Linertech 'sparks' safety improvement drive within dry bulk food transportation

18th May 2009.

Linertech  is an industry leader in development and manufacture of container liners for use with intermodal box containers.Linertech has developed a new conductive liner, approved to ISO 22000 standards, which not only mitigates potential for explosions, but also meet the directive on the use of Carbon Black in conductive film that came into force at the beginning of May.The need for conductive liners arose from the requirement to carry powders that could ignite inside the container and cause a dust explosion.

Ordinary polyethylene film typically used for the manufacture of container liners show similar properties to conventional polymers, i.e. electrically insulating and prone to generation of high electrostatic charge accumulation and risk of incendiary spark. It is necessary to make the liners out of a non insulating "conductive" film, providing an adequate electrical earth which prevents electrostatic discharges (ESD's).

Linertech began development of the ‘conductive liner’ over 12 years ago. Initially the most cost effective way of achieving conductive properties was to load the polyethylene matrix with carbon black powder to a level whereby a good electrical continuum was formed however this practice resulted in weakening the film, and also being completely opaque, allowed no light into the container, making fitting of the liner problematic.

Carbon black is a generic term incorporating many chemical compounds that are remnants from the incomplete combustion of hydrocarbons. In addition to native carbon, stable as the allotrope graphite, there are many toxic hydrocarbons that persist in carbon black. As of May 1st 2009, the usage of more than 2.5% w/w of carbon black into plastics used for food contact is prohibited in the EU, effectively ruling out carbon black as a suitable candidate for this application.

The challenge was to source a permanently conducting material to fill the gap left by the carbon black.

A number of film technologies were available, but none had been extruded into the large diameters required for preferred seamless single piece liner films. Seamless tube forms of film are easier to prevent unwanted contaminants from getting inside the liners during extrusion of the film, and also during fabrication into liners; a pivotal consideration when forming a "food grade liner". Modern polymers such as polyaniline salt, and other "inherently conducting polymers" were instantly attractive over the non-permanent additives that are referred to as being "anti-static".

The inherently conducting polymers in addition to providing a permanent and reliable dissipation of electrical charge also possess the following attributes:

We are pleased to have found solutions to this long standing industry problem. The new conductive liner has worked very well for carriage of sugar and starch products and there is much potential for use with a number of other food grade materials.

The conductive liner is pushing back the boundaries of bag-in-box technology and giving further incentives for a range of companies to send potentially explosive food grade products by more sustainable intermodal means, thus saving cost and also helping the environment through reduced CO2 emissions compared to traditional transport infrastructure.

• suitable for contact with foodstuffs
• translucent and therefore safer to fit into containers and also giving loading and discharge more visual indicators
• stronger polymeric structure = lighter and less manual handling issues