Enhancement of electrical conductivity of trees—study and applications

24 February 2020

Computer Engineering student, Joselle Bontilao, has studied through samples testing the electrical conductivity of radiata pine and investigated how it could be enhanced.

  • Pinus radiata seedlings

    Figure 1. Radiata pine seedlings at Proseed nursery

Timber expansion stresses

Figure 2. The directions (red lines) of hypothesised expansion stresses caused by freezing

Over last summer (2019/2020), Joselle Bontilao, a 2020 Third Pro Computer Engineering student, studied the electrical properties of green radiata pine, under the supervision of Dr Nurzhan Nursultanov. She investigated the enhancement of electrical conductivity of trees watered with several ionic solutions. This research is of potential benefit for the log Joule heating project, as the conductivity enhancement would allow applying a lower voltage across logs, reducing the electrical equipment rating and the overall cost of Joule heating machine.

This investigation started in 2018 in collaboration with Proseed, a nursery owned by Te Rūnanga o Ngāi Tahu. Back then, Dr Bill Heffernan selected 53 radiata pine seedlings, each grown in individual Easigrip-45 45-litre bag at the nursery (Figure 1). The seedlings have been watered regularly either with pure water, water+boron, saline, or saline+boron solutions. The first sample set was collected in February 2019 and had been stored in a freezer to slow the drying process, before being processed by Joselle. She found that the electrical conductivity of these samples was much higher than the samples collected at McVicar sawmill and assessed in 2017 by Dr Nursultanov; the average enhancement was about six-times.

In January 2020, Joselle collected a new set of samples—stem and branches—from the same seedlings. While being more conductive than the 2017 samples, these new samples were more resistive than the previously frozen samples from the same source. A potential cause for such behaviour is a change in watering schedule, which was confirmed at the nursery. Also, Joselle found that freezing wood enhances its electrical conductivity. To study the enhancement due to freezing, she collected new samples from the McVicar sawmill and measured electrical conductivity of fresh and frozen wood. She found that the enhancement was less noticeable in cubic samples. She hypothesised that the difference between cylindrical and cubic samples is caused by the variation in wood tissue expansion in the radial direction (Fig. 2). Unfortunately, limited by the duration of the summer scholarship programme, Joselle could not test her hypothesis with a larger dataset.

Joselle’s work has provided invaluable insight informing future research.

The EPECentre wishes Joselle the very best in her final undergraduate year and the future.