Santamaria Razo, D. and Pellerej, D., "Control of Gaseous Emission During the Curing of Novolac Phenolic Resin in Friction Materials Production: Production Cycle, Physical Properties and Tribological Properties Improvements," SAE Int. J. Mater. Manf. 7(1):10-16, 2014, doi:10.4271/2013-01-2058.
Thermosetting resins such as Novolac phenolic resin are commonly used as binders in the production of friction materials. It is known that the reactions between the Novolac resin and hexamethylenetetramine (used as catalyst) produce volatile compounds as ammonia. Emitted gases give rise to pores in the friction material. This forces producers to create specific pressure-no pressure cycles to avoid cracking of the material during production.The contribution of this paper deals with the reduction of volatile compounds emission during curing by modifying the composition of the mix formula using two approaches:The first one consists in adding to the formulation suitable fillers that are able to absorb volatile compounds and not to release them for temperatures up to 200°C. These substances must have high surface area and acidic properties to effectively absorb ammonia and other volatile compound and shall be chosen between commercial fillers already used in the formulation of brake pad to minimize the effect of their introduction in the production cycle and cost. The following materials were investigated: a zeolite (HY) and a clay (montmorillonite) that are known to fulfill the above-described requirements.The second way for volatile removal consists in modifying the surface properties of fillers already present in the formulation of brake pads by chemical functionalization, a technique that is widely use to design absorbents suitable for chosen substances. Carbon was chosen to be functionalized, that is present in brake pad formulation as graphite and carbon black. In particular active carbon, that is already known for its adsorbent properties, has been functionalized with sulphonic groups.Both approaches were then compared to evaluate gas removal by means of termogravimetric analysis. Adsorbent powders were then introduced in the friction lining formulation. A reference material was produced and compared to materials produced with the use of the best absorbent raw materials. Production cycle and tribological properties were then evaluated and compared.A suitable technique to produce adsorbent materials has been evaluated. It has been then used as a method to control gaseous emissions during the curing of Novolac phenolic resins with positive results. An important improvement in the production process of friction linings has been developed. Industrial development has to be evaluated ant its impact on production costs has to be studied. Low cost functionalization have to be evaluated with raw materials producers.