MEASURING SPONTANEOUS HEATING TENDENCY OF ART MATERIALS

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1 MEASURING SPONTANEOUS HEATING TENDENCY OF ART MATERIALS Charles M. Stopford, Woodhall Stopford, and Thomas O. Brock December 25, 1996 INTRODUCTION There is a fire hazard involved with using of some oil-based art materials, because of their spontaneous heating tendency (SHT) as they dry. Spontaneous heating of an oil occurs because of an exothermic reaction that takes place as it polymerizes and cures. Retention of heat further accelerates the process. In this investigation we are developing a method for testing the spontaneous heating tendency of oil-based art materials so that they may be labeled appropriately. Two other ASTM methods for measuring SHT (D 3523 Standard Test Method for Spontaneous Heating Values of Liquids and Solids (Differential Mackey Test) and E 771 Standard Test Method for Spontaneous Heating Tendency of Materials) are not easily reproducible: this investigation defines a method that can be used for inter-laboratory protocols. In 1953 the Louisville Club 1 described measurements of the spontaneous heating tendencies of various oil vehicles mixed with driers. They found that the degree of spontaneous heating depended on the amount of driers present (to a maximum of 0.44% metal), the type of drier used, the percentage of oil present, and the type of oil used (linseed oil being most active). Spontaneous heating tendency was always evident within 8 hours. With the more active oils, spontaneous heating tendency was evident within one hour. This report further investigates the effect of the amount of drier present on SHT. Anstenius (1978) 2 investigated the effect of added air and apparatus temperature on the degree of spontaneous heating of linseed oils. He found that the time to reach peak temperature 1 Louisville Club (1953) A study of spontaneous combustion tendencies of paint vehicles. Official Digest 20: Anstenius CE (1978) Sjalvantandning I farg (Self ignition in paints). Farg Och Lack 1:

2 decreased with the addition of an extra air supply and by increasing the apparatus temperature above ambient (in his experiments to 100 o C.). In this report we also investigate the effects of an extra air supply. To decrease testing time and allow a stable control temperature, we used a constant temperature water bath set at above ambient (70 2 o C.) MATERIALS! Constant Temperature Water Bath - water bath that can maintain water temperature at 70 2 C. (modified Mackey Apparatus 3 )! K Thermocouple! Maximum Temperature Recorder - Barnant 100, Model No , Barnant Co., Barrington, IL.! Stainless Steel Water Bath Chamber - Available with water bath from Lab-Line Instruments, Inc. Melrose Park, IL, Model No ! Aluminum Holder (for paper cloth) - holes are machined an average of 2 in. above the base with a total air hole surface area of 3 /10 in. 2.! Non-woven paper cloth (Scott Rags)! Saw Dust (kiln-dried Yellow Pine (Pinus echinata)) - saw dust sized using three stainless steel sieves to 1-1.5mm, mm and <0.5mm fractions.! Kitchen paper towels! Cotton percale (200 threads per square inch)! manganese drier (manganese naphthenate-2-ethylhexanoate, 6% Mn, Huls, Piscatoway, NJ) METHODS A constant temperature water bath is filled with water and heated until the water is at 70 C 2 C. Prepare liquid or paste oil-based art material to times the weight of the cellulose matrix. Mix liquid or paste oil-based art material thoroughly with 6% manganese drier. Pour or spread the drier-oil-based art material mixture evenly over the cellulose matrix. Place the test material in the aluminum holder and then place the holder into the stainless steel water 3 ASTM Standard Test Procedures 500, Mackey Apparatus for Spontaneous Combustion. Available from ASTM, 1916 Race St., Philadelphia, PA 19103

3 bath chamber. Insert the K thermocouple in the center of the test material. Record peak temperature with a peak recording thermocouple thermometer. RESULTS Operating Conditions To determine appropriate operating conditions, we investigated three major variables: the amount of available air, the type of cellulose matrix and the amount of drier mixed with the cellulose matrix. The amount of air available to the oil-based art material can be varied by opening or closing the lid of the stainless water bath steel chamber. In one experiment using non-woven paper cloth and drying oil, the peak temperature rose 81 C. in 10 minutes after the top was opened 170 minutes after the beginning of the experiment (see Table 1). A lid opening of 7 /16 in. was chosen to allow air to reach the test material, but limit temperature fluctuations. The porosity of the cellulose matrix that is used can also effect the amount of air reaching the oil-based art material. Some of the more porous cellulose matrixes are porous paper toweling, non-woven paper cloth and course (1-1.5 mm) saw dust. With similar intra-laboratory precision, any of these would be a good cellulose matrix to use in an experiment (see Table 2). Some of the less porous cellulose matrixes are non-porous paper toweling, woven cloth and fine to medium (<1.0 mm) saw dust (see Table 3). Use of these materials results in lower and delayed peak temperatures. The amount of manganese drier added to an oil-based art material does effect the maximum peak temperature. When the ratio of drier to oil is appreciably greater or less than 1:50, peak temperatures are diminished (see Table 4). Testing of Art Materials When testing for the effect of inorganic contaminants on the spontaneous heating tendency of refined linseed oil using a porous paper cloth matrix, we found that any contaminant acts as a catalyst for polymerization when used in a small amount. Small amounts (an average of 1:40 contaminant to oil) of burnt umber oil paint, red iron oxide, 45 m farm soil, or calcined

4 diatomaceous earth added to refined linseed oil were similarly effective with peak temperatures averaging 125 C above the control temperature (see Table 5). However, when a small amount of burnt umber oil paint is added to a linseed oil-manganese drier mixture, peak temperatures drop. When a large amount of burnt umber oil paint is added to this mixture, temperature increase is suppressed (see Table 6). Some oil-based art materials, like thickened or stand linseed oil, have already been partially polymerized. When these oil-based art materials are mixed with a drier, their peak temperatures are much lower and take longer to reach a maximum temperature rise than with an un-polymerized oil (see Table 7). They appear to pose less threat as a fire hazard than unpolymerized oils. Disposal of Contaminated Rags Another condition that we investigated is to see if letting oily rags dry out would eliminate the spontaneous heating tendency of an oil/drier mixture. This method of disposal is not effective in changing the SHT of oily rags. When letting rags soaked in a drying linseed oil medium dry out for 1 hour, 24 hours and 48 hours, there is no appreciable change in peak temperatures with the average peak temperature at 115 C above the control temperature (see Table 8). Since rags began smoking and charring at 150 C, this approach to rag disposal would not eliminate fire hazards. SUMMARY AND CONCLUSIONS The most appropriate operating conditions for testing for spontaneous heating tendency of oil-based art materials as follows:! It is best to prepare times the cellulose matrix=s weight of oil-based art material.! A lid opening of 7 /16 in. allows air flow to reach the test material, but limits the temperature fluctuations.! Using a porous cellulose matrix is best for obtaining higher peak temperatures.! Any porous cellulose matrix can be used.! A ratio of about 1:50 drier to oil based art material is best for obtaining higher peak

5 temperatures. When using this method to test spontaneous heating tendency of various art material mixtures we find that:! Any contaminant acts as a catalyst for exothermic polymerization including inorganic pigments and dirt. The most effective catalyst of the materials we tested is a 6% manganese drier.! Mixing an oil paint with a drying oil can decrease SHT of the drying oil.! Pre-polymerized oil-based art materials do not have a high SHT.! The method of letting oily rags dry out to eliminate SHT of an oil-based art material/drier mixture is ineffective.! In order to get the most information on SHT of an oil-based art material, record peak temperature with a peak recording thermocouple thermometer both at 75 minutes and at 8-16 hours. Materials such as refined linseed oil, which have a peak temperature rise in less than 75 minutes, may pose a greater hazard than those reaching a peak temperature more gradually. Materials with a higher peak temperature rise are likely more hazardous than those with a lower peak temperature rise. Table 1: Effect of Air Supply on Maximum Spontaneous Heating Temperature Description time (min) DELTA T ( o C) Paper Toweling Drying oil only: top closed top opened Course saw dust (1-1.5 mm) Drying oil only: top closed top opened Table 2: Variability in Maximum Spontaneous Heating Temperature Measurements Using

6 Refined Linseed Oil/Manganese Drier Mixture and Cellulose Matrixes Matrix Type Oil type # of Control Maximum Delta T Trial s Peak Temp ( o C Peak Temp ( o C sd) ( o C sd) sd) Ts TD Tc Sawdust ( mm kiln-dried Pinus echinata) single batch Paper toweling single batch Non-woven paper cloth single batch Non-woven paper cloth Mixed with variable Mn levels Table 3: Effect Cellulose Matrix on Maximum Spontaneous Heating Temperature When Mixed with a Refined Linseed Oil/Manganese Drier Mixture Paper Toweling (porous) Paper toweling (non-porous) Paper non-woven cloth Woven Cloth 75 21

7 Course saw dust (1-1.5 mm) Medium saw dust ( mm) Fine saw dust (<0.5 mm)

8 Table 4: Effect on Drier Concentration on Maximum Spontaneous Heating Temperature When Mixed with Refined Linseed Oil and Using Non-woven Paper Cloth as a Matrix Refined Linseed Oil No drier No drier Mn drier (1:156) Mn drier (1:85) Mn drier (1:47) % Mn drier #2 (1:47) Mn drier (1:15) Table 5: Effect of Inorganic Contaminants on Maximum Spontaneous Heating Temperature of Refined Linseed Oil Using a Paper Cloth Matrix refined linseed oil (trial #1) refined linseed oil (trial #2) refined linseed oil + burnt umber oil paint (35:1)

9 refined linseed oil + red iron oxide (38:1) refined linseed oil + 45 m farm soil (37:1) refined linseed oil + calcined diatomaceous earth (50:1) Table 6: Effect of Earth Color Oil Paint on Maximum Spontaneous Heating Temperature of a Drying Oil Tested with a Paper Cloth Matrix drying oil only Drying oil/burnt umber oil paint (23:1) Drying oil/burnt umber oil paint (1:1) burnt umber oil paint only Table 7: Maximum Spontaneous Heating Temperature Using Partially Polymerized Oil and a Non-Woven Paper Cloth Matrix Thickened Linseed Oil No drier No drier Mn drier (1:39) Stand Linseed Oil

10 No drier No drier Mn drier (193:1) Mn drier (76:1) Table 8: Effect of Drying Time on Maximum Spontaneous Heating Temperature Using Drying Oil and a Non-woven Paper Cloth Matrix No drying of towel hr drying hour drying hour drying

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