Enhanced efficiency fertilizers (EEF) are an important subject for sustainable materials. It is fundamental for the released nutrient and biodegradation in the soil to have synergy to ensure material harmlessness. Chitosan, montmorillonite, and KNO3 were considered to develop the EEF because of the high biodegradation potential of the final product.
Carbohydrate Polymers 257 (2021) 117635 Contents lists available at ScienceDirect Carbohydrate Polymers journal homepage: www.elsevier.com/locate/carbpol Biodegradation and viability of chitosan-based microencapsulated fertilizers Luciana Moretti Angelo a, Debora Franỗa a, b, Roselena Faez a, b, * a b Laboratory of Polymeric Materials and Biosorbents, Federal University of S˜ ao Carlos, UFSCar, 13600970, Araras, SP, Brazil Graduate Program in Materials Science and Engineering, University of S˜ ao Paulo, USP- FZEA, 13635900, Pirassununga, SP, Brazil A R T I C L E I N F O A B S T R A C T Keywords: Bartha’s respirometric Clay KNO3 Sustainable agriculture Enhanced efficiency fertilizers (EEF) are an important subject for sustainable materials It is fundamental for the released nutrient and biodegradation in the soil to have synergy to ensure material harmlessness Chitosan, montmorillonite, and KNO3 were considered to develop the EEF because of the high biodegradation potential of the final product We correlated the material biodegradability and release in water and soil to their formulation We assume the materials are biodegradable since the biodegradation efficiency achieved over 30 % As the nutrient diffusion and matrix degradation happen concomitantly, we also observed that the clay delays degra dation and the KNO3 improved it Likewise, the storage period can change the biodegradability properties once the material started to degrade Hereupon, the amount of nutrient delivered will match the amount consumed by the plant, the matrix will degrade and no residue will be left in the soil Introduction Currently, agriculture has the problem of excess fertilizers, pesti cides, and growth regulators left in the soil These agrochemicals are used to enhance the plant development and, usually, placed in quantities higher than necessary to compensate the losses through volatilization, solubilization, or leaching into the soil (Chen et al., 2018; El Assimi et al., 2020) Studies have been performed to improve fertilization ef ficiency using chemical modification or physical coating to reduce nutrient waste (Shaviv & Mikkelsen, 1993) Some requirements for the ideal enhanced efficiency fertilizer (EEF) are the compatibility between the nutrient release and the absorption by the culture, the biodegrad ability of the coating material, and the cost-effectiveness of the product However, the EEFs are difficult to obtain due to the nutrient coating process The matrix composition and the need for chemical and physical modification are important points to consider during the EEF develop ment (Chen et al., 2018) Consequently, a bio-based and biodegradable matrix for fertilizers is the interest of many research (Chen et al., 2018; El Assimi et al., 2020; Lubkowski & Grzmil, 2007; Pandey, Kumar Verma, & De, 2018) Chen et al (2018) list chitosan, alginate, starch, cellulose, lignin, agricultural residues, biochar, and polydopamine as the most used materials for the fertilizer coating Although they comply with the prerequisites already mentioned, there are some disadvantages, for example, chitosan, has the potential to be used as a fertilizer coating matrix as it is cheap, biodegradable, and renewable (Chen et al., 2018; Lubkowski & Grzmil, 2007; Pandey et al., 2018), besides having anti microbial properties (Pandey et al., 2018) However, it has the disad vantage of usually being soluble in acid, and for chitosan to be soluble in water, it needs an expensive preparation, which would result in an expensive fertilizer, and therefore, raising the chances of market refusal (Chen et al., 2018) Chen et al (2018) also concluded that the greatest difficulty in preparing efficient fertilizers is to maintain the nutritional supply in the phase of most need, which is the growth phase The burst effect occurs when most of the nutrient releases during the initial period of the tests To reduce the burst effect, some researchers had added montmorillonite clay to chitosan materials, which promotes a slowdown in the water diffusion (El Assimi et al., 2020) and can delay the nutrient release (Franỗa, Medina, Messa, Souza, & Faez, 2018) Given these considerations, our research group has been focusing on the structure-properties understanding of matrices formulations to be efficient in terms of nutrient release and biodegradability, based on materials that meet the necessary prerequisites, such as potassium ni trate fertilizer (KNO3) encapsulated with chitosan and montmorillonite clay (Franỗa et al., 2018; Messa, Souza, & Faez, 2020; Santos, Bacalhau, * Corresponidng author at: Laborat´ orio de Materiais Polim´ericos e Biossorventes, Departamento de Ciˆencias da Natureza, Matem atica e Educaỗ ao, Universidade Federal de S ao Carlos, Rod Anhanguera, km 174 - SP-330, P.O BOX 153, 13600-970, Araras, S˜ ao Paulo, Brazil E-mail address: faez@ufscar.br (R Faez) https://doi.org/10.1016/j.carbpol.2021.117635 Received September 2020; Received in revised form December 2020; Accepted January 2021 Available online 16 January 2021 0144-8617/© 2021 Elsevier Ltd This article is made available under the Elsevier license (http://www.elsevier.com/open-access/userlicense/1.0/) L.M Angelo et al Carbohydrate Polymers 257 (2021) 117635 Pereira, Souza, & Faez, 2015) Chitosan (CS) is a bio-based polymer, abundant, and renewable on earth, with high biocompatibility, biodegradation and easy to obtain from the chitin deacetylation Chitin is a polysaccharide present in the exoskeletons of crustaceans, insects and fungal mycelia The chitin deacetylation process consists of removing the acetyl branch from the compound, which results, predominantly, in 2-amino-2-deoxy-D-gluco pyranose units However, deacetylation is not complete, and it is necessary to have a deacetylation percentage of 60 % or more to ˆme, 2013) Clay is also a natural consider it as chitosan (Croisier & J´ero and abundant material on the earth Montmorillonite clay is structured by lamellae composed of silicate groups (Si-O) and aluminum (Al3+) that can be replaced by magnesium (Mg2+) This provides the negative character on the lamellae and the load is balanced by the presence of cations, hydrated or not, in these interplanar spaces (Coelho, Santos, & Santos, 2007) Thus, the cationic exchange between the lamellae, without any structural modification, can help the retention of K+ and slow the release of the ions, reducing the burst effect Potassium nitrate was used as a fertilizer because it is a source of nitrogen and potassium Nitrogen is a limiting factor for plant growth and important for the absorption of other elements such as potassium The nitrate form is preferred because it is absorbed by most plant species, even though, it is also the form most susceptible to leaching (Moreira & Siqueira, 2006; Ueda, Konishi, & Yanagisawa, 2017) Potassium, one of the most important macronutrients, is associated with the immune system and avoids plant stress caused by adversities when there are adequate quantities (Sustr, Soukup, & Tylova, 2019) CS, MMt, and KNO3 have been considered to develop enhanced ef ficiency fertilizers because it is possible to reach a high biodegradation potential in the final product Those are eco-friendly materials and chitosan is a polysaccharide susceptible to physical and chemical decomposition actions promoted by microorganisms The higher biodegradation of the chitosan is caused by the enzymatic activity, which can be degraded into smaller, non-toxic oligosaccharides (Crois ˆme, 2013) These properties are of interest, considering an EEF ier & J´ero coated with chitosan and MMt that will be biodegraded by the micro organisms present in the soil when the nutrient release occurs As a result, these EEFs can avoid the overuse of nutrients and the residues of the coating into the soil Franỗa et al (2018) have processed the CS, MMt, and KNO3 together using the spray-drying technique because of the advantages of obtaining a material quickly, with great reproducibility and productivity The equipment parameters were essential to promote good reproducibility and these were configured using the 3-fluid atomizer nozzle for the formation of microcapsules, shell-core structures (Franỗa et al., 2018) The formulations were evaluated for nutrient release in water and soil The CS has great water retention potential that allows the swelling of the chitosan matrix and affects the nutrient release mechanism Franỗa et al (2018) have concluded the release behavior is a swelling-controlled transport, which means the CS microcapsule swells and then releases the KNO3 from the core (Franỗa et al., 2018) They have also observed that adding MMt clay in the formulation, delayed the nutrient release, and decreased the swelling degree However, as in many studies, they did not evaluate the biodegradation of the material To overcome this lack of information in the literature, the present work seeks to quantify the biodegradation and understand the chitosan biodegradation mech anism in the presence of clay and KNO3 The microbial activity provides carbon dioxide release due to aerobic metabolism and substrate degradation Other factors as temperature, pH, oxygen concentration, luminosity, and humidity, also allow biodegradation, by stimulating the development and growth of micro organisms’ colonies (Moreira & Siqueira, 2006) Taking into account these factors, it is possible to evaluate the polymer biodegradation profile from the amount of carbon dioxide released in a closed and controlled system The biodegradation assessment was based on the respirometry test standardized by the NBR14283 (Brazilian standard by ˜o Paulo State based on the the Environmental Protection Agency of Sa o Brasileira de Normas Tecnicas, ABNT, 1999; ASTM D5988) (Associaỗa "Standard Test Method for Determining Aerobic Biodegradation of Plastic Materials in Soil,” 1989) Therefore, it was possible to quantify the carbon dioxide produced through spontaneous chemical reactions and evaluate the material biodegradability according to their formula tion modifications and the influence of inorganic compounds on this process Another point to be considered in this work is the storage time effect Franỗa et al (2018) also observed the color change and charac teristic smell during the storage period, which could be attributed to the degradation of these materials Regarding this, the biodegradation evaluation was also redone after months with the stored material to assess the feasibility of stocking it in powder form rather than the ma terial just after being processed, and to verify the difference in the biodegradation performance We hypothesize that the CS-based EEF is biodegradable and depen dent on clay and, encapsulated nutrients Also, we argue that the EEF provides the nutrients needed for plants as it is degraded Experimental 2.1 Materials Chitosan powder (C6H11O4)n (Polymar S/A, 85 % deacetylation degree and average molar mass 1.8.105 g mol− 1(Santos et al., 2015)), Glacial acetic acid 99 % (Synth− Brazil), Fertilizer based on potassium nitrate (Saltpetre Krista K (KNO3) Yara Brazil Fertilizantes S.A., Brazil), Sodium montmorillonite clay (Brasgel Aỗo A granted by Bentonit Union, CTC 85 mmol/100 g clay) All reagents were used with any prior purification 2.2 Preparation and characterization of the EEF The materials for biodegradation analysis were processed according to Franỗa et al (2018) in the Spray Dryer using the 3-fluid atomizer nozzle, in order to have microcapsules (a core-shell structure) The core is based on CS, MMt and KNO3 (CSMMtKNO3) and the shell CS-based (CS) Briefly, shell solutions were based on g of CS dissolved into 100 ml of acetic acid % (v/v) The core of CS/KNO3 was prepared with 40 g of KNO3 added to a solution of wt.% of CS For CSMMtKNO3, montmorillonite clay was previously soaked with some drops of water and KNO3 (1:3 MMt:KNO3 mass ratio), ground and mixed in a mortar for 10 and then dried at 80 ◦ C for h Next, the MMt:KNO3 was added to chitosan solution and stirred for under Turrax homogenizer at 10,000 rpm The Spray Dryer parameters were 3-fluid nozzle, Ø =2.80 mm (extern Ø =2.0 mm/intern Ø =0.7 mm), inlet temperature at 180 ◦ C, aspirator 100 %, airflow around 670 Lh− 1, outer flow at 10 mL min− (30 %) and inner flow at ml.min− (5 rpm) The final percentage of each component is expressed in Table The materials were characterized by Fourier transform infrared spectroscopy (FTIR) in the Tensor II model - Bruker equipment, with the OPUS software (v 7.5), with the analysis range between 550–4000 cm− and 32 scans The diffractometry X-ray analysis (DRX) was performed in the Rigaku Miniflex 600 model equipment, in the operating condition of 40 kV and 15 mA, and with the analysis range of 2◦ to 90◦ 2θ 2.3 Biodegradation analysis by the respirometric method The biodegradation analysis was based on the NBR 14283 standard, a Brazilian normative standardized by the Environmental Protection o Paulo State (Associaỗ Agency of Sa ao Brasileira de Normas T´ecnicas, ABNT, 1999), which determines biodegradation by the respirometry method using Bartha’s respirometer This technique measures the mass of carbon dioxide (CO2) produced during the degradation of organic materials In this closed system, the microorganisms of the soil will absorb the carbon from the polymeric material and release carbon L.M Angelo et al Carbohydrate Polymers 257 (2021) 117635 Table EEF materials formulations and the amount of material for biodegradation analysis Materials CS (%) Clay (%) KNO3 content (%) Amount of CS for biodegradation (g)* CS 100 – – 0.20 CSMMt 86.3 13.7 – 0.23 CSKNO3 50 – 50 0.40 CSMMtKNO3 50 12.5 37.5 0.40 Illustration (initial solution concentration) * Those quantities are different because 0.2 g of polymer was considered in each formulation in order to have the same amount of polymeric material to be degraded during the test dioxide through respiration In this study, the source of carbon is the chitosan-based material The soil used in the tests was the red latosol from UFSCar- Araras (latitude 22◦ 18′ S, longitude 47◦ 23′ W) According to ABNT-NBR 14283, the field capacity should be between 50–70 % and it was established at 60 % by previous works in the group, so 17.2 mL of water is needed for every 50 g of red latosol The materials were mixed with the soil and the control test was the soil without any materials The newly processed and 3-months stored (3-MS) material were evaluated to compare the storage effect on material degradation The amount of 0.2 g, referred to as the CS, used in the test was based on previous analyzes (Franỗa et al., 2018) which determined the percentage of the components on the developed materials, Table The system was oxygenated with an air pump and sealed with an ascarite filter and stoppers to avoid gas exchange be tween the system and the external environment The carbon dioxide produced by microbial activity will react with the 10 ml of KOH (0.2 M) placed in the attached flask, according to the chemical reaction (Eq 2) CO2 + KOH → K2CO3 + H2O profile of the materials in the soil The evaluation was performed in three replicates The biodegradation efficiency was calculated considering the amounts of carbon produced from CO2 released during the test, and the amount of carbon (from polymer) added to the soil First, we have theoretically calculated the carbon amount in the 0.2 g of polymer, considering the 85 % deacetylated CS Eq (5) was used to determine the values of carbon produced where Cb is the carbon mass produced by the material biodegradation, mg CO2 soil residue is the sum of the mass of CO2 produced, mg CO2 soil control is the sum of the mass of CO2 produced in the control test, and 12/44 is the conversion factor from mg CO2 to mg Carbon Cb = (mg CO2 KOH + HCl → H2O + KCl (4) soil control) 12/44 EB (%) = Cb / Cl.100 (6) (5) (6) where EB is the biodegradation efficiency, Cb is the mass of Carbon produced by the material biodegradation, and Cl is the mass of the theoretical carbon amount in the material applied to the soil at the beginning of the test Daily CO2 values obtained from the biodegradation activity were analyzed with a one-way ANOVA (analysis of variance) Tukey test was used to qualify the differences The difference in the average CO2 emitted daily by the different materials was analyzed and statistically significant differences were accepted when p < 0.05 The solution on the attached flask was periodically removed and titrate to quantify the amount of CO2 produced The reaction inside the closed system is spontaneous: the production of carbon dioxide by mi croorganisms and the reaction between CO2 and KOH To perform the titrations, barium chloride was added to the potassium carbonate/water solution to precipitate barium carbonate Therefore, the KOH that remained unreacted, was neutralized, by titration, with 0.1 M HCl so lution (Eq and 4) (3) - mg CO2 After, we determined the biodegradation efficiency according to ABNT standard (1999), Eq (6) (2) K2CO3 + BaCl2 → BaCO3 + KCl soil residue 2.4 Nutrient release profile in water and soil Alongside the biodegradation behavior evaluation, it is important to correlate it with the nutrient release (from material to the environment) to understand how it will behave in the soil and guarantee the With the titrated HCl values, the amount of carbon dioxide released was determined These data were used to determine the biodegradation L.M Angelo et al Carbohydrate Polymers 257 (2021) 117635 harmlessness of the material During our previous work, the release behavior was evaluated in water and soil (Franỗa et al., 2018) However, it lacks a correlation between both the nutrient release profiles and their biodegradability (shown in the present study) Briefly, 0.2 g of micro capsules were added to 50 mL of water The potassium (K+) content released through time was measured by flame photometry The solvent was changed in every measurement, three repetitions and the accumu lative concentrations were taken to plot the potassium releasing curve In the soil medium, g of material was placed into a 10 cm deep hole at the center of a container with 10 Kg of soil Psamment (sandy Entisol), classified accordingly (Soil Survey Staff, 1999) Three TDR probes were placed at cm spacing and named central and lateral (left and right probes) The containers were soaked with 2.5 L of distilled water, to reach the soil field capacity The measurements of electrical conduc tivity and moisture were performed daily by the TDR1000 Reflectometer (Campbell Scientific) and PCTDR software The correlation along with the nutrient release behaviors and its biodegradability were done by interpreting data from the respective tests and it is shown and discussed in this paper non-modified montmorillonite so it is more difficult for the polymer to enter the interlamellar space, Fig (Bari, Chatterjee, & Mishra, 2016; El Assimi et al., 2020; Rimdusit, Jingjid, Damrongsakkul, Tiptipakorn, & Takeichi, 2008) Furthermore, MMt particles also restricted the segmental motion at the interface and decreased the access of micro organisms to attack the polymer Fig 1.B shows the daily CO2 emission The first 25 days of the test demonstrated the peaks of high and low CO2 released which are not concomitant with each other, as observed after this period The CSMMtKNO3 and CSKNO3 displayed a similar cumulative CO2 release profile (Fig 1.A) However, CSMMtKNO3 showed the daily CO2 release curve higher than the CSKNO3 on the first days and, lower on the following days This was attributed to the nutrient diffusion through the polymeric matrix, as the nutrient is released from the microcapsule The water molecules and microorganisms have more sites to interact with the polymeric matrix At the same time, the microorganisms have their growth favored by nitrogen (released from the material to the medium) Meanwhile, the clay acts to delay the degradation as it increases the crystallinity of the material, reducing the swelling degree of the polymer and, consequently, reducing the access of water and/or microorganisms to the hydrocarbon chain to degrade it Another point to consider is the higher CO2 production at the beginning of the test, which could be related to inactive microorganisms left in the material, and when placed in a favorable environment to development they reactivate metabolically Consequently, the control test is important to state that the difference in CO2 release is related to the material biodegradation and to consider the interferences of the natural abiotic and biotic mechanisms on the neat soil Gonỗalves and cols (2002) also considered the control sample on CO2 emission after the soil re-moistening They conclude that the inactive microorganisms restart their metabolic activities and the multiplication of the microbiota (Gonỗalves, Monteiro, Guerra, & De-Polli, 2002) Also, abiotic activities related to the neutralization of the pH of the medium can occur, resulting in the production of CO2 Even with such considerations about the soil, the CO2 production curves are directly related to the biodeg radation mechanism, and they can also be associated with microbial cycles The interaction among the components of the microparticles in terferes with the biodegradation process Therefore, structure and morphological (FTIR, XDR, and MEV) analysis were realized and dis cussed later in the text Furthermore, a degradation progression during storage under un controlled conditions takes place, mainly for microparticles matrix of chitosan processed with clay Fig shows the daily CO2 emission for the 3-months stored (3MS) materials compared to the non-stored The CO2 release profile of chitosan was similar for both the CS and CS3MS, but Results and discussion 3.1 Biodegradation and CO2 analysis The CS, CSMMt, CSKNO3 and, CSMMtKNO3 materials, newly pro cessed and the 3-months stored, were evaluated according to their biodegradability Fig shows the biodegradation profile for 60 days according to the CO2 emission from the newly processed materials Based on the cumulative curve, we observe a similar production of carbon dioxide up to the 15th day, but at the end of the test, the CS keeps the highest CO2 release rate, which means higher biodegradability, and CSMMt the lowest rate, Fig 1.A Xu, Yong, Lim, and Obbard (2005) verified that chitosan enhanced the biodegradability of polycyclic aro matic hydrocarbons according to their studies of hydrocarbon biodeg radation in contaminated sediments (Xu et al., 2005) The biodegradation of the microcapsules can be related to the swelling deư gree Franỗa et al (2018) tested that spray-dried chitosan swells up to 1172 % before solubilizing They have also verified that for the CSKNO3 the swelling degree decreases to 534 % and for the CSMMtKNO3, it is under 488 % As the swelling degree was reduced, its biodegradability was affected, as it was confirmed here On the other hand, the clay can decrease the biodegradation due to the unavailability of the microor ganism growth in the clay particles reducing its functionality (Perotti, Kijchavengkul, Auras, & Constantino, 2017) Even though some litera ture confirmed the presence of clay facilitated the growth of the microorganism due to the increase of d-spacing, we applied the Fig Biodegradation profile of the CS, CSMMt, CSKNO3 and CSMMtKNO3 of (A) cumulative CO2 release and (B) daily CO2 release measurements Carbohydrate Polymers 257 (2021) 117635 L.M Angelo et al Fig Biodegradability profile of materials newly processed and stored for months, by daily measurements of CO2 release (A) CS; (B) CSKNO3; (C) CSMMt and (D) CSMMtKNO3 the values for the CSMMt3MS, CSKNO33MS, and CSMMtKNO33MS were higher than the CSMMt, CSKNO3, CSMMtKNO3, correspondently This comparison was done by the accumulated final mass and by the biodegradation efficiency values (Table 2) Considering the accumula tive values of CO2 emission of 241.1 and 255.1 mg for the CS and the CS3MS, respectively, they presented no significant difference in biodegradation profile after storage time (± 0.87) However, the CO2 emission increased from 144.4–208.4 mg for the CSMMt3MS; the greatest difference in biodegradation efficiency among the tested ma terials, from 28.25 % for the CSMMt to 43.28 % for the CSMMt3M (variation of 15.04) The CO2 emitted increased from 195.2–269.0 mg for the CKNO33MS, as the biodegradation efficiency increased from 44.92 % to 59.39 % And finally, the CO2 emission of the CSMMtKNO3 is altered from 190.0–248.3 mg for the CSMMtKNO33MS and the biodegradation efficiency increased from 43.22%–53.57% Since the polymer was already in the process of degradation, more microorganisms were developed during the test due to the greater vol ume of organic matter available The daily CO2 emission showed the first measurement was similar for all the formulations, but from the second one, it increased for the CSKNO33MS and CSMMtKNO33MS, maintain ing higher levels of CO2 throughout the test period, which are indicators of the fertilizer effect on degradation during storage Meanwhile, the CSMMt matrix showed lower amplitude for biodegradation peaks compared to the KNO3-based microcapsules and the CS remained with the same profile in both evaluations These findings are corroborated by the analysis of variance (ANOVA), including F-test and P-values, and Tukey test (Fig 3) ANOVA and Tukey test results have shown that there are significant differences for all materials compared to the control sample, except for the CSMMt that showed the lower biodegradability Also, the CSMMt-3MS showed a biodegradation behavior lower than the other storage materials, even though they are not significantly different Besides the fertilizer effect, other aspects should be considered, i.e., the possibility that the degradation started during the microencapsula tion process, due to the high temperature (180 ◦ C) and pressure which the material was submitted during the spray drying process Also, the acetic acid presence can induce the amorphous domains in the CS after the material has been dried (Wang et al., 2005) Here, the leftover acetic acid from the spray-drying process contributed to accelerating CS degradation The higher efficiency values for the stored materials corroborated the degradation process during storage under uncontrolled conditions and were attributed to the greater susceptibility of matrix degradation by the Table Biodegradation efficiency in percentage for newly processed and 3-months after storage samples Sample Biodegradation efficiency (%) Sample Biodegradation efficiency (%) CS CSKNO3 CSMMt CSMMTKNO3 59.88 44.92 28.25 43.22 CS-3MS CSKNO3-3MS CSMMt-3MS CSMMTKNO33MS 59.01 59.39 43.29 53.57 ± 1,22 ± 5,29 ± 0,97 ± 13,44 ± 7,17 ± 0,09 ± 2,77 ± 4,81 L.M Angelo et al Carbohydrate Polymers 257 (2021) 117635 and the nutrient was completely released Regarding the nutrient release in water (Fig C–D), the KNO3 released reached a plateau after two hours, indicating the nutrient was released Hence, we suggest the relationship of water-soil, which means a one-hour release in the water is equal to 20 days in soil Therefore, we can state a relationship comparing the release profile in water and soil and the biodegradation curves (Fig 4) For example, we observed 40 % of nutrients released in water in the first measurement for the CSKNO3 (Fig 4.C) and low mobility of the ions in the soil (Fig A) However, the CSMMtKNO3 shows the same nutrient release profile in water as the CSKNO3 (Fig 4.D) but differs in nutrients soil release (Fig 4.B) and biodegradation profile (Fig 4.F) In soil, the ionic mobility was low and suggests a faster nutrient release This can be justified by the presence of clay already in the soil, which can exchange cations with the nutrients from the fertilizer and also with the water ions from irri gation, trapping those ions and giving lower conductivity signals on the TDR probe measurements The biodegradation of the CSMMtKNO3 dis played an accentuated peak at the second measurement, while the CSKNO3 sample showed the first peak accentuated The biodegradation test describes the biotic activity by quantifying the CO2 emission as the microorganisms degrade the material The first peaks of biodegradation were a result of the high biotic activity consuming the nutrient released and the polymeric matrix, after 25 days it is only due to matrix degraư dation Franỗa et al (2018) have shown the nutrient release mechanism was swelling controlled for chitosan-based fertilizer, depending on the humidity to swell the matrix and then release the nutrient to the envi ronment The matrix swelling mechanism also had an important effect on the degradation as it aids the polymer chain relaxation allowing the microorganisms access to the matrix sides and degrades it Fig The ANOVA and Tukey Test for a significant difference in the level of biodegradability microorganisms compared to the non-stored material The stored ma terials started to degrade during the storage period, which can affect its ability to retain and release the nutrient in a programmable way In such a way, the microorganisms were able to consume the fertilizer matrix more quickly, which caused an increase in the amount of fungi, which were visualized with the naked eye and confirmed with the analysis described here According to the NBR 14,283 standard, the material should be considered biodegradable when the biodegradation efficiency is over 30 % In this sense, all materials, except the CSMMt, are considered biodegradable materials (Table 2) 3.3 Structural and morphological analysis of materials Fig shows the SEM images of the CS, CSKNO3, and CSMMtKNO3; the FTIR spectra and XRD diffractograms for all net components and microcapsules The morphology of the CS, CSKNO3 and CSMMtKNO3 are spherical and smooth, suggesting that the material has been encapsu lated, as it was expected for spray-dried materials The FTIR spectrum of CS displayed the following bands at 3415 cm− 1, attributed to the O–H – O due to the bond, at 1637 cm− 1, the characteristic vibration of C– acetyl groups on the polymer chain, at 1559 cm− due to the secondary amine, and the CH3 molecular bonds vibrate at 1381 cm− The MMt and KNO3 spectra showed the characteristic bands of O-Si-O vibrate at 472 cm-1 and of N–O bond at 1389 cm− The CSKNO3 maintained the most bands of CS, but it was overlapped at 1389 cm− due to the N–O bond from the KNO3 For the CSMMt, the band attributed to the silicate remained stronger than others For the CSMMtKNO3, the spectral characteristics vibration of N–O and silicates were observed but new bands were not displayed, suggesting the lack of chemical interactions The XRD curves show the CS peaks at 2θ = 15◦ and 22◦ due to the crystalline structures (020) and (110) The XRD peak at 2θ = 6◦ for the MMt is referring to the basal interlayer spacing (001) For the KNO3, the characteristic crystalline peaks appear at 2θ = 23◦ and 28 (Franỗa et al., 2018; Santos et al., 2015) The CS characteristic peaks were observed in all microcapsules However, after adding the KNO3, the peak around 2θ = 22◦ narrowed, though the others remained the same Also, for the CSMMtKNO3 we observed a peak displacement at 2θ = 6.0◦ to 7.24◦ due to the increase in the lamellar distance, evidencing the ion exchange between the cations K+, from the potassium nitrate, and Na+, from the interlamellar space of montmorillonite clay The new peaks at 2θ = 30◦ and 41◦ , attributed to the NaNO3, corroborate this statement (Franỗa et al., 2018) By comparing the XRD pattern of the CS and CSMMt, we observed amorphous characteristics of the CS corroborating the higher CO2 emission during the biodegradation test Amorphous materials are easier for microorganisms to access and degrade than crystalline ones Thus, we can assume that the MMt plays a role in delaying the biode gradability and keep the nutrient longer within its interlayers 3.2 Correlation between the nutrient release behavior and the biodegradability profile As previously stated, the correlation along the nutrient release pro files in water and soil added to the biodegradation behavior is important to predict how harmless those materials will be to the environment To better understand how we have correlated these three different tests, follow a brief explanation of measurements of electrical conductivity and moisture by TDR probes Time Domain Reflectometry (TDR) determines the dielectric con stant by measuring the propagation time of electromagnetic waves, sent from a pulse generator of a cable tester immersed in a medium (in our case, the soil) Electromagnetic waves propagate through a coaxial cable to a TDR probe, which is usually a rod, made of stainless steel or brass Part of an incident electromagnetic wave is reflected at the beginning of the probe because of the impedance difference between the cable and the probe The remainder of the wave propagates through the probe until it reaches the end of the probe, where the wave is reflected The round-trip time (t) of the wave, from the beginning to the end of the probe can be measured by a sampling oscilloscope on the cable tester Placing probes in the container where the material was being tested allows us to measure the ion mobility as the nutrient is released The ionic mobility of the nutrient was calculated according to the difference in conductivity values between the central and lateral probes (λ) We assume that the higher conductivity value in the central probe is related to a higher ionic concentration (nutrient) due to their concen tration near the central probe On the other hand, similar conductivity values of probes indicate higher ion mobility, i.e., the nutrient deposited near the central probe was dislocated to the extremities so the readings of the probes were identical After 40 days, the conductivity difference between the central and lateral probes was constant for all materials as it reached the plateau (Fig A–B) The ionic mobility was similar for all probes measurements L.M Angelo et al Carbohydrate Polymers 257 (2021) 117635 Fig Correlation along with the nutrient release in (A-B) soil, in (C-D) water, and (E-F) the biodegradation behavior for the (left) CSKNO3 and (right) CSMMtKNO3 Conclusion Therefore, the composition of the material can be designed to focus on how much longer the nutrient should be delivered and when the biodegradation should start The chitosan-based microencapsulated fertilizer materials have great potential for the improved efficiency of fertilizers as it has biodegrad able properties discussed in this paper, low-cost coating and an efficient nutritional release capacity However, there are many factors affecting material degradation and they need to be considered: (i) different formulation has different biodegradation behavior The inorganic components MMt reduced the biodegradability of the polymeric matrix as it increased the crystallinity of the material, but, the nutrient KNO3 facilitated biodegradation; (ii) nutrient diffusion and matrix degrada tion happen concomitant, so the matrix swelling mechanism is impor tant; (iii) the storage period should be considered since the material started to degrade, affecting its release and biodegradability properties Credit author statement Luciana Moretti Angelo: Methodology, Data curation, Investigation, Writing - original draft Debora Franỗa: Methodology, Data curation, Formal analysis, Investigation, Writing - original draft, Writing - review & editing Roselena Faez: Conceptualization, Funding acquisition, Project administration, Resources, Supervision, Writing - review & editing L.M Angelo et al Carbohydrate Polymers 257 (2021) 117635 Fig SEM images of (A) CS, (B) CSKNO3, and (C) CSMMtKNO3; (D) DRX; (E.1) FTIR and (E.2) Enlarged FTIR graphs for all components and 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Testing, 81(October 2019), Article 106196 https://doi.org/10.1016/j polymertesting.2019.106196 Moreira, F M S., & Siqueira, J O (2006) Microbiologia e Bioquímica Solo Editora UFLA Pandey, P., Kumar Verma, M., & De, N (2018) Chitosan in agricultural Context-A review Bulletin of Environment, Pharmacology and Life Sciences Perotti, G F., Kijchavengkul, T., Auras, R A., & Constantino, V R L (2017) Nanocomposites based on cassava starch and chitosan-modified clay: Physico ... facilitated the growth of the microorganism due to the increase of d-spacing, we applied the Fig Biodegradation profile of the CS, CSMMt, CSKNO3 and CSMMtKNO3 of (A) cumulative CO2 release and (B) daily... condition of 40 kV and 15 mA, and with the analysis range of 2◦ to 90◦ 2θ 2.3 Biodegradation analysis by the respirometric method The biodegradation analysis was based on the NBR 14283 standard,... evaluate the biodegradation of the material To overcome this lack of information in the literature, the present work seeks to quantify the biodegradation and understand the chitosan biodegradation