The thermal resistance, flame retardance, and smoke control mechanism of nano MH/GF/NBR composite material
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Qilei Wang
Abstract
In order to produce a rubber sealing material with decent physical and mechanical properties, heat resistance, and flame retardance, a nano MH/GF/NBR composite material was made by using nitrile butadiene rubber (NBR), glass fiber (GF), and nano magnesium hydroxide (MH). The physical and mechanical performances, heat resistance, and flame retardance of the composite material were investigated for different fractions of nano MH and GF. The results showed that nano MH reinforces the internal structure of the composite material. The bond strength between GF and the rubber matrix decreases with the increase in the amount of GF in the composite. The proportion of nano MH and GF can improve the physical and mechanical performances of NBR. The tensile strength, tear strength, permanent compression deformation, and hardness also increase. The nano MH/GF composite has good flame retardance, which improves the thermal stability of NBR. Additionally, the total smoke production of the composite material is reduced and the lifetime of the material is extended. The results established a foundation for further applications using the nano MH/GF/NBR composite material as a sealant.
1 Introduction
Most polymers are combustible, especially rubbers that are widely used and produced. Some common rubber materials are silicone rubber, ethylene-propylene rubber, and nitrile butadiene rubber (NBR). Some rubber materials, which are not combustible under normal conditions, have the properties of being flame retardant, non-flammable, or self-extinguishing. Some such as silicon and neopren can combust under special circumstances. During the combustion of these rubber materials, a massive load of heat is produced. Incomplete combustion with heavy black smoke is also common. Harmful and corrosive gases such as hydrogen chloride, hydrogen cyanide, hydrogen fluoride, and styrene are formed. All these characteristics create problems and difficulties for escaping, rescuing, and firefighting during an accident [1, 2]. Furthermore, as an important material for engineering applications, the physical and mechanical properties of rubber greatly influence its use effect. Currently, research on the heat resistance and flame retardance of rubber is focused on adding flame retardants such as magnesium hydroxide (MH), montmorillonite, and halogen flame retardants. These retardants reduce the rate of pyrolysis and heat release after ignition. The purpose of adding retardants is to delay the flow of mass and heat among the flammable materials, oxygen, and the heat source; therefore, the combustion is hindered. Flame retardants of rubber material have always been a hot topic in research worldwide [3–5].
In Lei Ye’s work [6], it is found that MH enhances the thermal and flame retardant properties of EVA/MH/MWNT composite, which effectively protects the composite material from being burnt/ignited. Alsayed et al. [7] investigated the residual tensile properties of newly developed glass fiber reinforced polymer (GFRP) bars after being subjected to elevated temperatures for different periods. They concluded that glass fiber (GF) improves the heat resistant ability of the polymer bars. Soong et al. and Sharma et al. [8, 9] researched the fundamental mechanisms of bonding between GFRP bars and discovered that GFRP bars are inherently sensitive to environmental factors such as temperature, exposure to liquids, gases, electrical fields, and radiation. These factors significantly affect the lifetime of GFRP bars. The mechanical properties are measured by tensile, hardness, and flexural tests. Results were compared with those found for fiber reinforced neat epoxy composites. Arikan [10] analyzed the fabrication and mechanical properties of UV-curable GFRP-matrix composite. The experimental results showed an 11.5% increase in tensile strength for the reinforced composite, and a 51.4% increase with GF treated by coupling agent.
It can be seen from this research results that there are different kinds of retardants that can improve the properties of composite materials. There is sufficient research on improving the physical properties of rubbers by GF, but little research is done on nano MH and GF flame retardants and the physical and mechanical properties of the corresponding composite materials. In this paper, nano MH and GF are used as the basis for modifying additives to produce composite materials. The effects of nano MH and GF on the physical and mechanical properties, thermal resistance and flame retardant properties, and smoke production are also discussed.
2 The production of the composite material
Nano MH and GF are used for the production to ensure the uniform distribution of the additives in the NBR matrix. The basic sample of the composite material is 80 phr of NBR rubber, 5 phr of zinc oxide, 1.5 phr of DM accelerant, 20 phr of carbon black, 1.5 phr of age resister, 1.5 phr of sulfur, 1 phr of stearic acid, and 0.5 phr of graphite. Ten, 20, and 30 phr of MH and GF are added to three samples for comparison. The nano fillers are easy to assemble but hard to disperse. This means that the fillers tend to create stress concentration. Therefore, it adds more advantages to the physical and mechanical properties when the fractions of the fillers are low. The melt mixing process is carried out on the SK-168B open mill. The ingredients and NBR rubber are added to the mill in normal order. The roller temperature is set to 180–185°C. The mixing process takes 10–12 min. The products are weighed after the process. The weight of each sample should be within ±1% of the total weight of the ingredients, otherwise the sample is discarded and the process is repeated. The product mixture is placed on a flat and clean metal plate for 6 h before being vulcanized. The timing of the vulcanization starts after suppressing and preheating the material for 1 min by the vulcanizer. The temperature of the vulcanization process is 155±0.5°C, and the process takes 15 min.
3 Property testing
The environment temperature during all the tests is 21±2°C. The relative humidity is 30–50%. The tear strength, tensile strength, and the break elongation are tested according to Standard GB/T528-1998 on the electronic tensile testing machine (Yangzhou Jing Bo test machinery Ltd., Yangzhou, China) where the dimension of the sample is 6 mm×2 mm. The Shore A hardness is tested according to Standard GB/T531-1999 using the MC010-TH200 type rubber hardness tester (Shanghai Machinery company, Shanghai, China) where the sample size is φ24.5 mm×8 mm. The JSM-5600LV low vacuum scanning electron microscope (SEM) (JEOL, Japan) is used to observe the micro morphology of the material surface. The thermogravimetric analysis is carried out using a TGA 27 type thermogravimetric analyzer by PE with N2. The heating rate is 10°C/min. The heat released rate is measured by the combustion property test conducted by the standard type cone calorimeter from British company FFT. The irradiance is 35 kW/m2. The amount of smoke and its composition is analyzed by the arioplus type multi-component smoke analyzer (Kane, UK).
4 Property analysis
4.1 Structure of the composite material
It can be seen that the internal structure changes for different compositions of the ingredients in Figure 1. When no filler is added, as shown in Figure 1(A), the NBR has an uneven surface where defects can be found in some local areas. When 30 phr of MH and 10 phr of GF are added, as shown in Figure 1(B), changes in the internal structure can be observed. Nano MH can effectively modify the internal structure of the composite material. It reinforces the composite and reduces the amount of defects in the material, which is shown in the “b” area in the figure. The reason is that MH particles have high surface energy, whereas polymers like NBR have low surface energy. Materials with low surface energy tend to adhere to the surface of materials with high surface energy because the unbalanced force field can be compensated after the adherence, leading to a reduction of free enthalpy of the system. Meanwhile, as the composition of GF is relatively low, it does not have a large impact on the structure and is distributed with a certain direction, as pointed out in area “a”. Some breaks and bulges can be seen in the figure. The interface between the matrix and the dispersions is vague, showing a good interaction between the two phases. When the fraction of the ingredients changes to 10 phr of MH and 30 phr of GF, clear changes in the internal structure of the composite can be observed as shown in Figure 1(C). As the fraction of GF increases, some local accumulations and uneven mixing can be found. The anchoring strength is reduced. Moreover, due to the reduction of the fraction of MH, the number of defects in the composite material grows. Nevertheless, the observation shows that the changes in the internal structure of the composite material are not great enough to impact its properties.
Internal structure of the nano MH/GF/NBR composite material with different MH/GF ratio.
4.2 Physical and mechanical properties
The 300% tensile stress curves and the tensile strength curves for the composite material with different MH/GF fraction ratios are shown in Figures 2 and 3.
The 300% tensile stress curves for nano MH/GF/NBR composite materials.
Tensile strength curves for nano MH/GF/NBR composite materials with different MH/GF fraction ratio.
Figures 2 and 3 show that when the amount of nano MH is 10 phr, with the increasing of GF, the 300% tensile stress and the tensile strength of the material is gradually increasing, but the increasing tendency is decreasing. The reason for the increasing strength of the material after adding GF is that GF is a high strength, high modulus, and high tensile strength material. When mixed in the rubber matrix, GF effectively increases the tensile strength of the composite material. When there are 20 phr of nano MH, the tensile strength is further improved due to the decent reinforcing action provided by MH. The nano MH fills the cavities in the material, leading to an additional rise in the 300% tensile stress and tensile strength for the material. However, when there are 30 portions of MH in the material, it can be seen that the strength of the material drops. It can be explained by the fact that with the increase of the fraction of the MH particles, the interaction between the rubber matrix phase and the dispersions phase decreases. Therefore, the interface area between the two phases grows, resulting in a reduction in the growth trend, or even a decline, in the strength of the material.
Figure 4 shows that the compression permanent deformation performance gets better after adding the nano MH/GF composite. It can be seen from the comparison that both ingredients improve the elasticity and the resilience of the composite material, but the effect caused by the GF is superior to that caused by the MH. The reason is that although the reinforcing action of the MH improves the internal structure of the material, the GF has a better mechanical strength and elasticity coefficient, which is more favorable to the improvement of the elasticity and the resilience of the material.
Compression permanent deformation curves for the nano MH/GF/NBR composite material.
It can be seen from Figure 5 that the Shore A hardness of the material increases after adding the nano MH/GF. When both of MH and GF are at 10 phr, the hardness of the material is 66 HA. With the increase of the fraction of GF, the hardness of the material grows. When the composition for nano MH/GF is 10 phr and 30 phr, the hardness of the material is 70 HA. The increase in the hardness is caused by the high mechanical strength of GF. When the GF is fixed at 10 phr, with increase in the portion of MH, the hardness of the material increases by a higher rate than that when GF is added to the material. When the nano MH/GF are at 30 phr and 10 phr, the hardness of the material is 73 HA. Both GF and MH increase the hardness of the material, but nano MH has a better interaction with the rubber matrix than nano GF. Nano MH fills up the cavities of NBR, resulting in a better reinforcing action. Therefore, an increase in the fraction of MH is more beneficial to the hardness of the material.
Shore A hardness curves for the nano MH/GF/NBR composite material.
It can be seen from the above analysis that the addition of GF increases the strength and the resilience of permanent deformation of the material, whereas the addition of MH reinforces the material and improves its hardness. Therefore, a combination of the two ingredients ameliorates the physical and mechanical performances of the composite material.
4.3 Thermal stability
The thermogravimetric curves of pure NBR and the composite material with different fraction ratio of nano MH and GF are shown in Figure 6. It can be seen from the figure that pure NBR starts to decompose at 281°C. When the temperature is 427°C, the thermal weight loss reaches equilibrium. NBR almost decomposes completely. The residue is the reinforcing phase white carbon black and some impurities. When the fraction ratio of MH/GF is 10 phr/10 phr, it can be observed that the decomposition temperature slightly increases to 307°C. With the elevation of the temperature, the rate of weight loss is lower. The thermal weight loss reaches equilibrium at 460°C. When the fraction of MH and GF is 10 phr/30 phr, the decomposition temperature further increases, which indicates that the addition of GF increases the thermal resistance of the material. The rate of weight loss is also lower. But the material with 30 phr MH/10 phr GF has an even better thermal resistance. It indicates that the crystal water in the MH decomposes before the decomposition of rubber, shifting the thermogravimetric curve to a lower temperature. As a result, nano MH has a better thermal resistance performance than nano GF, but the composite material with 10 phr MH/30 phr GF has more residual mass after the decomposition, showing that GF is hard to decompose when heated, which enhances the high temperature performance of the material.
Residual mass of the MH/GF/NBR composite material.
4.4 Combustion performance
Cone calorimeter is used for the combustion performance test for pure NBR and the composite material with different fraction ratios of MH and GF. The results are shown in Table 1.
Combustion performances for composite materials with different MH/GF mass ratios.
| Sample | Pure NBR | MH/GF | MH/GF | MH/GF | MH/GF |
|---|---|---|---|---|---|
| Addition phr | 10/10 | 10/30 | 30/10 | 30/30 | |
| TTI (s) | 32 | 35 | 37 | 39 | 43 |
| AvEHC (MJ/kg) | 35.3 | 29.4 | 27.6 | 25.3 | 24.1 |
| PHRR (kW/m2) | 1013 | 912 | 828 | 747 | 689 |
| AvHRR (kW/m2) | 654 | 572 | 527 | 462 | 423 |
It can be seen from Table 1 that the time to ignition (TTI) for all of the four composites is longer than that for pure NBR. It can also be observed that both MH and GF can effectively improve the combustion performance of the composite material by extending the TTI and reducing peak heat release rate (PHRR), average heat release rate (AvHRR), and average effective heat combustion (AvEHC). The reason is that when MH decomposes after being heated, the hydrate water evaporates and absorbs large amount of latent heat. This results in a decrease in the surface temperature of the composite material in the flame, which suppresses the decomposition of the polymer and cools the combustible gases which are produced by the decomposition. GF is a good heat-resistant material. When mixed with NBR, it can effectively improve the heat resistant performance of the composite material. However, the flame retardance of nano MH is better than that of GF. The combination of the two ingredients not only increases the decomposition rate of the material, but also improves the heat resistance of the material.
It can be seen from Figure 7 that the PHRR and the AvHRR for the nano MH/GF/NBR composite material have an obvious decrease compared to those for pure NBR. Additionally, the peak times are delayed. With the increase of the addition of MH/GF, the PHRR and the AvHRR of the composite are further dropped. However, the performance for material with 30 phr MH/10 phr GF is superior to that for material with 10 phr MH/30 phr GF. It can be concluded that both of the additives can decrease the PHRR as well as the heat resistance and flame retardance of the composite material, which decreases the fire risk of the material.
PHRR curves for the nano MH/GF/NBR composite material with different MH/GF fraction ratio.
4.5 The smoke production test
The smoke production curves for nano MH/GF/NBR with different MH/GF fraction ratios are shown in Figure 8. It can be seen from the figure that the total suspended particulates (TSP) of nano MH/GF/NBR composite material is clearly lower than that of pure NBR. When nano MH is the only additive, the TSP of the composite decreases with increasing fractions of nano MH. When there are 30 phr of MH, the TSP is 640 m2/kg. However, after adding different fractions of GF, the TSP of the composite decreases with increasing fractions of GF. When the fraction ratio for MH/GF is 0/30, the TSP is 1110 m2/kg, whereas the TSP is 640 m2/kg for a fraction ratio of 30/0. This can be explained by the fact that MH has a better smoke control property than GF, which effectively reduces the smoke production of NBR.
TSP curves for nano MH/GF/NBR composite material with different MH/GF fraction ratio.
5 Conclusions
The nano MH/GF/NBR composite material has decent physical and mechanical performances. Nano MH reinforces NBR, increasing the hardness of the material, whereas nano GF improves the strength of the material. Using the two ingredients in combination improves the mechanical properties of the composite material.
Nano MH increases the decomposition temperature of the composite material, whereas nano GF reduces the decomposition rate of the material. Both of the ingredients improve the thermal stability of the material, which increases the efficiency of the material under high temperature.
The combustion performance of the nano MH/GF/NBR is improved by the addition of nano MH and GF. With the increasing of the amount of nano MH in the composite, the TTI of the composite material is extended and the heat releasing rate and the TSP are decreased. Nano GF can also improve the combustion performance of the composite material. The combination of the two materials further improves the heat resistance and flame retardance of the material, which also increases the lifetime of the material.
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©2014 by Walter de Gruyter Berlin Boston
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- Frontmatter
- Original articles
- Microstructures and physical properties of laser amorphous reinforced composite coatings
- The thermal resistance, flame retardance, and smoke control mechanism of nano MH/GF/NBR composite material
- The effect of sodium hydroxide treatment and fiber length on the tensile property of coir fiber-reinforced epoxy composites
- Evaluation of morphological characteristics and mechanical performance of Rockforce mineral fiber- and glass fiber-reinforced polyamide-6 composites
- Synthesis of superabsorbent resin with the properties of temperature tolerant, salt tolerant, and water absorbency deferred
- A study on tribological characterization of Al-Cu-Mg-B composites subjected to mechanical wear
- Microstructure and wear behavior of TiAl3 matrix self-lubricating composites by addition of fluoride solid lubricants
- Mechanical properties of Ni-nano-Al2O3 composite coatings on AISI 304 stainless steel by pulsed electrodeposition
- Improvement of Khorasan mortar with fly ash for restoration of historical buildings
- Combined effect of waste colemanite and silica fume on properties of cement mortar
- Effect of heat treatment temperature on ground pumice activation in geopolymer composites
- Stress intensity factor analysis of epoxy/SWCNTs based on global-local multiscale method
- Numerical elastoplastic analysis of the shear stress distribution in the adhesive layer for single-lap joints
- Analysis of three-layer composite plates with a new higher-order layerwise formulation
- Ceramic-polytetrafluoroethylene composite material-based miniaturized split-ring patch antenna
- Prediction of the influence of processing parameters on synthesis of Al2024-B4C composite powders in a planetary mill using an artificial neural network
- Different method to make laminates by shear thickening fluid
- Thermal control design for an automated fiber placement machine
- Estimate of cutting forces and surface roughness in end milling of glass fiber reinforced plastic composites using fuzzy logic system
- Electrical discharge machining of Al-TiB2 with a low-frequency vibrating tool
- Vibration behavior of a radially functionally graded annular disc with variable geometry
- Buckling behaviors of the impacted composite plates
Artikel in diesem Heft
- Frontmatter
- Original articles
- Microstructures and physical properties of laser amorphous reinforced composite coatings
- The thermal resistance, flame retardance, and smoke control mechanism of nano MH/GF/NBR composite material
- The effect of sodium hydroxide treatment and fiber length on the tensile property of coir fiber-reinforced epoxy composites
- Evaluation of morphological characteristics and mechanical performance of Rockforce mineral fiber- and glass fiber-reinforced polyamide-6 composites
- Synthesis of superabsorbent resin with the properties of temperature tolerant, salt tolerant, and water absorbency deferred
- A study on tribological characterization of Al-Cu-Mg-B composites subjected to mechanical wear
- Microstructure and wear behavior of TiAl3 matrix self-lubricating composites by addition of fluoride solid lubricants
- Mechanical properties of Ni-nano-Al2O3 composite coatings on AISI 304 stainless steel by pulsed electrodeposition
- Improvement of Khorasan mortar with fly ash for restoration of historical buildings
- Combined effect of waste colemanite and silica fume on properties of cement mortar
- Effect of heat treatment temperature on ground pumice activation in geopolymer composites
- Stress intensity factor analysis of epoxy/SWCNTs based on global-local multiscale method
- Numerical elastoplastic analysis of the shear stress distribution in the adhesive layer for single-lap joints
- Analysis of three-layer composite plates with a new higher-order layerwise formulation
- Ceramic-polytetrafluoroethylene composite material-based miniaturized split-ring patch antenna
- Prediction of the influence of processing parameters on synthesis of Al2024-B4C composite powders in a planetary mill using an artificial neural network
- Different method to make laminates by shear thickening fluid
- Thermal control design for an automated fiber placement machine
- Estimate of cutting forces and surface roughness in end milling of glass fiber reinforced plastic composites using fuzzy logic system
- Electrical discharge machining of Al-TiB2 with a low-frequency vibrating tool
- Vibration behavior of a radially functionally graded annular disc with variable geometry
- Buckling behaviors of the impacted composite plates
