70 FORMULATING


and analysis were performed at the Institute of Material Science at the University of Connecticut, Storrs. Special acknowledgement to Dr. Dennis Ndaya for his collaboration and expertise. A Discovery HR20 rheometer (DHR20, TA) was employed utilizing a serrated Peltier plate fixture. The test configuration featured a modified


cross-hatched 40 mm cone plate. Samples were loaded and zero gap determination was performed at the designated test temperature. A Peltier temperature control system connected to a recirculating water bath maintained the system at the required temperature throughout the tests. Yield stress measurements were performed using dynamic stress sweep experiments at 25 °C and 6.28 rad/s. The yield stress was determined from the cross over point (G´ = G´´).


Crystallization behaviour of natural products As previously stated, the crystallization process of natural waxes is influenced by factors such as temperature, cooling rate, and the presence of extraneous materials, e.g. impurities or additives. Typically, slow cooling results in the formation of larger, more well-defined crystals, whereas rapid cooling tends to produce smaller, less organized structures. Close attention to the crystallization behaviour can enhance the performance and stability of products incorporating natural plant waxes.


Plasticizing is accomplished by the plasticizer


molecules embedded in the wax matrix between the molecules. Besides the thermodynamic or mechanistic theories (discussed above by the molecular movement of attachment–detachment cycles), the free-volume theory explains that additional volume is created between the wax molecules.10


This is evident by examining the


branched chain configuration in Kester Wax K-70P (Figure 1).


The embedded plasticizer molecules will


also provide more separation between the wax molecules weakening the interaction between them (Gel Theory) and providing some lubricity (Lubricity Theory).11


These will modify


the crystallization characteristics, alter the crystallization kinetics and crystal morphology.


106


All Over Body Balm Base No Plasticizer


105 105


TABLE 2: MODULUS AND STRESS VALUES FOR ALL OVER BODY BALM IN ABSENCE AND PRESENCE OF PLASTICIZER


Modulus (Pa) 155.5


Base Formula (No Plasticizer) Stress (Pa)


45581.9 The result is a more flexible and pliant wax


matrix with a uniform distribution of smaller crystals throughout the material. This reduces the materials’ brittleness, i.e. enhances their ability to withstand higher stress and deformation without fracturing, while maintaining the necessary protective and moisturizing properties. Understanding and controlling this crystallization behaviour is essential for creating high-quality, effective personal care products that meet consumer expectations. Building upon our prior discussion regarding


the pivotal role of plasticizers in conferring emolliency through enhanced molecular mobility


Storage Modulus (Pa) ■ Loss Modulus G” (Pa) ■ 106


All Over Body Balm Base +15% Kester Wax K-70P


Modulus (Pa)


Base Formula +15% Kester Wax K-70P Stress (Pa)


131.9 44644.5


and flexibility within topical formulations, it is instructive to extend this analysis to the two complementary mechanistic pillars of skin moisturization: occlusivity and humectancy. The molecular-level uniformity previously


elucidated, arising from the plasticizer’s capacity to disrupt inter-chain crystalline domains and promote a homogeneous amorphous phase, directly translates into the formation of a continuous, defect-free lipid film upon application. This macroscopic homogeneity manifests as a highly coherent and impermeable barrier on the stratum corneum surface, significantly reducing transepidermal water loss (TEWL).3


Storage Modulus (Pa) ■ Loss Modulus G” (Pa) ■


104


104


103


103


102


102


101


10-1


100


101


102 Oscillation Stress δ (pa) Figures 3 and 4: Dynamic stress sweep results for All Over Body Balm in absence and presence of plasticizer PERSONAL CARE MAGAZINE April 2026 www.personalcaremagazine.com


103


104


101


10-1


100


101


102 Oscillation Stress δ (pa)


103


104


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