Efficient pH neutralisation for effective hair care products
South African Pharmaceutical & Cosmetic Review
By Mary Redmond of ANGUS Chemical Company
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AMINOMETHYL PROPANOL (AMP™) has remained a standard in the hair care industry for over 30 years. AMP’s physical properties are excellent for the production of high-quality hair care products. By Mary Redmond of ANGUS Chemical Company
The primary role of a neutraliser is the pH adjustment, but efficacy of a neutraliser can vary across alternative chemistries. This fluctuation in performance poses significant challenges for the production of optimised consumer products, but may be overcome through the use of efficient neutralisers strategically engineered for multi-functionality.
ANGUS’ AMP-ULTRA® PC, the personal care grade of AMINOMETHYL PROPANOL (INCI), is a highly regarded mainstay of the hair care industry. It continues to adapt to the upgraded performance needs in hair fixatives (e.g., aerosols, mousses, and gels), hair relaxers and straighteners, hair maintenance products, hair treating products (semi and permanent curl) and hair colouring (semi and permanent).
Product health and safety
These are the foremost concerns of any hair care formulator, and are the first considerations addressed during formulation. Formulations must be compatible with consumer ideals and perceptions of health and safety. Individual ingredients can often become targets of consumer distrust and suspicion due to clinical facts, media coverage or general reputation surrounding irritation effects, toxicology and cancer-causing risk.
Odour is one major factor that can impact consumer perception of health and safety, particularly if accompanied by eye and skin irritation. A sterically hindered neutraliser, such as AMP-ULTRA PC, possesses only a slight odour and mild contact profile, presenting fewer risks to consumer perception than high-odour products like ammonia and MEA.
Fortunately, AMP-ULTRA PC has a stellar reputation among personal and hair care products, and has been used in the latter for over three decades. The AMINOMETHYL PROPANOL molecule is a primary amine, and the personal care grade AMP-ULTRA PC is processed to reduce to trace (less than 0.5 percent) secondary amines (proven precursors to cancer-causing nitrosamines). This qualifies AMP-ULTRA PC for the most stringent global health and safety standards, including: European Union Regulation No. 1223/2009; USA Food, Drug and Cosmetics Act; People’s Republic of China Hygienic Standards for Cosmetics (2007 version); Japan Standards for Cosmetics and Amendments; ASEAN 2008 Cosmetics Directive (Annex updated February 2011); Mexico Prohibited and Restricted Substances in Perfumes and Cosmetics (current); Brazil ANVISA Mercosur Resolution on Cosmetics and Personal Care Products.
AMP-ULTRA PC has also been thoroughly tested, approved and used in sensitive applications like leave-on products at usage levels customary to pH adjustments for personal care products.
Effective pH neutralisation
Optimisation begins with a strong commitment to health and safety, but can be further enhanced with AMP’s efficacy profile, resulting in pH that neutralises acid moieties and solubilises raw materials in formulations. AMP-ULTRA PC is engineered with chemical and structural components that act throughout the life cycle of hair care formulations. Its high pKa, or logarithm of the acid dissociation constant, equals 9.82, ensuring that product pH can approach the 9 to 11 range without overdosing in response to tapering efficacy.
Given its high pH capability, mild nature and low odour potential, AMP-ULTRA PC easily finds its way into hair care neutralisation—including raw material neutralisation like hair fixative resins and Carbomer (INCI) hair gel thickening agents, as well as neutralisation of final products like hair treatments and colour applications that require high pH with non-aggressive contact to safely open hair cuticles for process styling.
Both hair fixative resins and polyacrylic acid polymers (Carbomer thickener) require neutralisation of carboxylic acid groups on the backbone of the polymers. The hair fixative resin will not solubilise into a formula without being neutralised and utilising AMINOMETHYL PROPANOL’s hydroxyl group and hydrocarbon chain. Carbomers carboxylic acid groups must be neutralised to break intermolecular bonds that allow the carbomer molecule to fully affect thickening. A fast and stable pH development allows the carbomer to reach its rheological potential without prolonged batch hold times. Final products using both of these raw materials will see critical clarity. For shelf stability in a clear bottle, this clarity pairs with non-yellowing, a property caused by AMINOMETHYL PROPANOL’s lack of abstractable hydrogens from the carbon adjacent to the amine group that would cause yellowing.
pKa, the main physical property of AMP-ULTRA PC along with its low molecular weight, ensures rapid pH development, better and faster clarity development, and rheological reliability. As Figure 1 demonstrates, AMP-ULTRA PC is a more effective neutraliser than TEA.Figure 1: Neutralisation curve of acid-functional components
Low molecular weight, a favourable boiling point and vapour pressure
Combined properties of AMP-ULTRA PC provide a relatively fast evaporation rate after the solubilised hair fixative film has coated the hair. These step-wise mechanisms balance the uncompromised properties of hair hold (even in high humidity), resulting in soft feel and easy washability. AMP-ULTRA PC eliminates a sticky sensorial feel that leaves residual “gummy” particles upon washout. This balance of properties has remained unmatched by any other neutraliser since the conception of hair fixative styling agents.
The favourable boiling point and vapour pressure of AMP-ULTRA PC also enables the additive to rise into the headspace of a container. In the headspace, AMP exhibits some hydrotropic properties by having a preferential association with the substrate and acting as a barrier to rust-forming mechanisms. This is particularly critical in hair spray aerosol packaging, where corrosion resistance is a priority factor in creating a safe, effective can that is pressurised with propellants. The formation of rust in the head-space can also drop rust particles to the bottom of the can and cause dip-tube clogging.
An effective additive
The characteristics of AMP-ULTRA PC aid formulation that also benefits the manufacturing stage of the life cycle of a finalised formula. Poor clarity, rapid temperature rises, off-spec colour and prolonged viscosity development are among the specification checks that can delay batch processing time—along with additional mix directives, post-add adjustments, and repeat spec testing—and have the potential to almost double batch hold times. Quickly attaining pH and maintaining it throughout the development of product properties accelerates batch production by allowing batches to rapidly pass both interim and final quality control checks.
These products are available in South Africa from Savannah Fine Chemicals, the authorised agent for ANGUS Chemical Company.
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*References available on request
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