oil chemistry tutorial

8/6/2019 Oil Chemistry Tutorial

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THE CHEMISTRY OF OILS from http://swiftcraftymonkey.blogspot.com 1

THE CHEMISTRY OF OILS AND TRIGLYCERIDES

This beautiful molecule to the left is atriglyceride. It is a molecule with a glycerol(or glycerine) backbone and three fattyacids attached to it. If you look at thismolecule - around the middle, before theOH bonds - you'll see a double line. This is

a double bond, which means this is an unsaturated molecule.

In asaturatedtriglyceride, thecarbons are singlebonded, which are

hard to break. (You can tell there are no double bonds in this triglyceridebecause it doesn’t have those double lines!) They are stable over long periodsof time because there isn't going to be oxidation. Most of these are buttery fatslike coconut oil, babassu oil, palm oil, and animal oils. Oils like beeswax andcandelilla wax are also saturated (yep, I don't think of beeswax as an oil either,but it fits the description!) Jojoba is another saturated triglyceride, whichexplains its long shelf life.

You can tell a single bond by the name "-ane". Squalane, for example, containsonly single bonds, which means it is more resistant to rancidity. "-ene" means

there are double bonds in the molecule. And "-yne" means triple bonds! Theseare going to have shorter shelf lives!

In an unsaturated triglyceride, these double bonds can bebroken easily and oxidation occurs. The more double bonds,the more potential for oxidation. This explains the shelf life ofsomething like grapeseed oil. It has 3 double bonds in thechain (it is a C18:3 triglyceride, meaning is has 18 carbonbonds and 3 double bonds), which means it has three placeswhere the bonds can be broken and the oxidation can occur!

Most of the oils we use are "class 5: plant derived products,C18, unsaturated" meaning they contain 18 carbon atoms inthose long chains. The unsaturated part means they havedouble bonds. Some of our oils have more than 18 carbonmolecules - like meadowfoam (C20:1) and jojoba - but what's

really important is the number of double or triple bonds when it comes to




rancidity.

Sweet almond oil is a C18:1 triglyceride, meaning it has 18 carbon moleculesand 1 double bond. Other C18:1 oils are olive oil, hazelnut oil, avocado oil, ricebran oil, and cocoa butter. So we know these oils are going to last longer thanthe C18:2 oils like soybean, sunflower, safflower, and wheat germ. And theseoils will last longer than the C18:3 oils like grapeseed and borage.

A QUICK ASIDE ABOUT BONDING!

Carbon has 4 electrons that want to connect with other atoms (the blue dots).Hydrogen has 1 electron that wants to connect with other atoms (the reddots). Atoms really like to have 8 electrons, so they connect with other atomsto make up 8 electrons. As you can see from this picture, carbon likes to besurrounded by 4 hydrogen atoms to make up this 8 electron configuration.

Atoms are so desperate to make up this 8electron configuration, sometimes they willbond doubly or triply with another atom toget to that number.

In the case of a double bond in a fatty acid,the carbon doesn't connect with ahydrogen, it connects with another carbon

in a double bond, leaving the hydrogen outin the cold. Normally when we look at afatty acid chain, we see a top row of

hydrogen atoms, then a row of carbons, then a row of hydrogens. This wouldbe a single bonded or saturated fatty acid because there are double bonds. Ifyou look at the unsaturated fatty acid chain, there are missing hydrogenatoms where the carbon atoms are double bonded! This the double bond, andit is easily broken so something else can get in that place of the missinghydrogen.

FATTY ACIDS!

If you're a lotion maker, you're familiar with stearic acid as a thickener.Stearic acid is a C18 fatty acid, which means it is a long chain (C18) fatty acidwithout any double bonds, so it's a long chain saturated fatty acid. If we putthree of these fatty acids together with a glycerol molecule, we'd have asaturated glyceride, and one with a great shelf life!




But it's fairly uncommon for an oil to have three of the same fatty acids. Theytend to have at least 2 different kinds, and sometimes three, as you'll seebelow with sunflower and olive oil.

In the picture to the left, the three fattyacids attached to the glycerol backbone aredifferent. One is a single bonded fatty acid,one has 1 set of double bonds, and theother has three sets of double bonds!

The fatty acids connected to the glycerol backbone determine what the kind ofoil or butter. The fatty acids can have differing carbon chain lengths anddifferent types of bonding. They can also have different configurations (transfats - you've heard about those!) that determine if an oil is liquid or solid.

For instance, it looks like this triglyceride is composed of a C16 chain, a C18:1chain, and a C18:3 chain. I know C16 is palmitic acid. C18:1 is called oleic acid.And C18:3 is linolenic acid. This could be a corn, cottonseed, or palm oilmolecule. The polyunsaturated chain (the C18:3 or linolenic fatty acid hasmore than 1 double bond, which means it is unsaturated, and because there'smore than 1, it's called polyunsaturated!) can go rancid quite easily!

What this means in terms of making lotions or other creations is this molecule

has THREE double bonds on that last fatty acid, so it may go rancid morequickly than something like olive oil below.

Olive oil has between 55 and 85% oleic acid, 4.6% linoleic acid, 6.9% palmiticacid, and 2.3% stearic acid. In this sample molecule, we see a triglyceride withan oleic fatty acid (C18:1 - 1 double bond), linoleic acid (C18:2 - 2 doublebonds), and palmitic acid (C16 - no double bonds). If oleic acid makes up thebulk of the fatty acids with its 1 double bond, we are going to see an oil that isless likely to go rancid than one that is filled with linoleic acid (2 double

bonds).Okay, so this is fascinating and all, but what does this mean for bath & bodymakers? Olive oil is a liquid oil that is unlikely to go rancid quickly, but it willgo rancid eventually, as indicated by the double bonds. It also indicates it's aliquid oil.




This is a high oleic sunflower oilmolecule. I love sunflower oilsin my lotions and othercreations, but it tends to gorancid far too quickly for mytastes!

Normal sunflower oil will have about 25% oleic acid (C18:1), 66% linoleic(C18:2), 2% stearic (C18), and 5.6% palmitic (C16). What this means is about91% of the sunflower oil is composed of fatty acids with 1 or 2 double bonds,so it's going to go rancid quickly. A high oleic sunflower oil is composed of 80-92% oleic acid (C18:1) and 3 to 10% linoleic acid (C18:2), with some stearicand palmitic fatty acids thrown in (less palmitic - about 5.6%).

The high oleic sunflower oil will last longer than the regular sunflower oilbecause there are fewer double bonds to break. It will still go rancid morequickly than a saturated oil, but fewer polyunsaturated fatty acids and moremonounsaturated fatty acids (ones with 1 double bond) means you're goingto have a longer shelf life oil.

The down side to the high oleic sunflower oil is you are losing the linoleic fattyacid that can be beneficial to your skin, but I'll get into that in the sunflower oilpost shortly!

So what does this all mean? By looking at a oils and butter property chart youcan figure out which oils will go rancid more quickly than others. You can lookfor specific properties the fatty acids can offer to your product.

HYDROGENATION OF OILS

When a molecule has double bonds,that double bond can be broken andthe fatty acid now reacts chemically

with oxygen to produce all kinds ofmolecules we don't want in ourlotions that have horrible smells.

Hydrogenation is the process of breaking those double bonds in advance andinserting hydrogen into the open spaces. This makes an oil less likely to gorancid because you've pre-oxidized it, as it were. You've turned anunsaturated fat (one with at least 1 double bond) into a saturated fat (one




with no double bonds).

Oils can be saturated without the help of processing - animal fats, shea butter,and illipe butter are all naturally occurring saturated fats.

Saturated fats lie in a straight line (more about this below), so they packtogether more easily. When triglyceride molecules are packed together well,they become a solid oil with a higher melting point. And they have longer shelflives because the double bonds have been eliminated, so they are moreresistant to rancidity. You can see why this has some appeal, eh?




FATTY ACID SHAPESDouble bonds in a fatty acidshape can make it go from thelovely straight line we see in thesaturated fatty acids like stearicand palmitic acid, to the kinkyline you see in the oleic acid(C18:1 - 1 double bond) anderucic acid (C22:1 - 1 doublebond, found in rapeseed andmustard seed). When we addanother double bond, it canmake the fatty acid contort in allkinds of ways, as we see in the

linoleic acid (C18:2) or arachidonic (C20:4 - 4 double bonds, an omega-6 fattyacid).

So what does this mean for us? A double bond makes the fatty acid kinky,which means it can't pack in as tightly as those without double bonds. So weget a liquid oil. If you look at the oils with more double bonds - grapeseed,sunflower, or safflower oils - you'll notice they are considered "light" oils.Whereas oils like olive oil, avocado oil, and rice bran oil have fewer doublebonds and are heavier.

So the heavier oils have fewer double bonds, which means they go rancid lessquickly than the lighter oils. (I'm not talking about fractionated oilshere...more on this in another post.) The butters will go rancid in the distantfuture because they don't have any double bonds at all!




CIS AND TRANS FATS

When we have a double bond on a fatty acid, it can be in either the cis- ortrans- configuration. What exactly does this mean?

In the cisconfiguration, themissing hydrogenatoms are on the sameside of the doublebond (cis means"same"). The

molecules bend at the site of the double bond, giving us a kinky molecule thatwon't pack in nice straight, dense lines like the saturated fatty acids. Put abunch of these together and you have a liquid oil!

In the trans configuration, the missing hydrogen atoms are on the oppositesides of the double bonds. The chain doesn't bend much, so they have astraighter shape. Meaning they can pack in more densely, resulting in an oilthat behaves as a solid saturated oil instead of a liquid oil. It has a highermelting point, doesn't need refrigeration, and is cheaper than saturated oilslike coconut or palm oil.

The process of partial hydrogenation can force the hydrogen atoms in a

normal cis configuration to become a trans configuration. The double bondsare broken, then re-formed in the trans configuration. You are unlikely to finda trans configuration in the oils we use in bath & body products as it usuallyarises out of processing and would likely cost more than a regular vegetableoil.

RANCIDITY!The main destructors of our oils are heat, exposure to light, exposure to air,and time. In lotions, water can also be our enemy.

Heat and time are pretty basic concepts. When we heat anything, the chemicalprocess speeds up. Let's say it take 6 months for an oil to go rancid. When weheat it, we reduce that time dramatically. It can take a few hours instead ofmonths!

This is attributed to the rate of reaction . Every chemical reaction has a rate ofreaction, which is determined by various factors. When we heat up a chemical




reaction, the molecules bounce around more, which increases the number ofcollisions (this is called collision theory ). The more bouncing molecules, themore collisions, the faster the reaction. So when we heat up an oil, evenslightly, we increase the bouncing around of the molecules, which means morepossibility of colliding into a free radical, which can cause oxidation. Mostchemical reactions are rated at SATP - standard atmosphere (1 atm, or sealevel) and temperature (25C).

And time...well, it's the enemy of all things, isn't it? Time is what makes ouroils go rancid, even if we have stored them in a cool, dark place with awonderful bottle and seal! (Time is really not accurate as it is really thechemical reaction happening over time, but it is still our enemy!)

If heat can speed up a chemical reaction, then, logically, cold can slow down achemical reaction, at least with oils. Hence the suggestion to keep your oils ina cool, dark place to avoid sunlight and heat!

The main culprit in rancidity is the free radical . A free radical is an atom,molecule, or ion with unpaired electron. As you might remember, atoms reallylike to have 8 electrons and will do just about anything - no matter howfoolhardy! - to get those 8 electrons. So they are highly reactive, looking forelectrons to make up that complete valence shell.

The free radicals that we worry most about

are O2 (oxygen, but can be found alone inO form), H2O2 (hydrogen peroxide, moreabout this later), and OH- (hydroxide).When these free radicals are involved inrancidity, we call it an oxidative process(because of the oxygen atoms). And theoxidative process is pretty much the maincause of rancidity (with the possibleexception of microbial contamination).

MECHANISMS OF RANCIDITY

There are different ways by which our oils can become rancid, most of theminvolving oxygen. I know we need it to live, but it's such a nuisance!

OXIDATIVE RANCIDITYThe double bonds of the fatty acid react chemically with oxygen. This turnsthe fatty acid molecules into other molecules that smell awful!




This can be a result of photo-oxidation or auto-oxidation.

PHOTO-OXIDATIONThe double bond interacts with a singlet oxygen (1O2), which is produced bythe light. It is highly reactive with unsaturated lipids. The process is evenquicker when you introduce sensitizers like chlorophyll and various otherorganic substances (like blood, bile, and riboflavin, but those shouldn't beissues for lotion makers - I hope!)

This is why we try to keep our oils away from strong light - bright light canproduce more oxygen in the bottle, which can increase the process of photo-oxidation. This is a much faster process than auto-oxidation. Variouscarotenoids in our oils can slow this process - derivatives of lycopene, likelutein, violaxanthin, and neoxanthin, as well as beta-carotene - and many oilscontain these ingredients. These are natural anti-oxidants found in our oils,and most of them contain at least a few to fight rancidity!

AUTO-OXIDATIONEven in the absence of air, we find oxygen. Oh oxygen, you are so necessarybut so annoying! Through the breaking of the double bonds, the oxygens helpsthe the fatty acids break down into hydrocarbons (the H-C-H chains you see,which can be methane - 1 carbon, 4 hydrogens - or ethane - 2 carbons, 6hydrogens), ketones, aldehydes, epoxides, and alcohols, some of which are

smelly ingredients!

This process is a slow one when anti-oxidants are found in the oils. When theanti-oxidants are gone, it's a really fast process and takes very little time at allif the oil is heated as well. (Which gives you a good reason to get some VitaminE into your oils when you get them from the supplier!)

Metal ions in the water at low levels can promote auto-oxidation. This is whywe use chelating agents (also called sequestering agents) like citric acid and

EDTA to bind the metals so they won't be a nuisance in our lotions. (And whywe use distilled water that should not contain these metals!) The main culpritis iron, and the process can be speeded up by exposure to light.

HYDROLYTIC RANCIDITYHydrolysis is a chemical reaction in which a molecule is cleaved into two partsby the addition of a water molecule ("hydro" is water, "lysis" is splitting"). Thefatty acids are split away from the glycerol backbone, and the water is split




into H (hydrogen) or OH (hydroxide) ions. When this happens, our lovely fattyacid molecules are morphed into a new molecule and we have rancidity.

Interestingly enough, this process - the hydrolysis, not the rancidity part - issaponification or soap making. Saponification is the hydrolysis of a fat and anaqueous base like sodium hydroxide or potassium hydroxide. Glycerol (orglycerine) is formed as the fatty acids are removed from the triglyceride formand converted into salts! So hydrolysis can be a benefit for soap makers and abane to lotion makers!

MICROBIAL RANCIDITYYes, our little beastie friends can cause rancidity in our lotions! (Which is whyyou must ALWAYS use a preservative!) Microorganisms use their littleenzymes (usually lipases) to break down the chemical structure in the fat.Which, again, results in rancidity.

Wow, when you consider how many ways a lotion can go wrong - betweenrancidity and flocculation and separation and so on - it's a wonder we canmake them at all. Fortunately, we have anti-oxidants ready and waiting tostave off rancidity as long as possible!




ANTI-OXIDANTS!

Anti-oxidants can stave off rancidity in our oils, giving them a longer shelf lifein our products. Nothing can make the possibility of rancidity go awaycompletely, but anti-oxidants are huge weapons in our fight on ickiness!

Free radicals are constantly running around in our lotions, seeking outelectrons to fill its valence shell. When we add an anti-oxidant, we providethat free radical with those electrons. The radical is content with its electronshell and bothers us no more! How awesome is that?

VITAMIN E is one of the main lipophilic anti-oxidants you'll find for bath andbody products, and it's the most commonly used by homecrafters. It comes infour varieties of tocopherols and four varieties of tocotrienols. We will befocusing mainly on the alpha tocopherol, which is the one you're most likely tosee in suppliers' shops.

Vitamin E is found in our stratum corneum and is secreted by our sebaceousglands to the surface of our skin. Studies have demonstrated - at least on labrodents - that it sinks readily into our skin and can inhibit lipid peroxidation,which is like oxidiation of the oils on our skin! It has also been shown toreduce sunburn irritation in mice (which just shows you albino creatures andsunlight don't mix!).

The interesting thing about Vitamin E is it can lose its anti-oxidating power, soit's unable to contribute an electron to the free radical. But in an excitingredox process, it gets its electron back, so the cycle continues again. Ah, youhave to love chemistry!

You can use it at rates as low as 0.01 to 0.05% in your creations or oils. I liketo use it at 1% because it has such wonderful qualities for skin, but you canuse lower amounts.

VITAMIN C, or ascorbic acid, is one of the most common hydrophilic anti-oxidants. It's present in high amounts in our skin, and it can chase awayscurvy (arrr, be gone scurvy!). Unfortunately, it's not very stable and can beesterified with phosphates.

For our purposes, it works well with iron found in our water, specificallyconverting Fe(III) to Fe(II).




Honestly, although Vitamin C does have some nice properties for skin, givenits instability, it's probably not the anti-oxidant to use most in a lotion. As well,it's hydrophilic, meaning it's going to hang out mostly in the water section ofthe lotion, and rancidity takes place in the oil part of our lotion.

EDTA – CHELATING INGREDIENT

EDTA (or ethylenediaminetetra acetic acid) is awonderful polyamino carboxylic acid that hasthe ability to chelate, sequester, and offer anti-oxidizing properties to our lotions. And weonly need to use 0.20% to get maximumbenefits in our lotions and surfactant basedproducts!

What exactly is a chelating or sequesteringingredient? EDTA binds with metal ions(mostly calcium and iron ions) and keeps them from being reactive with ourvarious ingredients. These metal ions can precipitate in our creations, forminga metallic solid that is really unpleasant. And the metal ions can keep oursurfactant mixes from foaming as well as they should, and can remove thescum that builds up on the tub after a bath.

We know auto-oxidation of metals in the oils and water can promoterancidity, so adding EDTA to our creations will bind those metals to the EDTAand slow down the auto-oxidation process. (Which is also another reason touse purified or distilled water - get rid of those naughty metal ions!)

On top of all of this metal binding goodness, EDTA can behave as an auxiliarypreservative to kill off those nasty microbes. There's always a chance a beastiewill adapt to the preservative in our lotion and learn to live there - eek! - butthe chelating agent disrupts the outer lipid layer of the microbes (wherestability is calcium and magnesium ion dependent), which increases thepenetration of the other anti-microbial preservatives into the bacterial cell!

EDTA is found in a salt form when we buy it from our suppliers - eithercalcium or sodium - to increase solubility in our creations. It is suggested youuse tetrasodium EDTA for alkaline products (pH over 7) and disodium EDTAfor products in the pH range of 3.0 to 9.0. We can use it in lotions andsurfactant based creations at up to 0.20%, which is enough to do the job (butcheck your suppliers' recommendations). Add it to your water phase.




CITRIC ACID – CHELATING INGREDIENT

Citric acid (or 2-hydroxy-1, 2, 3-propanetricarboxylic acid) is a chelating,anti-oxidizing, and pH altering ingredientthat can bind metal ions, help preventrancidity, and alter the pH of our lotionsand surfactant mixtures. It's also a key

ingredient in bath bombs.

There are two types of citric acid we can buy - anhydrous (water free) andmonohydrate (contains water). I have found the anhydrous citric acid I'vebought tends to be a powder and, for me, makes bath bomb creation a fareasier process than using the monohydrate, which I've noticed tends to bemore like a grain. The anhydrous is much less likely to fizz in high humidity,

which means you can use it in bath bombs even when its damp outside! (Iused to get mine at Voyageur, but they've stopped carrying the powder form,so I get it at Aquarius. Ask your supplier which one you have!) For otherapplications, it's irrelevant which one you choose.

It is a chelator likeEDTA, which we can use to bind metal ions like calcium,magnesium, copper, zinc, nickel, and cobalt to keep our products fromexperiencing auto-oxidation. By binding these metals, it also keeps surfactantmixes nice and clear! It also helps to boost the efficacy of your preservative.

The difference in using citric acid as your chelating or sequestering agent isthe pH changes you might find with it. Citric acid is a weak organic acid, whichmeans it has a pH less than 7 (it ranges between 3.13 to 6.4 depending uponthe concentration). When we add it to a lotion or surfactant mix, it can changethe pH of our product. For something like a hair care product, we want a pHaround the pH of our hair, which is 5.6 to 6.2. For a lotion, we want a pHaround 5 to 6 - our skin is about 5.5.

Including too much citric acid in something like a shampoo can change yourhair colour! Remember "Sun In"? (It was all the rage when I was a teenager -eek, I'm dating myself here!) It can lighten your hair if you're using too muchof it! (You do have to use a decent amount - say 1% or more, so the 0.1%suggested below should be fine!)

Citric acid can be used as anAHA type acid in facial products, but as I've notused it in that context before, I'm not comfortable making any suggestions foruse. It can also be used as a buffer (something that maintains the pH of a




product) with sodium citrate if you're using things like AHA or Multifruit orPhytofruit or another acidic ingredient.

How much to add? You only want a titch when you're using it as a chelatorand anti-oxidant - 0.1% or so - and this shouldn't be enough to change the pHdramatically. If you're using citric acid at higher levels, I'd suggest getting a pHmeter (it's on my Christmas list) or using those pH strips.




I hope you’ve enjoyed this little tutorial thingie on the chemistry of oils. Feelfree to share these recipes with whomever you choose, but if you are postingit on a website, please give credit to Swift or Susan Barclay-Nichols and notemy blog (http://swiftcraftymonkey.blogspot.com ) or e-mail [email protected] . That would be great!

If you really like this little tutorial thingie, please consider donating a fewdollars to the Chilliwack Youth Library program fund (Our programs arecollectively called Rated T for Teen). If you want to donate, you can reach meat [email protected] through hyperwallet (Canada) or through PayPal.

We provide different programs to youth at the Chilliwack and YarrowLibraries (in Chilliwack, B.C., Canada) and most of the funding comes from thevolunteers’ pockets. We offer craft groups to teens, tweens, and pregnant andparenting teens. We provide two card and board game clubs, two video gameclubs, and a Japanese pop culture program, as well. We also offer parent-childcrafting programs. All of our programs are free of charge and we provide allsupplies for all craft projects free so no one is left out. We average 15 to 20youth per group from every part of the community – foster children, pregnantand parenting teens, students in alternate schools, home schooled youth, andeveryone in between. We have had over 7,000 youth participate in ourprograms since 2005, and we would love to be able to continue the programsand expand to other communities. If you can donate a little to our groups,we’d be incredibly grateful!

Okay, the mooching ends here…but they are pretty awesome programs. We’vedone so many bath & body projects - hair care products, body wash, bubblebath, mineral make-up, and so on – which is a fantastic opportunity to sharethoughts and discuss self-esteem, personal hygiene, applying make-up, and soon. We’ve made packages for women in transition houses and collected for thefood bank. They really are amazing kids and so enthusiastic. If the idea of ayoung woman taking chemistry so she can learn more about bath and bodyproducts makes you smile…if the idea of youth enjoying the library andgetting their own cards makes you happy…or if seeing a young person makeher own purse and crochet scarves for Christmas presents, then pleaseconsider donating a little.

Okay, the mooching really ends now. I promise!

Happy formulating!Susan Barclay-Nicholshttp://[email protected]

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