LIGNIN-BASED FRICTION MATERIAL

Abstract: This invention provides for a friction material composition suitable for friction element formulation. The composition comprises an essentially sulfur-free lignin with low water solubility. The lignin replaces from about 1 to about 30 % on a weight basis with the phenolic resin in the friction material composition. A method of reducing noise within the range of human hearing resulting from friction element performance is also provided.

Description: LIGNIN-BASED FRICTION MATERIAL BACKGROUND OF THE INVENTION When the brakes of a vehicle are applied, the brake lining on each wheel frictionally engages another member to reduce the rotary motion of the wheel . During the frictional engagement, thermal energy is created as the drum or disc slide on the brake lining. Conventional organic brake linings are made up of a mixture of asbestos or steel fibers and modifiers held together in a fixed matrix created by a phenolic resin. The asbestos or steel fibers remain stable when subjected to thermal changes up to 800° F. However, asbestos deteriorates at higher temperatures due to loss of water. When asbestos dehydrates, it is transformed into forsterites or olivine while the phenolic resin is reduced to a carbonaceous resin as the matrix engages the drum or disc. However, when a phenolic resin iε utilized, a melting of the phenolic resin at the surfaces of all particles occurs to wet the same and reduce the wear of the friction producing elements. Upon curing the phenolic resin reestablishes the matrix bond which holds the friction modifiers and asbestos in a fixed relationship. Phenolic resins are produced through the condensation of a phenol with formaldehyde in the presence of a catalyst. Phenol is derived from benzene and the supply of benzene has been reduced because of industry changes. Because of the reduction in the supply of phenol and the elevated price of phenol, it has been a necessity to find an extender or substitute for phenolic resin. In view of the foregoing, it was suggested that lignin or a lignin derivative be combined with a phenolic resin to produce a fixed matrix. In U.S. Patent No. 4,239,666 it is disclosed a composition for a friction material for use in friction elements such as brake pads, brake linings and clutch facings. In the friction material, lignosulfonate or kraft lignin are substituted for a portion of the phenolic resin binder. However, such a combination presented severe limitations since the resulting friction elements emitted sulfur-based odors upon normal use and erratic brake performance. The choice of lignin or lignin derivative that can be combined in friction material is greatly affected by the environmental considerations which affect the development of pulping technologies. Due to increasing environmental demands during the last three decades, traditional sulfite pulping has almost completely been replaced by the kraft pulping process. Both sulfite and kraft pulping processes are noted for their contribution to air and water pollution, which requires costly pollution control equipment to bring kraft and sulfite pulping operations into environmental compliance. These pulping technologies can now be economically replaced by more environmentally friendly processes. One of these processes is the organosolv pulping process which has minimal impact on the environment. Unlike the traditional sulfite process, the organosolv process allows for the recovery of a highly pure, essentially sulfur-free and hydrophobic form of lignin with low water solubility. This lignin can be suitable for the preparation of a lignin-based friction material for use in friction elements. By the method of the present invention is provided an environmentally friendly lignin-based friction material composition. The composition when formulated in friction elements can greatly reduce the noise, wear and sulfur-based emissions which are generally encountered with prior art friction elements. SUMMARY OF THE INVENTION The invention provides for a friction material composition for use in friction elements wherein an essentially sulfur-free lignin low water solubility replaces from about 1% to about 30% of the phenolic resin in the composition. The friction material composition when formulated into friction elements such as brake pads results in a significant reduction in wear, noise level, and sulfur-based emissions resulting from the performance of the friction element. Novel features and aspects of the invention, as well as other benefits will be readily ascertained from the more detailed description and claims which follow. DESCRIPTION OF THE FIGURES Figures 1 and 2 show the effect of 20% lignin replacement on the uniformity of the coefficient of friction of the resulting brake pad as a function of temperature. Figures 3 and 4 show the effect of 20% lignin replacement on the noise performance of the resulting brake pad at different frequencies. DESCRIPTION OF THE PREFERRED EMBODIMENT This invention provides for a friction material composition having stability in the thermal operating range of most vehicle friction elements. The friction material composition when used in friction elements such brake pads reduces noise levels and improves the wear of the friction element. The friction material composition comprises a highly pure, essentially sulfur-free and hydrophobic form of lignin with low water solubility at neutral or acidic pH. A lignin which can be combined into the friction material can be selected from steam explosion, autohydrolysis extraction or soda lignins. A preferred lignin to accomplish the objectives of this invention is the lignin described in U.S. Patent No. 4,764,596. Such a lignin is a high purity organosolv lignin and is separated as a coproduct of the pulping and chemical delignification of plant biomass with organic solvents, for example ethanol. This lignin is an essentially sulfur-free powder. It has low water solubility at neutral or acidic pH and is soluble in aqueous alkali and selected organic solvents. It is generally characterized by its hydrophobicity, high purity, melt flow and a low level of carbohydrates and inorganic contaminants. In a preferred embodiment, organosolv lignin can be used as a partial replacement for the phenol- formaldehyde resin binder used in friction material formulations wherein powder phenol-formaldehyde resin is used. Lignin can be formulated to replace on a weight basis from about 1 to about 30% of the phenolic resin. An example of such a friction material formulation comprises from about 20% to about 35% iron powder, from about 0.1% to about 1.5% hexamethylene tetramine, from about 10% to about 15% steel fiber or asbestos, from about 8% to about 14% phenolic resin, from about 7% to about 11% graphite and the balance is a modifier which comprises friction coefficient modifiers such as barium sulfate, aluminum oxide and in certain formulations, brown or black organic particles. Such a formulation can comprise lignin of from about 0.08% to about 4.2% on a weight basis with the resulting friction material composition. An important property of the lignin-based friction material composition of this invention is its water solubility. It has been observed that the water solubility of a friction material composition comprising a lignosulfonate shows a tenfold increase in water solubility as compared to a friction material composition comprising the same level of substitution with organosolv lignin. This observation can be explained by the fact that the lignosulfonate-based friction material composition has not been incorporated into the phenolic matrix to the same extent as the lignin of this invention. Brake pads are manufactured by blending the friction material composition and then pressing the blend at from about 375°F to about 500°F for from about 10 minutes to about 45 minutes and at a pressure of from about 350 psig to about 750 psig. Manufacturing techniques are well known in the art. In order to evaluate the friction material composition, a series of tests were performed on friction elements such as brake pads comprising the lignin-of the invention. The pads were all formed by techniques well known in the art. Figures 1 and 2 show that replacing 20% of the phenolic resin with organosolv lignin did not affect the stability of the coefficient of friction as the temperature was changed. A stable coefficient of friction is a requirement of friction element products since drivers require the same braking power or feel regardless of the temperature of the friction elements. The friction material composition of this invention when formulated in brake pads result in an improvement in wear characteristics (Table 1) . Table 1 Inner Outer Average (mm/crm of brake pad) Control 0.102 0.142 0.122 10% Lignin 0.071 0.122 0.096 20% Lignin 0.090 0.139 0.114 A reduction of organic deposits on the rotor can also be observed resulting in an improvement in vibration characteristics as confirmed by noise data as shown in Figure 4 (20% lignin) as compared to Figure 3 (control) . The use of the lignin in brake pad formulations were tested at about 300 rpm, 50 psig and 300°F according to a modified Ford Test. Figure 4 demonstrates a shift of the peak of the frequency to the (human) non-audible part of the spectrum (approximately above 16 KHz) . The invention and many of its attendant advantages will be understood from the foregoing description, and it will be apparent that various modifications and changes can be made without departing from the spirit and scope of the invention or sacrificing all of its material advantages, the compositions and processes hereinbefore described being merely preferred embodiments.

Claims: We claim : 1. A friction material composition comprising an essentially sulfur-free lignin with low water solubility, said lignin replacing from about 1 to about 30% on a weight basis with the phenolic resin in said friction material composition. 2. The composition of claim 1 wherein said lignin is an organosolv lignin. 3. A friction material composition comprising on a weight basis from about 20% to about 35% iron powder, from about 0.1% to about 1.5% hexamethylene tetramine, from about 10% to about 15% steel fiber or asbestos, from about 8% to about 14% phenolic resin, from about 7% to about 11% graphite and of from about 0.08% to about 4.2% of an essentially sulfur-free lignin with low water solubility on a weight basis with said composition. 4. The composition of claim 3 wherein said lignin is an organosolv lignin. 5. A method for reducing noise within the range of human hearing, said noise resulting from friction element performance, said method comprising the step of incorporating in a friction element formulation a friction material composition comprising an essentially sulfur-free lignin with low water solubility, said lignin replacing from about 1 to about 30% on a weight basis with the phenolic resin in said friction material composition. 6. The method of claim 5 wherein said lignin is an organosolv lignin. 7. A method for reducing noise within the range of human hearing, said noise resulting from friction element performance, said method comprising the step of incorporating in a friction element formulation a friction material composition comprising on a weight basis from about 20% to about 35% iron powder, from about 0.1% to about 1.5% hexamethylene tetramine, from about 10% to about 15% steel fiber or asbestos, from about 8% to about 14% phenolic resin, from about 7% to about 11% graphite and of from about 0.08% to about 4.2% of an essentially sulfur-free lignin with low water solubility on a weight basis with said composition. 8. The method of claim 7 wherein said lignin is an organosolv lignin.

Inventors: NEHEZ NICHOLAS JOHN, NEHEZ, NICHOLAS, JOHN
Applicants: ALCELL TECH INC, NEHEZ NICHOLAS JOHN, ALCELL TECHNOLOGIES INC., NEHEZ, NICHOLAS, JOHN
Application year: 1995
Main classification: C08K5
IPC codes: C08J5, C08L97, F16D69