(148a) Characterisation of Eco-Friendly Calcium Carbonate-Polydopamine Microcapsules with Superior Mechanical, Barrier, and Adhesive Properties

Introduction: There is a rising need to effectively deliver perfume molecules onto fabric surfaces during laundry washing to enhance consumers’ satisfaction. To this end, core-shell microcapsules fabricated with synthetic polymers (e.g. melamine-formaldehyde) have long played a pivotal role in detergent manufacturing industry. Despite their excellent performance, synthetic polymers are non-biodegradable and accumulate as microplastics in the environment [1]. Consequently, the development of novel eco-friendly microcapsules is imperative, without undermining their performance. In the literature, inorganic materials have proven effective to form microcapsule shells [2]. Indeed, calcium carbonate (CC) is environmentally benign and can yield robust, cost-effective microcapsules. However, scarce information on the performance of the ensuing microcapsules is available, possibly suggesting that their barrier and adhesive properties were unsatisfactory [3]. Bioinspired by the extremely adhesive properties of catecholamines (CA) in mussels, dopamine is a promising CA-rich building block monomer. In its polymerised form, namely polydopamine (PDA), it can form a homogeneous layer onto many surfaces [4].

Methods: This work aims to develop core-shell hybrid microcapsules with a core of model perfume oil hexyl salicylate (HS) within a solid inorganic (CC) shell via interfacial crystal ripening followed by the deposition of an organic coating via oxidative alkaline auto-polymerisation of dopamine (pH 8.5). Their morphology, mechanical and barrier properties were characterised via fluorescence sensing/scanning electron microscopy (SEM), a micromanipulation technique, and UV-Vis spectrophotometry, respectively. Moreover, a bespoke microfluidic device was employed to investigate the retention performance of PDA-coated microcapsules onto a model fabric substrate (polyethylene terephthalate (PET)) in washing-mimicked conditions.

Results: There appeared to be mostly spherical core-shell microcapsules (D_[3,2]=31.2±0.4 μm) with a smooth PDA-coated surface beneath which CC was porously formed. After one month in water, only ~40% of HS was released, whereas PDA-free CC microcapsules had released the whole HS load within <4 hours. Under compression, the microcapsules yielded a mean nominal rupture tension of 51.8±6.2 N/m, which is similar to commercial microcapsules [5]. At pH 9 of a typical detergent, their retention performance on PET films was significantly high (~60%) under washing-like hydrodynamic shear stress (1 Pa), which may be appealing to industries [1].

Conclusions: The results suggest that hazard-free perfume microcapsules with a hybrid shell can be fabricated effectively, leading to superior adhesive properties and sustained release, with potential applications in multiple fast-moving consumer goods.

Learning objectives: Attendees will identify new tools for characterising and enhancing the key performance properties of microcapsules. Participants will be able to appraise the potential of microplastic-free hybrid microcapsules for potential controlled release applications.

Acknowledgments

This work was supported by EPSRC, UK (Grant Number EP/V027654/1).

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