In hot molding processes of woody material, it is important to understand the effect of oven-dry heating on the property of woody biomass material, such as thermal fluidity. In this study, thermal flow tests of untreated and steam treated bamboo powder were conducted to investigate the effects of heating at an oven-dry state on thermal fluidity. The test temperature was set to 200°C. Before the thermal flow test, powder was dry-heated in a capillary rheometer at 200°C with a variable heating time. Thermogravimetry was conducted to understand the thermal changes of the powder during an increasing temperature and constant temperature. Fluidity of untreated powder was improved with a short dry-heating but decreased with a long dry-heating. In contrast, steam treated powder fluidity was high compared to untreated one, but its fluidity did not improve from dry-heating. From these thermogravimetry results, the chemical changes associated with component volatilization relate with the thermal fluidity. Therefore, the decrease in fluidity from dry-heating occurred because fluidity related components escape from the powder through volatilization.
Effective use of woody biomass resources is environmentally friendly because woody biomass resources are carbon neutral and sustainable. However, applications for woody biomass materials are limited because of some inherent practicality issues. One issue is material workability. Woody biomass is generally processed through machining, bending, or compacting. However, processing complex shapes is difficult, and some problems, such as limited extraction rates and productivity, exist with these methods.
In order to resolve these problems, various research studies on woody material processing methods have been conducted. For example, wood plastic composites (WPC), which are made by mixing woody materials and plastics, can be processed with general plastic processing methods such as extrusion or injection molding [
Woody material properties are affected by heating not only during the wet state, such as steaming, but also during the dry state. For example, research about woody material dry-heating has shown that dynamic viscoelastic properties of dry wood change in relation to its heating temperature or time [
In this study, a thermal flow test for woody materials dry-heated for different treating time was conducted using a capillary rheometer. Bamboo powder, which was untreated or steam treated, was studied because an effective use of the timber from bamboo thinning is desired in Japan [
Moso bamboo powder was used. To obtain the powder, a stem was shaved and shavings were then milled in a pin mill. The powder passed through a
Particle size distribution of bamboo powder.
Figure
Schematic diagram of steam treatment.
A capillary rheometer (CFT-500D, Shimadzu) was used to dry-heat the powder and for the thermal flow test. Figure
Schematic diagram of the capillary rheometer.
Thermogravimetry was conducted with a thermogravimetry/differential thermal analyzer (TG/DTA 6200, Seiko Instruments Inc.). The air-dried bamboo powder was placed in an aluminum pan, and an empty aluminum pan was used as a reference. Figure
Thermogravimetry temperature schedule.
Flow behavior of untreated and steam treated bamboo powder was investigated. Figure
Effect of steam treatment temperature
As shown in Figure
Figure
Effect of steam treatment time
Figure
Effect of dry-heating time
Untreated
Figure
Mass change rates of bamboo powder untreated and steam treated with a variable steam treatment temperature
Warm-up period
Constant temperature period
Figure
Mass loss rate for steam treated bamboo powder with a variable steam treatment time
Warm-up period
Constant temperature period
It was reported that water-soluble components are produced from hemicellulose by steam treatment and some of these components change to volatile components, such as furfural, from high temperature at a prolonged exposure time [
Relationship between thermal fluidity and mass loss during warm-up and constant temperature periods is discussed. As shown in Figures
Next, we discuss the effect of dry-heating time on thermal fluidity in an oven-dry state and the chemical changes during dry-heating. For untreated powder as shown in Figure
For steam treated powder, the flow showed a tendency to start later at a slower rate as
In this study, thermal flow tests of untreated and steam treated bamboo powder were performed using a capillary rheometer to investigate the effect of heating at an oven-dry state on thermal fluidity. The test temperature and dry heating temperature were set at 200°C. Untreated and steam treated bamboo powder at 180°C started to flow several minutes after the start of pressing. Steam treated powder at 200°C flowed immediately after pressing. When the powder dry-heating time increased in an oven-dry state before pressing, the untreated powder flow began earlier with an increase in dry-heating time from 1 to 5 min but started later with an increase in dry-heating time from 5 to 20 min. The flow of the steam treated powder started later with an increase in dry-heating time from 1 to 20 min. From the thermogravimetry results during the increasing and constant temperature periods, it was confirmed that chemical changes associated with component volatilization relate with thermal fluidity. For untreated powder, fluidity is improved from chemical changes during a short dry-heating, but fluidity decreases because the powder loses its fluidity related components from volatilization with a long dry-heating. For steam treated powder, fluidity was high when the dry-heating was short because of the chemical change intensity associated with volatilization. It was easy to slow fluidity with dry-heating because the powder readily loses its fluidity related components due to the large amount of volatilization.
The authors declare that there is no conflict of interests regarding the publication of this paper.
This work was supported by JSPS KAKENHI (Grant nos. 24360309 and 26-9571).