Cellulose Flame-retardant Film using Lettuce Residue as Raw Material

This study had the objective of developing a product having as raw material the residual parts of lettuce, which are its roots and residual leaves. To this effect, a thought experiment was performed in order to create a flame-retardant cellulose film using a green-sourced, vegan, and biodegradable raw material. This product was designed with the goal of protecting furniture, however, the product could also be effectively applied in paintings and other cellulose-based materials. A production line was proposed, and through economic analysis, it was determined that the manufacture of this product is profitable, with a production price of 2.15 € per unit (m2) and a retail price of 6 € per unit (m2). This flame-retardant film is unique compared to the others on the market, which are mainly plastic-based, since it is developed from a biodegradable material, making it a sustainable option for a zero-carbon economy. This film has a fire delay of approximately 4.5 minutes when exposed to fire.


Introduction
Necessity creates business and functionality extends it. The value provided by the developed product comes from its flame-retardant properties, while its functionality is enhanced by the invisibility of the film. While the flame-retardant film was never actually created, the final product, should it ever be manufactured, would be able to protect wood, artwork, and valuables. Its fire protection properties protect the piece from heat damage without affecting its appearance as it is a transparent film (Carosio et al. 2016;Dhali et al. 2021; Barhoum et al. 2019). The developed product is not the first flame-retardant film on the market; however, it has unique features, its biodegradability and sustainable raw material.
Finally, manufacturing the cellulose flame-retardant film allows for the future company to maintain a lower investment in marketing since trying to acquire a market share in the more competitive clothing or sport equipment markets would require a far larger commercial campaign than establishing a niche product on the market. According to APSEI (Associação Portuguesa de Segurança), thousands of household fires occur every year in Portugal. These fires represent a hazard to its occupants and a significant risk to the property's valuable assets. Therefore, there is a necessity for an affordable flameretardant that can provide substantial protection while also being aesthetically appealing since the object will be permanently exposed.

Selection -flame-retardant cellulose film
The selected idea has, from the research, a lot of potential to gain a substantial market share because it comes with the unique feature of being wholly renewable and easy to use. The product will protect everyday objects from damage by fire and can be used on most organic surfaces. Since the film is a thin sheet composed of one part cellulose and one part binding agent, it uses drastically less cellulose than many of the other products that were looked up. Therefore, it will be possible to produce and sell more to increase the profit margin. By analysing other flame-retardant films on the market, it's possible to conclude that they are plastic-based and, therefore, non-biodegradable (Shanghai Huzheng Nano Technology Co., Ltd. UL94 VTM-0). Due to concerns about plastic's impact on earth's ecosystems and human health, there has been a public push to minimise the use of this material in several products. This concern, compounded with the desire to better manage the use of natural resources, means that this plant-based film made from agricultural waste can stand out in the market by appealing to the consumer's environmental awareness.

Flame-retardant Film Conception
To create the flame-retardant film, it will be essential to divide the project into two parts, namely the extraction of cellulose nanofibres and the film's design. For the flame-retardant cellulose film production, a solution of CNF and a solution of montmorillonite bentonite (MTM) are prepared. The cellulose solution will be prepared by dissolving 1wt% of the extracted cellulose nanofibres in deionised water under high shear mixing. A 1wt% hydrocolloidal MTM solution was prepared by dispersing 10g of MTM in 1L of deionised water under vigorous stirring. The cellulose solution will be slowly added to the MTM dispersion until a 1:1 wt ratio and then stirred for 24h. The mixture is then poured into a Teflon mould and dried in an oven at 55°C until it reaches a thickness of 50-60μm (Carosio et al. 2016). To industrialise this method, the solutions will be prepared in baffled stainless-steel tanks with continuous stirring. The cellulose solution will then be transferred to the MTM solution and mixed until homogeneous. To create the flame-retardant film, the mixture will be extruded onto a conveyor belt which passes through an oven until thickness specifications are met.

Product manufacture
The manufacture of this product will be carried out in three parts. The first stage consists of the pre-treatment of the raw material. The second consists of the solvent treatment to extract the cellulose nanofibres. The third is the conception of the film, together with clay and water.  As observed in Figure 1, the pre-treatment (the first stage of the process) consists of sieving the lettuce dirt in a rotatory sieve while cleansing it with a hose jet. It is subsequently dried before the milling process, which turns the lettuce residue into a chip. The main idea was to use the saturated air to heat the stirred reactors in the next phase of the process, which is the chemical treatment. It should be noted that the heat capacity of the air is not high, which does not provide much energy in the form of heat to the reactors channeled to heat them, but it was accounted as an energy-saving process. However, this idea was quickly discarded since this water, coming from the air saturation in the dryer, will have another beneficial and better use, washing the lettuce in the first stage of the process. Related to the chemical treatment of the raw material, in the first stirred reactor, the "alkali" treatment will be carried out on the chips, as explained before. After each treatment, the solvent mixture is drained through the reactor base, and a filtering mesh retains the chips (product of interest in this process step). The same process will happen in the next reactor with the "bleaching" treatment. The lyophilization freeze-dries the pellets, and then they move on to the "acid hydrolysis" treatment, where the reactor will work in the same way, filtering the pellets, but each time, with a much narrower filter mesh, after leaving the reactor, the effluent has to be neutralized, this is done by washing it a total of 10 times with 4,3m 3 reverse osmosis water. In the original lab scale process, this was done with deionized water instead of reverse osmosis water; however, since the projection of the manufacturing facility already accounts for a distilled water production centre this option was favoured as a more economically viable alternative. This decision was considered to be feasible for industrial-scale adaptation due to the somewhat similar pHs of both samples of water, which is the dominant factor in a neutralization reaction (Kulthanan, Nuchkull, and Varothai 2013;Riché et al. 2006;Rudyk et al. 2022). The solid mixture is then centrifuged to induce particle sedimentation.
The liquid containing the cellulose nanofibres will finally be processed in a dialysis machine. After obtaining the cellulose nanofibres, in a stirred reactor, the film mixture is manufactured with water, montmorillonite clay and cellulose nanofibres to obtain the film, which will leave the treatment station on a Teflon coated conveyor belt, which passes through an oven. The final product will be sold by area. To assess how many square meters of the film are contained within a kilogram, Equation (1) was used. The film nanofibre density (ρfilm) was estimated to be 1,575kg/m 3 due to it being 50% (w/w) cellulose (1,500kg/m 3 ) (Hermans and Vermaas 1946) and 50%(w/w) a mixture of slightly wet clay (1,650kg/m 3 ), the thickness of the film was considered to be the midpoint of the expected range (55μm). The m 2 /kg ratio was determined to be 11.54. In Equation (1), represents the 50-60μm thickness.

Application procedure
The adhesive used in the application of the flame-retardant film should be selected in accordance with the surface of application. For wood-based products, which are predicted to be the main market for this product, a methylcellulose water-based solution, commonly used as a wood and cellulose content material, "glue," would be a suitable binding agent (Kumar et al. 2012). Since the binding agent is a separate product from the flame-retardant film, it's considered to be out of the scope of this article.

Product specifications
This cellulose film has flame-retardant properties that, according to Carosio et al. (2016), delay the ignition time by approximately 4.5 minutes. To achieve its best resistance, the film needs to be made up of one part cellulose nanofibres (CNF) and one-part Montmorillonite Bentonite solution (MMB + water 1:1). In addition to the chemical characteristics, the film must be 50-60μm, which allows it to be transparent and applied smoothly and continuously on the intended surface. Table 1 presents additional data that constitutes the flame-retardant properties of this film.
The following values were obtained by cone calorimetry. Through Figure 2, it is possible to observe how this material will affect the general appearance of the object on which it is applied. The material is transparent, which means that the application of this film does not affect the appearance of the piece of wood.

Water and Reagents recuperation
The method that is going to be used in this project to purify the water of chemical agents used during the extraction process, such as sodium hydroxide ( ), sodium hypochlorite ( ) and sulfuric acid ( 2 4 ), is going to be reverse osmosis. This method consists of a semipermeable membrane with a pore size of 0.5nm, with an area of high concentration on one side of the membrane (contaminated water) and an area of low concentration. Only the water with a low concentration of contaminants will pass through. It prevents the passage of chemical agents and other substances that are undesired. To avoid biofouling (or membrane fouling), a pre-treatment such as a filtration process must be implemented. The water passes through a filter, preventing larger particles such as organic compounds or even solvents used during the process from interfering in reverse osmosis. To accelerate the filtration process, an organic, eco-friendly coadjuvant (land of diatoms) will be used so that the obstruction of the filter is avoided by increasing its porosity. It will also increase the longevity of the membranes used in the reverse osmosis process, improve the water's quality, and decrease the maintenance cost. At the end of the reverse osmosis process, the water will be tested with ultraviolet light to confirm its purity.

Details of production on a large scale
To analyse how much this product is worth on the market and the possible profit margin to be obtained through the use of this raw material (lettuce root and residual leaves), it was decided to scale up to an industrial perspective. This led to the creation of a company headquartered in the district of Leiria, in Alcobaça. The factory would work 20 days a month and 24 hours a day with three 8-hour shifts per day. It is important to note that the market study was conducted between December 2021 and January 2022. The information given below represents only the final results of the economic analysis. A more in-depth evaluation can be found in the given complementary material. To produce the flame-retardant film as previously mentioned, several pieces of equipment must be procured; the individual pieces of equipment acquired, as well as the costs related to its acquisition, are described below in Table 2. It was also decided to establish a water purification system along the manufacturing process. The equipment required for this endeavour and its costs is shown in Table 3.

Reagents
All of the final prices referred were calculated considering the amount of volume of pure reagent needed and its price on the market. The water contribution is going to be discussed later on. For the alkali treatment, a solution of 0.5mol/L (CAS 1310-73-2) is needed, with a ratio of 1:50w/v. This means that per day/batch (and considering that this treatment needs to be done thrice), 64,406L are necessary. Therefore, the final annual cost of sodium hydroxide is 124k€. The same ratio of 1:50w/v has been considered for the bleaching treatment, which leads to daily consumption of 64,406L of (CAS 7681-52-9), reflected in a final annual cost of 194k€. For acid hydrolysis, the ratio is 10mL/g acid-to-cellulose. Therefore, daily it is necessary to use 858,75L of 2 4 (CAS 7664-93-9) 0.98%, which leads to an annual cost of 35k€. This cost was lastly consulted on 13-01-2022. Its price is not constant since it is listed on the stock market. To conceive the nanofilm, 20.6 tons of Montmorillonite Bentonite Clay (CAS 1302-78-9) powder are required, with an annual cost of 5.5k €.

Marketing / Distribution
For marketing, as this product is intended to be purchased by companies (B2B), not direct consumers, we must have a market study and product placement done by someone with a portfolio of clients in the wood industry (carpenters). With this in mind, it was decided that a hardware distributor for furniture would provide the best product placement. As it is going to be mentioned further, the selling price for the distributor is going to be 6€/m 2 . In addition to working with a distributor, the company would participate in fairs and other events to present the flame-retardant film to potential business partners in the industry. To make sure this is properly done, an initial budget of 100k€ will be allocated to implement the company in the market. After that, a yearly budget of 30k€ will be allocated to maintain the acquired market share.

Retail price and profit
In order to start not only a fully operational plant but also an appropriate distribution network, several initial investments in machinery for the plant must be considered, a truck for raw material collection and transportation, a warehouse in which to base the operations, the costs for an initial marketing campaign, a safety net of 50k€ to deal with unforeseen expenses and a start-up cost equal to a month of operational costs to make sure the plant will be fully functional by day one. The total investment cost would equal 1,6€, and this would be financed by a loan with an effective interest rate of 12% a year, to be paid in two years (Table 4).

Safety net 50,000€
Total 1,587,370€ To maintain the business fully operational, it's necessary to factor in the costs of reagents, machinery maintenance, truck maintenance, water, electricity, wages, raw matter, quality control, marketing and real estate tax. These costs would amount to 1,024,401€ per year ( Table 5).
The projected plant, if fully operational, would produce 41.22 metric tonnes or 475,844m 2 per year. The product will be sold to distributors at the final price of 6€/m 2 . Thus, it can be concluded that the factory would generate an income of 2,855€/year if all the stock is liquidated. If the stock isn't completely sold, however, the business would need to sell 35.67% of the produced film to break even, or it could sell all of the stock at 2.15€/m 2 . Assuming that the stock is fully liquidated, the company would generate a taxable profit of 1,836,619€ every year, except for the first two years in which the initial loan must be fully repaid, and the taxable profit would be 897,710€. To the taxable profit, the IRC (Portuguese corporate profit tax) and a Municipal Tax must be deducted, 21% and 1.5%, respectively. The final net profit would be 695,725€ in the first two years and 1,423,380€ in the years after.

Market placement
The authors are aware that there are other flame-retardant films on the market. What distinguishes the current product from its competitors are the biodegradable, non-pollutant, plant-based/vegan properties (Bio raw material). Plus, the conception of this product uses agricultural waste as a raw material, which is a sustainable form of business. The competitive market offers various forms of plastic-based flame-retardant films (Shanghai Huzheng Nano Technology Co., Ltd. UL94 VTM-0) that will be pollutant to the environment and nonbiodegradable. They are sold for an estimated value of 2.56€/ 2 online, which approximately doubles the price when considering the shipping and import fees.

Conclusions
Carrying out this project proved that it is possible to use uncommon raw materials to create new products with value on the market and a solid profit margin. Plus, the conception of this product uses agricultural waste as a raw material, which is a sustainable form of business. Besides having a green sourced raw material, this project always looked up to include methods 1 EDP. n.d. of resource recovery, such as water and heat exchange (not efficient in this case). This will not only contribute to long-term savings but also diminish waste. If all the stock is liquidated, the factory will generate an income of 2,855€/year. However, if the stock isn't completely sold, the business would need to sell 35.88 % of the produced film to break even, or it could sell all the stock for 2.15€/m 2 . Considering a market analysis, it became clear that there are, in fact, other flame-retardant films; however, they are not biodegradable, vegan or green in origin like this product. The product retails at 6€/m 2 for its distributor. However, there is a good margin to lower the final price if the sales do not meet expectations due to the company's break-even price (2.15€/m 2 ) being lower than the selling price of other similar films on the market that cost 5.12€/m 2 (including shipping and import fees). It is then possible to conclude that there is space on the market for this film to be profitable and, more importantly, usable since its purpose is to preserve and give longevity to furniture and valuables. between tires, simple diesel, insurance and general maintenance (oil, mechanic, inspection and tax). Four 195/70 R15C tires should cost around 280€, while insurance costs would be 400 € and general maintenance 600€. Finally, assuming a price of 1.50€/L, the fuel cost would be 4,940k€ 3 .

Quality control
For this matter, a specialised laboratory, "Instituto de Ciência e Inovação em Engenharia Mecânica e Engenharia Industrial" (INEGI), is going to analyse samples of this product by conducting a weekly cone calorimetry mechanical test in order to guarantee the quality of the manufactured product. These quality control experiments may guarantee this product's continuous improvement and help detect malfunctions in the production process. This requires 442.86€ monthly, which reflects 5,314k€ yearly.

Water
Water is crucial to manufacturing cellulose nanofibers, mainly in the extraction process from the lettuce. Approximately 129m 3 are required daily to wash the lettuce; preparing the , and solutions require nearly 129m 3 of water daily split evenly among both. Regarding the manufacturing process itself, the sulfuric acid used in the acid hydrolysis phase needs to be diluted by 1.7m 3 per day. The neutralization reaction that occurs prior to liophilization is done exclusively with reverse osmosis water, and this water is readily available; however, this process will further increase the overall need for water by 4.3m 3 per day. Preparing the clay from its initial powder also requires water at a rate of 1.7m 3 per day. The total volume of water required for the whole process is 261m 3 , with the cost of water in the municipality of Alcobaça being 0.85€/m 3 plus a monthly fee of 17.63€. These costs would add to a total of 221.76€/day or 53,434k€/year 4 . Taking into account the above considerations, open tanks were acquired to store rainwater. This water will be used to clean the lettuce in the first step of the process by hose jet in the rotational dirt sieve and the recuperated water from the dryer. In order to calculate how much rainwater could be collected per month/year in Alcobaça, data was researched in Weather Spark and IPMA (Instituto Português do Mar e da Atmosfera).  Table S2: Rainwater per month in Alcobaça h(m) -(rainfall) water height that falls by m 2 , V (m 3 ) -volume of rain water.

Water recuperation
Since the environmental and economic cost of using such a large amount of water would be significant, it was decided to implement water-saving measures. The first measure was to condense the water in the moist air that exited the tubular dryer, a measure that saves, on average, 8.16m 3 or 6.94€ every day. The second measure was to implement a reverse osmosis plant for water treatment that could retrieve up to 75% of water processed. The retail cost for the main reverse osmosis equipment, which can filter 264 m 3 /day, is 48.8k€ (IDEAS Y DESARROLLO DEL AGUA S.L., OI4380); this equipment uses 12 membranes that cost 12k€ (IDEAS Y DESARROLLO DEL AGUA S.L., RO4037). The retail cost for the pre-treatment filter is 3.5k€ and can filter 360m 3 /day (IDEAS Y DESARROLLO DEL AGUA S.L., FI 1006-06). For the pump selection, it was decided to contact a company that provides personalised industrial pumping solutions. After researching a 50bar pump that would meet the given specifications, it was decided to use two D6-50x2 pumps (Depump Technology Shijiazhuang Co., Ltd.D6-50x2) operating in parallel to be obtained at the cost of 8.4k€. At the end of the process, an ultraviolet-light would be used for quality control, costing 305€ (JARPIS, S.L., 71427), and 30 tanks would be used to store the water for a price of 3.2k€. (Dezhou Huili Water Tank Co., Ltd., HL-FRP). The total investment cost of the reverse osmosis plant is 76k€. The annual cost of electricity is 30.5k€ (working 22 hours a day and 240 days a year), but since the plant saves 75% of the daily water consumption (260m 3 ), the plant's financial impact is a net gain of 9.3k€. When also considering the water obtained from the dryer, 1,958m 3 /year, the company can save up to 48,930m 3 of water every year.