A

    Abrasion Resistance

    A function of tear strength, friction co-efficient, resilience, heat dissipation and other properties. Generally, copolymer elastomers are superior to flexible materials such as vinyl and some rigid plastics.

    acid value

    The amount of free acid present in one gram of fatty or oily material as measured by the amount
(in milligrams) of potassium hydroxide needed to neutralize it.

    active ingredient

    Substance added to a formulation to deliver a specific observable
and desirable effect. The substance may or may not be a drug substance and/or deliver a drug-like effect. Generally speaking, in the United States, a finished product is not a drug product, subject to drug regulations, even if it has drug substances in it. The finished product is regulated based on the claims made for it.

    active pharmaceutical ingredient (API)


    Substance that may be used at specified level(s) in a formulation to deliver specified pharmaceutical benefit(s). In the United States, the finished product must be manufactured to—and have label copy that conforms with— regulations established by the Food and Drug Administration and published in the Federal Register.

    AIR OVEN AGING

    A procedure to determine the influence of elevated temperature on the physical properties of various polymers.

    amide

    The reaction product of an oxoacid — typically a carboxylic acid — with an amine (-NH), releasing water. (See ester).

    AMORPHOUS

    Having no real or apparent crystalline form.

    amphoteric

    Having both acidic and basic functional groups. In personal care ingredients, this typically means having both anionic carboxylate- and cationic amino-functional groups in the same molecule.

    anhydrous

    Containing no water.

    anionic surfactant

    Surface active agent that has a negative charge; well suited for cleansing products.

    ASTM 1 OIL

    Characterized as a high aniline point, moderate viscosity immersion/extraction fluid used for rubber applications. Extracting oil in ECO and NBR. Swelling oil in CR, SBR, EPDM.

    ASTM 2 OIL

    Characterized as a medium aniline point, moderate viscosity immersion/extraction fluid used for rubber applications. Represents service fluids – engine oil, power steering fluid, etc. and has slight swelling effect. Usually used to test seal compounds.

    ASTM 3 OIL

    Characterized as a low aniline point, high viscosity immersion/extraction fluid used for rubber applications. Extracts plasticizer from compound. Will be absorbed by compound.

    ASTM (REFERENCE) FUEL A

    100% Isooctane. Generally an extracting fuel in NBR.

    ASTM (REFERENCE) FUEL B

    70% Isooctane, 30% Toluene. Represents high octane leaded fuels.

    ASTM (REFERENCE) FUEL C

    50% Isooctane, 50% Toluene. Represents high octane unleaded fuels.

    B

    BANBURY

    The name of the inventory of an internal mixer for rubber. See Internal Mixer.

    binder

    Substance added to form dry ingredients into a solid mass or to maintain an even consistency throughout a liquid or semi-liquid substance.

    BLOOM

    A liquid or solid material that has migrated to the surface of the elastomer and changes its appearance.

    BRITTLE POINT VALUES

    Temperature at which five specimens fist “pass”.

    broad-spectrum

    Sunscreen that reduces the amount of both UVB and UVA radiation that reaches the skin.

    C

    carrier

    A diluent, usually inactive, to which an active ingredient or agent is added so it can be applied or transferred to the skin, hair, etc.

    cationic surfactant

    Surface active agent that has a positive charge, which is attracted to the negatively charged proteins in skin and hair. Those with more than one long, linear fatty tail are especially useful as emulsifiers
in skin care, and impart a soft feel to skin.

    chelant

    Substance that causes chelation, a chemical process in which a molecule encircles and binds to a metal to isolate it in a formulation so it is physically and/or biologically inactive.

    citral

    Aroma compound present in the oils of several plants, including lemon myrtle, lemon grass, and lemon verbena. It has a strong citrus odor and is used in cosmetics products for its fragrance and anti- microbial effects. Citral should be avoided by people with perfume allergies.

    combo bar

    A mixture of synthetic surfactants and natural soap, which combines the economy and ease of processing of natural soap with the mildness of syndets.

    comedogenicity

    The likelihood of an ingredient or combination of ingredients to cause pores to clog and produce acne comedones (blackheads and whiteheads). Comedogenicity is rated on a scale of 0–5. The lower the number, the less likely that the ingredient, when used by itself, will clog pores. Products with high concentrations of comedogenic ingredients should be avoided by people with acne-prone skin.

    concealer

    Pigmented makeup used specifically to mask or cover imperfections such as blemishes, uneven skin tone, and enlarged pores.

    COPOLYMER

    A polymer formed from two types of monomers.

    covalent bond

    A chemical bond between atoms formed by the sharing of valence electrons (the outmost electrons of atoms, which are usually involved in bonding). Much stronger than a hydrogen bond or hydrophobic interaction.

    cP (centipose)

    A unit of absolute (dynamic) viscosity. 1cP=1mPa•s:the viscosity of water at 20°C. cP = cSt • density (g/cm3)

    CRYSTALLINE

    An arrangement of polymer segments of repeating patterns into geometric symmetry.

    cSt (centistoke)

    A unit of kinematic viscosity. The ratio of a liquid’s absolute viscosity to the density of that liquid.

    D

    dielectric constant

    A measure of the relative ability of a material to store an electric charge for a given applied field strength. A higher dielectric constant indicates greater polarity.

    DUROMETER

    An instrument for measuring the indentation hardness of rubber.

    E

    electrolyte

    Substance that dissociates into ions when dissolved in a fluid, thereby imparting the ability to conduct electricity to the fluid. In personal care, the most common electrolytes include water-soluble inorganic salts (e.g., Sodium Chloride), amino acids, and protein hydrolyzates, dissolved in water.

    ELONGATION

    The extension of a uniform section of a specimen expressed as percent of the original length.

    (final length – original length)
    Elongation % = ——————————————X 100
    original length

    emollient

    Substance that makes skin feel smoother. Emollients are used to correct or mask dryness and scaling, and are key ingredients in creams, lotions, body oils, bath oils, massage oils, lipsticks, and other cosmetic products. Note: Sometimes people use “moisturizer” and “emollient” interchangeably. However, “moisturizer” usually refers to finished product.

    emulsifiers

    Surface active ingredients that, when appropriately selected, will align at the interface of two immiscible liquids (e.g., oil and water). Put under shear, a quasi-stable dispersion of droplets of one of the liquids in the other, called an emulsion, is formed. Depending on its consistency, the emulsion may be called a milk (very fluid), a lotion (at least somewhat flowable under gravitational force), a cream (readily flowable when rubbed on the skin), or a paste (quite resistant to flow when rubbed on the skin).

    erythema

    Abnormally intense redness of the skin. The minimum erythemal dose (MED) of UV radiation induces barely perceptible erythema. The sunburn protection factor (SPF) of a product indicates how much more sun skin that has been treated with the product can be exposed to before exhibiting perceptible erythema (which is mainly caused by UVB, rather than UVA rays).

    ester

    The process by which two substances (typically an alcohol and an acid) combine to form an ester.

    ethoxylate

    A product of ethoxylation, the industrial process by which ethylene oxide is added to a fatty substance with at least one free hydroxy and/or carboxyl group, enhancing its water solubility and surfactant properties.

    excipient

    An inactive ingredient used to dilute or convey an active ingredient and/or give form and consistency to a finished product.

    EXTRUDER

    Machine designed to force a rubber or rubber mix through an orifice, which is often shaped to the geometry of the desired product.

    EXTRUDER TYPES

    BARWELL EXTRUDER: A short barrel ram extruder used to convert stripped form elastomers into what is referred to as “shots” for molding.

    COLD FEED: This extruder is generally fed rubber compound at room temperature in the form of strips or pellets. The screw must transmit sufficient mechanical energy to plasticizer the compound to near minimum viscosity as well as to overcome the head restriction.

    HOT FEED: An extruder which is fed rubber compound at a temperature above ambient. A hot feed extruder receives rubber compound at near minimum viscosity and must overcome the head restriction with a minimum temperature rise and hold time.

    EXTRUSION CURING METHODS

    HEAT TRANSFER FLUID (SALT BATH): The bath must be totally inert to the elastomeric composite over the entire operating range of temperatures of the process. It is used in continuous vulcanization processes, more commonly, but not exclusively. It is non-pressurized and provides reasonably rapid temperature rise and moderate vulcanization speeds.

    HOT AIR OVEN: Ovens can be used to vulcanize thin articles which have been preshaped. The system is not too efficient due to the poor heat transfer of hot air and this requires longer cure times at lower temperatures.

    LEAD PRESS: This process uses molten lead to cover soft, large extruded sections with a protective cover for vulcanization in steam. The process is used for garden and other hose.

    RADIATION: Systems using either gamma radiation from cobalt 60 or electron beams have been used for vulcanization. The electron beam method has been used to cure both polyethylene and silicone rubber. This is generally accomplished by passing the materials through the beam on a conveyor.

    UHF (ULTRA HIGH FREQUENCY): UHF fields are developed by alternating electromagnetic circuits to warm up or vulcanize articles with large or uneven cross sections. The process requires polar rubber or additives within the mixture to absorb electromagnetic energy and vibrates rapidly thereby producing a very localized temperature rise.

    EXUDATION

    A delayed phase separation of incompatible material. Also called bleeding, spewing or sweating. See Bloom.

    F

    feel modifier

    Ingredient added to enhance the skin feel of a formulation.

    FLUID AGING

    A procedure to compare the ability of rubber and rubber like compositions to withstand the effect of liquids.

    G

    GEHMAN VALUES

    T2, T5, T10, T100 – Temperature for which the relative modulus is 2, 5, 10, 100. The relative modulus at any temperature is the ratio of the modulus at that temperature to the modulus at 23°C.

    gellant

    Substance used to convert a liquid to a gel.

    GREEN STRENGTH

    The resistance to deformation of a rubber stock in the uncured state.

    ground state energy

    The lowest energy level of a system (the energy level it normally occupies), also known as zero-point energy.

    H

    HARDNESS

    The resistance to indentation as measured under specified conditions.

    hemisynthetic

    Produced from a naturally occurring substance that has been treated to incorporate desired properties. Semisynthetic.

    HLB Value Functionality

    4–6 Water-in-oil (W/O) emulsifier 4–8 Antifoaming agent
7–9 Wetting agent
10–16 Oil-in-water (O/W) emulsifier 13–15 Detergent

    13–18 Solubilizer

    For PEG esters, the HLB is 20 multiplied by (1–S/A), where S is the saponification value of the ester and A is the acid value of the fatty acid from which it is derived.

    humectant

    An ingredient in skin (or hair) products that draws moisture from the air to moisturize the skin and also promotes the retention of moisture in the skin, e.g., glycerin.

    hydroglycolic

    Consisting of water and one or more glycols.

    hydrophile-lipophile balance (HLB)

    Measure of the relative hydrophilicity of a surfactant, especially of an emulsifier. An ingredient’s HLB is a major factor in its ability to deliver its intended purpose:

    hydrophilicity

    Degree to which a substance absorbs, dissolves in, or is attracted to water.

    hydroxides

    The chemical opposite of acids, also known as caustics and alkalis.

    hydroxy acid

    Molecule with an hydroxy group either adjacent (alpha-hydroxy, or AHA) or one carbon removed (beta- hydroxy, or BHA) from a carboxylic acid moiety in a compound. These acids promote skin renewal by enhancing the rate of cell turnover and loosening the bonds that hold dead cells together so they can be removed more effectively.

    hypoallergenic

    Product in which care has been taken in ingredient selection and formulation to reduce the likelihood of causing an allergic reaction

    I

    INTERNAL MIXER

    A machine with a closed cavity in which a specially shaped rotor (or rotors) masticates the rubber to incorporate and disperse compounding materials into the rubber.

    ionic compound

    Substance with two or more ions (charged moieties) held in close proximity by electrical attraction. Examples include table salt

    (Na+ Cl–), amino acids such as glycine (H3N+-CH2-COO–), and sodium stearate
(Na+ – OOC(CH2)16CH3).

    L

    “label-copy” ingredient

    Ingredient added to a formulation to elicit consumer interest and enhance purchase intent, typically without contributing appreciably to product performance.

    lamellar

    Arranged in thin plates. Surfactants form lamellar phases at low water content, forming hydrophobic lipid bilayer sheets with hydrophilic heads directed outward, in contact with the water phase.

    lecithin

    Phospholipid found in animal and plant cells which forms colloidal solutions in water and has emulsifying, wetting, and antioxidant properties.

    lipid

    “Fat.” Molecule that has one or more long fatty chains, is alcohol soluble, and is water insoluble. Examples include plant-derived waxes and oils (triglycerides), animal fat (tallow), and plant- and animal-derived sterols.

    LIQUID CURING MEDIUM (LCM)

    Molten phase that is used as a heating medium for the continuous vulcanization of a rubber mix, usually following extrusion. A commonly used material is a mixture of sodium nitrite and potassium nitrate.

    lubricant

    Ingredient that enhances slip or glide across the skin.

    M

    matte

    Dull, not shiny, anti-glare.

    minimum erythemal dose (MED)

    The amount of UV radiation it takes to turn the skin slightly red. Used to determine sun protection factor (SPF) of sunscreen.

    ML, MH

    The minimum torque reported when doing Rheometer testing is ML. MH is the highest torque obtained during a specified period of time. Both are measure in dN*M (lbf*in) – dynes per meter or pounds force per inch.

    MODULUS

    (or Tensile Stress at a given Elongation)
    The stress required to stretch the uniform cross section of a test specimen to a given elongation. Represents functional strength of compound. Plasticizers reduce modulus.

    moiety

    A portion or part of a whole; e.g., a portion of a molecule.

    moisturizing agent

    Ingredient added to a formulation so the finished product makes skin feel “moisturized” (softer and more pliable, as it would if it were more hydrated). True hydration is the result of increasing the water content of the stratum corneum by reducing evaporative loss through inclusion of humectants and/or creating a water vapor-resistant barrier.

    MOLDING PRESSES

    COMPRESSION: A molding process in which the material is placed directly in a mold cavity and compressed to shape by closure of the mold.

    INJECTION: The process of forming a material by forcing it from an external heated chamber through a runner system and gate into cavity of a closed mold by means of a pressure gradient that is independent of the mold clamping force.

    TRANSFER: The process of forming a material by forcing it from an auxiliary heated chamber through a sprew and gate into the cavity of a closed mold by means of a pressure gradient that is dependent upon the mold clamping force.

    MONOMER

    A low molecular weight substance consisting of molecules capable of reacting with like or unlike molecules to form a polymer.

    MOONEY VALUES

    Minimum Viscosity – The minimum value during the test interval
    t5: The time required for an increase above the
    minimum viscosity.
    t35: The time required for a 35 unit increase
    above the minimum viscosity.

    MOONEY VALUES

    A measure of the viscosity of a rubber or rubber compound determined in a Mooney shearing disc viscometer.

    MORIYAMA

    An internal mixer that does not imploy ram pressure and used primarily for low viscosity polymers such as silicone rubber compounds and adhesives. See Internal Mixer.

    multivalent

    Having more than a single charge. For example, cationic Ca+2, Mg+2, and Al+3; and anionic CO3-2, SO4-2 and PO4-3 ions.

    N

    Newtonian fluid

    A fluid, such as water, motor oil, or honey; for which viscosity is independent of applied shear.
It does not shear thin like styling gels or shear thicken like highly concentrated pigment dispersions.

    nonionic surfactant

    Surface active agent that is uncharged. As a result, performance is not impacted by pH (over the range of pH in which the surfactant is stable). A greater degree of ethylene oxide or propylene oxide incorporation increases water solubility and HLB.

    O

    occlusive

    Obstructing movement (of water from the skin). This is typically accomplished by putting a water-insoluble barrier/film on
the skin, which slows water loss and increases the moisture content of the skin.

    oil

    Liquid water-insoluble substance that has one or more long fatty chains or linear hydrocarbon chains that increase slip, shine, and softness of skin.

    oil phase

    The oil-soluble or nonpolar components of an emulsion.

    oil-phase polarity optimization

    Controlling the polarity of a solvent system to minimize the rate of photodecay of a UV filter.

    opacifier

    Ingredient added to make a finished product opaque, or more opaque.

    O/W (oil-in-water)

    An emulsion in which an oil is the dispersed (internal) phase and an aqueous fluid is the dispersion medium (the external, or continuous, phase).

    oxidative stability

    The ability of a substance to withstand formation of oxidation by-products.

    P

    parabens

    Esters of p-Hydroxy Benzoic Acid, a common class of preservatives (Butylparaben, Ethylparaben, Methylparaben, Isobutylparaben and Propylparaben) used in pharmaceuticals and cosmetics to prevent microbial growth. Used at low levels (less than one percent).

    payoff/payout

    The deposition properties of a stick or balm product during application.

    pearlizing agent

    Ingredient added to make a product pearlescent (impart a luster or gloss similar to that of a pearl).

    PEG (polyethylene glycol)

    A polymer of ethylene oxide, also referred to as PEO (polyethylene oxide) or as POE (polyoxyethylene). The chain length of the polymer may be identified by the average number of mols of ethylene oxide monomer in the polymer (e.g., PEG- 150) or by the average molecular weight of the polymer (e.g., PEG 6000). Regardless of the polymer’s length, it has a free hydroxyl group at each end. Mono- and di-esters of PEGs are frequently utilized in personal care products.

    persistent pigment darkening (PPD)


    Physiological response of skin to UVA radiation that occurs within several hours of exposure.

    PFA

    Protection factor UVA (see UVA protection factor).

    photostability

    Degree to which a substance can remain unchanged upon exposure to light.

    photostabilizer

    Inactive/excipient ingredients added sunscreen to prevent active ingredients from losing their effectiveness during sun exposure.

    polarity

    Separation of electron density in a molecule. It helps determine physical properties such as surface tension, solubility, and melting and boiling points.

    POLYMER

    A substance consisting of molecules characterized by the repetition of one or more types of monomeric units.

    polyolefin

    Class of synthetic resins made from the polymerization of olefins, including ethylene and propylene.

    polysaccharide

    Polymeric carbohydrate made up
of a long chain of simple sugar molecules. Starch and cellulose are two examples of polysaccharides.

    POST CURE

    Some products because of the elastomer characteristics, the article size or its shape may require a post cure. That is additional heat and energy must be applied after the press cure. The post cure might occur in a hot air oven or in a liquid heat bath.

    propanediol

    Actually, 1,3-Propanediol. Propylene Glycol is 1,2-Propanediol. Both are humecatants used in cosmetics and personal care products.

    R

    RATE OF CURE

    The rate at which crosslinking and the development of the stiffness of the compound occur after the scorch point.

    required HLB

    The optimal HLB for an emulsifier (or a group of emulsifiers) to efficiently disperse (emulsify) one phase (oil or water) of a formulation into another (water or oil).

    REVERSION

    A phenomenon whereby a vulcanized product is exposed to conditions that result in devulcanization. Natural Rubber reverts if over cured.

    rheology

    The form and flow a substance, including elasticity, viscosity, and plasticity. (See Newtonian Fluid)

    RHEOMETER VALUE

    ML: Minimum torque
    MH: Highest torque attained during specified time.
    For C. P. Hall this specified time is at the
    central point of one lbf.in rise with 5 min.
    ts2: Time to 2 lbf.in rise above ML
    t’c(90): Time to 90% of torque increase
    Cure Rate Index: 100/ (tc (90) – t52)

    S

    saponification value

    The amount (in milligrams) of Potassium Hydroxide required to react with one gram of fat or oil to convert it entirely into soap.

    SATURATED ELASTOMERS

    An elastomer with no unsaturation, thus not susceptible to ozone attach. Some elastomers have saturated backbones with pendant unsaturated cure sites.

    SCORCH

    Premature (and usually unwanted) vulcanization of a rubber compound.

    sebum

    The oily secretion of the sebaceous glands, consisting primarily of fatty esters, free fatty acids, cholesterol, squalene, and other unsaponifiable matter; that acts as a lubricant for the hair and skin.

    sequestrant (chelant)

    An agent that removes metal ions from solution, often by chelation. Benefits include making the metal ions biologically inactive (thereby inhibiting microbial growth), pre- venting them from combining with other substances to form insoluble precipitates or chromophores, and preventing them from acting as undesired catalysts.

    silicone

    Ingredient containing at least silicon, carbon and oxygen that offers a very low surface tension, allowing for better spreading and more efficient film formation. Cyclopentasiloxane is a volatile silicone that is used as a carrier and to offer transient wetting. Dimethicone, a polymer available in a wide range of molecular weights, may be used as a defoamer during manufacture and as a skin protectant in finished skin care products.

    singlet quencher

    Photostabilzer that uses singlet energy transfer to prevent UV-filter molecules from reaching the triplet state, thereby precluding degradation, and so enhancing performance.

    slip agent

    Ingredient that helps a finished product flow more smoothly and easily.

    soap

    A cleansing agent typically made by treating animal fat (tallow) or vegetal oils or butters with an alkali, such as Sodium or Potassium Hydroxide, and consisting chiefly of the sodium or potassium salts of the fatty acids contained in these triglycerides and a small amount of released glycerin.

    solubilizer

    High-HLB surfactant that micro- emulsifies (forms clear solutions of) water-insoluble ingredients (such as fragrance oils) in an aqueous formulation; allowing a clear, rather than milky or opaque, end product.

    solvent

    Liquid capable of dissolving other substances, forming an entirely liquid base for a formulation.

    stabilizer

    Ingredient that helps maintain
the integrity of some aspect
(e.g., consistency, color, microbiology, active ingredient) of the finished product during storage or in use.
A photostabilizer helps maintain stability of the product under light.

    STATE OF CURE

    A terms used to indicate the development of a property of the rubber as cure progresses. Frequently good state of cure is thought of as being representative of good compression set.

    stratum corneum

    The top part of the epidermis, composed of biologically dead but biochemically active cells arranged in a “brick and mortar” type structure. It moderates external stimuli of the living tissue beneath and maintains its moisture level by both absorbing water and inhibiting evaporation (regulating trans-epi- dermal water loss, or TEWL).

    structurant

    Substance used to impart desired structure and form (resistance to flow) to a composition, thereby maintaining product uniformity and defining product deformation and release characteristics.

    substantivity

    Resistance to rinse or rub off —
a desirable trait for a leave-on skin product.

    sulfate

    A salt or ester of sulfuric acid.

    sun protection factor (SPF)

    The ratio of the minimum erythemal dose (MED) — the amount of UV radiation it takes to turn the skin slightly red — of skin protected with sunscreen to unprotected skin.

    surface active agent

    Molecule with a fatty, lipophilic (“lipid-loving”) tail and a hydrophilic (“water-loving”) head that reduces surface tension between ingredients to enable efficient emulsification or solubilization. (See anionic, cationic, and nonionic.)

    surfactant

    Shortened form of surface active agent.

    suspending agent

    Ingredient that helps prevent settling (sedimentation), creaming (flotation) and flocculation (agglomeration) of the dispersed phase in a suspension- or emulsion-based finished product.

    syndet

    Synthetic detergent. A surfactant developed as an alternative to nat- ural soap to provide better foaming and/or reduced irritation potential.

    syneresis

    The extraction or expulsion of a liquid from a gel, such as when temperature changes cause a diluent to exceed its solubility limit in a polymer.

    T

    T2, T5, T10, T100

    See Gehman.

    t5, t35

    See Mooney Values.

    TEAR STRENGTH

    The maximum force required to tear a specified specimen, the force acting substantially parallel to the major axis of the test specimen.

    TENSILE STRENGTH

    The maximum tensile stress applied during stretching a specimen to rupture or ultimate tensile.
    Plasticizers reduce tensile strength.

    TENSILE ULTIMATE

    The maximum tensile stress applied during stretching a specimen to rupture. Also known as tensile strength.

    thickener

    Ingredient that changes the rheology or viscosity of a formulation such that it becomes less fluid.

    thioglycolate

    Sulfurous compound that is the salt of a weak acid and a weak base, also known as perm salt. Solutions containing ammonium thioglycolate swell hair, rendering it permeable. Hence, it is used in solutions to permanent-wave hair, or combined with caustic to remove hair (depilate).

    triplet quencher

    Photostabilizer that uses triplet energy transfer to slow the photodecay of sunscreen active ingredients.

    ts2, t’c(90)

    See Rheometer Value

    U

    ultraviolet (UV) radiation

    Having a wavelength shorter than those of visible light and longer than those of x-rays (radiation).

    UNSATURATED ELASTOMERS

    Compounds with the ability to united directly with certain other substances such as iodine, bromine, hydro-bromic acid and ozone to form saturated addition products. Sulfur cure systems require unsaturated elastomers (double bonds) to achieve crosslinking. The ability to add iodine or bromine and the amount added is nearly always used as the test and measure of unsaturation.

    UV filter

    Active ingredients added to a sunscreen to absorb, disperse,
or reflect UV radiation. UV-filter ingredients that break down when exposed to sunlight require photostabilization.

    UVA protection factor (PFA)

    Longer-wavelength (320–400 nm) sun rays that penetrate the skin through the epidermis, into the dermis. Known as the “tanning rays,” long-term exposure can also cause photo-aging and skin cancers.

    UVB radiation

    Shorter-wavelength (290–320 nm) sun rays that can penetrate the epidermis and produce effects ranging from sunburn to carcinomas.

    V

    viscosity

    A measure of the resistance to flow (deformation) of a material.

    visible light

    Electromagnetic radiation in the wavelength range from 400 nm to 700 nm. The higher the wavelength, the less energetic the light.

    volatility

    The tendency of a liquid to evaporate. Liquids with high boiling points have low volatility, and vice versa.

    VULCANIZATION

    An irreversible process during which a rubber compound through a change in its chemical structure (i.e. crosslinking), becomes less plastic and more resistant to swelling by organic liquids while elastic properties are conferred, improved or extended over a greater range of temperature.

    W

    water phase

    The water-soluble portion of an emulsion.

    W/O (water-in-oil)

    An emulsion in which an aqueous fluid is the dispersed (internal) phase and an oil is the dispersion medium (the external, or continuous, phase).