After the journey of a nano-material from wheat to plastic

After the journey of a nano-material from wheat to plastic

Stringent chemical treatments of bleached pure pulp are the most common method used to obtain cellulose nanofibers. These operations incur significant expenses and harm the environment.

Study: Production of Lignocellulosic Nanomaterials from Wheat Straw by Pre-treatment with Paraacetic Acid and their Application in Plastic Compounds. Image Credit: OskarsK / Shutterstock.cAround

A research paper published in the journal Carbohydrate Polymers reports the synthesis of lignocellulosic nanofiber (LCNF) using wheat straw (WS) feeds. LCNF shows great promise in bioplastics applications.

Cellulose nanofibers – a green alternative to plastic

The demand for products manufactured from green and renewable sources is increasing. Cellulose, an abundant natural resource, is renewable, non-toxic and biodegradable.

The accumulation of plastic waste due to the regular dumping of non-biodegradable plastics, causing severe pollution to terrestrial and marine environments. Cellulose nanofibers (CNFs) are a more environmentally friendly alternative to plastics in a variety of applications.

The poor manufacturing scale and large production costs of cellulose nanofibrils prevent them from reaching their true potential in various industries. Therefore, inexpensive and efficient production techniques must be developed to encourage the use of cellulose nanofibers as viable alternatives to plastics.

How are cellulose nanofibers made?

Cellulose nanofibers are usually made using bleached kraft fibres, a high-quality raw material that provides almost pure cellulose. Kraft fibers are mechanically shaken to extract cellulose nanofibers.

Mechanical fibrillation processes require a great deal of energy. To enhance the fibrillation phase and reduce energy needs, pre-treatment procedures may be used.

The widely used pretreatment process for the manufacture of cellulose nanofibers is the oxidation of TEMPO (2,2,6,6 Tetramethylpiperidin-1-oxyl). This technology catalyzes the oxidation of cellulose fibers, increasing the charge density on their surface. This ultimately leads to the electrostatic repulsion between the cellulose nanofibers and results in large fibrillation outputs.

Disadvantages of using TEMPO

The downsides to using TEMPO oxidation technology include significant chemical expenditures and the toxic nature of TEMPO. Moreover, costly removal methods such as dialysis are required to remove small amounts of TEMPO residues from cellulose nanofibers, which makes scalable application of this approach very challenging.

The fabrication of cellulosic nanofibers needs a more economical conversion technology if the scalable implementation of cellulosic nanofibers is to be achieved.

Development of Lignocellulosic Nanofibers with Wheat Straw

To avoid the drawbacks of TEMPO oxidation, LCNF fabrication may be key. Production of LCNF requires less expensive raw materials bearing lignin rather than completely bleached pulp. Furthermore, moderate treatment actions of LCNF may suffice, resulting in the production of high-output products consisting of lignin, cellulose, and hemicellulose components.

Wheat production results in a by-product known as wheat straw. WS contains the stem left after harvesting the wheat grain.

Wheat straw serves as a suitable raw material for the manufacture of LCNF because it is abundantly available. Being an agricultural residue, the costs of using wheat straw are much lower than the costs of other raw materials.

Therefore wheat straw provides an abundant and low-cost source of non-wood fiber for LCNF production.

Advantages of peracetic acid treatment

Peracetic acid (PAA) is a biodegradable reagent that can participate in reactions with lignocellulose biomass at temperatures below 100°C. Therefore, the use of PAA for LCNF pretreatment appears to be a viable strategy.

Processing of PAA produces greater yields due to its higher antioxidant capacity, which selectively eliminates lignin while preventing the solubilization of carbohydrates.

Peracetic acid can oxidize the reduced parts of carbohydrates, resulting in a negative charge on the surface. This can assist the nano-fibrillation process and produce stable colloidal suspensions.

Compared with the traditional TEMPO oxidation process for nanocellulose synthesis, treatment with paracetic acid offers many benefits. PAA has less toxicity and is more environmentally friendly than TEMPO, and allows more control over the removal of hemicellulose and lignin from the pulp.

The structure and content of nanofibrils produced by peroxide acid treatment are significantly different from cellulose nanofibrils produced by conventional TEMPO oxidation.

Applications of cellulose nanofibers in plastic composites

Cellulose nanofibers can be used as reinforcements in plastic composites to reduce the amount of petroleum components while also improving the properties of plastic composites.

Hydrophilic and biodegradable polymers, such as polyvinyl alcohol (PVA), exhibit weaker mechanical properties than their synthetic alternatives, necessitating the addition of various additives to improve their qualities.

Higher aspect ratios and better interactions of the interface with the polyvinyl alcohol group enable the cellulose nanofibers to enhance the mechanical properties of the PVA nanocomposites when introduced in small amounts (<5% by weight).

Results

The team demonstrated that it is possible to synthesize lignocellulose nanofibrils with excellent plastic reinforcing properties using low-cost agricultural waste. They achieved this by separating the alkaline peroxide fibres, after which the LCNF was treated with PAA.

The lignin and hemicellulose portions of the nanofibers, formed using wheat straw, which were needed to enhance productivity, were retained.

While the PAA treatment produced nanomaterials with lower charge density on the surface than TEMPO oxidation, the material properties were not affected. All samples showed high colloidal stability under aqueous conditions.

Materials treated with PAA have improved thermal stability due to lower charge density and increased lignin level. Moreover, regardless of the charge density, all nanofibers are well dispersed in the polyvinyl alcohol matrix. This enhanced the tensile strength and Young’s modulus of the compounds, demonstrating a unique case of simultaneous stiffening and stiffening.

The study established a new method for producing lignocellulose nanofiber from agricultural waste. This economically feasible approach has the potential to enable scalable production of nanomaterials with commodity product costs, allowing their use in high-volume industries such as bioplastics.

reference

Pascoli, D.U., Dichiara, A., Roumeli, E., Gustafson, R., & Bura, R. (2022). Production of Lignocellulosic Nanomaterials from Wheat Straw via Peroxyacetic Acid Pretreatment and Application in Plastic Compounds. Carbohydrate polymers. Available at: https://doi.org/10.1016/j.carbpol.2022.119857

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