Chemistry of Life: Soaps and Cleaning Agents

UGEB2380: The Chemistry of Life (2024-25)

• Course offered by Dr. Sam CK HAU, Chemistry Department
• Covers Cleaning Agents, Personal Care, and Cosmetics

Cleaning Agents, Personal Care, and Cosmetics Industry

• Extensive market for personal care and household products
• Annual market size is nearly 450 billion US dollars (and growing)
• Includes soaps, shampoos, toothpastes, mouthwashes, cosmetics, moisturisers, laundry detergents, and household cleaners

Surface Tension

• Property of liquids, causing them to behave as if they have a thin membrane.
• Molecules in liquids exert cohesive forces on neighbouring molecules.
• Water molecules at the surface exert stronger attraction forces on neighbouring molecules compared to those submerged in the water. This creates a tension at the surface.

Soaps and Detergents

• Romans are believed to have discovered soaps.
• Soaps are made by heating goat fat with extracts of wood ashes (containing strong bases)
• Soaps help remove oily and greasy dirt from various surfaces (including skin, hair, fabrics, and dishes)

How Soap is Made

• Involves hydrolysis of naturally occurring fats and oils, using a base like sodium hydroxide.
• Results in alcohol and the salt of a carboxylic acid.
• This process is called "saponification."
• Sodium salts of fatty acids (with 10-18 carbon chains) are the most effective soaps.

Effect of Detergents

• Detergent molecules disrupt the cohesive forces between water molecules at the surface. This process reduces surface tension.
• Nonpolar (hydrophobic) tails of detergent molecules push outwards from the water surface.
• Polar (hydrophilic) heads of detergent molecules stay embedded among water molecules at the surface..

Surfactants and Micelles

• Substances that accumulate at water surfaces, altering surface properties drastically, often lowering tension.
• Detergents aggregate into micelles within water.
• Micelles form microscopic spheres with hydrophobic tails pointing inwards and hydrophilic heads pointing outwards, shielded from water molecules.

How Detergents Clean

• Water must penetrate fabrics to clean effectively .
• Detergents lower water's surface tension to enable water to penetrate fabric and carry detergent micelles into the fabric.
• Micelles trap oily dirt within their hydrophobic interiors.
• When micelles become coated with grease, they are dispersed in the water and removed through rinsing.
• Micelles are negatively charged due to carboxylate groups (-CO₂⁻).

Types of Surfactants

• Common structure: hydrophobic tail and hydrophilic head.
• Anionic surfactants have negatively charged heads.
• Cationic surfactants have positively charged heads.
• Nonionic surfactants have no electrical charge

Cosmetic and Skin Care

• Aims to improve appearance and body odor.
• Includes henna-extracted dyes, cosmetic preparations, and various products.
• Includes anything applied to the body for cleansing, beautifying, promoting attractiveness, or altering appearance.

Cosmetic and Skin Care Categorisation

• Four main categories: hair care, skin care, hand/face/body soaps, and perfumes/colognes.
• Raw materials like detergents, moisturisers, fragrances, and solvents account for a significant portion of the retail costs. Other costs include packaging, distribution, marketing, and research and development expenses.

Cosmetic and Skin Care — Key Components

• Surfactants are critical components in soaps, shampoos, and toothpastes.
• Fragrances contribute less than 1% to the total weight of personal care products but constitute 25% of the raw-material costs.

Skin Care

• Skin is the largest organ in the body, covering the body and protecting from damage.
• Regulates body temperature and senses external stimuli.
• Synthesizes components like vitamin D.
• Composed of two basic layers: epidermis and dermis.

Skin Care - Epidermis and Stratum Corneum

• Epidermis is the outermost layer composed of multiple layers of dead cells.
• Stratum corneum is the outermost layer of dead, lifeless cells.
• Conditions like water content affect skin health, impacting moisture levels, and susceptibility to microbes and irritation.

Skin Lotions

• Emulsions of two or more insoluble liquids, intended to keep skin soft and moist.
• Classified as either water-in-oil or oil-in-water emulsions, depending on the main ingredient noted first.

Antiperspirants and Deodorants

• Body controls temperature through perspiration (sweating) and its evaporation.
• Eccrine glands produce sweat, containing inorganic ions, lactic acid, urea, and glucose.
• Apocrine glands release odorless secretions, which can generate unpleasant odors through bacterial interaction.
• Antiperspirants contain aluminium compounds which reduce sweat production.
• Deodorants mask odors with fragrances and antibacterial agents.

Colouring Cosmetics

• Includes lipsticks, eye colourings, nail polishes, and face powders.
• Dyes and pigments are categorized as organic or inorganic.
• Organic dyes commonly use highly conjugated structures.
• Inorganic dyes, often transition metal ions, absorb or scatter light to produce color.

Fragrances

• Perfumes are concentrated mixtures of synthetic/natural chemicals dissolved in alcohols.
• Colognes have a more dilute mixture compared to perfumes.
• Fragrances are volatile, allowing them to mix with air and be sensed.
• Rate of fragrance evaporation varies due to chemical structures and body warmth.

Fragrance Notes

• Fragrances typically have top, heart, and base notes to allow for specific experiences based on the different evaporation rates of chemical compounds.

Sunscreen

• Protects skin from UV radiation (UVA and UVB).
• UVA damages deeper collagen and elastin fibres and can cause premature aging.
• UVB, which is more energetic, causes skin burning and is a key factor in skin cancer development.
• Skin's melanin is a defence mechanism against UV radiation, reducing radiation damage.

Sunscreen - UV Absorbers and Scattering Agents

• UV absorbers are organic compounds that absorb UV radiation (PABA, avobenzone, octocrylene).
• Scattering agents are inorganic compounds that scatter UV radiation, typically zinc oxide or titanium oxide.

Sun Protection Factor (SPF)

• SPF is a measure of sunscreen's ability to protect from UVB radiation.
• Higher SPF values correlate with stronger protection.
• Products labeled as SPF 30 reduce UVB by a factor of 30 (compared with no protection).

Hair Care

• Serves to help protect the skin and regulate the temperature of the body.
• Keratin, the main protein in hair structure, dominates hair structure.
• Sulphur containing cysteine amino acids are essential elements for strength.
• Disulfide linkages provide strength within and between chains.

Hair Structure

• Hair is composed of a central core (cortex), covered by a scaly outer sheath (cuticle), also lubricated by oily sebum (produced by sebaceous glands)
• Sufficient sebum is essential to prevent drying/damage to the cuticle.

Hair Treatment

• Permanent wave treatments, use reducing agents to break disulphide bonds.
• Hair relaxers use alkaline compounds to disrupt disulphide bonds.

Explore the chemistry behind cleaning agents, personal care, and cosmetics in the course UGEB2380. This quiz will cover topics from surface tension to the historical context of soaps, including their composition and market significance.