Development and Application of Green Composites: Using Coffee Ground and Bamboo Flour
Development and Application of Green Composites: Using Coffee Ground and Bamboo Flour
Development and Application of Green Composites: Using Coffee Ground and Bamboo Flour
DOI 10.1007/s10924-013-0581-3
ORIGINAL PAPER
Hyun-Joong Kim
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grounds (CG) are discharged from food industries. Table 2 Chemical components of coffee ground
Approximately 6,000,000 tons of CG are generated world- Component Range (g/kg)
wide. Developing technology to reuse CG for useful pur-
poses would help convert this large amount of waste into a Crude fiber 466510
new resource [7]. However, CG and bamboo flour are Ether extract 225283
hydrophilic, which leads to a gap between natural fillers and Nitrogen free extract 143168
polymer. Therefore, green composites are restricted for Crude proteins (N 9 6.25) 102130
commercial applications. Ash 78
The aims of this study were to determine a substitute for Etc. 1.42.0
a petroleum-based polymer in green composites, and to
examine the interface bond of green composites enhanced
by a coupling agent using food industry waste, such as CG. Sample Preparation
Natural fillers contain hydroxyl groups. However, the
character of the polymer is hydrophobic. Isocyanate groups To manufacture the green composites, the CG and BF were
of MDI react with the terminal hydroxyl or carboxyl dried at 105 C for 24 h to adjust the moisture content to
groups of PLA and the hydroxyl groups of natural fillers to 13 %. PLA, natural fillers, and coupling agent were
produce a urethane linkage [8]. MDI was used to improve compounded using a twin screw extruder (BA-19, Bau
the interface bond between natural fillers and polymer. Tech., South Korea). The temperature of the mixing zone
in the extruder was maintained at 165185 C and the
screw speed was 200 rpm. Extruded samples are passes
Experimental through a water bath to lower the temperature. Cooling
sample put into the pelletizer and cut to about 5 mm pellet.
Bio-Based Polymer Pellets were dried at 50 C for 4 h to remove moisture. The
pellets were manufactured into the test specimens using a
PLA (Polylacic acid) was obtained from Nature Works injection molding machine (Bau Tech., South Korea).
LLC Co., USA. (MFI: 15 g/10 min, (190 C/2,160 g) Before the mechanical test, it was conditioned at 50 5 %
density: 1.22 g/cm3). RH for at least 40 h according to the ASTM D618-99.
Natural Fillers
Tensile Test
Bamboo flour (BF) and CG were used as reinforcing nat-
ural fillers. BF was purchased from Hangyang Advanced A universal testing machine (UTM, Zwick Co.) was used
Materials Co., South Korea, and the CG were supplied by to evaluate the tensile strength. The tensile test was
CJ Co., South Korea. After brewing the coffee, it was determined according to ASTM D 638-08. The test con-
recycled as a natural filler in the green composites. Table 1 dition was a crosshead speed of 5 mm/min and a temper-
shows the composition of the natural fillers. Table 2 shows ature of 24 2 C. Five measurements were performed
the chemical component of CG [9]. and averaged for the final result.
MDI (4,40 -Methylene diphenyl diisocyanate) was pur- The flexural strength was evaluated according to ASTM D
chased from BASF Co., Germany. The solid content of 790-07 using a universal testing machine (UTM, Zwick
MDI is 97 %. The isocyanate group of MDI was used as a Co.). A crosshead speed of 5 mm/min was used to deter-
coupling agent to improve the interface bond between the mine the flexural strength. Five specimens were evaluated
polymer and natural fillers (Table 3). and averaged for the final result.
Table 1 Composition ingredients of the natural fillers (BF and coffee ground)
Cellulose (wt %) Hemicellulose (wt %) Lignin (wt %) Etc. (wt %)
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60
The TGA measurements were carried out using a thermo
gravimetric analyzer (TGA Q500, TA Instruments). The
samples, 8 * 10 mg, were evaluated from 25 to 600 C at 50
Tensile strength (MPa)
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(a) 120
120
PLA-BF
PLA-CG
100 90
Flexural strength (MPa)
Stress (MPa)
80
60
60
PLA
30
PLA:CG=70:30
40 PLA:CG=70:30 MDI 1%
PLA:CG=70:30 MDI 3%
PLA:CG=70:30 MDI 5%
0
20 0 2 4 6 8 10 12
0 10 20 30 40
Strain (mm)
Flour (wt.%)
(b) Fig. 3 Stress-strain behavior of the coffee ground (CG)/PLA
120 composites
100 from 34.6 to 54 MPa and from 27.5 to 37.3 MPa, respec-
tively. In the case of the BF/PLA composites, MDI
Flexural strength (MPa)
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706 J Polym Environ (2013) 21:702709
Fig. 4 FT-IR spectra of the natural fillers (bamboo flour and coffee
grounds)
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J Polym Environ (2013) 21:702709 707
(a)
3000 PLA
PLA:CG=70:30
PLA:CG=70:30 MDI 1%
PLA:CG=70:30 MDI 3%
Storage modulus (MPa)
PLA:CG=70:30 MDI 5%
2000
1000
0
20 40 60 80 100
Temperature (C)
(b)
4000
PLA
PLA:BF=70:30
PLA:BF=70:30 MDI 1%
PLA:BF=70:30 MDI 3%
Storage modulus (MPa)
3000
PLA:BF=70:30 MDI 5%
2000
1000
0
20 40 60 80 100
Temperature (C)
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708 J Polym Environ (2013) 21:702709
the interface induced by the addition of MDI as a coupling of the green composites without coupling agent at 30 wt %
agent increases the thermal stability. of fillers loading, a gap was observed due to the difference
in character between the natural fillers and polymer. This
Field Emission-Scanning Electron Microscopy results in a decrease in mechanical strength. However, the
(FE-SEM) gap of the BF/PLA composites was decreased with the
addition of MDI 3 phr. In addition, the interface adhesion
Figure 9 shows the tensile fractured surface of the BF/PLA of the CG/PLA composites was increased. This improved
and CG/PLA composites with or without MDI. In the case interfacial adhesion might be due to the compactable effect
of MDI by the hydroxyl groups of natural fillers and the
3 isocyanate groups of MDI producing a urethane linkage.
PLA
PLA:BF=70:30
PLA:CG=70:30
PLA:BF=70:30 MDI 3% Conclusions
PLA:CG=70:30 MDI 3%
Deriv. Weight (% /C)
2
This study examined the effect of natural fillers and coupling
agent in green composites. The tensile and flexural strength
was decreased by increasing the natural fillers. This was due
to the difference character, the polymer was hydrophobic but
1 the natural fillers were hydrophilic. However, the mechani-
cal strength was increased by the addition of MDI due to a
reaction between MDI and the hydroxyl groups of natural
fillers. The CG/PLA composites showed higher elongation
0 than the BF/PLA composites due to the ether compounds
250 300 350 400 450 in CG.
Temperature (C)
The storage modulus of the green composites increased
Fig. 8 Derivative weight loss curves of the green composites with according to natural filler loading. This is due to stress
bamboo flour and coffee grounds transfer from the matrix to the fiber. The green composites
(a) (b)
(c) (d)
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J Polym Environ (2013) 21:702709 709
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