Development of bio-composite mulch film from cotton gin wastes: Study of pesticide residue and outdoor stability and degradation.

Non-degradable plastic mulch films used in agriculture are polluting the environment by leaving residues and microplastics in the soil. They are also difficult to recycle due to contamination during their use. Biodegradable mulch films are needed as alternatives so that they can be used effectively during the growing season and later be ploughed to be degraded in soil. However, market-available so-called biodegradable mulch films are very slow to degrade in the natural environment and thus do not fit with crop rotation demands or annual cultivation. In this study, we have developed mulch films from cotton gin trash (CGT) and/or gin motes (GM) in combination with biodegradable polycaprolactone and demonstrated their effectiveness over 3 months in outdoor conditions. Both the stability and degradation behaviours of mulch film samples were observed when they were placed on top of the soil and buried in the soil, respectively. Pesticide residue analysis also was carried out on CGT powder to identify and quantify individual pesticides against a matrix of known pesticides. The mulch films prepared in this study showed comparable and stable mechanical properties compared to commercial biodegradable mulch film, though were much quicker to degrade when buried in the soil. No pesticides were detected in the CGT samples. The films produced were vapour-permeable and may be useful in practical agricultural settings by being able to maintain consistent soil moisture and allowing precipitation to penetrate gradually. The lab-scale production cost for the film was 98.8 AUD/kg, which could be lowered by integrating a continuous film line in large-scale production.

Sustainable Cotton Gin Waste/Polycaprolactone Bio-Plastic with Adjustable Biodegradation Rate: Scale-Up Production through Compression Moulding.

Cotton gin trash (CGT), a lignocellulosic waste generated during cotton fibre processing, has recently received significant attention for production of composite bio-plastics. However, earlier studies were limited to either with biodegradable polymers, through small-scale solution-casting method, or using industrially adaptable extrusion route, but with non-biodegradable polymers. In this study, a scale-up production of completely biodegradable CGT composite plastic film with adjustable biodegradation rate is proposed. First using a twin screw extruder, the prepared CGT powder was combined with polycaprolactone (PCL) to form pellets, and then using the compressing moulding, the pellets were transformed into bio-plastic composite films. Hydrophilic polyethylene glycol (PEG) was used as a plasticiser in the mixture and its impact on the biodegradation rate was analysed. The morphology of CGT bio-plastic composite films showed even distribution of CGT powder within the PCL matrix. The CGT incorporation improved the UV resistance, thermal stability, and Young's modulus of PCL material. Further, the flexibility and mixing properties of the composites were improved by PEG. Overall, this study demonstrated a sustainable production method of CGT bio-plastic films using the whole CGT and without any waste residue produced, where the degradation of the produced composite films can be adjusted to minimise the environmental impact.

Nanocellulose reinforced lightweight composites produced from cotton waste via integrated nanofibrillation and compounding.

Cotton is a natural fiber containing more than 95% of cellulose. With worldwide cotton consumption continuously increasing, the amount of cotton waste generated is enormous. Most of the cotton waste ends up in landfill or incinerators, resulting in a huge waste of this excellent natural resource. In this project, cotton waste was recycled to produce polypropylene nanocomposites. Instead of using the traditional two-step nanofiber extraction and compounding technique, an integrated process was adopted to combine nanofibrillation and compounding into one step. Results showed that cotton fibers with a slight prefibrillation and hydrophobic surface modification were successfully fibrillated into tens to hundreds of nanometers in width during compounding. The nanofibers reinforced polypropylene composites exhibited significantly enhanced tensile and flexural strength and moduli. For instance, when 30% fibers from bleached white and indigo-dyed denim fabrics were introduced, the tensile moduli of the resultant composites reached 4.57 and 4.59 GPa, respectively, compared to 1.60 GPa, the modulus of neat PP. Meanwhile, denim fabrics had a remarkable reinforcing effect on the composites' impact strength attributing to the hydrophobic indigo dyes that improved the interfacial bonding between cotton fibers and the matrix. The highest impact strength of denim reinforced composites was 4.96 kJ/m2 with 20% fiber loading; while the impact strength of neat polypropylene was 2.46 kJ/m2. The low water uptake of the composites further indicated the excellent adhesion at the filler/matrix interface. In general, a very promising processing technique to recycle cotton waste for high-value products was demonstrated.

Biodegradable UV-Protective Composite Film from Cellulosic Waste: Utilisation of Cotton Gin Motes as Biocomponent.

With an increase in environmental pollution and microplastic problems, it is more urgent now to replace non-biodegradable films with biodegradable films that are low-cost and from renewable resources. Cotton gin motes (GM), a type of cellulosic waste that is generated from cotton ginning, is an excellent candidate for fabricating biodegradable films due to its properties and abundance. In this study, GM was first mechanically milled into a fine powder, followed by compounding with polycaprolactone (PCL) and extruded to produce composite pellets which were then compress-moulded into composite films. This environmentally friendly process used physical processing and all the materials were consumed in the process without generating any waste residue. To improve the compatibility and mixing properties between GM and PCL, the use of a plasticiser (polyethylene glycol) was considered. A high content of GM powder (up to 50%) was successfully compounded with the polymer. The SEM images of the composite films showed smooth surface morphology and well-distributed GM powder in the PCL matrix. The added advantage of compounding GM with the polymer matrix was that the composite film developed UV-shielding properties due to the presence of lignin in the GM powder. This property will be critical for films used in UV-resistance applications. Furthermore, the composite even with high GM content (50%), showed good mechanical properties, with 9.5 MPa yield strength and 442% elongation, which was only a 50% decrease in elongation when compared with clear PCL film. The soil biodegradation of GM composite films under controlled temperature (20 °C) and humidity (50%) for 1 month showed around 41% weight loss. Overall, this study demonstrates the potential of GM to be used as a biodegradable and UV-protective composite film for a wide array of applications, such as packaging and UV-protective coverings.

Nanocellulose from recycled indigo-dyed denim fabric and its application in composite films.

In this study, nanocellulose was extracted from indigo-dyed denim fabric and the resultant nanocellulose properties were evaluated in comparison with those derived from bleached cotton fabric and wood pulp in order to investigate the potential of recycling denim waste for nanocellulose production and application. Sulfuric acid hydrolysis and (2,2,6,6-tetramethylpiperidin-1-yl) oxyl (TEMPO)-oxidation were utilized to produce cellulose nanocrystals (CNC) and cellulose nanofibers (TOCN), respectively. A stable CNC suspension with blue color was obtained after acid hydrolysis and the TEMPO process yielded colorless TOCN. The denim-derived nanocellulose possessed similar yield, morphology, size, crystallinity, and thermal stability to those derived from bleached cotton but higher crystallinity and thermal stability compared to the nanocellulose from wood pulp. When used to reinforce polyvinyl alcohol film, the blue indigo-CNC not only enhanced mechanical properties of the film but also provided the film with outstanding UV blocking.