Poly(lactide-co-glycolide) (PLGA) nanoparticles of different physical characteristics (size, size distribution, morphology, zeta potential) can be synthesized by controlling the parameters specific to the synthesis method employed. The aim of this review is to clearly, quantitatively and comprehensively describe the top-down synthesis techniques available for PLGA nanoparticle formation, as well as the techniques commonly used for nanoparticle characterization. Many examples are discussed in detail to provide the reader with an extensive knowledge base on the important parameters specific to the synthesis method described and ways in which these parameters can be manipulated to control the nanoparticle physical characteristics.

An emulsion evaporation method was used to synthesize spherical poly(DL-lactide-co-glycolide) (PLGA) nanoparticles with entrapped α-tocopherol. Two different surfactants were used: sodium dodecyl sulfate (SDS) and poly(vinyl alcohol) (PVA). For SDS nanoparticles, the size of the nanoparticles decreased significantly with the entrapment of α-tocopherol in the PLGA matrix, while the size of PVA nanoparticles remained unchanged. The polydispersity index after synthesis was under 0.100 for PVA nanoparticles and around 0.150 for SDS nanoparticles. The zeta potential was negative for all PVA nanoparticles. The entrapment efficiency of α-tocopherol in the polymeric matrix was approximately 89% and 95% for nanoparticles with 8% and 16% α-tocopherol theoretical loading, respectively. The residual PVA associated with the nanoparticles after purification was approximately 6% ( w/w relative to the nanoparticles). The release profile showed an initial burst followed by a slower release of the α-tocopherol entrapped inside the PLGA matrix. The release for nanoparticles with 8% α-tocopherol theoretical loading (86% released in the first hour) was faster than the release for the nanoparticles with 16% α-tocopherol theoretical loading (34% released in the first hour).

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The effects of heat and UV exposure on the degradation of free a-tocopherol (oil form), a-tocopherol dissolved in methanol, and a-tocopherol dissolved in hexane were measured. Results showed that degradation of free a-tocopherol due to heat followed first order kinetics, with the samples held at 180°C showing the greatest degradation rate. Free a-tocopherol degraded faster at high temperatures than dissolved a-tocopherol. In contrast, free a-tocopherol did not degrade when exposed to UV light for as long as 6 h, but the hexane and methanol samples degraded significantly as a matter of time. The a-tocopherol dissolved in hexane and methanol degraded by 20 and 70%, respectively over this time span. A mechanism for degradation of a-tocopherol was proposed to explain the higher degradation rate of a-tocopherol in methanol, as compared to hexane for times longer than 180 min. Knowledge of degradation kinetics of pure a-tocopherol as a result of temperature or exposure to UVA light whether in free or dissolved form is critically needed to understand how different processing parameters affect the amount of a-tocopherol during extraction, stabilization, storage or encapsulation processes.

This review discusses polymeric nanocarriers for agrochemical delivery, from synthesis, characterization, and release, to benefits for agrochemical efficiency and sustainability.

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