Controlled-Release Fertilizer Prepared Using a Biodegradable

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Controlled release fertilizer prepared using a biodegradable aliphatic copolyester of poly(butylene succinate) and dimerized fatty acid Krzysztof Lubkowski, Aleksandra Smorowska, Barbara Grzmil, and Agnieszka Koz#owska J. Agric. Food Chem., Just Accepted Manuscript • DOI: 10.1021/acs.jafc.5b00518 • Publication Date (Web): 26 Feb 2015 Downloaded from http://pubs.acs.org on March 4, 2015

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Journal of Agricultural and Food Chemistry

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Controlled-Release Fertilizer Prepared Using a Biodegradable Aliphatic

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Copolyester of Poly(butylene succinate) and Dimerized Fatty Acid

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Krzysztof Lubkowski*, Aleksandra Smorowska, Barbara Grzmil, Agnieszka Kozłowska

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West Pomeranian University of Technology, Institute of Chemical and Environment

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Engineering, ul. Pułaskiego 10, 70-322 Szczecin, Poland

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*

Corresponding author (Tel: +48 91 449 4730; Fax: +48 91 449 4686; E-mail:

[email protected]) 1 ACS Paragon Plus Environment


1

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ABSTRACT

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The preparation and characterization of a controlled-release multicomponent (NPK)

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fertilizer with the coating layer consisting of a biodegradable copolymer of poly(butylene

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succinate) and a butylene ester of dilinoleic acid (PBS/DLA) is reported. The morphology and

6

structure of the resulting polymer-coated materials and the thickness of the covering layers

7

were examined using X-ray diffraction and scanning electron microscopy coupled with

8

energy dispersive X-ray analysis. The mechanical properties of these materials were

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determined with a strength testing machine. Nutrient release was measured in water using

10

spectrophotometry, potentiometry and conductivity methods. The results of the nutrient

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release experiments from these polymer-coated materials were compared with the

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requirements for controlled-release fertilizers. A conceptual model is presented describing the

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mechanism of nutrient release from the materials prepared in this study. This model is based

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on the concentrations of mineral components inside the water-penetrated fertilizer granules,

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the diffusion properties of the nutrients in water and a diffusion coefficient through the

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polymer layer. The experimental kinetic data on nutrient release were interpreted using the

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sigmoidal model equation developed in this study.

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KEYWORDS: controlled-release fertilizers, biodegradable materials; aliphatic copolyesters

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2 ACS Paragon Plus Environment

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INTRODUCTION

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Global consumption of mineral fertilizers has systematically increased in recent years

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from 135.4 Mt (80.8 Mt N, 32.4 Mt P2O5, 22.2 Mt K2O) in 2000/2001 to 177.2 Mt (107.9 Mt

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N, 41.4 Mt P2O5, 28.0 Mt K2O) in 2011/2012, with a slight decrease in consumption

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occurring in 2008/2009 due to the crisis in the banking system. Fertilizer consumption in the

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2012/2013 season was 178.6 Mt, while worldwide demand is forecast to reach 187.9 Mt and

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200.3 Mt in 2014/2015 and 2018/2019, respectively.1

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While fertilizer production and soil fertilization continue to increase, nutrient use

35

efficiency (NUE) remains relatively low. Nutrient assimilation by crops is estimated to reach

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50-60% for nitrogen and potassium in the first year and 10-25% for phosphorous in the first

37

year, with a further 1-2% per year reduction in following years.2-4 The low effectiveness of

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mineral component assimilation causes serious problems in view of environmental protection,

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and it also adversely affects the human and animal health.3,5-7 This low NUE has adverse

40

economic effects as well, including material losses, energy expenditures and wasted labor,

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negatively affecting the overall economic balance of the agrochemical production process.

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Additionally, non-renewable energy sources such as natural gas are often used for the

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production of mineral fertilizers.8

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Improvements in nutrient use efficiency resulting from developments in fertilizer

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production and utilization have been thoroughly discussed and summarized elsewhere.9,10

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Increases in the effectiveness of nutrient assimilation can be achieved by the production of

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liquid fertilizer both in solution and suspension forms (elimination of drying and granulation

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stages of the process), stabilized fertilizers (with nitrification or urease inhibitors) and urea

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supergranules or urea supergranules containing P and K nutrients for deep placement. These

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increases can be also achieved by developing, producing and applying fertilizers with a



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delayed release of mineral nutrients. The so-called "intelligent fertilizers" release mineral

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components according to the nutrient requirements of the plants4: examples of such materials

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are slow release fertilizers (SRF) and controlled-release fertilizers (CRF).

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According to AAPFCO (Association of American Plant Food Control Officials),11 slow

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release fertilizers (SRF) are chemically or biologically degradable materials with a high

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molecular weight, complex structure and low solubility, whereas controlled-release fertilizers

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(CRF) are materials that release the mineral components through a polymer layer or a

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membrane. A fertilizer is commonly referred to as a slow or controlled-release fertilizer if the

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following requirements are fulfilled: no more than 15% of nutrients are released within 24 h,

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no more than 75% of nutrients are released within 28 days, and at least 75% of nutrients are

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released by the stated release time.12 The application of SRF/CRF that release their nutrients

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in a way that better matches plant requirements improves the effectiveness of fertilization by

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minimizing losses between application and absorption. At the same time, using SRF/CRF

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reduces the negative environmental influence of fertilizers by avoiding the deposition of an

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excessively large amount of highly soluble nitrogen compounds. As SRF/CRF release their

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nutrients slowly and gradually during all vegetation seasons, they only need to be applied

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once, greatly reducing both time and energy consumption. A better and more efficient use of

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nutrients can lead both to a reduction of waste material produced by the fertilizer industry and

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to a reduction in natural gas consumption.

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One of the drawbacks of CRFs, particularly polymer-coated CRFs, is that after nutrient

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consumption, a considerable amount of non-functional polymer remains in the soil,

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amounting to approximately 50 kg/ha per year.4 It should be kept in mind in that context that

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the average consumption of nutrients (NPK) in European Union is approximately 100 kg/ha

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per year. One possible solution that has not yet been implemented on a large scale, is to

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produce CRF using biodegradable materials,13 either natural materials or biosynthetic


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materials manufactured from renewable raw materials. Among the various biodegradable

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materials used for this purpose, starch and its derivatives seem to be the most extensively

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investigated,14,15 although cellulose and its derivatives,16-18 chitosan,19,20 and polylactic acid21

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have also recently been examined for this application as described in the literature.

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All the products with prolonged nutrient release, available on the market, including

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commercially successful ones like OsmocoteTM, MulticoteTM, MeisterTM, NutricoteTM,

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BasacoteTM or PolyonTM, are manufactured with the use of polymers that are not

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biodegradable. The objective of this research was to obtain materials with controlled-release

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properties by coating granules of a mineral fertilizer with a layer of biodegradable aliphatic

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copolymer of poly(butylene succinate) and a butylene ester of dilinoleic acid (PBS/DLA)

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using an immersion method, the characterization of the prepared materials and evaluation of

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the nutrient release kinetics. As far as we know this kind of copolyester (PBS/DLA) has not

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been used in the preparation of controlled-release fertilizer, however copolyesters of succinic

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acid with starch22 and maleic anhydride23 have been evaluated as biodegradable matrix

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materials for the controlled release of bacterial fertilizers.

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MATERIALS AND METHODS

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Materials

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The source of active, mineral, macronutrient components (nitrogen, phosphorous,

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potassium) for this experiment was the commercial, granulated, multicomponent fertilizer

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NPK(S) 6-20-30-(7). This fertilizer contains at least 92% of particles within the range of 2-5

98

mm. Its bulk density is approximately 0.9-1.0 kg/dm3. For the experiment, the granule fraction

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with a diameter of 3-4 mm was selected.



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The fertilizer was commercially produced according to the Dorr-Oliver method.24 The

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mixture of phosphoric and sulphuric acid was neutralized in the saturator with ammonia to

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obtain monoammonium phosphate and ammonium sulphate slurry, which was then granulated

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in the blunger with potassium chloride and small amounts of magnesium carbonate as a filler.

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Fertilizer granules were dried, crushed, sieved and conditioned to obtain the final product.

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The contents of the three main components of the fertilizer, namely nitrogen (5.9 wt% N-

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NH4+), phosphorous (19.8 wt% total P2O5, 18.2 wt% water-soluble P2O5), and potassium

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(29.5 wt% K2O) were determined by potentiometry with an Orion 9512 ion selective

108

electrode (Thermo Fisher Scientific, Beverly, MA), spectrophotometry with a Spekol 11

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instrument (Carl Zeiss, Oberkochen, Germany) and emission flame photometry with a BWB-

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1 instrument (BWB Technologies, Newbury, U.K.), respectively. These measured contents of

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the mineral components are consistent with the data declared by the fertilizer producer.

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The aliphatic copolymer of poly(butylene succinate) and a butylene ester of dilinoleic

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acid (PBS/DLA) was used as a coating material. The aliphatic copolyester was synthesized

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through direct melt polycondensation in the presence of 1,4-butanediol.25 This copolyester is a

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multi-block thermoplastic elastomer composed of soft sequences containing flexible chains of

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butylene ester of dilinoleic acid (DLA) and poly(butylene succinate) (PBS) as hard segments.

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The obtained copolymer contains 60 wt% PBS and 40 wt% DLA. This material was shown to

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be biodegradable in biodegradation tests carried out on thin polymer films (60×60×0.5 mm)

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under controlled conditions at 50 °C for 3 months in a mixture of sand and compost,

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according to the previously reported procedure.26 The weight losses of the PBS/DLA

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copolyester were approximately 5 wt% after one month, 8 wt% after 2 months and 10 wt%

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within 3 months of incubation,25 however there are reports on complete biodegradation of

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PBS and PBS blends with various organic materials.22,23,27


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Despite the fact that the use of PBS/DLA in the preparation of controlled-release

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fertilizers may bring many benefits, especially in the context of environment protection, it

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should be kept in mind that poly(butylene succinate) is not a cost-effective material. The price

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of commercially available PBS is approximately 5.4-5.6 euro/kg and it is comparable with

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other synthetic biodegradable polyesters28 but slightly higher than the price of bio-based,

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biodegradable polymers from natural resources and several times higher than the price of

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conventional, not biodegradable synthetic polymers. The high price of PBS, being the main

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obstacle of its possible acceptance as a fertilizer component, can be lowered by the

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preparation of PBS blends with various organic materials from natural resources, for example

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with dilinoleic acid.

134 135

Preparation

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The granules of the multicomponent fertilizer in the 3-4 mm fraction were weighed and

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coated with a layer of biodegradable copolyester of PBS/DLA by the immersion method. For

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this purpose, appropriate amounts of solid polymer were dissolved, gradually and with the use

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of a magnetic stirrer, in appropriate amounts of chloroform (preferably 10 g ± 0.1 g of

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PBS/DLA and 90 g ± 0.1 g of chloroform) to obtain 10 wt% solution. Fertilizer granules were

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placed separately as a monolayer on the stainless steel wire cloth (opening size 1.6 mm x 1.6

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mm) and dipped into the solution, with a contact time of 2-3 s, at a constant temperature of 25

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°C, and then dried at 60 °C to evaporate the solvent residue. Repeating this dipping/drying

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procedure controlled and determined the amount of polymer layer coating the granules. After

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preparation, the coated fertilizer granules were weighed again. This method was used to

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prepare materials with various polymer to fertilizer (P/F) mass ratios.

147 148

Methods



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The morphology of the polymer-coated granules and the thickness of the coating layers

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were examined using an SU8020 scanning electron microscope with cold field emission and

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resolving power 1.3 nm (Hitachi High-Technologies Corporation, Tokyo, Japan) coupled with

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an energy dispersive NSS 312 X-ray analyzer (Thermo Fisher Scientific, Madison, WI).

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Granules of the prepared fertilizer materials were mechanically polished to achieve a flat

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cross section and then placed on double-sided adhesive tape kept on an aluminum stub.

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Granules were sprayed with a thin conductive film of chromium in a Q150T ES turbo-

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pumped sputter coater (Quorum Technologies, Laughton, U.K.). Coated fertilizers were

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observed at an accelerating voltage of 138 eV. Cross sections through the granules of the

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prepared fertilizer materials were recorded at a magnification of 20X. The thickness of the

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polymer layers was measured at a magnification of 100X. EDX mapping was also performed.

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XRD experiments were performed on an X′Pert PRO powder diffractometer

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(PANalytical, Almelo, Netherlands) with a proportional detector, computer-aided data

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acquisition and a copper lamp as an X-ray radiation source. The XRD patterns were recorded

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over the 2θ range from 10-60o.

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The mechanical strength of the prepared material granules was measured using a

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commercial table-top Zwick/Roell Z2.5 strength testing machine (Zwick GmbH, Ulm,

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Germany) with the TestExpert II ver. 2.2 software. The granules were individually

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compressed in the radial direction between two rigid plates with a maximum testing force

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Fmax of 2.5 kN at a constant crosshead test speed of 10 mm/s. The load at which the granule

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fractured was recorded as the crushing strength. For each sample, a total of 25 parallel

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measurements were carried out. Crushing strength was normalized to the granule diameter

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and compared with the mechanical properties of a commercial fertilizer.

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Nutrient release from the prepared fertilizer materials was measured over time in water.

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A sample of the prepared material (preferably five granules, weighted with the accuracy of


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0.0001 g) was placed in a plastic cap beaker with 50 mL ± 0.5 mL of distilled water. The

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sample was incubated at a constant temperature of 25 oC ± 0.5 oC. After 1 h of incubation the

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solution was decanted and the beaker was again filled with 50 mL ± 0.5 mL of distilled water.

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This procedure was repeated after 3, 6, and 24 h and after 3, 5, 7, 14, 21 and 28 days.

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Spectrophotometric and potentiometric methods were used to determine the amounts of

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released phosphates and ammonium, respectively.

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The overall release of water-soluble mineral components of the fertilizer was also

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monitored and analyzed with the use of CPC 505 pH/conductivity meter with temperature

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compensation (Elmetron, Zabrze, Poland). Polymer-coated granules with a given polymer to

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fertilizer ratio (P/F) were placed into distilled water at ambient temperature, and the

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conductivity was measured automatically every hour for six days (144 h). At the end of the

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experiment, the granules were mechanically crushed to determine the final conductivity value.

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Data analysis software system STATISTICA version 10.0 was used to evaluate

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descriptive statistics, i.e. standard deviation and standard error. To describe experimental data

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related to nutrient release experiments with model lines OriginPro 8 software was used.

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RESULTS AND DISCUSSION

191 192

Morphology and structure

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Granules of the NPK fertilizer are initially of regular, spherical shape and uniform light-

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grey to dark-grey color. No permanent caking of the fertilizer granules are observed: they are

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hard, although when subjected to adequate crushing force they can be easily crumbled into

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small pieces that can then be milled into a powder. XRD measurements (Figure 1)

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demonstrate that the NPK fertilizer includes nitrogen, phosphorus and potassium mainly in

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the form of dihydrogen ammonium phosphate, ammonium chloride and potassium chloride.



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Nonetheless, as the multicomponent NPK fertilizer is an example of a complex fertilizer,

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some small amounts of additional compounds resulting from reactions between initial

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substrates may also be observed and identified.

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Fertilizer granules were coated with PBS/DLA copolyester by the immersion method to

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create over forty samples of materials with different polymer to fertilizer mass ratios and with

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various layer thicknesses. The mass ratio of polymer to fertilizer P/F was determined based on

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the mass balance of the process. Fertilizer materials have been obtained with mass ratios P/F

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ranging from 0.18 up to 0.26. The fertilizer granules are completely covered with the

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polymer. The prepared materials consist of a fertilizer core surrounded by an inert polymer

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layer. The surface of the prepared materials is uniform, dense and compact. There are no

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visible cracks or fractures on the material surfaces. The degree of coverage of granules with

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the polymer, i.e., the polymer to fertilizer mass ratio, increased with the number of immersion

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cycles and the contact time.

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Cross sectional SEM images of the NPK fertilizer granules covered with PBS/DLA at

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two different polymer to fertilizer mass ratio extremes of 0.18 and 0.26 are presented in

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Figure 2. As the thickness of the layer varies around the granule, twenty measurements were

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made to ensure accurate evaluation, with five measurements for every quarter of the granule

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cross-section. Based on the performed measurements, the mean value of the polymer coating

217

thickness was determined to be 190.4 µm (with a standard deviation of 9.21 and a standard

218

error of 2.06) in the case of the material with P/F = 0.18 (Figure 2A) and 231.2 µm (with a

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standard deviation of 8.81 and a standard error of 1.97) in the case of the material with the

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mass ratio P/F = 0.26 (Figure 2B).

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The distribution of elements in the prepared materials was characterized using a

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scanning electron microscope coupled with the energy dispersive X-ray analyzer. The EDX

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mapping of the cross-section of the material with P/F = 0.18 is presented in Figure 3. The


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EDX analysis demonstrates that only carbon and oxygen are present in the polymer coating

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layer. This observation is consistent with the chemical composition of the polymer used in the

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experiment. The structure of the formed layer is rather homogeneous, with carbon and oxygen

227

atoms spread quite uniformly throughout the layer. The EDX analysis demonstrates that the

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components of the polymer coating do not penetrate into the granule core, which appears to

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be quite heterogeneous. The EDX mapping exhibits areas with higher concentrations of

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potassium (red dots) and chlorine (bright pink dots). The increased incidence of these

231

elements results from the presence of larger particles of potassium chloride in those places. It

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is expected that the concentrations of oxygen (green dots) and phosphorus (dark blue dots), as

233

the components of ammonium phosphate salts, are significantly lower in these areas. The

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EDX mapping also indicates that small amounts of sulphur (light blue dots) are spread evenly

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throughout the granule. Setting aside the location and arrangement of the elements in the

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granule core, the EDX analysis demonstrates that fertilizer components from the granule core

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do not pass into the polymer layer. To confirm that observation, a granule covered with a

238

polymer layer was cut in half and the mineral components of the fertilizer were rinsed off

239

with water. A meticulous and thorough inspection of the polymer layer revealed no

240

differences in appearance between the inside and outside surfaces of the layer.

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To investigate whether any interactions occur between the fertilizer components and the

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polymer material used to cover the granules, XRD analysis was also performed. The XRD

243

spectra of the prepared materials (not presented here) were compared with the spectrum of the

244

initial NPK fertilizer. These spectra are highly similar, with no differences observed in the

245

position and intensity of the peaks between the spectra of the prepared materials and the initial

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NPK fertilizer. All recorded peaks can be assigned only to the fertilizer components. Based on

247

the fact that no new peaks are present in the spectra of the prepared materials, no new phases

248

are formed during the coating process. Therefore, the interactions between the fertilizer



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components of the granule and the polymer layer components are physical but not chemical in

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nature.

251 252

Mechanical properties

253

Crushing strength was measured for samples of prepared materials with the lowest and

254

highest polymer to fertilizer mass ratios of 0.18 and 0.26 respectively, and for the initial NPK

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fertilizer. For each sample, 25 parallel measurements were performed and the mean value of

256

the crushing strength was then calculated. The dependence of the crushing strength on

257

deformation for the polymer coated materials and for the initial NPK fertilizer are presented

258

in Figures 4.

259

Fertilizers can be considered typical materials with a brittle failure mode. Fertilizer

260

granules are porous, containing various mineral compounds with many flaws, dislocations and

261

crystal edges.29,30 Any discontinuity in the fertilizer granule bulk should be treated as a defect

262

and the reason for the stress concentration. The mechanical damage to the fertilizer granule

263

results from brittle failure due to an abrupt disastrous increase of a decisive defect under

264

tensile stress induced in the material bulk. In the case of the initial NPK fertilizer, fracture or

265

rather cracking of the granule occurred at the crushing strength of 21 N, with the mean

266

deformation of 17% (Figure 4). The obtained crushing strength (21 N) corresponds to

267

pressure of 2.1 kg/granule and is comparable with the literature data for various granulated

268

fertilizer compounds: urea (1.5-3.5 kg/granule), triple superphosphate (TSP) (1.5-3

269

kg/granule), monoammonium phosphate (MAP) (2-3 kg/granule) or ammonium sulphate (1.5-

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2.5 kg/granule).31 Compared with the starting NPK fertilizer, polymer-coated granules

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exhibited significantly higher resistance towards the crushing force (Figure 4). For both

272

prepared and examined materials, the crushing force continuously increased with deformation

273

up to 50%, and no fracture or cracking of the samples were observed. The crushing force


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reached the value of almost 170 N in the case of the material with the polymer to fertilizer

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mass ratio of 0.26, and 120 N for the material with the polymer to fertilizer mass ratio of 0.18.

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Based on the experiments and dependencies presented here, it is not possible to determine the

277

maximum crushing strength for the prepared polymer-coated materials because of their

278

ductile properties. Instead of a brittle failure, only a plastic deformation of these samples can

279

be observed, evidently within the deformation region from 0-50%.

280 281

Nutrient release

282

All prepared polymer-coated materials were tested in water release experiments. This

283

kind of approach (nutrient release in water) is fully acceptable: several papers using that

284

approach have been published recently.16,18,32-35 Nutrient release in water and nutrient release

285

in soil are quite different aspects of the topic. Undoubtedly, field experiments are necessary in

286

the further and final assessment of the product, but these experiments will be addressed in

287

another paper. Besides, as it was clearly indicated in the relevant references,16,36 nutrient

288

release in soil can be easily predicted from release experiments performed in water, although

289

the nutrient release rate depends on the medium used, with the fastest release rate observed in

290

water, followed by water-saturated sand, and finally by sand.36

291

Figure 5 presents the results of the investigation of phosphate release from the prepared

292

polymer-coated materials over 24 h. The data presented here show that for the group of

293

materials with polymer to fertilizer mass ratios in the range from approximately 0.23-0.26,

294

less than 15% of phosphates is released within 24 h. Additionally, long-term release

295

experiments have demonstrated that the release of phosphate from this group of materials is

296

less than 75% within 28 days. On the other hand, for the group of materials with polymer to

297

fertilizer mass ratios less than 0.23, more than 15% of phosphates are released within 24 h.

298

Based solely on these phosphate release results, the materials prepared here with polymer to



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fertilizer mass ratios ranging from approximately 0.23-0.26 meet the first and second criteria

300

of controlled-release fertilizers, while those with mass ratios less than 0.23 do not.

301

A series of papers36-39 reported that the release rate of phosphates is lower than those of

302

K, N-NH4+ and N-NO3-. There is no consensus as to the margin of that discrepancy. In some

303

experiments, the release rate of phosphates was 45-70% slower than that of nitrates,36 but only

304

a 10% difference was observed in another study.38 The presence of strong interactions among

305

nutrients in the fertilizer granule and differences in nutrient solubility could lead to this

306

observed difference in release rate.36 Generally, the phosphate release rate can be treated as a

307

“bottleneck” for overall nutrient release. The kinetics of chemical processes are known to be

308

controlled by their slowest steps. The release of phosphates from controlled-release fertilizers

309

is the slowest step, therefore their release rate determines the overall nutrient release from that

310

type of material. To define controlled-release fertilizers, however, rather than knowing which

311

fertilizer component is released the slowest, it is important to know which is released the

312

fastest or to determine the overall nutrient release rate.

313

Additional experiments have been conducted to more accurately assess the release

314

properties of the materials prepared here. The release of ammonium and phosphate ions for

315

the sample of prepared material with the highest mass ratio of polymer to fertilizer (P/F =

316

0.26) is compared in Figure 6A. Throughout the whole experiment, the release of phosphates

317

is slower than the release of ammonium ions. However, the most significant difference in

318

release is observed during the first 24 h. After that time, the cumulative release for phosphate

319

and ammonium ions is 13% and 37%, respectively, whereas after 7 days it is 58% and 80%.

320

The average difference between the release of phosphate and ammonium ions is 19%.

321

Figure 6B presents the results of nutrient release measured by conductivity for the

322

sample of prepared material with the highest mass ratio of polymer to fertilizer (P/F = 0.26).

323

The release of the mineral components of the fertilizer R(%) was calculated according to the


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following equation, where σt represents the measured conductivity at time t and σF represents

325

the final conductivity value:

σ t ⋅ 100 σF

326

R=

327

Several studies have shown36,40,41 that nutrient release from polymer-coated CRF can be

328

described in three stages: lag period, linear stage and decay period. In the experiment

329

presented here (Figure 6B), the lag period is quite long. Placing the tangent line onto the

330

experimental curve at the inflection point (31st hour) enables a rough estimate of the lag time,

331

which is between 5 and 14 h. The linear stage of the release profile cannot be identified

332

because the release rate constantly increases until the maximum release rate is reached at the

333

thirty first hour of the process. From that point, the release rate slowly decays, almost

334

reaching zero after 140 h. Two further observations are worth mentioning. First, between

335

hours 8 and 14, the release rate substantially increases, which might be related to the earlier

336

differences in the release rates of fertilizer components. Secondly, after 24 h the release of all

337

water-soluble fertilizer components is approximately 11%, significantly below the limit of the

338

first requirement of slow/controlled-release fertilizers.

(1)

339

Based on the experimental results presented here, the following conceptual model of

340

nutrient release from the prepared fertilizer material can be proposed. At the very beginning

341

of the process, after immersion of the polymer-coated fertilizer in water, water starts to

342

diffuse through the polymer layer to penetrate the inner part of the granule. The fertilizer

343

material is mainly composed of readily water-soluble compounds with similar water

344

solubilities (KCl – 342 g/dm3, NH4Cl – 370 g/dm3, NH4H2PO4 – 370 g/dm3). The fertilizer

345

components begin to dissolve in water. Based on the initial fertilizer composition and XRD

346

measurement results (Figure 1), it is obvious that the same amounts of ammonium and

347

phosphate ions result from the dissolution of dihydrogen ammonium phosphate. However, an

348

additional amount of ammonium ions is present within the granule due to ammonium chloride 15 ACS Paragon Plus Environment


Page 16 of 34

349

dissolution. Therefore, it seems reasonable to conclude that the concentration of ammonium

350

ions in the water-penetrated fertilizer granule is greater than the concentration of phosphate

351

ions. Moreover, the concentration of phosphate ions is lower because slight amounts of

352

phosphorous (approximately 8%) are bound up in the form of water-insoluble compounds.

353

Differences in these ion concentrations may be one of the factors affecting nutrient release

354

from polymer-coated fertilizer. Water-dissolved components of the fertilizer diffuse through

355

the polymer layer outside the granule. As the driving force for diffusion depends on the

356

component concentration gradient, the release of ammonium ions surpasses the release of

357

phosphate ions. In discussing the release of ions (nutrients) from polymer-coated fertilizer,

358

two other parameters should be considered, diffusion coefficients in water and ionic radii of

359

non-hydrated and hydrated ions (Supporting Information Table SI-A).42-46 As the ionic

360

potential |Zi|/ri increases, where |Zi| is the absolute value of the charge of ion i and ri is the

361

crystal ionic radius of ion i, the ionic diffusion in water decreases. The reason for that

362

dependence is that the hydration layer of the water molecules around the ion becomes thicker,

363

thus hindering movement of the ion. The diffusion of phosphate ions in water is around three

364

times less than the diffusion of ammonium ions in water, thus contributing to the slower

365

release of phosphate ions from the polymer-coated granule.

366

Summarizing the previous considerations, both the observed discrepancy between the

367

release of phosphate and ammonium ions (Figure 6A) and the substantial increase in the

368

release rate between hours 8 and 14 of the process (Figure 6B) can be explained by the

369

influence of nutrient concentration and diffusion properties of those nutrients in water.

370

However, based on the available experimental data, it is not possible to assess the mutual

371

interaction of these factors in this phenomenon.

372

The release of phosphates and nutrients in general from the prepared polymer-coated

373

materials depends on the polymer to fertilizer mass ratio (Figure 5). The phosphate release


Page 17 of 34


374

decreases as the mass ratio of polymer to fertilizer increases and as the layer thickness

375

increases. The diffusion mechanism of the release can be noted as a reason for that

376

correlation.36 As the layer thickness increases, the value of the diffusion coefficient D

377

decreases and the release process becomes increasingly hindered. The value of the diffusion

378

coefficient D through the polymer layer can be calculated according to the equation: h2 6 ⋅ t lag

379

D=

380

Taking the value of the polymer layer thickness (h = 231 µm) (Figure 2) and the value

381

of the lag period (tlag = 5-14 h) (Figure 6B) for the material with the highest polymer to

382

fertilizer mass ratio (P/F = 0.26), the estimated value of the diffusion coefficient D may be in

383

the range of 0.176-0.494⋅10-8 cm2/s. The diffusion coefficient through the polymer layer D is

384

around four orders of magnitude smaller than the diffusion coefficients in water Do presented

385

earlier. The obtained D value refers to the diffusion of all water-soluble components of the

386

fertilizer. We cannot provide detailed values for particular ions based on this experimental

387

data, but this will be addressed in future research.

(2)

388

Note that all release experiments presented here were conducted in water. As mentioned

389

earlier, nutrient release from polymer-coated controlled-release fertilizers is mainly controlled

390

by diffusion. When materials with biodegradable polymer coatings are investigated in those

391

conditions (water release experiments), the diffusion through the polymer layer has a critical

392

impact on the release pattern. If the release experiments from materials coated with these

393

biodegradable polymers were performed in soil, then some other factors and parameters

394

would be important, especially microorganism-induced biodegradation of the polymer layer.

395

While microorganism-related biodegradation of the polymer layer and its influence on

396

nutrient release is not addressed in the current work, that issue should be the topic of future

397

research.



Page 18 of 34

398

Figure 7 presents the results of 28 day release experiments for the polymer-coated

399

materials with polymer to fertilizer mass ratios of 0.18, 0.20, 0.24 and 0.26 and the NPK

400

fertilizer. During these experiments, the amounts of released phosphates were determined as a

401

function of time at a constant temperature of 25 °C. The release of phosphates from the NPK

402

fertilizer was very fast, with all phosphates released within 55-60 min. Based on the results

403

presented here, all coated materials exhibit slower release of phosphates in comparison with

404

the starting fertilizer.

405

Nutrient uptake by plants exhibits a sigmoidal relationship with the point in the plant’s

406

vegetation cycle.3,4,46,47 Therefore, all experimental data presented related to nutrient release

407

from the prepared polymer-coated materials were described and interpreted with a kinetic

408

model. To interpret the kinetic data, a sigmoidal model equation was applied:

409

R=

410

where Mt/M∞ is the fraction of nutrients released at time t and a, b, c, d are the parameters of

411

the sigmoidal equation.

Mt = M∞

a−b +b t −d  1 + exp   c 

(3)

412

The experimental data of nutrient release from the prepared polymer-coated materials

413

and the predicted values calculated using the sigmoidal equation are compared in Figures 6-7.

414

The sigmoidal model satisfactorily fits the experimental data, with the best result obtained for

415

the experiment performed using the conductivity method (Figure 6B). Based on the applied

416

sigmoidal model, the constants and correlation coefficients of the equations were determined

417

and are given in Supporting Information Table SI-B.

418

The sigmoidal equation produces model lines that fit the experimental data very well as

419

expressed by correlation coefficients. Keeping in mind the fact that the nutrient uptake by

420

plants follows a sigmoidal curve and that the sigmoidal model has already been applied to


Page 19 of 34


421

describe controlled release,48-50 the sigmoidal equation used in the present work satisfactorily

422

predicts the release of phosphates from the prepared polymer-coated materials.

423 424

In conclusion, the new, innovative, biodegradable copolymer of poly(butylene

425

succinate) and the butylene ester of saturated dilinoleic acid was successfully applied in the

426

preparation of fertilizer materials with controlled and prolonged nutrient release.

427

Multicomponent fertilizer granules can be coated with a polymer layer using the immersion

428

method, which creates an incentive to use the process on a larger scale, for example by

429

spraying in a drum granulator or in the Wurster bed.

430

The obtained polymer-coated materials differ from each other in the layer thickness and

431

the polymer to fertilizer mass ratio. The mass ratio of polymer to fertilizer ranged from 0.18-

432

0.26, and the layer thickness ranged from 190-230 µm. The interactions between the fertilizer

433

components of the granule and the polymer layer components were found to be physical

434

rather than chemical in nature. The mechanical properties of the fertilizer granules coated

435

with the copolyester layer are significantly better than those of the NPK fertilizer.

436

Release experiments have shown that polymer-coated materials with polymer to

437

fertilizer mass ratios of 0.23-0.26 meet the requirements of controlled-release fertilizers. The

438

overall nutrient release was less than 15% within 24 h and approximately 75% after 28 days,

439

although the ammonium ion release during first 24 h of the experiment was significantly

440

higher than the release of phosphate ions. The concentrations of the mineral components

441

inside the water-penetrated fertilizer granules and the diffusion properties of the nutrients in

442

water have been indicated as the reasons for that discrepancy. Nutrient release from the

443

polymer-coated materials decreased with the increasing layer thickness. The diffusion

444

mechanism of release has been noted as a reason for that correlation. The diffusion coefficient

445

through the polymer layer was estimated as D = 0.176-0.494⋅10-8 cm2/s. The experimental



Page 20 of 34

446

kinetic data of nutrient release from the prepared polymer-coated materials have been

447

accurately described using a sigmoidal model equation.

448 449

SUPPORTING INFORMATION

450

Tables SI-A and SI-B. This material is available free of charge via the internet at

451

http://pubs.acs.org.

452 453

REFERENCES

454 455

1.

Heffer, P.; Prud’homme, M. Fertilizer outlook 2014-2018, 82nd IFA Annual Conference,

456

Sydney, 2014, 1-7;

457

http://www.fertilizer.org/imis20/images/Library_Downloads/2014_ifa_sydney_summary.

458

pdf?WebsiteKey=411e9724-4bda-422f-abfc-

459

8152ed74f306&=404%3bhttp%3a%2f%2fwww.fertilizer.org%3a80%2fen%2fimages%2

460

fLibrary_Downloads%2f2014_ifa_sydney_summary.pdf (15 January 2015).

461

2.

technology and use; Engelstad, O. P., Ed.; SSSA, Madison, Wisconsin, 1985; 293-322.

462 463

Hauck, R. D. Slow release and bio-inhibitor-amended nitrogen fertilizers. In Fertilizer

3.

Shaviv, A.; Mikkelsen, R. I. Controlled-release fertilizers to increase efficiency of

464

nutrient use and minimize environmental degradation – a review. Fert. Res. 1993, 35, 1-

465

12.

466

4.

Trenkel, M. E. Slow- and controlled-release and stabilized fertilizers: an option for

467

enhancing nutrient use efficiency in agriculture; International Fertilizer Industry

468

Association, Paris, France, 2010.


Page 21 of 34

469


5.

Finck, A. Fertilizers and their efficient use. In World Fertilizer Use Manual; Halliday, D.

470

J.; Trenkel, M. E.; Wichmann W., Eds.; International Fertilizer Industry Association,

471

Paris, France, 1992.

472

6.

8, 443-458.

473 474

7.

Newbould, P. The use of nitrogen fertilizer in agriculture. Where do we go practically and ecologically? Plant Soil 1989, 115, 297-311.

475 476

Forman, D. Are the nitrates a significant risk factor in human cancer? Cancer Surv. 1989,

8.

Cruse, M. J.; Liebman, M.; Raman, D. R.; Wiedenhoeft, M. H. Fossil energy use in conventional and low-external input cropping systems. Agron. J. 2010, 102, 934-941.

477 478

9.

Roberts, T. L. Improving nutrient use efficiency. Turk. J. Agric. For. 2008, 32, 177-182.

479

10. Chien, S. H.; Prochnow, L. I.; Cantarella, H. Recent developments of fertilizer production

480

and use to improve nutrient efficiency and minimize environmental impacts. Adv. Agron.

481

2009, 102, 267-322.

482

11. Association of American Plant Food Control Officials (AAPFCO), Official Publication

483

No. 50, T-29. Association of American Plant Food Control Officials, Inc., West

484

Lafayette, Indiana, 1997.

485

12. European Standard EN 13266, Slow-release fertilizers - Determination of the release of

486

the nutrients - Method for coated fertilizers. European Committee for Standardization,

487

Brussels, Belgium, 2001.

488 489 490 491

13. Akelah, A. Novel utilizations of conventional agrochemicals by controlled release formulations. Mater. Sci. Eng. C. 1996, 4, 83-98. 14. Niu, Y.; Li, H. Controlled release of urea encapsulated by starch-g-poly(vinyl acetate). Ind. Eng. Chem. Res. 2012, 51, 12173-12177.



Page 22 of 34

492

15. El Diwani, G.; Motawie, N.; Shaarawy, H. H.; Shalaby, M. S. Nitrogen slow release

493

biodegradable polymer based on oxidized starch prepared via electrogenerated mixed

494

oxidants. J. Appl. Sci. Res. 2013, 9, 1931-1939.

495

16. Perez-Garcia, S.; Fernandez-Perez, M.; Villafranca-Sanchez, M.; Gonzales-Pradas, E.;

496

Flores-Cespedes, F. Controlled release of ammonium nitrate from ethylcellulose coated

497

formulations. Ind. Eng. Chem. Res. 2007, 46, 3304-3311.

498

17. Fernandez-Perez, M.; Garrido-Herrera, F. J.; Gonzalez-Pradas, E.; Villafranca-Sanchez,

499

M.; Flores-Cespedes, F. Lignin and ethylcellulose as polymers in controlled release

500

formulations of urea. J. Appl. Polym. Sci. 2008, 108, 3796-3803.

501

18. Costa, M. M. E.; Cabral-Albuquerque, E. C. M.; Alves, T. L. M.; Pinto, J. C.; Fialho, R.

502

L. Use of polyhydroxybutyrate and ethyl cellulose for coating of urea granules. J. Agric.

503

Food Chem. 2013, 61, 9984-9991.

504

19. Melaj, M. A.; Daraio, M. E. Preparation and characterization of potassium nitrate

505

controlled-release fertilizers based on chitosan and xanthan layered tablets. J. Appl.

506

Polym. Sci. 2013, 130, 2422-2428.

507

20. Corradini, E.; de Moura, M. R.; Mattoso, L. H. C. A preliminary study of the

508

incorporation of NPK fertilizer into chitosan nanoparticles. eXPRESS Polym. Lett. 2010,

509

4, 509-515.

510

21. Wu, C.-S. Polylactide-based renewable composites from natural products residues by

511

encapsulated film bag: characterization and biodegradability. Carbohydr. Polym. 2012,

512

90, 583-591.

513 514 515 516

22. Wu, C.-S. Controlled release evaluation of bacterial fertilizer using polymer composites as matrix. J. Control. Release 2008, 132, 42-48. 23. Wu, C.-S. Promoting fertilizer use via controlled release of a bacteria-encapsulated film bag. J. Agric. Food Chem. 2010, 58, 6300-6305.


Page 23 of 34

517 518


24. Lutz, W. A. Production of ammonium phosphate. Patent US3310371, United States Patent Office, 1967.

519

25. Kozłowska, A.; Gromadzki, M.; El Fray, M.; Štĕpánek, P. Morphology evaluation of

520

biodegradable copolyesters based od dimerized fatty acid studied by DSC, SAXS and

521

WAXS. Fibres Text. East. Eur. 2008, 16, 85-88.

522 523

26. Diamond, M. J.; Freedman, B.; Garibaldi, J. A. Biodegradable polyester films. Int. Biodeterior. Biodegrad. 2001, 48, 219-224.

524

27. Reddy, M. M.; Mohanty, A. K.; Misra, M. Optimization of tensile properties

525

thermoplastic blends from soy and biodegradable polyesters: Taguchi design of

526

experiments approach. J. Mater. Sci. 2012, 47, 2591-2599.

527

28. Changsha Green Mountain Chemical Co., Organic Products, Polybutylene succinate,

528

http://greenmountchem.en.alibaba.com/product/526875229-

529

213189775/Polybutylene_succinate.html (15 January 2015).

530

29. Kelbaliyev, G. I.; Samedli, V. M.; Samedov, M. M.; Kasimova, R. K. Experimental study

531

and calculation of the effect of intensifying additives on the strength of superphosphate

532

granules. Russ. J. Appl. Chem. 2013, 86, 1478-1482.

533 534 535 536

30. Nie, X.; Besant, R. W.; Evitts, R. W. An experimental study of moisture uptake and transport in a bed of urea particles. Granul. Matter 2008, 10, 301-308. 31. Clayton, W. E. Physical properties of fertilizers. In Modern techniques in fertilizer distribution and handling, Muscle Shoals, Alabama, 1995.

537

32. Bortolin, A.; Aouada, F. A.; de Moura, M. R.; Ribeiro, C.; Longo, E.; Mattoso, L. H. C.

538

Application od polysacharide hydrogels in adsorption and controlled-extended release of

539

fertilizers processes. J. Appl. Polym. Sci. 2012, 123, 2291-2298.



Page 24 of 34

540

33. Calabria, L.; Vieceli, N.; Bianchi, O.; de Oliveira, R. V. B.; Filho, I. N.; Schmidt, V. Soy

541

protein isolate/poly(lactic acid) injection-molded biodegradable blends for slow release of

542

fertilizers. Ind. Crop. Prod. 2012, 36, 41-46.

543

34. Pereira, E. I.; Minussi, F. B.; da Cruz, C. C. T.; Bernardi, A. C. C.; Ribeiro, C. Urea-

544

montmorillonite-extruded nanocomposites: A novel slow-release material. J. Agric. Food

545

Chem. 2012, 60, 5267-5272.

546

35. Bortolin, A.; Aouada, F. A.; Mattoso, L. H. C.; Ribeiro, C. Nanocomposite

547

PAAm/methyl cellulose/montmorillonite hydrogel: evidence of synergetic effects for the

548

slow release of fertilizers. J. Agric. Food Chem. 2013, 61, 7431-7439.

549 550 551 552

36. Du, C.; Zhou, J.; Shaviv, A. Release characteristics of nutrients from polymer-coated compound controlled release fertilizers. J. Polym. Environ. 2006, 14, 223-230. 37. Shoji, S.; Gandeza, A. T. Controlled release fertilizers with polyolefin resin coating, Kanno Printing Co. Ltd. Sendai, Japan, 1992.

553

38. Huett, D. O.; Gogel, B. J. Longevities and nitrogen, phosphorus and potassium release

554

patterns of polymer-coated controlled-release fertilizers at 30°C and 40°C. Commun. Soil

555

Sci. Plant Anal. 2000, 31, 959-973.

556

39. Shaviv, A. Advances in controlled release of fertilizers. Adv. Agron. 2000, 71, 1-49.

557

40. Du, C.; Zhou, J.; Shaviv, A.; Wang, H. Mathematical model for potassium release from

558

polymer-coated fertilizer. Biosystems Eng. 2004, 88, 395-400.

559

41. Du, C.; Tang, D.; Zhou, J.; Wang, H.; Shaviv, A. Prediction of nitrate release from

560

polymer-coated fertilizers using an artificial neural network model. Biosystems Eng.

561

2008, 99, 478-486.

562 563

42. Li, J.-H.; Gregory, S. Diffusion of ions in sea water and in deep-sea sediments. Geochim. Cosmochim. Acta 1974, 38, 703-714.


Page 25 of 34

564 565


43. Gourary, B. S.; Adrian, F. J. Wave functions for electron-excess color centers in alkali halide crystals. Solid State Phys. 1960, 10, 127-247.

566

44. Chua, K. S. Experimental multivalent ionic radii. Nature 1968, 220, 1317-1319.

567

45. Conway, B. E. Ionic Hydration in Chemistry and Biophysics (Studies in Physical &

568

Theoretical Chemistry), Elsevier, New York, 1981.

569

46. Shaviv, A. Controlled Release Fertilizers, IFA International Workshop on Enhanced-

570

Efficiency Fertilizers, Frankfurt, International Fertilizer Industry Association, Paris,

571

France, 2005.

572

47. Shoji, S.; Takahashi, C. Innovative fertilization methods. In Meister controlled release

573

fertilizer – properties and utilization, Konno Printing Company Ltd. Sendai, Japan, 1999.

574

48. Jarrell, W. M.; Boersma, L. Model for the release of urea by granules of sulphur-coated

575

urea applied to soil. Soil Sci. Soc. Am. J. 1979, 43, 1044-1050.

576

49. Shaviv, A.; Raban, S.; Zaidel, E. Modelling controlled nutrient release from polymer

577

coated fertilizers: diffusion release from single granules. Environ. Sci. Technol. 2003, 37,

578

2251-2256.

579

50. Shaviv, A.; Raban, S.; Zaidel, E. Modelling controlled nutrient release from a population

580

of polymer coated fertilizers: statistically based model for diffusion release. Environ. Sci.

581

Technol. 2003, 37, 2257-2261.

582 583 584 585 586 587 588



Page 26 of 34

589

FIGURE CAPTIONS

590

Figure 1. XRD image of the commercial, multicomponent fertilizer NPK(S) 6-20-30-(7).

591

Figure 2. SEM images of the fertilizer granules coated with PBS/DLA with extreme polymer

592

to fertilizer mass ratios (A – P/F = 0.18; B – P/F = 0.26).

593

Figure 3. EDX mapping of the elements for the material with polymer to fertilizer mass ratio

594

P/F = 0.18. Elements correspond to the color code indicated at the top of each panel.

595

Figure 4. Crushing strength as a function of deformation for materials with different polymer

596

to fertilizer mass ratios and for the uncoated, starting NPK fertilizer.

597

Figure 5. Release of phosphates vs. the polymer to fertilizer mass ratio P/F after 24 h.

598

Figure 6. The comparison between the release of ammonium and phosphate ions (A) and the

599

nutrient release measured by conductivity (B) for the sample of prepared material with the

600

highest polymer to fertilizer mass ratio (P/F = 0.26).

601

Figure 7. Release of phosphates within 28 days from: A – polymer-coated materials with

602

polymer to fertilizer mass ratios of 0.18, 0.20, 0.24, and 0.26; B – uncoated NPK fertilizer.


Page 27 of 34


FIGURE 1

intensity, arb. u.

KCl NH4H2PO4 NH4Cl

10

20

30

40

50

60

70

2θ, deg



Page 28 of 34

FIGURE 2


Page 29 of 34


FIGURE 3



Page 30 of 34

FIGURE 4


Page 31 of 34


FIGURE 5



Page 32 of 34

FIGURE 6


Page 33 of 34


FIGURE 7



Page 34 of 34

FOR TABLE OF CONTENTS ONLY


Controlled-Release Fertilizer Prepared Using a Biodegradable

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