Injection Molding Using Only 200 °C Steamed Bamboo Powder by Controlling Metal Mold Temperature

Abstract

Injection molding of steamed bamboo powder was attempted by controlling the metal mold temperature. Bamboo powder was steamed at 200 °C for 20 min in a small pressure vessel. A thermal flow test of the steamed powder was conducted in order to investigate the flowability of the powder. The powder flowed at 160-220 °C, and had good flowability at 180 and 200 °C. Injection molding was conducted under the condition that the injection temperature was 180 or 200 °C and the metal mold temperature was 80-160 °C. It was possible to obtain products through this process. In particular, products with a gloss surface similar to plastic were obtained when the metal mold temperature was 140 or 160 °C. Injection pressure was affected by temperature; the material flowed inside the metal mold under low pressure when the injection and the metal mold temperatures were high. However, the flowability inside the metal mold did not have an effect on the surface texture of the product.

Full text

Procedia Engineering 81 ( 2014 ) 1186 – 1191
1877-7058
© 2014 Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license
(
http://creativecommons.org/licenses/by-nc-nd/3.0/).
Selection and peer-review under responsibility of the Department of Materials Science and Engineering, Nagoya University
doi: 10.1016/j.proeng.2014.10.095
ScienceDirect
Available online at www.sciencedirect.com
11th International Conference on Technology of Plasticity, ICTP 2014, 19-24 October 2014,
Nagoya Congress Center, Nagoya, Japan
Injection molding using only 200
°C steamed bamboo powder by
controlling metal mold temperature
Shohei Kajikawa*, Takashi Iizuka
Kyoto Institute of Technology, Matsugasakigoshokaido-cho, Sakyo-ku, Kyoto 606-8585, Japan
Abstract
Injection molding of steamed bamboo powder was attempted by controlling the metal mold temperature. Bamboo powder was
steamed at 200 ºC for 20 min in a small pressure vessel. A thermal flow test of the steamed powder was conducted in order to
investigate the flowability of the powder. The powder flowed at 160-220 ºC, and had good flowability at 180 and 200 ºC.
Injection molding was conducted under the condition that the injection temperature was 180 or 200 ºC and the metal mold
temperature was 80-160 ºC. It was possible to obtain products through this process. In particular, products with a gloss surface
similar to plastic were obtained when the metal mold temperature was 140 or 160 ºC. Injecti
on pressure was affected by
temperature; the material flowed inside the metal mold under low pressure when the injection and the metal mold temperatures
were high. However, the flowability inside the metal mold did not have an effect on the surface texture of the product.
© 2014 The Authors. Published by Elsevier Ltd.
Selection and peer-review under responsibility of Nagoya University and Toyohashi University of Technology
Keywords: Woody biomass; Injection molding; Flowability; Bamboo; Steaming.
1. Introduction
The utilization of woody biomass materials as industrial materials is expected to be effective. However,
conventional processing methods of woody biomass, such as machining or plastic forming, have several problems
that workability and productivity is poor. Productivity of woody biomass in particular should be improved because
* Corresponding author. Tel.: +81-75-724-7376; fax: +81-75-724-7300.
E-mail address: d3821003@edu.kit.ac.jp
© 2014 Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license
(
http://creativecommons.org/licenses/by-nc-nd/3.0/).
Selection and peer-review under responsibility of the Department of Materials Science and Engineering, Nagoya University

1187
Shohei Kajikawa and Takashi Iizuka / Procedia Engineering 81 ( 2014 ) 1186 – 1191
products need to be mass-produced for the use as an industrial material. In addition, arbitrary shaped products need
to be processed using woody biomass more effectively.
The authors have developed an injection molding method for woody biomass in order to resolve these problems.
The flowability of the material is an important factor in injection molding. Under heat and pressure, woody
biomass that contains water flows due to the softening and decomposition of lignin and hemicellulose (Yamashita
et al., 2007). Miki et al. (2004) fabricated a complexly shaped product by injection molding wood powder saturated
with water. However, water inside the material has negative effects on molding because much water vapor and
pyrolysis gas are produced when heated. In addition, it was reported that injection molding of wood powder
saturated with water was impossible when a conventional electric injection molder for thermoplastic polymers was
used (Miki et al., 2005).
To resolve these problems, woody biomass should have good flowability under a dry state for use in molding.
However, it was reported that the temperature of the softening points increased when dry wood was heated (Hillis
and Rozsa, 1985). Thus, injection molding using only woody biomass is difficult. On the other hand, the
preparation of woody biomass via heating and water can be seen as effective because the woody biomass
components are decomposed before molding. Takahashi et al. (2010) reported that the thermal flow temperature of
wood powder became low when prepared by steaming. In addition, the authors conducted an injection test of
steamed bamboo powder, and confirmed that the injectability of the powder was improved by steaming (Kajikawa
and Iizuka, 2013).
In this study, injection molding was attempted using steamed bamboo powder in an oven-dry state. An injection
molder was constructed with an injection part and a metal mold part. It was preferable that the injection
temperature be high for fluidization of the material. On the other hand, the metal mold temperature should be low
so the molded product is cooled effectively. However, the material does not flow adequately inside the metal mold
when the metal mold temperature is too low. For this reason, injection molding was attempted while controlling the
metal mold temperature. In the experiment, bamboo powder was steamed, and the flowability of the steamed
bamboo powder was investigated by thermal flow test. In addition, an injection molding test was conducted using
the steamed bamboo powder. The influence of the metal mold temperature on the appearance of the molded
product and the pressure variation during molding was evaluated.
Nomenclature
T
f
the test temperature of the thermal flow test
T
c
the temperature inside the cylinder during injection molding
T
mi
the temperature inside the metal mold during injection molding
T
mo
the temperature of the outside surface of the metal mold during injection molding
2. Materials and methods
2.1.
Preparation of materials
Moso bamboo powder was used as material. First, bamboo culms were planed by automatic feed planer to
obtain bamboo shavings. After that, bamboo powder was obtained by milling the shavings in a pin mill. Powder
that passed through a
I300 ȝm screen was used in this experiment. Fig. 1(a) shows the grain size distribution of
the powder. As shown in this figure, the grain size of the powder was mainly 75-300
ȝm.
A small pressure vessel was used to steam the bamboo powder. The powder was treated with saturated water
vapor by heating the small pressure vessel containing the powder and water. The moisture content of the powder
was prepared to 200% of the powder’s dry weight before steaming, and the powder was steamed at 200 ºC for 20
min. After steaming, the powder was brought to an air-dry state by drying at 30 ºC. In addition, the powder was
dried at 105 ºC in order to bring it to an oven-dry state before experiments. Fig. 1(b) and (c) show the appearances
of both the steamed and unsteamed bamboo powder. The color of the powder changed to ginger when steamed.

1188 Shohei Kajikawa and Takashi Iizuka / Procedia Engineering 81 ( 2014 ) 1186 – 1191
Fig. 1. Materials: (a) grain size distribution of bamboo powder; (b) the appearance of bamboo powder before steaming; (c) the appearance of
bamboo powder after steaming.
2.2.
Thermal flow test
The thermal flow test was conducted according to JIS K 7210 in order to investigate the flowability of the
steamed bamboo powder. For the flow test, a capillary rh
eometer (Shimadzu flow tester CFT-500D) was used. The
diameter of a cylinder and a die were
I11 mm and
I 2 mm, respectively, while the length of a die was 8 mm.
First, a cylinder was heated to the test temperature, T
f
. Powder with a weight of 1.5 g was placed in a cylinder,
and the piston was inserted into the cylinder. In this state, the powder was preheated for 6 min. The piston was
temporarily compressed to vent gas for 3 min after the start of preheating. After that, the piston was compressed at
49 MPa, and the material was extruded from the die. The test temperatures were 140, 160, 180, 200 and 220 ºC.

2.3. Injection molding test
Fig. 2(a) shows a schematic drawing of the device used for the injection molding test. The powder placed in a
cylinder flows by heating and pressing, and it reaches the metal mold through a nozzle and a sprue. The injection
part and the metal mold part were heated separately by band heaters and cartridge heaters. Temperature was
measured in three places: the inside of the cylinder
T
c
, the inside of the metal mold T
mi
, and the outside surface of
the metal mold T
mo
. Configurations of the cylinder, the nozzle, the sprue, and the metal mold are shown in Fig.
2(b) and (c).
Fig. 2. Schematic drawings of the device used for injection molding test: (a) overall view; (b) configuration of the cylinder, the nozzle and the
sprue; (c) configuration of the metal mold.

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Shohei Kajikawa and Takashi Iizuka / Procedia Engineering 81 ( 2014 ) 1186 – 1191
First, the bamboo powder was placed in the heated cylinder, and the punch was inserted into the cylinder. The
powder was preheated for 5 min in this state. After that, the punch was pressed at a constant speed, and the
pressure was held constant for 1 min once it reached 200 MPa. Finally, the device was cooled with an air blower,
and a molded product was removed from the device when
T
mo
became lower than 80 ºC. The punch speed was 100
mm/min,
T
c
was 180 and 200 ºC, and T
mi
was 80, 100, 120, 140 and 160 ºC.
3.
Results and discussion
3.1.
Flowability of steamed bamboo powder
The steamed bamboo powder flowed and was extruded from the die by pressure under the condition of
T
f
= 160,
180, 200 and 220 ºC, as shown in Fig. 3(a). Fig. 3(b) shows the stroke of the piston during the test. For each
temperature, the stroke increased to 1 mm as soon as the powder was compressed because the powder was
compacted into the cylinder. Under the condition of
T
f
= 180 and 200 ºC, the powder was extruded completely in a
shorter time compared with that of any other temperatures. This result indicates that the flowability of the powder
became good when the temperature was 180-200 ºC. Goring (1963) reported that the softening temperature of
lignin and hemicellulose was 134-230 ºC and 167-217 ºC, respectively. Hence, the flowability of the powder was
considered to be good under the condition that the temperature is over the softening temperature of hemicellulose.
However, the flowability decreased under the condition of
T
f
= 220 ºC. This result raised the possibility that
softening and decomposition at high temperatures over 200 ºC have negative effects on the flowability.
3.2.
Appearance of injection-molded products
T
c
was determined to be 180 and 200 ºC as a result of the thermal flow test. It was possible to obtain molded
products by injection molding under several conditions. Fig. 4 shows the appearance of a typical injection molded
product when the metal mold was filled with the material completely. The color of the product turned to black, and
the product had a gloss surface similar to plastic.
Fig. 5 shows the influence of the metal mold temperature on the appearance of injection molded product. As
shown in Fig. 5(a), under the condition of
T
c
= 180 ºC, the metal mold was not filled with the material completely
when
T
mi
= 80 and 100 ºC. The surfaces of these products were rough. When
T
mi
was 120 ºC, the metal mold was
almost completely filled, but the surface of the product was a little rough. However, the metal mold was filled
completely and the product had a gloss surface in cases when
T
mi
= 140 and 160 ºC.
In contrast, the metal mold was filled with the material completely under the condition of
T
mi
= 100, 120, 140,
and 160 ºC when
T
c
was 200 ºC, as shown in Fig. 5(b). On the other hand, the products had a gloss surface when
T
mi
= 140 and 160 ºC, as well as when
T
c
was 180 ºC. These results indicate that the injection temperature should
Fig. 3. Thermal flow test results: (a) appearance of extruded materials; (b) thermal flow curve.

1190 Shohei Kajikawa and Takashi Iizuka / Procedia Engineering 81 ( 2014 ) 1186 – 1191
Fig. 4. Appearance of typical injection molded product when material filled the metal mold completely (T
c
= 200 ºC, T
mi
= 160 ºC): (a) overall
view; (b) view of the eject pin side; (c) view of the sprue side.
Fig. 5. Influence of metal mold temperature on the appearance of injection molded product: (a) T
c
= 180 ºC; (b) T
c
= 200 ºC.
be high when filling a metal mold with the material at a low temperature. However, the metal mold temperature
should be high to obtain the product with a gloss surface, regardless of the injection temperature.
3.3.
Injection pressure variations during injection molding
Fig. 6 shows the injection pressure variations during inje
ction molding. In each condition, two peaks of pressure
were seen. It was reported that similar behavior was seen when a capillary flow test of a wood powder-plastic
mixture was conducted, and the material started to flow when pressure was decreased (Imanishi et al., 2005). The
material was first compacted in a cylinder. Next, the material was injected from the nozzle at the first pressure
peak. After that, the material reached the metal mold, and it was compacted again at the exit of the sprue. Finally,
the material started to flow in a vertical direction toward the injection site at the second pressure peak.
In the case of
T
c
= 180 ºC, the first pressure peak was unchanged by T
mi
. The second pressure peak was changed
by
T
mi
, and the pressure at the peak increased with the decrease of
T
mi
. In addition, the pressure after the second
peak was also large when
T
mi
was low. The first pressure peak when
T
c
= 200 ºC was almost the same as when T
c
=
180 ºC. However, the second pressure peak when
T
c
= 200 ºC was lower than that of T
c
= 180 ºC. In addition, the
second pressure peak was unchanged by
T
mi
. The pressure increased with the decrease in
T
mi
when the material
flowed inside the metal mold, as is the case when T
c
= 180 ºC.
These results indicate that the material flowed easily at a high temperature at the injection site and in the metal
mold. However, although pressure variation at
T
c
= 180 ºC and T
mi
= 160 ºC was similar to that at T
c
= 200 ºC and
T
mi
= 120 ºC, appearances of these products were different, as shown in Fig. 6.
Hence, it is considered that the
factor that determines the surface texture is not only the fluidity inside the metal mold, but also the metal mold
temperature.

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Shohei Kajikawa and Takashi Iizuka / Procedia Engineering 81 ( 2014 ) 1186 – 1191
Fig. 6. Pressure variations during injection molding: (a) T
c
= 180 ºC; (b) T
c
= 200 ºC.
4. Conclusion
In this study, a thermal flow test of steamed bamboo powder was conducted, and injection molding of the
steamed bamboo powder was attempted by controlling the metal mold temperature. The steamed bamboo powder
flowed under the condition that the test temperature was 160-220 ºC. In particular, the flowability was good at 180
and 200 ºC. It was possible to fabricate molded products by injection molding. In cases when the injection
temperature was 180 ºC, products that completely filled the mold were obtained under the condition that the metal
mold temperature was 140 or 160 ºC. Moreover, these products were obtained at a metal mold temperature of 100-
160 ºC when the injection site temperature was 200 ºC. However, products with a gloss surface similar to plastic
were obtained at metal mold temperatures of 140 and 160 ºC regardless of injection site temperature. Regarding
injection pressure variation, the injection pressure in cases when material could flow inside the metal mold
decreased with the increase in the temperature of the injection site and the metal mold. However, the flowability
inside the metal mold did not have an effect on the surface texture of the product.
Acknowledgement
This work was supported by JSPS KAKENHI Grant Number 24360309. We greatly appreciate this kind
contribution from the foundation.
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