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|Title:||PHOSPHORUS BINDING TO MODIFIED WOOD PULP FIBERS DESIGNED FOR SOILLESS AGRICULTURE|
|Abstract:||The long-term goal of this work was to develop a new organic plant substrate from wood pulp that can be used in soilless (hydroponics) agriculture. This work explored the usage of wood pulp as disposable plant substrate that is chemically active and has the capacity to bind and release important plant nutrients such as phosphorus. The cationic cellulosic pulp fibers had been prepared from softwood bleached kraft pulp according to a water-based modification method involving first the oxidation of pulp with 2,2,6,6-tetramethyl-1-piperidinyoxy radical (TEMPO) followed with the adsorption polyvinylamine (PVAm) on pulp surface. The total carboxyl group contents of the TEMPO oxidized pulp fibers were determined via conductometric titration. After treating the oxidized fibers with PVAm, polyelectrolyte titration was used to determine the nitrogen (cationic charges) content on fibers. The fibers’ nitrogen content varied with the fibers’ carboxyl charge content; 45.5 μmol/g-pulp of carboxyl group content had 18.6 μmol/g- pulp nitrogen content (least observed nitrogen content adsorbed onto pulp), and 207.1 μmol/g-pulp of carboxyl group content had 69.75 μmol/g-pulp nitrogen content (highest observed nitrogen content adsorbed onto pulp). The adsorption and the release of negatively charged phosphate ions onto/from the treated and untreated pulp were evaluated. A maximum adsorption of ~ 10 μmol/g-pulp of phosphate ions was achieved on oxidized fibers treated with PVAm. Although a layer of adsorbed PVAm greatly increases the anion exchange capacity of cellulose fibers, the modified pulp showed a very low phosphate binding capacity of 0.16 mol phosphates per mol of nitrogen. Phosphates adsorbed on the PVAm coated fibers release depended on the pH and ionic strength of the surrounding media. Neutral pH conditions (6.0-7.5) released the least amount of phosphates, which was 30%-40% of the phosphates initially retained on pulp fibers. However, high molarity salt solutions (5 mM) and sulfonic groups (in buffer solutions) released 90%-100% of the adsorbed phosphates at all pH ranges. Cationic pulp fibers matrices with varying phosphate treatment were used to grow Arabidopsis (phosphate sensitive seeds). Arabidopsis grown on cationic pulp fibers displayed the highest total fresh weight, highest leaves weight, and healthiest look. The total fresh weight of the Arabidopsis increased upon growing on cationic pulp fibers by 57% - 67% at the low phosphate treatments. The free phosphates destination in the plant growing media is unpredictable. Free phosphates could end up adsorbing to mineral surfaces or forming secondary compounds with plant nutrients, which make them unavailable for the plants. Even though the PVAm coated fibers had very low phosphate binding capacity, the fibers’ cationic surface can bind enough phosphates, at low phosphate treatment, needed for Arabidopsis cultivation. By binding the phosphates on the fibers’ surface, less phosphates are available in the plant growing media to react or precipitate with other plant nutrients. However, at intermediate or high phosphate treatment PVAm coated fibers didn’t have a great impact on the Arabidopsis plant growth; this is because phosphates available in the plant growing media were relatively greater than the bound phosphates on the PVAm coated fibers.|
|Appears in Collections:||Open Access Dissertations and Theses|
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