In this preliminary investigation, dolomite was added to the low-density polyethylene/kenaf core fiber (LDPE/KCF) biocomposites by using an internal mixer at 150°C, followed by compression molding at the same temperature. The dolomite contents were varied from 0 to 18 wt.%. The processing and stabilization torques, the stock and stabilization temperatures, the tensile and impact strengths, and the thermal decomposition properties of the prepared biocomposites have been characterized and analyzed. The processing recorder results of the LDPE/KCF biocomposites indicated that the stabilization torques and stabilization temperatures have increased with the addition of dolomite. Mechanical testing results showed that the presence of dolomite has increased the tensile stress, tensile modulus, and impact strength of the LDPE/KCF biocomposites. Thermogravimetric analysis results displayed that the thermal decomposition properties of the biocomposites have also increased with the increase of the dolomite content. This research led to the conclusion that the addition of dolomite in lower amounts (<20 wt.%) could act as a secondary filler for improving the processing, mechanical and thermal properties of LDPE/KCF biocomposites without surface treatments of the natural fiber.
The use of natural fibers as an alternative primary filler for polymer biocomposites has become attractive to researchers and industries. Natural fibers can replace synthetic fibers, such as glass, aramid, and carbon, since they have low cost and low density, nonabrasive, and renewable and have fairly good mechanical properties (high toughness and high specific strength) [
On the other hand, although natural fibers can reduce the production cost of the biocomposite products, they are also can lessen the performance of prepared polymer composites [
The use of a mineral like dolomite as a secondary filler in biocomposite systems is very promising as its abundance in nature, low cost, nontoxic, and environmentally friendly [
The polymer matrix used is a low-density polyethylene, LDPE (coating grade), purchased from Lotte Chemical Titan Sdn. Bhd., Malaysia. The primary filler of the biocomposites is kenaf core fiber (
The biocomposites were prepared through melt mixing by using a Brabender internal mixer equipped with a real-time processing recorder. The mixing was carried out at a temperature of 150°C, and the rotor speed was fixed at 60 rpm. LDPE (24 g) was added into the Brabender mixing chamber at the beginning for 3 min, followed by KCF (16 g) for 6 min and dolomite for 3 min. Then, the mixing time was continued for another 3 min, where the plateau torque was reached. The duration of the whole process was 15 min. The mixed biocomposites obtained from the internal mixer were converted into a 1 mm sheet via the compression molding technique by using a hydraulic hot press machine [
The tensile stress, tensile modulus, and tensile strain properties were ascertained according to the ASTM D638 [
The impact strength of the biocomposites was measured according to the ASTM D4812 by using a CEAST impact testing machine (model 9050) via the Izod impact test method. The samples for the impact test were cut into a rectangular bar with a nominal size of 60 × 13 × 1.0 mm3 by using a scroll saw machine, and then they were notched up to 1 mm depth. The samples were supported by a vertical cantilever beam and they were broken by a single swing of the 0.5 joule pendulum. The average data from ten samples of each composition were calculated and the corresponding standard deviations were also reported.
Thermogravimetric analysis (TGA) was performed by using a TA Instruments TGA (model Q500) to investigate the initial and maximum decomposition temperatures of the prepared biocomposites. The analysis was conducted with a heating rate of 10°C min−1 and the temperature ranged from 30 to 800°C. A sample of 10 to 11 mg of the prepared biocomposite was heated in the sample pan in an atmosphere of nitrogen gas at a flow rate of 50 mL min−1.
Figure
Processing torque-time curves of the LDPE/KCF biocomposites with different contents of dolomite.
Figure
Effects of dolomite content on the stabilization torque of the LDPE/KCF biocomposites.
Stock temperature-time curves of LDPE/KCF biocomposites with different contents of dolomite are indicated in Figure
Stock temperature-time curves of the LDPE/KCF biocomposites with different contents of dolomite.
The effects of the dolomite content on the stabilization temperature of the LDPE/KCF biocomposites are displayed in Figure
Effects of dolomite content on the stabilization temperature of the LDPE/KCF biocomposites.
Figures
Effects of dolomite content on (a) tensile stress and (b) tensile modulus of LDPE/KCF biocomposites.
Figures
Effects of dolomite content on (a) tensile strain and (b) impact strength of LDPE/KCF biocomposites.
Thermogravimetric analysis (TGA) thermograms of the LDPE/KCF biocomposites with different contents of dolomite are represented in Figure
The values of the initial and maximum decomposition temperatures of the LDPE/KCF biocomposites obtained from TGA thermograms.
Sample | Initial decomposition temperature (°C) | Maximum decomposition temperature (°C) |
---|---|---|
0% | 305.45 | 467.28 |
3% | 306.93 | 468.12 |
6% | 308.74 | 469.96 |
9% | 310.14 | 470.17 |
12% | 311.75 | 471.78 |
15% | 312.98 | 472.14 |
18% | 315.20 | 472.77 |
TGA thermograms of the LDPE/KCF biocomposites with different contents of dolomite.
In this preliminary investigation, the stabilization torques and stabilization temperatures of the LDPE/KCF biocomposites have increased with the addition of dolomite, as indicated by the processing recorder results. The tensile stress, tensile modulus, and impact strength of the biocomposites have increased with the presence of dolomite as shown by the mechanical testing results. The thermal decomposition properties of the biocomposites have also increased with the increase of the dolomite content as displayed in the thermogravimetric analysis results. It can be concluded that the processing, mechanical and thermal properties of the LDPE/KCF biocomposites could be improved with the addition of lower amounts of dolomite (<20 wt.%), which acted as a secondary filler with no surface treatments of the natural fiber required.
The authors have declared that none of them has a direct financial relationship with the commercial products mentioned in this paper that might lead to a conflict of interests for any of the authors.
The authors would like to thank the Laboratory of Biocomposite Technology, Institute of Tropical Forestry and Forest Products, and the Department of Mechanical and Manufacturing Engineering, Faculty of Engineering, Universiti Putra Malaysia, for providing the facilities and technical supports. The materials and service charges for this project were fully sponsored by the Ministry of Science, Technology and Innovation (MOSTI) under the ScienceFund Grant Scheme (Project no. 06-01-04-SF1815).