Series editors' preface - Wood Tools

on the application. It has been suggested that
increasing gel viscosity significantly reduces
the deposition of surfactant and detergent
residues, so if these materials are included in
a gelled cleaning solution viscosity should be
as high as practicable (Wolbers, 1990). Watermiscible
solvents such as ethanol and acetone
can be added to a pre-prepared water gel
based on a low substitution methyl cellulose.
Pure ethanol and acetone gels will require a
methyl cellulose with a high substitution
number.
Hydroxypropyl cellulose (HPC) has hydroxy
propyl groups substituted onto the free
hydroxy groups of the cellulose molecule. It
is non-ionic, pH-neutral and water-soluble
below 60 °C. A range of HPC products are
produced by Hercules and marketed under the
name Klucel ® . Low molecular weight Klucels
are more readily soluble in water but produce
less viscous solutions (Table 11.13, Figure
11.25). The Klucels vary in the viscosity of the
gel they produce and their solubility in organic
solvents. According to the manufacturer,
Klucels tend to hydrate rapidly, leading to the
agglomeration of particles into lumps, which
significantly increases gel preparation time.
They recommend making a slurry of Klucel in
either water hotter than 60 °C or in a nonsolvent
and then adding cold water whilst
agitating the mixture. Empirical experience
suggests that some Klucels may not thicken in
solvents such as alcohol without the inclusion
of a small proportion (c.4%) of water.
Solubility in organic solvents varies from type
to type. Acetone will produce a clear gel with
Klucel E but will produce a hazy and
somewhat granular gel with Klucel G (Table
11.14). The solubility of Klucel can be manipulated
by the use of small quantities of soluble
co-solvents such as water or ethanol in
relatively small proportions (5–15%) (Table
11.15). Even non-solvents can be used to form
solutions if the Klucel is first dissolved in a
compatible solvent that is miscible with the
non-solvent (e.g. ethanol and toluene).
Klucels are surfactants and will therefore
reduce the surface tension of water and play
a role in stabilizing emulsions. Hydroxypropyl
substitution makes Klucels more lipophilic
than other water-soluble cellulose derivatives
and they are compatible with a wide range of
anionic, non-ionic and cationic surfactants.
Principles of cleaning 555
Table 11.13 Molecular weight of Klucel ®
Klucel type Molecular weight
Klucel H 1 150 000
Klucel M 850 000
Klucel G 370 000
Klucel J 140 000
Klucel L 95 000
Klucel E 80 000
Typical properties, these values do not represent a specification.
Source: Information courtesy of Hercules
Table 11.14 Comparative viscosity of Klucel ® in
water and some solvents
Solvent Viscosity (mP/sec)
Klucel H Klucel G Klucel L Klucel E
at 1% at 2% at 5% at 10%
conc conc conc conc
Water 2100 270 80 275
Methanol 800 85 25 75
Ethanol 1600 210 65 255
Isopropyl alcohol B B 145 570
(99%)
Isopropyl alcohol — — 130 420
(95%)
Acetone B B 50 175
Methylene chloride 4500B — 1240B 14 600B
Methylene chloride: 5500 — 400 —
methanol (9:1)
Propylene glycol 6000 6640 5020 > 10 000
B, borderline solvent, solutions are granular and may be hazy.
Typical properties, these values do not represent a specification.
Source: Information courtesy of Hercules
Table 11.15 Solubility of Klucel ® G 2% w/v
Soluble Borderline Insoluble
Acetic acid Acetone Aliphatic
Acetone:water 9:1 Butyl acetate hydrocarbons
Ethanol Butyl cellosolve Mineral oils
Formic acid Isopropanol 99% Toluene
Isopropanol 95% Methylethylketone Xylene
Methanol Methylene chloride
Methyl cellosolve Naptha:ethanol 1:1
Methylene chloride: Xylene:isopropanol 1:3
methanol 9:1
Toluene:ethanol 3:2
Water
Typical properties, these values do not represent a specification.
Source: Information courtesy of Hercules