Formulating Waterborne Coatings for Agricultural Applications
Creators: name: HALL, JOE LOUIS
Publisher: name: University of Surrey
Year: 2022

description: Seed coating is the process of applying exogenous materials to the surface of seeds before planting. Seed coatings provide numerous benefits, including targeted delivery of active ingredients, addition of weight, and shape standardisation to aid plantability. Seed coatings typically contain a binder (often a synthetic colloidal polymer, called ‘latex’), filler particles (such as clay or calcium carbonate, CaCO3), surface modifiers (wax additives), and other ingredients such as dispersants and rheology modifiers. This thesis explores film coatings, which are a few micrometers thick. Despite the benefits of coated seeds, problems such as dust-off and clumping can arise if the formulation is not optimised. Seed coatings must not be brittle and should have a high adhesion strength to the seed, without adhering to adjacent seeds during storage. Current studies on waterborne polymer composites do not systematically investigate the effects of the co-formulants adequately, and there is a particular need to characterise coating properties, rather than bulk material properties. This thesis addresses this need within the agrochemical industry.<br>
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description: Relative humidity (RH) and temperature can vary when coated seeds are in storage and in use. A single indentation cycle was used to investigate the effects of these environmental factors on the hardness, creep, and tack adhesion properties of composite coatings. Introducing hygroscopic additives, such as poly(acrylic acid, sodium salt) solution and xanthan gum, imparts RH-sensitivity to the coatings, and can cause increased tack adhesion and decreased stiffness at high RH. The addition of CaCO3 fillers increased stiffness and reduced adhesion, which is important when trying to reduce blocking. At temperatures above the glass transition temperature of the polymer binder, the tack adhesion increased and the stiffness decreased.
description: Friction between seeds and mechanical planting equipment can impede seed flow and plantability. The friction of composite coatings at two extremities of RH (10% and 90%) was studied. In dry conditions the addition of wax softened the coating, increasing the coefficient of kinetic friction (µk) compared to wax-free coatings. CaCO3 addition increased hardness, which decreased the µk. High RH softened wax-free coatings, leading to higher µk values, but wax-containing coatings had a lower µk at 90% RH, due to a lubricating layer of water on the coating surface.<br>
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description: The flowability and dust-off of coated corn seeds were studied, and possible correlations between these and multiple other properties were investigated. Dust-off is increased when CaCO3 (especially large particles) is added. Adding wax improves flowability and reduces dust-off. Friction was studied in the plastic regime (under relatively high pressure), so it is not expected to correlate with the elastic flow of coated seeds.<br>
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description: The results presented in this thesis highlight the role of individual co-formulants and the importance of environmental factors during seed storage and planting. This information can be used by formulators to improve existing products and to advise end-users on optimum storage and usage conditions.<br>