This paper describes the flexural properties of biodegradable composites made using natural fiber and biodegradable plastics. Biodegradable composites were fabricated from bamboo fiber bundles and PLA (polylactic acid) resin. In this research, effect of molding temperature and fiber content on flexural properties of bamboo fiber reinforced composites was investigated. The flexural strength of this composite increased with increasing fiber content up to 70%. The flexural strength of composites decreased at molding temperature of 180 °C. Biodegradable composites possessed extremely high flexural strength of 273 MPa, in the case of molding temperature of 160 °C and fiber content of 70%.
Recently, consciousness to recycling and zero emission is increasing. FRP (fiber reinforced plastics), including glass and carbon fiber reinforced plastics, have good characterizes, such as high strength, low density and corrosion resistance. Therefore, these FRPs are extensively used in a wide range of fields, including a exterior of a motorboat, automobile parts and sport goods, etc. However, these FRPs impact the environment. They are made from fossil fuels and they are non-biodegradable. From these perspectives, the usage and disposal of conventional FRP clearly contribute to the global concerns of recycling and zero-emissions and emphasis need to be placed on the involving FRP once they have been disposed.
In the past, bamboo was used as part of daily life (e.g., bamboo shoots for food and stalks for building materials). However, recently, bamboo forests have fallen into ruin because of the appearance of plastic products and the import of inexpensive bamboo shoots. The present study investigated whether bamboo can be effectively used to replace plastic and FRP materials.
The use of natural fibers in FRP to replace glass and carbon fibers is receiving attention, because of advantages such as biodegradability, renewability, low cost and more over. Recent researches [
The purpose of this work is to develop the material with the biodegradability and high strength with excellent mechanical properties comparable to GFRP. In this study, long bamboo fiber bundles were selected as a reinforcement of the biodegradable composites due to their high strength. In order to increase the fraction of fibers, emulsion type PLA was used for the matrix. The unidirectional fiber reinforced composites were fabricated by hot press method. And, their mechanical properties were investigated.
In this research, fiber bundles of bamboo which have diameter of 100 - 300 μm and length of 100 mm were used.
In order to produce biodegradable composites that have high fiber content, an emulsion-type PLA (Miyoshi Oil & Fat Co., LTD.; PL-1000) was used (
First, preliminary composites were produced by putting the biodegradable resin on the surface of bamboo fibers
and drying at 105˚C for 120 min in an oven. Next, biodegradable composite specimens were fabricated by hot pressing using a pressing machine. In this process, the preliminary composites were set in a metallic mold and heated to 120˚C, 140˚C, 160˚C, 180˚C and 200˚C with hot-press machine. The metallic mold was held at 120˚C - 200˚C for 5 min and specimens were hot-pressed at 10 MPa. The dimensions of the biodegradable composite specimens were 15 mm × 100 mm × 3 mm for flexural testing (
Three-point flexural tests were conducted using a testing machine (SIMADZU Model AG-250kNE), following JIS K7171 (plastics determination of flexural properties). Flexural tests were performed at a crosshead speed of 1 mm/min and a span length of 48 mm as shown in
Molding temperature (˚C) | Bamboo fiber (%) | PLA (%) |
---|---|---|
120 | 50 | 50 |
140 | ||
160 | 0 | 100 |
30 | 70 | |
50 | 50 | |
70 | 30 | |
180 | 50 | 50 |
200 |
The top view of the biodegradable composites with 0 and 70 % of fibers molded at 160˚C are shown in
The relationship between the density of the composites of 50% fibers and molding temperature is shown in
However, density decreased dramatically at 200˚C. This was expected as it was known bring many voids at temperatures above 200˚C, from
The relationship between the density of the specimens molded at 160˚C and fiber content is shown in
The density of products molded at 0% and 50% of fibers are 1.24 and 1.31 g/cm3, respectively.
Figures 11-13 show fracture behavior after flexural testing.
In the case of specimens molded at 200˚C (
Density (g/cm3) | Flexural strength (MPa) | Flexural modulus (GPa) | |
---|---|---|---|
Bamboo fiber 50% 120˚C | 1.26 | 191.52 | 3.23 |
Bamboo fiber 50% 140˚C | 1.29 | 199.00 | 5.43 |
Bamboo fiber 50% 160˚C | 1.30 | 197.60 | 5.89 |
Bamboo fiber 50% 180˚C | 1.29 | 158.97 | 5.78 |
Bamboo fiber 50% 200˚C | 1.16 | 106.38 | 5.32 |
Bamboo fiber 0% 160˚C | 1.24 | 44.50 | 0.73 |
Bamboo fiber 30% 160˚C | 1.29 | 148.08 | 3.69 |
Bamboo fiber 70% 160˚C | 1.28 | 273.28 | 6.83 |
PE | 0.94 | 34 - 39 | 1.00 - 1.55 |
PP | 0.90 | 41 - 55 | 1.17 - 1.73 |
PS | 1.05 | 23 - 69 | 1.10 - 2.69 |
PC | 1.20 | 83 - 97 | 2.28 - 2.35 |
POM | 1.41 | 94 - 110 | 2.62 - 3.38 |
GFRP (cross ply 54%) | 1.65 | 274 | |
GFRP (random 25%) | 1.48 | 140 | 7.45 |
GFRP (random 50%) | 1.63 | 222 | 13.52 |
The flexural strength of common plastic materials, PP (polypropylene) is 41 - 45 MPa. Measurements of the press molded product of PLA resin of 100% indicated strengths nearly identical to that of PP. Measurements (197.6 MPa) of composite of 50% fibers and at molding temperature of 160˚C indicated a flexural strength nearly identical to that of GFRP (random). The flexural strengths (273 MPa) of the specimen of the fiber of 70% fabricated at 160˚C exceeded the flexural strengths of GFRP (cross ply).
Based on these results, it is consider possible that bamboo fiber/powder composites could substitute effectively for conventional FRP products.
High strength biodegradable composites were made using an emulsion-type PLA resin as the matrix and bamboo fiber bundles as the reinforcement. The results obtained are as follows:
1) Density of composites indicated about 1.2 - 1.3 g/cm3. This value is numerals value compare as PC and PP and low density than GFRP.
2) Unidirectional biodegradable composites fabricated using an emulsion-type biodegradable resin and bamboo fiber bundles with a fiber content of 70% at 160˚C have high flexural strengths of 273 MPa and flexural modulus of 6.8 GPa.
3) The flexural strength and modulus increased linearly with increasing fiber content up to 70%. Thus excellent mechanical properties are achieved for composites fabricated by the novel technique proposed in this study in which the composites are fabricated with an emulsion-type biodegradable resin.
4) The flexural strengths were exceeded the general-purpose engineering plastics and FRP such as POM and GFRP.