Rajan B. Bodkhe

The effect of formulation variables on fouling-release performance of stratified siloxane–polyurethane coatings

The effects of formulation variables, such as type of polyol, solvent type and solvent content, and coating application method, on the surface properties of siloxane–polyurethane fouling-release coatings were explored. Fouling-release coatings allow the easy removal of marine organisms from a ship’s hull via the application of a shear force to the surface. Self-stratified siloxane–polyurethane coatings are a new approach to a tough fouling-release coating system. Combinatorial High Throughput Experimentation was employed to formulate and characterize 24 different siloxane–polyurethane coatings applied using drawdown and drop-casting methods. The resulting coatings were tested for surface energy using contact angle measurements. The fouling-release performance of the coatings was tested using a number of diverse marine organisms including bacteria (Halomonas pacifica and Cytophaga lytica), sporelings (young plants) of the green macroalga (Ulva linza), diatom ((microalga) Navicula incerta), and barnacle (Amphibalanus amphitrite). The performance of the majority of the coatings was found to be better than the silicone standards, Intersleek® and Silastic® T2. An increase in solvent content in the formulations increased the surface roughness of the coatings. Coatings made with polycaprolactone polyol appeared to be somewhat rougher compared to coatings made with the acrylic polyol. The adhesion strength of sporelings of Ulva increased with an increase in solvent content and increase in surface roughness. The adhesion strengths of Ulva sporelings, C. lytica, and N. incerta were independent of application method (cast or drawdown) in contrast to H. pacifica adhesion, which was dependent on the application method.

Comparison of laboratory and field testing performance evaluations of siloxane-polyurethane fouling-release marine coatings

Abstract A series of eight novel siloxane-polyurethane fouling-release (FR) coatings were assessed for their FR performance in both the laboratory and in the field. Laboratory analysis included adhesion assessments of bacteria, microalgae, macroalgal spores, adult barnacles and pseudobarnacles using high-throughput screening techniques, while field evaluations were conducted in accordance with standardized testing methods at three different ocean testing sites over the course of six-months exposure. The data collected were subjected to statistical analysis in order to identify potential correlations. In general, there was good agreement between the laboratory screening assays and the field assessments, with both regimes clearly distinguishing the siloxane-polyurethane compositions comprising monofunctional poly(dimethyl siloxane) (PDMS) (m-PDMS) as possessing superior, broad-spectrum FR properties compared to those prepared with difunctional PDMS (d-PDMS). Of the seven laboratory screening techniques, the Cellulophaga lytica biofilm retraction and reattached barnacle (Amphibalanus amphitrite) adhesion assays were shown to be the most predictive of broad-spectrum field performance.

Synthesis and characterization of novel polysiloxane based ABA-type triblock copolymers using ATRP

Abstract Novel polysiloxane based ABA-type triblock copolymers having a secondary amine at the junction point were synthesized using a combination of ring opening equilibration polymerization (ROEP), Michael addition and atom transfer radical polymerization (ATRP). Polysiloxane based bifunctional ATRP macroinitiators were synthesized and subsequently used for controlled radical polymerization of t-butyl acrylate (t-BA) and sulfobetaine methacrylate (SBMA). Gel permeation chromatography (GPC) analysis of the triblocks based on t-BA showed high chain end functionality, due to the disappearance of peaks related to the macroinitiator. ROEP can be used to control the block length of the polysiloxane while ATRP can be used to control the chain length of the outer blocks, making the ABA- type triblock a unique material with secondary amine functionality which can be used for further reaction.