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Dr. Pendo Bigambo: Centering Sustainability

Tackling textile processing to protect people and planet.

Headshot of Pendo wearing a blue and yellow top.
Photo of Pendo Bigambo from Oltremare


The Cotton Conundrum

We all love cotton. It’s soft, versatile, and most importantly, comfortable to wear. In fact, about half of all textiles – from shirts to bath towels – are made of cotton. But did you know that growing cotton is extremely unsustainable?

Picture of a white t-shirt, blue pool, and green cotton plant with labels.
Making just one cotton t-shirt takes only 1.5kg of cotton but uses up 22,500 liters of water.

Making just one simple cotton t-shirt takes only 1.5kg of cotton but uses up to 22,500 liters of water: that’s enough water to keep the average adult hydrated for nearly 20 years! It’s thought that the Aral Sea, once the world’s 4th largest lake, is now all dried up as a consequence of extensive cotton cultivation.

This drastic water use is just one of the many environmental impacts of growing cotton. Current cotton farming practices lead to soil erosion and contamination of waterways due to chemical insecticides and pesticides. To make matters worse, the fast-fashion industry encourages us to dispose of the clothes we buy at an alarming rate. These used clothes often end up in landfills, where they can take more than 200 years to fully decompose. These issues all add up to make cotton cultivation, textile manufacturing, and its disposal increasingly unsustainable.

So we find ourselves in a bit of a conundrum: cotton is so comfortable, but so unsustainable! Is there a way that we could keep our comfy cotton t-shirts while treating the planet better? Dr. Pendo Bigambo, a lecturer and researcher at the University of Dar es Salaam in Tanzania, is working to solve this very problem. By studying the chemistry of textile recycling, she hopes to make cotton comfortably sustainable once again.


Traveling to Textiles

Dr. Bigambo grew up shuffling between Iringa, Arusha and Mwanza regions in Tanzania. Since middle school, Dr. Bigambo has been fascinated by the practical applications of science and how you can find it nestled into every aspect of your life! Inspired by her father, she decided to study engineering and studied mechanical engineering at the University of Dar es Salaam. After getting her degree, she worked at a cement manufacturing company as a mechanical engineer for a while, but her heart always lay in teaching.

Map of Africa showing Tanzania (on the middle right of the continent) in yellow and several provinces within Tanzania.
A map showing regions of Tanzania.

To Pendo’s excitement, her university offered her a chance to come back to teach for them on one condition. The school had just started a textile program and needed scientists to become experts in this field. This was a completely new direction for Tanzania, for the university, and for Pendo. But she was committed to return to teaching, so she moved to the UK to get degrees in this new field. It was there that she discovered her love for textile engineering! She realized how studying textiles connected her to the people around her, “because you’re talking about what people are wearing, something they’re connected to … you can explain it to someone, and they can understand it easily.”

Having developed a love for working with textiles, Pendo is now back home in Tanzania, as a lecturer and researcher at the University of Dar es Salaam. Not only does she teach courses in textile technology, mechanical engineering, and materials sciences, but she is also a successful research scientist and a fierce advocate for the advancement of women in STEM. She is the co-founder and vice-chair for Tanzania’s National Chapter of the Organization for Women in Science for the Developing World where she works tirelessly to mentor and support women in STEM fields and organizes conferences and workshops to make sure that they have the resources they need to succeed.


Rethinking Recycling

Dr. Bigambo explains the cotton conundrum in her community simply: “Tanzania’s population is rising. Farmers here need to grow food. If we ask a farmer to grow cotton instead of wheat, that would be crazy!” To address this problem, and the problem of the environmental impact of cotton, Dr. Bigambo wants to improve how we recycle cotton - so we don’t have to grow as much of it!

So how do we go from that used red t-shirt in your closet that you don’t wear anymore to an entirely new garment? There are two main ways we can recycle that cotton: mechanical and chemical. For mechanical recycling, we would take that t-shirt, put it in a big blender, shred its fabric to get fibrous material, and then spin it to make new fiber. Effectively, your t-shirt’s cotton fibers would be directly remolded.

But mechanical recycling comes with a few challenges. First, since your original t-shirt is dyed red, we can only get red fiber from it. If we’re mechanically recycling on a larger scale, we’d have to make sure that all the t-shirts we start with are the same color. This makes large scale mechanical recycling unfeasible. More importantly, because mechanical recycling just remolds the original fiber, it can’t be done multiple times on the same piece of fiber. If the fiber were to be mechanically recycled again and again, it would lose strength and tear more easily. Thus, the quality of the recycled garments would deteriorate over time.

Top: A red t-shirt with an arrow pointing to a blender with an arrow pointing to fiber with an arrow pointing to "spin into new fiber". Bottom: A red t-shirt with an arrow pointing to parts of a shredded t-shirt with arrow pointing to two tins of cotton rich and polyester-rich waste, with an arrow pointing to cellulose fiber and polyester, with an arrow pointing to cotton and polyester yarn.
Top: The process of mechanically recycling a red t-shirt. Bottom: The process of chemically recycling a red t-shirt.

Chemical recycling, on the other hand, uses chemical reactions to dissolve the original fiber and create a fiber slurry. This slurry can then be spun into fiber that’s as strong as the starting material, since it’s effectively new. This means that cotton that is recycled chemically can undergo the recycling process over and over again, making this technique more sustainable.


Crafting Chemicals

A cotton plant, with white cotton surrounded by three clusters of three leaves.
Illustration of a cotton plant.

Chemical recycling sounds great and could solve our cotton conundrum, but chemical recycling is a fairly new scientific process. This means that chemical recycling methods have not yet been fully established. This is where Dr. Bigambo comes in. Her research group is working on crafting a careful recycling process of curated chemicals that are sustainable and safe to use.

To understand Pendo’s work, let’s get back to the basics, back to your old red cotton t-shirt. Let’s think about cotton itself. What is it?

Cotton is a fiber that is extracted from Gossypium plants. These are small shrubs that grow in tropical regions of our planet. Its seeds are surrounded by fiber. These fibers are what we extract to produce cotton. Cotton is made up almost entirely of cellulose, which is a carbohydrate made up of long chains of glucose molecules. To go from raw cotton fiber to your finished red t-shirt, the cotton must first be dyed. Most dyes in common usage are synthetic and can be made up of chemicals such as mercury, lead, chromium, or copper. For a steady, permanent color, these dyes react chemically with the cotton to form strong covalent bonds. This makes sure that the red is attached firmly to the cotton. So, the red is not on the cotton, it’s actually in the cotton!

A red t-shirt and a small zoomed in region which shows the chemical structure of cellulose.
A red t-shirt, zoomed in to show the structure of cellulose bound chemically by red dye.

This brings us back to our recycling problem. Since synthetic dyes bind so strongly with the cellulose within cotton, the solvent used in chemical recycling can’t dissolve the dyed cotton. This is because the cotton has already reacted with the red dye and so isn’t available to react with the solvent. So the first step of chemical recycling is removing this dye. This is what Dr. Bigambo and her lab are working to improve! If you’re an expert chemist, you can figure out the combination of chemicals needed to break the bonds between the dye and cotton. Dr. Bigambo figured out that treating dyed cotton with an acid to break some of these bonds, followed by strongly basic sodium dithionite to strip the dye and ending with bleaching by hydrogen peroxide can do the trick! Her team of scientists saw a significant loss of color and an increase in the ability to dissolve these chemically treated cotton fabrics. These dissolved fabrics can then be spun into new fiber that retains its original quality.

Left: A red square of dyed cotton. next: treating the cotton with acid. Next: treating the cotton with a strong base. Next: treating the cotton with bleach.
A set of processes to break the chemical bonds between dye and cotton.


Naturally Beautiful

Photo of three individuals painting designs on brown fabric, and one individual watching.
Artists working on handmade Batik in Tanzania.

While Pendo has had tremendous success in understanding how to remove these cross-linked dyes, she wonders whether there is a better way to make the whole process more sustainable. Her inspiration, again, comes from her community. In Tanzania, batik, a form of dyeing that originated in Indonesia, is prevalent. Often, batik is a technique that is perfected by women in their own houses. Pendo recalls a story of watching a woman with young children working on batik in the back of her house. She noticed how unsafe it was to have volatile dyeing chemicals without proper safety procedures in place. The gears in her head started turning immediately as she began thinking of a way in which the women in her community could continue doing their work safely.

Illustrated picture of tumeric root, an onion peel, and cabbage.
Sources of natural dies include tumeric, onion peels, and cabbage.

To make these dreams a reality, Dr. Bigambo is actively working on finding ways to extract dyes from natural sources such as onion peels, purple cabbage, and turmeric (if you want to learn more about natural dyes and the way chemists can preserve them, check out our post on Dr. Rangi Te Kanawa). She’s excited by this prospect because natural dyes don’t react as strongly with the fabric as synthetic ones, making naturally dyed cotton much easier to recycle while making the task of dyeing much safer. Nature always surprises us, and Dr. Bigambo believes that natural dyes offer us a way of producing colors that we would never even have thought of! She’s already working with local women to help implement natural dyes in their production process, so the science that Dr. Bigambo is so passionate about is seeing immediate application. Not to mention, her trainees are already discovering new sources of dyes. Two months after the first training, Pendo received a phone call from one of her trainees who had made beautiful garments using dye extracted from roselle fruits, a flowering plant native to West Africa. Encouraged by this local excitement, Pendo and her team are working hard to find new sources of natural dyes and to make the process from dye extraction to application as simple as possible.

When asked what her favorite thing about being a scientist is, Dr. Bigambo immediately said it was “finding a solution.” She went on, “at the end of everything, there will be a solution that will solve problems … it won’t be today, it won’t be tomorrow, but eventually everybody will adapt.” With her love for her work and her commitment to her community, Dr. Bigambo is striving to center sustainability. She is finding local solutions that benefit her community, and her science is making sure we can continue enjoying the comfort of cotton without destroying our planet in the process.

Written by Manasvi Verma

Edited by Taylor Contreras and Caroline Martin

Illustrations by Sachi Weerasooriya

Other contributions by Katherine Fraser and Madelyn Leembruggen

Photo Credits:


Learn more about dyes, textiles, and recycling!

Create (60-90 minutes): Use plant dyes and other natural materials to create colorful clothes that help you express yourself.

Reflect (45-90 minutes): Perform a closet audit. Look through your clothes and use a notebook or piece of paper to answer the questions below for each piece of clothing:

  • What type of clothing is this? Describe the piece of clothing using details like color and texture.

  • When was this piece of clothing bought? Where was it bought?

  • What is the fabric made of? Where was it made? (Check the tags for this information)

  • How often do I wear this?

  • Do I want to keep this, or should I get rid of it?

Conclude your closet audit by writing a response to this prompt:

  • I will reduce my textile waste to protect the planet by...

If you decide to get rid of some clothes you don't wear often, consider donating them to a thrift store, hosting a clothing swap with your friends, or taking them to a textile recycling center (try Googling "textile recycling center near me"). When you buy new clothes, think about buying them second hand or from a sustainable brand (you can check a brand's sustainability rating here, or use Google to research a brand's commitment to sustainability).

Make (2 hours active, 2 days total): Try the mechanical recycling process for yourself by making your own paper at home! To make recycled paper you will grind papers into a slurry and then mold the fibers into a new shape. This is very similar to the mechanical recycling process for textiles, where the textiles are ground up and the fibers are molded into new threads. What will you make with your homemade paper?


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