Thermal Characteristics of Expandable Graphite–Wood Particle Composites
Abstract
:1. Introduction
2. Materials and Methods
2.1. Material Selection and Composite Fabrication
2.2. Cone Calorimetry Experiment
3. Results and Discussion
3.1. DSC and XRD Analyses
3.2. Physical Characteristics of the Expandable Graphite Composites
3.3. Thermal Characteristics of Expandable Graphite Composites
3.4. Changes in the Microstructure of Expandable Graphite
4. Conclusions
- As a result of the DSC analysis, a faster heat absorption rate compared that of the pure expandable graphite was observed when the expandable graphite was added to the wood particles. This was due to the absorption of a large amount of heat for the carbonization of the wood particles in the specimen. In the XRD analysis after combustion, the diffraction peak level of the wood particles decreased, and carbon was detected by the combustion of the wood particles and thermal decomposition of expandable graphite.
- Analysis of the physical properties of the expandable graphite–wood particle composites revealed that increasing the expandable graphite content from 0 to 50 wt.% increased the expansion rate from 0% to 341.7%. Given that expandable graphite is a mixture of sulfuric acid and an oxidant and is produced from processes that involve oxidation, washing, drying, heating, and expansion, such an observation was shown to result from the wide expandability layer that arises when expandable graphite expands upon exposure to heat and produces gas.
- Analysis of the thermal characteristics of the expanded graphite layer (Lwp) composites with added expandable graphite showed that increasing the expandable graphite content from 0 to 50 wt.% decreased the total heat released from 38.63 to 2.50 MJ/m2, and when expandable graphite contained more than 30%, it showed a stable fire retarding effect. It was concluded that this resulted from the delay in ignition time and decrease in the total heat released with increasing expandable graphite content.
- Increasing the expandable graphite content from 0 to 50 wt.% decreased the thermal conductivity of the expanded graphite layer from 24.62 to 7.83 W/m·K. In general, the thermal conductivity of expandable graphite tends to increase when it exists in the unburnt state. However, when expandable graphite undergoes combustion upon exposure to heat, both the expandability of graphite and the thickness of the expanded layerincrease, which in turn tends to decrease the thermal conductivity in the expanded layer due to the hindered transport of heat caused by the heat transfer shielding effect.
- Smoke toxicity tests with the 30 wt.% expandable graphite specimen showed that the time to inactivity of the white mouse was 14.9 min on average, which meets the lethal toxic potency standard (time to inactivity > 9 min) of a fire retardant. In the case of wood particles, the time to inactivity was 5.8 min, which does not meet the standard. In the case of the expandable graphite 30 wt.% composite material, the time to inactivity appears to have increased because of the smaller burned mass as compared to that in wood particles, thus reducing the generated amount of harmful gases such as CO and CO2.
- The structure of expandable graphite before combustion was characterized by a laminated layer structure 120–550 μm in width, 100–430 μm in length, and approximately 10 μm in thickness. The microstructure of the expanded graphite was revealed to be a worm shape, and the amount of expanded graphite was observed to increase in proportion with increase in the expandable graphite content. Additionally, the microstructure of expanded graphite was characterized by a fine lattice layer with a 16–22-μm interlayer spacing, repeating at a thickness of 0.1–0.4 μm and an interval of 1.0–2.5 μm, and the enhanced thermal resistance of the composite was due to the decrease in thermal conductivity.
Author Contributions
Funding
Acknowledgments
Conflicts of Interest
References
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Composition | Wood Particles | Expandable Graphite |
---|---|---|
Content (%) | Cellulose ≤ 50% Hemicellulose ≤ 25% Lignin ≤ 25% Chemical Content - Carbon: 55.61 wt.% - Oxygen: 44.39 wt.% | Fixed carbon: 93.8% Ash: 6.2% Moisture: 0.68% pH: 4.5 Expansion volume: 210 mL/g Expansion temperature: 180–200 °C |
Size | 80–100 mesh | 80 mesh (82%) |
Morphology | | |
Specimen | Mass of Composite Materials (g) | ||||
---|---|---|---|---|---|
Case | EG wt.% | Expandable Graphite | Wood Particles | Common Binder | Sum |
Case 1 | EG 0 wt.% | 0 | 100 | 300 | 400 |
Case 2 | EG 5 wt.% | 21 | 100 | 300 | 421 |
Case 3 | EG 10 wt.% | 45 | 100 | 300 | 445 |
Case 4 | EG 15 wt.% | 71 | 100 | 300 | 471 |
Case 5 | EG 20 wt.% | 100 | 100 | 300 | 500 |
Case 6 | EG 25 wt.% | 134 | 100 | 300 | 534 |
Case 7 | EG 30 wt.% | 172 | 100 | 300 | 572 |
Case 8 | EG 40 wt.% | 267 | 100 | 300 | 667 |
Case 9 | EG 50 wt.% | 400 | 100 | 300 | 800 |
Item | Semi Noncombustible Material | Flame Retardant Material |
---|---|---|
THR (MJ/m2) | Below 8 MJ/m2 | Below 8 MJ/m2 |
Time in which the heat release rate is exceeded 200 kW/m2 continuously | Below 10 s | Below 10 s |
All core melt, penetrating cracks, slot change, etc., | No core melt, penetrating cracks, slot change | No core melt, penetrating cracks, slot change |
Toxicity | Experimental mouse Activity over 9 min | Experimental mouse Activity over 9 min |
Test time | 10 min (600 s) | 5 min (300 s) |
Specimen | EG 0 wt.% (Wood Particles 100%) | EG 30 wt.% |
---|---|---|
No.1 | 5.5 | 14.8 |
No.2 | 6.2 | 15.4 |
No.3 | 5.7 | 14.5 |
Average | 5.8 | 14.9 |
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Chun, K.; Kim, J.; Rie, D. Thermal Characteristics of Expandable Graphite–Wood Particle Composites. Materials 2020, 13, 2732. https://doi.org/10.3390/ma13122732
Chun K, Kim J, Rie D. Thermal Characteristics of Expandable Graphite–Wood Particle Composites. Materials. 2020; 13(12):2732. https://doi.org/10.3390/ma13122732
Chicago/Turabian StyleChun, Kwanok, Jeonggon Kim, and Dongho Rie. 2020. "Thermal Characteristics of Expandable Graphite–Wood Particle Composites" Materials 13, no. 12: 2732. https://doi.org/10.3390/ma13122732