Coventry Still Makes Transport; Unique Molecular Delivery Systems for Functional Polymers

Coventry based advanced technology company Exilica Limited has recently teamed up with Rondol Technology Limited, a producer of polymer processing equipment, to produce prototype composite plastics containing Exilica's µ-Sq beads and Hollow silica shells.

What are µ-Sq beads

To look at µ-Sq beads are a blue-black intractable powder, although they can be disintegrated using acid / peroxide mixtures. µ-Sq beads contain C, H, N and O and have no particular magnetic, electronic or optical properties that would otherwise set them apart from other organic polymers, neither do they have any advantageous surface tribological properties (ie. they are not good for use as a dry lubricant).

What they do have is an ability to absorb elemental and small molecular species as well as attract a whole range of small, medium and large molecular and biomolecular species to their surface. They have been shown to absorb, in varying amounts, all of the metal elements from lithium to bismuth in the periodic table, including the lanthanides, except for beryllium, tellurium and the radioactives (which we haven't tried yet).

We are currently examining which of these metals the µ-Sq beads retain once absorbed (like selenium) and which can be released upon further washings (like copper). Those that can be released (that we currently know of) do so very readily although we are currently examining the use of µ-Sq beads in chromatography and the separation of elemental species down a column of µ-Sq beads.

SEM image of µ-Sq beads

Thus far, elemental species have been absorbed into the beads by soaking in aqueous solutions of the elements in any of their water (or acid) soluble forms as well as their ammonium anion species (like ammonium phosphate or ammonium tungstate). The release of such species from µ-Sq beads can be significantly slowed if the µ-Sq beads are spun in commercial polymers, which they do so very readily.

What are Hollow Silica Shells

Hollow silica shells are prepared by a three-stage process and utilise the unique surface properties of µ-Sq beads. Silicon precursors will directly adhere to the surface of µ-Sq beads, thus additional polymerisation of the adsorbed silicon and subsequent removal of the template bead by thermal treatment yields hollow silica shells with shell wall thicknesses of 10% the overall diameter. The resultant size of any individual shell is exactly 50% of that of the template.

Hollow Silica Shells

Hi-Tech Molecular Transport Vehicles for Functional Polymers

Both µ-Sq beads and Hollow silica shells have specific physical characteristics that overcome many problems where chemical actives (such as fragrances, anti-bacterials, lubricants etc) cannot be directly added to a polymer melt because of either the physical or chemical conditions involved. In such cases both µ-Sq beads and Hollow silica shells serve as transport vehicles for the actives, carrying these through harsh processing procedures to then allow them to leach slowly out through the host matrix. Exilica's particles ensure the even distribution of actives throughout the finished polymer with the release of each active depend upon several environmental factors.

Particle composites of polypropylene, polyester, nylon and polymethylmethacrylate are being prepared using Rondol's unique 10 mm twin-screw compounder. Current additives that the µ-Sq beads are being used to contain fragrances and organic anti-bacterials. In comparison, the Hollow silica shells are being used for organic anti-bacterials and essential oils. Prototypes are being produced in both panel and fibre form with the intention of weaving the fibres into cloth.

The underlying challenges for Exilica in this work are to create fragranced polymers, an alternative to silver based anti-bacterial polymer additives, and synthetic fibres that contain and leach essential oils. This work is being done in conjunction with studies where composites of fragrance loaded beads in polypropylene have retained their impregnated fragrance smell for over 4500 hours at 45ºC.