Controlled-release formulations for pesticide applications act as depot systems that continuously
release the active ingredients into the environment over a speci ed period,
usually from months to years. However, some applications require fast-dissolving drug
delivery. The interest of this research is in fast-release of water-insoluble pesticides into
aquatic environments. This study considered the use of dextrin starch and urea eutectics
as fast release, solid dosage carrier forms that contain an active ingredient. The chosen
active for this study is an acaricide called amitraz (N-methylbis-(2,4-xylyliminomethyl)-
methylamine). The focus is on matrix-based dosage forms such as tablets, granules or
bres that either disintegrate or dissolve to release a water-insoluble active. These types
of dosage forms can be fabricated using processes such as lyophilisation, spray drying,
solvent casting, hot melt extrusion, compression moulding, wet granulation, compaction
and electrospinning. A simple melt-casting procedure has been discussed in the present
work.
Dextrin is a water-soluble form of partially hydrolysed starch and is a promising candidate
matrix material for dissolving solid dosage forms. The molecular weight of the
dextrin was analysed with MALDI-TOF methods and rheological relations. Glycerolplasticized
thermoplastic dextrin-based nanocomposites were prepared with a twin-screw
extrusion-compounding process. The nano llers included a layered double hydroxide
(LDH), cellulose nano bres (CNF) and stearic acid. The time-dependent retrogradation
of the compounds was monitored by X-ray di raction (XRD) and dynamic mechanical
thermal analysis (DMA). XRD showed that the inclusion of stearic acid in the formulations
led to the formation of an amylose-lipid complex and a stable crystallinity during
ageing.
Dissolution rates in water for samples containing dextrin starch, were characterised using
an iodine indicator and UV-visible spectroscopy. High pressure di erential scanning
calorimetry (HPDSC) indicated that the addition of stearic acid led to the formation of
amylose-lipid complexes (ALC's). An additive system containing stearic acid and CNF
was deemed suitable for compounding with amitraz. Compounding at temperatures
above the melting point of the latter led, on dissolution in water, to the release of much
ner particles of the acaricide, which was con rmed with particle size analysis (PSA). The addition of the acaricide caused an apparent increase in the dissolution rate of the
thermoplastic dextrin.
Two eutectic urea systems were considered for casting with amitraz. A eutectic system
of urea and acetamide was found to display a melting point of 44 C at a 37 wt.%
urea composition. The other system consisting of urea and 1,3-dimethylurea displayed a
eutectic point at 32 wt.% urea composition which melted at 59 C. Di erential scanning
calorimetry (DSC), however, con rmed a melting point depression due to a high moisture
content caused by the compounds high hygroscopicity. The endotherm of the sample
containing no excess moisture showed a melting point of 70 C. The 1,3-dimethylurea
system was deemed suitable for casting with amitraz. XRD of the eutectic composition
indicated a small amount of co-crystallisation. The samples were cast as disks of various
diameters while keeping the height of the disks constant. The creation of the cast disks
showed automatic generation of a nely dispersed form of the active through the process
of melting the deep eutectic solvent, the dissolution of the active and its phase separation
on cooling and solidi cation of the eutectic. This implies that ne grinding of the actives
might not be necessary. Eutectic casts containing 20 wt.% amitraz dissolved at a slower
rate than casts not containing the hydrophobic active ingredient. The advantageous
features of these casts were exempli ed using the acaricide incorporated into the urea &
1,3-dimethylurea eutectic.
This work provides two safe, biodegradable and water soluble materials for use as a
matrix to contain active ingredients. One material, the eutectic organic salt casts, can be
produced at low temperatures (<100 C) and can be directly cast into storage containers.
The complete dissolution of the cast compounded with a hydrophilic active is rapid (4-6
min). The second material, a thermoplastic dextrin, was melt compounded in an extruder
at temperatures not exceeding 120 C. This compound containing 20 wt.% of the active
dissolved over a 12 hour period. Dextrin, known to be widely used as an adhesive, will
aid in the adhesion of the active ingredient to the surface where it must be used. / Dissertation (MEng (Chemical Engineering))--University of Pretoria, 2020. / PAMSA / Department of Science and Innovation under Grant DST/CON 0004/2019 / Chemical Engineering / MEng (Chemical Engineering) / Unrestricted
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:up/oai:repository.up.ac.za:2263/81724 |
| Date | January 2020 |
| Creators | Phillips, Justin |
| Contributors | Focke, Walter Wilhelm |
| Publisher | University of Pretoria |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Dissertation |
| Rights | © 2021 University of Pretoria. All rights reserved. The copyright in this work vests in the University of Pretoria. No part of this work may be reproduced or transmitted in any form or by any means, without the prior written permission of the University of Pretoria. |
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