EPSRC DTP-Understanding Microplastic Release from Protective Paint

With an estimated 14 billion tonnes of microplastics accumulated on the ocean floor, concern for the damage inflicted on marine ecosystems is growing. Recently published data indicate that the paint industry could be a significant contributor to primary microplastics (MPs) released into the marine environment, with land-based protective and architectural paints an abundant source.

There is, therefore, an urgent need to address the unknown loss rate and mechanism of microplastic release from paints over the service lifetime. Moreover, at present, neither microplastic release, nor coating thinning are assessed during the development cycle of paints and coatings, nor have the formulation parameters to minimise microplastic release been defined.

Furthermore, fundamental aspects of thermoset polymer degradation mechanisms are ill-understood, i.e., the chemical breakdown mechanism of these polymers when UV illumination, thermal aging and water sorption are combined. To address this knowledge gap, this overriding goal of this PhD is to test the following hypothesis:

Microplastic release by protective coatings can be measured using standard accelerated testing regimes, and predicted on the basis of polymer chemistry.

In sharp contrast to the vast majority of work undertaken in this area, research will not be focused on the quantification and analysis of microplastics collected from the environment. Instead, effort will focus on developing tests and mechanistic insight as predictive tools for use in the development cycle of paints and coatings. Industrial paint formulations will be exposed to standard accelerated cyclical testing regimes currently employed in R&D, using industrial grade environmental chambers (QSun).

Released material will be captured and quantified via filtration, and an in-depth understanding of the degradation mechanism will be developed via forensic analysis of the released particles and paints surface. This will be used to deliver guidelines for the reformulation of protective paint systems.

To facilitate research delivery, a series of measurable research objectives have been devised, i.e.,

(i) Implement suitable experimental setups/procedures suitable for laboratory studies of coating degradation / weathering.

(ii) Quantify microplastic release rates and thinning of exemplary high performance coating systems supplied by industrial partners. High and low durability systems will be compared based on the most common binder chemistries (2 x epoxy barrier coatings with and without a polyurethane topcoat).

(iii) Characterize surface degradation phenomena prior to the release of material (i.e., polymer oxidation, matrix-pigment delamination, cross-linking and UV embrittlement)

(iv) Identify key microstructural parameters associated with local cracking and flake release (e.g., binder degradation, solvent release, pigment chemistry, coating defects).

(v) Identify, for each coating, the primary environmental driver used in cyclical tests for microplastic release (temperature, UV exposure, water spray). (vi) Use experimental data to develop and test knowledge-based guidelines for formulation.

The student will combine standard bulk organic analysis techniques (thermal analyses, vibrational spectroscopy, gravimetric tests etc.) with microscopic characterization of the released material and the top surface of coatings, using advanced electron microscopy and scanning probe techniques (peakforce nanomechanical AFM, AFM-IR).

It is anticipated that this program will initiate a step-change in our understanding of composite material durability, providing detail on the fundamental processes underpinning network polymer degradation. At the same time, test methodologies and predictive proxies for microplastic release will be identified for formulators, to enable the development of more environmentally benign coatings.