Instrumental Assessment of the Effectiveness of Silicone Replacement Materials in Lip Balms
Podium 54
Presented by: Milica Stevic
Introduction
Silicones are widely used in personal care formulations for their versatility and high functionality, but an emerging trend towards silicone-free cosmetics has become evident. This is due to consumer perceptions of silicones as environmentally problematic and strict regulations in this area. Sensorial evaluation is the approach most frequently applied to assess the effectiveness of silicone replacements in cosmetic products. It requires a statistically sufficient number of subjects and involves extensive planning of the experiment to obtain reliable conclusions. Instrumental characterisation of cosmetic products, as an alternative approach, was investigated in this project. It focused on lip balms (LBs), of which three different types were investigated: (1) with a silicone, (2) without a silicone, and (3) with silicone replacement materials. The aim of the project was to assess the suitability of chosen silicone replacement ingredients in the LB samples by comparing their thermal, rheological, and textural properties.
Methods
LBs consisted of the following ingredients: candellila wax (CanW), carnauba wax (CarW), beeswax, shea butter, capryl/caprylic triglycerides, and castor oil. The silicone used was a multidomain Cetyl/hexacosyl dimethicone with 53% of the alkyl content. Polyglycerol esters: ester 1 (E1), ester 2 (E2), ester 3 (E3), and ester 4 (E4) acted as silicone replacement materials. E1, E2, and E3 contained different ratios of behenyl/iso-stearyl groups – 56:44, 78:22, and 30:70, respectively. E4 contained isostearyl/stearyl groups with the ratio of 50:50. The LBs were manufactured by heating the ingredients to 80°C, then homogenised at 9,000 rpm for 2 min using T18 digital Ultra-Turrax mixer (IKA, UK). Three series of LBs with different ratios of CanW and CarW were formulated: Series A, with the same amount of CanW and CarW; Series B, with 10% more of CarW; and Series C, with 10% more of CanW. LBs with no silicone were labelled A, B, and C; those with a silicone were labelled ASi, BSi, and CSi; those with esters were labelled AE1-AE4, BE1-BE4, and CE1-CE4. DSC was performed by scanning at 10oC/min using Q2000 DSC (TA Instruments, USA). Rheological characterisation was performed using MARS iQ Air (Thermo Fisher, UK) in oscillatory amplitude sweep mode with a constant frequency of 1 Hz. Texture analysis was carried out by a TA.XT Plus Texture Analyser (Stable Micro System, UK) with a 2-mm diameter needle probe.
Results
DSC analysis of the silicone and esters have revealed the following melting points (Tm): Tm (silicone)=35°C, Tm (E1)=50°C, Tm (E2)=67°C, Tm (E3)=45°C, and Tm (E4)=40°C. Rheological data for yield stress (YS) and texture data for hardness (H) of all LB series were collected and their average values and standard deviations for ten replicas analysed. It was found that E4 has the H and YS values closest to the silicone-based formulations, as illustrated here: H values - ASi=(53.5±4.9) g, AE4=(62.5±3.9) g, BSi=(36.8±2.7) g, BE4=(59.7±3.1) g, CSi=(56.0±3.9) g, CE4=(76.1±4.6) g; YS values - ASi=(37.5±3.1) Pa, AE4=(39.7±2.5) Pa, BSi=(38.5±5.0) Pa, BE4=(39.8±5.9)Pa; CSi=(38.1±6.1) Pa, CE4=(40.4±4.6) Pa.
Discussion
DSC analysis has revealed that the silicone and E4 had the closest melting points, 35°C and 40°C. This indicated that the silicone and E4 had similar structural arrangements and types of non-covalent bonds. Rheological and textural analysis both found that the most effective silicon replacement material was E4. Comparing H and YS values, it can be observed that the formulation ASi was similar to BE4. Therefore, if the starting formulation is A, with the same amount of CanW and CarW, the way to effectively replace the silicone will be to increase the concentration of CarW for about 10%, which corresponds to formulation B. The silicone, which is composed of Cetyl (C16)/hexacosyl (C26) groups, has stronger intermolecular interactions and internal structure than E4, which is composed of isostearyl (branched C18)/stearyl (linear C18). Hence, the silicone cannot be replaced with E4 only, without an increase of the wax.
Conclusion
This study explored the effectiveness of silicone replacement with four polyglycerol esters in three different types of lip balms, using the combination of instrumental methods. Melting point, hardness, and yield stress were the parameters assessed. It was found that ester E4 was the most effective material to replace the silicone. The combination of rheology, texture analysis, and DCS has proven effective in determining suitable silicone replacements.
Silicones are widely used in personal care formulations for their versatility and high functionality, but an emerging trend towards silicone-free cosmetics has become evident. This is due to consumer perceptions of silicones as environmentally problematic and strict regulations in this area. Sensorial evaluation is the approach most frequently applied to assess the effectiveness of silicone replacements in cosmetic products. It requires a statistically sufficient number of subjects and involves extensive planning of the experiment to obtain reliable conclusions. Instrumental characterisation of cosmetic products, as an alternative approach, was investigated in this project. It focused on lip balms (LBs), of which three different types were investigated: (1) with a silicone, (2) without a silicone, and (3) with silicone replacement materials. The aim of the project was to assess the suitability of chosen silicone replacement ingredients in the LB samples by comparing their thermal, rheological, and textural properties.
Methods
LBs consisted of the following ingredients: candellila wax (CanW), carnauba wax (CarW), beeswax, shea butter, capryl/caprylic triglycerides, and castor oil. The silicone used was a multidomain Cetyl/hexacosyl dimethicone with 53% of the alkyl content. Polyglycerol esters: ester 1 (E1), ester 2 (E2), ester 3 (E3), and ester 4 (E4) acted as silicone replacement materials. E1, E2, and E3 contained different ratios of behenyl/iso-stearyl groups – 56:44, 78:22, and 30:70, respectively. E4 contained isostearyl/stearyl groups with the ratio of 50:50. The LBs were manufactured by heating the ingredients to 80°C, then homogenised at 9,000 rpm for 2 min using T18 digital Ultra-Turrax mixer (IKA, UK). Three series of LBs with different ratios of CanW and CarW were formulated: Series A, with the same amount of CanW and CarW; Series B, with 10% more of CarW; and Series C, with 10% more of CanW. LBs with no silicone were labelled A, B, and C; those with a silicone were labelled ASi, BSi, and CSi; those with esters were labelled AE1-AE4, BE1-BE4, and CE1-CE4. DSC was performed by scanning at 10oC/min using Q2000 DSC (TA Instruments, USA). Rheological characterisation was performed using MARS iQ Air (Thermo Fisher, UK) in oscillatory amplitude sweep mode with a constant frequency of 1 Hz. Texture analysis was carried out by a TA.XT Plus Texture Analyser (Stable Micro System, UK) with a 2-mm diameter needle probe.
Results
DSC analysis of the silicone and esters have revealed the following melting points (Tm): Tm (silicone)=35°C, Tm (E1)=50°C, Tm (E2)=67°C, Tm (E3)=45°C, and Tm (E4)=40°C. Rheological data for yield stress (YS) and texture data for hardness (H) of all LB series were collected and their average values and standard deviations for ten replicas analysed. It was found that E4 has the H and YS values closest to the silicone-based formulations, as illustrated here: H values - ASi=(53.5±4.9) g, AE4=(62.5±3.9) g, BSi=(36.8±2.7) g, BE4=(59.7±3.1) g, CSi=(56.0±3.9) g, CE4=(76.1±4.6) g; YS values - ASi=(37.5±3.1) Pa, AE4=(39.7±2.5) Pa, BSi=(38.5±5.0) Pa, BE4=(39.8±5.9)Pa; CSi=(38.1±6.1) Pa, CE4=(40.4±4.6) Pa.
Discussion
DSC analysis has revealed that the silicone and E4 had the closest melting points, 35°C and 40°C. This indicated that the silicone and E4 had similar structural arrangements and types of non-covalent bonds. Rheological and textural analysis both found that the most effective silicon replacement material was E4. Comparing H and YS values, it can be observed that the formulation ASi was similar to BE4. Therefore, if the starting formulation is A, with the same amount of CanW and CarW, the way to effectively replace the silicone will be to increase the concentration of CarW for about 10%, which corresponds to formulation B. The silicone, which is composed of Cetyl (C16)/hexacosyl (C26) groups, has stronger intermolecular interactions and internal structure than E4, which is composed of isostearyl (branched C18)/stearyl (linear C18). Hence, the silicone cannot be replaced with E4 only, without an increase of the wax.
Conclusion
This study explored the effectiveness of silicone replacement with four polyglycerol esters in three different types of lip balms, using the combination of instrumental methods. Melting point, hardness, and yield stress were the parameters assessed. It was found that ester E4 was the most effective material to replace the silicone. The combination of rheology, texture analysis, and DCS has proven effective in determining suitable silicone replacements.