Chemistry Reference
In-Depth Information
between chemical structure and biological susceptibility, the following general
rules have developed, which seem to cover most surfactant types:
1. The chemical structure of the hydrophobic group is the primary factor
controlling biodegradability; high degrees of branching, especially at the
alkyl terminus, inhibit biodegradation.
2. The nature of the hydrophilic group has a minor effect on biodegradability.
3. The greater the distance between the hydrophilic group and the terminus of
the hydrophobe, the greater is the rate of primary degradation.
1.7. PETROCHEMICAL VERSUS ''
RENEWABLE
''
OLEOCHEMICAL-BASED SURFACTANTS
As will be shown in Chapter 2, all surfactants have the same basic structure:
a hydrophilic (water-loving) ''head'' and a hydrophobic (water-hating) ''tail,''
which is almost always a long chain of carbon atoms. The tails, which are hydro-
phobic, interact with nonaqueous phases or surfaces (or themselves) while the
heads try to improve the relationship of the system with the aqueous phase. One
might think of the surfactant as the arbiter in the conflict between water and
the nonaqueous world.
Presently, about 50% of the surfactants used in the surfactant industry are
derived from petrochemical raw materials, and the other 50% are derived from
oleochemical raw materials. The most important surfactants used in consumer
detergents are anionic and nonionic materials. The alcohols used are linear or
essentially linear, which results in a more rapid and complete biodegradation of
both oleochemical- and petrochemical-derived detergent surfactants.
The surfactants currently available for industrial applications can be separated
into two groups: those that have a ''natural'' or renewable origin derived from
oil seed crops, animal fats, or trees, and those derived from petroleum distillates.
There has been a great deal of debate on the pros and cons of these two types of
sourcing. Renewable surfactant feedstocks are often perceived as being better for
the environment and should therefore be the first choice for environmentally
''friendly'' products. But is that ''analysis'' of the situation scientific fact or spiri-
tually pleasing fiction? Are renewable chemicals necessarily better for the environ-
ment because they are derived from plant and animal fats and oils? As with most
scientific, political, and social questions, there is no easy answer.
The popular perception that ''natural'' products are always better for the envir-
onment than are ''synthetics'' has led to the suggestion that petrochemical surfac-
tants should be replaced with surfactants based on renewable oilseed or animal-fat-
derived materials because the change would improve the environmental profile or
impact of surfactant containing products. While there may be good arguments
for switching based on perceived long-term raw-materials availability and the
renewable nature of the beast, a total substitution is not possible or possibly even
desirable for many reasons.
