Sustained and controlled release of natural volatile organic compounds from hydrophilic-lipophilic balance-optimized...

Existing approaches for applying essential oils to indoor environments remain limited by their temporary effects and insufficient control over release behavior. This study develops a sustained natural volatile organic compounds (NVOC) release system using a hydrophilic-lipophilic balance (HLB)-optimized phytoncide emulsion-zeolite composite. Phytoncide oil and hydrosol were emulsified with nonionic surfactants (Tween 80 and Span 80) across various HLB values and loaded into zeolite. High-HLB emulsions (HLB 14) showed enhanced stability, generating small and uniform droplets (∼170 nm, polydispersity index ∼0.13). It was confirmed that NVOC was adsorbed into zeolite pores without significant morphological or structural deterioration of the zeolite. The optimized composite achieved a loading capacity of up to 47%, surpassing previously reported zeolite-based carriers through finer droplets and more uniform adsorption. Short- and long-term release behavior followed the Weibull model (R² ≥ 0.99), with release exponents consistent with Fickian diffusion-influenced transport. The optimized emulsion-zeolite composite markedly improved release persistence, reducing the cumulative release after 14 days by approximately 55% compared with pure phytoncide oil. Quantitative analysis of VOC emissions emitted from the composite revealed that twenty-five NVOC species were detected-mainly cymene, limonene, and valencene. To provide a regulation-relevant context for indoor use, the measured VOC concentrations were evaluated against health-based indoor guideline values, confirming that hazardous VOCs and major terpenes remained below the most stringent guideline under the test conditions. Overall, the composite shows potential as a bio-based controlled-release material for moderating NVOC emission intensity and extending release persistence under indoor-use conditions.