Although termites serve the ecologically important function of converting dead trees into organic matter, they annually cause damage worth billions of dollars to human structures such as houses, power poles and bridges throughout the world. This led to the development of various chemical and physical measures that primarily aimed at preventing the termites from causing damage to wooden structures. While the adverse effects of the chemical methods on the environment and human health has made them widely unacceptable, physical methods are costly and difficult to implement. There is a specific need to develop an environment friendly, cost effective, easily applicable and durable alternative barrier that would effectively protect a wide range of wooden structures. This study aims at designing and developing an eco-friendly, robust and easy to apply barrier material to protect wooden structures. Ether polyurethane (EPU) was chosen as the base material considering its toughness, resilience, hydrolytic stability due to the presence of ether group and easy applicability on large, irregular surfaces. EPU was upgraded to a ‘termite effective’ material by the incorporation of a synthetic pyrethroid, Bifenthrin®. Bifenthrin® was chosen over other termiticides due to its less pervasive nature to the environment along with its repellent/ killer effect on termites. The EPU/ Bifenthrin® system incorporates the specific features of durability of the polymer and slow release of Bifenthrin®, making it more acceptable to the environment and public health. Termite damage resistance of EPU was analyzed by testing the polymer, along with various other polymers (HDPE, PP, PVC and Nylon), with Coptotermes acinaciformes and correlating the termite properties (mandibular force, hardness) with those of the polymeric materials (surface and tensile properties). EPU resisted termite damage, though its softer form incurred 5 times more material damage than the robust cast type. EPUs with high values of hardness incurred ~40% less damage than HDPE and were comparable with the damages on PP. The depth and width of termite damage on HDPE was 5 and 4 times, respectively, than that of PVC. This part of the study inferred that, although hardness of polymeric materials helps prevent termite damage, toughness and resilience too can make it difficult for termites to find a pathway through the material. XPS, FTIR, termite mortality bioassays in an applied setting and elusion tests of Bifenthrin® from EPU in water, acetone and soil were employed to understand the interaction of EPU with Bifenthrin®. Water and soil were chosen as test mediums due to their practical nature. These studies confirm that Bifenthrin® at concentrations as low as 0.5 wt% enriches the surface of EPU due to preferential migration of CF3 group to the surface of EPU. Furthermore, Bifenthrin® incorporated in EPU does not compromise its insecticidal activity and diffuses in a controlled manner at the rate of ~10–8 cm2 s–1 and ~10–7 cm2 s–1 when kept in water and soil media respectively. The durability of EPU/ Bifenthrin® system was analyzed by conducting degradation studies on EPU. The effect of Bifenthrin® on the ageing of EPU was also investigated. The studies involved ageing of the system in natural and accelerated conditions and validating the results by use of Arrhenius models. The sub-soil conditions do not degrade EPU beyond the oxidative levels as the activation energy required to cause changes in properties of EPU are unphysically small (0.02 kJ mol-1). It was found that EPU can sustain its physical integrity for 12 years at room temperature and Bifenthrin® may remain in a 5 mm thick barrier material for up to 10 years. The effect of Bifenthrin® on the tensile properties of EPU is negligible. Studies to analyze the performance of the barrier material, involved testing of timber coated with the EPU/ Bifenthrin® system under real-life conditions against termites in field trials located at two tropical locations in Northern Queensland. EPU/ Bifenthrin® system with nominal concentrations of Bifenthrin® incurred no damage when the concentration of Bifenthrin® was above 0.07 wt% in EPU. The degradation of Bifenthrin® under sub-soil conditions is unlikely. Given that favourable characteristics of EPU and Bifenthrin® the design and development an effective and long-lasting termite barrier material seems feasible.
| Identifer | oai:union.ndltd.org:ADTP/286655 |
| Creators | Sharad Rajendran |
| Source Sets | Australiasian Digital Theses Program |
| Detected Language | English |
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