Evaluation of a Low VOC Wax Stain under Extreme Environmental Conditions

 

Woodcrest Manufacturing

 

Peru, Indiana

 

Prepared by

 

Rick Bauer

Professional Assistant for Coating Application Technology

 

 

1.      Introduction

 

The scope of this project was to test the application and curing performance of a low volatile organic compound- (VOC) containing wax stain system under conditions of extreme temperature and humidity. The possibility of using alternative solvents, specifically Oxsol 100* and/or acetone for the reduction of the wax stain coating, was also investigated.

 

* The use of a product name in this report does not serve as an endorsement of the product by Purdue University, the Indiana Clean Manufacturing Technology and Safe Materials Institute or the State of Indiana.

 

Very humid conditions can sometimes adversely affect the appearance and curing of a wood finish. This is especially true with low VOC products. Blushing (a whitish cloudy appearance in the finish) is a very common occurrence on very hot, humid days. When this phenomenon occurs, the affected substrate must be stripped of the old finish and then refinished. The repair process may as much as triple the amount of VOCs released during the finishing operation of that substrate.

 

When the temperature cools to below 70F, curing problems may occur as many low VOC coatings dry more slowly than their high VOC counterparts. During colder conditions, these coatings may not reach full cure within the specified time period and are then packaged prior to achieving cure. Many times two pieces stacked on top of each other will actually bond during shipping. When separated, the finish may be marred, or in some cases, pull completely free from the substrate.

 

The following tests were performed to insure that the low VOC coating and solvent blend chosen by Woodcrest will perform in a manner that does not increase the amount of coating repair or rework required, especially under extreme conditions.

 

 

2.      Instrumentation, Apparatus, and Materials

 

2.1              Substrate

 

Two species of wood were used in this testing procedure:

 

1.      Ponderosa Pine, substrate dimensions - 2.5"x 6"x 0.75"

2.      Yellow Pine, substrate dimensions - 2.5"x 6"x 1"

 

Wood moisture content ranged from 12.1% - 13.3% in all samples. Woodcrest Manufacturing supplied the wood samples used in the tests.

 

 

2.2              Coatings

 

Two coatings were used in this evaluation. The first was the wax stain coating currently used by Woodcrest, WS-2535 (6.83 lbs. VOCs, per gallon). The second wax stain was a low VOC wax stain blend, WS-2675 (3.48 lbs. VOCs, per gallon). Woodcrest Manufacturing supplied both of the coatings used in these tests.

 

2.3              Solvents

 

Three solvents were used during this testing procedure.

 

1.      100% Mineral spirits (100% VOCs)

2.      Oxsol 100 (0% VOCs)

3.      100% Acetone (0% VOCs)

 

2.4              Walk-In Environmental Chamber

 

The chamber air supply unit is a Thomas and Batts International system utilizes a Herrtronics Humidifier control unit. The chamber itself is a 6'x12'x 8' insulated walk-in room, designed and built by Purdue University.

 

2.5              Temperature/Humidity Recorder

 

The temperature and humidity readings were recorded using a Barnant Temperature Humidity Logger, model number 691-9000.

 

2.6              Temperature & Humidity Control Chamber

 

A Thermotron model SM32 C temperature and humidity control chamber was used during this test.

 

2.7              Application System

 

The wax stains were applied using a Kremlin pump: Model STD9 attached to an air-assisted airless spraygun, Kremlim MX, using a 20-136 spray tip. The system was operated at low pressure (less than 20 psi) to simulate a flow coating system.

 

2.8 Wood Moisture Content

 

The moisture content of the test sample substrates was measured using a Delmhorst Wood Moisture Meter.

 

 

3.      Testing Procedure

 

3.1              Test 1 Procedure

 

Four coating/solvent combinations were prepared. Each of the test coatings was thinned until it achieved an 8-second reading, using a #2 Zahn cup at 75 F.

 

1.      Test Coating A, wax stain WS-2535 mixed with two parts mineral spirits (this is the wax stain, reducer, and reducing ratio currently used at Woodcrest)

2.      Test Coating B, wax stain WS-2675 mixed with one part mineral spirits

3.      Test Coating C, wax stain WS-2675 mixed with 0.5 parts mineral spirits and 0.5 parts Oxsol 100.

4.      Test Coating D, wax stain WS-2675 mixed with 0.5 parts acetone and 0.5 parts Oxsol 100.

 

The temperature in the walk-in environmental chamber was set at 95 Fahrenheit, with a 95% relative humidity. After the unit had stabilized, the test coatings and substrates were placed in the chamber. The wood substrates and coatings remained in the chamber for one-half hour prior to proceeding with the test. The substrates were then coated using the following coating and reducer combinations.

 

Test Substrates 1A-2A, (ponderosa pine) were coated using Test Coating A

Test Substrates 3A-4A, (ponderosa pine) were coated using Test Coating B

Test Substrates 5A-6A, (ponderosa pine) were coated using Test Coating C

Test Substrates 7A-8A, (ponderosa pine) were coated using Test Coating D

Test Substrates 11A-12A, (yellow pine) were coated using Test Coating A

Test Substrates 13A-14A, (yellow pine) were coated using Test Coating B

Test Substrates 15A-16A, (yellow pine) were coated using Test Coating C

Test Substrates 17A-18A, (yellow pine) were coated using Test Coating D

 

The coatings were applied, within the chamber, using an air assisted airless spray gun. The system was operated using very low fluid pressures, with no shaping air, to simulate the flow coat operation used at Woodcrest.

 

After the coating application procedure was completed, the substrates were allowed to drain in the chamber for two minutes. After two minutes, the substrates were removed from the walk-in chamber and placed in the Thermotron, operating at 95F, 95% relative humidity. The substrates were allowed to soak in the chamber for a total of 15 minutes.

 

After the 15 minutes elapsed, the substrate pairs were stacked one on top of the other. A twenty pound weight was placed on top of each pair, exerting a force of four pounds per square inch. The substrates remained within the confines of the Thermotron for an additional half hour. The substrates and weights were then removed from the chamber and allowed to reach ambient conditions.

 

After one hour, the weights were removed and the substrate pairs were separated and inspected for coating defects. The color, appearance, and feel of the substrates were then compared to a sample which was coated using Woodcrest's current flow coating system.

 

3.2              Test 2 Procedure

 

As in Test 1, four coating/solvent combinations were prepared. Each of the test coatings was thinned until it achieved an 8-second reading using a #2 Zahn cup at 75 F.

 

1.      Test Coating A, wax stain WS-2535 mixed with two parts mineral spirits (this is the wax stain, reducer, and reducing ratio currently used at Woodcrest)

2.      Test Coating B, wax stain WS-2675 mixed with one part mineral spirits

3.      Test Coating C, wax stain WS-2675 mixed with 0.5 parts mineral spirits and 0.5 parts Oxsol 100.

4.      Test Coating D, wax stain WS-2675 mixed with 0.5 parts acetone and 0.5 parts Oxsol 100.

 

The temperature walk-in environmental chamber was set at 60 Fahrenheit, with 95% relative humidity. After the unit had stabilized, the test coatings and substrates were placed in the chamber. The wood substrates and coatings remained in the chamber for one-half hour prior to proceeding with the test. The substrates were then coated using the following coating and reducer combinations.

 

Test Substrates 1B-2B, (ponderosa pine) were coated using Test Coating A

Test Substrates 3B-4B, (ponderosa pine) were coated using Test Coating B

Test Substrates 5B-6B, (ponderosa pine) were coated using Test Coating C

Test Substrates 7B-8B, (ponderosa pine) were coated using Test Coating D

Test Substrates 11B-12B, (yellow pine) were coated using Test Coating A

Test Substrates 13B-14B, (yellow pine) were coated using Test Coating B

Test Substrates 15B-16B, (yellow pine) were coated using Test Coating C

Test Substrates 17B-18B, (yellow pine) were coated using Test Coating D

 

The coating was applied, within the chamber, using an air assisted airless spray gun. The system was operated using very low fluid pressure with no shaping air, to simulate the flow coat operation used at Woodcrest.

 

After the coating application was completed, the substrates were allowed to drip in the chamber for two minutes. After two minutes, the substrates were removed from the walk-in chamber and placed in the Thermotron, operating at 60F, 95% relative humidity. The substrates were allowed to soak in the chamber for a total of 15 minutes.

 

After the 15 minutes had elapsed, the substrate pairs were stacked one on top of the other. A twenty pound weight was placed on top of each pair, exerting a force of four pounds per square inch. The substrates remained within the confines of the Thermotron for an additional one and one-half hours. The substrates and weights were then removed from the chamber and allowed to reach ambient conditions.

 

After one and one-half hours, the weights were removed and the substrate pairs were separated. The substrates were then inspected for coating defects. The color, appearance and feel of the substrates were then compared to a sample, which was coated using Woodcrest's current flow coating system.

 

 

4.      Test Results

 

4.1     Test 1 Results

 

There was virtually no difference in appearance or wax finish feel of the sample from Woodcrest's coatings line and the test substrate samples, 1A-6A &11A-18A. Substrates 7A, 8A, 17A, & 18A showed some minor grain raising on the wood's surface, which resulted in a rough finish. These four test substrates did not possess the waxy feel that is desired by Woodcrest.

 

After 15 minutes, none of the samples had incurred any visible damage to the finish as a result of the stacking. Woodcrest currently allows the substrates to air dry a minimum of 30 minutes prior to stacking or packaging.

 

One observation made during the test concerned the samples coated using Oxsol as the reducing solvent. Even after a four-hour cure at room temperature, these samples emitted a rather strong solvent odor. This odor could be a problem if the products are packaged soon after the finishing operation and are packaged in a way that does not allow additional evaporation of the solvent. Customers opening the sealed container could find the odor to be unpleasant.

 

 

Table 1

Test 1 Results, 95 F, 95% R.H.

 

Sample

Wood

Coating

Solvent

Appearance

Wax Feel

1A

Ponderosa Pine

WS-2535

M. Spirits

Good

Good

2A

Ponderosa Pine

WS-2535

M. Spirits

Good

Good

3A

Ponderosa Pine

WS-2675

M. Spirits

Good

Good

4A

Ponderosa Pine

WS-2675

M. Spirits

Good

Good

5A

Ponderosa Pine

WS-2675

M. Spirits/Oxsol

Good

Good

6A

Ponderosa Pine

WS-2675

M. Spirits/Oxsol

Good

Good

7A

Ponderosa Pine

WS-2675

Acetone/Oxsol

Poor

Marginal

8A

Ponderosa Pine

WS-2675

Acetone/Oxsol

Poor

Marginal

11A

Yellow Pine

WS-2535

M. Spirits

Good

Good

12A

Yellow Pine

WS-2535

M. Spirits

Good

Good

13A

Yellow Pine

WS-2675

M. Spirits

Good

Good

14A

Yellow Pine

WS-2675

M. Spirits

Good

Good

15A

Yellow Pine

WS-2675

M. Spirits/Oxsol

Good

Good

16A

Yellow Pine

WS-2675

M. Spirits/Oxsol

Good

Good

17A

Yellow Pine

WS-2675

Acetone/Oxsol

Fair

Marginal

18A

Yellow Pine

WS-2675

Acetone/Oxsol

Fair

Marginal

 

 

 

4.2     Test 2 Results

 

As in Test 1, there was virtually no difference in appearance or wax finish feel of the sample coated using Woodcrest's current coatings system and test substrate samples, 1A-6A &11B-18B. Substrates 7B, 8B, 17B, & 18B showed minor grain raising on the wood's surface, which resulted in a rough finish and did not possess the desired waxy feel. After 15 minutes, no evidence of damage to the finish as a result of the stacking was detected.

 

Once again, the odor of products coated with a wax stain reduced with Oxsol and promptly packaged and shipped, without the opportunity to experience additional cure time, may result in a strong solvent odor when unpacked by the customer.

 

 

 

Table 2

Test 2 Results, 60 F, 95% R.H.

 

Sample

Wood

Coating

Solvent

Appearance

Wax Feel

1B

Ponderosa Pine

WS-2535

M. Spirits

Good

Good

2B

Ponderosa Pine

WS-2535

M. Spirits

Good

Good

3B

Ponderosa Pine

WS-2675

M. Spirits

Good

Good

4B

Ponderosa Pine

WS-2675

M. Spirits

Good

Good

5B

Ponderosa Pine

WS-2675

M. Spirits/Oxsol

Good

Good

6B

Ponderosa Pine

WS-2675

M. Spirits/Oxsol

Good

Good

7B

Ponderosa Pine

WS-2675

Acetone/Oxsol

Marginal

Marginal

8B

Ponderosa Pine

WS-2675

Acetone/Oxsol

Marginal

Marginal

11B

Yellow Pine

WS-2535

M. Spirits

Good

Good

12B

Yellow Pine

WS-2535

M. Spirits

Good

Good

13B

Yellow Pine

WS-2675

M. Spirits

Good

Good

14B

Yellow Pine

WS-2675

M. Spirits

Good

Good

15B

Yellow Pine

WS-2675

M. Spirits/Oxsol

Good

Good

16B

Yellow Pine

WS-2675

M. Spirits/Oxsol

Good

Good

17B

Yellow Pine

WS-2675

Acetone/Oxsol

Good

Marginal

18B

Yellow Pine

WS-2675

Acetone/Oxsol

Good

Marginal

 

 

 

5. Conclusion

 

The results of both Test1 and Test 2 indicate that replacing Woodcrest's current high VOC coating with the low VOC coating, WS-2675, should result in little, if any, changes in its current coating line. No evidence of blushing was observed with any of the WS-2675/solvent mixtures, even when the coating was applied and cured in very humid conditions.

 

WS-2675, when reduced one to one with mineral spirits or a mineral spirit Oxsol blend, produces the same quality of finish achieved by the WS-2535 system, but with much lower VOC emissions. As applied, Woodcrest's current coatings system, WS-2535, has a VOC content of 6.54 pounds per gallon. WS-2675 mixed with mineral spirits has a VOC content of 4.94 pounds per gallon, while WS-2675 reduced with an Oxsol mineral spirit blend has a 3.34 pounds per gallon VOC content as applied. WS-2675, which was reduced with an Oxsol acetone blend, had the lowest VOC content of the four tested. This mixture has a VOC content of 1.74 pounds per gallon as applied. However, this mixture resulted in minor grain raising and did not produce the desired finish.

 

Using the usage figures provided by Woodcrest, the facility should expect a reduction of 8.9 tons per year by replacing its current wax stain with WS-2675. With increased production, this reduction will be significantly higher. Mineral spirit consumption will be reduced by as much as 50%, since WS-2675 requires only a 1:1 reduction with mineral spirits. However, due to the increase in price per gallon of stain, the savings may be minimal.

 

Table 3

 

Projected Annual Reduction in VOC Emissions

Coating

Solvent

Tons per Year

WS-2675

Mineral Spirits

8.9

WS-2675

Mineral Spirits/Oxsol

16.3

WS-2675

Acetone/Oxsol

24.3

 

 

If WS-2675 is reduced using a mixture of Oxsol and mineral spirits, an annual VOC reduction of over 16 tons could be expected. However, there are a few drawbacks that Woodcrest should consider before implementing this system. Oxsol is not considered a VOC or HAP, but does carry a relatively high price tag. It also has an evaporation rate of 0.9 at 25C, as compared to mineral spirits rate of 0.1. Thus, more Oxsol will be lost to evaporation, compared to the same amount of mineral spirits. Finally, the aforementioned solvent smell may cause complaints from customers as well as coating line personnel.

 

To help reduce solvent loss due to evaporation and, thus make the Oxsol/mineral spirits blend more feasible, Woodcrest should investigate systems that activate the flow coater only when a part is passing through the flow coater. This can easily be achieved using an electronic eye at the opening of the flow coat system. A timer would then be used to shut down the system until the next part triggers the electronic eye.