 (115 g/crosslink) and #2 (106 g/crosslink). This is not unexpected as Coating #3 contained the modified oil and thus two crosslinks per LO molecule are possible (approx. MW = 982 g/mol), or a theoretical 5 4 0 g/crosslink based solely on MACLO. Since excess hydroxyethylmethacrylate was added, TDI-diethoxymethacrylate was likely formed to some extent and thus reduced the weight per crosslink.

Coating Physical Properties

Coating properties are shown in Tables IV and VI. All coatings showed excellent gloss (-80 @ 2001, adhesion (5B), and pencil hardness on wood panels. When a wood filler was used as a first down coating, pencil hardness and adhesion was improved. The gouge pencil hardnesses for coatings #1 and #2 (9H) outperformed coating #3 (6H). Moreover, coating #3 (MACLO) gave the lowest tensile strength and glass transition temperature (T,) , which we have attributed to insufficient cure’. This was confirmed via swelling ratios (see Table IV) which demonstrated that coating #3 had the highest and coating #2 the lowest swelling ratio, respectively.

Coatings formulated with ALO were superior to the control with respect to direct and reverse impact resistance on cold rolled steel. Cross-hatch adhesion confirmed poorer adhesion to steel for the control (lB, or 20%) than either coating #2 (4B, 80%) or # 3 (5B, 100%). Moreover, coating #2 possessed better cross-hatch adhesion to aluminum ( 3 B , 60%) than either coating #I or #3 (OB, 0%).

The W cured,coatings demonstrated excellent chemical resistance (Table VI), where MEK resistance followed the order of Coating #1 > coatings # 2 > coating #3. A 20% H,SO, solution treatment did not change the appearance of coatings #1 and #2, but stained coating #3, a likely result of lower crosslinking density.

CONCLUSIONS

Acxylated lesquerella oil derivatives were synthesized for the first time, and formulated into W cured coatings. Structural characterization was performed by FTIR, ’H-NMR and I3C- NMR analyses. The use of MACLO in W curing coating formulations provided for improvements in flexibility” and adhesion to metal. Coatings formulated with HEMAL0 showed significantly improved adhesion to both steel and aluminum substrates. Lesquerella oil modification increases flexibility at the expense of T, and solvent resistance.

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n m - m 2

v w 0 D m m 4

a r X r m W

m 0

m Ln

N W r m =r:

r

0 0

drl O 0 N ? 2

d m X m m m

m m

m Ln

m m m m X

CD

m m X m m m

m 0

m Ln

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ACKNOWLEDGMENT

This material is based upon work supported by the Cooperative State Research Service, U.S. Department of Agriculture, under Grant/Cooperative No. 93-COOP-1-9529. The authors wish to express appreciation to Drs. Daniel Kugler and Harry Parker and Mrs. Carmela Bailey for their Support,

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REFERENCES

1. Pappas, S.P. (ed.). In: W Curing: Science & Technology. Vol. 2. Technology Marketing Corp., Norwalk, Connecticut , 1980. p. 3.

2 . Turner, G.P.A. u: Introduction of Paint Chemistry and Principles of Films. Chapman and Hall, New York, 1991. p . 2 2 5 .

3 . Smith, C.R. , Jr., Wilson, T . K . , Miwa, H. , Zobel, R.L. , Lomar, and wolff, I.A. Lesquerolic acid. A new hydroxy acid from lesquerella seed oil. J. Org. Chem. 26: 2903, 1961.

4. Carlson, K.D., Chaudhry, A . , Peterson, R.E. , and Bagby, M.O. Preparative chromatographic isolation of hydroxy acids from lesquerella fendleri and lesquerella gordonil seed oils. JAOCS. 67: 495, 1990.

5. Levy, G.C. I,r: Carbon-13 Nuclear Magnetic Resonance Spectroscopy. 2nd ed. John Wiley and Sons, New Ydrk, 1980. p . 62.

6. Thames, S.F., Yu, H., Wang, M.D., and Schuman, T.P. Dehydration of lesquerella oil. Accepted JAOCS. 1994.

7. Crompton, T.R. LQ: Practical Polymer Analysis. Plenum Press, New York, 1993. p. 5 8 5 .

8. Sperling, L.H. In: Introduction to Physical Polymer' Science. Wiley-Interscience, New York, 1986. p. 343.

9; Tramontano, V.J. Crosslinking of waterborne polyurethane dispersions. , In: Proceedings of the Twenty-first Waterborne, High-Solids, & Powder Coatings Symposium, Part 1. Southern Society for Coatings Technology and University of Southern Mississippi, New Orleans, Louisiana, 1994. p . 83.

IO. Wolf, B.A. Polymer-solvent- interaction.parameters. u: J. Brandrup and E.H. Immergut (eds.), Polymer Han-ok. 2nd ed., John Wiley and Sons, New York, 1.975. p . IV 191.

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