Holy cow! I can’t believe it’s been two years since I did my last plastic reduction mission! I have definitely found that the easiest way for me to reduce my plastic usage is to avoid buying things that come in plastic bottles. Last time, it was laundry detergent. I’ve been using homemade laundry detergent for awhile now, and I’ve really liked the results. I’ve also really liked my DIY fabric softening results…and it’s just occurred to me that I haven’t bought a bottle of fabric softener in two years either…so why not post about it?
If you’re really into plastic reduction, or just reduction in general, the obvious choice is to forgo a fabric softener altogether. I did this all throughout my co-op years with no ill-effects. The detergent I used then was Seventh Generation’s powdered detergent, which is a mostly washing soda based product like my homemade stuff is. However, now that I’m using my homemade stuff, I have noticed that if I do not use a fabric softener, my clothes feel a good bit stiffer after drying than they did before. A little research and some basic high school chemistry eventually brought me to the conclusion that the soap in my homemade detergent might be bonding with the few hard water deposits (calcium and magnesium cations) in our water and leaving a very fine residue of soap scum in my fabrics that was contributing to the stiffer feel. Any residual alkalines (the borax and washing soda) in the clothing would only serve to increase the scratchy feel. The solution here is really simple: introduce an acid to the rinse cycle to dissolve the soap scum and neutralize residual alkalines. Enter my first DIY softener: distilled white vinegar.
As it turns out, I’m not the first person to think of this. Martha Stewart advocates using between 1/4 and 1 cup of white distilled vinegar in the final rinse cycle as a fabric softener. I’ve started to do this, either by pouring vinegar directly into the machine’s softener dispenser (mine takes about 1/4 cup) or by putting greater amounts into a Downy Ball and putting it into the machine, and I’ve been pretty pleased with the results. My fabrics aren’t ultra-soft in the way they become using commercial fabric softener, but they’re definitely softer than using detergent alone, no matter whether the detergent it is homemade or commercial. Moreover, using vinegar in place of laundry detergent has been promoted by Frugalistas all across the Internet. After all, a 120-load bottle of Downy (103 oz or 0.8 gallons) costs about $11, but two gallons of Four Monks white vinegar (which would do 128 loads using 1/4 cup) cost me $3.91 at Costco last week.
Unfortunately for me, using vinegar as a fabric softener doesn’t exactly help me reduce my plastic load as I would have to purchase two larger plastic bottles of vinegar to get the same number of softened loads as the smaller Downy bottle. Since doubling my plastic dependency isn’t the goal of this challenge, I need something that can work the same as vinegar, but is sold in solid form so that it doesn’t need a plastic or glass container. I need a weak acid that comes in a powdered form.
I think I have found a winner in citric acid. Like acetic acid–the acid which in an 5% solution with water forms vinegar–citric acid is a weak acid. It’s also not uncommon to use citric acid in the household: solutions of citric acid and water are is the recommended way to descale–or to remove hard water buildup–from expensive espresso machines, dishwashers, washing machines, boilers, radiators, and water softeners. Citric acid is also an active ingredient in many commercially prepared cleansers. In short then, I really think this could work.
Chemically, there are some differences between acetic acid and citric acid. Acetic acid has a relatively simple chemical structure with only 8 atoms [CH3COOH]. It’s also a monoprotic acid, which means that it has only one proton to potentially donate to a water molecule (to form one hydronium molecule). Citric acid, on the other hand, is a larger molecule with 21 atoms [C(OH)(CH2CO2H)2CO2H] and is a triprotic acid, which means that it has 3 protons to potentially donate to 3 different water molecules (to form 3 hydronium molecules). The acid dissociation constants for each of these proton donations are very close together (with pKa values of 3.13, 4.76, and 6.40), but are also in the same general range of acetic acid’s dissociation constant (pKa=4.75). What this means is that the buffer region (the region where the solution will resist a change in pH despite the addition of a base) for citric acid is a lot broader than it is for acetic acid. For my laundry purposes, this means that if I have two equivalent amounts of citric acid and acetic acid in solution and I add the same amount of a basic (or alkaline) substance to each, the citric acid solution will stay at its pH for a longer amount of time. If I want to make sure to dissolve all the residual alkalki and soap scum in my fabrics, this is an incredibly attractive property.
At this point, all I really need to know is what concentration to make my citric acid solution for effective fabric softener use. Alas, this is also the point where my chemistry knowledge is very imperfect. My first instinct was to create a citric acid solution with a pH close to distilled vinegar (which hovers around 2.4). According to this online pH calculator, a citric acid solution of pH 2.36 has a concentration of 0.03 M. This means that there are 0.03 moles of citric acid per liter of the total solution, which then translates to 5.76 grams of citric acid per liter of solution or 21.82 grams per gallon. Since there are 453.6 grams per pound, a 50 pound bag of citric acid ($2.50 a pound, shipping included), will yield 1039 gallons of solution (at a cost of $0.12 a gallon!).
When I mixed this concentration up, though, I was slightly disappointed. The resulting solution was definitely sour–perhaps a little less so than lemon juice–and it definitely created a reaction with baking soda…but that reaction wasn’t as complete as it was when I used similar amounts of baking soda and vinegar. Ultimately, I decided that this concentration wasn’t going to cut it in my laundry…especially when 1/4 cup of the solution would be further diluted by several gallons of water in my laundry’s rinse cycle! I decided that my next step would be to prepare a citric acid solution of the same concentration as that of vinegar, which the bottle says has a 5% acidity.
A 5% acidity is basically a volume ratio, which means that 95 parts of distilled water are added to 5 parts of glacial acetic acid (pure acetic acid, which is in liquid form). To get the weight/volume ratio, you need to factor in the density of acetic acid, which is 1.049 g/mL, which means that 5% v/v acetic acid solution is 5.25% w/v solution. To make an equivalent concentration of citric acid, then, you would need 5.25 grams of citric acid and 95 mL water. This works out to 209.2 grams of citric acid for every gallon of water (or 0.288 M), which is almost exactly the amount of 1 cup of citric acid (211 grams). If I used 1 cup of citric acid for every gallon of water, my cost per gallon would be $1.16, which is still a 40% savings on my vinegar budget of $1.95 per gallon).
Although the pH of this stronger citric acid solution is 1.85, which looks like a scary decrease from the 2.36 pH of our 1.5 weaker citric acid solution, it is only about 5 times more acidic than the solution made using 1.5 tablespoons citric acid per gallon of water. In fact, it’s about the same pH as fresh lime juice. This solution won’t dramatically burn through your skin, but it would be irritating with prolonged contact. You should obviously take care not to splash any in your eyes and to rinse it off your skin. If you were to try to use it to clean something, you’d want to further dilute it, too–just as you would with vinegar.
I’ve now done several loads of laundry using my homemade detergent and my 5.25% w/v citric acid solution as the softener, and I’ve been pretty impressed. My clothes were noticeably softer than they were when I used vinegar, and there appears to be no ill-effects to any of the fabrics I’ve washed.
After I did a mountain’s worth of laundry, I got so excited at the prospect of using citric acid as a fabric softener that I looked to see if anyone else had the idea. I actually discovered two European companies that do just this. The German company Sodasan and the Swedish company Tangent both offer citric acid based fabric softeners. Tangent’s also been getting a lot of press lately with write-ups in Swedish Vogue, so I suppose there’s a bit of an upper-class vibe with these products. The two products are practically identical: Sodasan lists its ingredients as “>30% water, 15-30% citric acid, <5% xanthan gum, essential oil, vegetable betaine, citrate, Aloe Vera” and Tangent lists its ingredients as “>30% Aqua, 15-30% citric acid, <5% xanthan gum, lauryl polyglucose, essential oils from peaches, vegetable betaine, potassium citrate and aloe vera”. Sodasan also recommends using 40ml (2.7 tablespoons) of its softener per load of laundry.
What I took away from these products (which are essentially stronger concentrations of citric acid and water plus a few thickening ingredients and scents) is that you can make up much stronger concentrations than even my 1 cup per gallon of water. I’m not entirely sure how strong these commercial formulations are, but if the percentages given are by weight and we assume that the final solution weighs about the same as water, then a gallon of the solution would be 8.35 pounds, which means that a 22% citric acid solution would have 1.84 pounds of citric acid per solution. That’s almost 4 times as much citric acid as my 5.25% w/v solution has, and you use only 32% less solution per load than I do! Clearly your clothes can take a lot of citric acid!