What is the application of HPMC in personal cleansing preparations?

In the field of modern cosmetic science and surfactant formulation engineering, Hydroxypropyl Methylcellulose (HPMC), as a non-ionic semi-synthetic cellulose ether, has become an important functional additive in cleaning products such as shower gel and hand sanitizer due to its unique rheological properties and biocompatibility. This article will systematically explain the application value of HPMC in liquid cleansers from three dimensions: molecular action mechanism, formulation synergy and performance verification.

1. Structural characteristics and core functions of HPMC

1. Molecular structure-activity relationship analysis

HPMC (CAS No.: 9004-65-3) is double-substituted by hydroxypropoxy and methoxy groups on the hydroxyl group of the cellulose skeleton (typical substitution degree: methyl DS = 1.8-2.0, hydroxypropyl MS = 0.15-0.25) to form a polymer with a three-dimensional network structure. Its molecular weight distribution range (usually 10,000-1,500,000 Da) directly affects the solution viscosity (2% aqueous solution viscosity range: 5-100,000 mPa·s).

2. Key performance advantages

Rheological modification: Through hydrogen bonding and van der Waals forces, a shear-thinning system (pseudoplastic fluid properties) is formed, and the dynamic viscosity can achieve 2-3 orders of magnitude changes in the shear rate range of 1-1000 s⁻¹, significantly improving the pourability and spreadability of the product.

Temperature tolerance: The gel point temperature (T_gel) is positively correlated with the degree of substitution, and the viscosity stability (Δη＜10%) is maintained in a wide temperature range (5-50℃), which is better than traditional anionic thickeners.

Electrolyte compatibility: The non-ionic properties enable it to maintain structural viscosity in a system containing 5% NaCl or 15% SLES (retention rate＞85%).

Interfacial synergistic effect: through the association of hydrophobic blocks with surfactant micelles, a rigid interfacial film is formed (interfacial tension is reduced to 28-32 mN/m), and foam stability is improved (Ross-Miles method determines 4min foam retention rate>70%).

2. Functional extension and synergistic enhancement in the formula system

1. Moisturizing and barrier strengthening mechanism

Dynamic water retention network: HPMC forms multiple hydrogen bonds with water molecules through hydroxyl groups (binding energy is about 20-25 kJ/mol), and constructs a three-dimensional hydration layer on the skin surface (measured by Corneometer, the skin water content increased by 35±5% in 4h).

Film-forming protective effect: A continuous oxygen-permeable film is formed during the drying process (film thickness is about 0.5-2 μm, moisture permeability is 1200±200 g/m²·24h), which effectively reduces the TEWL caused by surfactants (transepidermal water loss rate is reduced by 18-22%).

2. Sensory modification and user experience optimization

Shear thixotropic response: low viscosity (η₁₀₀₀≈50 mPa·s) when pumped out, and high viscosity (η₁≈5000 mPa·s) quickly restored after contact with the skin, achieving a balance between "drawing effect" (filament length>15cm) and instantaneous spreading.

Suspension stability system: pearl powder (particle size D50=10-50 μm) or frosted particles are supported by zero shear viscosity (η₀＞1000 mPa·s) to prevent sedimentation (centrifugal stability＞3000g×30min).

3. Verification of green chemical properties

Tested according to OECD 301B standard, the 28-day biodegradability rate reached 82-89%, which meets the EU EC No 1272/2008 environmental protection standard.

Cytotoxicity test (MTT method) showed IC50＞5000 μg/mL, and HRIPT test confirmed that it was non-allergenic.

III. Formula development suggestions and verification methods

1. Compatibility optimization plan

| Functional requirements | Recommended compatibility system | Mechanism of action |

|---------------|-----------------------------------|--------------------------|

| High temperature stability | HPMC K100M (0.3%) + xanthan gum (0.2%) | Formation of thermoreversible gel network |

| Low temperature fluidity | HPMC E5 (0.4%) + glycerol (5%) | Lowering glass transition temperature (Tg) |

| Foam enhancement | HPMC + decyl glucoside (8%) + PEG-75 lanolin | Lowering surface tension to 29.5 mN/m |

2. Key performance verification indicators

Rheological properties: Measured by HAAKE MARS IV rheometer, requiring shear thinning index n value <0.5 (power law model fitting)

Low temperature stability: After 3 cycles of -15℃/40℃ alternation, the viscosity change rate is <8%

Moisturizing effect: Using CK MPA multi-probe system measurement, skin capacitance value increase within 2h> 25%

IV. Technical innovation direction

1. Functional modification: Development of cationic HPMC (such as quaternary ammonium modification) to enhance antistatic performance

2. Nanocomposite technology: Compound with nanocellulose (CNC) to construct a double network structure and increase the yield stress to more than 50 Pa

3. Intelligent response system: Introduce pH sensitive groups (such as carboxyl groups) to achieve automatic viscosity adjustment with skin pH (5.5-6.5)

Conclusion

HPMC, through its unique molecular designability and multiple action mechanisms, can not only meet the basic thickening needs of cleaning products, but also expand value-added functions such as moisturizing repair, sensory optimization, and environmental friendliness. It is recommended to combine the QbD (quality by design) concept in formula development and optimize the three-dimensional relationship between degree of substitution, molecular weight and addition amount through response surface methodology to achieve a precise balance between performance and cost.