Synergistic effects of tung oil and heat treatment on physicochemical properties of bamboo materials

Abstract

The search for green and sustainable modification method to produce durable bamboo materials remains a challenge in industry. Here, heat treatment in tung oil at 100-200 °C was employed to modify bamboo materials. Oil permeation and distribution in the structure of bamboo samples during heat treatment were explored. The synergistic effects of tung oil and heat treatment on the chemical, physical and mechanical properties of bamboo materials, and their mutual relationships were also investigated in detail. Results showed that the tung oil heat treated bamboo not only had an enhanced hydrophobic property and dimensional stability, improved fungi resistance, but also displayed good mechanical performance. Compared with the untreated sample, the water-saturated swelling reduced from 3.17% to 2.42% for the sample after oil heat treatment at 200 °C, and the contact angles of the sample after oil heat treatment at 200 °C can keep >100° after 300 s in radial direction. Such improvement can be attributed to changes of chemical components, increased crystallinity structure, and the formation of oily films inside or over the bamboo surface. Therefore, tung oil heat treatment can be a highly promising technology for bamboo modification in the industry.

Figure 1

Schematics of the heterogeneous structure of bamboo.

Figure 2

Schematic illustration of the bamboo samples after heat treatment in tung oil.

Figure 3

(a) Images of the bamboo samples after heat treatment in tung oil and Sudan black solution in transverse section, (a1) surface, (a2) removed 1 mm from surface, (a3) removed 5 mm from surface, (a4) removed 10 mm from surface. (b) Images of bamboo in radial section, (b1) surface, (b2) removed 0.5 mm from surface, (b3) removed 1.25 mm from surface, (b4) removed 2.5 mm from surface.

Figure 4

SEM images of different bamboo samples. (a) Parenchyma cells in transverse section, (b) pits at the radial wall of metaxylem vessels.

Figure 5

CLSM images of bamboo in transverse section. (a,b) Parenchyma cells, (a) the bamboo sample after oil heat treatment, (b) untreated bamboo. (c,d) Fibers, (c) the bamboo sample after oil heat treatment, (d) untreated bamboo.

Figure 6

Wetting behavior of different bamboo samples. Images of a water droplet on the surface (a) in transverse section, (b) in radial section, (c) contact angle-time curve in radial section, (d) contact angles in transverse section.

Figure 7

Anti-swelling efficiency of the bamboo samples at room temperature (a) tangential direction, (b) radial direction.

Figure 8

Fungi resistance of bamboo (a) microscope images of bamboo samples, (b) microscope images of bamboo samples after exposed to Aspergillus niger for 3 days, (c) SEM images of bamboo after exposed to Aspergillus niger for 8 weeks.