52 SKIN CARE
TABLE 2: FORMULATION OF ZNO AND TIO2 AQUEOUS SUSPENSIONS
Formula 8 (F8) Formula 9 (F9) Formula 10 (F10) Formula 11 (F11) Formula 12 (F12) Formula 13 (F13)
20%ZnO
20%ZnO+0.1%SF 20%ZnO+0.5%SF 20%ZnO+1%SF 20%TiO2 20%TiO2
+1%SF
(Wilmar), Sodium Chloride (Xilong Scientific); 1,2-Hexanediol (Symrise); Zinc Oxide (micron- sized, K.S. Pearl); Titanium Dioxide (micron- sized, K.S. Pearl); Sodium Surfactin (Bloomage Biotechnology); Sodium Stearoyl Glutamate (Evonik), IKA T 25 Digital Disperser (IKA-Werke); Malvern Mastersizer 3000 (Malvern Panalytical); Ultraviolet-Protection Chromameter/System (UV- PC, ECT Testing Group).
Preparation of formulations for powder dispersibility testing Seven distinct aqueous suspensions were formulated according to the compositions detailed in Table I. The baseline formulation, designated as Formula 1, consisted of 10% (w/w) micron-sized ZnO dispersed in deionized water. This dispersion was facilitated using a magnetic stirrer operating at 400 rpm, maintained at 60°C for a duration of 30 minutes. Subsequently, Formulas 2 through 7 were prepared by incorporating the same 10% (w/w) ZnO loading into aqueous solutions of surfactin, with the surfactant concentration systematically varied from 0.1% to 1% (w/w). All these formulations were then subjected to an identical magnetic stirring protocol (400 rpm, 60°C, 30 min) to ensure consistent mixing and dispersion.
Particle size analysis Formulas 8–11 were formulated by dispersing 20% (w/w) ZnO in deionized water, with surfactin incorporated at 0.1%, 0.5%, and 1% (w/w), respectively. Similarly, Formulas 12 and 13 contained 20% (w/w) TiO2 without and with 1% (w/w) surfactin (Table 2). All suspensions were homogenized under magnetic stirring at 400 rpm and 60°C for 30 minutes. Particle size was assessed using laser diffraction (Mastersizer 3000, Malvern Panalytical) at 25°C. Prior to measurement, each sample was redispersed in deionized water under magnetic stirring at 800 rpm for five minutes. Triplicate measurements were performed
for every formulation, and the volume-based percentiles (D10, D50, D90) are reported as mean values.
Preparation of sunscreen formulations Sunscreen formulations containing ZnO or TiO2
are
presented in Table 3. All oil-phase components were combined and
mixed at 500 rpm for ten minutes. Aqueous phase I and aqueous phase II were prepared separately. The powder phase was then incorporated into oil or aqueous II phase, followed by homogenization at 5000–5500 rpm for one minute. Aqueous phase I and aqueous phase II were
PERSONAL CARE MAGAZINE March 2026
TABLE 3: FORMULATION OF SUNSCREEN EMULSIONS Phase
Ingredient Oil
Caprylyl Glycol Dimethicone
Disteardimonium Hectorite PEG-10 Dimethicone Caprylyl Methicone Butyloctyl Salicylate
Butylene Glycol Diparylate/Dicaprate
Ethylhexylglycerin Dimethicone
Lauryl Polyglyceryl-3 Polydimethylsiloxyethyl Dimethicone
C12-15 Alkyl Benzoate Sodium Surfactin
Aqueous I Aqua Glycerin
Sodium Chloride 1,2-Hexanediol
Powder Zinc Oxide (Micron-Sized)
Titanium Dioxide (Micron-Sized)
Aqueous II Sodium Surfactin
Sodium stearoyl glutamate (SG)
Aqua
Formula 14 (F14)
0.2 9.5 1 1
4 5
6
0.3 5
1
3 -
20 4 1
0.5 10
- - -
28.5
then blended at 500 rpm for 1 minute. The combined aqueous phases were introduced into the oil phase under continuous mixing, and the final mixture was homogenized at 7000–8000 rpm for three minutes to obtain a homogeneous sunscreen emulsion. The incorporation procedures of powder phase
for each formula varied as follows: ■ Formula 14: ZnO (powder phase) was added to the oil phase. ■ Formula 15: ZnO (powder phase) was incorporated into the oil phase. ■ Formula 16: ZnO (powder phase) was added to aqueous II phase. ■ Formula 17: ZnO (powder phase) was incorporated into the oil phase. ■ Formula 18: ZnO (powder phase) was added to aqueous II phase. ■ Formula 19: TiO2
(powder phase) was added to
the aqueous II phase. ■ Formula 20: TiO2 to the aqueous II phase.
(powder phase) was added
In vitro sun protection factor (SPF) assessment SPF was determined using the ultraviolet phototropy method. Formulas 14-20 were applied to the substrate as uniform layers at a density of 2.0 ± 0.1 mg/cm2
using latex finger-cots, followed
by drying under dark, controlled conditions (21 ± 1°C, 50 ± 10% RH) for 30 minutes.
Content (%)
Formula 15 (F15)
0.2 9.5 1 1
4 5
6
0.3 5
1
3 -
20 4 1
0.5 10
-
0.25 -
28.25
Formula 16 (F16)
0.2 9.5 1 1
4 5
6
0.3 5
1
3 -
20 4 1
0.5 10
-
0.25 -
28.25
Formula 17 (F17)
0.2 9.5 1 1
4 5
6
0.3 5
1 3
0.25 20 4 1
0.5 10
- - -
28.25
Formula 18 (F18)
0.2 9.5 1 1
4 5
6
0.3 5
1
3 -
20 4 1
0.5 10
- -
0.25 28.25
Formula 19 (F19)f
0.2 9.5 1 1
4 5
6
0.3 5
1
3 -
20 4 1
0.5 -
10 - -
28.5 After drying, the treated substrates were
irradiated using a calibrated UV-PC system equipped with a solar-simulated xenon arc source and integrated colorimetric detection. The irradiation intensity was set at 16 μW/cm2 multiplied by the estimated SPF value with a fixed exposure time of two seconds. Three replicate measurements were performed for each sample and the SPF standard control.
The SPF value is calculated using the following formula: SPF =
Eunprotected
Eunprotected Eprotected
: Ultraviolet irradiance required to
induce a specific colorimetric change (ΔE) on the unprotected (uncoated) ultraviolet phototropic substrate. Eprotected
: Ultraviolet irradiance required to induce
the same ΔE on the protected (sunscreen-coated) ultraviolet phototropic substrate.
Sensory evaluation A panel of 15 volunteers (aged 23–40 years) assessed the sunscreen formulations by applying 50 μL of each to the volar forearm using standardized circular motions. Spreadability, light texture upon application, and non-sticky afterfeel were evaluated for three ZnO-based formulations (Formulas 14, 16, and 18).
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Formula 20 (F20)
0.2 9.5 1 1
4 5
6
0.3 5
1
3 -
20 4 1
0.5 -
10
0.2 -
28.3
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