The Application of Dimethyl Carbonate (DMC) in Several Coating Materials

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Preface

• DMC, considered a new chemical material to the United States market and has gained some breakthroughs in the past decade and is becoming more popular as researched has broadened its application range.

• Dimethyl Carbonate, shortened as DMC, is a colorless transparent liquid with light smell and sweet taste. Some key properties are listed below:– Melting point of 4 ℃– Boiling point of 90.1℃– Density of 1.069/gcm3, – Refrangibility (nD20)1.3687, – Able to mix with almost all organic solvents, such as aethers, alcohols, ketones, etc.– Very low toxicity – Average lethiferous quantity for mice and rates LD50 =6400~12800mg/kg. – Contains a unique molecular structure, that can replace dimethyl sulfate as a methylating agent and phosgene

as a carbonating agent. Can be used as a gasoline additive for improving the octane number and oxygen content.

• In paint and coating industries that are developing product in accordance to VOC guidelines (Volatile Organic Chemicals) and low HAP (Hazard Air Pollution) DMC is a fine low-toxic solvent that shows a promising future.

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Physical and Chemical PropertiesSpecs Parameters Specs Parameters

CAS NO. Molecular Formula Molecular Formula C3H6O3

Molecular Weight 90.08 Appearance Lightly fragrant, transparent liquid

Solubility Mixed with aethers, alcohols, and ketones

Content ≥99.5%

Moisture ≤0.1% Methanol ≤0.3% Boiling Point 90.3 ℃ Melting Point 4.0 ℃Flash Point 22 (Hold the flash point of ℃

cup) Vapor Pressure 5.6Kpa(20 ) ℃

Viscocity 0.625Mpa.s(20 ) ℃ Density 1.07ml(20 ) ℃Acidity Value, pH 6.8 - 7 Toxicity Low

The structure of DMC (Dimethyl Carbonate) CH3—O—C—O—CH3

║ O

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Tests on the volatile speed of DMC • A Solvents’ volatile speed is one of the important factors in choosing coating solvents. • Six different common solvents for coatings were tested (acetone, butanone, dimethyl carbonate , butyl

acetate, toluene and xylene). • For testing, a shell film evaporator is applied according to ASTMD3539-76 (81): A amount of solvent is

expanded over a standardized glass plate with a quantity of air stream passing by at a certain temperature and humidity over a designated period of time. The volatizing quantity is recorded at set intervals.

Table 1: Volatile Speed of Some Common Solvents

Items Molecular Formula

Molecular Weight

Boiling Point Comparative Volatile Speed

Acetone CH3COCH3 58.08 56.1 7.2

Butanone CH3COC2H5 72.1 79.6 7.65

Dimethyl Carbonate CH3OCOOCH3 90.08 90.03 3.4

Butyl Acetate CH3COOC4H9 116.15 126.5 1.0

Ethyl Acetate CH3COOC2H5 88.10 77.0 5.25

Toluene C6H5CH3 92.13 111.0 1.95

Xylene C6H4(CH3)2 106.13 135.0 0.68

From table 1 we can get that the volatile speed of DMC is faster than that of acetone, butanone or ethyl acetate, but slower than that of butyl acetate, toluene, or dimethylbenzene.

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Acrylic Acid Resin Solvency

Items Solvency parameter

Acetone 10

Butanone 9.3

Dimethyl carbonate 10.4

Butyl acetate 8.5

Toluene 8.9

Xylene 8.8

Table 2: Solvency of six common solvents.

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Solvency to Acrylic Acid Resins A-01• All six solvents above were tested on their solvencies to thermoplastic acrylic acid resin. • A-01 solid acrylic acid resin is the referenced resin used for testing, whose molecular weight 62000, and

vitrification temperature 55 . ℃• The resin is later dissolved into the thicknesses of 50%, 40%, 30%, and 25% respectively with the six solvents. • Then viscosities are measured of the different densities with a rotation viscosimeter and the actual data is

showed as follows:

Table 3: A-01 Thermoplastic Acrylic Acid Resin of Different Viscosities

Solvents Solid %

Acetone Butanone Dimethyl Carbonate

Butyl Acetate Toluen Dimethyl-benzene

50% 402 410 1050 1050 1190 1190

40% 93.2 108 347 261 375 380

30% 25.7 35.8 94.7 80.2 103 113

25% 14.3 22.4 45.1 43.3 55.7 59.8

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Solvency to Acrylic Acid Resins A-06

Solvents Solid %

Acetone Butanone Dimethyl Carbonate

Butyl Acetate Toluene Dimethyl-benzene

50% 402 410 1050 1050 1190 1190

40% 93.2 108 347 261 375 380

30% 25.7 35.8 94.7 80.2 103 113

25% 14.3 22.4 45.1 43.3 55.7 59.8

All six solvents were again tested on their solvencies but this time to A-06 acrylic acid resin, whose molecular weight is 42000 and vitrification temperature 44 .℃Likewise, the resin was diluted into densities of 50%, 40%, 30% and 25% respectively, and measured viscosities of different densities.

Table 3: A-06 Acrylic Acid Resin of Different Viscosities

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Solvency• From table 3 and table 4 we can conclude that the solvency of acetone is the largest,

followed by butanone, butyl acetate, dimethyl carbonate, toluene and dimethylbenzene. • However, when taking into account the solvency parameters, DMC’s solvency ability is

stronger than that of acetone because the solvency parameters apply to a nonpolar system, so this is incorrect in a strong polar system.

• The items and their Hydrogen bond values are listed in table 5.• Acetone, butanone and butyl acetate are considered medium level hydrogen bonds, while

DMC, toluene and dimethylbenzene are considered weak.• So the three former solvents, whose solvent abilities from strong to weak are acetone,

butanone are butyl acetate, own a stronger solvency than the three latter ones, whose solvent abilities from strong to weak are DMC, toluene and dimethylbenzene. Therefore, to their solvent abilities, their arrangement is acetone, butanone, butyl acetate, DMC, toluene and dimethylbenzene (Table 5).

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Table 5 the solvency parameters and hydrogen bond values

Items Solvency Parameter Hydrogen Bond Value

Acetone 10 9.7

Butanone 9.3 7.7

Dimethyl Carbonate 10.4 8.8

Butyl Acetate 8.5 8.8

Toluene 8.9 4.5

Xylene 8.8 4.5

Solution to Nitro Resin:Acetone, butanone or butyl acetate can solute nitrified cotton powder at normal temperatures, but DMC, toluene and dimethyl cannot. According to the theory of comparativeness, a polar material, like nitrified cotton power, can only be soluted by apolar solvents, but cannot by soluted by any hydrocarbonic organic compounds. If some acetone or butanone is partly mixed with DMC, the situation improves ─ after a series of experiments it’s been found that the nitrified cotton powder will be soluted from mixing proportions of 1:3 to 1:10.

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Substitution Experiments• The property of coating depends on the materials themselves, and their solvents

decide their four properties– viscosity – flow – drying period – luster.

• Experiments were conducted on these four properties: • DMC replaced Butyl acetate in the solvent system:

– Cyclohexanol, butyl acetate, and glycol ether acetate in a 1:1:1 ration- in proportions of 20%, 40%, 60%, and 80% to 100%.

• By appearance of samples, we can see smooth paint surface and slightly improved luster, and are able to draw a conclusion that the adding of DMC doesn’t affect much on drying time of paint coatings.

• Table 7 and table 8 show us the results of the tests on varnish and matt paint properties after applying 100% DMC instead of butyl acetate.

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Table 7: Test results of Polyurethane Varnish Paints

Items Results

Appearance White and Smooth

Drying Time

surface drying/hours 2

thoroughly drying/hours 10

Adhesive power/Grade 1

Hardness 2H

Luster (60°C)≥ 90

Anit-impacting / cm 50

Flexibility/mm 1

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Table 8: Test results of Polyurethane matte paintsItems Results

Appearance White and Smooth

Drying Time

surface drying/hours 2

thoroughly drying/hours 10

Adhesive power/Grade 1

Hardness 2H

Luster (60°C)≥ 10

Anit-impacting / cm 50

Flexibility/mm 1

These results indicate that the paint coating properties meet all the requirements and can replace the above-stated polyurethane varnish white paint or matt white paint.

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The Application of DMC with Several Coating Materials • A. DMC, used as a substitute for butyl acetate and ethyl acetate mixed solvent (1:1) in nitryl-modified

thermoplastic acrylic acid orange rind paint, makes the varnish clear and transparent on a glass plate, and the coating of ready orange rind paint appear smooth:

• 1) time of Drying: surface drying for 5 Min, • thoroughly drying for 30 Min • 2) adhesive power: 1st grade • 3) making all the other indexes

• B. Diaphaneity will be finer if the mixed solvent of acetone and dimethylbenzene in acrylic polyurethanes are thoroughly substituted by DMC and the diluted varnish appears clear.

C. Hammer paint shows clear veins if the mixed solvent of acetone- substituted by 50% DMC- and xylene in bicomponent acrylic polyurethanes hammer paint is thoroughly substituted by DMC.

• 1) Time of Drying: surface drying for 1 hr, thoroughly drying for 24 hrs • 2) Making all the other indexes

• D. Applying DMC in alkyd woodwork paints instead of toluene or ethyl acetate • If the ready PU woodwork paint is made by a 10% cyclohexanol mix of the total quantity (of the half-to-half mixed

solvent of toluene or ethyl acetate ) the coating surface will be smooth and level with fine flowing-flat properties, brilliant luster and desiccated rigidity, all of which meet the PU woodwork paint application demands.

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Items Results

Appearance Smooth and Shiny

Drying Time (h)

(25°C) surface drying/hours 4

thoroughly drying/hours 16

Adhesive power/Grade 2

Rigidity≥ 0.60

Luster (60°C)≥ 95

Construction merits Easy for spraying or brushing

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DMC Storage Stability Experiments

• As paints are sometimes not put into use in a certain period of time after production, an ideal property of a paint is that it should not be prone to deteriorate over time (i.e. it should be of the same quality when ready to use as when manufactured and sold).

• According to GB/T6753.3-86, the method of testing storage stability is to put a sample into a 0.4L metal gland cover container, tighten up the cover and take necessary measurements.

• After that, put it into a cabinet dryer in accelerated conditions at 50±2 for 30days.℃

• Then remove and measure its weight and viscosity after keeping it at normal temperature for 24 hrs. The following shows the results:

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Items Before Experiment After Experiment

Weight 259.703g 258.641g

Viscosity 25.6S 26.2S

Luster 90.5% 89.2%

From the results, we can conclude:-It underwent a 0.4% decrease in weight (less than 1%), -A 2.3% increase in viscosity (less than 5%) -A 1.4% decease in luster degree.

In conclusion this test proves that in reference to the storage stability of thermoplastic acrylic acid resin with DMC as its solvent, DMC passes standard tests with little issues.

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DMC Conclusion• Tested by a series of experiments on usages with thermoplastic acrylic acid resin, alkyd, nitryl-modified

thermoplastic acrylic acid, nitro resin and bicomponent polyurethane coating; DMC, a low toxic solvent, is proved to be:

• 1) Because of its volatile speed and solvency, DMC is not advised being used singularly as a coating material solvent. It, however, can be a part of the paint or coating system to adjust the viscosity etc.

• 2) Compared with toluene and dimethyl benzene, DMC has a more fine solvency with a similar volatile speed to toluene, therefore, the rather high toxic solvents -toluene and dimethylbenzene- can be wholly or partly replaced by DMC.

• 3) Acetate can be wholly replaced by DMC to make the appearance and the luster better, without changing drying time of the coating in bicomponent polyurethane coatings.

• 4) DMC can also be applied with acrylic acid resin or alkyd, making little adjustments for the volatile speed. If a right methods are used, volatility should hardly be affected.

• 5) It’s advisable to use 10%--30% polar solvents additionally in nitro resin applications.

• 6) The performance and qualification as an environmental friendly solvent should alleviate any small impact on production cost (if any ) that is experiences for DMC replacement the more toxic solvents currently used.