Sugarcane Bagasse Fibers Derivatives and Their Application in Chitosan-Based Composite Films for NPK Fertilizer Release

Encapsulation and release of NPK fertilizer by composite films were systematically demonstrated by casting dispersions of chitosan (CS) and sugarcane bagasse (SCB) derivatives (holocellulose (HC), cellulignin (CL), and cellulose (CEL)) fibers under varied CS-to-NPK and CS-to-SCB derivatives mass ratios. SCB derivatives were obtained from sugarcane bagasse as agricultural waste by following the alkali dissolution (4% NaOH, 70 °C for 5 min), sodium chlorite delignification (1.4% NaClO2, pH 3.5, 70 °C, 5 h), or from a combination of both. Nutrientadsorption capacity can be tunable by the chemical composition of SCB derivatives, i.e., fibers with noncellulosics exhibited higher adsorption capacities while the absence of noncellulosics lessened their adsorption capacity. Oven-drying (60 °C, 5 h) of optimal 1:0.5 CS/NPK film-forming solution produced highly uniform films with shape with 0.31 ± 0.02 mm thickness while increasing fiber content in the solution to 25 or 50% prevents films retraction effect. The release of highly water-soluble NPK fertilizer from these composite films was lower with hemicelluloses (52-82%) or lignin (55-92%) contents in SCB fiber than in noncellulosics absence (71-100%), thus could be tuned by varying the chemical composition SCB derivative, followed by a quasi-Fickian diffusion mechanism in water.


Introduction
Brazil is characterized by its agricultural activity as one of the principal economic bases of the country. 1 Soil fertilization is one of the factors contributing to these criteria. 2However, Brazilian agriculture is responsible for 7% of the world's fertilizer consumption, preceded by China, India, and the United States, with approximately 70% of the used amount being imported, 3 making the country highly dependent on imports.Additionally, chemical fertilizers are used in excessive and disproportionate quantities, resulting in fertilizer losses from 40 to 90%, causing environmental and financial adverse impacts. 4Therefore, there is a clear need to explore new agricultural technological practices to reduce or replace the use of chemical fertilizers and, consequently, mitigate their imports.
Enhanced efficiency fertilizers (EEFs) are specifically designed formulations that control or delay the release of nutrients aiming to enhance nutrient use efficiency without suffering from agricultural input losses. 5Over time, various materials have been explored for EEFs production.[10][11][12][13][14] However, most of these EEFs need additional chemicals (i.e., sealing agents, synthetic polymers, crosslinking reagents, polymerization initiators, organic solvents, etc.) or are fabricated through complex production processes, add extra expense to the final product, and can be harmful if accumulated in the environment.In recent years, bio-based polymers such as alginate, 15,16 starch, [17][18][19][20] chitosan (CS), [21][22][23][24] polyhydroxybutyrate, 25 and cellulose 26,27 have been investigated to overcome these economic and environmental obstacles.Chitosan-based materials have garnered considerable attention due to their ability to interact with anionic species, 28,29 besides their known characteristics of biodegradability, [30][31][32] renewability at relatively low cost, 33 and non-toxicity. 30However, these CS-based materials suffer from drawbacks such as poor tensile strength and insufficient elasticity. 34Combining CS with other polymers could be a suitable way to solve this problem. 35ugarcane bagasse (SCB), the most abundant agricultural biomass in Brazilian agriculture, could be applied as reinforcing fiber to prepare composite materials with enhanced properties due to their high content of cellulose, 36 which is characterized by being fibrillar and crystalline. 37After cellulose (42%), hemicelluloses (28%), and lignin (22%) are the most abundant components found in SCB. 38The large functional groups on this lignocellulose complex, such as hydroxyl, carboxyl, carbonyl, phenol, methoxyl, quinone, and others, 39,40 make SCB possible to act as adsorption material for binding to a variety of ionic species. 41Besides, natural fibers are also known to be incompatible with polymeric matrices due to their hydrophilic characteristic 42 and the presence of noncellulosics on their surface. 43][46][47] Thus, this work aimed to design new composite films based on CS and chemically modified SCB fibers to exhibit tunable release capability.First, alkali and oxidation treatments of SCB were performed to remove lignin, hemicelluloses, or both.Then, cast films were obtained by mixing different amounts of SCB derivatives into CS solution with NPK fertilizer in various loadings, intending to delineate the effects of noncellulosics on composite properties, mainly controlled release properties.For agriculture crops, complete fertilizer such as NPK provides the three most important macronutrients for the growth and development of plants. 48Thus, the prolonged delivery of this agricultural input is particularly of interest to avoid loss during fertilization.

Material
The SCB was gathered from the 2017 harvest (São Paulo, Brazil).Chitosan powder (C 6 H 11 O 4 ) n (Polymar S/A, 85% deacetylation degree and average molar mass 1.8 × 10 5 g mol −1 ), glacial acetic acid, sodium hydroxide, potassium chloride, monobasic sodium phosphate, ammonium sulfate were purchased from Synth (São Paulo, Brazil).Sodium chlorite was obtained from Sigma-Aldrich (São Paulo, Brazil).Ammonia High Range reagent was purchased from Hanna (São Paulo, Brazil), Fósforo UV-PP Kit from Gold Analisa (São Paulo, Brazil), and used to determine ammonium and phosphate, respectively.All reagents were of analytical grade and used as received.The water used was from the Milli-Q water purification system (EMD, Millipore Corporate).

Adsorption capability of the SCB derivatives
The ability of the HC, CL, and CEL fibers to adsorb nitrogen (NH 4 + ), phosphorous (H 2 PO 4 -), and potassium (K + ) nutrients were systematically investigated by aqueous adsorption studies adapted from a previously reported method. 50Briefly, each SCB derivative (50 mg) was put into 100 mL of multi-element solution at 10 mg L -1 of NH 4 + , H 2 PO 4 -, and K + ions with vigorous shaking at pH 3.5.This process was conducted at varying ions-substrate contact times (10-60 min) to find the optimal time condition for the saturated adsorption.Suspensions were rapidly filtered at the end of time intervals to separate the phases.Finally, the collected SCB derivatives having adsorbed nutrients were dried and stored under a vacuum for further characterization.

Preparation of films
Chitosan powder (2.0 g) was solubilized into 100 mL aqueous acid acetic solution at 0.5% v/v using magnetic stirring under 25 ºC for 24 h.Next, NPK fertilizer (N-P 2 O 5 -K 2 O mass ratio of 1:1:1) was dispersed adequately in 20 mL CS solution at loading levels of 0.1-0.4wt.% under vigorous stirring to form homogeneous filmforming solutions.Next, the film-forming solutions were homogenized for 15 min using the Ultra Turrax disperser (15.000 rpm, IKA T 25 digital) and then poured into polystyrene Petri dishes (90 mm diameter × 15 mm deep) and dried at 60 °C for 5 h.After drying, the resulting Vol.34, No. 5, 2023   CS/NPK films were stored for characterizations and denoted by their fertilizer loads, i.e., 1:0.25, 1:0.5, 1:0.75, and 1:1 CS/NPK.Lastly, composite films were prepared by adding the HC, CL, or CEL fibers at 5, 10, 25, and 50 wt.%into 20 mL of 1:0.5 CS/NPK solution, followed by the same homogenization and drying procedures as already described.

Solid-state characterizations
Fourier transform infrared spectroscopy (FTIR) FTIR samples were analyzed by grinding into KBr pellets (1:100, m/m), and the spectra were collected using a Bruker Tensor II spectrometer (Billerica, United States) in transmittance mode from an accumulation of 128 scans at 4 cm -1 over 4000-400 cm -1 region under ambient conditions.

Thermogravimetric analysis (TGA)
TGA was conducted on 5 mg of each sample at 10 °C min -1 heating rate from 30 ºC up to 800 °C under purging nitrogen (50 mL min -1 ) using a PerkinElmer TGA 4000 thermogravimetric analyzer (Waltham, United States).The derivative thermogravimetric curve (dTG) was the first derivative from the TGA data.

Scanning electron microscopy (SEM)
SCB derivatives were mounted with the conductive carbon tape, sputter-coated with gold, and then examined by FEI Inspect S50 scanning electron microscope (Hillsboro, United States) at 15 kV accelerating voltage.Elemental analysis of each sample was conducted using an EDS detector (Silicon Drift Detector (SDD) Apollo X, EDAX) coupled with the SEM with 10 kV accelerating voltage.The energy-dispersive X-ray spectroscopy (EDS) characterization of the chemical surface of samples was based on the well-established method reported previously. 52he width measurements of SCB derivatives were obtained through ImageJ software. 53

Adsorption capacity of SCB derivatives
The concentration of potassium, ammonium, and phosphate ions was quantified from the filtered multielement solution.Potassium was determined by Digimed DM 62 flame emission photometer (São Paulo, Brazil), and ammonium and phosphate with appropriate reagents for the determination by Thermo scientific Genesis 10S UV-Visible spectrophotometer (Waltham, United States), as reported previously by Messa and Faez. 49The amount of nutrient adsorbed by SCB derivatives was calculated from equation 2, 54 (2) where adsorption capacity is the amount of ion adsorbed per gram of substrate (mg g -1 ); c 1 and c 2 are the initial and final concentrations (mg L -1 ) at time t (min), respectively; v (mL) is the volume of multi-element solution; and m (g) is the mass of SCB derivative.All derivatives ranged 15-115 µm wide and hundreds of micrometers long.The averages and standard deviations were obtained from three measurements under the same conditions.

Size and organoleptic characteristics of films
The films sample were cut into circle pieces (17.1 ± 1.1 mm diameter and 0.31 ± 0.02 mm thickness) at different areas in the cast film.The weight of each sample was measured using a Sartorius TE214S analytical balance (Gottingen, Germany), and an MTX digital caliper measured their thickness.The average and standard deviation values were obtained from three measurements and reported.The physical appearance was evaluated by visual inspection to determine the homogeneity.The most representative pictures are shown in this work.

In-water nutrients release capacity
The ability of the films to release NH 4 + , H 2 PO 4 -, and K + ions was investigated using the optimal CS/NPK sample reinforced with -HC, -CL, or -CEL.The in-water release of nutrients from films (ca.32 ± 1 mg) was monitored by placing each into a polypropylene nonwoven sachet (7 × 5 cm) immersed in 50 mL deionized water under ambient conditions and without stirring.First, the aqueous solution was sampled at predetermined intervals to quantify the nutrient concentration.Then the sachet was transferred to another fresh 50 mL of deionized water.An average value and standard deviation for each sample were determined from three measurements and reported.

Nutrient release mechanism and kinetics
The mechanism and parameters kinetics of the first 60% nutrient release from composite films were investigated using the Korsmeyer-Peppas model (equation 3), 55 which is commonly applied to predict the release of drugs from the polymeric materials, (3)   where Mt/M∞ is the fraction of potassium released at time t.The release system characteristic is defined as k, and n is the exponent of diffusion of the release mechanism.

Characterization of SCB derivatives from sugarcane bagasse
The FTIR spectra and TGA of SCB derivatives were compared (Figure S1, Supplementary Information (SI) section).The FTIR spectra of CL showed characteristic bands for phenolic compounds at 1515 and 834 cm -1 , corresponding to the aromatic skeletal vibration and aromatic C-H out-of-plane bending, 56,57 while hemicellulose carboxyl C=O and C-O stretching bands 58 at respective 1733 and 1254 cm -1 were eliminated.HC was synthesized by sodium chlorite delignification (1.4% NaClO 2 , pH 3.5, 70 °C, 5 h) of SCB, resulting in pale yellow solids, possibly due to the less lignin content.Characteristics bands of hemicelluloses at 1733 and 1254 cm -1 were verified in HC.The absence of 1515 and 834 cm -1 bands corresponding to phenolic components significantly reduced to barely observable, signifying near-complete lignin removal after delignification.Subsequently, the alkali treatment of HC turned the pale-yellow HC to white CEL and caused the disappearance of bands at 1733 and 1254 cm -1 , manifesting the complete removal of hemicelluloses.Additionally, this product showed characteristic bands of O-H at 3000-3600 cm -1 , C-H at 2900 cm -1 , and glycosidic C-H deformation at 897 cm -1 , representing pure cellulose. 52HC, CL, and CEL exhibited an initial slight mass loss of 4-6% around 150 °C from the evaporation of adsorbed water, and then derivatives lost near 65-70% mass rapidly up to 390 °C, corresponding to the decomposition of SCB components, leaving 9.7-20.6%char residue at 600 °C.The first derivative curve of SCB and HC showed an additional event corresponding to hemicellulose decomposition at around 298 °C, which decomposes at low temperatures. 59Higher maximum degradation temperature (T max ) of CEL (352 °C) than SCB (329 °C), HC (347 °C), and CL (343 °C) samples is expected 60 and corroborates with the removal of both lignin and hemicellulose, as evidenced in the FTIR.The char residue of SCB was 20.6%, higher than HC (15.7%),CL (19.8%), and CEL (9.7%), indicating reduced chars with the procedures to remove the noncellulosics.Therefore, these results confirmed the presence of the respective hemicellulose in HC and lignin in CL, while none of the noncellulosics was found in CEL, providing evidence to support the formation of material with distinct chemical compositions.
SEM coupled with EDS examined the surface morphologies and elemental composition of SCB derivatives.All four products had a long fiber structure 15-115 µm wide and hundreds of micrometers long.The width of SCB fiber bundles reduced moderately from 115 ± 33 µm (Figure 1a) to 92 ± 16 µm HC and 78 ± 13 µm CL (Figures 1c, 1e) after delignification or alkali dissolution, respectively.When these procedures were combined, SCB fiber bundles became individualized, disintegrating significantly to much finer 15 ± 7 µm wide CEL (Figure 1g).Energy-dispersive X-ray spectroscopy (EDS) revealed that the surface of each derivative mainly consists of C and O; both are typical of cellulose 52 (Figures 1b, 1d, 1f, 1h), while the Si peak at 2.13 keV was only found in SCB, attributing residual silica ash.Na and Cl peaks at 1.06 and 2.18 keV correspond to the residual chemicals from chemical procedures, while the Al peak at 1.51 keV is probably from the milling step.

Adsorption capability of SCB derivatives
All three SCB derivatives exhibited adsorption capacities ranging from 1.6 to 14.6 mg per g toward a wide range of nutrients in soluble form, including cationic (NH 4 + , K + ) and anionic (H 2 PO 4 -) species (Figures 2a-2c).At optimal time conditions, the maximum adsorption capacities of these derivative cellulose fibers toward K + were lower, ranging from 1.6 to 3.6 mg g -1 (Table 1), indicating some electrostatic interaction with all three fibers' surfaces.More interestingly, HC fibers showed the highest adsorption capacity for NH 4 + (7.8 mg g -1 ) followed by H 2 PO 4 -(3.0 mg g -1 ), probably due to numerous surface polar hydroxyls and carboxyls groups from hemicellulose serving as adsorption sites.With distinct surface phenolic hydroxyl groups from lignin, CL exhibited a more substantial adsorption capacity for H 2 PO 4 -(14.6 mg g -1 ), 4-5 times higher than HC and CEL.In contrast, NH 4 + and K + adsorptions were lower at 2.6 and 1.6 mg g -1 , respectively, suggesting that phenolic compounds enormously increase the adsorption capacity of phosphorus.Even with increased specific surface area as previously observed by SEM (Figure 1g), CEL adsorption capability of 6.1, 3.9, and 2.2 mg g -1 for respective NH 4 + , H 2 PO 4 -and K + was intermediate to the HC and CL samples.These relatively low values are consistent with only hydroxyl groups as the significant adsorption sites from cellulose.Overall, adsorption data provide direct evidence that noncellulosics in SCB derivatives lead to a higher nutrient retention capability, which is highly desirable for material development as composites with a slowing-release property.
All SCB derivatives had similar SCB XRD patterns, i.e., with diffractions at 2θ = 14.7, 16.6, 22.6° assigned to the 1 -10, 110, and 200 crystallographic planes in a monoclinic lattice, 61,62 maintaining the Iβ crystalline structure of cellulose after chemical (alkali and delignification procedures) and adsorption processes (Figure 2d).Additionally, no additional crystalline peaks were found after adsorption, possibly due to some interaction of ionic species with SCB derivatives, affecting the crystallization of salts.The SCB derivatives with adsorbed nutrients had CrIs values ranging from 49 to 63%, 4-12% lower than their counterparts (53-69%) (Table 1).These reduced CrIs, in essence, suggest some disorientation of cellulose crystals when ionic species are adsorbed on the SCB derivatives surface, leading to slightly less ordered structures.
In conclusion, the ability of SCB derivatives to adsorb higher and varied quantities of cationic and anionic nutrients reflects the distinct chemistry surface of fibers.Higher adsorption capacities for H 2 PO 4 -and NH 4 + were significantly dependent on hydroxyl, carboxyl, or phenolic hydroxyl groups from surfaces in noncellulosic components through ion-dipole interactions.In contrast, the lower potassium adsorption driven by ion exchange was due to the scarce charged sites.Essentially, the adhesion of the ions to the SCB derivatives surface from adsorption was evident from the XRD, which may be linked to crystalline properties discussed earlier. 63eparation and characterization of NPK-loaded CS films CS solubilized completely in 0.5% v/v aqueous acetic acid under magnetic stirring for 24 h, forming a solution of CS 2 wt.%.CS solution at pH 3.9 appeared homogeneous and slightly translucent, indicating excellent solubility without agglomerates (Figure S2a, SI section).Under an acidic medium, amino groups (-NH 2 ) are expected to be protonated and converted to -NH 3 + .Mixing NPK with CS solution at 0.25, 0.5, 0.75, or 1:1 NPK/CS mass ratios caused slight opacity (Figure S2b), probably due to electrostatic interactions between protonated amine groups of CS and anionic species from NPK, including sulfate (SO 4 2- ), dihydrogen phosphate (H 2 PO 4 -) and chloride (Cl -)   ions.CS solutions containing varied NPK loads remained homogeneous and with no precipitation, indicating the solubility of CS was not significantly affected.Pure CS solutions could be dried in an oven (60 °C, 5 h) to form slightly yellow, opaque, and uniform films (Figure S2c).However, oven-drying of 1:0.25 CS/NPK solution yielded films with a shape highly deformed macroscopically (Figure S2d).Doubling NPK loading in the CS solution led to oven-dried films of 1:0.5 CS/NPK with the most regular shape (Figure S2e).Further increasing in NPK loading to 75 and 100% did not change the general appearance of the films, but 1:0.75 and 1:1 CS/NPK had surface cracks and irregularities (Figures S2f, S2g), suggesting the capacity of film-forming during oven-drying is greatly affected by the NPK loads.Therefore, the most uniform film from 1:0.5 CS/NPK composition was selected for further studies and named simply CS/NPK from here on.The FTIR spectra of CS/NPK showed broadband in the 3600-3000 cm -1 region, which is evident for overlapped N-H and O-H stretching vibrations from CS and NPK (Figure 4a).The distinct bands at 1409 and 528 cm -1 are assigned to the bending vibrations of NH 4 + and O-P-O(H), 64,65 while those at 1116 and 616 cm -1 correspond to two vibrational modes of the SO 4 2-group. 66 more prominent band in the 1200-900 cm -1 region is possibly from the overlapping sulfate adsorption vibrations at 1116 and 616 cm -1 , and the 1230-850 cm -1 adsorption bands belong to the glycosidic ring of the CS structure. 67ore importantly, the diminished band at 1561 cm -1 characteristic of N-H vibrations of protonated amines 68 confirms the electrostatic interactions between -NH 3 + from CS with anionic species from NPK, consistent with the visual evidence of chemical reaction by color-changing of CS solution after fertilizer loaded. 69S remained thermally stable at up to 180 °C, then showed a mass loss at 241 °C (T max1 ), followed by another smaller decomposition event at 309 °C (T max2 ), corresponding to degradation of the respective protonated amine and acetyl surface groups (stage I) and glucopyranose of CS (stage II), 70,71 leaving 21.1% residue at 800 °C (Figures 4b, 4d).On the other hand, CS/NPK exhibited increased thermal stability that started below 240 °C, showing more intense and separated mass loss in two stages at 286 °C (T max1 ) and 356 °C (T max2 ).This distinct thermal behavior suggests non-simultaneous decomposition of the chloride, sulfate and/or phosphate amines surfaces and final degradation of CS organic matter.This behavior corroborates the electrostatic interaction between the protonated amine groups of CS with anionic species of NPK.Despite NPK load, char residues of CS/NPK at  800 °C (27.2%) were similar to CS, due to the compounds that thermally decompose below 600 °C from NPK.

CS/NPK composite films with SCB derivatives
Optimal CS/NPK film-forming reinforced with SCB derivative fiber at a different percentage (5, 10, 25, and 50 wt.%)could be cast into slightly dark yellow films.Then, adding 5-10 wt.% of fiber to the CS/NPK solution resulted in film retraction during drying, becoming denser and irregular (Figures S4a, S4b).However, increasing fiber content to 25 or 50 wt.%prevented the retraction effect and led to more regular films in shape, probably because fibers were better distributed throughout the film when higher quantities were added (Figures S4c, S4d).In addition, the augmented color intensity of composite films was consistent with increasing fiber content and closer microfibril association with the CS matrix.Therefore, considering both content fiber required and resulting film quality, the optimal condition to produce composite films was CS/NPK film reinforced with 25 wt.% fiber.
The effect of noncellulosics on the fertilizer retention ability of CS/NPK films was elucidated by in-water release studies.Normalized by weight, CS/NPK/HC, CS/NPK/CL, and CS/NPK/CEL films exhibited similar release behavior at two stages, including an initial rapid release followed by another slow and continuous one.In contrast, no change in physical integrity underwater for one week (Figure 5).CS/NPK/HC released a maximum of 64.8, 51. , and K + within seven days, respectively (Figure 5a).The lowest H 2 PO 4 -rate released may be linked to electrostatic attractions with protonated amine groups in CS and interfacial hydrogen bonds in HC fibers, among the hydroxyls and carboxyls.In the case of the faster K + release rate, electrostatic attractions seem to dominate over surface interaction effects among ions potassium, CS, and HC.Meanwhile, the slowing release rate of NH 4 + was intermediate to H 2 PO 4 -and K + , probably due to its hydrogen bonding with HC fibers.In the case of CS/NPK/CL, films had different release rates for all three nutrients, in which 54.8% NH 4 + was released slower.In contrast, 58.0%H 2 PO 4 2-and 91.5% K + were faster released than CS/NPK/HC films (Figure 5b), affirming the slower releasing of cationic and anionic species driven by interfacial hydrogens bonds than only electrostatic attractions.The release data suggest that hemicelluloses or lignin in the composite films affect fertilizer retention.In contrast, the absence of noncellulosics in composite films led to inferior release ability compared to the CS/NPK/HC and CS/NPK/CL, in which a maximum of 71.0%NH 4 + , 77.8% H 2 PO 4 -and 100% K + were substantially faster released at the same time condition (Figure 5c).These nutrient release data showed that hemicelluloses and lignin in SCB derivatives could improve nutrient retention from composite films.
Cumulative release of NH 4 + and H 2 PO 4 -from CS/NPK/HC and CS/NPK/CL fitted the Korsmeyer-Peppas model well, and correlated coefficients (R 2 ) varied from 0.9616 to 0.9998 (Figures 5d, 5e).Composite films had a release exponent (n) lower than 0.5 for the first 60% of ammonium and dihydrogen phosphate ions released, corresponding to the quasi-Fickian diffusion mechanism.Therefore, the results support that these cationic and anionic nutrients diffuse through swollen and positively charged CS matrix.The slowing release of anionic and cationic nutrients was driven by attractive electrostatic forces and van der Waals interactions with protonated CS.At the same time, the noncellulosics in SCB derivatives reinforcement could improve the nutrient retention of composite films.Furthermore, their simple development approach requiring no additional chemicals or complex processes adds economic benefits to the production costs.This work demonstrates a facile and feasible strategy to explore naturally abundant polysaccharides and feedstocks as composite films with the slowing-release capability of NPK fertilizer for the first time to our knowledge.

Conclusions
The SCB derivatives (holocellulose, cellulignin, and cellulose) were evaluated as K + , NH 4 + , and H 2 PO 4 adsorption properties to increase the release properties of CS and SCB derivatives fibers.The derivatized SCB fibers exhibited distinct morphologies with widths ranging 15-115 µm and hundreds of micrometers long.The most intriguing nutrient-adsorption behavior for HC is NH 4 + (7.8 mg g -1 ), whereas CL showed a more substantial adsorption capability for H 2 PO 4 -(14.6 mg g -1 ).The absence of noncellulosics in CEL fibers lessened their adsorption capacity, resulting in lower adsorbed nutrients following adsorption.Composite films produced by oven-dried (60 °C, 5 h) from the optimal condition were regularly shaped with 0.31 ± 0.02 mm thickness.While NPK loading into CS solution at a moderate amount (1:0.5 CS/NPK) preserves the polymer film-forming capacity, the high fiber content of 25 or 50% prevents the film's retraction effect.Furthermore, NPK fertilizer incorporated into composite films exhibited SCB derivative chemical compositiondependent release followed by a quasi-Fickian diffusion mechanism in water.This work demonstrates a facile and feasible strategy to explore chemically modified fibers from SCB along with CS as composite films to chemically bind and control the releases of ammonium, dihydrogen phosphate, and potassium for the first time to our knowledge.

Figure 5 .
Figure 5. Cumulative release of H 2 PO 4 -, NH 4 + , and K + from CS/NPK composite films with (a) HC, (b) CL, and (c) CEL fibers; and Korsmeyer-Peppas kinetic model parameters and fitting of first 60% of ammonium and dihydrogen phosphate releases and in water from (d) CS/NPK/HC and (e) CS/NPK/CL.