Sulfur Carriers 269
9.4.2.1.6 Biodegradability
Depending on the raw materials and on the sulfurization process, sulfurized products cover the
whole range from nonbiodegradable to readily biodegradable. Besides the raw material, the produc-
tion technology plays a predominant role. Catalysts used, impurities in the raw materials, and side
components formed during the synthesis have a strong infl uence on the biodegradability. Therefore,
biodegradability cannot be predicted but has to be tested for every single product. Biodegradable
sulfur carriers are available for various applications [38].
9.4.2.1.7 Stability
Storage stability is obtained by total reaction of the double bonds in the sulfur carrier and in elimi-
nating H 2 S and mercaptans. Especially mercaptans, but also H 2 S, are left over from the sulfuriza-
tion process. If H 2 S or mercaptans are not removed completely, they will evaporate under severe
conditions in the fi nal application or even under unfavorable storage conditions. Mercaptans can
react with the polysulfanes and thereby release H 2 S. Depending on the raw materials and the type of
sulfurization process, some sulfurized products continue to polymerize during storage. Especially
triglycerides, sulfurized with fl ower of sulfur under atmospheric pressure, show a steady and some-
times very strong polymerization during storage.
9.5 COMPARATIVE PERFORMANCE DATA
IN PERTINENT APPLICATION AREAS9.5.1 METALWORKING
9.5.1.1 Cutting/Forming
In principle, we have to deal in all cutting processes with abrasive wear (i.e., cutting) and adhesive
wear (i.e., build up edges). Depending on the particular process, the machining parameters, one of
these wear types, play a dominant role. At low machining speeds, like in most of the forming opera-
tions, adhesive wear (cold welding), the formation of build up edges, and wear on the fl ank of the
cutting edge are very often the limiting factors for tool life. At high machine speeds and increasing
contact temperatures, the abrasive wear determines the tool life. The reactivity of additives depends
on temperature and pressure. Field and laboratory tests showed that different types of sulfur carriers
(same sulfur content but varying raw materials or production processes) lead to signifi cantly differ-
ent results in a metalworking operation [39].
9.5.1.2 Contribution of Sulfur Carriers to Metalworking
Sulfurized products can be designed to meet technical and ecological requirements in metalwork-
ing processes. They are used successfully for more than 80 years to avoid abrasive and adhesive
wear and enhance lubricity. In cutting operations, their main function is to support the cut and to
prevent wear of the tool, whereas in forming processes, sulfurized products should form a pressure-
stable lubricant fi lm and prevent adhesive wear.
9.5.1.3 Replacement of Sulfur Flowers
In the past, it was very common to dissolve sulfur fl owers in metalworking fl uids to obtain a high
reactivity and good EP properties. This procedure is very cost-intensive because it has to be done
under controlled temperature conditions below the melting point of sulfur and has several disad-
vantages such as limited solubility (maximum 0.8% S), limited stability (sulfur dropout), and high
corrosivity toward yellow metals. Also, there is a risk of H 2 S generation, a highly toxic gas well
known because of its rotten-egg odor. Today, this process is widely substituted by using sulfurized
products. If just reactivity is required, sulfurized olefi ns with high total and active sulfur content are