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Bio-Based Superabsorbent Polymers: A Sustainable Solution for Hygiene Products

Getting to the core of the matter with bio-based SAPs

Could hemp be the answer to the realisation of sustainable, bio-based superabsorbent polymers (SAPs) for absorbent hygiene products (AHPs)?
Researchers at Purdue University in the USA believe so and have recently patented a process for manufacturing them. If successfully industrialised, these bio-based SAPs would perfectly complement the ongoing commercialisation of nonwoven fabrics based on natural or recycled fibres and resins.

Bast fibres
Such fibres include hemp itself, with companies such as INDEX™ exhibitor Bast Fibre Technologies (BFT), headquartered in Victoria, British Columbia, currently accelerating production specifically for the nonwovens industry.
As renewable crops, bast plants like hemp and flax can be produced in just 90 days with a high yield per acreage. They are also rotational, enriching other crops grown after them and providing an effective carbon sink based on natural rainfall, with no need for irrigation, pesticides, or chemical fertilizers.
Bast plants also transport nutrients through their cores, which is something Bast Fibre Technologies is exploiting for superior liquid handling in terms of retention and release in nonwovens. Other advantages of the fibres obtained from these plants include their strength, suitability for the carding process and natural coloration without the use of chemical dyes.
Having completed a successful financing round in 2022, Bast Fibre Technologies is working towards building up an annual capacity of 50,000 tons of hemp and flax fibres by 2026.
The company has secured a portfolio of its own patents relating to all aspects of processing, and in addition has an exclusive licensing agreement on other patents held by Georgia Pacific, with whom it is working on new solutions for industrial and food service wipes, while adapting them for its own fibres for disposables.
Bast Fibre Technologies wide-ranging preparation to become a major player in the hygiene market has involved establishing a supply chain from field to final product with full quality control and quality assurances, while also achieving a geographical spread enabling it to adapt to issues such as drought and floods that natural fibre crops are always susceptible to.

Super Absorbent Polymers (SAPs)
With their introduction in the mid-1980s, SAPs enabled the weight of baby diapers to be reduced by around two-thirds, requiring much less fluff pulp for effective absorption. They also convincingly prevented potential diaper leakage.
With a typical SAP amount of around 12 grams, today’s baby diapers not only successfully prevent urine leakage, but stay dry for hours and protect the skin from moisture, helping to avoid diaper rash.
One gram of SAP can absorb up to 500 grams of pure water and the liquid is not only absorbed but also locked up inside the particles even under external pressure. The result is a soft gel that is still capable of absorbing further liquid.
Today’s SAPs are made by polymerizing single molecules of sodium acrylate to form long molecular chains. The polymerization is activated by an initiator, and a crosslinker connects the single molecules together to form a polymer network. The crosslinker ensures that the granules remain insoluble when exposed to liquid, maintaining their absorbent properties and structure. Upon contact with aqueous liquid the sodium ions become disassociated, generating an osmotic pressure which drives more liquid into the SAP, binding it tightly within.
The SAP market was estimated to have a value of $6.5 billion in 2023 with production of approaching 5 billion tons and annual growth to 2030 projected at 8.1%. Key manufacturers include BASF , Evonik, Nippon Shokubai and Sumitomo.

Biobased alternatives
Over the past 20 years, numerous attempts have been made to develop replacements for SAPs derived from oil which are not renewable or biodegradable.
Agricultural giant Cargill, for example, attempted to make biobased acrylic acid from both 3-HP (3-Hydroxypropionic acid) and lactic acid in partnership with BASF and Novozymes. BASF, however, dropped out of the development in 2015 over concerns about the economic feasibility of the project. Undeterred, Cargill has subsequently licensed technology from Procter & Gamble that converts lactic acid into acrylic acid and is working with other companies to scale up the technology.
In 2021, Nippon Shokubai Europe also advanced its development of biobased SAPs by obtaining certification from the ISCC (International Sustainability and Carbon Certification) for a bio-based propylene for making acrylic acid.
Various other natural products have also been proposed as the basis for new SAPs, including algae, bamboo, chitosan, wheat gluten protein and natto – a fermented soy-based food that is popular in Japan.
Purdue University researchers, however, are now proposing cellulose extracted from hemp, refined through a sequence of treatments to create their patent-pending new SAPs.

Unique benefits
“Hurds and bast are two parts of the hemp plant that offer unique benefits for sustainable material development, particularly in absorption technologies,” says Senay Simsek, head of the Department of Food Science who is leading the development. “Hemp hurds, found in the inner woody core of the hemp stalk, are highly absorbent due to their high cellulose content and low lignin levels. This makes them an excellent alternative for superabsorbent applications. Hemp bast, the fibrous outer layer, while less absorbent, provides strength and durability.”
The cellulose extracted from these parts is particularly effective because its molecular structure can be modified to enhance its water retention capabilities, making it ideal for products requiring high absorbency.”
“The treatments we have developed break down the natural structure of the cellulose, increasing its surface area and porosity which allows it to absorb and retain more water,” Senay Simsek explains. “This a dramatically improves its ability to soak up and hold moisture, which is crucial for applications that demand high absorbency. The uniqueness of our technology lies in its versatility, making it highly tuneable for diverse applications of superabsorbent materials across various industries.”
Plans are now underway for the scaling up of production and the development team is pursuing further collaborations with industry leaders who share its vision of replacing traditional SAPs with these new biodegradable and sustainable alternatives.

 

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