Plant Pad
ABSTRACT
Wood derived fluff pulp is used in a variety of essential products such as diapers and menstrual pads. However, many of these products remain out of reach for many. Roughly 500 million women, majority residing in LMIC countries, lack access to safely manage their menstruation. Meanwhile, cellulosic fibers exist in great abundance in a variety of diverse biomes. The leaves of one drought-tolerant crop, Agave sisalana (sisal), can be transformed into highly absorbent and retentive material. The process involves delignification combined with mechanical fluff to increase affinity for water and porosity, respectively. This process leads to a material with an absorption capacity exceeding those found in commercially available products such as menstrual pads.
BIG QUESTION
“Can we design a highly-absorbent menstrual product that is entirely flushable using all natural and local materials? To what extent can we apply the same process to other biomasses to produce highly-absorbent materials?”
suffering from period poverty:
500
million
global sisal production:
208,000
tonnes
sisal fluff pulp absorption:
up to 23
g/g
cotton absorption:
up to 15
g/g
What is the approach to PlantPad?
While there are strategies toward menstrual hygiene, such as reusable pads and newly emerging menstrual cups, there is still a growing demand and preference toward disposable menstrual pads that needs to be addressed. Our approach to PlantPad is to produce compostable menstrual pads using only plant-based materials in the context of small-scale manufacturing. The key functional material in the vast majority of commercially-available disposable menstrual pads is fluff pulp composed of cellulosic fibers derived from wood while some others consist of cotton. Currently, more than 50% of the world’s forest resources are concentrated in just five countries. This unequal distribution of timber along with the necessary large-scale Kraft processing to produce fluff pulp from timber yields an imbalance in access to quality fluff pulp. Meanwhile, production of cotton embodies a large carbon footprint due to the comparatively large amount of energy needed for upstream fertilizer production.
Currently, our work has focused on using Agave Sisalana (sisal), an extremely robust and drought-resistant plant, to produce the functional absorbent core within menstrual pads. Even though sisal has been used as a fiber feedstock (for cordages) in semi-arid regions for centuries, current applications remain limited. Expanding our capacity for obtaining useful materials from drought-resistant commodity crops is critical for adapting to a warming planet and associated changes in biomass distribution. So far, we have demonstrated fluff-pulp produced from sisal having an absorbance capacity (23 g/g) exceeding that of cotton from commercially available menstrual pads (15 g/g).
Agave Sisalana plants (top), dried decorticated fibers (bottom)
How do we transform plants into highly-absorbent cellulosic microfibers?
When working with non-wood feedstocks, fiber property and quality depend both on the growing conditions and how the fibers are harvested and extracted. For sisal, micro cellulosic fibers are held together in a binding matrix of hemicellulose, lignin, and protein and form larger fiber bundles which are surrounded by plant tissue (primarily composed of parenchymal cells). Sisal leaves are first mechanically decorticated to remove the initial layer of plant tissue. Once decorticated, fibers are dried to remove excess liquid. The dried fibers then undergo a mild delignification using a peroxyformic acid treatment and an alkali (sodium hydroxide) wash.* This step cleaves and solubilizes the hydrophobic lignin and hemicellulose, freeing the hydrophilic cellulose fibers. The subsequent water washes remove any remaining chemicals and defibrillize/debundle the cellulose fibers. The wet pulp is then air dried to form a fluff board. To form fluff pulp, the fluff board is cut and dry blended. The process of dry blending reintroduces porosity which was lost during the air drying process.
*Initial processing was done using 10% peroxyformic acid (PFA) activated by 10% sulfuric acid (SA) and washed with 4% sodium hydroxide (NaOH). To optimize on chemical use, later processing was done using 1% PFA activated by 4% SA and Iron (II) and washed with 4% sodium hydroxide.
Schematic of the mild delignification process (top), SEM images of the fibers following each step throughout the delignification process (bottom)
Data
We measure the materials’ absorption of a viscous test liquid under an applied load as a means for evaluating the absorption capacity of the fluff pulp produced.** Using the mild delignification process mentioned above (10% PFA), we were able to reach an absorbent performance of ~23 g/g, exceeding that of cotton found in commercially available pads at ~15 g/g. Even the chemical concentrations were reduced (1% PFA), we were still able to match the absorbent performance of cotton.
To understand the parameters that affect absorption performance, we characterized the physical and chemical properties of individual fibers and assemblies thereof. We see that with each subsequent step throughout the mild-delignification process, the fiber diameter and contact angle reduce, while the Fourier transform infrared (FTIR) spectra increasingly collapses with that of cotton (considered as a reference to pure cellulose). However, despite the near-identical chemical properties of the various fluff pulp, when we plot all of the test data with respect to porosity, we see that absorption capacity is also a function of porosity.
**Fluff pulp was first molded into a standard template to form square test “pads” and weighed. Each test square was subjected to the absorption under pressure test and reweighed to assess the quantity of liquid that was imbibed and retained.
Project status
We’re expanding this study to include a number of other biomasses (i.e. water hyacinth, bamboo, banana pseudostem, flax, hemp). We’ve begun collaboration with researchers, tool builders, and local entrepreneurs to test this local manufacturing concept in the field (Kenya and Nepal).
Project collaborators
The following groups are a part of the ongoing PlantPad consortium with a collective goal of bringing distributed manufacturing capacities to produce menstrual pads using locally-available biomass
Olex Technoenterprises, NIDISI, LGP2 (University of Grenoble), MitiMeth
Project is funded by the Gates Foundation.
