Promoting pulp and paper mill material circularity: functionalised organic-inorganic cellulosic mulch films

Water scarcity, fertiliser run-off, and weeds competing for resources reduce forestry and agricultural productivity. Conventionally, fossil-fuel-based synthetic mulch films have been used to mitigate soil water loss, as a matrix for the slow-release of fertiliser, and for UV-vis light blocking to retain water, limit nutrient loss and prevent weed growth, respectively. However, microplastics remaining from poorly biodegradable mulch films, and the release of typical mulch film UV-absorbent additives bioaccumulate, which harms the environment. Concurrently, paper and pulp mills (PPMs) generate substantial amounts of inorganic and organic wastes, such as cellulose fibres, lignosulfonate (LS), and titanium dioxide (TiO₂), which are useful components for making functional mulch films but are either landfilled or burned, further polluting the environment. The aim of this study was to improve the material circularity within the PPMs by connecting waste stream sinks to source streams in the plantation through the formation of a green, soil-degradable mulch film (MF) with water retention, fertiliser slow-release, and UV-vis blocking capabilities. The aim was achieved by identifying and selecting reinforcing and plasticising additives based on the compounds found in PPM waste streams for the formation of a baseline mulch film. The mulch film’s composition was further optimised by varying the crosslinker, reinforcer, and plasticiser concentration. In addition, the synergistic UV-vis blocking ability of lignosulfonate coated TiO₂ (LS@TiO₂) was investigated by evaluating the performance of the MFs with and without added LS@TiO₂. And the performance of the optimised films was benchmarked against the baseline and commercially available control mulch films. Urea (40%NaCMC) served as a model fertiliser for the slow release, and commercial sodium carboxymethyl cellulose (NaCMC) at 2%wt/vol as a proxy for functionalised cellulosic waste found in PPM waste streams, while 10%NaCMC citric acid (CA) was used as a crosslinker. The best reinforcing fibre at 10%NaCMC between microfibrillated cellulose (MFC) and cellulose nano fibres were identified in a one-factor-at-a-time experiment. Similarly, the plasticiser at 30%NaCMC was selected among xylitol (Xyl), sorbitol, glycerol, and glucomannan. The mulch films were assessed for water swelling ratio (SR), water solubility after 48 hours (sol%), and water vapour permeability (WVP). The CA MFC and Xyl concentrations were optimised by varying them 6.59–23.4%NaCMC, 0.796–9.20%NaCMC, and 3.18–36.8%NaCMC, respectively, in a central composite designed experiment, and using response surface methodology in Statistica to maximise SR, WVP, tensile strength (TS), and elongation at break (EaB), while minimising sol%. The best performing mulch film (BF) was found to have a composition of Xyl:CA:MFC 10:10:2.5 %wt/wtNaCMC with SR of 84%, but had a poor EaB, 35.1%. The TS (13.7 MPa) was comparable to other biodegradable films. The mulch films displayed a rapid complete soil degradability within 3 weeks. Adding 5%NaCMC LS@TiO₂ to the BF reduced UV-vis transmittance in the photosynthetically active region from >70% to below 0.5%, demonstrating weed growth prevention potential, without drastically impacting other properties. All films had a high water solubility, >60%, and consequently failed to achieve slow release of urea in water (>80% released within 20 minutes). Cellulose acetate coatings increased the time it took to release >80% of the urea by 15–40 minutes. By XRD and ATR-FTIR analysis a goldilocks concentration of 1.0 g·L⁻¹ LS coated onto TiO₂ was found to have both bridging bidentate and monodentate coordination bonds, resulting in a decreased crystal lattice strain and more Ti³⁺ self-doping during coating for better UV-vis blocking performance. The synergistic performance of LS@TiO₂ showed great potential for UV-relevant applications such as plastic degradation protection and catalysis in addition to MFs. The study has demonstrated the potential for the utilisation of PPMs waste streams through MFs for improving forestry/agricultural resource use, thus promoting material circularity. However, there is a need for further research on improving the MFs attributes by reducing the water solubility.

Grantor dc:publisher

Stellenbosch : Stellenbosch University

Year dc:date.issued

2026

Author dc:creator

• Du Toit, Jacobus Christiaan Faure

Advisors dc:contributor.advisor

• Chimphango, Annie Fabian
• Mapholi, Zwonaka

Language dc:language.iso

en

Repository record dc:identifier.uri

https://scholar.sun.ac.za/handle/10019.1/135776

OAI identifier oai:identifier

oai:scholar.sun.ac.za:10019.1/135776