SKIN PROTECTION
Citrate compared to C12-15 Alkyl Benzoate. The use of emollients with higher polarity has previously been described as resulting in higher UVA protection.6
Sensory profiling of sunscreen with organic UV filters To evaluate the sensory performance of Tributyl Citrate and Triethyl Citrate compared to C12-15 Alkyl Benzoate as a reference, the test formulations as described in Table 4 were presented to a sensory panel trained for personal care leave-on products. The samples were anonymised and evaluated by the panel in two replicate sessions under standardised conditions (sensory booths, 20.6–21.5°C, 51–52% relative humidity). Descriptive profiling was based on a method adapted from ASTM Standards E 1490-92.7,8 Data collection and analysis was performed using FIZZ Network/ SENPAQ software. The samples were ranked on a scale from 0 (attribute not pronounced) to 100 (attribute strongly pronounced). The detailed sensory profiling of citrate esters
in the test emulsions showed that Tributyl Citrate was rated similar to C12-15 Alkyl Benzoate, whereas Triethyl Citrate actually outperformed it in a range of attributes (Fig 3). Based on these data, Tributyl Citrate can be regarded as an economic 1:1 replacement for C12-15 Alkyl Benzoate. The formulation with Triethyl Citrate came with further sensory benefits, including reduced peaking, better gliding effect, lighter consistency, better spreadability and a smoother after feel. Tributyl and Triethyl Citrate fell behind slightly in only one attribute, which was related to residues in after feel. Overall, these results highlight the potential of both types of citrate esters to improve product functionality and aesthetics simultaneously.
Formulating with inorganic UV filters for certified-natural sunscreens In view of rising concerns regarding the environmental and health safety profiles of many organic UV filters, the demand for products containing exclusively inorganic UV filters is increasing. This is caused by a stricter regulatory framework especially in the US, where the FDA lists only the inorganic filters titanium dioxide (TiO2
) and zinc oxide (ZnO) as GRASE
(generally recognised as safe and effective) for use in over-the-counter sun protection products.9 Moreover, consumers increasingly prefer natural sun protection products. To date, TiO2
and
ZnO are the only UV filters which are COSMOS approved by Ecocert for use in COSMOS-certified natural cosmetic products. Although inorganic UV filters do not require the presence of specific solvents, the choice of emollients does have a profound influence on dispersion stability. For the formulation to be considered natural, the emollient itself must, of course, satisfy the relevant criteria.
Dispersion of inorganic UV filters When preparing dispersions of inorganic, particulate UV filters in emollients, the physico- chemical characteristics of each phase play an important role in product appearance, stability and performance. Generally, molecular weight, structure and especially polarity of an emollient
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TABLE 4: COMPOSITION OF TEST FORMULATIONS USED FOR SPF AND UVA-PF IN VITRO DETERMINATION AND SENSORY PROFILING.
Phase A Aqua Glycerine
Sodium Gluconate Xanthan Gum
B
Cetyl Alcohol, Glyceryl Stearate, PEG-75 Stearate, Ceteth-20, Steareth-20 (Emulium® Delta MB)
Dibutyl Adipate (Cetiol® B)
C12-15 Alkyl Benzoate (Cetiol® AB) Triethyl Citrate (CITROFOL® AI) Tributyl Citrate (CITROFOL® BI)
Diethylamino Hydroxybenzoyl Hexyl Benzoate (Uvinul® A Plus)
Ethylhexyl Triazone (Uvinul® T 150)
Bis-Ethylhexyloxyphenol Methoxyphenyl Triazine (Tinosorb® S)
C
Ethylhexyl Salicylate (Eusolex® OS) Preservative
Peaking*
Cohesiveness/Stringiness Lubricating effect*
Stickiness Consistency*
Spreadability* Oiliness
Whitening during application Whitening after application Freshness
Absorption Sticky after feel Product residues oily
Product residues greasy Product residues waxy* Residual film*
Powdery after feel Smooth after feel/Silky touch* 0 10 20 30 40 50 60 70 80
Figure 3: Sensory profiling of test formulations with different emollients (Tributyl Citrate vs. Triethyl Citrate vs. C12-15 Alkyl Benzoate). Values are means of n = 8 panelists. Asterices denote attributes which were evaluated as differing significantly between test formulations.
influence the dispersion. For example, in the case of uncoated ZnO higher emollient polarity promotes better dispersion.10 Focusing on UV filters suitable for natural
formulations, two grades of uncoated ZnO (Z-COTE® and COSMOS-approved ZinClear® XP) and one COSMOS-approved TiO2
(Eusolex®
T-S) were investigated for their dispersibility in COSMOS-approved emollients. Coco-Caprylate/ Caprate and Caprylic/Capric Triglyceride served as benchmarks for comparison with Triethyl Citrate. The particulate filters were dispersed in the emollient at a ratio of 1:9 using an ULTRA- TURRAX® homogeniser at a high shear rate (13,000 rpm) for 5 min. The dispersion was
monitored by microscopy. The microscopic evaluation of uncoated ZnO
revealed profound differences between the tested emollients (Figure 4). Triethyl Citrate proved to be a suitable matrix in which to uniformly disperse both ZnO products, resulting in images showing an adequate dispersion as described in the literature.11 The use of Coco-Caprylate/Caprate and Caprylic/ Capric Triglyceride led to the formation of particle aggregates depending on ZnO types. Certain surface modifications, such as the
vegetable-derived surface coating on the tested filter, are permitted for TiO2
even in certified
natural products. Triethyl Citrate provided the most uniform dispersion for TiO2
among the tested June 2021 PERSONAL CARE
Tributyl Citrate ■ Triethyl Citrate ■
C12-15 Alkyl Benzoate ■ INCI/Name
Reference formula [%]
q.s. to 100 3.0 0.2 0.4
4.0
10.0 15.0
Formula with
Triethyl Citrate [%]
q.s. to 100 3.0 0.2 0.4
4.0 10.0 15.0
6.0 2.5
2.0
5.0 q.s.
6.0 2.5
2.0
5.0 q.s.
15.0 6.0 2.5
2.0
5.0 q.s.
Formula with
Tributyl Citrate [%]
q.s. to 100 3.0 0.2 0.4
4.0 10.0
29
Attribute
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