Comparative evaluation of thermal conductivity of bark cloth epoxy composites.
Samson Rwawiire1,2, Blanka Tomkova1
1Technical University of Liberec, Department of Material Engneering,
2BusitemaUniversity, Department of Textile and Ginning Engineering rsammy@eng.busitema.ac.ug
KEYWORDS Bark cloth, Thermal conductivity, Thermal Insulation
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ABSTRACT
Natural fiber composites exhibit low specific weight, are biodegradable and are easily available and supplied by nature.
Due to growing concerns of climate change and greenhouse gas emissions arising from synthetic materials, these days polymers are being reinforced with natural fillers so as to produce materials which can be used in automotive, building and civil engineering applications. In this work, Ugandan bark cloth, a natural non- woven fabric usually obtained from three species of trees: Ficus natalensis, Ficus brachypoda and Antiaris toxicaria was used for composite processing by Vacuum Assisted Resin Transfer Molding (VARTM) using four plies for each species.
For bark cloth to find applications in building and civil engineering applications, its thermal insulation properties have to be characterized. In this present work for the first time, we present the thermal conductivity of bark cloth reinforced epoxy composites from three species.
The obtained results show that Ficus b. had the highest thermal conductivity followed by Ficus n. and lastly Antiaris with values 0.224W/mK;
0.206W/mK and 0.182 W/mk respectively.
EXPERIMENTAL APPROACH Materials
Bark cloth from Ficus natalensis, Ficus brachypoda and Antiaris toxicaria were obtained from Uganda. Laminating epoxy resin LG 285 (bisphenol-A-epichlorohydrin, diglycidylether) and hardener HG 285 (2,2- dimethyl-4,4-methylen bisoychlorohexylomin) were obtained from GRM systems s.r.o, Czech Republic.
Chemical silicon paste was supplied by elchemeo.
Methods
The extraction of bark cloth was done by the hand extraction method as described by Rwawiire et al., 2013 [1]. Epoxy resin and hardener were mixed in the ratio of 100:40 and the mixture was used to prepare bark cloth composite specimens.
Four bark cloth plies giving rise to specimen thickness ranging between 2-3mm of the species were used and VARTM method used for the preparation of the composites. The samples were left under vacuum pressure for 72 hours for complete setting.
Figure 1. (A) Ficus brachypoda; (B) Ficus natalensis and (C) Antiaris toxicaria
Alambeta thermal conductivity measuring device [2] which measuresthermo conductivityof specimens up to 8mm was used under room temperature.
The composites (Figure 1) were grinded using sandpaper so as to achieve a uniform smooth surface for thermal conductivity tests. Chemical silicon paste was used to condition the samples such that it aides as both a lubricant to prevent damage to the device’s measuring probes and also aide in the fastening of the device heating plate to the samples.
RESULTS AND DISCUSSION Thermal conductivity,k
The amount of heat transmitted through a unit area of the composites was measured as the thermal conductivity coefficient (k) and it was observed that the ficus species Ficus brachypoda had a higher thermal conductivity among the measured specimens followed byFicus natalensis and lastly Antiaris toxicaria
The high thermal conductivity coefficient is attributed to partially the epoxy polymer used whose thermal conductivity is approximately 0.2W/mK. Rwawiire & Tomkova, 2014 [3]
showed that bark cloth from Ficus natalensis
had a higher thermal conductivity compared to other natural fibers. Therefore this property directly benefits the ficus species samples.
Table I: Thermal Insulation properties of bark cloth reinforced epoxy composites Species Thermal
Conductivity [W/mK]
Thermal Diffusivity [m2/s]x10-6
Thermal Absorptivity [Ws1/2/m2K]
Thermal Resistance
[m2K/W]
Sample Thickness
[mm]
Antiaris toxicaria
0.182 0.083 630 13.8 2.50
Ficus brachypoda
0.224 0.089 752 9.5 2.12
Ficus natalensis
0.206 0.083 725 14.2 2.93
CONCLUSIONS
Bark cloth reinforced epoxy composites have been investigated for their thermal insulation properties. It’s observed that the composites have considerable thermal conductivity values comparable and some cases better than other natural fibers.
FUTURE WORK
There’s need to increase or lower the thermal conductivity coefficients of the developed composites through additional fillers to widen the application of bark cloth as an engineering composite reinforcement and also to study the fire behavior of the composites if they are to find applications as composite boards.
ACKNOWLEDGMENTS
The first author wishes to thank Prof.Ing. Lubos Hes, CSc., for his help in operating the Alambeta device.
REFERENCES
[1] S. Rwawiire, G.W. Luggya, B. Tomkova;
Morphology, thermal and mechanical characterization of bark cloth from Ficus natalensis, ISRN Textiles, Vol 2013, (2013)
[2] L. Hes and I. Dolezal; New Method and equipment for measuring thermal properties of textiles; Journal of the Textile Machinery Society of Japan, 42, T124-T128
[3] S. Rwawiire and B. Tomkova;
Thermophysiological and comfort properties of Ugandan bark cloth from Ficus natalensis, The Journal of The Textile Institute, ahead of print, (2014); 1-6
