Biostatic film as a primary treatment against pole failure in soil
A A W Baecker, M Behr
Field liners of low density polyethylene (LDPE) film applied as primary treatment of soil-contact surfaces of creosote-treated poles prevented their detoxification and premature failure by establishing hurdles against microbiological colonisation. These hurdles include low water activity, low oxygen tension and nutrient limitations. Moreover, under conditions of high soil moisture, field trials showed that the hurdle of toxicity provided by creosote is maintained by LDPE films which prevent it from leaching. However, such liners must remain intact to confer sustained protection. Susceptibility of LDPE to termite damage and to possible microbiological damage in the long term led to the development of materials resistant to biodeterioration. A dry film preservative (DFP) was incorporated with masterbatch for use in LDPE manufacture. Laboratory tests showed the masterbatch granules to be biocidal against soil microorganisms, confirming that neither the moulding temperature nor the immobilisation of the DFP in the masterbatch had neutralised the antimicrobial properties of the DFP. The masterbatch was then used to produce LDPE film which, with unpreserved control film, was applied as liners to surfaces of untreated Eucalyptus grandis posts. All posts were placed under flood-irrigation in termite-infested soil in Natal for eight months. Preserved liners remained intact and the wood under these was uncolonised by microorganisms or termites. Some control films, and the wood under them, had been destroyed by termites, and wood surfaces under the other control films which appeared intact were visibly colonised by fungi.